BISC 307L 1st Edition Lecture 27 Current Lecture Blood Vessels o o Tension in wall of vessels proportional to radius and pressure inside conclusion aorta gives a lot of wall tension where as a capillary is not very much tension in the walls Aneurisms only occur in arteries o 3 have smooth muscle arteries and arterioles and veins vascular smooth muscle is capable of contracting and not contracting vaso constriction and dilation vasoconstriction of arteries and arterioles increases resistance to blood flow make it possible to redirect blood flow in systemic system Regional vasoconstriction will redirect blood flow one way or the other after a meal vasodilation in intestine is coming from other areas that are inducing vasoconstriction o 2 do not capillaries and venules Microcirculation o o o o o o o o o o o o Dow from the top and across from the right and up is the flow The artery is heavily reinforced by strong fibrous connective tissue Arterioles don t have this protective sheath Smooth muscle cells can generate force for long periods of time can maintain contraction all night and day long Always contracted to some extent 24 hours a day The amount of contraction is called MUSCLE TONE Capillaries have no smooth muscle besides the pre capillary sphincters that regulate the amount of blood flowing through the capillaries In most tissues most cells are no further than a couple cells away from a capillary In order to get from the arteries to the veins it gets though either arteriovenous bypasses or thoroughfare channels Inner diameter of the capillaries is about the size of a red blood cell Some white blood cells are actually bigger so they must go through these other channels instead of capillary beds Angiogenesis o o Tumor that is attracting blood vessels o Growth factors that promote angiogenesis o VEGF formation of abnormal formation of blood vessels in the retina for diabetes o FGF proteases that digest molecules in the extracellular matrix which is important in angiogenesis because they stimulates endothelial cells to migrate and form new blood vessels Migration to a site that needs vascularization o Angiostatin and endostatin inhibit angiogenesis Pressure In Blood Vessels o o Graph in upper right shows pressure in various places in the systemic circulation o In arteries in general the pressure goes down as you go deeper in the vascular system pressure drive o In the left ventricle the pressure changes are extreme o Arteries are moderalteyl compliant and highly elastic Compliance tendency of an object to deform under pressure Elasticity ability to come back to original form after stretching o Due to high elasticity the stretching of the elastic walls stores some of the energy that the forward rushing blood has Keeps the arterial diastolic pressure form going as low as the ventricle goes 120 80 instead of 0 Pulse pressure is the difference between the diastolic and systolic pressure o Arterioles are a lot smaller and therefore the resistance is much higher and this diminishes the pressure changes no more surges of pressure Makes for more efficient exchange of materials in the capillaries o If the arteries were to lose elasticity there would be more pulsing Called hardening of the arteries when this elasticity is lost or arteriosclerosis Causes calcification of arteries and atherosclerosis Plaques Result stiffer arteriole walls pressure fluctuations in artery bigger pressure pulses propagate further even in the capillaries inhibiting function Their pulse is very large o Can calculate MAP just by calculating blood pressure 1 Cardiac output X peripheral resistance 2 Diastolic 1 3 pulse o Low blood pressure hypotension Results in poor vascularization of organs Lack of adequate blood flow to the brain dizziness o High blood pressure Hypertension If MAP is too high because peripheral resistance is too high Aneurisms damage to kidney increased probability of bleeding especially in brain o It is in the arterioles that blood encounters first resistance This resistance is adjustable Many factors that regulate this Regulation of Arteriolar Resistance o o Changing arteriolar resistance main way systemic blood pressure is regulated o 1 Myogenic autoregulation stretch activated ca2 channels in arterioles so they can respond actively to change in blood pressure When the pressure goes up the resistance of the arteriole squeezes and increases causing less flow In a perfect world the increase in blood pressure would cause the stretching to be just enough to increase the resistance just enough to keep the flow constant And this is what happens if didn t have this the flow would change as the pressure changes o 2 Local hormones 1 Vasopressin ADH 2 Angiotenson 2 made by liver o 3 Autonomic innervations sympathetic o Vasoconstriciton 1 Norepi on smooth muscle cells baroreceptor reflex 2 ADH increases BP by causing arteriolar vasoconstriction which maintains BP during hemorrhage 3 Angiotensin 2 maintains sodium reabsorption in the kidney Builds up blood volume build up blood pressure o Vasodilation Epinephrine Binds to beta 2 adrenergic receptors in the heart and on arterioler smooth muscle but the binding is weak Part of fight or flight response Vasodilation in skeletal muscle and heart and liver ACh Mostly arterioles don t have parasympathetic nerves except for in penis and clitoris and release of ACh in these releases NO which causes erection Also coronary arterioles have parasympathetic ACh releasers Why nitroglycerine are useful in pain in the chest associated with hypoxia Serves as a substrate for NO NO Look above Adenosine Signs of metabolism change when local tissue is metabolizing more