Physiology Flashcards
What is external respiration?
Exchange of oxygen and carbon dioxide between body cells and the external environment
What is internal respiration?
The intracellular mechanisms that consume oxygen and produce carbon dioxide.
Which 4 body systems are involved in external respiration?
- Respiratory system 2. Cardiovascular system 3. Haematology system 4. Nervous system
In terms of respiration what does the term “ventilation” refer to?
The mechanical process of moving air between the alveoli and the atmosphere
What is Boyle’s Law?
At a constant temperature, the pressure exerted by a gas varies inversely with the volume the gas is contained within. (as volume increases, exerted pressure decreases)
Using Boyle’s Law, describe why the lungs must expand to allow air to enter them during inhalation.
As the volume of the lungs (and thoracic cavity) increase, the pressure decreases. This means atmospheric pressure is high than intrathoracic pressure. Gas (air) flows down the pressure gradient into the lungs
Which two forces hold the thoracic walls and the lungs in close contact?
- The intrapleural fluid cohesiveness (fluid tension) 2. The negative intrapleural pressure
A transmural pressure gradient exists between lung walls. What is this?
A difference in pressure between any separtation
What causes the increase in thoracic volume during inspiration? (2)
- Contraction of the diaphragm 2. External intercostal muscle contraction
During expiration, which two factors contribute to the recoil of the lungs?
- Elastic properties of the involved muscles 2. Alveolar surface tension
What sort of situation would result in a lung collapse?
Any situation involving pleural pressure equalising with or exceeding atmospheric pressure e.g. a puncturing wound
What is alveolar surface tension?
The attraction between water molecules at the liquid air interface of the alveoli - water molecules pull towards each other
What does alveolar surface tension allow for?
A resistance to lung stretching - the water molecules are attracted together so oppose stretching forces
What does the law of LaPlace state?
Smaller alveoli have a higher tendency to collapse due to the increased proximity of the water molecules
What is pulmonary surfactant and where is it produced?
Pulmonary surfactant is a complex mixture of lipids and proteins. It is produced by type II alveoli
What is the effect of pulmonary surfactant?
It reduces surface tension by “diluting” the effect the water molecules have by interspersing them
Why do some infants suffer from respiratory distress syndrome?
Foetal lungs cannot synthesise surfactant meaning premature babies do not have enough surfactant in their lungs. Breathing will them become strenuous as the babies must overcome the high surface tension (of the water droplets) to inflate the lungs
Describe alveolar interdependence
Alveolar interdependence describes the fact that adjacent alveoli protect each other from collapse. If one alveoli begins to collapse, others around it will compensate and stretch. As volume increases in the surrounding alveoli, pressure decreases meaning air flows to the collapsed alveoli to reinflate it. This is due to the pressure gradient.
What are the three types of muscles involved in respiration?
- Accessory muscles (scalenus, sternocleidomastoid) 2. Major muscles (diaphragm, external intercostal muscles) 3. Muscles of active expiration (abdominal muscles, internal intercostal muscles)
What is the tidal volume?
The volume of air entering or leaving the lungs in a normal breath (around 500ml)
What is the inspiratory reserve volume?
This is the extra volume of air that can be breathed in over and above the tidal volume (around 3000ml)
What is the inspiratory capacity?
The maximum volume of air that can be breathed in (inspiratory reserve volume + tidal volume)
What is the expiratory reserve volume?
This is the extra volume of air that can be breathed out over and above the tidal volume (around 1000ml)
What is the residual volume?
This is the minimum volume of air remaining in the lungs even after a maximal expiration - it is always present
What is functional residual capacity and how is it calculated?
Resting lung volume (Expiratory reserve volume + residual volume)
What is vital capacity and how is it calculated?
This is the total volume of air available to be expired in the lungs (inspiratory reserve volume + tidal volume + expiratory reserve volume)
What is total lung capacity and how is it calculated?
This is the total volume of air the lungs can hold (vital capacity + residual volume) Around 5.7 litres
Why is total lung capacity hard to measure in real life?
Residual volume must be known and this cannot be measured
What could lead residual volume to increase?
Reduction in elastic recoil of the lungs - as in emphysema
Which two measurements can be plotted on volume/time curve, and what are they?
FVC - forced vital capacity - maximum volume of air inspired, the maximum volume of air that can be forcibly expelled FEV1 - Volume of air that can be expelled (after full inspiration) in one second
For normal healthy patients, FEV1/FVC x 100 should equal what?
80%
What does a low FEV1/FVC ratio indicate?
Obstructive lung disease
What type of results do individuals with restrictive lung disease give for a FEV1/FVC ratio test?
Normal, if not slightly elevated. They can instead be diagnosed by an initially low FVC
What is the primary determinant of airway resistance?
The radius of the conducting airway
How does the autonomic nervous system affect the resistance to airflow?
Sympathetic - decreases resistance (bronchodilation) Parasympathetic - increases resistance (bronchoconstriction)
Why are sufferers from obstructive lung conditions likely to suffer from collapsing airways?
Driving pressure (during exhalation) upwards from obstruction cannot occur. Relative airway pressure falls onward from obstruction leading to airway compression due to rising pleural and lung pressure. This problem is exacerbated if elastic recoil of airways is also lost as in emphysema.
How is peak flow rate measured?
Using a peak flow meter
Describe how to use a peak flow meter
A short sharp block is given into the meter The score on the scale at the side is taken 3 attempts are given to allow for poor initial technique The best value is recorded This test can highlight obstructive lung disease
What is pulmonary compliance?
This is a measure of the effort required to stretch or distend the lungs
What are the two methods to measure pulmonary compliance clinically?
- Static - the change in volume for any given pressure is measured (measures elastic resistance only) 2. Dynamic - change in volume for any given pressure during the movement of air (measure both elastic resistance and airway resistance)
The less compliant the lungs are the _____ work must be done to inflate them
More
List 3 factors that decrease pulmonary compliance
Pulmonary fibrosis Pulmonary oedema Lung collapse Pneumonia Absence of surfactant
How may a patient present clinically if they have less complaint lungs
Breathless Low exercise tolerance
When would pulmonary compliance increase?
When elastic recoil is lost
Describe a condition in which pulmonary compliance is increased
Emphysema Hyperinflation occurs causing increased difficulty during exhalation Age also increases compliance
List 3 factors which will increased the required work done by the lungs
- Decreased pulmonary compliance
- Increased pulmonary compliance
- Increased airway resistance (potentially when bronchoconstricted)
- Decreased elastic recoil
- Increased elastic recoil
- Need for increased ventilation (low O2)
What is airway physiological “dead space”?
This is the area within the airway (anatomical) and alveoli that is unsuitable for diffusion to occur
How is alveolar ventilation calculated?
Dead space volume must be subtracted from the tidal volume
What is the difference between pulmonary and alveolar ventilation?
Pulmonary - volume of air breathed in and out per minute (includes dead space) Alveolar - volume of air exchanged between atmosphere and alveoli (excludes dead space)
How can pulmonary ventilation be increased?
Increasing depth and rate of breathing
Why is pulmonary ventilation increase advantageous?
Amount of inhaled air increases but dead space does not - this causes relative increases in alveolar ventilation
What is ventilation?
Rate at which gas passes through the lungs
What is perfusion?
Rate at which blood passes through the lungs
What is the ventilation perfusion match?
This ensures ventilation of gas can match the blood flow for optimised gas transfer - local controls can ensure this can happen
What will happen when perfusion is greater than ventilation?
CO2 build up in alveoli Airway resistance is reduced in these situations as well as contraction of arteriolar smooth muscle to reduce blood flow to match the airflow
What will happen when the ventilation is greater than perfusion?
Increased alveolar oxygen concentration Pulmonary vasodilation will occur to incease blood flow to match the ventilation Constriction of airways also increases resistance to reduce ventilation
Which four factors can influence alveolar gas exchange?
- Partial pressure gradient (of O2 and CO2) 2. Diffusion coefficient (of O2 and CO2) 3. Surface area of alveolar membrane 4. Thickness of alveolar membrane
What is Dalton’s law of partial pressure?
The total pressure of a gaseous mixture of a sum of all the partial pressure of individual gases
What is the partial pressure of a gas?
The pressure one gas would exert if it were the only gas making up the full volume
How is partial pressure of oxygen calculated?
PaO2 = PiO2 - [PaCO2/0.8] 0.8 = respiratory exchange ratio (ratio of CO2 produced/O2 consumed)
How is mmHg easily converted to KPa?
Divide by 7.5
Why is partial pressure for carbon dioxide much lower than oxygen?
CO2 is much more soluble than O2
What is the diffusion coefficient?
This is the solubility of a gas in a membrane
Why is there always a small pressure gradient between oxygen in the alveoli and the arteries?
Ventilation and perfusion matching is always slightly out of sync
What could be the cause of a large oxygen partial pressure difference in alveoli and arteries? (2)
- Significant gas exchange problems in the lungs 2. Left to right heart shunt
What is Fick’s law?
The amount of gas that moves across a sheet of tissue in unit time is proportional to the area of the sheet but inversely proportional to its thickness
What does Henry’s law state?
The amount of given gas dissolved in a given type and volume of liquid at a constant temperature is proportional to the partial pressure of the gas in equilibrium with the liquid
In which two forms is oxygen found in the blood?
- Bound to haemoglobin 2. Physically dissolved
What is the primary factor determining the percentage saturation of haemoglobin with oxygen?
Partial pressure of oxygen
Which factors can impair oxygen delivery to tissues?
- Decreased PiO2 2. Respiratory disease 3. Anaemia 4. Heart failure
What term is used to describe the increased affinity Hb has for O2 with each subsequent oxygen molecule bound?
Cooperativity (sigmoid curve is shown)
Why is the sigmoidal curve of oxygen cooperativity significant? (2)
- Moderate alveolar PO2 fall does not greatly impact O2 loading 2. Small drop in capillary PO2 means oxygen affinity is hugely decreased greatly reducing oxygen load
What is the Bohr effect?
O2 dissociation curve shifts to the right Factors reduce oxygen affinity and aid offload
Give examples of factors that will reduce oxygen affinity of haemoglobin
- Increase PCO2 2. Increase H+ 3. Increase temperature 4. Increase 2,3-biphosphoglycerate (allosteric haemoglobin inhibitor)
Why does foetal haemoglobin have increased affinity for oxygen?
Interacts less with 2,3-biphosphoglycerate O2 dissociation curve is shifted to left Allows for O2 transfer from mother even in low PaO2
What is myoglobin?
Present in voluntary muscle and provides storage of oxygen Oxygen is released at low partial pressures Presence indicates muscle damage
What are the three ways carbon dioxide is transported in the blood?
- Solution (10%) 2. Bicarbonate (60%) 3. Carbamino compounds (30%)
How is bicarbonate formed in the blood?
CO2 + H2O ⇌ H2CO3 ⇌ H+ + HCO-3
In relation to the two reactions which produce bicarbonate, which catalyst acts on the first reaction?
Carbonic anhydrase
In the two equilibria used to form bicarbonate, why is it that they always run in the forward direction? (2)
- Haemoglobin buffers hydrogen ions and produces HbH 2. Chloride shift allows Cl- to enter the red blood cells as bicarbonate leaves into the plasma
How are carbamino compounds formed?
When CO2 combines with the terminal amine groups in blood proteins
How is HbCO2 formed?
Haemoglobin is provided by the breakdown of oxyhaemoglobin into O2 and Hb.
Hb combines with CO2 forming HbCO2.
This process is rapid and does not require an enzyme
What is the Bohr effect?
The Bohr effect states that the affinity of haemoglobin for oxygen decreases inversely with increasing acidity and carbon dioxide concentration. The oxygen-haemoglobin curve shifts to the right
For the oxygen-dissociation curve what are the axis labels?
Which factors would cause a right shift in the oxygen-haemoglobin curve?
Which factors would cause a left shift in the oxygen-haemoglobin curve?
Describe the Haldane effect
Removing O2 from Hb increases the ability of Hb to pick-up CO2 and CO2 generated H+
(and vice versa)
How does the presence of oxygen (at the lungs) affect the oxygen-haemoglobin curve?
It will shift it to the right causing increased CO2 (and H+) offload from haemoglobin
(Haldane effect)
How is oxygen released at a tissue cell?
Due to the Bohr effect
Increased CO2 and H+ reduces haemoglobin’s affinity for oxygen causing it to ofload
During gas exchnage at tissues, why is choliride shift important?
It ensures the equilibria for bicarbonate remain producing products in the forward direction.
By removind the end product (HCO3) and replace it for chloride ions, the reaction will continue to run in the forward direction
During gas exchnage at tissues, which haemoglin associated compound is broken down, and which two are synthesised?
Oxyhaemoglobin (HbO2) - broken down
HbH - synthesised
HbCO2 - synthesised
During gas exchange at the alveolus, which haemoglobin associated compounds are broken down and which one is resyntheised?
HbH - broken down - H+ released (used for HCO3- equilibria)
HbCO2 - CO2 released (diffuses into alveoli)
HbO2 - resynthesised (O2 diffuses from alveoli)
Carbon dioxide diffuses into the alveolus from whcih three sources?
- Plasma
- HbCO2 breakdown
- HCO3- equilibrium
(HCO3- + H+ (from HbH breakdown) → H2CO3 → H2O + CO2)
What controls the rhythm of respiration?
Medulla oblongata
What is the pre-Botzinger complex?
A complex of neurones responsible for the rhythm of breathing in the medulla
How does the pre-Botzinger complex function?
It excites the dorsal neurones by initiating action potentials in bursts to allow muscles to contract during inspiration and lack of firing allows pssive expirtion to occur
Active expiration involves increased firing rate of which neurones?
Usually dorsal which activate respiratory neurones subsqequently activating intercoastal, abdominal and other neurones.
What is the role of the pons?
The pins is an area of the medulla that modifies the produced rhythm of breathing
When dorsal respiratory neurones fire which area within the pons is activated?
The pneumotaxic centre
What is the function of the pneumotaxic centre in the pons?
It will cause termination of inspiration
Without it apneustic breathing wil occur - a prolonged inspiration with insufficient short expiration
What is a function of the apneustic centre?
Influences breathing rhythm, by prolonging inspiration
What is the Hering-Breuer reflex?
A reflex which prevents over stretching of the lungs, due to the activation of stretch receptors.
Inspiration will be inhibited by activation of these receptors
What are joint receptors?
J receptors pick up impulses from moving muscles and adjust breathing according to intensity of movement
What is the function of the cough reflex?
To clear dust, dirt, excess mucous etc out of the respiratory tract
What does a cough relfex stimulate? (5)
- Short intake of breath
- Closure of larynx
- Contraction of abdominal muscles
- Opening of larynx
- Expulsion of air
What can chemoreceptors do in relation to the respiratory system?
Sense and control values of blood gas tensions
Where are chemoreceptors found in relation to the respiratory system? (2)
- The CNS (central) - at surface of medulla
- The rest of the body (peripheral)
What can peripheral chemoreceptors do?
Sense O2 and CO2 tensions as well as H+ concentration
What can central chemoreceptors detect?
Concentrations of H+ in cerebrospinal fluid
Of the three substances listed below, which are able to permeate the blood brain barrier?
- CO2
- H+
- HCO3-
Only CO2 is permeable
How are H+ and HCO3- produced in cerebrospinal fluid if they cannot pass the blood brain barrier?
CO2 dissociates across the BBB forming carbonic cid which can dissociate to form both H+ and HCO3-
(CO2 + H2O ⇔ H2CO3 ⇔ H<span>+</span> + HCO3-)
What effect on ventilation do central chemoreceptors have?
By sensing high H+ concentrations in cerebrospinal fluid, they can increase ventilation
What is hypercapnia?
When there is excess CO2 in the blood
What is hypoxia?
When abnormally low amounts of O2 is present in tissues
What is the effect of decreasing partial pressure of oxygen on ventilation?
It will increase rapidly up until a point where neural action becomes depressed (due to low oxygen) and ventilation then rapidly decreases
What happens at high altitudes?
Partial pressure of oxygen is very low
Hyperventilation and increased cardiac output will occur to attempt prevention of hypoxia.
What is the H+ drive of respiration?
Increased H+(mediated by peripheral chemoreceptors) in the blood (along with increased PaCO2) causes increased ventilation
As CO2 produces H+ and is eliminated, H+ load is decreased.
