BISC 307L 1st Edition Lecture 28 Current Lecture Blood Flow to Organs at Rest o o Left heart puts out blood that is being distributed to the various organ systems and shows the fraction that goes to the various systems o The block points percent of the total cardiac output that goes to the brain o The right heart pumps out one hundred percent of what it receives from the left starling law Must have same cardiac output o Since closed circuit if this wasn t the case then this would cause accumulation of blood somewhere else in the system o Plot of normalized cardiac outputs o The kidney receives the most blood function to continuously filter and adjust the composition of the blood receives high pressure blood o Regulation by vasoconstriction and vasodilation of cardiac output received by the various organs This can be adjusted and redirected Blood Pressure Velocity and CSA o o Relationships between BP blood velocity and cross sectional area o Rate at which fluid flows is the same at all points in the tube but in order for this to happen the velocity must be fastest in the small diameter and slower in the big part o The most narrow places move the fastest but it is the same amount moving through o Total cross sectional area of all the blood vessels chart on right and you see that the arteries have large diameter so their cross sectional area total is small and the capillaries have total largest cross sectional area and so the flow velocity increases in the veins and slow in the capillaries even though the pressure falls in the capillaries This facilitates the exchange of materials Cappilarries o o Single layer of endothelial cells and a mesh of fibrous cells that fill in the gaps The gaps are pores so fluid can leak out o The endothelial cells themselves have pores in adjacent to the junctions in between the endothelial cells o Can actively transport materials across the cells by transcytosis where there is endocytosis on one side and exocytosis on the other o Implication for pores in kidney and digestive tract important for fast transport of material o Capillaries in the brain and spinal cord DO NOT have these open junctions but rather are sealed to each other by tight junctions form the blood brain barrier Material must diffuse across the endothelial cell or transported by active and passive transport o Consider the forces that push through these holes always leaking fluid Fluid Exchange across capillaries o o Bulk flow across capillaries left receiving blood from arterioles and draining into venules o 32 mmHg near arterioles and 15 mmHg on the venule side creating a pressure gradient of about 17 mmHg o Liquid part of blood is being filtered by the protein mesh which excludes protein but all of the ions and small organic molecules can leak our freely through the capillaries o The small volume of water being pushed out is proportional to the pressure pushing it so upstream since there is more pressure the water is moving out quicker o There is an inward force due to the protein in the plasma does not leak out exerts osmotic pressure in the plasma pushing water back into the capillaries This is about 25 mmHg called pi or colloid osmotic pressure o Assuming that since there is little protein outside of capillaries that the osmotic pressure on the outside is near 0 o The concentration of proteins stays about the same along the capillary o In some tissues there may be some hydraulic pressure in the surrounding tissue kidney but in most tissues it is 0 o 32 outward and 25 in this makes a total of 7 mmHg push out at the upstream end and a 10 mmHg net inward gradient at the end o Downstream NET INWARD CURRENT o Upstream NET OUTWARD CURRENT o In between fluid movement interstitial fluid in circulation and constant movement o Is the amount of fluid filtered out of capillaries in a day the amount that is taken up in a day NO filtration is about 20L day not counting kidney and reabsorption is about 18L day Not all the fluid coming out comes back in and the extra 2L is drained by the lymphatic system Capillary Lymph Exchange and Edema o o Venous system starts with the lymph capillaries o Fluid flowing toward the heart is due to the skeletal muscle moving o When everything works right the balance causing lymph to leave capillaries and carried back to the hear so everything is in balance o Swelling or accumulation of fluid in tissues Edema 1 Blockage of lymphatic vessels drainage is poor elephantiasis accumulation of fluid 2 High central venous pressure vena cava and pulmonary veinnormally low if high heart failure blood will accumulate in the right atrium and this high pressure will propagate back The high pressure in the capillaries and veins will cause increase in leakage of fluid and in the absence of change in lymphatic system this will result in improper drainage 3 Low concentrations of plasma protein which is the main force that drives absorption of fluid back into capillaries but filtration remains the same so there is accumulation of fluid severe protein malnutrition kwasiorkor or liver disease where liver cannot make these plasma proteins Victims of famine children can have fluid accumulation in the abdomen which results in the swollen bellies we see called ascites fluid 4 Increased concentration of interstitial protein which is normally zero but in conditions of inflammation the capillaries become so porous that the proteins can leak out and this causes high interstitial protein content which diminishes the outside colloid pressure diminishing the amount of fluid coming back in causes swelling Baroreceptor Reflex Anatomy o o Most important reflex for controlling blood pressure o Happens within a second or two o Lying down versus standing up this is important in controlling venous return to the heart o Baroreceptors pressure sensitive nerve endings in the aortic arch and the carotid body of the carotic artery Positioned in the highest pressure sides of circulation so in good position to sense left sided cardiac pressure and they are near the brain because the brain cannot deal with changes in pressure for more than a second or two o In response to a drop in blood pressure Stimulates the stretch sensitive nerves which causes activity to go up axons to the brainstem medulla which will control the cardiovascular system adjustments in sympathetic activity to the SA node ventricles veins and arterioles and adjustment in parastym activity to the SA node to fix changes Baroreceptor Reflex