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41 Cards in this Set
- Front
- Back
What are the functions of the respiratory system?
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Gas exchange
Regulation of humidity and pH - CO2 levels Vocalisation Olfaction Protection against microorganisms |
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What are the 4 processes of respiration?
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Ventilation - air into and out of lungs
External respiration - gas exchange between air-filled alveoli and blood Gas transport - cardiovascular system Internal respiration - gas exchange between blood and tissues |
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What is partial pressure?
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Pressure exerted by each type of gas in a mixture and is proportional to its concentration in a mixture
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What is Dalton's Law?
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Total pressure exerted by mixture of gases is equal to the sum of partial pressures exerted by each gas
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How do you calculate a gas's partial pressure
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Multiply its concentration by total pressure
e.g. 21/100 x760 = 160 mm Hg take away water vapour pressure at body temperature |
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What factors influence the diffusion of gases in the body?
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Thickness and surface area of respiratory membrane
Partial pressure gradient, diffusion coefficient, solubility of gases Alveolar ventilation and perfusion |
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How does oedema/pneumonia affect gas exchange in the alveoli?
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Increases distance for gas diffusion between alveolus and blood
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How does emphysema affect gas exchange in the lungs?
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Destruction of alveolar walls, low PO2 due to loss of elasticity of lungs, can decrease surface area for gas exchange
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How does asthma affect gas exchange in the lungs?
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Increases airway resistance by decreasing radius/diameter of bronchioles, decreases airway ventilation
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What does the composition of gases in alveolus affect?
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Gives the same composition in pulmonary vein going to left side of heart
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Oxygen cascade shows
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Partial pressure of O2 at different levels in respiration
Hypoventilation causes decrease in O2 levels in alveolus and tissue |
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What causes the decrease from 100mm Hg to 90mm Hg from pulmonary capillaries to systemic capillaries?
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Shunting of blood
Deoxygenated blood returning to pulmonary vein from bronchial circulation O2 dilution returning from coronary circulation (Thebesian veins) |
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Why is there a much smaller partial pressure difference with CO2 compared to O2?
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Same volumes of gas move because CO2 is 20x more soluble and therefore moves quicker than O2
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How does change in ventilation affect partial pressures of O2/CO2 in alveoli?
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Increasing ventilation to alveoli increases PO2, decreases PCO2 in alveoli -> not enough O2 taken in and co2 put out
Makes gas exchange more inefficient |
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What happens to alveoli gas composition if they have a high V:Q ratio?
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High ventilation:low perfusion
high PO2, low CO2, closer to inspired air than mixed venous blood |
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What happens to pulmonary capillaries if hypoxic?
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Vasoconstriction, blood diverted away from poorly ventilated areas
(low v:q ratio = hypoxic = vasoconstriction) |
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Where are central and peripheral chemoreceptors found?
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Central - medulla
Peripheral - coronary sinus and aortic arch |
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What do peripheral chemoreceptors respond to?
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PO2 and [H ions] in arterial blood
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What do central chemoreceptors respond to?
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Arterial CO2 (indirectly) and [H ions] in cerebral spinal fluid
COS crosses bbb and dissociates into H ions |
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What increases respiratory rate during exercise?
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Proprioceptors sense movement during exercise (increases h rate too)
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What are the respiratory centres in the medulla and what do they control?
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Dorsal respiratory group in nucleus tractus solitarius - inspiration
Ventral respiratory group - inspiration and expiration Pneumotaxic and apneustic centre |
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How do impulses form the dorsal respiratory group in the medulla control inspiration and expiration?
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Impulses from DRG activate motor neurones in diaphragm/intercostal externals to cause inspiration
Stop firing, expiration begins |
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What is eupnoea?
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Normal quiet breathing
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What is apnoea?
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Cessation of breathing
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How is the VRG involved in breathing?
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Only forced breathing - neurones activated accessory muscles (abdominals and internal intercostals for forced expiration during exercise)
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Which respiratory group in medulla is not involved in eupnoea?
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VRG
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What controls the firing from the DRG?
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Neuronal input from pons
Central pattern generator - ability to produce action potentials and then stop |
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What is the effect of the pneumotaxic centre on the DRG?
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Acts as an "off-switch" to DRG neurones that can cut short inspiration
and can affect respiratory rate (weak signal to DRG = slower rate) |
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How does the apneustic centre affect the DRG?
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Can prevent or retard off-switch to DRG - prolong inspiration or breath hold during inspiration
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What is the ongoing stimulus for ventilation?
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Normal levels of CO2 - low levels would induce hypoventilation
CO2 - crosses BBB, dissociates to H ions which stimulate central chemoreceptors H causes increased depth and rate of breathing -> initiates inspiration |
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How do peripheral chemoreceptors respond to PO2 and [H ions]?
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Respond to decreased PO2 and increased [H ions] (low pH)
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Which peripheral chemoreceptors are more sensitive?
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Carotid bodies - higher blood flow
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Describe how peripheral chemoreceptors respond to low PO2
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Normal levels of O2 keep K channels open -> hyperpolarisation
Low O2 shuts K channels and opens Ca voltage-gated channels -> depolarisation -> neurotransmitter dopamine is released -> excitation of sensory nerves and increased impulses to medulla-> increased ventilation to return O2 to normal levels |
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What types of sensory receptors are in the lungs/airways?
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Stretch and irritant receptors
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Where are stretch receptors found?
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Smooth muscle in bronchi/bronchioles
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What is the Hering- Breuer reflex?
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In response to large lung inflation during high tidal volume -> enhances off-switch to DRG -> inhibits inspiration and promotes expiration
protection against lung overstretch? |
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Where are irritant receptors located?
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Epithelium of airways
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What are irritant receptors stimulated by and what does their response depend on?
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Irritants
Location of irritant (cough, sneeze, rapid breathing) |
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Describe cough reflex
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Deep inspiration, epiglottis and vocal cords shut, forced expiration, lung pressure rises, epiglottis and v.cs open -> explosion of air
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What makes you want to breathe again after holding your breath?
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Levels of CO2 increase -> stimulates chemoreceptors
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What stimuli can also affect breathing?
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Temperature - increased temp = increased breathing, emotion - laughing, pain - apnoea, baroreceptor - fall in b.p. (e.g. haemorrhage) increased breathing
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