Physiology Flashcards
4 steps of external respiration
Ventilation
Gas exchange between alveoli and blood
Gas transport in blood
Gas exchange at tissue level
Ventilation
The mechanical process of moving air between the atmosphere and alveolar sacs
Boyle’s law
As the volume of gas increases the force expected by the gas decreases
Two forces which make lungs and thorax move together
- Intrapleural fluid cohesiveness
2. Negative intrapleural pressure - lungs push outwards, chest squeezes inward
What does the external intercostal muscle do?
Lift the ribs and move the sternum out
alveolar surface tension
Attraction between water molecules at liquid air interference
LaPlace Law
P = 2T/r i.e. smaller alveoli have a higher tendency to collapse
What is causes respiratory distress syndrome in a newborn
Lack of surfactant
3 forces that keep the alveoli open
Transmural pressure gradient
Pulmonary surfactant
Alveolar interdependance
2 forces which promote alveolar collapse
Elasticity of stretched pulmonary connective tissue fibres
Alveolar surface tension
Accessory muscles of inspiration
Sternocleidomastoid
Scalenus
Major muscles of inspiration
External intercostal muscles
Diaphragm
Muscles of active expiration
Internal intercostal muscles Abdominal muscles (TIRE)
Tidal volume
Volume of air entering or leaving the lungs during a single breath
Inspiratory reserve volume
Extra volume of air that can be maximally inspired over and above the typical resting tidal volume
Inspiratory capacity
Maximum volume of air that can be inspired after a normal expiration
Expiratory 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
Residual volume
Minimum volume of air remaining in the lungs after maximal expiration
Vital capacity
Maximum volume of air that can be moved out during a single breath following maximal inspiration
Total lung capacity
Maximum volume of air that the lungs can hold = VC + RV
Forced Vital capacity
The volume of air that can be forcefully expelled following maximal inspiration
Forced Expiratory Volume in 1 sec (FEV1)
The volume of air that can be expelled during the first second of expiration
Spirometry results for obstructive lung disease
FVC = Normal FEV1 = Low FEV1/FVC% = low
Spirometry results for restrictive lung disease
FVC = Low FEV1 = Low FEV1/FVC% = Normal
What happens to intrapleural pressure during inspiration
Falls - diaphragm moves down
What happens to intrapleural pressure during expiration
Rises - diaphragm moves up
Compliance
A measure of the effort that has to go into stretching to distending the lungs
What decreases pulmonary compliance?
Pulmonary fibrosis Pulmonary oedema Lung collapse Pneumonia Absence of surfactant
Decreased pulmonary compliance on spirometry?
Restrictive
Increased compliance
Emphysema - patients have to work harder to get air out of the lungs
Age
Increase in work of breathing
Decreased pulmonary compliance
Increased airway resistance
Decreased elastic recoil
Increased ventilation
Pulmonary Ventilation
Tidal volume x respiratory rate
Alveolar ventilation
(tidal volume - dead space) x respiratory rate
What represents new air available for gas exchange within the blood
Alveolar ventilation - volume of air exchanged between atmosphere and alveoli per min
Ventilation
The rate at which gas is passing through the lungs
Perfusion
The rate at which blood is passing through the lungs
Alveolar dead space
ventilated alveoli which are not adequately perfused
effects of decreased O2
Pulmonary arterioles vasoconstrict
Systemic arterioles vasodilate
Effects of increased O2
Pulmonary arterioles vasodilate
Systemic arterioles vasoconstrict
Dalton’s law
The total pressure exerted by a gas mixture = the sum of the partial pressures of each individual component in the gas mixture
Partial pressure of gas
The pressure that one gas in a mixture of gases would exert if it were the only gas present in the whole volume occupied
Fick’s Law of diffusion
The amount of gas to pass across a tissue per unit time is directly proportional to its area and inversely proportional to its thickness
Henry’s law
The amount of a given gas in a given type and volume of liquid is proportional to the partial pressure of the gas in equilibrium with the liquid
2 forms of O2 present in the blood
- Bound to haemoglobin - 98.5%
2. Physically dissolved - 1.5%
What is Po2?
the primary factor which determines the % saturation of haemoglobin with O2
Oxygen delivery index
DO2I = CaO2 x Cl
What is the O2 content of arterial blood determined by?
Haemoglobin conc.
Saturation of Hb
Impairment of O2 delivery to tissue
- Decreased partial pressure of inspired O2
- Respiratory disease
- Anaemia
- Heart failure
Means of CO2 transport in the blood
Solution
Bicarbonate
Carbamino compounds
Which is more soluble - CO2 or O2 in blood
CO2 - 20x more soluble
How are carbamino compounds formed?
Combination of CO2 with terminal amine groups in blood proteins
Haldane effect
Removing O2 from Hb increased the ability of Hb to pick up CO2 and H+
The major rhythm generator of respiration
Medulla
Which neurones generate breathing rhythm and where are they located?
Pre-Botzinger complex - near upper end of medullary respiratory centre
Which neurones are excited in active expiration?
Ventral respiratory neurones
What has to be stimulated to terminate inspiration?
Pneumotaxic centre
When is the pneumotaxic centre stimulated?
When dorsal respiratory neurones fire
Apneusis
Prolonged inspiratory gasps with brief expiration
Which part of the brain modifies rhythm of breathing?
Pons
Involuntary modifications of breathing
Pulmonary stretch receptors
Joint receptors reflex
Stimulation of respiratory centre - temp. or adrenaline
Cough reflex
When are pulmonary stretch receptors activated?
During inspiration, inhibits it - Hering-Breuer reflex
Chemical control of respiration variables
Blood gas tension i.e. CO2
Location of peripheral chemoreceptors
Carotid bodies and aortic bodies
Location of central chemoreceptors
Surface of medulla
What do the central chemoreceptors respond to?
THE concentration of H+ ions of the cerebrospinal fluid
Which chemoreceptors are involved in the hypoxic drive?
Peripheral
