PBL 2- Hypertension Flashcards
Describe the structure and function of blood vessels.
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
What are the functional properties of arteries due to their structure?
The structure of arteries give them 2 functional properties:
- elasticity
- contractility
What do endothelial cells lining the blood vessels do?
Endothelial cells release important chemical mediators like Nitric Oxide (NO) which helps with vasoconstriction and vasodilation.
How does contractility of a vessel come about?
It comes from its elastic tissue which is arranged longitudinally and in rings around the lumen.
How does vasoconstriction of a vessel occur?
Sympathetic fibres of ANS innervate the vascular smooth muscle. Increase in sympathetic stimulation -> smooth muscle contracts -> vasoconstriction.
What are arteries? and what are its contents
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.
Describe the types of arteries.
- 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
What are capillaries? and what are its contents
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.
What are the types of capillaries?
- 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.
What are veins? and what are its contents
Veins carry blood from the organs of the body to the heart. Have a larger diameter and a thinner wall than arteries.
Define blood pressure.
Hydrostatic pressure of blood exerted against the walls of the blood vessels
What is normal blood pressure.
Normal blood pressure is 120/80
What are the haemodynamics factor regulating blood flow?
1) blood volume
2) Vascular resistance (lumen size, blood viscosity, total blood vessel length)
3) venous return
4) velocity of blood flow
Define hypertension.
It is commonly called high blood pressure, it is systolic or diastolic pressure that is above normal all the time
What do the NICE guidelines say about hypertension?
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
What are the risk factors for hypertension?
- Age (BP rises with age)
- obesity
- excessive alcohol intake
- high salt intake
- genetic susceptibility
- high plasma cholesterol
- chronic stress
What are the clinical complications of hypertension?
- 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
Name the drugs used for anti-hypertensive therapy.
- B-adrenoreceptors blockers
- A-adrenoreceptor blockers
- ACE inhibitors
- Angiotensin II receptor blockers
- Diuretics
- Calcium Channel blockers
Describe the mechanism, side-effects and give examples of B-adrenoreceptors blockers.
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)
Describe the mechanism, side-effects and give examples of A-adrenoreceptors blockers.
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)
Describe the mechanism, side-effects and give examples of ACE inhibitors.
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
Describe the mechanism, side-effects and give examples of Angiotensin II receptor blockers.
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
Describe the mechanism, side-effects and give examples of Diuretics.
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)
Describe the mechanism, side-effects and give examples of Calcium channel blockers.
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
Explain the types of L-type channel blockers.
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
Define postural hypotension.
This is due to the failure in the baroreceptor reflex.
Defined as a decrease in systolic blood pressure of >15mmHg on standing
What are the response to changes in posture?
- venous pooling in vessels below the heart
- venous pressure increases
- stroke volume and cardiac output falls
- person can faint
- lightheaded
Describe the baroreceptor reflex.
- 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.
What is rational prescribing?
It is the principles of drug selection.
What is poor compliance?
compliance = degree to which a patient follows medical/ lifestyle advice.
What are the NICE guidelines on hypertension for a person <55 years?
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
What are the types of veins?
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.
What are the NICE guidelines on hypertension for a person <55 years?
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
