Regulation of Blood Pressure, Capillary Exchange Flashcards
What does i)cardiac output and ii)peripheral resistance in arterioles determine?
i) cardiac output determines the rate of blood flow into the aorta
ii) peripheral resistance in the arterioles determines the rate of blood flow out of the arteries
Why is the resistance to blood flow greatest in arterioles and capillaries
due to their narrow diameter
What is the total peripheral resistance?
The resistance to blood flow through the entire arteriole system
-determines rate of blood flow of arterial system
Mean arterial pressure formula
MAP = Cardiac output x total peripheral resistance
CO = stroke volume x heart rate
How does the body detect chnages in blood pressure?
-Stretch-sensitive mechanoreceptors (baroreceptors) located in the walls of the acrotid artery and aortic arch
-Increase in blood pressure causes the walls of these blood vessels to stretch
-Baroreceptors become more active in response
-Baroreceptors activate sensory nerves that return to cardiovascular control centree in the medulla oblongta
-The cardiovascular control centre modulates the autonomic ns to regulate blood pressure by altering HR, SV and TPR
Vasoconstriction vs vasodilation
-Both control resistance in arterioles
vasocontraction - contraction
vasodilation - relaxation
How does contraction take place in the arterioles?
-Vascular smooth muscle cells are innervated by sympathetic nerve fibres only
-Express alpha adrenergic receptors whihc bind noradrenaline released by activated sympathetic nerves
What will happen to counteract a reduction in blood pressure?
Increased sympathetic nerve activity will:
-Increase cardiac output by increasing both cardiac rate and stroke volume
-Contract venous smooth muscle promoting venous return
-Stimulate contraction of arterial smooth muscle (vasoconstriction) increasing peripheral resistance
-Vasoconstriction in kidney arterioles also minimises urine formation
-reduction in vagus nerve activity will diminish inhibitory effect on heart rate
What counteracts an elevation of blood pressure?
-Stimulation of vagus nerve activity will reduce cardiac output by slowing heart rate
-Inhibition of sympathetic nerves activity will reduce cardiac output by slowing heart rate and stroke volume and cause relaxation of arterial smooth muscle (vasodilation) to decrease peripheral resistance
-Kidneys are also stimulated to exctrete more water as urine - reducing blood volume
What is the function of the baroreceptor reflex?
To counter chnages in blood pressure and is v rapidly activated when pressure increases or decreases
-more sensitive to decrease in blood pressure which causes reduction in stretch of arterial walls
-mor sensitive to rapid changes in pressure
-corrects the light headed feeling when standing up too fast
Look at slide 14 and 15
What happens when there is a sudden reduction in cardiac output and/ or increased vasodilation
Immediate drop in MAP
-short drop in bp reduces blood flow and thus O2 and glucose delivery to the brain
-Within 3-5 sceonds - fainting (syncope)
-Within 5 minutes - irreversible brain damage
Effect of total blood volume on MAP
-Increased blood volume - MAP will rise
-Decreased bv - MAP will fall
What happens in the kidneys?
-Vital role in regulating blood volume bc urine is derived from blood plasma
-Plasma filtered through glomeruli to form filtrate
-99% of water and salts are reabsorbed back into vascular system
-1.5L urine éxcreted daily but rate of salt and water reabsorption can be regulated to control bv
-play central role in long-term regulation of blood pressure
Look at slide 19
What are the 2 types of hypertension?
1) Essential hypertension
-unclear, multifactorial causes such as diet and genetics
-accounts for 95% of cases
2) Secondary hypertension
-resulting from another condition like chronic renal disease triggered by diabetes
-chronically elevated salt and water reaborption in the nephron will increase blood volume and chronically raise blood pressure
What damage does hypertension cause?
-Ventricles must contract more forcefully to maintain adequate stroke volume resulting in long term damage to heart muscle
-High pressure in arteries damages endothelial lining of vessels, this promotes formation of atherosclerotic plaques
Which is more fatal hypertension or hypotension?
Hypertension will take years to kjill while hypotension can be fatal within minutes
What is interstitial fluid?
tissue fluid
-lies outside the cells and the circulatory system, it directly bathes the cells oif the tissues
-material passes from capillaries into intersititial fluid and then into cells
Filtration and absorption in the capillaries?
-Flow of plasma out of the capillaries into the tissues - filtration
-Flow of intersititial fluid into capillaries - absorption
Hyrostatic pressure
-Filtration is driven by the blood pressure in capillaries (hydrostatic pressure)
-38mmHg (arterial end) - 16mmHg (venous end)
-Pressure falls as blood moves through capillaries
What is osmolarity?
The conc of solutes in fluid
Ions, salts and organic molecules inm plasma can pass freely through capillary walls thus their conc in tissue fluid is identical to that in plasma
What promotes movement of water out of tissue fluid and into capillaries
Colloid osmotic / oncotic pressure- osmotic pressure created by plasma proteins
-Protein conc of plasma = 7g/100ml
-Protein conc of tissue fluid = 2g/100ml
Large plasma proteins cxannot pass through capillary walls
What is the net colloid osmotic pressure/ oncotic pressure value?
25 mmHg and is constant across the length of capillaries
