BISC 307L 1st Edition Lecture 38 Current Lecture Response to Changes in Blood Volume and Pressure o o There are 2 different types of baroreceptors in the body 1 In carotid and aortic body pressure high pressure arteries referred to as the high pressure baroreceptors 2 Low pressure baroreceptors blood volume in low pressure parts of the vascular system stretch sensitive nerves in the atria pulmonary blood vessels and the big veins these are highly compliant parts of the vascular system often called volume receptors whereas the high pressure ones are called pressure receptors Water Balance in the Body o o o o o The water has to be in water balance Gain and loss of water every day Main regulated route of water loss in the urine No mater how much water one drinks 99 of that water is reclaimed proximal tubule and loop of henle and first part of distale tubule Osmolarity Within Kidney o o juxtamedullary nephron o kidney has an osmotic gradient where the cortex and the outer medulla have 300mOsM but as you go deeper it gets very highly concentrated due to high amounts of salt and urea o Filtrate in bowmans capsule has the same osmolarity as blood o Descending loop of henle epithelial cells are permeable to water but not salt Only water is reabsorbed raising the osmolarity level Salt cannot follow increasing concentration of salt o Ascending loop of henle permeable to salt but not water Salt reabsorbed and osmolarity becomes very low 100 In the thin part there is little active transport of salt just passive but in the thick part there is more active transport of salt because not as big of a concentration gradient Becomes lower than body fluids 100 Reabsorption of Na K Cl in Ascending Limb o o Mechanism of reabsorption of salt K and Cl in ascending limb of loop of henle o Important thing here is the K Na pump in the basolateral membrane o Low Na concentration inside drives the Na K 2Cl symporter in the apical membrane unique to this area of the body loop diuretics inhibit this transport o Na ions that get pumped in get pumped out across the basolateral membrane o K ions get short circuited out or goes through channels in the basolateral membrane o Cl goes out through the transporters in the basolateral membrane o Since water cant come in this creates a hypoosmotic fluid one of the only places in the membrane o Can produce a lot of dilute urine without losing too much salt this is the mechanism since water cannot follow salt in reabsorption Countercurrent Multiplier and Exchanger o o Creation of the osmotic gradient Loop of henle going through the medulla Descending limb permeable to water not salt Once you get to active transport section of ascending limb salt will leave despite there being no osmotic gradient assuming there wasn t one so fluid is slightly salty goes through again and there is a little osmotic gradient so water leaves and osmolarity keeps changing this establishes the osmotic gradient called the counter current multiplier THE MORE SALT THAT IS EXCRUDED THE EASIER IT BECOMES TO EXCRUDE SALT o 2 problems with this system 1 Why doesn t the water that comes out the descending limb dilute the salty inner medulla 2 Why on the ascending limb isn t the salt coming in washed out by blood ANSWER IMPORTANCE OF THE VASORECTA AS COUNTERCURRENT EXCHANGERS loops of capillaries that parallel the loop of henle diagram on the right Not going to be tested on this diagram above look below Simpler explanation fluid in capilarries going in opposite direction as loop of henle fluid Vasorecta is regular endothelial cells with pores and leaky Diffusion as the blood goes down on the right hand side it moves into an environment that is more and more salty will gain salt and loses water so by the time the blood gets to the bottom this makes the blood very high osmolarity shrivels the RBC and then goes back up on the lef and is moving through and environment that is becoming less osmotic so it will gain water and lose salt The salt that the blood gains as it travels down is the same salt that it loses on the way up and vice versa for water But water doesn t just move into capillaries by osmosis but also by bulk flow These capillaries are very low pressure because very downstreamthe balance of forces strongly favors reabsorption of water by bulk flow in addition which is important because that s where a lot of the water that comes out gets reabsorbed into the blood the volume coming out of the vaso recta on the left is twice the volume that came in this is due to bulk flow Reabsorption of H2O from Collecting Duct o o Coming in the osmolarity is 100 and then comes through the collecting duct o Modification happens if the walls are permeable to water then water will be reabsorbed small volume of high osmolarity urine what happens when your body needs to conserve water o If not then the walls are not permeable to water excrete a large volume of urine o Controlled by vasopressin increases water permeability of collecting duct to conserve water Vasopressin ADH Increases H2O Permeability o o How vasopressin works to conserve water o Inserts aquaporin 2 channels into the apical membrane retrieved from the apical membrane by endocytosis so if you don t have the ADH system then they will be removed o The basolateral membrane is always permeable to water though o Most potent stimulus for this is dehydration sensed as an increase in blood osmolarity o Also excitatory input form the volume receptors in atria and veins and the high pressure baroreceptors less so o Strong circadian rhythm in secretion don t secrete much at night so urine in the morning is more concentrated allows us to sleep without peeing Aldosterone Stimulates Na Reabsorption o o Regulation of Na content o Aldosterone stimulates reabsorption of Na because steroid hormone that binds to carrier and alters gene expression for mitochondria to produce ATP and Na K pumps to reabsorb Na and Cl flows and then H2O follows Renin Angiotensin Aldosterone Pathway o o Aldosterone is secreted as part of a bigger scheme o Increases volume and lowers osmolarity of the blood o Go through this on your own o Renin enzyme that converts angiotensin form the liver to angiotensin 1 causes vasocontriction and raises blood pressure o Angiotensin II is produced from angiotensin I from ACE on the surface of capillaries and this is more potent of a signal stimulates the adrenal cortex to secrete aldosterone and causes vasoconstriction and raises blood pressure and