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Phys U4 - Resp
Physiology Unit 4 - Respiratory - Fofi
| Question | Answer |
|---|---|
| Respiratory system functions | to supply body with oxygen, dispose of CO2 |
| Respiration—four processes | pulmonary ventilation, external ventilation, transport, internal respiration |
| Pulmonary ventilation | moving air into and out of lungs |
| External respiration | gas exchange b/t lungs and blood |
| Transport | transport of O and CO2 b/t lungs and tissues |
| Internal respiration | gas exchange b/t systems blood vessels and tissues |
| Respiratory system components | conducting and respiratory zones, respiratory muscles |
| Conducting zone | provides rigid conduits for air to reach sites of gas exchange; nose, nasal cavity, pharynx, trachea, primary bronchi, smaller bronchi; air passages undergo 23 orders of branching in the lungs, significantly increasing cross sectional area for flow |
| Respiratory zone | site of gas exchange; consists of bronchioles, alveolar ducts, alveoli; approximately 300 million alveoli; account for most of the lung’s volume, provide tremendous surface area for gas exchange |
| Internal respiration | exchange of gases between interstitial fluid and cells |
| External respiration | exchange of gases between interstitial fluid and the external environment; steps include pulmonary ventilation, gas diffusion, transport of O and CO2 |
| Pulmonary ventilation | physical movement of air into and out of lungs; mechanical process that depends on volume changes in thoracic cavity; volume changes lead to pressure changes, which lead to flow of gases to equalize pressure. Gas moves from high pressure to low pressure |
| Boyle’s Law | relationship b/t pressure and volume of gases; P1V1=P2V2; P=pressure of gas in cubic millimeters; V=volume of a gas in cubic mm; inversely proportional, so as pressure decreases, volume increases; as volume decreases, pressure increases |
| Diaphragm movement | at rest diaphragm relaxed; as diaphragm contracts, thoracic volume increases; diaphragm relaxes, thoracic volume decreases |
| Pressure relationships in thoracic cavity | respiratory pressure is always described relative to atmospheric pressure |
| Atmospheric pressure (pATM) | pressure exerted by the air surrounding the body (760mmHg at sea level); negative respiratory pressure is less than pATM; positive respiratory pressure is greater than pATM |
| Intrapulmonary pressure | pressure within the alveoli is ~760mmHg when even with pATM |
| Intrapleural pressure | pressure within the pleural cavity which adheres lungs to thoracic cavity; ~756mmHg |
| What holds the thoracic wall and lungs together? | the two forces of intrapulmonary and intrapleural pressure hold the thoracic wall and lungs in close apposition—stretching the lungs to fill the thoracic cavity |
| Intrapleural fluid cohesiveness | polarity of water attracts wet surfaces |
| Transmural pressure gradient | pATM (760mmHg) is greater than intrapleural pressure (756mmHg) so lungs expand; elastic recoil of chest wall tries to pull chest outward; elastic recoil of lung creates inward pull |
| Intrapulmonary & intrapleural pressure relationships | intrapulmonary pressure and intrapleural pressure fluctuate w/ phases of breathing; intrapulmonary pressure always eventually equalizes itself w/ pATM; intrapleural pressure is always less than intrapulmonary pressure and pATM |
| Respiratory mechanics | changes in intra-alveolar pressure produce flow of air in & out of lungs; if this pressure is < pATM, air enters; if > pATM, air exits; boyle’s law states—any constant temp, pressure exerted by a gas varies inversely w/ the volume |
| Inspiration | diaphragm, external intercostals contract—rib cage rises; lungs stretched, intrapulmonary vol increases; intrapulmonary pressure drops below pATM (-1); air flows into lungs down pressure gradient, until intrapulmonary pressure = pATM |
| Expiration | inspiratory muscles relax, rib cage descends; thoracic cavity vol decreases; lungs recoil, intrapulmonary vol decreases; intrapulmonary press. Rises > pATM +1; gases flow out of lungs down pressure gradient until intrapulmonary pressure is equalized |
| Respiratory cycle | single cycle of inhalation and exhalation; amount of air moved in one cycle is tidal volume |
| Tidal volume (TV) | amount of air moved in one respiratory cycle (single cycle of air inhalation and exhalation) |
| Physical factors influencing ventilation | friction is the major nonelastic force of resistance to air flow; compliance, elastic recoil |
| Resistance and ventilation | relationship b/t flow (F), pressure (P), and resistance (R) is Flow= ΔP /R; friction is the major non-elastic source of resistance |
| Compliance | ability to stretch; ease with which lungs can be expanded due to change in transpulmonary pressure; determined by distensibility of lung tissue and surrounding thoracic cage and surface tension of alveoli; can be high or low |
| Restrictive lung diseases | fibrotic lung diseases and inadequate surfactant production will produce low compliance. |
| Elastic recoil | return to resting vol when stretching force released; connective tissue elasticity--lungs assume smallest possible size; surface tension of alveoli draws them to their smallest possible size; elastance—measure of how readily lungs rebound after stretching |
| Alveolar surface tension | attraction of liquid molecules to one another at liquid-gas interface; thin layer b/t alveolar cells and air; always acting to reduce alveoli to smallest poss size; surfactant reduces to keep alveoli from collapsing |
| Surfactant | detergent-like complex secreted by type II alveolar cells; reduces surface tension and helps keep the alveoli from collapsing |
| Airway resistance | gas flow is inversely proportional to resistance with the greatest resistance being in the medium-sized bronchi; severely constricted or obstructed bronchioles—COPD |
| Emphysema | destruction of alveoli reduces surface area for gas exchange |
| Fibrotic lung disease | thickened alveolar membrane slows gas exchange; loss of lung compliance |
| Pulmonary edema | fluid in interstitial space increases diffusion distance |
| Asthma | increased airway restriction decreases airway ventilation |
| Lung capacity/volume | lungs can be filled to over 5.5L on max inspiratory effort; emptied to 1L on max expiratory effort; normally operate at “half-full” 2-2.5L; on avg. 500ml moved in/out w/ each breath |
| Tidal volume (TV) | air that moves in and out of lungs with each breath (~500ml) |
| Inspiratory reserve volume (IRV) | air that can be inspired forcibly beyond the tital volume (2100-3200ml) |
| Expiratory reserve volume (ERV) | air that can be evacuated from the lungs after a tidal expiration (1000-1200ml) |
| Residual volume (RV) | air left in lungs after strenuous expiration |
| Inspiratory capacity (IC) | total amount of aire that can be inspired after a tidal expiration (IRV + TV) |
| Functional residual capacity (FRC) | amount of air remaining in lungs after tidal expiration (RV+ERV) |
| Vital capacity (VC) | total amount of exchangeable air (TV+IRV+ERV) |
| Total lung capacity (TLC) | sum of all lung volumes (~6000ml in males) |
| Anatomical dead space | volume of conducting respiratory passages (150ml) |
| Alveolar dead space | alveoli that cease to act in gas exchange due to collapse or obstruction |
| Total dead space | sum of alveolar and anatomical dead spaces |
| Factors influencing movement of O and CO2 across respiratory membrane | partial pressure gradients & gas solubilities; matching of alveolar ventilation and pulmonary blood perfusion; structural characteristics of respiratory membrane |
| Dalton’s law | total pressure exerted by mixture of gases=sum of pressures exerted independently by each gas in mixt; partial pressure of ea gas directly proportional to its % in mix; PO2 air is 20.93% O2; total pressure of air is 760mmHg; PO2=.2093x760=159mmHg |
| Henry’s law | when mixture of gases in contact w/ a liquid, each gas will dissolve in the liquid in proportion to its partial pressure; amount gas dissolved also depends on solubility; CO2 most soluble; O2 1/20th as soluble; nitrogen practically insoluble in plasma |
| Gas diffusion | gases diffuse from high to low partial pressure between lung and blood/between blood and tissues |
| Respiratory membrane | only .5-11 mm thick, allowing for efficient gas exchange; total surface area of about 60m2; air-blood barrier composed of alveolar and capillary walls; alveolar walls are single layer type I epithelial cells |
| Alveolar gas | contain more CO2 & water vapor, while atmosphere is mostly nitrogen and oxygen; differences result from gas exchanges in lungs, humidification of air, mixing of alveolar gas w/ each breath |
| Partial pressure gradients | PO2 of venous blood is 40mmHg; PO2 in alveoli is ~100mmHg; steep gradient allows PO2 gradients to rapidly reach equilibrium; blood can move quickly thru pulmonary capillary and still be adequately oxygenated |
| Internal respiration | factors promoting gas exchange b/t systemic capillaries & tissue cells are same as in lungs—partial pressures & diffusion gradients reversed; PO2 in tissue always lower than in systemic arterial blood; PO2 venous blood draining tissues—40mmHg, PCO2 45mmHg |
| Ventilation-perfusion coupling | ventilation—amt gas reaching alveoli; perfusion—blood flow reaching alveoli; must be tightly regulated for efficient gas exchange; chgs in PCO2 in alveoli causes chgs in diameters of pulmonary arterioles |
| Alveolar CO2 high/O2 low | vasoconstriction |
| Alveolar CO2 low/O2 high | vasodilation |
| O2 transport in blood | 3 methods—dissolved in plasma; bound to Hb in blood—oxyhemoglobin (O2 bound to Hb) or deoxyhemoglobin (O2 not bound to Hb) |
| Saturated hemoglobin | when all four hemes of the molecule are bound to oxygen |
| Partially saturated hemoglobin | when one to three hemes are bound to oxygen |
| Rate that hemoglobin binds with oxygen | regulated by PO2, temperature, blood pH, PCO2 |
| Hemoglobin saturation curve | Hb saturation plotted against PO2 produces oxygen-hemoglobin dissociation curve; at 100mmHg, Hb 98% saturation; saturation of Hb is why hyperventiliation has little effect on arterial O2 levels |
| Influence of PO2 on Hb saturation | 98% saturated arterial blood—20ml O2/100ml blood (20%vol); only 20-25% of bound O2 unloaded during one systemic circulation; if O2 levels in tissues drop, more O2 dissociates from Hb, used by cells; respiratory rate/CO output need not increase |
| Factors influences Hb saturation | temperature, H+, PCO2, and BPG alter Hb affinity for O2; increases of factors decreases Hb affinity for O2 and enhance O2 unloading from blood; these paramteres are high in tissue capillaries where O2 unloading is goal |
| Bohr effect | H+ and CO2 modify the structure of Hb |
| CO2 transport | in blood in three forms—dissolved in plasma, chemically bound to Hb as carbaminohemoglobin; bicarbonate ion in plasma |
| Transport and exchange of CO2 | CO2 quickly diffuses into RBCs and combines with H20 to form carbonic acid H2CO3, which quickly dissociates into hydrogen ions and bicarbonate ions; CO2+H20«H2CO3«H+HCO3- |
| Carbonic acid-bicarbonate buffer system | system resists blood pH changes; if H+ in blood increases, excess H+ is removed by combining w/ HCO3; if H+ decreases, carbonic acid dissociates, releasing H+ |
| Chloride shift | at tissues, bicarbonate quickly diffuses from RBCs into plasma; chloride ions move from plasma into RBCs to counterbalance out rush of negative bicarbonate ions |
| CO2 transport at lungs | bicarbonate ions move into rBCs, bind w/ H+ ions, form carbonic acid; Carbonic acid split by carbonic anhydrase to release CO2 and H20; CO2 diffuses from blood into alveoli |
| Haldane effect | removing O2 from Hb increases ability of Hb to pick up CO2 and CO2 generated H+ ; works in synch w/ bohr effect to facilitate O2 liberation, uptake of CO2 & H+ |
| Control of respiration | medullary respiratory centers |
| Dorsal respiratory group DRG | inspiratory center; inspiratory neurons, thought to be set by basic rhythm “pacemaking”; excited inspiratory muscles and sets eupnea (12-15 breaths/min); cease firing during expiration |
| Ventral respiratory group | inspiratory & expiratory neurons; remains inactive during quiet breathing; activity when demand is high; involved in forced inspiration and expiration |
| Pons respiratory centers/pontine respiratory group | influence and modify activity of medullary centers to smooth out inspiration & expiration transitions; consists of pneumotaxic center, apneustic center |
| Pneumotaxic center | part of pontine respiratory group; sends impulses to DRG to switch off inspiratory neurons, limiting duration of inspiration; dominates to allow expiration to occur normally |
| Apneustic center | prevents inspiratory inhibition to provide increase inspiratory drive when needed |
| Depth & rate of breathing | inspiratory depth—determined by how actively respiratory center stimulates respiratory muscles; rate of resp determined by how long inspiratory center is active; resp centers in pons/medulla sensitive to both excitatory & inhibitory stimuli |
| Input to respiratory centers | cortical controls, hypothalamic controls, temperature, pulmonary irritants, inflation reflex |
| Cortical controls | input to respiratory centers; direct signals from cerebral motor cortex that bypass medullary controls (ex. voluntary breath holding, taking a deep breath) |
| Hypothalamic controls | input to respiratory centers; act through the limbic system to modify rate and depth of respiration; ex. breath holding that occurs in anger |
| Temperature and respiratory rate | input to respiratory centers; rise in body temperature acts to increase respiratory rate |
| Pulmonary irritant reflexes | input to respiratory centers; irritants promote reflexive constriction of air passages |
| Inflation reflex (Hering-Breuer) | input to respiratory centers; stretch receptors in lungs are stimulated by lung inflation; upon inflation inhibitory signals sent to medullary inspiration center to end inhalation, allow expiration |
| PCO2 and breathing depth and rate | PCO2 lvls monitored by brain stm chemoreceptors; blood CO2 diffuses into CSF & hydrated, H2CO3 dissociates, releases H+ ions; PCO2 increases, increases breathing depth/rate; CO2 rise is stimulus, control of breathing @ rest regulated by H ion brain conc. |
| Peripheral chemoreceptors | regulate ventilation; located in carotid and aortic arteries; specialized glomus cells; sense changes in PO2, pH, PCO2 |
| Hyperventilation | increased depth and rate of breathing that quickly flushes CO2 from blood; occurs in response to hypercapnia (increased PCO2); though CO2 is original stimulus, control of breathing at rest is regulated by H+ ion concentration in brain |
| Hypoventilation | slow, shallow breathing due to abnormally low PCO2 levels |
| Apnea | may occur until PCO2 levels rise |
| Arterial pH + breathing | changes can modify respiratory rate even if CO2 & O2 levels are normal; increased ventilation in response to falling pH mediated by peripheral chemoreceptors |
| Acidosis | condition may reflect CO2 retention, accumulation of lactic acid, excess fatty acids in patients with diabetes mellitus |
| Low pH | respiratory system controls will attempt to equilibrate by increasing respiratory rate and depth |
| High pH | respiratory system will attempt to equilibrate by decreasing rate and depth of breathing |
Created by:
michellerogers
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