Physiology Flashcards
3 pressures important in ventilation
Atmospheric Pressure
Intra-alveolar (intra pulmonary) Pressure
Intra-pleural (intrathoracic) pressure
Inspiration
An active process brought about by contraction of inspiratory muscles
Expiration
A passive process brought about by relaxation of inspiratory muscles
Changes in intra-alveolar and intra-pleural pressures during the respiratory cycle
Falls during inspiration, rises during expiration.
transmural pressure gradient remains relatively constant
Pneumothorax
Air in the pleural space
What causes the lungs to recoil during expiration?
Elastic connective tissue in the lungs
Alveolar Surface Tension
Pulmonary Surfactant
A complex mixture of lipids and proteins secreted by type 2 alveoli.
Lowers alveoli surface tension by interspersing between the water molecules lining the alveoli.
Alveolar Interdependence
If an alveolus start to collapse the surrounding alveoli are stretched and then recoil exerting expanding forces in the collapsing alveolus to open it
Forces keeping the alveoli open (3)
Alveolar Interdependence
Pulmonary Surfactant
Transmural Pressure Gradient
Forces promoting alveolar collapse (2)
Elasticity of stretched lung connective tissue
Alveolar surface tension
Major inspiratory muscles
Diaphragm
External intercostal muscles
Accessory muscles of inspiration
Sternocleidomastoid
Scalenus
Pectoral
Muscles of active expiration
Abdominal muscles
Internal intercostal muscles
Tidal Volume (TV) and avg value
Volume of air entering or leaving lungs during a single breath
0.5L
Inspiratory Reserve Volume (IRV) and avg value
Extra volume of air that can be maximally inspired over and above typical resting tidal volume
3.0L
Expiratory Reserve Volume (ERV) and avg value
Extra volume of air that can be actively expired by maximal contraction beyond the normal volume of air after a resting tidal volume
1.0L
Residual Volume (RV) and avg value
Minimum volume of air remaining in the even after a maximal expiration
1.2L
Inspiratory Capacity (IC) + avg volume
Maximum volume of air that can be inspired at the end of a normal quiet expiration
3.5L
(IC= TV+IRV)
Functional Residual Capacity (FRC)
Volume of air in lungs at end of normal passive expiration
2.2L
(FRC = ERV + RV)
Vital Capacity (VC)
Maximal volume of air that can be moved out during a single breath following a maximal inspiration
4.5L
(VC= IRV+TV+ERV)
Total Lung Capacity (TLC)
Total volume of air the lungs can hold
5.7L
(TLC=VC+RV)
Normal FEV1/FVC ratio
> 70%
Intrapleural pressure during inspiration and expiration
Falls during inspiration
Rises during expiration
Peak flow rate
Velocity at which you can breathe out of lungs
Used to assess airway function
Pulmonary compliance
Measure of effort that has to go into stretching or distending the lungs
Volume change per unit of pressure change across the lungs
Factors which decrease pulmonary compliance (5)
pulmonary fibrosis, pulmonary oedema, lung collapse, pneumonia, absence of surfactant
Factors which increase pulmonary compliance
elastic recoil of lungs is lost-emphysema
Pulmonary Ventilation
Tidal volume x respiratory rate
The volume of air breathed in and out per minute
Alveolar Ventilation
(Tidal volume-dead space volume) x respiratory rate
The volume of air exchanged between the atmosphere and alveoli per minute
Ventilation Perfusion Match
Local controls act on the smooth muscles of airways and arterioles to match airflow to blood flow
Four factors which influence 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 would a big gradient between PAO2 (alveolar) and PaO2 (arterial) indicate?
Problems with gas exchange in the lungs
Right to left shunt in the heart
Non-respiratory functions of respiratory system (7)
Route for water loss and heat elimination
Enhances venous return
Helps maintain normal acid-base balance
Enables speech, singing and other vocalisations
Defends against inhaled foreign matter
Removes, modifies, activates or inactivates various materials passing through pulmonary circulation
Nose serves as the organ of smell
Oxygen delivery index (DO2l)
Oxygen content of arterial blood(CaO2) x Cardiac index (CI)
What determines the oxygen content of arterial blood
The haemoglobin concentration [Hb] and the saturation of Hb with O2
CaO2 = 1.34 x [Hb] x SaO2
Factors that affect oxygen delivery to the tissues (4)
Decreased partial pressure of inspired oxygen
Anaemia (decreases Hb concentration and hence decreases O2 content of the blood)
Heart Failure (decreases cardiac output)
Respiratory disease(decrease arterial PO2 hence decrease Hb saturation with O2 and O2 content of blood)
Function of myoglobin
Provides a short-term storage of O2 for anaerobic conditions
Present in skeletal and cardiac muscles
Means of CO2 transport in the blood
Solution (10%)
As bicarbonate (60%)
As carbamino compounds (30%)
What is the effect of partial pressure on gas solubility?
If the partial pressure in the gas phase is increased the concentration of the gas in the liquid phase would increase proportionally
How are carbamino compounds formed?
Combination of CO2 with terminal amine groups in blood proteins
How is bicarbonate formed in the blood?
Co2 diffuses from capillaries into red blood cells where it reacts with water in the presence of carbonic anhydrase to produce carbonic acid
It then dissociates into hydrogen ions and bicarbonate
What is the haldane effect?
Removing O2 from Hb increases the ability of Hb to pick-up CO2 and CO2 generated H+
What part of the brainstem is the major rhythym generator?
Medulla oblongata
Which network of neurones displays pacemaker activity?
Pre-botzinger complex
Which neurones are excited which give rise to active inspiration?
Dorsal respiratory group neurones
Which neurones are excited which give rise to active expiration?
Ventral respiratory group neurones
What terminates inspiration upon stimulation?
Pneumotaxic Centre (PC)
Which neurones in the pons stimulate the pneumotaxic centre?
Dorsal respiratory group neurones
Apneusis
Prolonged inspiratory gaps with short expiration (when there is no PC)
Apneustic centre
Impulses from these neurones excite inspiratory area of medulla
Areas respiratory centres receive stimuli from? (7)
Higher brain centres Stretch receptors Juxtapulmonary receptors Joint receptors Baroreceptors Central chemoreceptors Peripheral chemoreceptors
Higher brain centres that influence respiratory centres
Cerebral cortex
Limbic system
Hypothalamus
Stretch receptors
In the walls of bronchi and bronchioles
Hering-breuer reflex guards against hyperinflation
Juxtapulmonary receptors
Stimulated by pulmonary capillary congestion and pulmonary oedema (caused by e.g.left heart failure)
Or pulmonary emboli if capillaries are blocked
Rapid shallow breathing
Joint receptors
Stimulated by joint movement
Baroreceptors
Increased ventilatory rate in response to decreased blood pressure
Examples of involuntary modification of breathing (4)
Pulmonary stretch receptors hering-breuer reflex
Joint receptors reflex in exercise
Stimulation of respiratory centre by temperature, adrenaline or impulses from cerebral cortex
Cough reflex
Cough Reflex
Short intake of breath
Closure of larynx
Contraction of abdominal muscles increases intra-alveolar pressure
Opening of larynx and expulsion of air at high speed
Peripheral chemoreceptors
Sense tension of oxygen and carbon dioxide
Sense [H+] in blood
Central Chemoreceptors
Respond to [H+] in CSF
Blood-brain barrier
Separates CSF from blood
Relatively impermeable to [H+] and HCO3-
CO2 diffuses across readily
Hypercapnia
Carbon dioxide retention so can’t hold breath for a long time
What causes hypoxia at high altitudes?
Decrease partial pressure of inspired oxygen (PiO2)
Chronic adaptations to high altitudes hypoxia
Increased RBC production (polycythaemia) 2,3 BPG produced within RBC Increased number of capillaries Increased number of mitochondria Kidneys conserve acid
Increased RBC production leads to…
O2 carrying capacity increases
2,3 BPG produced within RBC leads to…
O2 offloaded more easily into tissues
Increased number of capillaries means that…
Blood diffuses more easily
Increased number of mitochondria means that…
O2 can be used more efficiently
Kidneys conserving acid leads to…
Decrease in arterial pH
