Flashcards in Control of Blood Pressure Deck (12)
What is the neuronal control of blood pressure?
What is the hormonal control of blood pressure?
RAAS system (renin-angiotensin-aldosterone system)
Where are the baroreceptors for blood pressure found?
in the carotid sinus in the internal carotid above the bifurcation of the carotid arteries
How do the baroreceptors detect changes in blood pressure?
the stretch in the carotid sinus receptors is proportional to BP so the stretch causes a continuous train of action potentials in the sensory nerve endings (vagus and glossopharyngeal, X and IX)
Which nerve fibres do the baroreceptors stimulate?
Vagus nerve (CNX) and glossopharyngeal (IX)
How does the neuronal system detect an increase in blood pressure?
Increase in BP stretches baroreceptors (aortic and carotid sinuses) and increases rate of AP to vagus and glossopharyngeal afferents which feed into the vasomotor centre of the medulla of the brainstem which contain a 'set-point' for BP which corresponds to a certain level of baroreceptor afferent activity during systole and diastole
Where is the aortic sinus?
just above semilunar valve of aorta
What does the vagus nerve do if the BP is too high?
if baroreceptor input is too high, then the vasomotor centre is inhibited leading to inhibition of sympathetic outflow --> vasodilation, lowered HR, reduced TPR. Also stimulates nucleus ambiguous of medulla in cardioinhibitory centre to increase vagal parasympathetic output to heart, acts on SAN to reduce HR
What does the sympathetic nervous system do if the BP is too low?
If baroreceptor firing too low, output of vasomotor centre increased and sends APs down reticulospinal tract to stimulate preganglionic nerves in thoracic cord to stimulate outflow -> vasoconstriction, increases HR, increases CO and TPR
Where do the axons project from the vasomotor centre?
through the lateral reticulospinal tract to the sympathetic preganglionic neurones in the intermediate part of the lumbar and thoracic ventral horn
Describe the RAAS system
Macula densa cells in kidney detect Na+ levels in tubule fluid, if Na+ in DCT too low juxtaglomerular cells release renin, this renin travels to the liver in the blood where it catalyses angiotensin I production from angiotensinogen in the liver. Angiotensin I exposed to ACE in the lungs to produce angiotensin II which stimulates the adrenal cortex and acts directly on arterioles (vasoconstriction). Adrenal cortex secretes aldosterone which acts on the kidney tubules to increase Na+ uptake and this increases water reabsorption so increases blood volume, then pressure to return pressure to normal range