Lecture 16; The role of sympathetic nerve fibres

Question 1

What changes the pressure natriuresis curve from acute to chronic?

Answer 1

Neurohormonal factors that influence pressure natriuresis.

ANG 2
Aldosterone
ADH
ANP
Sympathetic Nerve Activity

Question 2

Describe the action of ANG 2 on pressure natriuresis;

Answer 2

Stimulus:
- Decreased renal blood flow

Primary action;
- Increased water reabsorption of water in proximal tubules, aldosterone, vasoconstriction

Question 3

Describe the action of aldosterone;

Answer 3

Stimulus;
- ANG 2

Primary action;
- Increased reabsorption of Na in collecting duct

Question 4

Described the action of ADH;

Answer 4

Stimulus;
- Increased ECH osmolarity

Primary action
- Increased reabsorption of water in distal tubules

Question 5

Describe the action of ANP;

Answer 5

Stimulus;
-Increase in atrial stretch

Primary Action;
- Inhibits tubular re-absoprtion of Na

Question 6

Describe the action of SNA;

Answer 6

Stimulus;
- Decrease in arterial blood pressure, stress, ANG 2

Primary action;
- Vasoconstriction, Renin release, Increase tubular reabsorption of Na and water

Question 7

Describe renin release;

Answer 7

Granular cells in afferent arteriole (Juxtagolmerular apparatus) release renin in response to

• Low NaCl in the distal tubule
• Decrease perfusion pressure (by granular cells themselves)
• Increased sympathetic activity (baroreceptors)

i.e
low BP
Low BV
Low Na content

Guaranteed question;

Question 8

Describe what renin does;

Answer 8

Renin is the rate limiting enzyme to convert Angiotensinogen to ANG 1

Then ACE to ANG2

Then this stimulates aldosterone production

Vasconstriction (ANG2) and Na retention (some ANG 2 mostly aldosterone)

Question 9

What is ANG2 essential for?

Answer 9

ANG 2 is essential for buffering changes in Na intake

Gets rid of Na excess

Question 10

What happens if you have blunted ANG 2 system?

Answer 10

You become Na sensitive and this can change blood pressure dramatically as cant get rid of salt. (cant decrease ANG 2)

Ability to change ANG 2 levels is important (blunted cant do this) i.e hypertensive patients must watch diet as even with ace inhibitors they are susceptible to Na

Question 11

What happens to people who have drugs that lower ANG 2 levels?

Answer 11

Anti-hypertensives, people who take drugs to lower ANG2 result in blood pressure being maintained at a lower level

Question 12

What happens to pressure natriuresis curve with low ANG 2 levels?

Answer 12

(blood pressure increases, urine output increases, so equilibrium shifts up)

Curve shifts to the left.

Question 13

What happens to the pressure natriuresis curve with high ANG 2 levels?

Answer 13

Arterial pressure decreases thus ANG 2 increases, pressure natriuresis curve shifts right, reduced urine output (equilibrium points shifts down) (thus when ang 2 changes, you switch between curves not moving up and down the same curve)

This creates a chronic curve (neural and hormonal influences)

Question 14

What does an intact ang2 system do to the pressure natriuresis curve?

Answer 14

Creates a chronic curve that has INFINITE GAIN

Integrate the effects of changing ANG2 levels and the natural change in pressure natriuresis with changing blood pressure (acute curve)

Question 15

Where do sympathetic nerves innervate in the kidney?

Answer 15

• Vasculature
• Tubules
• Change the release of renin from the granular cells int he JGA

Question 16

Describe the effects of an increase in SNA;

Answer 16

Increase SNA;

• Increase Renin secretion
• Decrease urinary Na excretion (inc reabsorption)
• Decrease renal blood flow (vasoconstriction)

Question 17

Describe the sensitivity of SNA to the kidney;

Answer 17

1) Low levels of activity firstly cause increased renin release (thus when Hz of SNA increases, renin increases rapidly) (1Hz)
2) then Na reabsoprtion is affected at slightly higher Hz (2Hz)
3) Larger Hz changes renal blood flow (4Hz)

This means that renin is more sensitive to SNA than vasculature

Question 18

Describe the SNA affect on pressure diuresis curve;

Answer 18

Loss of SNA (nerves cut) shifts the pressure natriuresis and diuresis curves to the left (operates at a lower blood pressure)

Blood pressure drops.

Question 19

Describe ANG 2 and SNA overlap;

Answer 19

Both have similar affects!

SNA can increase ANG2 and ANG2 in the brain can increase SNA

Exaggerates situation and redundancy!!