PBL 2- Hypertension

Question 1

Describe the structure and function of blood vessels.

Answer 1

All 3 vessels, Arteries, veins and capillaries have this structure:

Tunica externa/adventitia- Loose, fibrous connective tissue. Thick, outer layer consisting of elastin. Functions to anchor the vessel to the surrounding structures and provide protection.

Tunica media- middle, muscular layer. consisting mainly of smooth muscle cells and elastin fibres. has 2 layers. Smooth muscle is arrange concentrically around the lumen and allows adjustment of vessel diameter through vasodilation and vasoconstriction.

Tunica Intima- endothelial cells, innermost epithelial lining, has 4 layers. semi-permeable. Framework of collagen fibres and high tensile strength provides a firm base and anchorage for the endothelial lining to the lamina propria

Question 2

What are the functional properties of arteries due to their structure?

Answer 2

The structure of arteries give them 2 functional properties:

• elasticity
• contractility

Question 3

What do endothelial cells lining the blood vessels do?

Answer 3

Endothelial cells release important chemical mediators like Nitric Oxide (NO) which helps with vasoconstriction and vasodilation.

Question 4

How does contractility of a vessel come about?

Answer 4

It comes from its elastic tissue which is arranged longitudinally and in rings around the lumen.

Question 5

How does vasoconstriction of a vessel occur?

Answer 5

Sympathetic fibres of ANS innervate the vascular smooth muscle. Increase in sympathetic stimulation -> smooth muscle contracts -> vasoconstriction.

Question 6

What are arteries? and what are its contents

Answer 6

Arteries carry blood away from the heart to other organs of the body.
Their tunica media has greater muscular and elastic thickness that in veins = enabling their walls to stretch easily with a small increase in blood pressure.

Question 7

Describe the types of arteries.

Answer 7

• Elastic (large) arteries: conduct blood from heart to muscular arteries. E.g. aorta and common iliac artery.
• Muscular (medium) artery: they repeatedly branch until reaching their target organs. E.g. axillary, ulnar and radial arteries.
• Arterioles: leads into capillaries

Question 8

What are capillaries? and what are its contents

Answer 8

Capillaries are smallest of the body’s blood vessels. Consist of one layer of endothelium and its Basement membrane.
They connect the small arteries and veins.
provide a short diffusion distance for nutrient and gaseous exchange with the tissues they supply.

Question 9

What are the types of capillaries?

Answer 9

• Continuous
• Fenestrated
• Sinusodial

Each has variably sized gaps between the endothelial cells. These gaps act as a sieve- controlling which molecules can enter or exit the capillary.

Question 10

What are veins? and what are its contents

Answer 10

Veins carry blood from the organs of the body to the heart. Have a larger diameter and a thinner wall than arteries.

Question 11

Define blood pressure.

Answer 11

Hydrostatic pressure of blood exerted against the walls of the blood vessels

Question 12

What is normal blood pressure.

Answer 12

Normal blood pressure is 120/80

Question 13

What are the haemodynamics factor regulating blood flow?

Answer 13

1) blood volume
2) Vascular resistance (lumen size, blood viscosity, total blood vessel length)
3) venous return
4) velocity of blood flow

Question 14

Define hypertension.

Answer 14

It is commonly called high blood pressure, it is systolic or diastolic pressure that is above normal all the time

Question 15

What do the NICE guidelines say about hypertension?

Answer 15

Stage 1 hypertension: Clinic blood pressure is 140/90 mmHg
Stage 2 hypertension: Clinic blood pressure is 160/100 mmHg
Severe hypertension: Clinic systolic blood pressure is 180 mmHg or higher, or clinic diastolic blood pressure is 110 mmHg or higher

Question 16

What are the risk factors for hypertension?

Answer 16

• Age (BP rises with age)
• obesity
• excessive alcohol intake
• high salt intake
• genetic susceptibility
• high plasma cholesterol
• chronic stress

Question 17

What are the clinical complications of hypertension?

Answer 17

• left ventricular hypertrophy: increased muscle mass has greater O2 demand, when coronary circulation cannot keep up –> myocardial infarction
• renal failure
• heart failure
• Increased arterial pressure can lead to development of:
  arteriosclerosis
  haemorrhages
  aneurysms
  retinopathy

Question 18

Name the drugs used for anti-hypertensive therapy.

Answer 18

• B-adrenoreceptors blockers
• A-adrenoreceptor blockers
• ACE inhibitors
• Angiotensin II receptor blockers
• Diuretics
• Calcium Channel blockers

Question 19

Describe the mechanism, side-effects and give examples of B-adrenoreceptors blockers.

Answer 19

Mechanism- it is a competitive reversible antagonist
• Decrease in blood pressure via blockade of b1 sympathetic tone on heart and reduction in renin release from kidney
• Decrease in heart rate and stroke volume
• Decrease in cardiac output

Side- effect:

• Exacerbate asthma
• hypoglycaemia
• intolerance to exercise

e.g. Propranolol (non-selective β1 and β2)
Atenolol (β1 selective)

Question 20

Describe the mechanism, side-effects and give examples of A-adrenoreceptors blockers.

Answer 20

Mechanism- it is a competitive reversible antagonist
• Decrease in blood pressure via decrease in sympathetic tone in arterioles (a1)
• Decrease in peripheral resistance

Side-effects:
• Postural hypotension (loss of sympathetic vasoconstriction)
• Reflex tachycardia (via baroreceptors)
• Can cause impotence
• Increase closure of internal sphincter bladder can cause benign prostatic hyperplasia

e.g. phentolamine (a1 and a2) doxazosin (a1 selective)

Question 21

Describe the mechanism, side-effects and give examples of ACE inhibitors.

Answer 21

Mechanism- Lowers blood pressure by:
• Reduced formation of the vasoconstrictor angiotensin II (decrease in peripheral resistance)
• Reduced blood volume (loss of angiotensin II stimulated release of aldosterone, thus reduction of renal reabsorption of Na+ and water)

Side-effects:
• Sudden fall in BP on 1st dose
• Persistent irritant/dry cough

e.g. captopril and enalapril and Ramapril

Question 22

Describe the mechanism, side-effects and give examples of Angiotensin II receptor blockers.

Answer 22

Mechanism- blocks the AT1 receptor (which mediates the vasoconstrictor and aldosterone releasing actions of Angiotensin II).

Side-effects:
- no irritant cough like ACE inhibitors.

e.g. Losartan and candesartan

Question 23

Describe the mechanism, side-effects and give examples of Diuretics.

Answer 23

Mechanism:
• Lower blood pressure by reducing blood volume
• Mechanism is through reduced renal reabsorption of Na+ and water
- more urine produced so decreasing plasma volume

Side-effects:
Hypokalaemia (Decrease in plasma K+)

e.g. bendroflumethiazide (a thiazide)

Question 24

Describe the mechanism, side-effects and give examples of Calcium channel blockers.

Answer 24

Mechanism:
These drugs work by blocking L-type (long-type) voltage operated calcium channels. These channels allow Ca2+ entry into cardiac and vascular smooth muscle. When these channels are blocked, there is reduced Ca2+ entry. This results in:
- Reducing peripheral resistance
- Reducing cardiac output

Side-effects:
• Headache
• Constipation
• Cardiac dysrhythmias (abnormal heart beat)

e.g. verapamil, diltiazem and nifedipine

Question 25

Explain the types of L-type channel blockers.

Answer 25

1) Open channel block (cork in a bottle):
pore through which Ca2+ enters is blocked.
e.g. Verapamil and Diltiazem

2) Allosteric Modulation:
drug binds to an allosteric site- changes receptor shape which limits channel opening
e.g. Nifedipine

Question 26

Define postural hypotension.

Answer 26

This is due to the failure in the baroreceptor reflex.

Defined as a decrease in systolic blood pressure of >15mmHg on standing

Question 27

What are the response to changes in posture?

Answer 27

• venous pooling in vessels below the heart
• venous pressure increases
• stroke volume and cardiac output falls
• person can faint
• lightheaded

Question 28

Describe the baroreceptor reflex.

Answer 28

• upon standing = decreased blood volume = decreased BP = baroreceptors decrease their firing rate
• increases the sympathetic outflow from the CNS, resulting in an increased HR and contractility.
• Peripheral vasoconstriction increases total peripheral resistance, which helps restore blood pressure.

Question 29

What is rational prescribing?

Answer 29

It is the principles of drug selection.

Question 30

What is poor compliance?

Answer 30

compliance = degree to which a patient follows medical/ lifestyle advice.

Question 31

What are the NICE guidelines on hypertension for a person <55 years?

Answer 31

NICE guidelines on hypertension:

1) ACE inhibitor or angiotensin II receptor blocker
2) 1 + Calcium channel B
3) 1 + 2 + Diuretics
4) 1+2+3+ more dieuretics or alpha or beta blocker

Question 32

What are the types of veins?

Answer 32

Small and medium veins- well developed tunica externa and a thin tunica intima and media.

Large veins- greater diameter and a thicker tunica intima. They have well developed longitudinal smooth muscle in the tunica externa.

Question 33

What are the NICE guidelines on hypertension for a person <55 years?

Answer 33

NICE guidelines on hypertension:

1) Calcium Channel Blocker
2) ACE inhibitor or angiotensin II receptor blocker + Calcium channel B
3) 1 + 2 + Diuretics
4) 1+2+3+ more dieuretics or alpha or beta blocker