STEPH Physiology Flashcards
Describe the respiratory cycle
The oxygen saturated blood moves from lungs to heart to capillary beds to muscles. While Carbon goes the reverse.
Explain how the pressure in the pleural space of the lungs is negative
It is a sealed sac, with the potential space between visceral and parietal pleura is touching, with a little serous fluid within.As thoracic cavity is larger than lungs, the lungs are semi-expanded at rest, which means that there is recoil from the lungs which want to collapse and this generates the negative pressure in the pleural space.
Describe how inspiration and expiration affects pressures in the lungs and pleural space
Inspiration = a further decrease of intrapleural pressure, from the diaphragm and other inspiratory muscles contracting.The alveolar which is pulled by the pleural space also becomes more negative than the atmosphere Expiration = relaxing of the diaphragm, contraction of intercostal muscles
Define lung volumes and capacities.4 different volumes?4 capacities (two or more volume combined)
4 different volumes Inspiratory reserve volume Tidal volume Expiratory reserve volume Residual volume
4 capacities (two more more volumes combined) Inspiratory capacity ( IRV + TV/Vt) Functional residual capacity (FRC) Vital capacity (IRV + TV/Vt +ERV) Total lung capacity (TLC)
Identify the most important factor contributing to resistance
Radius of the airways is the most important factor
Describe how obstructive lung disease affect airways with an example
Eg asthma of horse or catdecrease radius of airways and increased mucous productionWhich increases resistance Early dynamic small airway closureUltimately leads to reduced expiration capacity and increased residual volume
Describe minute and alveolar ventilationwhich is more important?
Minute ventilationvolume of air reaching the alveoli per minuteVE- BF x VTAlveolar ventilationtaking into account dead space (in trachea)Va = Bf x (VT - VD)Alveolar ventilation is more important as dead space is not functional alveolar, but minute ventilation is easier to measure. Changes in minute ratio still has functional useBeing mindful of the ratio of dead space and anaesthesia tubing is also dead space
Define compliance and elastance
Compliance = ability of lungs to stretch and expandvolume/pressure = complianceDue to elastic fibres + surface tensionC facilitates “appropriate functional residual capacity”Elastane = the reciprocal of compliancepressure change required to elicit a volume changeTherefore increased elastane = increased work of breathing
Describe the principle of surface tension
Water is drawn to other water molecules more than air, thus water clumps together
Explain how surface tension is generated in the alveoli
Alveoli fluid/water covers the alveolar surface, because of the air-water interface
Describe the role of type II pneumocystis and surfactant
Type II pneumocystis produces surfactantSurfactant lines the alveoli to reduces the surface tension by reducing air-water interface in the alveoli
Explain the effect of surfactant on surface tension in the lung
As due to the law of Laplace, the larger the alveoli the easier it is to inflate as there is less surface tension.IMPORTANT = Surfactant makes it easy to inflate the lungs regardless of size of the alveoli
Define work of breathing
Energy required to perform tidal ventilation over a set period of time
Explain how the rate of breathing relates to the total work of breathing (need to go over again)
Rate is the frequency of breathing, thus how much work is done
Explain the relationship between pulmonary artery pressure and pulmonary blood resistance
Pulmonary arterylow pressureLow resistance (much less resistance than systemic blood flow)
Describe the effects of distension and recruitment on pulmonary blood pressure
Hydrostatic pressure of the blood in the vessels is affected.
Describe the effect of gravity on pulmonary blood flow
Lower regions of vessels are affected by gravity more, so the blood vessels are more distended, thus there is less resistance. Thus three zones are used to describe the variationZ1 = no gas exchange at rest ( as the pressure of the vessel doesn’t get higher than the alveolar pressure)Z2 = intermittent at rest, flows during systole, not diastole.Z3 = flow through the whole cardiac cycle, as Ventilation-perfusion mismatch- too much blood flow for the air in the alveolar
Explain the effects of exercise on pulmonary blood flow
The top region has the greatest difference in the increase of blood flow. While bottom may increase in blood flow less.
Overall more capillaries are diffused and increase dilation of though already diffused3 ways that lungs accommodate for the increased blood flow
Increase in no. of open capillaries (3x)
Distension of all capillaries (2x)
Increase pulmonary pressure increase- this end up reducing resistance poiseuille law (bigger diameter = less resistance)
Describe the effect of hypoxia on pulmonary blood flow
Alveolar with lower than 70% oxygen = vasoconstriction This allows the blood to be distributed to where it is most needed.Sending blood to the alveolar with higher O2 saturation.
Describe the principle of gas diffusion
High concentration to low concentration
Describe the normal ranges of PAO2, PaO2 and PvO2
PaO2 = arterial blood oxygen partial pressure(40)
PAO2 - partial pressure oxygen in alveoli (104)
PvO2 - partial pressure of oxygen in mixed venous blood (100)
the rate of diffusion is based on the difference in pp and rate in which the alveolar air is replaced.
Eg when there is less O2 in the blood at the arterial end, the rate of diffusion will be higher
Describe the normal ranges of PaCO2, PACO2 and PvCO2
PaCO2 = 45PACOs = 40PcCO2 = 40However solubility of CO2 is around 20x of oxygen in both blood and alveolar fluid means that the rate of diffusion is quite similar
Explain the modes of O2 transport
DissolvedBound to Hb
Describe the structure of haemoglobin
4 subunits, each subunit is bound to a heme molecule
Describe the relationship between oxygen affinity and oxygen binding sites of haemoglobin
Each O2 molecule that is bound to the Hb results in a conformational change which makes the subsequent O2 binding easier. Hb now has a higher affinity to bind to O2 molecules after each O2 bound. The same in reverse.
Explain the conditions associated with right and left shift of the oxygen-haemoglobin dissociation curve and describe the impact this has on offloading oxygen at peripheral tissues
Shifting to the left or the right is based on the P50
Left = O2 binds easier to Hb, but less dissociates at the periphery tissues
Temperature increases = righter
PCO2 increased amount = right
pH decrease = right Increase of DPG (increase in blood
metabolism = righter
Describe the modes of CO2 transport and role of bicarbonate
DissolvedCO2 solubility5-7%Bound to Hb- 5-23%Related to 2 contentHb Binding ( CO2 binds to the Hb molecule)In form of HCO3-carbonic anhydraseRBC involvement70-90%
Compare the O2 and CO2 hb dissociation curves
CO2 is higher partial pressure in the tissue not the lungs like O2Amount of O2 bound to Hb impacts on binding of CO2. The lower the partial pressure of O2 ( the less O2 bound) the more CO2 can be boundDissociation curve is linear, not sigmoid shape like the O2 curvePressure of CO2 in blood = 40-45mmHg
<p>Compare hypoxia and hypoxemia</p>
<p>Hypoxia <br></br>reduced availability of O2 at tissues <br></br>Under-oxygenation of organs, tissues and cells<br></br>Impairs normal metabolism<br></br>If severe, can lead to cellular death<br></br><br></br>Hypoxaemia<br></br>- an abnormally low concentration of oxygen in the blood.</p>
List the common causes of tissue hypoxia
<p>Four main types</p>
<p>Cytopathic</p>
<ul><li>cells unable to utilise O2</li><li>Eg mitochondrial dysfunction and septic shock</li></ul>
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<p>Anaemic</p>
<ul><li>Blood not carrying enough O2</li></ul>
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<p>Stagnant</p>
<ul><li>low flow of blood</li><li>Eg low cardiac output and low tissue perfusion</li></ul>
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<p>Hypoxemic</p>
<p>- low Pa O2, leading to low delivery of O2 to tissues</p>
<p>Explain the steps by which the body corrects hypoxia</p>
<p>learn. more in-depth in later years</p>
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<p>List the mechanisms by which hypoxaemia can occur (4)</p>
<p>The main 4</p>
<ul><li>hypoventilation or low PiO2</li><li>Diffusion impairment</li><li>Right to left shunt</li><li>V/Q mismatch</li></ul>
<p>Describe how decreases in PIO2 and hypoventilation can lead to hypoxaemia</p>
<p>Decrease in PIO2 means that there is a decrease in the concentration of the O2 which is reaching the lungs.</p>
<ul><li>causes of this = hyperbaric conditions (altitude)</li></ul>
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<p>Hypoventilation =</p>
<ul><li>fibrosis = increased airway resistance</li><li>Emphysema = Decreased pulmonary compliance</li></ul>
<p>Describe how a diffusional impairment can lead to hypoxaemia</p>
<p>nadequate amount of gas exchange at the blood-gas barrier</p>
<p>Depends on</p>
<p>Thickness of membrane</p>
<p>Surface area</p>
<p>Diffusion coefficient</p>
<p>Partial pressure of the gas difference</p>
<p>Describe how a right to left shunt leads to hyperaemia</p>
<p>Non-Deoxygenated mixes with the oxygenation of the blood, which leads to mixing of the blood, lowering the concentration of O2 in the blood being pumped out.</p>
<p>Describe how a ventilation defect impacts oxygen saturation</p>
<p>Inequality of alveolar ventilation and perfusion</p>
<p>= a mismatch between the amount of air being ventilated and blood flow</p>
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<p>Ventilation reduced = Low V/Q</p>
<p>= not enough ventilation</p>
<ul><li>lung disease</li><li>Air way obstruction</li><li>Stiffening of lung due to inflammation</li></ul>
<p>Describe how a perfusion defect impacts oxygen saturation</p>
<p>Perfusion of blood reduced = High V/Q ratio</p>
<p>= not enough perfusion, more ventilation than the blood can carry</p>
<ul><li>vascular obstruction</li><li>Pulmonary hypotension</li></ul>
<p>Describe the mechanisms by which horses experience arterial hypoxaemia and hypercapnia during high intensity exercise and quantify their relative contributions</p>
<p>Post pulmonary shunts between the bronchial an pulmonary circulation around 1%</p>
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<p>V/Q mismatch: 25-40% of the increase in the widening of the alveolar-arterial O2 gradient</p>
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<p>60-75% related to diffusion limitations and/or alveolar hypoventilation</p>
<p>List factors which should contribute to improve diffusion during exercise</p>
<p>PvO2 as low as 16mmHg during intense exercise</p>
<p>= widens the alveolar-arterial O2 gradient</p>
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<p>Increased surface area available for gas exchange</p>
<p>= dilation and recruitment of poorly- perfused or non-perfused sections</p>
<p>= 50-60% increase in volume</p>
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<p>However the 8 times increase in cardiac output during high intensity exercise</p>
<p>= substantially decreased capillary transit time and decreased time for O2 equilibration</p>
<p>Describe hypercapnia and list the mechanisms by which it can occur</p>
<p>Excess carbon dioxide in the blood</p>
<p></p>
<p>mechanisms</p>
<ul><li>decreased alveolar ventilation</li><li>Severe V/Q mismatch = low V/Q ratio = hypercapnia (the opposite of O2 V/Q ratios)</li><li>CO2 production occurring without appropriate ventilatory compensation</li></ul>
Identify the 2 parameters that can be controlled to alter ventilation
Respiratory rateHow deep breathing (tidal volume)
Describe the control and regulation of breathing
Autonomic nervous systemNeural inputs - central chemo receptors H+Peripheral chemoreceptors O2, CO2, H+Pulmonary receptors - stretch and irritantsJoint and muscle receptors - stretch and tensionAll these are sent to a respiratory control centre, then the centres send an efferent signal to res muscles
Identify the respiratory control centres
Three groups this is bilateral Medulla oblongatadorsal respiratory group (inspiration)Ventral respiratory group (inspiration and expiration)Pons (which is in two parts)pneumotaxic centreApneustic centre
Compare and describe the inspiration and expiration processes
Dorsal respiratory group set general patternVentral respiratory group provides powerful expiration signals to muscles during heavy breathingPneumataxic centres control the duration of each breath to prevent over inflation (strong = short, weak = long)Apneustic centre control for gasping by inhibiting DRG delaying inspiratory off and then it self inhibited by pulmonary stretch receptorsCerebral cortex and somatic control of res muscles override the 4 aboveHypothalamus and limbic system - sympathetic fight or flight and holding your breath override of 4 above
Explain the importance of central chemoreceptors in breathing
Provide on the most importance feedback loops with the dorsal respiratory group
Describe the importance of hydrogen ions in the proper functioning of central chemoreceptors
Charged ions cannot cross the blood brain barrier, but CO2 can. When it crosses over the carbonic anhydrase reaction occurs. DRG and VRG are influenced by the increase of H+ ions from the reaction (the decreasing pH)
Identify the location of peripheral chemoreceptors
Carotid bodies and aortic bodies
Describe the function of peripheral chemoreceptors
Detect O2 changes in the blood Respond to CO2 and H = ions Receive afferent signals from the autonomic nervous system Type 1 glomus cells Carotid bodies send signals via the CNXI Aortic bodies send signals via CNX Fx, L type voltage gated Ca2+
Describe the effect of anaesthesia on respiration
Anaesthetic drugs at on specific ion Chanels and receptors
If ventilation is not occurring properly sympathetic response occurs which includes tachycardia and increased blood pressure.
Describe how a descent into water impacts barometric pressure and lung volume
Descent = increase pressure, decrease volume
Describe how an ascent from depths of water impacts barometric pressure and lung volume
Ascent= decrease pressure, increase volume
Explain how gills functions as a gas exchange
Water flows through the gills and O2 is diffused through it
Explain counter current flow
The water flows in the opposite direction of the blood flow
Describe the avian respiratory system
No mixing of air Allows counter-current multiplication
avian air capillaries are interconnected
Pulmonary capillaries Thickness of the blood-gas barrier is 30% less than in mammalian alveoli
List the adaptation of high flying birds
Experienced at high altitudes = altitude hypoxia and increased PCO2 and acidosis
