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Cardiovascular System > Long term control of blood pressure > Flashcards

Flashcards in Long term control of blood pressure Deck (21):
1

Features of long-term control of blood pressure

- Is probably not mediated by the arterial baroreflex
- Revolves around the control of plasma volume by the kidney
- Involves at least three hormone systems: Renin-angiotensin-aldosterone, Antidiuretic factor (ADH, vasopressin), atrial natriuretic peptide.
- Relevent to hypertension

2

What are basic functions of the kidney?

- Excretion of waste products
- Maintenance of ion balance
- Regulation of osmolarity
- Regulation of plasma volume

3

What is the control of plasma volume used to regulate?

It is used to regulate MAP

4

How does the kidney regulate plasma volume?

- The clever renal counter-current system creates a very high osmorality outside the collecting duct.
- Control over Na+ transport determines how big that osmotic gradient is.
- Control over the permeability of the collecting duct to water determines if water follows that osmotic gradient or not.
- Hence you can control how much water is lost in the urine, and how much is retained.

5

How does the kidney conserve plasma volume?

Making the collecting duct very permeable to water will result in lots of water reabsorption, little urine, and conserve plasma volume.

6

How does the kidney reduce plasma volume?

Making the collecting duct very impermeable to water will result in little reabsorption, lots of urine (=diuresis), and a reduction in plasma volume.

7

Where is Renin produced in the renin-angiotensin-aldosterone system?

From the juxtaglomerular (=granule cells) of the kidney!!

8

What triggers Renin production?

- Activation of sympathetic nerves to the juxtaglomerular apparatus
- Decreased distension of afferent arterioles (the "renal baroreflex")
- Decreased delivery of Na+/Cl- through the tubule

All of these are signs of low MAP

9

What is reduced distension a sign of?

Reduced MAP

10

What does Renin do?

- Converts inactive angiotensinogen to angiotensin I.
- Which is in turn converted by angiotensin converting enzyme to angiotensin II.

11

What does angiotensin II do?

- Stimulates release of aldosterone from the adrenal cortex.
- Increases release of ADH (antidiuretic hormone) from the pituitary
- Is a vasoconstrictor: therefore increases TPR.

12

What does aldosterone do?

- Increases Na+ reabsorption in the loop of Henle
- Therefore reduces diuresis and increase plasma volume.

13

What does increasing the release of ADH from the pituitary do?

- Increases water permeability of the collecting duct.
- Therefore reduces diuresis and increases plasma volume
- And increases sense of thirst

14

How is the renin-angiotensin-aldosterone system a negative feedback system?

- Multiple mechanism detect any decrease in MAP
- Stimulates release of renin
- This evokes multiple mechanisms which increase MAP.

15

Where is ADH produced?

- Synthesised in the hypothalamus
- Released from the posterior pituitary

16

What triggers ADH release?

- A decrease in blood volume (as sensed by cardiopulmonary baroreceptors and relayed via medullary cardiovascular centres).
- An increase in osmolarity of interstitial fluid (as sensed by osmoreceptors in the hypothalamus)
- Circulating angiotensin II (triggered by the renin-angiotensin-aldosterone system)

17

Where is ANP (atrial natriuretic peptide) produced?

- Produced in, and released from myocardial cells in the atria.

18

What triggers ANP release?

Increased distension of the atrium

-This is a sign of increased MAP

19

What does ANP do?

- Increases excretion of Na+ (natriuresis)
- Inhibits the release of renin
- Acts on medullary CV centres to reduce MAP

20

How is atrial natriuretic peptide a negative feedback system?

- A mechanism that detects any increase in MAP.
- Stimulates release of ANP
- This evokes multiple mechanisms which reduce MAP

21

What basic drug treatments are there for hypertension?

- Ca2+ channel antagonists
- b-adrenoceptor antagonists
- Thiazide diuretics: affect how much water is being reabsorbed or not.
- Angiotensin converting enzyme inhibitors