Control of blood pressure

Question 1

Short term regulation

Answer 1

Baroreceptor reflex

Question 2

Baroreceptor reflex adjusts:

Answer 2

• Sympathetic and parasympathetic inputs to the heart to alter cardiac output
• Sympathetic input to peripheral resistance vessels to alter TPR

Question 3

Where are baroreceptors found?

Answer 3

Carotid sinus and aortic arch

Question 4

Where do the baroreceptors signal to?

Answer 4

Medulla

Question 5

Longer term control of blood pressure

Answer 5

• Complex interaction of neurohumoral responses
• Directed at controlling sodium balance and thus extracellular fluid volume
• Therefore control of plasma volume

Question 6

Four parallel neurohumoral pathways controlling circulating volume

Answer 6

• Renin angiotensin aldosterone system
• Sympathetic nervous system
• Antidiuretic hormone (ADH)
• Atrial natriuretic peptide (ANP)

Question 7

Renin is released from

Answer 7

• Released from granular cells of juxtaglomerular apparatus (JGA)

Question 8

Factors that stimulate renin release

Answer 8

• Reduced NaCl delivery to kidney
• Reduced perfusion pressure in kidney (detected by baroreceptors in afferent arterial)
• Sympathetic stimulation to JGA increases release of renin

Question 9

Effects of angiotensin II

Answer 9

• Stimulates aldosterone (from adrenal cortex)
• Stimulates Na+ reabsorption at kidney
• Vasoconstriction

Question 10

Angiotensin II receptors

Answer 10

• AT1(main action) and AT2

- G protein coupled receptor

Question 11

Angiotensin II receptor sites and action: Arterioles, sympathetic NS, hypothalamus

Answer 11

• Vasoconstriction
• Increased release of noradrenaline
• Increases thirst sensation (stimulates ADH release)

Question 12

Action of aldosterone on the kidney

Answer 12

• Acts on principle cells of collecting ducts
• Stimulates Na+ reabsorption
• Activates apical Na+ channel (ENaC, Epithelial Na Channel) and apical K+ channel
• (therefore high aldosterone = low K+)
• Increases basolateral Na+ extrusion via sodium potassium pump

Question 13

What does angiotensin converting enzyme (ACE) also break down?

Answer 13

Bradykinin, a vasodilator

Question 14

Effects of using ACE inhibitors

Answer 14

A dry cough, due to accumulation of bradykinins

Question 15

Examples of ACE inhibitors

Answer 15

Ramipril, Lisinopril, Perindopril, Enalapril

Question 16

Sympathetic stimulation effect on renal blood flow

Answer 16

• Vasoconstriction of arterioles

- Decreased glomerular filtration rate so decreased Na+ excretion

Question 17

Role of sympathetic nervous system in maintaining blood pressure

Answer 17

• High levels of sympathetic stimulation reduce renal blood flow
• Activates apical Na/H exchanger and basolateral Na/K ATPase in proximal convoluted tube
• Stimulates renin release from JGcells

Question 18

Antidiuretic hormone effects on blood pressure

Answer 18

• Increases water reabsorption in distal nephron (AQP2) to control plasma osmolarity
• ADH release is stimulated by increases in plasma osmolarity or sever hypovolaemia
• Stimulates Na+ reabsorption via apical Na/K/Cl cotransporter
• Also called arginine vasopressin, causes vasoconstriction

Question 19

Natriuretic peptide control on blood pressure

Answer 19

• Atrial natriuretic peptide (ANP) promotes Na+ excretion
• Synthesised and stored in atrial myocytes
• Released from atrial cells in response to stretch
• Reduced effective circulating volume inhibits release of ANP to support BP (reduced filling of heart, less stretch, less ANP released)

Question 20

Actions of ANP

Answer 20

• Causes vasodilation of the afferent arteriole
• Increased blood flow increases glomerular filtration rate
• Inhibits Na+ reabsorption along the nephron
• Causes natriuresis (loss of sodium into urine)
• If circulating volume is low ANP release is inhibited