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41 Cards in this Set

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Respiration, the process of obtaining O2 from the environment and eliminating CO2 from the body, can be subdivided into 2 separate processes
2 processes of respiration
1) internal respiration
2) external respiration
Define internal respiration.
def. this refers to the intracellular metabolic processes that take place within mitochondria, which use O2 and produce CO2 during the derivation of energy from nutrient molecules.
Define external respiration.
def. this refers to the entire sequence of events involved in exchanging O2 and CO2 between the environment and the cells of the body. It is composed of four subprocesses, the first two of which are accomplished by the respiratory system.
Processes of external respiration
1) breathing - the alternate movement of air in and out of the lungs to exchange gas between the environment and the alveoli.
2) alveolar gas exchange - exchange of O2 and CO2 between gas in the alveoli and blood in the pulmonary capillaries
3) gas transport - the transport of O2 and CO2 by the blood from the lungs to the tissues of the body
4) blood gas exchange - the exchange of O2 and CO2 between the blood and the tissues
Repiratory System
def. the system responsible for the first two stages of external respiration
Respiratory Airways
def. these are the tubes that carry air between the atmosphere and the alveoli.

nasal passages - nose
pharynx - common passageway for the lungs and the stomach
larynx - voice box located at the entrance to the trachea
trachea - tube through which air is conducted to the lungs
bronchi - division of the trachea into two main branches
bronchioles - small branches of the respiratory airway
alveoli - tiny, air-filled chambers (~300 μm dia) within the lungs that serve as the site for the exchange of O2 and CO2 with the blood
Lungs - a pair of organs, housed within the thoracic cavity, consisting of the lower portion of the respiratory airways, the pulmonary circulation, and connective tissue.
Pleural Sacs - a pair of thin, fluid-filled, membranes that enclose the lungs. The space between the pair of membranes is referred to as the pleural cavity (Figure 13-5).
Respiratory Mechanics
def. a gradient in pressure between the alveoli and the atmosphere provides the force to move air into and out of the lungs. The mechanical properties of the lungs and the thoracic cavity provide the forces that regulate the flow of air. Several different pressures and forces are important in determining the mechanics of respiration
Pressures and Forces Important in Dtermining the mechanics of respiration
Equal to 760 mm of Hg.
Intra-alveolar pressure - the pressure within the alveoli. Continuous with the atmosphere.
Intra-pleural pressure - the pressure within the pleural sac. Usually 4 mm of Hg less than atmospheric pressure (i.e. 756 mm Hg). This pressure does not equilibrate with the atmosphere, because the pleural sacs are closed chambers.
Intra-pleural fluid cohesion - the force acting to attract two surfaces when they are separated by a layer of fluid. This force acts to keep the outer surface of the lungs stuck to the inner surface of the thoracic wall.
Transmural pressure gradients - These are the differences in pressure between the intra-pleural space and the intra-alveolar and atmospheric spaces (Figure 13-8).
is an extremely dangerous condition that occurs when air is allowed to enter the plural cavity (either by a puncture wound in chest, or a hole in lung) (Figure 13-9). As a result, the transmural pressure gradient is lost and the lungs and thorax separate and assume their own inherent dimensions (lungs collapse and thoracic wall expands).
Boyle’s law
At any constant temperature, the pressure exerted by a gas varies inversely with the volume of the gas. Restated, as the volume of a gas increases, the pressure exerted by the gas decreases proportionately, and conversely, the pressure increases proportionately as the volume decreases
Changes - in lung volume and intra-alveolar pressure during inspiration and expiration.
Before inspiration - system is equillibrated; no net movement of air
During inspiration - size of the lungs increases as they are stretched to fill the expanded thorax. As the lungs increase in volume, intra-alveolar pressure decreases creating a pressure gradient that favors the flow of air into the alveoli.
During expiration - as the lungs recoil to their pre-inspiratory size, intra-alveolar pressure increases, establishing a pressure gradient that favors the flow of air out of the alveoli into the atmosphere
Expiration has passive and active compenents:
Passive expiration - the ribs, sternum, and diaphragm return to resting position upon relaxation of the inspiratory muscles.
Active expiration - contraction of abdominal muscles causes the diaphragm to be pushed upward, further reducing the vertical dimension of thoracic cavity. Also, contraction of the internal intercostal muscles flattens the ribs and sternum further reducing the size of the thoracic cavity.
Elastic recoil
this is the force that restores the lungs to their preinspiratory volume after the inspiratory muscles relax at the end of inspiration. It is similar to the force that restores the shape of a balloon when the air within it is released. It is determined by two factors:
2 factors contributing to elastic recoil
elastic properties of pulmonary tissue - pulmonary tissue contains large quantities of elastin fibers. They are arranged in a meshwork that provides the tissue with a high degree of elasticity.
alveolar surface tension - this is the force exerted at the interface between a liquid and a gas that tends to minimize the surface area at the interface. It results from the preferential attraction of water molecules for each other. In the alveoli, surface tension acts to resist any increases in alveolar surface area and thereby oppose alveolar expansion during inspiration. Similarly, surface tension acts to minimize alveolar surface area and thereby reduce the size of the alveoli. This force is so strong that it must be counteracted in order to prevent alveolar collapse. This is achieved by the production of a pulmonary surfactant that is synthesized by the type II cells and released into the alveoli (Figure 13-16).
Law of LaPlace - Magnitude of inward-directed pressure (P) in a bubble = 2 x surface tension (T)/ radius (r) of bubble. In the presence of surfactant, inward pressure in the smaller alveolus is reduced to a level comparable to that of the larger alveoulus. Thus, the smaller aveolus will not collapse.
Variations in lung volume:
- For an average male, total lung capacity at maximum inflation = 5,700 ml
- For an average male, minimal lung volume at maximum deflation = 1,200 ml
- For an average male, maximal amount of air exchange between max inflation
and max deflation = 5,700 ml – 1,200 ml = 4,500 ml (“vital capacity”)
- For an average male, variation in lung volume with normal quiet breathing
= 2,700 ml – 2,200 ml = 500 ml (“tidal volume”)
device for measuring the volume of air breathed in and out. The device is an air filled drum floating in a water-filled chamber. As a person breathes air in and out of the drum through a connecting tube, the resultant rise and fall of the drum are recorded as a spirogram
TV = Tidal volume (500 ml),
variation in lung volume with normal breathing
IRV = Inspiratory reserve volume (3,000 ml),
the extra volume of air that can
be maximally inspired over and above the typical resting tidal volume
IC = Inspiratory capacity (3,500 ml),
max volume of air that can be inspired at
the end of a normal, quiet expiration (IC = IRV +TV)
ERV = Expiratory reserve volume (1,000 ml),
the extra volume of air that can
be actively expired by maximal contraction of the expiratory muscles
RV = Residual volume (1,200 ml),
the minimum volume of air remaining in the
lungs even after a maximal expiration
FRC = Functional residual capacity (2,200 ml),
the volume of air in the lungs at
the end of a normal passive expiration (FRC=ERV+RV)
VC = Vital capacity (4,500 ml),
the maximum volume of air that can be moved out
during a single breath following a maximal inspiration (VC=IRV+TV+ERV)
TLC = Total lung capacity (5,700 ml)
the maximum volume of air that the
lungs can hold (TLC= VC+RV)
Gas Exchange
During external respiration O2 and CO2 are continuously exchanged between the external environment and the tissues of the body. This exchange occurs at two sites: in the lungs, at the interface between the pulmonary capillaries and the atmosphere, and in the tissues of the body, at the interface between the systemic capillaries and the tissue cells. The movement of these gases takes place by passive diffusion down partial pressure gradients
partial pressure (PG)
this is the independent pressure exerted by a particular gas contained within a mixture of gases. It is directly proportional to the percentage of the gas in the mixture (Figure 13-24). Gases move passively by diffusing from regions of high partial pressure to low partial pressure. Atmospheric gas contains 79% nitrogen, 21% oxygen, and approximately .004% carbon dioxide.
Other factors influencing gas exchange
alveolar-capillary distance - gas exchange is proportional to the diffusion distance
alveolar surface area - gas exchange is proportional to the surface area over which diffusion can take place
diffusion coefficient - the rate of diffusion of a gas in a liquid depends on the solubility of the gas and its molecular weight. The solubility of CO2 in body tissues is approximately 20 times higher than O2. It therefore diffuses across the respiratory membranes 20 times more rapidly than O2. This offsets the greater partial pressure gradient of O2 and enables approximately equal amounts of O2 and CO2 to be exchanged during respiration.
Gas Transport
this refers to the processes by which O2 and CO2 are transported between the systemic tissues and the lungs.
O2 transport
O2 is transported from the lungs to the systemic tissues in two forms: dissolved in the blood, and chemically bound to hemoglobin. Approximately 1.5% of the O2 available in blood is dissolved leaving the vast majority of O2 bound to hemoglobin. Only the portion of O2 that is dissolved in the blood contributes to the partial pressure. Thus PO2 is not a measure of the O2 content of blood but only the portion that is dissolved.
Oxygen storage
hemoglobin serves as a reservoir for O2 without affecting the partial pressure gradient that is necessary for gas exchange
this is a soluble protein present in the cytoplasm of erythrocytes (red blood cells) that can reversibly bind 4 molecules of O2 (Figure 11-3) to a specialized iron-containing component referred to as a heme group. Hemoglobin has 4 heme groups (each with an iron atom), each of which can reversibly combine with an O2 molecule.
Hb + O2 ↔ HbO2
hemoglobin saturation
hemoglobin is considered fully saturated when all of the Hb present in the blood is carrying its maximum load of O2. The extent of Hb saturation in the blood can vary from 0% to 100%. The most important factor determining the % Hb saturation is the PO2 of the blood, which is related to the concentration of O2 dissolved in the blood. The % Hb saturation is proportional to the PO2 of the blood and this relationship follows a non-linear S-shaped function known as the oxygen-hemoglobin dissociation curve (Figure 13-27). Several physiological factors can influence the properties of the dissociation curve (
Physiological factors can influence the ppt of the dissociation curves
CO2 - CO2 shifts the dissociation curve to the right, decreasing the affinity of Hb for O2. When blood reaches the systemic capillaries the increase in PCO2 promotes a further dissociation of O2 from Hb.
pH - H+ shifts the dissociation curve to the right, decreasing the affinity of Hb for O2. When blood reaches the systemic capillaries the lowered pH, resulting from the increase in PCO2, promotes a further dissociation of O2 from Hb.
temperature - an increase also shifts the dissociation curve to the right, decreasing the affinity of Hb for O2.
the binding affinity of Hb for carbon monoxide is approximately 240 times greater than for O2. Thus, in the presence of CO, less Hb is available for binding to O2 and the O2 carrying capacity of the blood is reduced. CO is not a normal constituent of inspired air (it’s produced during the incomplete combustion of carbon products such as gasoline, coal, tobacco). CO is particularly dangerous because it is odorless, colorless, tasteless, and non-irritating. CO can reach lethal levels without the victim ever being aware of the danger.
oxygen storage
because only the O2 dissolved in the blood contributes to its partial pressure, hemoglobin can serve as a reservoir for O2 without affecting the partial pressure gradient that is necessary for gas exchange (Figure 13-29). Only after Hb is fully saturated, will the diffusion of O2 contribute to a change in PO2.
CO2 transport
CO2 is transported from the systemic tissues to the lungs in three forms: dissolved in the blood, chemically bound to hemoglobin, and as bicarbonate (HCO3-). Approximately 10% of the blood CO2 is dissolved, 30% is combined with hemoglobin, and the remaining 60% is converted to HCO3- and dissolved in the blood. As with O2, only the portion of CO2 that is dissolved in the blood contributes to the partial pressure (Figure 13-30).
carbamino hemoglobin (HbCO2
this is the form of Hb in which CO2 is bound to the globin portion of the protein. The affinity of Hb for CO2 is greater when Hb is in its reduced form (i.e. dissociated from O2). Thus, when O2 is released in the systemic capillary circulation this facilitates the binding of CO2 to Hb and thereby increases the rate of CO2 transport out of the tissues.
bicarbonate (HCO3-)
CO2 is converted to HCO3- within red blood cells by carbonic anhydrase:
CO2 + H2O ↔ H2CO3 ↔ H+ + HCO3-
Because HCO3- is readily soluble this greatly increases the CO2 carrying capacity of the blood. As the reaction proceeds HCO3- is reversibly transported out of the cell and into the blood plasma by exchange with Cl- (referred to as the “Chloride Shift”). The remaining H+ facilitates the dissociation of O2 from Hb. H+ also binds to the reduced form of Hb after O2 has dissociated and this serves to buffer the pH of the venous blood.
Neural Control of Respiration
several respiratory centers in the brainstem (pons and medulla) establish a rhythmic firing pattern which drives motor neurons in the spinal
cord to stimulate the skeletal inspiratory muscles (Figure 13-32). These centers respond to changes in arterial PCO2 by increasing their activity, and thereby increasing the rate of ventilation. These responses are mediated by central chemoreceptors located near the respiratory centers in the medulla oblongata.
occurs if a person is underbreathing. IF this occurs, then PCO2 is above normal and PO2 is below normal
occurs if a person is overbreathing. IF this occurs, then PCO2 is below normal and PO2 is above normal.