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159-463: Nalty first gained notoriety for a video featured on YouTube's front page the first week of January 2007 - "Viral Video Genius - Loses His Cool When Confronted" - where he plays a skivvy-wearing, geeky intellectual passionate about viral video making. His second featured video, "Farting in Public," showed a young teenager named Spencer (Nalty's nephew's friend) using a fart machine in public places, all

318-455: A diving chamber or decompression chamber . However, as one rises above sea level the density of the air decreases exponentially (see Fig. 14), halving approximately with every 5500 m rise in altitude . Since the composition of the atmospheric air is almost constant below 80 km, as a result of the continuous mixing effect of the weather, the concentration of oxygen in the air (mmols O 2 per liter of ambient air) decreases at

477-427: A fibrinolytic system that dissolves clots that may have arrived in the pulmonary circulation by embolism , often from the deep veins in the legs. They also release a variety of substances that enter the systemic arterial blood, and they remove other substances from the systemic venous blood that reach them via the pulmonary artery. Some prostaglandins are removed from the circulation, while others are synthesized in

636-405: A partial pressure of carbon dioxide of 5.3 kPa (40 mmHg) (i.e. the same as the oxygen and carbon dioxide gas tensions as in the alveoli). As mentioned in the section above , the corresponding partial pressures of oxygen and carbon dioxide in the ambient (dry) air at sea level are 21 kPa (160 mmHg) and 0.04 kPa (0.3 mmHg) respectively. This marked difference between

795-436: A respiratory acidosis , or a respiratory alkalosis will occur. In the long run these can be compensated by renal adjustments to the H and HCO 3 concentrations in the plasma ; but since this takes time, the hyperventilation syndrome can, for instance, occur when agitation or anxiety cause a person to breathe fast and deeply thus causing a distressing respiratory alkalosis through the blowing off of too much CO 2 from

954-414: A continued decrease in subcutaneous fat and an obviously harder and more angular body form. Pubic hair distribution appears more adult but has not yet spread to the medial area of the thighs. The penis and scrotum are near adult size. Stage IV for boys, which occurs anywhere from 15 to 24 months after stage III, is difficult to pinpoint. At this time, the spurt of growth in height ends. There is facial hair on

1113-401: A deeper voice and larger Adam's apple in boys, and development of breasts and more curved and prominent hips in girls) and a strong shift in hormonal balance towards an adult state. This is triggered by the pituitary gland , which secretes a surge of hormonal agents into the blood stream, initiating a chain reaction. The male and female gonads are thereby activated, which puts them into

1272-480: A fairly regular sequence. The first places to grow are the extremities—the head, hands and feet—followed by the arms and legs, then the torso and shoulders. This non-uniform growth is one reason why an adolescent body may seem out of proportion. During puberty, bones become harder and more brittle. At the conclusion of puberty, the ends of the long bones close during the process called epiphysis . There can be ethnic differences in these skeletal changes. For example, in

1431-453: A friend's or parent's assumptions. Adolescents also develop a more sophisticated understanding of probability. The appearance of more systematic, abstract thinking is another notable aspect of cognitive development during adolescence. For example, adolescents find it easier than children to comprehend the sorts of higher-order abstract logic inherent in puns, proverbs, metaphors, and analogies. Their increased facility permits them to appreciate

1590-442: A girl is not fully fertile until several years after menarche, as regular ovulation follows menarche by about two years. Unlike males, therefore, females usually appear physically mature before they are capable of becoming pregnant. Changes in secondary sex characteristics include every change that is not directly related to sexual reproduction. In males, these changes involve appearance of pubic, facial, and body hair, deepening of

1749-563: A great deal of research has been done on the cognitive and emotional processes underlying adolescent risk-taking. In addressing this question, it is important to distinguish whether adolescents are more likely to engage in risky behaviors (prevalence), whether they make risk-related decisions similarly or differently than adults (cognitive processing perspective), or whether they use the same processes but value different things and thus arrive at different conclusions. The behavioral decision-making theory proposes that adolescents and adults both weigh

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1908-566: A growth rate nearly identical to that of a toddler—about 10.3 cm (4 inches) per year for males and 9 cm (3.5 inches) per year for females. In addition to changes in height, adolescents also experience a significant increase in weight (Marshall, 1978). The weight gained during adolescence constitutes nearly half of one's adult body weight. Teenage and early adult males may continue to gain natural muscle growth even after puberty. The accelerated growth in different body parts happens at different times, but for all adolescents, it has

2067-528: A high-fat diet and who are not physically active begin menstruating earlier, on average, than girls whose diet contains less fat and whose activities involve fat reducing exercise (e.g. ballet and gymnastics). Girls who experience malnutrition or are in societies in which children are expected to perform physical labor also begin menstruating at later ages. The timing of puberty can have important psychological and social consequences. Early maturing boys are usually taller and stronger than their friends. They have

2226-861: A live version of the digital talk show Tom Green Live, which was broadcast at the Digital Content NewFront in June, 2009. His blog, WillVideoForFood, lists media appearances in reverse chronological order. Nalty, divorced in 2020, has four adult children: Katie, Patrick, Grant, and Charlie. He lives in rural Pennsylvania with his cat Oliver. Nalty highlights the children in most of his videos. He graduated from Georgetown Preparatory High School in Rockville , Maryland , has an undergraduate degree from Georgetown, and an MBA in marketing and entrepreneurship from Babson College of Boston. Teenager Adolescence (from Latin adolescere  'to mature')

2385-646: A lower resting heart rate, a greater capacity for carrying oxygen to the blood, a greater power for neutralizing the chemical products of muscular exercise, higher blood hemoglobin and more red blood cells". Despite some genetic sex differences, environmental factors play a large role in biological changes during adolescence. For example, girls tend to reduce their physical activity in preadolescence and may receive inadequate nutrition from diets that often lack important nutrients, such as iron. These environmental influences, in turn, affect female physical development. Primary sex characteristics are those directly related to

2544-457: A major role in character and personality formation. Biological changes in brain structure and connectivity within the brain interact with increased experience, knowledge, and changing social demands to produce rapid cognitive growth (see Changes in the brain above). The age at which particular changes take place varies between individuals, but the changes discussed below begin at puberty or shortly after that and some skills continue to develop as

2703-410: A more sophisticated theory of mind . Adolescents reach a stage of social perspective-taking in which they can understand how the thoughts or actions of one person can influence those of another person, even if they personally are not involved. Compared to children, adolescents are more likely to question others' assertions, and less likely to accept facts as absolute truths. Through experience outside

2862-407: A much more even distribution of blood flow to the lungs than occurs at sea level. At sea level, the pulmonary arterial pressure is very low, with the result that the tops of the lungs receive far less blood than the bases , which are relatively over-perfused with blood. It is only in the middle of the lungs that the blood and air flow to the alveoli are ideally matched . At altitude, this variation in

3021-1061: A newfound priority in sexual attraction and dating, and risk-taking is required to impress potential mates. Research also indicates that baseline sensation seeking may affect risk-taking behavior throughout the lifespan. Given the potential consequences, engaging in sexual behavior is somewhat risky, particularly for adolescents. Having unprotected sex, using poor birth control methods (e.g. withdrawal), having multiple sexual partners, and poor communication are some aspects of sexual behavior that increase individual and/or social risk. Aspects of adolescents' lives that are correlated with risky sexual behavior include higher rates of parental abuse, and lower rates of parental support and monitoring. Related to their increased tendency for risk-taking, adolescents show impaired behavioral inhibition, including deficits in extinction learning . This has important implications for engaging in risky behavior such as unsafe sex or illicit drug use, as adolescents are less likely to inhibit actions that may have negative outcomes in

3180-480: A normal mammal, the lungs cannot be emptied completely. In an adult human, there is always still at least 1 liter of residual air left in the lungs after maximum exhalation. The automatic rhythmical breathing in and out, can be interrupted by coughing, sneezing (forms of very forceful exhalation), by the expression of a wide range of emotions (laughing, sighing, crying out in pain, exasperated intakes of breath) and by such voluntary acts as speech, singing, whistling and

3339-598: A notable broadening of the hips as well as an adult fat distribution. Additionally, breast development is complete and hair in both the pubic region and armpits (axillary hair) will be darker and more widespread. In comparison to girls, it can be tricky to define when exactly sexual development in boys begins. For boys, puberty typically takes around 5 years to finish, as opposed to just 3 + 1 ⁄ 2 years for girls (menarche). By this point in time, they have already experienced their growth spurt and there are evident changes in their body shape – wider hips and fat distribution

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3498-428: A partial pressure of CO 2 of also about 6 kPa (45 mmHg), whereas that of the alveolar air is 5.3 kPa (40 mmHg), there is a net movement of carbon dioxide out of the capillaries into the alveoli. The changes brought about by these net flows of individual gases into and out of the alveolar air necessitate the replacement of about 15% of the alveolar air with ambient air every 5 seconds or so. This

3657-445: A process referred to as metacognition . It often involves monitoring one's own cognitive activity during the thinking process. Adolescents' improvements in knowledge of their own thinking patterns lead to better self-control and more effective studying. It is also relevant in social cognition, resulting in increased introspection , self-consciousness , and intellectualization (in the sense of thought about one's own thoughts, rather than

3816-461: A rise in arterial blood pressure . Large amounts of the angiotensin-converting enzyme responsible for this activation are located on the surfaces of the endothelial cells of the alveolar capillaries. The converting enzyme also inactivates bradykinin . Circulation time through the alveolar capillaries is less than one second, yet 70% of the angiotensin I reaching the lungs is converted to angiotensin II in

3975-424: A single trip through the capillaries. Four other peptidases have been identified on the surface of the pulmonary endothelial cells. The movement of gas through the larynx , pharynx and mouth allows humans to speak , or phonate . Vocalization, or singing, in birds occurs via the syrinx , an organ located at the base of the trachea. The vibration of air flowing across the larynx ( vocal cords ), in humans, and

4134-406: A specific order during puberty: The first facial hair to appear tends to grow at the corners of the upper lip, typically between 14 and 17 years of age. It then spreads to form a moustache over the entire upper lip. This is followed by the appearance of hair on the upper part of the cheeks, and the area under the lower lip. The hair eventually spreads to the sides and lower border of the chin, and

4293-442: A state of rapid growth and development; the triggered gonads now commence mass production of hormones. The testes primarily release testosterone , and the ovaries predominantly dispense estrogen . The production of these hormones increases gradually until sexual maturation is met. Some boys may develop gynecomastia due to an imbalance of sex hormones , tissue responsiveness or obesity . Facial hair in males normally appears in

4452-936: A typical aspect in maturing females. Because of their bodies' developing in advance, pubescent girls can become more insecure and dependent. Consequently, girls that reach sexual maturation early are more likely than their peers to develop eating disorders (such as anorexia nervosa ). Nearly half of all American high school girls' diets are to lose weight. In addition, girls may have to deal with sexual advances from older boys before they are emotionally and mentally mature. In addition to having earlier sexual experiences and more unwanted pregnancies than late maturing girls, early maturing girls are more exposed to alcohol and drug abuse . Those who have had such experiences tend to not perform as well in school as their "inexperienced" peers. Girls have usually reached full physical development around ages 15–17, while boys usually complete puberty around ages 16–17. Any increase in height beyond

4611-399: A variety of molecules that aid in the defense of the lungs. These include secretory immunoglobulins (IgA), collectins , defensins and other peptides and proteases , reactive oxygen species , and reactive nitrogen species . These secretions can act directly as antimicrobials to help keep the airway free of infection. A variety of chemokines and cytokines are also secreted that recruit

4770-432: A very rich blood supply, thus bringing the air into close contact with the blood. These air sacs communicate with the external environment via a system of airways, or hollow tubes, of which the largest is the trachea , which branches in the middle of the chest into the two main bronchi . These enter the lungs where they branch into progressively narrower secondary and tertiary bronchi that branch into numerous smaller tubes,

4929-419: A watery surface (the water-air interface) tends to make that surface shrink. When that surface is curved as it is in the alveoli of the lungs, the shrinkage of the surface decreases the diameter of the alveoli. The more acute the curvature of the water-air interface the greater the tendency for the alveolus to collapse . This has three effects. Firstly, the surface tension inside the alveoli resists expansion of

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5088-559: A wide range of circumstances, at the expense of the arterial partial pressure of O 2 , which is allowed to vary within a very wide range of values, before eliciting a corrective ventilatory response. However, when the atmospheric pressure (and therefore the partial pressure of O 2 in the ambient air) falls to below 50-75% of its value at sea level, oxygen homeostasis is given priority over carbon dioxide homeostasis. This switch-over occurs at an elevation of about 2500 m (or about 8000 ft). If this switch occurs relatively abruptly,

5247-452: A willingness to take risks, teenagers would not have the motivation or confidence necessary to leave their family of origin. In addition, from a population perspective, there is an advantage to having a group of individuals willing to take more risks and try new methods, counterbalancing the more conservative elements more typical of the received knowledge held by older adults. Risk-taking may also have reproductive advantages: adolescents have

5406-412: Is spermarche , the first ejaculation , which occurs, on average, at age 13. For females, it is menarche , the onset of menstruation, which occurs, on average, between ages 12 and 13. The age of menarche is influenced by heredity, but a girl's diet and lifestyle contribute as well. Regardless of genes, a girl must have a certain proportion of body fat to attain menarche. Consequently, girls who have

5565-597: Is 10–11 for girls and 11–12 for boys. Every person's individual timetable for puberty is influenced primarily by heredity , although environmental factors, such as diet and exercise, also exert some influences. These factors can also contribute to precocious and delayed puberty . Some of the most significant parts of pubertal development involve distinctive physiological changes in individuals' height, weight, body composition, and circulatory and respiratory systems. These changes are largely influenced by hormonal activity. Hormones play an organizational role, priming

5724-569: Is a biological system consisting of specific organs and structures used for gas exchange in animals and plants . The anatomy and physiology that make this happen varies greatly, depending on the size of the organism, the environment in which it lives and its evolutionary history. In land animals , the respiratory surface is internalized as linings of the lungs . Gas exchange in the lungs occurs in millions of small air sacs; in mammals and reptiles, these are called alveoli , and in birds, they are known as atria . These microscopic air sacs have

5883-590: Is a difficult task due to multiple factors such as family life, environment, and social status. Empirical studies suggest that this process might be more accurately described as identity development , rather than formation, but confirms a normative process of change in both content and structure of one's thoughts about the self. The two main aspects of identity development are self-clarity and self-esteem. Since choices made during adolescent years can influence later life, high levels of self-awareness and self-control during mid-adolescence will lead to better decisions during

6042-456: Is a sign of, illness. ) It ends in the microscopic dead-end sacs called alveoli , which are always open, though the diameters of the various sections can be changed by the sympathetic and parasympathetic nervous systems . The alveolar air pressure is therefore always close to atmospheric air pressure (about 100  kPa at sea level) at rest, with the pressure gradients because of lungs contraction and expansion cause air to move in and out of

6201-451: Is a stage in the adolescent life cycle. For most, the search for identity begins in the adolescent years. During these years, adolescents are more open to 'trying on' different behaviours and appearances to discover who they are. In an attempt to find their identity and discover who they are, adolescents are likely to cycle through a number of identities to find one that suits them best. Developing and maintaining identity (in adolescent years)

6360-504: Is a transitional stage of physical and psychological development that generally occurs during the period from puberty to adulthood (typically corresponding to the age of majority ). Adolescence is usually associated with the teenage years, but its physical, psychological or cultural expressions may begin earlier or end later. Puberty typically begins during preadolescence , particularly in females. Physical growth (particularly in males) and cognitive development can extend past

6519-455: Is an excitatory neurotransmitter. During the synaptic pruning that occurs during adolescence, most of the neural connections that are pruned contain receptors for glutamate or other excitatory neurotransmitters. Because of this, by early adulthood the synaptic balance in the brain is more inhibitory than excitatory. Dopamine is associated with pleasure and attuning to the environment during decision-making. During adolescence, dopamine levels in

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6678-442: Is at sea level). This reduces the partial pressure of oxygen entering the alveoli to 5.8 kPa (or 21% of [33.7 kPa – 6.3 kPa] = 5.8 kPa). The reduction in the partial pressure of oxygen in the inhaled air is therefore substantially greater than the reduction of the total atmospheric pressure at altitude would suggest (on Mt Everest: 5.8 kPa vs. 7.1 kPa). A further minor complication exists at altitude. If

6837-426: Is breathed in or out, either through the mouth or nose or into or out of the alveoli are tabulated below, together with how they are calculated. The number of breath cycles per minute is known as the respiratory rate . An average healthy human breathes 12–16 times a minute. In mammals , inhalation at rest is primarily due to the contraction of the diaphragm . This is an upwardly domed sheet of muscle that separates

6996-459: Is constructed via the choices and actions of an individual within the context of their historical period and social network. In 1984, the Society for Research on Adolescence (SRA) became the first official organization dedicated to the study of adolescent psychology. Some of the issues first addressed by this group include: the nature versus nurture debate as it pertains to adolescence; understanding

7155-405: Is determined by the blood gas homeostat , which regulates the partial pressures of oxygen and carbon dioxide in the arterial blood. This homeostat prioritizes the regulation of the arterial partial pressure of carbon dioxide over that of oxygen at sea level. That is to say, at sea level the arterial partial pressure of CO 2 is maintained at very close to 5.3 kPa (or 40 mmHg) under

7314-505: Is divided into an upper and a lower respiratory tract . The upper tract includes the nose , nasal cavities , sinuses , pharynx and the part of the larynx above the vocal folds . The lower tract (Fig. 2.) includes the lower part of the larynx , the trachea , bronchi , bronchioles and the alveoli . The branching airways of the lower tract are often described as the respiratory tree or tracheobronchial tree (Fig. 2). The intervals between successive branch points along

7473-450: Is fatal. Basic scientific experiments, carried out using cells from chicken lungs, support the potential for using steroids as a means of furthering the development of type II alveolar cells. In fact, once a premature birth is threatened, every effort is made to delay the birth, and a series of steroid injections is frequently administered to the mother during this delay in an effort to promote lung maturation. The lung vessels contain

7632-570: Is fresh warm and moistened air. Since this 350 ml of fresh air is thoroughly mixed and diluted by the air that remains in the alveoli after a normal exhalation (i.e. the functional residual capacity of about 2.5–3.0 liters), it is clear that the composition of the alveolar air changes very little during the breathing cycle (see Fig. 9). The oxygen tension (or partial pressure) remains close to 13–14 kPa (about 100 mm Hg), and that of carbon dioxide very close to 5.3 kPa (or 40 mm Hg). This contrasts with composition of

7791-471: Is involved in decision making and cognitive control, as well as other higher cognitive functions. During adolescence, myelination and synaptic pruning in the prefrontal cortex increases, improving the efficiency of information processing, and neural connections between the prefrontal cortex and other regions of the brain are strengthened. This leads to better evaluation of risks and rewards, as well as improved control over impulses. Specifically, developments in

7950-545: Is less bound to concrete events than that of children: they can contemplate possibilities outside the realm of what currently exists. One manifestation of the adolescent's increased facility with thinking about possibilities is the improvement of skill in deductive reasoning , which leads to the development of hypothetical thinking. This provides the ability to plan ahead, see the future consequences of an action and to provide alternative explanations of events. It also makes adolescents more skilled debaters, as they can reason against

8109-410: Is more adult-like. Breast development will also be completed by this stage. In boys, four stages in development can be correlated with the curve of general body growth at adolescence. The initial sign of sexual maturation in boys usually is the "fat spurt". The maturing boy gains weight and becomes almost chubby, with a somewhat feminine fat distribution. This probably occurs because estrogen production by

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8268-441: Is no unidirectional through-flow as there is in the bird lung ). This typical mammalian anatomy combined with the fact that the lungs are not emptied and re-inflated with each breath (leaving a substantial volume of air, of about 2.5–3.0 liters, in the alveoli after exhalation), ensures that the composition of the alveolar air is only minimally disturbed when the 350 ml of fresh air is mixed into it with each inhalation. Thus

8427-418: Is not limited to the limbic system: Several serotonin receptors have their gene expression change dramatically during adolescence, particularly in the human frontal and prefrontal cortex. Adolescence is a time of rapid cognitive development. Piaget describes adolescence as the stage of life in which the individual's thoughts start taking more of an abstract form and the egocentric thoughts decrease, allowing

8586-423: Is restored. Since the blood arriving in the alveolar capillaries has a partial pressure of O 2 of, on average, 6 kPa (45 mmHg), while the pressure in the alveolar air is 13–14 kPa (100 mmHg), there will be a net diffusion of oxygen into the capillary blood, changing the composition of the 3 liters of alveolar air slightly. Similarly, since the blood arriving in the alveolar capillaries has

8745-425: Is shaped by the period and location in which they grow up. The principle of the importance of timing in one's life refers to the different impact that life events have on development based on when in one's life they occur. The idea of linked lives states that one's development is shaped by the interconnected network of relationships of which one is a part and the principle of human agency asserts that one's life course

8904-428: Is the constructivist view of cognitive development. Based on the work of Piaget , it takes a quantitative, state-theory approach, hypothesizing that adolescents' cognitive improvement is relatively sudden and drastic. The second is the information-processing perspective , which derives from the study of artificial intelligence and attempts to explain cognitive development in terms of the growth of specific components of

9063-493: Is therefore almost the same at the end of exhalation as at the end of inhalation. Thirdly, the surface tension of the curved watery layer lining the alveoli tends to draw water from the lung tissues into the alveoli. Surfactant reduces this danger to negligible levels, and keeps the alveoli dry. Pre-term babies who are unable to manufacture surfactant have lungs that tend to collapse each time they breathe out. Unless treated, this condition, called respiratory distress syndrome ,

9222-478: Is very tightly controlled by the monitoring of the arterial blood gases (which accurately reflect composition of the alveolar air) by the aortic and carotid bodies , as well as by the blood gas and pH sensor on the anterior surface of the medulla oblongata in the brain. There are also oxygen and carbon dioxide sensors in the lungs, but they primarily determine the diameters of the bronchioles and pulmonary capillaries , and are therefore responsible for directing

9381-522: The American Psychological Association have shown that adolescents with a less privileged upbringing have a more difficult time developing their identity. The idea of self-concept is known as the ability of a person to have opinions and beliefs that are defined confidently, consistent and stable. Early in adolescence, cognitive developments result in greater self-awareness, greater awareness of others and their thoughts and judgments,

9540-518: The Great Depression and World War II , unique historical circumstances under which a generation of children grew up. The Oakland Growth Study, initiated by Harold Jones and Herbert Stolz in 1931, aimed to study the physical, intellectual, and social development of children in the Oakland area. Data collection began in 1932 and continued until 1981, allowing the researchers to gather longitudinal data on

9699-427: The arterial blood . This information determines the average rate of ventilation of the alveoli of the lungs , to keep these pressures constant . The respiratory center does so via motor nerves which activate the diaphragm and other muscles of respiration . The breathing rate increases when the partial pressure of carbon dioxide in the blood increases. This is detected by central blood gas chemoreceptors on

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9858-437: The bronchioles . In birds , the bronchioles are termed parabronchi . It is the bronchioles, or parabronchi that generally open into the microscopic alveoli in mammals and atria in birds. Air has to be pumped from the environment into the alveoli or atria by the process of breathing which involves the muscles of respiration . In most fish , and a number of other aquatic animals (both vertebrates and invertebrates ),

10017-463: The endothelial cells of the alveolar capillaries (Fig. 10). This blood gas barrier is extremely thin (in humans, on average, 2.2 μm thick). It is folded into about 300 million small air sacs called alveoli (each between 75 and 300 μm in diameter) branching off from the respiratory bronchioles in the lungs , thus providing an extremely large surface area (approximately 145 m ) for gas exchange to occur. The air contained within

10176-401: The limbic system increase and input of dopamine to the prefrontal cortex increases. The balance of excitatory to inhibitory neurotransmitters and increased dopamine activity in adolescence may have implications for adolescent risk-taking and vulnerability to boredom (see Cognitive development below). Serotonin is a neuromodulator involved in regulation of mood and behavior. Development in

10335-410: The red blood cells . The reaction can go in both directions depending on the prevailing partial pressure of CO 2 . A small amount of carbon dioxide is carried on the protein portion of the hemoglobin molecules as carbamino groups. The total concentration of carbon dioxide (in the form of bicarbonate ions, dissolved CO 2 , and carbamino groups) in arterial blood (i.e. after it has equilibrated with

10494-475: The sex organs . In males, the first stages of puberty involve growth of the testes and scrotum, followed by growth of the penis. At the time that the penis develops, the seminal vesicles , the prostate , and the bulbourethral gland also enlarge and develop. The first ejaculation of seminal fluid generally occurs about one year after the beginning of accelerated penis growth, although this is often determined culturally rather than biologically, since for many boys

10653-405: The skin plays a vital role in gas exchange. Plants also have respiratory systems but the directionality of gas exchange can be opposite to that in animals. The respiratory system in plants includes anatomical features such as stomata , that are found in various parts of the plant. In humans and other mammals , the anatomy of a typical respiratory system is the respiratory tract . The tract

10812-509: The trachea or nose , respectively. In this manner, irritants caught in the mucus which lines the respiratory tract are expelled or moved to the mouth where they can be swallowed . During coughing, contraction of the smooth muscle in the airway walls narrows the trachea by pulling the ends of the cartilage plates together and by pushing soft tissue into the lumen. This increases the expired airflow rate to dislodge and remove any irritant particle or mucus. Respiratory epithelium can secrete

10971-428: The ventilation/perfusion ratio of alveoli from the tops of the lungs to the bottoms is eliminated, with all the alveoli perfused and ventilated in more or less the physiologically ideal manner. This is a further important contributor to the acclimatatization to high altitudes and low oxygen pressures. The kidneys measure the oxygen content (mmol O 2 /liter blood, rather than the partial pressure of O 2 ) of

11130-460: The 19.7 kPa of oxygen entering the alveolar air. (The tracheal partial pressure of oxygen is 21% of [100 kPa – 6.3 kPa] = 19.7 kPa). At the summit of Mt. Everest (at an altitude of 8,848 m or 29,029 ft), the total atmospheric pressure is 33.7 kPa , of which 7.1 kPa (or 21%) is oxygen. The air entering the lungs also has a total pressure of 33.7 kPa, of which 6.3 kPa is, unavoidably, water vapor (as it

11289-453: The British pediatrician who devised the categorization system. The human brain is not finished developing by the time a person reaches puberty, or even finishes it. The frontal lobe of the brain has been known to shape itself well into one's 30s. Neuroscientists often cannot agree precisely on when this developmental period ends or if there is an exact age for the end of brain development. Below

11448-562: The Freudian definition as a defense mechanism). Adolescents are much better able than children to understand that people do not have complete control over their mental activity. Being able to introspect may lead to two forms of adolescent egocentrism, which results in two distinct problems in thinking: the imaginary audience and the personal fable . These likely peak at age fifteen, along with self-consciousness in general. Related to metacognition and abstract thought , perspective-taking involves

11607-477: The Leydig cells in the testes is stimulated before the more abundant Sertoli cells begin to produce significant amounts of testosterone. During this stage, boys may appear obese and somewhat awkward physically. Approximately 1 year after the scrotum begins to increase in size, stage II can be seen. During this time, there is a redistribution of subcutaneous fat and the start of pubic hair growth. Following 8 to 12 months of

11766-702: The United States, bone density increases significantly more among black than white adolescents, which might account for decreased likelihood of black women developing osteoporosis and having fewer bone fractures there. Another set of significant physical changes during puberty happen in bodily distribution of fat and muscle. This process is different for females and males. Before puberty, there are nearly no sex differences in fat and muscle distribution; during puberty, boys grow muscle much faster than girls, although both sexes experience rapid muscle development. In contrast, though both sexes experience an increase in body fat,

11925-510: The ability to think about abstract, future possibilities, and the ability to consider multiple possibilities at once. As a result, adolescents experience a significant shift from the simple, concrete, and global self-descriptions typical of young children; as children, they defined themselves by physical traits whereas adolescents define themselves based on their values, thoughts, and opinions. Respiratory system The respiratory system (also respiratory apparatus , ventilatory system )

12084-437: The actions of the intercostal muscles (Fig. 8). These accessory muscles of inhalation are muscles that extend from the cervical vertebrae and base of the skull to the upper ribs and sternum , sometimes through an intermediary attachment to the clavicles . When they contract, the rib cage's internal volume is increased to a far greater extent than can be achieved by contraction of the intercostal muscles alone. Seen from outside

12243-510: The adolescent ages. The dual systems model proposes a maturational imbalance between development of the socioemotional system and cognitive control systems in the brain that contribute to impulsivity and other behaviors characteristic of adolescence. Some studies like the ABCD Study are researching on the baseline of adolescent cognitive development. There are at least two major approaches to understanding cognitive change during adolescence. One

12402-423: The adult human has a volume of about 2.5–3.0 liters (Fig. 3). Resting exhalation lasts about twice as long as inhalation because the diaphragm relaxes passively more gently than it contracts actively during inhalation. The volume of air that moves in or out (at the nose or mouth) during a single breathing cycle is called the tidal volume . In a resting adult human, it is about 500 ml per breath. At

12561-480: The advantage in capturing the attention of potential partners and in being picked first for sports. Pubescent boys often tend to have a good body image, are more confident, secure, and more independent. Late maturing boys can be less confident because of poor body image when comparing themselves to already developed friends and peers. However, early puberty is not always positive for boys; early sexual maturation in boys can be accompanied by increased aggressiveness due to

12720-432: The age of about roughly 30, the human brain has been implicated in human behavior and social immaturity. However, there has been no empirical study indicating a causal relationship with the development of the prefrontal cortex in adolescence and into early adulthood with any irrational behaviors. The brain reaches 90% of its adult size by six years of age. Thus, the brain does not grow in size much during adolescence. Over

12879-453: The alveolar air) is about 26 mM (or 58 ml/100 ml), compared to the concentration of oxygen in saturated arterial blood of about 9 mM (or 20 ml/100 ml blood). Ventilation of the lungs in mammals occurs via the respiratory centers in the medulla oblongata and the pons of the brainstem . These areas form a series of neural pathways which receive information about the partial pressures of oxygen and carbon dioxide in

13038-460: The alveolar partial pressure of carbon dioxide has returned to 5.3 kPa (40 mmHg). It is therefore strictly speaking untrue that the primary function of the respiratory system is to rid the body of carbon dioxide "waste". The carbon dioxide that is breathed out with each breath could probably be more correctly be seen as a byproduct of the body's extracellular fluid carbon dioxide and pH homeostats If these homeostats are compromised, then

13197-423: The alveoli during inhalation (i.e. it makes the lung stiff, or non-compliant). Surfactant reduces the surface tension and therefore makes the lungs more compliant , or less stiff, than if it were not there. Secondly, the diameters of the alveoli increase and decrease during the breathing cycle. This means that the alveoli have a greater tendency to collapse (i.e. cause atelectasis ) at the end of exhalation than at

13356-454: The alveoli has a semi-permanent volume of about 2.5–3.0 liters which completely surrounds the alveolar capillary blood (Fig. 12). This ensures that equilibration of the partial pressures of the gases in the two compartments is very efficient and occurs very quickly. The blood leaving the alveolar capillaries and is eventually distributed throughout the body therefore has a partial pressure of oxygen of 13–14 kPa (100 mmHg), and

13515-400: The ambient atmospheric pressure is about 100 kPa, the moistened air that flows into the lungs from the trachea consists of water vapor (6.3 kPa), nitrogen (74.0 kPa), oxygen (19.7 kPa) and trace amounts of carbon dioxide and other gases (a total of 100 kPa). In dry air the partial pressure of O 2 at sea level is 21.0 kPa (i.e. 21% of 100 kPa), compared to

13674-414: The animal is provided with a very special "portable atmosphere", whose composition differs significantly from the present-day ambient air . It is this portable atmosphere (the functional residual capacity ) to which the blood and therefore the body tissues are exposed – not to the outside air. The resulting arterial partial pressures of oxygen and carbon dioxide are homeostatically controlled . A rise in

13833-454: The anterior surface of the medulla oblongata . The aortic and carotid bodies , are the peripheral blood gas chemoreceptors which are particularly sensitive to the arterial partial pressure of O 2 though they also respond, but less strongly, to the partial pressure of CO 2 . At sea level, under normal circumstances, the breathing rate and depth, is determined primarily by the arterial partial pressure of carbon dioxide rather than by

13992-470: The antero-posterior diameter is increased by the so-called pump handle movement shown in Fig. 4. The enlargement of the thoracic cavity's vertical dimension by the contraction of the diaphragm, and its two horizontal dimensions by the lifting of the front and sides of the ribs, causes the intrathoracic pressure to fall. The lungs' interiors are open to the outside air and being elastic, therefore expand to fill

14151-439: The arterial partial pressure of oxygen , which is allowed to vary within a fairly wide range before the respiratory centers in the medulla oblongata and pons respond to it to change the rate and depth of breathing. Exercise increases the breathing rate due to the extra carbon dioxide produced by the enhanced metabolism of the exercising muscles. In addition, passive movements of the limbs also reflexively produce an increase in

14310-435: The arterial blood. When the oxygen content of the blood is chronically low, as at high altitude, the oxygen-sensitive kidney cells secrete erythropoietin (EPO) into the blood. This hormone stimulates the red bone marrow to increase its rate of red cell production, which leads to an increase in the hematocrit of the blood, and a consequent increase in its oxygen carrying capacity (due to the now high hemoglobin content of

14469-447: The arterial partial pressure of CO 2 and, to a lesser extent, a fall in the arterial partial pressure of O 2 , will reflexly cause deeper and faster breathing until the blood gas tensions in the lungs, and therefore the arterial blood, return to normal. The converse happens when the carbon dioxide tension falls, or, again to a lesser extent, the oxygen tension rises: the rate and depth of breathing are reduced until blood gas normality

14628-422: The beginning of rapid growth, there is the development of breast buds and pubic hair. The peak period of physical growth occurs approximately one year later in concert with stage two of sexual maturity. Approximately 1 to 1.6 years after the onset of secondary sex characteristics, girls enter into the third stage which typically includes menarche. By this time, they will have finished their growth spurt and experience

14787-538: The belly to bulge outwards to the front and sides, because the relaxed abdominal muscles do not resist this movement (Fig. 7). This entirely passive bulging (and shrinking during exhalation) of the abdomen during normal breathing is sometimes referred to as "abdominal breathing", although it is, in fact, "diaphragmatic breathing", which is not visible on the outside of the body. Mammals only use their abdominal muscles during forceful exhalation (see Fig. 8, and discussion below). Never during any form of inhalation. As

14946-451: The blood into the outside air. Oxygen has a very low solubility in water, and is therefore carried in the blood loosely combined with hemoglobin . The oxygen is held on the hemoglobin by four ferrous iron -containing heme groups per hemoglobin molecule. When all the heme groups carry one O 2 molecule each the blood is said to be “saturated” with oxygen, and no further increase in the partial pressure of oxygen will meaningfully increase

15105-449: The blood). In other words, at the same arterial partial pressure of O 2 , a person with a high hematocrit carries more oxygen per liter of blood than a person with a lower hematocrit does. High altitude dwellers therefore have higher hematocrits than sea-level residents. Irritation of nerve endings within the nasal passages or airways , can induce a cough reflex and sneezing . These responses cause air to be expelled forcefully from

15264-435: The body to behave in a certain way once puberty begins, and an active role, referring to changes in hormones during adolescence that trigger behavioral and physical changes. Puberty occurs through a long process and begins with a surge in hormone production, which in turn causes a number of physical changes. It is the stage of life characterized by the appearance and development of secondary sex characteristics (for example,

15423-425: The body, the lifting of the clavicles during strenuous or labored inhalation is sometimes called clavicular breathing , seen especially during asthma attacks and in people with chronic obstructive pulmonary disease . During heavy breathing, exhalation is caused by relaxation of all the muscles of inhalation. But now, the abdominal muscles, instead of remaining relaxed (as they do at rest), contract forcibly pulling

15582-399: The brain are noted to be mature by 14 or 15, making 'maturity' hard to define and has often been disagreed with. Prefrontal cortex pruning has been recorded to level off by age 14 or 15, and has been seen to continue as late as into the sixth decade of life. White matter is recorded to increase up until around the age of 45, and then it is lost via progressive aging. Adolescents' thinking

15741-405: The breathing cycle, drawing air in and out of the lungs. The volume of air moved in or out of the lungs under normal resting circumstances (the resting tidal volume of about 500 ml), and volumes moved during maximally forced inhalation and maximally forced exhalation are measured in humans by spirometry . A typical adult human spirogram with the names given to the various excursions in volume

15900-418: The breathing rate. Information received from stretch receptors in the lungs' limits tidal volume (the depth of inhalation and exhalation). The alveoli are open (via the airways) to the atmosphere, with the result that alveolar air pressure is exactly the same as the ambient air pressure at sea level, at altitude, or in any artificial atmosphere (e.g. a diving chamber, or decompression chamber) in which

16059-506: The chin and the upper lip, adult distribution and color of pubic and axillary hair, and a further increase in muscular strength. The adolescent growth spurt is a rapid increase in the individual's height and weight during puberty resulting from the simultaneous release of growth hormones, thyroid hormones , and androgens . Males experience their growth spurt about two years later, on average, than females. During their peak height velocity (the time of most rapid growth), adolescents grow at

16218-406: The composition of the alveolar air and that of the ambient air can be maintained because the functional residual capacity is contained in dead-end sacs connected to the outside air by fairly narrow and relatively long tubes (the airways: nose , pharynx , larynx , trachea , bronchi and their branches down to the bronchioles ), through which the air has to be breathed both in and out (i.e. there

16377-473: The course of adolescence, the amount of white matter in the brain increases linearly, while the amount of grey matter in the brain follows an inverted-U pattern. Through a process called synaptic pruning , unnecessary neuronal connections in the brain are eliminated and the amount of grey matter is pared down. However, this does not mean that the brain loses functionality; rather, it becomes more efficient due to increased myelination (insulation of axons) and

16536-399: The diaphragm contracts, the rib cage is simultaneously enlarged by the ribs being pulled upwards by the intercostal muscles as shown in Fig. 4. All the ribs slant downwards from the rear to the front (as shown in Fig. 4); but the lowermost ribs also slant downwards from the midline outwards (Fig. 5). Thus the rib cage's transverse diameter can be increased in the same way as

16695-403: The dichotomy between identity formation and role fulfillment. Even with their different theories, these three psychologists agreed that adolescence was inherently a time of disturbance and psychological confusion. The less turbulent aspects of adolescence, such as peer relations and cultural influence, were left largely ignored until the 1980s. From the '50s until the '80s, the focus of the field

16854-408: The dorsolateral prefrontal cortex are important for controlling impulses and planning ahead, while development in the ventromedial prefrontal cortex is important for decision making. Changes in the orbitofrontal cortex are important for evaluating rewards and risks. Three neurotransmitters that play important roles in adolescent brain development are glutamate , dopamine and serotonin . Glutamate

17013-432: The dry outside air at sea level, where the partial pressure of oxygen is 21 kPa (or 160 mm Hg) and that of carbon dioxide 0.04 kPa (or 0.3 mmHg). During heavy breathing ( hyperpnea ), as, for instance, during exercise, inhalation is brought about by a more powerful and greater excursion of the contracting diaphragm than at rest (Fig. 8). In addition, the " accessory muscles of inhalation " exaggerate

17172-419: The end of exhalation, the airways contain about 150 ml of alveolar air which is the first air that is breathed back into the alveoli during inhalation. This volume air that is breathed out of the alveoli and back in again is known as dead space ventilation, which has the consequence that of the 500 ml breathed into the alveoli with each breath only 350 ml (500 ml – 150 ml = 350 ml)

17331-405: The end of inhalation. Since surfactant floats on the watery surface, its molecules are more tightly packed together when the alveoli shrink during exhalation. This causes them to have a greater surface tension-lowering effect when the alveoli are small than when they are large (as at the end of inhalation, when the surfactant molecules are more widely spaced). The tendency for the alveoli to collapse

17490-513: The example given. The differences between the atmospheric and intrapulmonary pressures, driving air in and out of the lungs during the breathing cycle, are in the region of only 2–3 kPa. A doubling or more of these small pressure differences could be achieved only by very major changes in the breathing effort at high altitudes. All of the above influences of low atmospheric pressures on breathing are accommodated primarily by breathing deeper and faster ( hyperpnea ). The exact degree of hyperpnea

17649-586: The family circle, they learn that rules they were taught as absolute are in fact relativistic. They begin to differentiate between rules instituted out of common sense—not touching a hot stove—and those that are based on culturally relative standards (codes of etiquette, not dating until a certain age), a delineation that younger children do not make. This can lead to a period of questioning authority in all domains. Because most injuries sustained by adolescents are related to risky behavior (alcohol consumption and drug use, reckless or distracted driving, unprotected sex),

17808-403: The first ejaculation occurs as a result of masturbation. Boys are generally fertile before they have an adult appearance. In females, changes in the primary sex characteristics involve growth of the uterus, vagina, and other aspects of the reproductive system. Menarche , the beginning of menstruation, is a relatively late development which follows a long series of hormonal changes. Generally,

17967-425: The flow of air and blood to different parts of the lungs. It is only as a result of accurately maintaining the composition of the 3 liters of alveolar air that with each breath some carbon dioxide is discharged into the atmosphere and some oxygen is taken up from the outside air. If more carbon dioxide than usual has been lost by a short period of hyperventilation , respiration will be slowed down or halted until

18126-425: The future. This phenomenon also has consequences for behavioral treatments based on the principle of extinction, such as cue exposure therapy for anxiety or drug addiction. It has been suggested that impaired inhibition, specifically extinction, may help to explain adolescent propensity to relapse to drug-seeking even following behavioral treatment for addiction. The formal study of adolescent psychology began with

18285-402: The hyperpnea at high altitude will cause a severe fall in the arterial partial pressure of carbon dioxide, with a consequent rise in the pH of the arterial plasma . This is one contributor to high altitude sickness . On the other hand, if the switch to oxygen homeostasis is incomplete, then hypoxia may complicate the clinical picture with potentially fatal results. There are oxygen sensors in

18444-650: The increase is much more significant for girls. Frequently, the increase in fat for girls happens in their years just before puberty. The ratio between muscle and fat among post-pubertal boys is around three to one, while for girls it is about five to four. This may help explain sex differences in athletic performance. Pubertal development also affects circulatory and respiratory systems as an adolescents' heart and lungs increase in both size and capacity. These changes lead to increased strength and tolerance for exercise. Sex differences are apparent as males tend to develop "larger hearts and lungs, higher systolic blood pressure,

18603-416: The increased space, pleura fluid between double-layered pleura covering of lungs helps in reducing friction while lungs expansion and contraction. The inflow of air into the lungs occurs via the respiratory airways (Fig. 2). In a healthy person, these airways begin with the nose . (It is possible to begin with the mouth, which is the backup breathing system. However, chronic mouth breathing leads to, or

18762-418: The individual is breathing freely. With expansion of the lungs the alveolar air occupies a larger volume, and its pressure falls proportionally , causing air to flow in through the airways, until the pressure in the alveoli is again at the ambient air pressure. The reverse happens during exhalation. This process (of inhalation and exhalation) is exactly the same at sea level, as on top of Mt. Everest , or in

18921-430: The individual to think and reason in a wider perspective. A combination of behavioural and fMRI studies have demonstrated development of executive functions , that is, cognitive skills that enable the control and coordination of thoughts and behaviour, which are generally associated with the prefrontal cortex . The thoughts, ideas and concepts developed at this period of life greatly influence one's future life, playing

19080-576: The individuals that extended past adolescence into adulthood. Jean Macfarlane launched the Berkeley Guidance Study, which examined the development of children in terms of their socioeconomic and family backgrounds. These studies provided the background for Glen Elder in the 1960s to propose a life course perspective of adolescent development. Elder formulated several descriptive principles of adolescent development. The principle of historical time and place states that an individual's development

19239-417: The interactions between adolescents and their environment; and considering culture, social groups, and historical context when interpreting adolescent behavior. Evolutionary biologists like Jeremy Griffith have drawn parallels between adolescent psychology and the developmental evolution of modern humans from hominid ancestors as a manifestation of ontogeny recapitulating phylogeny . Identity development

19398-430: The limbic system plays an important role in determining rewards and punishments and processing emotional experience and social information. Changes in the levels of the neurotransmitters dopamine and serotonin in the limbic system make adolescents more emotional and more responsive to rewards and stress. The corresponding increase in emotional variability also can increase adolescents' vulnerability. The effect of serotonin

19557-430: The lower edges of the rib cage downwards (front and sides) (Fig. 8). This not only drastically decreases the size of the rib cage, but also pushes the abdominal organs upwards against the diaphragm which consequently bulges deeply into the thorax (Fig. 8). The end-exhalatory lung volume is now well below the resting mid-position and contains far less air than the resting "functional residual capacity". However, in

19716-476: The lungs and released into the blood when lung tissue is stretched. The lungs activate one hormone. The physiologically inactive decapeptide angiotensin I is converted to the aldosterone -releasing octapeptide, angiotensin II , in the pulmonary circulation. The reaction occurs in other tissues as well, but it is particularly prominent in the lungs. Angiotensin II also has a direct effect on arteriolar walls , causing arteriolar vasoconstriction , and consequently

19875-585: The lungs can undergo is illustrated below (Fig. 3): Not all the air in the lungs can be expelled during maximally forced exhalation ( ERV ). This is the residual volume (volume of air remaining even after a forced exhalation) of about 1.0–1.5 liters which cannot be measured by spirometry. Volumes that include the residual volume (i.e. functional residual capacity of about 2.5–3.0 liters, and total lung capacity of about 6 liters) can therefore also not be measured by spirometry. Their measurement requires special techniques. The rates at which air

20034-437: The lungs during breathing rarely exceeding 2–3 kPa. During exhalation, the diaphragm and intercostal muscles relax. This returns the chest and abdomen to a position determined by their anatomical elasticity. This is the "resting mid-position" of the thorax and abdomen (Fig. 7) when the lungs contain their functional residual capacity of air (the light blue area in the right hand illustration of Fig. 7), which in

20193-455: The opposite direction, through orifices in the pelvic floor. The abdominal muscles contract very powerfully, causing the pressure inside the abdomen and thorax to rise to extremely high levels. The Valsalva maneuver can be carried out voluntarily but is more generally a reflex elicited when attempting to empty the abdomen during, for instance, difficult defecation, or during childbirth. Breathing ceases during this maneuver. The primary purpose of

20352-446: The oxygen concentration of the blood. Most of the carbon dioxide in the blood is carried as bicarbonate ions (HCO 3 ) in the plasma. However the conversion of dissolved CO 2 into HCO 3 (through the addition of water) is too slow for the rate at which the blood circulates through the tissues on the one hand, and through alveolar capillaries on the other. The reaction is therefore catalyzed by carbonic anhydrase , an enzyme inside

20511-407: The peak velocity in height gain, stage III ensues. This period is marked by an obvious widenening of hips with a more adult-like fat distribution and full development of the breasts. All together, these three stages culminate in a complete growth spurt for most individuals. At this time, axillary hair appears and facial hair appears on the upper lip only. A spurt in muscle growth also occurs, along with

20670-474: The playing of wind instruments. All of these actions rely on the muscles described above, and their effects on the movement of air in and out of the lungs. Although not a form of breathing, the Valsalva maneuver involves the respiratory muscles. It is, in fact, a very forceful exhalatory effort against a tightly closed glottis , so that no air can escape from the lungs. Instead, abdominal contents are evacuated in

20829-417: The post-pubertal age is uncommon. Girls attain reproductive maturity about four years after the first physical changes of puberty appear. In contrast, boys develop more slowly but continue to grow for about six years after the first visible pubertal changes. The physical development of girls during their teenage years can be broken down into three distinct stages. At the start, which generally coincides with

20988-486: The potential rewards and consequences of an action. However, research has shown that adolescents seem to give more weight to rewards, particularly social rewards, than do adults. Research seems to favor the hypothesis that adolescents and adults think about risk in similar ways, but hold different values and thus come to different conclusions. Some have argued that there may be evolutionary benefits to an increased propensity for risk-taking in adolescence. For example, without

21147-489: The publication of G. Stanley Hall 's Adolescence in 1904. Hall, who was the first president of the American Psychological Association , defined adolescence to be the period of life from ages 14 to 24, and viewed it primarily as a time of internal turmoil and upheaval ( sturm und drang ). This understanding of youth was based on two then-new ways of understanding human behavior : Darwin's evolutionary theory and Freud's psychodynamic theory . He believed that adolescence

21306-421: The reduction of unused pathways. The first areas of the brain to be pruned are those involving primary functions, such as motor and sensory areas. The areas of the brain involved in more complex processes lose matter later in development. These include the lateral and prefrontal cortices, among other regions. Some of the most developmentally significant changes in the brain occur in the prefrontal cortex, which

21465-519: The respiratory system consists of gills , which are either partially or completely external organs, bathed in the watery environment. This water flows over the gills by a variety of active or passive means. Gas exchange takes place in the gills which consist of thin or very flat filaments and lammellae which expose a very large surface area of highly vascularized tissue to the water. Other animals, such as insects , have respiratory systems with very simple anatomical features, and in amphibians , even

21624-443: The respiratory system is lined with mucous membranes that contain mucosa-associated lymphoid tissue , which produces white blood cells such as lymphocytes . The lungs make a surfactant , a surface-active lipoprotein complex (phospholipoprotein) formed by type II alveolar cells . It floats on the surface of the thin watery layer which lines the insides of the alveoli, reducing the water's surface tension. The surface tension of

21783-417: The respiratory system is the equalizing of the partial pressures of the respiratory gases in the alveolar air with those in the pulmonary capillary blood (Fig. 11). This process occurs by simple diffusion , across a very thin membrane (known as the blood–air barrier ), which forms the walls of the pulmonary alveoli (Fig. 10). It consists of the alveolar epithelial cells , their basement membranes and

21942-477: The rest of the lower face to form a full beard. As with most human biological processes, this specific order may vary among some individuals. Facial hair is often present in late adolescence, around ages 17 and 18, but may not appear until significantly later. Some men do not develop full facial hair for 10 years after puberty. Facial hair continues to get coarser, much darker, and thicker for another 2–4 years after puberty. The major landmark of puberty for males

22101-428: The same amount of oxygen to the lungs at altitude as at sea level. During inhalation, the air is warmed and saturated with water vapor during its passage through the nose passages and pharynx . Saturated water vapor pressure is dependent only on temperature. At a body core temperature of 37 °C it is 6.3  kPa (47.0 mmHg), irrespective of any other influences, including altitude. Thus at sea level, where

22260-539: The same change in lung volume at sea level results in a 50 kPa difference in pressure between the ambient air and the intrapulmonary air, whereas it result in a difference of only 25 kPa at 5500 m. The driving pressure forcing air into the lungs during inhalation is therefore halved at this altitude. The rate of inflow of air into the lungs during inhalation at sea level is therefore twice that which occurs at 5500 m. However, in reality, inhalation and exhalation occur far more gently and less abruptly than in

22419-480: The same rate as the fall in air pressure with altitude. Therefore, in order to breathe in the same amount of oxygen per minute, the person has to inhale a proportionately greater volume of air per minute at altitude than at sea level. This is achieved by breathing deeper and faster (i.e. hyperpnea ) than at sea level (see below). There is, however, a complication that increases the volume of air that needs to be inhaled per minute ( respiratory minute volume ) to provide

22578-413: The same route. A system such as this creates dead space , a volume of air (about 150 ml in the adult human) that fills the airways after exhalation and is breathed back into the alveoli before environmental air reaches them. At the end of inhalation, the airways are filled with environmental air, which is exhaled without coming in contact with the gas exchanger. The lungs expand and contract during

22737-422: The segmental bronchi (1 to 6 mm in diameter) are known as 4th order, 5th order, and 6th order segmental bronchi, or grouped together as subsegmental bronchi. Compared to the 23 number (on average) of branchings of the respiratory tree in the adult human, the mouse has only about 13 such branchings. The alveoli are the dead end terminals of the "tree", meaning that any air that enters them has to exit via

22896-445: The small airways lacking any cartilaginous support. The first bronchi to branch from the trachea are the right and left main bronchi. Second, only in diameter to the trachea (1.8 cm), these bronchi (1–1.4 cm in diameter) enter the lungs at each hilum , where they branch into narrower secondary bronchi known as lobar bronchi, and these branch into narrower tertiary bronchi known as segmental bronchi. Further divisions of

23055-408: The smaller bronchi and bronchioles . In response to low partial pressures of oxygen in the inhaled air these sensors reflexively cause the pulmonary arterioles to constrict. (This is the exact opposite of the corresponding reflex in the tissues, where low arterial partial pressures of O 2 cause arteriolar vasodilation.) At altitude this causes the pulmonary arterial pressure to rise resulting in

23214-532: The surge of hormones that affect them. Because they appear older than their peers, pubescent boys may face increased social pressure to conform to adult norms; society may view them as more emotionally advanced, despite the fact that their cognitive and social development may lag behind their appearance. Studies have shown that early maturing boys are more likely to be sexually active and are more likely to participate in risky behaviors. For girls, early maturation can sometimes lead to increased self-consciousness,

23373-470: The teens. Age provides only a rough marker of adolescence, and scholars have not agreed upon a precise definition. Some definitions start as early as 10 and end as late as 30. The World Health Organization definition officially designates an adolescent as someone between the ages of 10 and 19. Puberty is a period of several years in which rapid physical growth and psychological changes occur, culminating in sexual maturity. The average age of onset of puberty

23532-418: The thinking process. By the time individuals have reached ages 12–14 or so their critical thinking and decision-making competency are comparable to those of adults. These improvements occur in five areas during adolescence: Studies newer than 2005 indicate that the brain is changing in efficiency well past its twenties, a 'point of maturity' in the twenties is somewhat arbitrary as many important parts of

23691-409: The thoracic cavity from the abdominal cavity. When it contracts, the sheet flattens, (i.e. moves downwards as shown in Fig. 7) increasing the volume of the thoracic cavity in the antero-posterior axis. The contracting diaphragm pushes the abdominal organs downwards. But because the pelvic floor prevents the lowermost abdominal organs from moving in that direction, the pliable abdominal contents cause

23850-487: The traditional immune cells and others to the site of infections. Surfactant immune function is primarily attributed to two proteins: SP-A and SP-D. These proteins can bind to sugars on the surface of pathogens and thereby opsonize them for uptake by phagocytes. It also regulates inflammatory responses and interacts with the adaptive immune response. Surfactant degradation or inactivation may contribute to enhanced susceptibility to lung inflammation and infection. Most of

24009-555: The transition to adulthood. Researchers have used three general approaches to understanding identity development: self-concept, sense of identity, and self-esteem. The years of adolescence create a more conscientious group of young adults. Adolescents pay close attention and give more time and effort to their appearance as their body goes through changes. Unlike children, teens put forth an effort to look presentable (1991). The environment in which an adolescent grows up also plays an important role in their identity development. Studies done by

24168-473: The various branches of "tree" are often referred to as branching "generations", of which there are, in the adult human, about 23. The earlier generations (approximately generations 0–16), consisting of the trachea and the bronchi, as well as the larger bronchioles which simply act as air conduits , bringing air to the respiratory bronchioles, alveolar ducts and alveoli (approximately generations 17–23), where gas exchange takes place. Bronchioles are defined as

24327-448: The voice, roughening of the skin around the upper arms and thighs, and increased development of the sweat glands. In females, secondary sex changes involve elevation of the breasts, widening of the hips, development of pubic and underarm hair, widening of the areolae, and elevation of the nipples. The changes in secondary sex characteristics that take place during puberty are often referred to in terms of five Tanner stages , named after

24486-444: The volume of the lungs were to be instantaneously doubled at the beginning of inhalation, the air pressure inside the lungs would be halved. This happens regardless of altitude. Thus, halving of the sea level air pressure (100 kPa) results in an intrapulmonary air pressure of 50 kPa. Doing the same at 5500 m, where the atmospheric pressure is only 50 kPa, the intrapulmonary air pressure falls to 25 kPa. Therefore,

24645-492: The ways in which language can be used to convey multiple messages, such as satire, metaphor, and sarcasm . (Children younger than age nine often cannot comprehend sarcasm at all.) This also permits the application of advanced reasoning and logical processes to social and ideological matters such as interpersonal relationships, politics, philosophy, religion, morality, friendship, faith, fairness, and honesty. A third gain in cognitive ability involves thinking about thinking itself,

24804-590: The while seeming to be completely oblivious to the fact that he had done so. Another of his videos, "Crackberry Blackberry", was selected as an official honoree at the 11th Annual Webby Awards . Nalty made a video to announce his departure from his role as a Merck Product Director, and appears in many articles about memorable resignations. He is the voice of the knife in popular web series "Annoying Orange." He has been sponsored by Fox Broadcasting, MTV, Logitech, Microsoft, Holiday Inn Express, Crowne Plaza, and Mentos . Buzzfeed covered Nalty's history of pranks , and he

24963-428: Was a representation of our human ancestors' phylogenetic shift from being primitive to being civilized. Hall's assertions stood relatively uncontested until the 1950s when psychologists such as Erik Erikson and Anna Freud started to formulate their theories about adolescence. Freud believed that the psychological disturbances associated with youth were biologically based and culturally universal while Erikson focused on

25122-569: Was mainly on describing patterns of behavior as opposed to explaining them. Jean Macfarlane founded the University of California, Berkeley 's Institute of Human Development, formerly called the Institute of Child Welfare, in 1927. The institute was instrumental in initiating studies of healthy development, in contrast to previous work that had been dominated by theories based on pathological personalities. The studies looked at human development during

25281-488: Was on 2020 podcast discussing his divorce . and his videos have appeared on CNN , ABC Nightline , The Today Show , Good Morning America , CBS News , Fox News and the BBC segment "Click", where one of his videos was featured on the program. He appeared as a guest judge on "Viral Video Showdown," was featured in the film "I Want My Three Minutes Back," and his videos have been featured on MTV's "Pranked." He has also appeared on

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