Physiology Flashcards
What are the 4 stages of external respiration?
Ventilation
Gas exchange between alveoli and blood
Gas transport in blood
Gas exchange at tissue level
What is Boyle’s law?
At any constant temperature the pressure exerted by s gas varies inversely with the volume of gas
(Gas volume increase = pressure exerted by gas decrease)
How are the lungs linked to the thorax?
Intrapleural fluid cohesiveness
Negative intrapleural pressure
What 3 pressures are important in ventilation?
Atmospheric pressure
Intra-alveolar pressure
Intrapleural pressure
How is lung volume increased physiologically?
Flattening of the diaphragm
External intercostal muscle (lifts ribs and moves out sternum)
What nerve innervates the diaphragm?
Phrenic nerve
From C3,4,5
What can abolish the transmuted pressure gradient?
Pneumothorax (air in the pleural space)
How to lungs recoil after inspiration?
Elastic connective tissue
Alveolar surface tension
What is alveolar surface tension?
Attraction between water molecules at liquid air interface
Produces a force which resists the stretching of the lungs
What is LaPlace’s law?
Smaller alveoli have a higher tendency to collapse
What is pulmonary surfactant?
Mixture of lipids & proteins secreted by type II alveoli
Lowers the surface tension & stops collapse
What is respiratory distress of the newborn?
Not enough surfactant
What is alveolar interdependence?
When neighbouring alveoli collapse surrounding alveoli stretch then recoil pulling it open
What is tidal volume?
Volume of air entering or leaving the lungs during a single breath
What is inspiratory reserve volume?
Extra volume of air that can be maximally inspired over and above the typical resting tidal volume
What is the inspiratory capacity?
Max volume of air that can be inspired at the end of a normal quiet expiration
What is exploratory reserve volume?
Extra volume of air that can be actively expired by maximal contraction beyond the normal volume of air after a resting tidal volume
What is functional residual capacity?
Volume of air in lungs at end of normal passive expiration
What is the vital capacity
Max volume of air that can be moved out during a single breath following a maximal inspiration
What is total lung capacity?
Max volume of air that the lungs can hold
What is FEV1?
Volume of air that can be expired during the first second of expiration in an FVC determination
What is FVC?
Maximum volume of air that can be forcibly expelled from the lung follows a maximum inspiration
What does a restrictive lung pattern look like?
Low FEV1
Low FVC
Normal ratio
What does an obstructive pattern look like?
FEV low
FVC low or normal
Ratio low
What does parasympathetic stimulation do to bronchioles?
Bronchoconstriction
What does sympathetic stimulation do to bronchioles?
Bronchodilation
What so dynamic airway compression?
In expiration pressure on alveoli and airway
Pressure on alveoli = good pushes air out of lungs
Pressure on airway = bad
(Causes no problem in normal people)
What patients is peak flow useful for?
Obstructive (COPD & asthma)
What is pulmonary compliance?
A measure of the effort that has to go into stretching or distendjng the lungs
Low compliance = stuff lungs = more work to breath
What decreases pulmonary compliance?
Pulmonary fibrosis Pulmonary oedema Lung collapse Pneumonia Absence of surfactant
What pattern does decreased pulmonary compliance have in spirometry?
Restrictive
When would pulmonary compliance become abnormally increased?
If elastic recoil of the lungs is lost
Emphysema - hyperinflation of lungs
Does compliance increase or decrease with age?
Increase
When is the work of breathing increased?
Pulmonary compliance Decreased
Airway resistance Increased
Elastic recoil Decreased
Need for increased ventilation
What is internal respiration?
The intracellular mechanisms which consume O2 & produce CO2
What is external respiration?
Exchange of O2 & CO2 between external environment and cells
What is anatomical dead space?
Air that remains in the airway where it is not available for gas exchange
Difference between pulmonary and alveolar ventilation?
Pulmonary = TV x RR
(Volume of air breathed in and out per minute)
Alveolar = (TV - dead space) x RR
(Volume of air exchanged between the atmosphere and the alveoli per minute)
What is the difference between ventilation and perfusion?
Ventilation - rate at which gas is passing through the lungs
Perfusion - rate at which blood is passing through the lungs
What is alveolar dead space?
Ventilated alveoli which are not adequately perfused
Can significantly increase effect of disease
How to V/Q stay matched in the lungs?
Increased perfusion –> increased CO2 –> decrease airway resistance –> increased airflow –> V/Q match
Increased ventilation –> increased O2 –> pulmonary vasodilation –> increased blood flow
Effect of local change in O2
Decreased O2 Increased O2
Pulmonary arterioles Vasoconstriction Vasodilation
Systemic arterioles Vasodilation Vasoconstriction
4 factors that influence the rate of gas exchange across alveolar membrane
Partial pressure gradient of O2 and CO2
Diffusion coefficient for O2 and CO2
Surface area of alveolar membrane
Thickness of alveolar membrane
What is the partial pressure of gas?
The pressure that one gas I a mixture of gases would exert if it were the only gas present in the whole volume occupied by the mixture at a given temperature
How do you calculate the partial pressure of oxygen in alveolar air?
PAO2 = PiO2 -[PaCO2/0.8]
PiO2 = partial pressure of oxygen in inspired air 0.8 = respiratory exchange ratio
Why is the partial pressure gradient for CO2 is much smaller than that of O2?
CO2 is more soluble in membranes than O2
What does a big gradient between PAO2 and PaO2 indicate?
Problems with gas exchange or a right to left shunt in the heart
What is Ficks law of diffusion?
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 are alveoli?
Thin walled inflatable sacs
Function in gas exchange
Walls consist of a single layer of flattened Type I alveolar cells
Pulmonary capillaries encircle each alveolus
Narrow interstitial space
What are the non-respiratory functions of the respiratory system?
Route for water loss and heat elimination
Enhances venous return
Helps maintain normal acid-base balance
Enables speech and other vocalisations
Modifies materials that pass through the pulmonary circulation
Nose serves as organ of smell
What is Henry”s Law?
The amount of gas dissolved in blood is proportional to the gas’ partial pressure
How is most oxygen transported in the blood?
Bound to haemoglobin
How else is oxygen transported in the blood (very little)?
Physically dissolved
How many groups does each haemoglobin molecule have?
4
What does the oxygen haemoglobin disassociation curve show?
Haemoglobin affinity for oxygen
How do you calculate the oxygen delivery index?
DO2I = CaO2 x CI
CaO2 = oxygen content of arterial blood CI = cardiac index
How do you calculate the oxygen content of arterial blood?
CaO2 = 1.34 x [Hb] x SaO2
What can impair oxygen delivery to the tissues?
Respiratory disease
Heart failure
Anaemia
What is cooperativity?.
When the binds of 1 O2 to Hb increases the affinity of Hb for O2
(Flattens when all sites become occupied
What shape is the oxygen haemoglobin dissociation curve?
Sigmoid
What is the Bohr effect?
Shifting of oxygen haemoglobin curve to the right (less affinity)
What causes the Bohr effect?
Low pH
High temperature
Increased pCO2
Increased 2,3-BPG
What causes haemoglobin to have higher affinity for oxygen?
High pH
Low temperature
Low pCO2
Foetal haemoglobin.
Where is myoglobin found?
Skeletal & cardiac muscles
What does myoglobin do?
Provides short term storage for O2 under anaerobic conditions
Releases O2 at very low PO2
What does the presence of myoglobin in the blood indicate?
Muscle damage
3 means of CO2 transport in the blood?
Solutions
As bicarbonate
As carbamino compounds
How many times more soluble is CO2 than oxygen?
20
Where is bicarbonate formed?
Red blood cells
How are carbamino compounds formed?
Combination of CO2 with terminal amino groups in blood proteins
(Especially glob in of haemoglobin)
What is the haldane effect?
Removing O2 from Hb increases the ability of Hb to pick up CO2 and CO2 generated H+
What do the Bohr effect and the haldane effect with together to facilitate?
O2 liberation and uptake of CO2 & CO2 generated H+ at tissues
What complex in the brain controls the rhythm of breathing?
Pre-Botzinger complex
What is the neural control of inspiration?
Dorsal respiratory group neurones fire in bursts
Leads to inspiration
When firing stops, passive expiration
What is the neural control of hyperventilation?
Increased firing of dorsal neurones excites a second group:
Ventral respiratory group neurones
Excite internal intercostals, abdominals ect. –> forceful expiration
What can alter the rhythm generated in the medulla?
Neurones in the pons:
- pneumotaxic centre (PC) stimulation terminates inspiration
- stimulated when dorsal respiratory neurones fire
- inhibits inspiration
What is apeusis?
Breathing is prolonged inspiratory gasps with brief expiration
(What would happen if there was no PC)
What is the apneustic centre?
Impulses from these neurones excite inspiratory area of the medulla
Prolongs inspiration
Where do respiratory centres in the brain receive signals from?
Higher brain centresv(e.g. cerebral cortex)
Stretch receptors in the walls of bronchi/bronchioles
J receptors (stimulated left heart failure & pulmonary emboli)
Joint receptors (stimulated by joint movement)
Baroreceptors
Central chemoreceptors
Peripheral chemoreceptors
What does the Hering-Breur reflex do?
Stops hyperinflation of the lungs
Examples of involuntary modifications of breathing
Cough receptors
Joint receptors in exercise
Temperature, adrenaline changes
Factors that increase ventilation during exercise?
Reflexes originating from body movement Adrenaline release Impulses from cerebral cortex Increase in body temp Accumulation of CO2 and H+ generated by active muscles
What is the cough reflex for?
Helps clear airways of dust, dirt or excessive secretions
Activated by irritation of the airways or tight airways
Where in the brain is the cough reflex stimulated?
The medulla
What are the physiological aspects of the cough reflex?
Afferent discharge Stimulates short intake of breath Closure of the larynx Contraction of abdominal muscles (increases intraalveolar pressure) Opening of the larynx Expulsion of air
What is the role of peripheral chemoreceptors in breathing?
Sense tension of O2, CO2 and [H+] in the blood
Where are the central chemoreceptors involved in respiration situated?
Near the surface of the medulla of the brain stem
What do the central chemoreceptors involved in respiration respond to?
[H+] of the cerebrospinal fluid (CSF)
Why is CSF less buffered than blood?
Contains less protein
What shape is the myoglobin dissociation curve?
Hyperbolic
What separates CSF from the blood?
Blood brain barrier
Does CO2 diffuse across the BBB?
Yes
What is hypercapnia?
Increased CO2
When is the hypoxia drive off respiratoration important?
Chronic CO2 retentive patients
At high altitudes
When is the hoodie drive stimulated?
When PO2
What causes hypoxia at high altitudes?
Decreased partial pressure of inspired oxen
What is the body’s acute response to hypoxia?
Hyperventilation & increased cardiac output
Symptoms of acute mountain sickness
Headache Fatigue Nausea Tachycardia Dizziness Sleep disturbance Exhaustion Dyspnoea Unconsciousness
Chronic adaptations to high altitudes hypoxia?
Increased RBC (increases O2 carrying capacity of blood)
Increased 2,3 BPG produced within RBC (O2 offloaded more easy to tissues)
Increased number of capillaries (blood diffuses more easily)
Increased number of mitochondria (O2 can be used more efficiently)
Kidneys conserve acid (arterial pH drops)
Does H+ readily cross the BBB?
No
How does H+ excess affect respiration?
Peripheral chemoreceptors add non carbonic H+ to the blood
(e.g. lactic acid during exercise & diabetic ketoacidosis)
Causes hyoerventillation (blow off CO2)
IMPORTANT IN ACID BASE BALANCE
