Long term control of arterial blood pressure

Question 1

What happens to the baroreflex during exercise?

Answer 1

• neural impulses from the brain reset the baroreflex to **operate around a higher pressure**
• therefore, the arterial pressure can rise without consequently impairing/affecting the heart rate and cardiac output
• the baroreflex remains active around exercise and buffers the blood pressure around its new vaue

Question 2

Describe the pressure/response curve for baroreceptors

Answer 2

• curve on the left shows when the pressure rises abruptly
• curve on the right shows when the pressure has been kept at a high value for 20 mins or so … notice the shift to the right which indicates a reduced baroceptor activity
• this indicates that baroceptors are only control short term fluctuations in pressure

Question 3

what is the optimal sensitivity or gain of the reflex?

in relation to the** pressure - response curve**

Answer 3

• the max slope of the response curve
• this can be reduced by ageing and chronic hypertension as the distensibility of the arterial walls decreases

Question 4

what is the set point of the pressure response curve?

Answer 4

the pressure that the refkex strives to maintain

Question 5

what can the set point of the pressure- response curve be altered by?

Answer 5

• neural interactions with the CNS - central resetting
• physical changes in the receptor region (peripheral resetting)

Question 6

what are baroreceptors ineffective at?

Answer 6

they are ineffective monitors of the absolute blood pressure passing to the brain
* ie they are only short term regulators of blood pressure

Question 7

What is long term control of arterial blood pressure regulated by?

Answer 7

• blood pressure is regulated long term by maintenance of a normal extracellular fluid volume ie normal plasma blood volume

Question 8

what is extracellular fluid volume regulated by?

what organ? also any other mechanisms … hit hormonal

Answer 8

• regulated partly by the** kidneys** via Na+ and water reabsorption
• also by** hormonal mechanisms** - such as the release of ADH fom osmoreceptors in the hypothalamus, the renin-angiotensin-aldosterone system & also the secretion of atrial natriuretic peptides by the atrial myocytes

Question 9

Describe what are the 3 important cells that the juxtaglomerular apparatus (in kidney) contains?

Answer 9

• the macula densa cells - salt sensing cells
• granular cells - smooth muscle cells loctated in the wall of the afferent arteriole that sense changes in renal arteriole pressure via stretch receptors … ie an increase in stretch (high pressure) causes the granular cells to release renin
  * mesangial cells -smooth muscle cells

Question 10

what hormonal mechanism is involved in long term control of blood pressure ?

Answer 10

The RAAS system - renin angiotensin aldosterone system

Question 11

Describe the renin - angiotensin system

ie production of renin and what is produced after

Answer 11

• granular cells produce prorenin, after a drop in blood pressure prorenin is cleaved to form renin
• the release of renin causes angiotensin to be produced by the liver
• renin causes angiotensin to be converted to angiotensin I
• angiotensin I is converted to angiotensin II by the ACE enzyme

Question 12

what stimulates renin secretion?

Answer 12

• low blood pressure
• low ECF volume
• low NaCl

Question 13

what is angiotensin II?

Answer 13

• angiotensin is a hormone that binds to angiotensin II receptors that cause various effects

Question 14

what 3 effects does angiotensin II have?

Answer 14

• Angiotensin II causes vasoconstriction of the systemic arterioles and therefore increases TPR
• it also stimulates the release of aldosterone from the adrenal cortex, this causes an inrease in Na+ reabsorption in the late distal tubules of the nephron
• also acts on the posterior pituitary gland to release ADH which **promotes water retention in the kidneys and therefore increases plama volume**
• OVERALL EFFECT - increase in MAP

Question 15

what does RSNA stand for?

Answer 15

renal sympathetic nerve activity

Question 16

How does RSNA increase?

Answer 16

• when atrial baroceptors detect a** fall in arterial blood pressure **
• when the veno-atrial mechanoreceptors detect a fall in central blood volume

Question 17

what does an increased RSNA cause?

Answer 17

• increased RSNA increases renin secretion by granular cells and hence salt and water retention by the kidneys

Question 18

does adrenaline also cause an increase in renin secretion by the granular cells?

Answer 18

• yes
• adrenaline binds to the alpha adrenergic receptors on the granular cells

Question 19

What is ADH secretion stimulated by?

Answer 19

• angiotensin II
• reduced central blood volume & arterial pressure

Question 20

what stimulates natruiretic peptide production?

Answer 20

• the natruiretic peptides produced by the atrial and ventricular myocytes are stimulated by an increased blood volume (and pressure)
• opposite to renin system which is stimulated by low bp

Question 21

What is the **role **of the natriuretic peptides?

Answer 21

• they causes natriuresis - ie Na+ excretion
• also enhance renal water excretion

Question 22

How do the natriuretic peptides **enhance **renal excretion of Na+ and water?

Answer 22

• they cause vasodilatation of the afferent arteriole - which increases GFR ( ie more blood flowing in)
• they inhibit Na+ reabsorption
• they inhibit renin and aldosterone secretion