CVS - Hypertension

Question 1

How do baroreceptors reduce high blood pressure?

Answer 1

Nerve endings in the carotid sinus and aortic arch are stretched due to increased arterial pressure. They send an impulse via afferent pathways to the medulla oblongata, which sends an impulse causing bradycardia and vasodilation.

Question 2

Why does the baroreceptors reflex not work against long-term blood pressure increase?

Answer 2

The threshold for baroreceptor firing resets after a short period of time

Question 3

What are the four parallel neurohumoral pathways that control circulating volume and hence blood pressure?

Answer 3

• renin-angiotensin-aldosterone system
• sympathetic nervous system
• antidiuretic hormone
• atrial natriuretic peptide

Question 4

Where is renin released from?

Answer 4

The granular cells of the juxtaglomerular apparatus in the kidney

Question 5

Give some factors that stimulate renin release

Answer 5

• reduced NaCl delivery to distal tubule
• reduced perfusion pressure in the kidney
• sympathetic stimulation to juxtaglomerular apparatus

Question 6

What is the juxtaglomerular apparatus made up of?

Answer 6

Macula densa cells, granular cells and surrounding mesangial cells

Question 7

Summarise the mechanism of the RAAS

Answer 7

• Angiotensinogen is converted to angiotensin I by renin.
• angiotensin I is converted to angiotensin II by angiotensin converting enzyme (ACE).
• angiotensin II stimulates aldosterone, which stimulates Na+ reabsorption at the kidney
• angiotensin II also stimulates vasoconstriction

Question 8

What type of receptor are AT1 and AT2 (angiotensin II receptors)?

Answer 8

GPCR

Question 9

What is the action of angiotensin on the arterioles?

Answer 9

Vasoconstriction

Question 10

What is the action of angiotensin on the kidney?

Answer 10

Stimulates Na+ reabsorption

Question 11

What is the action of angiotensin on the sympathetic nervous system?

Answer 11

Increased release of noradrenaline

Question 12

What is the action of angiotensin on the adrenal cortex?

Answer 12

Stimulates release of aldosterone

Question 13

What is the action of angiotensin on the hypothalamus?

Answer 13

Increases thirst sensation by stimulating ADH release

Question 14

What are the actions of aldosterone?

Answer 14

• acts on principal cells of collecting ducts
• stimulates Na+ and therefore water reabsorption
• activates apical Na+ channel and apical K+ channel
• increases basolateral Na+ extrusion via Na/K/ATPase

Question 15

What is the role of ACE and bradykinin in the RAAS?

Answer 15

They further augment the system - bradykinin has vasodilator actions, but it is broken down by ACE to form peptide fragments.

Question 16

How does sympathetic nervous system stimulation regulation blood pressure?

Answer 16

• renal blood flow is reduced due to vasoconstriction of arterioles
• apical Na/H+ exchanger and basolateral Na/K ATPase in PCT are activated
• this stimulates renin release from cells

Question 17

What are the main roles of antidiuretic hormone?

Answer 17

Formation of concentrated urine by retaining water to control plasma osmolarity. It retains water by stimulating Na+ resorption in the kidney.

Question 18

What stimulates ADH release?

Answer 18

Increases in plasma osmolarity and severe hypovolaemia

Question 19

How does atrial natriuretic peptide work?

Answer 19

It is synthesised and stored in the atrial myocytes, from which it is released in response to stretch, it promotes Na+ excretion, meaning that more water is lost and blood pressure is reduced. It also causes vasodilation of afferent arteriole to increase filtration rate of the blood.

Question 20

What are the functions of prostaglandins?

Answer 20

• Act as vasodilators
• enhance glomerular filtration
• reduce Na+ resorption
• act as a buffer to prevent excessive vasoconstriction caused by SNS and RAAS

Question 21

What does dopamine cause?

Answer 21

• vasodilation
• increased renal blood flow
• reduces resorption of NaCl

Question 22

What is hypertension?

Answer 22

A sustained increase in blood pressure. There are three stages - stage one (over 140/90), stage two (over 160/100) and severe (over 180 systolic or over 110 diastolic)

Question 23

What is the difference between primary and secondary hypertension?

Answer 23

Primary - cause is unknown (95% of cases)

Secondary - cause can be defined, primary disease must be treated first

Question 24

How does renovascular disease lead to secondary hypertension?

Answer 24

• occlusion of renal artery causes fall in perfusion pressure in the kidney
• decreased perfusion pressure leads to increased renin production
• activation of RAAS
• vasoconstriction and Na+ retention at other kidney

Question 25

How does renal parenchymal disease lead to secondary hypertension?

Answer 25

Na+ and water retention due to inadequate glomerular filtration

Question 26

Give some adrenal causes of secondary hypertension

Answer 26

- Conn's syndrome (aldosterone secreting adenoma) - Cushing's syndrome (excess secretion of glucocorticoid cortisol) - tumour of adrenal medulla (secretes catecholamines)

Question 27

Why is it important to treat hypertension even if it's asymptomatic?

Answer 27

Can have unseen damaging effects on heart and vasculature, potentially leading to heart failure, MI, stroke, renal failure and retinopathy

Question 28

Give some consequences of arterial damage

Answer 28

Atherosclerosis and weakened vessels leading to: - cerebrovascular disease/stroke - aneurysm - nephrosclerosis and renal failure - retinopathy - myocardial ischaemia and MI

Question 29

Hypertension causes increased afterload. Give some consequences of this.

Answer 29

Left ventricular hypertrophy, increased myocardial oxygen demand, heart failure, myocardial ischaemia and MI

Question 30

Which organs are most likely to be damaged by hypertension?

Answer 30

Brain, eyes, heart, arteries, kidneys

Question 31

Give some non-pharmacological approaches to treating hypertension

Answer 31

- exercise - diet - reduced Na+ intake - reduced alcohol intake

Question 32

How can the RAA system be targeted when treating hypertension?

Answer 32

- use of ACE inhibitors | - Ang II receptor antagonists (this leads to NaCl and H2O retention)

Question 33

How can vasodilators be used to treat hypertension?

Answer 33

- L-type Ca2+ channel blockers reduce entry of Ca2+ to vascular smooth muscle cells and cause relaxation - alpha-1 receptor blockers reduce sympathetic tone and cause relaxation of vascular smooth muscle, but also cause postural hypotension

Question 34

How can diuretics be used to treat hypertension?

Answer 34

Thiazides diuretics inhibit the Na/Cl co-transporter on apical membrane of cells distal tubule. This leads to a reduction in circulating volume.

Question 35

In what situation would beta blockers be used to treat hypertension?

Answer 35

If there are other indications such as previous MI