Baroreceptor and Blood pressure Flashcards
What does total peripheral resistance depend on?
contractility radius of blood vessels - small radius = high resistance - large radius = low resistance circulating volume - can be increased by Na+ reabsorption as water will be retained
What is blood pressure? What is the type of pressure found in the body?
blood pressure
- pressure exerted on the arterial walls by blood
systolic pressure
diastolic pressure
What is systolic pressure? What is diastolic pressure?
What are their ideal pressure?
systolic pressure
- peak pressure in the arteries
- occurs during cardiac contraction
- ideal pressure is 90-120 mmHg
diastolic pressure
- minimum pressure in the arteries
- occurs when the heart is not actively contracting = ventricles are filling with blood
- ideal pressure is 60-80 mmHg
What is orthostatic hypotension?
orthostatic hypotension = postural hypotension
- occurs as blood pressure is affected by gravity
when lying down
- effect of gravity on blood pressure is minimal
- blood vessels are at the same vertical level as the heart
- blood pressure is affected only by the pumping action of the heart
- blood pressure at the head = blood pressure at the feet
when standing up
- gravity pulls blood downwards
= hydrostatic pressure is introduced
- gravity causes blood pressure above the heart to be high and blood pressure below the heart to be low
blood presser drops by at least 20 mmHg
- higher blood pressure at the feet
- decreased venous return to the heart, decreased end of diastolic pressure, decreased stroke volume, decreased cardiac output therefore decreased blood pressure
What are the mechanism for blood pressure homeostasis?
short term neural control
- achieved through the role of cardiovascular centres and baroreceptor stimulation
long term renal/hormonal control
- determined by renin-angiotensin aldosterone system
= RAAS
What are the two problems associated with a sudden drop in blood pressure?
survival
- to survive arterial pressure just be returned immediately to a high enough level that the person can live trough the acute episode.
return to normal level
- must return the blood volume eventually to its normal level so that the circulatory system can re-establish full normality
- includes the return of the arterial pressure all the way back to its normal value
What are baroreceptors? Where are they found? How are they stimulated?
baroreceptors are stretch receptors that help maintain blood pressure
they are located in the
carotid sinus
- in the carotid arteries just above the area where the common carotid artery splits in two
aortic arch
- between the ascending and descending aorta
- leads into 3 arteries
baroreceptors are stimulated by the distortion of the arterial wall when pressure changes
- rise or drop in pressure
What are the cardiovascular centres? What are the cardiovascular centres responsible for? Where are the cardiovascular centres located?
cardiovascular centres are part of the autonomic nervous system
- responsible for regulation of cardiac output
- located in the medulla oblongata = part of the brainstem
What is cardiac output? What are the different types of cardiovascular centres?
cardiac output = stroke volume x heart rate
- volume of blood pumped out of the ventricles/per unit of time
cardioaccelerator centre
- stimulates cardiac function by regulating heart rate and stroke volume via sympathetic stimulation from the cardiac accelerator nerve.
cardioinhibitor center
- slows cardiac function by decreasing heart rate and stroke volume via parasympathetic stimulation from the vagus nerve.
vasomotor center
- controls vessel tone or contraction of the smooth muscle in the tunica media (smooth muscle)
- changes in vessel diameter affect peripheral resistance, pressure, and flow, which in turn affect cardiac output.
What is the different between the afferent and efferent pathways for blood pressure regulation?
afferent pathway
- changes in blood pressure are detected
- impulse/signal sent to the cardiovascular centre in the medulla oblongata
efferent pathway
- impulse/signal sent back from the cardiovascular centre
What are the different effectors that can be stimulated by the cardiovascular centres?
heart
- sympathetic = innervates SA node, atria, ventricles = increases heart rate (cardioaccelerator nerve)
- parasympathetic = releases Act to decrease heart rate (vagus nerve)
kidneys
- sympathetic = stimulates renin secretion and activates RAAS, increases plasma volume
adrenal medulla
- sympathetic = induces secretion of adrenaline and noradrenaline to increase heart rate
blood vessels
- sympathetic = vasoconstriction to increase heart rate
- parasympathetic = vasodilation to decrease heart rate
What are the afferent pathways for increasing and decreasing heart rate/blood pressure?
increasing
- carotid sinus sends an impulse via the sinus nerve. impulse travels along via the glossopharyngeal nerves and enters the cardiovascular centre
- sends impulse via the cardioaccelerator nerve
decreasing
- aortic arch sends impulse via the aortic nerve. impulses travel along via the vagus nerve and enters the cardiovascular centre
- sends impulse via the vagus nerve
What is the process when blood pressure (MAP) rises?
arterial pressure rises
increased stretch arterial walls is detected by the baroreceptors
baroreceptors on the carotid sinus and aortic arch are stimulated
neuron firing rate of the carotid sinus (carotid sinus nerve) and aortic arch (vagus nerve) increases
- stimulates the cardioinhibitory centre = fires via the vagus nerve = parasympathetic
- inhibits the cardioaccelerator centre
- inhibits the vasomotor centre = vasodilation
sympathetic activity to the heart drops = HR, contractility and total peripheral resistance drop
parasympathetic activity to the heart rises = vasodilation and cardioinhibition rises so HR drops
What is the process when blood pressure (MAP) drops?
arterial pressure drops
decreased stretch arterial walls is detected by the baroreceptors
neuron firing rate of the carotid sinus nerve decreases, baroreceptors on the carotid sinus and aortic arch are inhibited
sympathetic activity to the heart rises = vasoconstriction, HR, contractility and total peripheral resistance rise
parasympathetic activity to the heart drops = vasodilation and cardioinhibition drop
- stimulates the cardioiaccelerator centre = fires impulses via the cardioaccelerator nerve
- stimulates the vasomotor centre = vasoconstriction
- inhibits the cardioinhibition centre = vagus nerve is inhibited
How does the RAAS system regulate blood pressure?
blood pressure falls
renin is released from the granular cells of renal juxtaglomerular apparatus
renin acts on angiotensinogen released from the liver
- cleaved into angiotensin 1
angiotensin 1 is converted into angiotensin 2 by angiotensin converting enzyme (ACE)
- occurs in the lungs by endothelial cells and in the kidneys = where ACE is found
angiotensin 2 has many functions
