Physiology Flashcards
Where is respiratory rhythm generated
In the resp centres in the brain stem - MEDULLA specifically for rhythm generation
What part of the brain stem modifies respiration
pons
Where do the resp centres receive stimulation from and as such modify breathing in response to these signals.
Central and peripheral chemoreceptors
Higher brain centers e.g.. cerebral cortex
Stretch receptors in the bronchi and bronchioles
Juxtapulmonary receptors
Joint receptors
Baroreceptors
Where are central chemoreceptors located
near the surface of the medulla
What do central chemoreceptors respond to
the hydrogen in the CSF
Why is CSF less easily buffered than blood
contains less protein
Can CO2 diffuse across the blood brain barrier
Yes - readily
Hydrogen and carbonate ions do not diffuse easily across the BBB
What will happen to the resp rate when there is hypercapnia
Hyperventilation
ie increases
What is the most potent stimulation of resp in most people
Increases hydrogen ions in the CSF due to arterial CO2 increase results in firing of central chemoreceptors and stimulates ventilation to ‘blow off’ the CO2 and reduce the hydrogen ion conc in the CSF
Where are peripheral chemoreceptors situated
Carotid and aortic bodies
What do peripheral chemoreceptors sense
The tension of oxygen and CO2 and hydrogen ions in the bloods
What initiates the hypoxic drive effect
peripheral chemoreceptors sensing low PO2 (less than 8kPa)
In what group of patients is their hypoxic drive important
COPD due to chronic CO2 retention
In what other circumstances is hypoxic drive important
high altitudes
What happens in the hypoxic drive
peripheral chemoreceptors sense low levels of PO2 and act to increase ventilation
What mediated the H+ drive of respiration
peripheral chemoreceptors
What does an increase in H+ cause
hyperventilation to blow off CO2 to reduce hydrogen ion conc in blood
In what circumstances may hydrogen ions be increased in the blood
DKA
exercise -lactic acidosis
Summarise which receptors play a main role in the following:
- Decreased arterial blood
- Increased arterial CO2 and therefore increased hydrogen ions in CSF
- Increased arterial hydrogen ions
- peripheral chemoreceptors
- central chemoreceptors
- peripheral chemoreceptors
What reflex guards against hyperinflation of the lungs
Herin-breur reflex
What stimulates juxtapulmonary receptors
pulmonary circulation congestion and oedema
PE
what stimulated baroreceptors
increased ventilation rate in response to low BP
What muscles move the ribs up and out
External intercostal muscles
What muscle increases the volume of the thorax vertically and what nerves supply it
Diaphragm
Phrenic nerve - C3, 4, 5
Accessory muscle of inspiration
SCM
Scalenus
Muscles of active expiration
Abdominal muscles
Internal intercostal muscles
Major muscle of inspiration
Diaphragm
External intercostal muscles
What three pressures are important in the lungs
Atmospheric and Intra alveolar = usually the same
Intrapleural
Is the intra pleural pressure usually more of less than atmospheric pressure
less
What happens to intra alveolar and intrapleural pressure during inspiration
both decrease
but intra pleural pressure is always less than intraalveolar pressure = transmural pressure gradient
What happens to intra alveolar and intra pleural pressure during expiration
both increase
In what circumstance is the transmural pressure gradient abolished
pneumothorax
Forces which keep alveoli open
Transmural pressure gradient
Surfactant (which opposes alveolar surface tension)
Alveolar inter dependence
Forces promoting alveolar collapse
Elasticity of stretch pulmonary connective tissue fibres
Alveolar surface tension
What stimulation causes bronchoconstriction and what causes bronchodilation
Parasympathetic = constriction Sympathetic = dilation
what diseases cause airway floow restirction
COPD and asthma
what does increased airway resistance result in
expiration is more difficult than inspiration
lungs hyperinflate
What happens in dynamic airway compression
The rising pleural pressure during active expiration compresses the alveoli and airway
Pressure in airway makes it more difficult for air to leave the lungs
Doesn’t cause problems in normal people but can be a problem in asthma etc
What is meant by compliance
The effort needed to inflate the lungs
i.e. less compliant lungs require more work to produce a given degree of inflation
Name a condition in which there is decreased compliance of the lungs
pulmonary fibrosis
How much of your total energy is required to be expended in quiet breathing
3 percent
What cells line the alveoli
Type 1 alveolar cells - single layer
O2 partial pressure gradient
60mmHg or 8kPa
CO2 partial pressure gradient
6mmHg or 0.8kPa
What happens to the rate of gas exchange in the lungs as the partial pressure gradients increase
increases
What is meant by diffusion coeffient
solubility of gas in the membrane
What results in decreased surface area in the lungs
emphysema
lung collapse
Increases thickness in lings
Fibrosis
Oedema
Pneumonia
reduced lung perfusion
PE
Define cardiac output
Volume of blood pumped by each ventricle per minute is known as the CO
What is the resting CO in a healthy adult
5 litres per minute (70ml SV x 70 bpm= 4900ml)
Define stroke volume
the volume of blood ejected by each ventricle per heart beat
Calculate Stroke volume
SV= end diastolic volume - end systolis volume
What determines the cardiac preload
end diastolic volume determined by the venous return to the heart
Describe frank starling law
“the more the ventricle is filled with blood during diastole (END DIASTOLIC VOLUME), the greater the volume of ejected blood will be during the resulting systolic contraction (STROKE VOLUME)
