Lecture 28. Pathophysiology and Treatment of Hypertension Flashcards
How does blood flow ?
From areas of higher pressure to areas of lower pressure
What is blood pressure ?
Force exerted in all directions
What plays a role in maintaining blood pressure ?
The recoil of arterial walls
What dissipates much of pressure ?
The resistance of blood flow in the narrow diameters of tiny capillaries and arterioles
What is systolic pressure ?
The pressure in the arteries during ventricular systole
What is the highest pressure in the arteries ?
Systolic pressure
What is pulse ?
Rhythmic bulging of artery walls with each heartbeat
What is diastolic pressure ?
The pressure in the arterioles during diastole, it is lower than systolic pressure
What is formula to measure flow ?
Flow = Pressure gradient/Resistance
What creates a pressure gradient for blood flow ?
Heart
What is the formula for resistance ?
Resistance = (Length x Viscosity)/ Radius ^4
What are the most important resistance vessel ?
Arterioles
How do homeostatic mechanisms regulate arterial blood pressure ?
By altering the diameter of arterioles (vasoactivity)
What is vasoconstriction ?
The contraction of smooth muscle in the arteriole walls increasing blood pressure
What is vasodilation ?
The relaxation of smooth muscles in the arterioles, causing blood pressure to fall
What is a major inducer of vasodilation ?
Nitric oxide
What is an inducer of vasoconstriction ?
The peptide endothelin
What is vasoconstriction and vasodilation often coupled to ?
Changes in cardiac output that affect blood pressure
What is vasoactivity influenced by ?
- Autonomic nerves
- Hormones
- Metabolism
Where is blood pressure measured from ?
The artery in the arm at the same height as the heart
What is the recommended blood pressure for a healthy young adult ?
At rest should be less than 120mm HG at systole and 70 mm Hg at diastole
What has a significant effect on blood pressure ?
Gravity
What is fainting cause by ?
Inadequate blood flow to the head
Where is blood pressure low ?
In veins
What is the return of blood enhanced by ?
Contraction of smooth muscle in vein walls and skeletal muscle contraction
What is the formula of cardiac output ?
Cardiac output = Mean arterial pressure/ total peripheral resistance
What is total peripheral resistance ?
The combined resistance of all blood vessels
What is mean arterial pressure regulated by ?
HR, SV, TPR
What is mean arterial pressure regulated by in the short term ?
- Baroreceptor reflex
What is mean arterial pressure regulated by in the long term ?
Regulation of blood volume
What happens to blood pressure in the parasympathetic division ?
Blood pressure decreases
What happens to blood pressure in the sympathetic division ?
Blood pressure increases
What are barorecptors ?
Specialised nerve endings that respond to stretch of vessel wall - indirect response to changes in blood pressure
Where are baroreceptors found ?
Carotid sinus and aortic arch
What are the two types of baroreceptors ?
- Type A
2. Type C
What are type A baroreceptors ?
- Myelinated
- Low pressure (30-90mmHg)
- Important at rest
What are type C baroreceptors ?
- Unmyelinated
- High pressure (70-140mmHg)
- Increasingly active at higher pressures
Where does baroreceptor input go ?
Nucleus tractus solitarius in the medulla
Where does the baroreceptor output from nucleus tractus solitarius go ?
- Parasympathetic nervous system
- Sympathetic nervous system
- Hypothalamus and amygdala
What does the output from nucleus tractus solitarius to the the parasympathetic nervous system travel via ?
Nucleus ambiguous
What does the output from the nucleus tractus solitarius to parasympathetic nervous system do ?
Cardiac control - limits heart rate
What does output from the nucleus tractus solitarius to the sympathetic nervous system do ?
Cardiac and blood vessel control
What does output from nucleus tractus solitarius to hypothalamus an amygdala ?
Allows theses areas to override the baroreceptor reflex during stress. This allows a stress associated increase in blood pressure to occur
What does renin-angiotensin-aldosterone system do ?
Regulates sodium ion and as a result water
What does a drop in blood pressure near the glomerulus cause ?
The juxtaglomerular apparatus of the kidney to release the enzyme renin
What does renin trigger ?
The formation of the peptide angiotensis II
What is the function of angiotensin II ?
- Raises blood pressure and decreases blood flow to the kidneys
- Stimulates release of the hormone aldosterone
What is the function of the hormone aldosterone ?
Increases blood volume and pressure
What are the factors affecting blood pressure ?
- Diet
- Smoking
- Obesity and type II diabetes
- Stress
- Low activity
- Age
- Sex
- Genes
What is the strategy when treating hypertension ?
Reduce blood volume and reduce cardiac output
What do thiazide diuretics do ?
Inhibit Na/K/Cl exchange in the distal renal tubule
What is the function of B-blockers ?
Reduce heart rate and contractility
What is the function of alpha-blockers ?
Reduce sympathetic tone, dilate arteriolar smooth muscle
What is the function of the mixed alpha and beta blocker: L-type Ca channel blocker ?
Relaxation of vascular smooth muscle - reduced resistance
What is the function of ACE inhibitors ?
Diuretic actions - inhibit aldosterone formation