Physiology Flashcards
Define internal respiration
Intracellular mechanism which consumes O2 to produce CO2
Define external respiration
The sequence of events leading to exchange of O2 and CO2 between the external environment and the cells of the body
What are the 4 steps of external respiration
Ventilation
Gas exchange between alveoli and blood
Gas transport in blood
Gas exchange at the tissue level
Explain the process of ventilation
Mechanical process of moving gas in and out of the lungs
State Boyle’s law
At any constant temperature the pressure exerted by a gas varies inversely with the volume of the gas
Why do the lungs move with the chest wall
Intrapleural fluid cohesivness, water molecuels in the intrapleural fluid are attached and resist seperation
The transmural pressure gradient across the lung wall and across the chest wall
(Lungs move out and chest wall moves in)
Explain the mechanics of inspiration
Diaphragm contracts increasing vertical thoracic volume (Phrenic nerve)
External intercostal muscles contract lifting ribs and moving out sternum
Explain the physical action of inspiration
As chest cavity volume increases by boyles law the pressure decreases
Air flows down its pressure gradient to restore the gradient
Which of normal inspiration or expiration is passive
Inspiration is active
Expiration if passive
Explain the mechanism of expiration
Diaphragm and intercostals relax to decrease the thoracic volume
This increases then interthoracic pressure by boyles law so, by elastic recoil air is expelled from the lungs down its pressure gradient
Explain the mechanism of pneumothorax
Traumatic the chest wall is damaged
Spontaneous the lung wall is damaged
In both cases it abolishes the transmural pressure gradient
What are the physical signs of pneumothorax
Hyperresonant percussive note
Decreased/absent breath sounds
What causes the lungs to recoil during expiration
Elastic connective tissue, lungs bounce back to original shape
Alveolar surface tension, alveolar surfactant surface tension pulls in
State the law of LaPlace
The inward pressure is relative to the surface tension and inverse to the bubble radius
How does LaPlace’s law apply to the lungs
It shows how smaller alveoli have greater tendency to collapse
Explain the mechanism behind respiratory distress syndrome of the newborn
Premature babies lack suficcient pulmonary surfactant
This causes an excessively strenuous inspiratory effort to overcome the high surface tension and inflate the lungs
Explain the alveolar interdependence
If an alveolus starts to collapse the surrounding alveoli are stretched and then recoil exerting a force to open the collapsing alveolus
State the major inspiratory muscle
Diaphragm
External intercostal muscles
State the accessory muscles of inspiration
Sternocleidomastoid
Scalenus
Pectoral
State the muscles of active expiration
Abdominal muscles and internal intercostal muscles
Define insipiratory capacity
The volume of air that can be inspired following normal passive expiration
Tidal volume + Inspiratory volume
Vital capacity - expiratory reserve volume
Define expiratory reserve volume
The volume of air which can be exhaled following normal passive exhalation
Define vital capacity
The volume of air which can be inhaled/exhaled following full exhalation/inhalation
Inspiratory capacity + expiratory reserve volume
Tidal volume + inspiratory reserve volume + expiratory reserve volume
Define inspiratory reserve volume
The volume of air which can be inhaled following normal inspiration
Define tidal volume
The volume of air moved in a normal inspiration or expiration
Define functional residual capacity
The volume of air left in lungs following normal passive expiration
Define residual volume
The volume of air remaining in the lungs following full expiration
Define total lung capacity
The maximum volume of air that can be within the lungs at any time
What increases the residual volume
When the elastic recoil of the lungs is lost
E.g emphysema
Define forced vital capacity
The maximum volume that can be forcibly expelled from the lungs following a maximum inspiration
Define forced expiratory volume in one second [FEV1]
The volume of air that can be expired during the first second of expiration in an FVC
What is the normal range for the FEV1/FVC ratio
Greater than 70%
State the equation for airway resistance
Flow = change in pressure over resistance
What is the primary factor effecting the airway resistance
The radius of the conducting airway
Explain dynamic airway compression
During expiration the rising pleural pressure compresses the alveoli and airway
This is overcome by the pressure downstream driving the airways open
Explain dynamic airway compression in the case of obstructive lung disease
An obstruction in the airway causes a loss of the pressure downstream increasing the risk of airway collapse
This is made worse by a loss of the elastic recoil of the lungs also
Briefly explain peak flow
A test useful for obstructive lung disease
Explain pulmonary compliance
Compliance is a measure of the effort that has to go into stretching or distending the lungs
Less compliant lungs require more work to inflate to the same degree
State some factors which decrease the pulmonary compliance
Fibrosis Oedema Lung collapse Pneumonia Surfactant absence
A decrease in pulmonary compliance results in what pattern on spirometry
Restrictive pattern
State some factors which increase the pulmonary compliance
Old age
Emphysema
What is a clinical sign of increased pulmonary compliance
Hyperinflation of the lungs
Explain the concept of work of breathing
Normal 3% of the total energy Lungs normally operate at ~ 50% capacity Work of breathing can increase when - Pulmonary compliance is decreased Airway resistance is increased - Elastic recoil is decreased - When a need for increased ventilation
Define pulmonary ventilation
The amount of air moved between the respiratory tract and the enviroment
Define the alveolar ventilation
The volume of air available for exchange at the alveoli
This is the pulmonary ventilation - anatomical dead space
Explain anatomical dead space
Areas of the respiratory tract which the air is not avaliable for gas exchange
Explain the best way to increase the pulmonary ventilation
Due to dead space it is more advantageous to increase the depth of breathing
Ventilation perfusion concept
The amount of gas transfer is dependent on the air moving through the lungs (ventilation) and the blood flow through the lungs (perfusion)
Explain alveolar dead space
The alveolar dead space are the alveolar spaces which are ventialted bur inadequately perfused
State the physiological dead space
The anatomical dead space + the alveolar dead space
State the control of V/Q matching in the lungs
Local controls act on smooth muscle of airways and arterioles
Accumulation of CO2 in the blood leads to increased airflow
Accumulation of O2 in the alveoli leads to increased blood flow
What are the 4 factors which influence the rate of gas exchange across the alveolar membrane
Partial pressure gradient of O2 and CO2
Diffusion coefficient of O2 and CO2
Surface area of alveolar membrane
Thickness of alveolar membrane
State Dalton’s law
The total pressure in a gaseous mixture is equal to the sum of the partial pressures of each individual component in the gas mixture
Define partial pressure
The pressure that one gas in a mixture would exert if it were the only gas in the whole volume
State the partial pressure of oxygen in the alveolar air
PaO2 = PiO2 - [PaCO2/0.8]
0.8 is the respiratory exchange rate
How does CO2 diffuse simialr to O2 with a far lower partial pressure gradient
The diffusion coefficient of CO2 is ~ 20x that of O2
State Fick’s law
The amount of gas that moves across a sheet of tissue in a unit time is proportional to the sheet area but inversly proportional to its thickness
State Henry’s law
The amount of gas dissolved in a given type and volume of liquid at constant temprature is proportional to the partial pressure of the gas in equilibrium with liquid
Explain O2 transport in the blood
A small volume is transported directly dissolved in the plasma (By Henry’s law)
Most O2 in the blood is bound to haemoglobin
Explain the O2 binding to haemoglobin
Each Hb molecule contains 4 haem groups
Each haem group reversibly binds to one O2 molecule
The PO2 is the primary facotr which determines the percentage saturation of haemoglobin
Shows co-operativity, one O2 increased the affinity of Hb for O2
Explain the Hb dissociation curve
The dissocaition of O2 is alosteric so forms a sigmoidal curve.
Define the oxygen delivery index
Oxygen delivery to tissues is equal to the ocygen content of the arterial blood times the cardiac index (the cardiac output per the surface area of the body)
Explain the factors on oxygen content of arterial blood
The Hb concentration, the % saturation of the Hb and the amount of O2 one gram of Hb can carry (1.34ml in normal)
State the Bohr effect
A shift of the O2 dissociation curve to the righ, more O2 released to tissues
State what shifts the oxygen dissociation curve to the right
Increased PO2
Increased H+
Increased temprature
Increased 2,3 BPG
Briefly explain HbF
Foetal haemoglobin differs in structure than that of an adult
Interacts less with 2,3BPG so HbF has a higher affinity for O2
Allows O2 to transfer from mother to foetus even when PO2 is lower
Briefly explain myoglobin
A protein present in the skeletal and cardiac muscles
One haem group per molecule, doesnt show co-operative binding
(Hyperbolic dissociation curve)
Myoglobin releases O2 at a very low PO2, allows a short term storage of O2 for anaerobic conditions
What does myoglobin in the blood indicate
Muscle damage
How is CO2 transported in the blood and in what proportions
Solution 10%
Bicarbonate 60%
Carbamino compounds 30%
How is CO2 transported as bicarboante ions
CO2 + H2O by carbonic anhydrase in red blood cells forms H2CO3
H2CO3 dissociated to form H+ and HCO3-
HCO3- is exchanged for Cl- in the blood (chloride shift)
How is CO2 transported as carbamino compounds
Carbamino compounds are formed by combination of CO2 with the terminal amine groups in blood proteins
(especially globin)
Explain the Haldane effect
Removing O2 from Hb increases the ability of Hb to pick up CO2 and CO2 generated H+
(Shifts the curve to the left so more O2 is given up in tissues)
Where are the major respiratory centres of the brain
In the medulla oblongata
Secondary in the pons: pneumotaxic and apneustic areas
What area of the medulla acts as a pacemaker for respiration
Pre-Botzinger complex
Located at superior end of medullary repsiratory centre
What is the neurological pathway to inspiration
Rhythm is generated by the pre-botzinger complex which excited the dorsal respiratory groups
Dorsal respiratory groups fire causing insipration, when firing stops passive expiration occurs
What is the neurological pathway of active expiration
Increased firing of dorsal neurones excite a second group (ventral respiratory groups)
The action potentials from the ventral group lead to the active expiration
How can the pons modify the rhythm to reduce inspiration
The pneumotaxic centre stimulated termination of inspiration
PC is stimualted when dorsal respiratory neurons fire
Apneusis with prolonged inspiratory gaps suggests PC damage
How can the pons modify the rhythm to prolong inspiration
Signals from the apneustic centre excite the dorsal respiratory centre
Explain the Hering-Breur reflex
Stretch receptors of the bronchi and bronchioles prevent hyperinflation
Explain the influence of joint receptors in breathing
Impulses from moving limbs reflexly increase breathing
What factors increase ventilation during exercise
Reflexes from body movement
Adrenaline release
Impulses from cerebral cortex
Increased body temperature
Later accumulation of CO2 and H+
State the chemical control of respiration
Chemoreceptors sense the values of gas tensions
State the location and purpose of peripheral chemoreceptors
Carotid bifurcation and aortic arch
Sense tension of oxygen and CO2 and H+ in the blood
State the location and purpose of central chemoreceptors
Situated near the surface of the medulla of the brainstem
In response to H+ in cerebrospinal fluid
Explain the idea of hypoxic drive
The effect via the peripheral chemoreceptors which is only stimulated when PO2 falls below 8kPa
Important in those with CO2 retention and at high altitudes
Explain the H+ drive of respiration
This is via the peripheral chemoreceptors
Play a major role in correction of acidosis
Stimualtion by H+ causes: hyperventilation to shed CO2
