now 2/3 of the heart is oriented left of the midsternal line the apex of the heart projects into a region of the left lung known as the cardiac Notch here the heart as well as the cardiac Notch occupies volume or space that would have otherwise been a third lobe in the left lung the leftward projection of the heart and the presence of the cardiac notch on the left lung account for why the left lung only contains two loes and is anatomically smaller compared to the right lung now Dalton's law maintains that we can think of the atmospheric air as a mixture of essentially three types of gases and the total pressure exerted by this mixture is equivalent to the sum of all the individual partial pressures exerted by each gas added together the partial pressure exerted by each gas in the mixture is proportional to the percentage of that gas in the atmosphere now if oxygen contributes to 21% of atmospheric air then the partial pressure of oxygen gas is also 21% of the total atmospheric pressure now nitrogen gas actually contributes to 78% of atmospheric air therefore the partial pressure exerted by nitrogen gas is also 78% of the total pressure exerted by the atmosphere this leaves a remaining 1% to be accounted for by carbon dioxide gas collectively these three gases comprise 100% of the atmospheric air this brings us to the first checkpoint question of this lecture recording now pulmonary ventilation includes two phases inspiration and expiration inspiration is synonymous with inhalation or moving air into the lungs and expiration is synonymous with exhalation or moving air out of the lungs we engage in normal inhalation and exhalation without any conscious effort now normal inhalation is an active process during which the diaphragm contracts and shifts down inferiorly into the abdominal pelvic cavity thereby increasing the top to bottom length of the thoracic cavity additionally during normal inhalation the external intercostal muscles also contract to elevate the rib cage thereby increasing the front to back backlength of the thoracic cavity both these events effectively increase the overall volume of the thoracic cavity when the volume of the thoracic cavity increases the volume of the lungs within them also increase now changes in the volume of the lungs will result in a corresponding change in the air pressure within those lungs since boils law maintains that volume and pressure are inversely proportional this increase in the volume of the lungs during inhalation will coincide with a decrease in the pressure within the lungs now partial pressure differences or gradients between the environment and our lungs determine the direction of gas movement since gases move down their pressure gradients this means that during inhalation gases will move from a region of higher pressure in the atmosphere towards a region of lower pressure in the lungs this is why during inhalation air is drawn into the lungs where pressure is lower now unlike normal inspiration normal expiration is a passive process during which no muscle contractions occur instead the diaphragm relaxes and shifts up into the thoracic cavity thereby decreasing the top to bottom length of the thoracic cavity additionally during exhalation the external intercostal muscles also relax to depress the rib cage thereby decreasing the front to back length of the thoracic cavity both these events decrease the overall volume of the thoracic cavity which in turn decreases the volume of the lungs when the volume of the lungs decreases the pressure within the lungs increases gases will now move from a region of higher pressure in the lungs towards a region of lower pressure in the atmosphere so during exhalation air is drawn out of the lungs into the environment where pressure is lower forced expiration is an active muscular process during which the internal intercostal muscles contract to depress the rib cage and therefore decreas the front to back length of the thoracic cavity Force expiration also involves the contraction of the abdominal muscles which forces the diaphragm up to decrease the top to bottom length of the thoracic cavity the actions of both sets of muscles decreases the volume of the thoracic cavity and thus decreases the volume of the lungs according to Bo's law a decrease in the volume of the lungs coincides with an increase in pressure within the lungs this causes pressure in the lungs to be greater than the pressure in the atmosphere forcing air out examples of force expiration include forcefully exhaling to blood a candle or forcefully exhaling to manually inflate an object the two types of respiration occurring in the body are external and internal respiration external respiration involves gas exchange occurring between the pulmonary blood capillaries and the alvioli since the alvioli are part of our open respiratory tree or tract that is is continuous with the external environment this accounts for why gas exchange between alveoli and blood is termed external respiration this type of gas exchange occurs in the lung tissue now internal respiration involves gas exchange occurring between the systemic blood capillaries and the cells of body Tiss isssues since both the systemic blood capillaries and the body tissues belong to entirely closed systems not continuous with the external environment this is why gas exchange between body tissues and blood is termed internal respiration this type of gas exchange occurs at the level of body tissues external respiration ation occurs as a function of partial pressure differences in oxygen and carbon dioxide between the alvioli and the blood inside pulmonary capillaries now the partial pressure of oxygen in the alvioli is about 104 mm of mercury whereas the partial pressure of oxygen in the blood of the pulmonary capillary is about 40 mm of mercury this difference is about 64 mm of mercury this large drastic difference in partial pressure creates a very strong pressure gradient that causes oxygen to rapidly cross the respiratory membrane from the alvioli into the blood now the partial pressure of carbon dioxide side is also different between the alvioli and the blood of the pulmonary capillary but to a lesser degree compared to the partial pressure difference of oxygen the partial pressure of carbon dioxide in the blood of the pulmonary capillary is about 45 mm of mercury whereas the partial pressure of carbon dioxide in the alvioli is about 40 mm of mercury here the partial pressure difference of carbon dioxide is less than that of oxygen only about 5 mm of mercury however this partial pressure difference is sufficient to drive the diffusion of carbon dioxide from the blood across the respiratory membrane and into the alviola internal respiration is gas exchange that occurs at the level of body tissues similar to external respiration internal respiration also occurs through the process of diffusion due to a partial pressure gradient however the partial pressure gradients in internal respiration are the reverse of those present in external respiration the partial pressure of oxygen in the blood of the systemic capillary is approximately 100 mm of mercury in contrast because oxygen is continuously used for cellular or aerobic respiration the partial pressure of oxygen in body tissues is low approxim o imately 40 mm of mercury this creates a pressure gradient that causes oxygen to dissociate from hemoglobin diffuse out of blood cross the interstial fluid and into the tissues now considering that cellular or aerobic respiration continually produces carbon dioxide as a byproduct in the tissue cells the partial pressure of carbon dioxide in the tissue cells is approximately 45 mm of mercury Which is higher than the partial pressure of carbon dioxide in the blood of the systemic capillary which is approximately 40 mm of mercury this again creates a pressure gradient that allows gas exchange to occur but by prompting carbon dioxide to diffuse out of the tissues cross the interstitial fluid and into the blood this brings us to the next checkpoint question of this lecture recording while chemo receptors in the body are sensitive to decreases in blood oxygen saturation levels they have even greater sensitivity to increases in blood carbon dioxide levels increased levels of carbon dioxide are hazardous or detrimental because carbon dioxide can bind to water to yield a compound known as carbonic acid carbonic acid has the chemical formula H2 Co 3 carbonic acid is a weak acid that dissociates into hydrogen ions and bicarbonate ions the release or liberation of hydrogen ions effectively lowers blood pH which in turn increases the acidity of blood as a result the body compensates for excessive carbon dioxide buildup or production by promoting increased depth and rate of breathing which is known as hyperia hyperia is increased ventilation in response to elevated levels of carbon dioxide a hyperia response results in the restoration of carbon dioxide levels back to normal set points now this breathing response is an example of a negative feedback loop where deviations from homeostasis will Kickstart a chain of reactions that reverse the original stimulus and return the individual to normal homeostatic set points in this case sensory receptors will detect increased levels of carbon dioxide and lowered blood pH sensory receptors will send input signals to our nervous system to coordinate an increase in breathing rate known as hyperia we breathe faster and more deeply expelling more carbon dioxide the lowered levels of carbon dioxide will raise our blood pH back up to normal in summary carbon dioxide is an even more potent influencer of breathing or respiration than oxygen although the body requires oxygen for metabolism low oxygen levels normally do not stimulate breathing rather we see that breathing is greatly stimulated by higher or elevated carbon dioxide levels a spirometer is a device that measures the volumes of air moving moving into and out of the respiratory system tital volume abbreviated TV refers to the volume of air breathe in and out during our normal quiet breathing without any conscious effort at rest title volume is about 500 mL of air the term title references the rising and falling pattern of air volumes breathed in and out of the lungs when we engage in normal quiet breathing inspiratory Reserve volume abbreviated Irv is the additional amount of air that enters the lungs when a person forcefully inhales past the tital volume at rest inspiratory Reserve volume is approximately 3,000 M of air expiratory Reserve volume abbreviated Erv is the additional amount of air that leaves the lungs when a person forcefully exhales past the tital volume at rest expiratory Reserve volume is approximately 1,000 mL of air vital capacity abbreviated VC corresponds to the maximum amount of air a person can expel from the lungs following maximum inhalation vital capacity is the sum of tital volume inspiratory Reserve volume and expiratory Reserve volume added together theoretically vital capacity is about 5,000 m of air not taking into account height nor gender residual volume abbreviated AR V corresponds to the volume of air still remaining in the lungs after expiratory Reserve volume is exhaled residual volume reflects the fact that lungs can never be completely empty now a residual volume is approximately 1,200 mL of air our total lung capacity abbreviated TLC is defined as the total volume of air present in the lungs at the end of Maximum inhalation it is the sum of vital capacity Plus residual volume under resting conditions our respiratory control centers in the nervous system produce a normal respiration rate of 12 to 18 breaths per minute in the graph we can observe tital volume increasing agressively as a person engages in Greater physical activity or exercise as tital volume increases it displaces or overtakes both the inspiratory and expiratory Reserve volumes as a result this increase in title volume during exercise where every breath taken becomes greater and greater results in a corresonding decrease in both the inspiratory reserve volume and expiratory Reserve volume because changes in title volume inspiratory Reserve volume and expiratory Reserve volume during exercise offset one another a person's vital capacity and total lung capacity do not change with greater physical activity or exercise vital capacity and total lung capacity are values that remain constant because the lungs can only expand so far to hold a given amount of air and during exercise lungs do not expand Beyond this fixed maximum size here is the next checkpoint question our respiratory control centers are located in the ponds and medulla of the brain stem our ability to control respiration allows the body to adjust to varying demands for oxygen supply and carbon dioxide removal sensory receptors such as chemo receptors and stretch receptors will relay input signals to the respiratory control centers of our brain stem to either limit or accelerate breathing so that we can respond accordingly to these varying demands hemo receptors located within the aorta and kateed artery are sensitive to and detect changes in oxygen carbon dioxide and blood pH levels stretch receptors located in the lungs and thorax are sensitive to the degrees of stretch displayed by lungs and the chest thus protecting respiratory organs from overinflation the prefix U translates to good or well therefore the term eia indicates normal unlabored breathing hyperventilation is an increase in ventilation beyond the normal metabolic need for carbon dioxide removal where we eliminate too much carbon dioxide resulting in an abnormal decrease in carbon dioxide levels and thus an abnormal increase in blood pH where the blood becomes too alkaline or basic this is a medical condition known as respiratory alkalosis where hyperventilation elevates the blood pH beyond the normal range of 7.35 to 7.45 now from a physiological standpoint the purpose of breathing into a bag repeatedly following a hyperventilation episode is to rebreathe or reinh the exhaled carbon dioxide in an attempt to restore carbon dioxide and blood pH levels back to homeostatic levels now hypoventilation is a decrease in ventilation below the normal metabolic need for carbon dioxide removal where we do not eliminate enough carbon dioxide resulting in an abnormal increase in carbon dioxide levels and thus an abnormal decrease in blood pH where the blood becomes too acidic this is a medical condition known as respiratory acidosis where hypoventilation lowers the blood pH below the normal range of 7.35 to 7 .45 now the prefix dis translates to difficult therefore the term dmia indicates difficult or labored breathing now the prefix a translates to without or lack of thus apnea indicates an individual has ceased or stopped breathing if the heart is still active but the individual fails to resume breathing on their own this condition is known as respiratory arrest which warrants immediate medical attention and first aid this brings us to the final checkpoint question of this lecture recording