Long and Short term BP control Flashcards
What is the main mechanism which controls BP short term?
arterial baroreceptors
Name the tow main arterial baroreceptors
aortic arch baroreceptor
carotid sinus baroreceptor
What makes baroreceptors fire APs?
stretch
They are stretch receptors so when they are have increased stretch they fire more APs
When BP is low, they fire less APs which causes a response from the sympathetic nerves.
Describe the mechanism and response from baroreceptors when BP is low.
- low BP
- less stretch
- less APs being fired
- the lower number of APs are fired up the vagus nerve (aortic baroreceptor) or glossopharyngeal nerve (carotid sinus baroreceptor)
- these signals are sent up to the medullary cardiovascular centres
- this causes the sympathetic nerves to be stimulated
- the sympathetic nerves release noradrenaline at the NMJ which act on alpha 2 receptors which causes vasoconstriction and increases the contractibility of the heart.
- the medulla also releases adrenaline
- this results in the blood being pumped harder through a smaller cross section area which results in an increase of BP
Describe the mechanism and response from baroreceptors when BP is high.
- high BP
- more APs are fired up the vagus or glossopharyngeal nerve to the medullary cardiovascular centres
- stimulates the parasympathetic nerves (vagus nerve)
- releases ACh on muscarinic receptors (B 2)
- reduces contractibility of the heart
- therefore reduces the BP
Name 5 other inputs to the medullary cardiovascular centres
- cardiopulmonary baroreceptors
- central chemoreceptors
- peripheral chemoreceptors
- joint receptors
- higher centres (eg. anticipation of exercise)
What effect does standing up have on the baroreceptors?
- gravity pulls the blood downwards
- blood pools in the venous system
- the venous valves are put under stress
- the hydrostatic force increases
- the venous return decreases as a higher pressure is required to push the blood back to the heart
- the EDV decreases
- the preload decreases so the cardiac output must decrease
- MAP decreases
- the baroreceptors are less stretched
- less APs are fired
- there is also decreased vagal tone
- causes stimulation of the sympathetic system
- increases contractibility, vasoconstriction
When does the valsalva manoeuvre occur?
when there is forced expiration against a closed glottis.
Describe the pattern of pressure change which occurs during valsalva manoeuvre
- initial increase of pressure
- gradual decrease of pressure
- stabilised BP
- sudden decrease of pressure when manoeuvre is stopped
- gradual increase of pressure up above normal
- pressure is back to normal
- volume is decreasing as the internal intercostal muscles are pushing the thorax together
- the mass of air in the thorax remains the same
- the pressure increases
- results in decrease in; VR, EDV, SV, CO, MAP
- there is less VR so the BP decreases as less blood is entering and hence leaving the heart
- pressure decreases
- baroreceptors detect the change in pressure and fire less APs
- stimulate sympathetic system to increase the BP
- maintain the BP at a stable value
- manoeuvre is stopped and the thorax pressure decreases which is transmitted through to the aorta baroreceptors
- causes a sudden dip in pressure
- VR begins to be restored as blood is able to get back to the heart as the pressure gradient is back to normal
- CO starts to increase to increase the BP but the baroreceptor reflex to increase the blood leaving the heart still hasn’t worn off
- therefore the BP increases to more than normal
- the reflex stops and BP goes back to normal
What factors affect the MAP?
radius of the vessel
viscosity of the blood
cardiac output
total peripheral resistance
What is the relationship between MAP, CO and TPR
MAP = CO x TPR
What mechanisms control BP long term?
Plasma volume by kidney permeability control
name three functions of the kidney
o Excretion of waste products
o Maintenance of ion balance
o Regulation of pH / osmolarity / plasma volume
what happens when the kidney is made:
- more permeable
- less permeable
more:
- more Na can leave the loop of Henle
- therefore more water is reabsorbed
- increases plasma volume
- produces more concentrated urine
less:
- Less Na can leave
- less water is reabsorbed so more water remains in the nephron
- decreases plasma volume
- results in diuresis
Name the three hormonal responses used by the kidney to alter the plasma volume
- Renin-Angiotensin-Aldosterone System
- ADH (antidiuretic hormone)
- Brain peptide hormone and Atrial natriuretic hormone
