Long Term Control of Blood Pressure

Question 1

What are the functions of the kidneys?

Answer 1

Excretion of waste, maintenance of ion balance, regulation of osmolarity and regulation of plasma volume

Question 2

What can be controlled to regulate MAP?

Answer 2

Plasma volume

Question 3

How is long term control of blood pressure mediated?

Answer 3

Kidneys
Not mediated by the arterial baroreflex

Question 4

How does the kidneys create osmotic gradient?

Answer 4

Renal counter-current system creates a very high osmolarity outside collecting duct
Control over Na+ transport do determines osmotic gradient
Control over permeability to water determines if water follows osmotic gradient
How then control how much water in urine is lost or retained

Question 5

What happens if the collecting duct is very permeable to water?

Answer 5

Lots of water reabsorption
Little urine and conserves plasma volume so increase MAP

Question 6

What happens if the collecting duct is impermeable to water?

Answer 6

Little reabsorption so lots of urine = diuresis
Reduction in plasma volume which decreases MAP

Question 7

What is the feedback system that senses disturbances in PV and MAP?

Answer 7

Renin-angiotensin-aldosterone system (RAAS)

Question 8

Where is renin produced?

Answer 8

From the juxtaglomerular (=granule cells) of the kidney

Question 9

What triggers the production of renin?

Answer 9

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

Question 10

What causes sympathetic innervation signals being released?

Answer 10

Reduced MAP
BP is low

Question 11

Describe high BP and filtration?

Answer 11

If high BP then more filtration so more Na+ and Cl- going out into proximal tubule so more Na+/Cl- delivered to Macula densa

Question 12

Describe low BP and filtration?

Answer 12

Less filtration and less delivery of Na+/Cl- so signals reduction in MAP and triggers release of renin

Question 13

What does renin do?

Answer 13

Converts inactive angiotensinogen to angiotensin I
Is then converted to angiotensin II by angiotensin converting enzyme

Question 14

What does angiotensin II do?

Answer 14

Stimulates release of aldosterone from adrenal cortex
Increases release of ADH from the pituitary
Is a vasoconstrictor
Is a negative feedback system

Question 15

How is RAAS a negative feedback system?

Answer 15

Multiple mechanisms detect any decrease in MAP, stimulates renin release and evokes multiple mechanisms which increase MAP

Question 16

What does release of aldosterone from adrenal cortex cause?

Answer 16

Increases Na+ reabsorption in the loop of Henle
Reduces diuresis and increases plasma volume as bigger osmotic gradient

Question 17

What does release of ADH from the pituitary cause?

Answer 17

Increases water permeability of collecting duct so less water excreted
Which reduces diuresis and increases plasma volume
Increases sense of thirst

Question 18

Where is ADH produced?

Answer 18

Synthesised in the hypothalamus
Released from the posterior pituitary into bloodstream

Question 19

What triggers ADH release?

Answer 19

A decrease in blood volume
An increase in osmolarity of ISF
Circulating angiotensin II
These show signs of low plasma volume and/or MAP

Question 20

Where is a decrease in blood volume sensed?

Answer 20

By cardiopulmonary baroreceptors and relayed via medullary cardiovascular centres

Question 21

Where is an increase in osmolarity in ISF sensed?

Answer 21

By osmoreceptors in the hypothalamus

Question 22

What does ADH do?

Answer 22

Increases the permeability of the collecting duct to H2O therefore reduces diuresis and increases plasma volume - more H2O reabsorbed and less excreted
Causes vasoconstriction causing increase MAP as increase in TPR

Question 23

Explain how Antidiuretic hormone is a negative feedback system?

Answer 23

Multiple mechanisms detect any decrease in MAP, stimulates release of ADH and evokes multiple mechanisms which increase MAP

Question 24

What is ANP and BNP?

Answer 24

Atrial natriuretic peptide and brain natriuretic peptide

Question 25

Where are ANP and BNP produced?

Answer 25

ANP is produced and released from myocardial cell in the atria
BNP is produced and released from ventricles

Question 26

What triggers a release of ANP and BNP?

Answer 26

Increased distension of the atria and ventricles - sign of increased MAP

Question 27

What does ANP and BNP do?

Answer 27

Increase excretion of Na+ (natriuresis)
Inhibit release of renin
Act on medullary CV centres to reduce MAP
Aim is to decrease MAP

Question 28

Explain ANP and BNP as a negative feedback system?

Answer 28

A mechanism detects any increase in MAP, stimulates release of ANP and BNP, and evokes multiple mechanisms which reduce MAP

Question 29

What are some drugs used for treatment of hypertension?

Answer 29

Ca2+ channel antagonist
B-adrenoceptor antagonist
Thiazide diuretics
Angiotensin converting enzyme inhibitors
Angiotensin II antagonists