Long Term Control of Blood Pressure

Question 1

Which organ is responsible for long term control of blood pressure?

Answer 1

•Revolves around the control of plasma volume by the kidney

Question 2

What are the functions of the kidney?

Answer 2

–Excretion of waste products

–Maintenance of ion balance

–Regulation of pH

–Regulation of osmolarity

–Regulation of plasma volume

Question 3

What are the following areas labelled on this nephron?

Answer 3

Question 4

What is the effect of the renal counter current system?

Answer 4

Creates a very high osmolarity outside the collecting duct

Question 5

How is control over how much water is lost with urine acheived?

Answer 5

Osmotic gradient exists between the collecting duct and outside the collecting duct.

Na+ transport determines this gradient

•Control over the permeability of the collecting duct to water determines if water follows that osmotic gradient or not

Question 6

Where is sodium pumped?

Answer 6

Pumped outside of the distal tube - concentration of the solute therefore decreases significantly before it reaches the collecting duct

Question 7

What is the affect of varying the permeability of the collecting duct?

Answer 7

• If collecting duct very permeable to water will result in lots of water reabsorption, little urine, and conserve 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

Question 8

What are the three main hormones that regulate water reabsorption?

Answer 8

Renin - angiotensin - aldosterone system

Antidiuretic factor (ADH, vasopressin)

Atrial natriuretic peptide

Question 9

Where is the renin produced?

Answer 9

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

Question 10

What triggers renin production?

Answer 10

–Activation of sympathetic nerves to the juxtaglomerular apparatus

–Decreased distension of afferent arterioles (the “renal baroreflex”)

–Decreased delivery of Na+/Cl- through the tubule

Question 11

What is responsible for detecting a reduced delivery of sodium and chlorine ions?

Answer 11

Macula densa

Question 12

Where do you find the macula densa?

Answer 12

The ascending loop of henle

(distal convulated tubule)

Question 13

Where is renin produced?

Answer 13

In the juxtaglomerular of the kidneys - granule cells

Question 14

What triggers renin production?

Answer 14

Signs of low mean arterial pressure:

• Activation of sympathetic nerves to the juxtaglomerular apparatus
• Decreased distension of afferent arterioles (renal baroreflex)
• Decreased delivery of sodium and chlorine through the tubule

Question 15

What does renin do?

Answer 15

Converts angiotensinogen to angiotensin 1

Angiotensin converting enzyme

Angiotensin 2

Question 16

How does angiotensin increase MAP?

Answer 16

Stimulates release of aldosterone from the adrenal cortex.

(this increases the amount of sodium reabsorption in the loop of henle - less diuresis and increased plasma volume)

Increases the release of ADH from the pituitary

(increases the permeability of the collecting duct, reduces diuresis. Increases sense of thirst)

Is a vasoconstrictor

(increases total peripheral resistance)

Question 17

How is the formation of angiotensin 2 a form of negative feedback?

Answer 17

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

Question 18

Where is ADH produced?

Answer 18

–Synthesised in the hypothalamus

–Released from the posterior pituitary

Question 19

What triggers ADH release?

Answer 19

A decrease in blood volume - (Baroreceptors from CVS relayed by medullary cardiovascular centres)

An increase in osmolarity in interstitial fluid (osmoreceptors in the hypothalamus)

Circulating angiotensin 2 (triggered by the renin-angiotensin-aldosterone system)

Question 20

What is the effect of ADH?

Answer 20

Increases the permability of the collecting duct to H2O

Causes vasoconstriction (hence why it is sometimes known as vasopressin)

Question 21

Why is the release of ADH classed as a negative feedback mechanism?

Answer 21

–Multiple mechanism detect any decrease in MAP

–Stimulates release of ADH

–This evokes multiple mechanisms which increase MAP

Question 22

What does ANP stand for?

Answer 22

Atrial natriuretic peptide

Question 23

Where is atrial natriuretic peptide formed?

Answer 23

Produced in and released from the myocardial cells in the atria

Question 24

What triggers release of ANP?

Answer 24

Increased distension of the atrium ( a sign of increased MAP)

Question 25

What does ANP do?

Answer 25

Increases the excretion of sodium (natriuresis) - (opposes the act of angiotensin 2 which causes lots of sodium to be reabsorbed by the loop of henle)

Inhibits the release of renin

Acts on the medullary CV centres to reduce MAP

Question 26

Why is the release of ANP described as a negative feedback mechanism?

Answer 26

–A mechanism that detects any increase in MAP

–Stimulates release of ANP

–This evokes multiple mechanisms which reduce MAP

Question 27

What percentage of hypertension cases are as a result of secondary (knoown) causes?

Answer 27

Only 5% to 10%

Question 28

What are the rational drug treatments for hypertension?

Answer 28

–Ca2+ channel antagonists

–b-adrenoceptor antagonists – specifically beta 1 receptor antagonist – reduces cardiac output and blood pressure

–Thiazide diuretics – work in sodium transporter in kidney – stops build up of sodium gradient – makes you excrete more water

–Angiotensin converting enzyme inhibitors

–Angiotensin 2 antagonist