Physiology Flashcards
Internal respiration
Intracellular mechanisms which consume O2 and produce CO2
External respiration
Sequence of events that leads to the exchange of O2 and CO2 between body cells and external environment
4 steps of external respiration
- Ventilation - the mechanical process of moving gas in and out of the lungs
- Exchange of O2 and CO2 between the air in the alveoli and the blood in the pulmonary capillaries
- Transport of O2 and CO2 in the circulating blood (between lungs and tissues)
- Exchange of O2 and CO2 between the blood and the tissues
4 body systems involved in external respiration
Respiratory
Cardiovascular
Haematology system
Nervous system
What is ventilation
Mechanical process of moving air between the atmosphere and alveolar sacs
What is Boyle’s law
At any constant temperature the pressure exerted by gas varies inversely with the volume of the gas
What is atmospheric pressure
Pressure caused by the weight of the gas in the atmosphere on the earths surface
760mmHg
What is intra-alveolar pressure
Pressure within the lung alveoli
760mmHg
What is intrapleural pressure
Pressure exerted outside the lungs within pleural cavity
Negative intrapleural pressure
The sub-atmospheric intrapleural pressure (intra-thoracic pressure) creates a transmural pressure gradient across the lung wall and across the chest wall
Means lungs expand outwards while chest squeezes inwards
Intrapleural cohesiveness
Water molecules in intrapleural fluid are attached to each other and resist being pulled apart
Pleural membranes stick together
How do you convert between mmHg and kilopascals
Divide by 7.5
4 steps of inspiration
- Diaphragm contracts and descends, increasing vertical chest dimension
-
External intercostal muscle lifts the ribs and moves out the sternum → increased volume of thorax
Bucket handle mechanism - Lung size increases so intra-alveolar pressure decreases (Boyle’s Law)
- Air enters the lungs down its pressure gradient until the intra-alveolar pressure becomes equal to atmospheric pressure
What is the difference in force inspiration compared to normal inspiration
Forced has:
- greater outflow of action potentials of longer duration causing maximal descension and flattening
- intercostal muscles contract forcefully to raise ribs maximally
- accessory muscles
What are the accessory muscles of inspiration
Pectoralis major
Pectoralis minor
Sterocleidomastoid
Scalenus anterior, medius, and posterior
3 steps of expiration
- Diaphragm relaxes and rises, intercostal muscles contract
-
Intra-alveolar pressure increases (Boyle’s Law)
Caused by relaxation of inspiratory muscles → passive process -
Lungs recoil to expell air from the lungs down its pressure gradient until the intra-alveolar pressure becomes equal to atmospheric pressure
Due to alveolar tension
Difference in forced expiration and normal respiration
In forced:
- right and left anterolateral abdominal wall muscles contract forcefully, increasing intra-abdominal pressure
- diaphragm forced superiorly by compressed abdominal contents
- Intrathoracic pressure increases, air moves from high to low pressure - out of lungs
What is alveolar surface tension
Attraction between water molecules at liquid air interface
Produces a force which resists stretching of the lungs in alveoli helping lungs to recoil during expiration
Law of LaPlace
Inward collapsing pressure is equal to 2x surface tension divided by radius
P = 2T / r
Means smaller alveoli are more likely to collapse
What is lung surfactant
Complex mixture of lipids and proteins secreted by type 2 alveoli
What does lung surfactant do
Intersperses water molecules lining alveoli reducing alveolar surface tension to prevent collapse
Lowers surface tension of smaller alveoli more than larger alveoli to prevent collapse at end of expiration
What is respiratory distress syndrome of the newborn
Developing fetal lungs are unable to synthesise surfactant until late pregnancy
There’re premature babies may not have enough pulmonary surfactant
At birth baby make strenuous inspiratory effects to overcome high surface tension and inflate lungs which can cause damage
What are the forces keeping the alveoli open
Transmural pressure gradient
Pulmonary surfactant
Alveolar interdependence
What is alveolar interdependence
if alveoli start to collapse the surrounding alveoli are stretched then recoil exerting expanding forces in the collapsing alveolus to open it
What forces promote alveolar collapse
Elastic recoil of lungs and chest wall
Alveolar surface tension
What are the major inspiratory muscles
Diaphragm
External intercostal muscles
Accessory muscles of inspiration
- Sternocleidomastoid
- Scalenus
- Pectoral
Muscles of active expiration
- Abdominal muscles
- Internal intercostal muscles
4 lung volumes
Tidal volume - TV
Inspiratory reserve volume - IRV
Expiratory reserve volume - ERV
Residual volume - RV
4 lung capacities
Vital capacity
Inspiratory capacity - IC
Functional residual capacity - FRC
Total lung capacity - TLC
Tidal volume
Volume that enters and leave with each breath
Normal quiet inspiration and expiration
Inspiratory reserve volume
Amount of air that can be forcibly inhaled after a normal tidal volume
Relies on; muscle strength, lung compliance (elastic recoil) and normal starting point
Expiratory reserve volume
The volume of air that can be exhaled forcibly after exhalation of normal tidal volume
Flies on muscle strength and low airway resistance
Residual volume
Volume of air remaining in lungs after maximal exhalation
Increases when elastic recoil of lungs is lost
Cannot be measured by spirometry
Vital capacity
Volume that can be exhaled after maximum inspiration
VC = IRV + TV + ERV
Inspiratory capacity
Volume that can be inhaled after quiet exhalation
IC = IRV + TV
Functional residual capacity
Volume of air in lungs at end of normal passive expiration
FRC = ERV + RV
Total lung capacity
Volume of air in lungs after maximal inspiration
Sum of all volumes
What do you call a graph that plots volume against time using data from spirometry test
Vitalograph
2 important spirometry volumes on Vitograph
Forced vital capacity (FVC)
- maximum volume of air subject can expel in maximal expiration from maximal inspiration
Forced expiratory volume in 1 second (FEV1)
- the maximal volume of air that a subject can expel in one second from point of maximum inspiration
In obstructive lung diseases what happens FVC and FEV1
FVC is only reduced slightly
FEV1 <80% of predicted
In restrictive lung diseases what happens FVC and FEV1
Both <80% of predicted
Airway resistance equation
F = ∆P / R
∆P = pressure gradient
R = radius
Which type of stimulation normally causes bronchoconstriction
Parasympathetic
Which type of stimulation normally causes bronchodilation
Sympathetic
What is dynamic airway compression
In active expiration lungs are compressed so air is pushed out of alveoli and airway
What is pulmonary compliance
The measure of effort that goes into stretching lungs. Volume change per unit of pressure change across lungs
Lungs normally operate at 1/2 full.
What causes work of breathing to increase (4)
Pulmonary compliance decreased
Airway resistance increased
Elastic recoil decreased
Increased need for ventilation
Pulmonary ventilation
Volume of air breathed in and out per minute
- tidal volume x respiratory rate
Alveolar respiration
Volume of air exchanged between the atmosphere and alveoli per minute
- (tidal volume - dead space) x respiratory rate
Anatomical dead space
Airways that fill but cannot perform gas exchange
Definition of Ventilation
Rate at which gas is passing through the lungs
Perfusion
Rate at which blood is passing through the lungs
Ventilation and perfusion (Q) at apex (top) of lung
Good V but poor Q
Ventilation and perfusion at base of lung
Poor V but good Q
What is alveolar dead space
Ventilated alveoli which are not adequately perfused with blood
What happens when perfusion is greater than ventilation
CO2 increases
- vasodilation of airways :. Airflow increases
O2 decreases
- Vasoconstriction of local blood vessels :. Blood flow decreases
What happens when ventilation is greater than perfusion
CO2 decreases
- Vasoconstriciton of airways :. Airflow decreases
O2 increases
- Vasodilation of local blood vessels :. Blood flow increases
4 factors that affect rate of gas exchange
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 equation for partial pressure of oxygen in alveolar air
PAO2 = PiO2 - PaCO2 / 0.8
What is the difference between CO2 diffusion coefficient and O2 coefficient
CO2 coefficient is 20x O2 coefficient
What are the non-respiratory functions of the respiratory system
Water loss and heat elimination
Enhances venous return
Helps maintain normal acid-base balance
Speech
Smell
Defence against inhaled foreign material
What is Henrys law of partial pressure
The amount of a given gas dissolved in a given type and volume of liquid (e.g. blood) at a constant temperature is proportional to the partial pressure of the gas in equilibrium with the liquid
What are the two ways oxygen is transported around the body
Dissolved in blood (1.5%)
Attached to haemoglobin (98.5%)
How is Oxygen delivery index calculated
DO2I = CaO2 x Ci
CaO2 - O2 consent of arterial blood
Ci = function of cardiac output (cardiac index)
How is Oxygen content of arterial blood calculated
CaO2 = 1.34 x [Hb] x SaO2
1 gram of [Hb] can carry 1.34ml of O2 when fully saturated
SaO2 = %[Hb] saturated with O2
How is foetal haemoglobin different to adult haemoglobin
Differs in structure - 2 alpha and 2 gamma haem groups
Has higher affinity for O2 compared to adult haemoglobin so that O2 can transfer from mother to foetus
What is Myoglobin
Oxygen carrier present in skeletal and cardiac muscle
Only has one haem group per molecule
Releases oxygen at very low PO2
Short term storage of oxygen in anaerobic conditions
What causes oxygen delivery to tissue to be impaired
Decreased partial pressure - at altitude
Respiratory diseases - decreased arterial PO2
Anaemia - decreased Hb conc
Heart failure - decreased CO
What are the 3 ways CO2 is transported in the blood ?
In solution (10%)
Carb amino compounds (30%)
(Includes haemaglobin)
Bicarbonate (60%)
What is the Haldane effect
Removing of O2 from [Hb] increases the ability of [Hb to pick up CO2 and CO2 generated H+
What is bicarbonate converted into in RBCs
What enzyme converts this product to CO2
Carbonic acid
Carbonic anhydrase
What is the network of neurones in the medulla that is believed to generate breathing rhythm
Pre-Botzinger complex
What are the 8 stimuli that influence respiratory centres
Higher brain centres
Stretch receptors
Juxtapulmonary receptors
Joint receptors
Exercise
Baroreceptors
Chemoreceptors
Cough reflex
