Lecture 16/17: Regulation of blood pressure

Question 1

Describe the baroreflex

Answer 1

signals from baroreceptors in carotid sinus, aorta, and coronary arteries go through vagal nerve and glossopharygeal nerve through petrosal and nodose ganglia to the nucleus tractus solatarius in the medulla. It then goes to interneurons located in the dorsal motor nucleus of the vagus and nucleus ambiguus (parasympathetic) and vasomotor area (sympathetic). Efferents then go to either the vasculature or the heart. Sympathetic efferents go to both from T1-L2, while parasympathetic efferents only go to the heart from T1-T4.

Question 2

Discuss the rein-angiotensin aldosterone system

Answer 2

Renin converts angiotensinogen to angiotensin I, then to angiotensin II by ACE. angiotensin II then goes to the adrenal cortex to release aldosterone (increase NaCl reabsorption, increase blood volume, causes vasoconstriction)

Question 3

How is renin secretion regulated?

Answer 3

1) decreased pressure going into the afferent arteriole sensed by granular cells
2) systemic pressure decreases, sensed by baroreceptors, increase sympathetic output
3) filtrate flow drops, [NaCl] in filtrate decreases, sensed by macula densa cells.

Question 4

How does pressure diuresis work?

Answer 4

As MAP increases, GFR increases, so there is more filtrate excreted, less water retained, so lower BV, lower VR, lower CO, lower MAP.

Question 5

How does ADH get regulated, and how does it work?

Answer 5

regulation: increase in plasma osmolarity (more water retained to dilute it), or decrease in blood pressure

ADH acts on V1a then Gq and PLC, also acts on V1a to activate PLD. PLD activates PKC as well. Finally, inhibits K+ channel so depolarization and Ca entry occurs

Also acts at collecting duct to increase number of aquaporin channels

Question 6

What is the mechanism for ANP?

Answer 6

increase in MAP means increased stretch in the right atrium. causes release of ANP. Decreases aldosterone, increases GFR. Less Na reabsorbed, more diuresis occurs, so lower plasma volume, lower VR, lower CO, lower MAP.

Also dilates vessels.

Question 7

Describe the difference between orthostatic hypotension and vasovagal syncope

Answer 7

orthostatic: occurs upon standing up, impaired baroreflex response. No increase in HR

vasovagal syncope: minor increase in HR and BP, but then fails

Question 8

How can hypotension be treated?

Answer 8

Lifestyle: salt loading, tilt training, head-up sleeping, drink more water, salt loading, exercise training

Medicine: fludrocortisone (mimics aldosterone), midodrine (vasoconstriction), pacemaker (only for syncope due to arrhythmia)

Question 9

How can hypertension be treated

Answer 9

diuretics, ACE inhibitors, angiotensin II blockers, Ca channel antagonists, Beta blockers

dietary: less sodium, fat, and caffeine
lifestyle: more activity, stop smoking, less alcohol and stress, better body weight