BIO 241 1st Edition Lecture 24 Outline of Last Lecture I. ExcretionII. Introduction to the urinary systemIII. External anatomy of the kidneyIV. Internal anatomy of the kidneyV. NephronVI. Endothelial-capsular membraneVII. Renal tubule histologyOutline of Current Lecture II. Renal blood supply and nerve supplyIII. Juxtaglomerular apparatusIV. Basic functions of the nephronV. Three processes in urine formationVI. Glomerular filtrationVII. Net filtration pressure (NFP)VIII. Glomerular filtration rate (GFR)IX. Renal autoregulationX. Hormonal regulation – RAA systemXI. Tubular reabsorption of solutesCurrent LectureII. 25% of total cardiac output goes to the kidneys. It follows this route: aorta → renal arteries →segmental arteries → interlobular arteries → arcuate arteries → afferent arteriole → glomerularcapillaries → efferent arteriole → peritubular capillaries and vasa recta capillaries → ultimately the renal veins → inferior vena cava. These vessels have a nerve supply made of sympathetic fibers. III. The juxtaglomerular apparatus is located at the junction of the distal tubule and afferent arteriole. The distal tubule has special cells called macula densa cells. These measure tubular flow rate and NaCl in filtrate. If too much filtrate is being produced, then it secretes paracrine message. There are also juxtaglomerular cells which are special cells of the afferent arteriole. These measure blood pressure. If too high, then they respond to paracrine messages by causing vasoconstriction. These notes represent a detailed interpretation of the professor’s lecture. GradeBuddy is best used as a supplement to your own notes, not as a substitute.IV. Nephrons have three basic functions: control blood concentration and volume, regulate blood pH, and remove toxic wastes from the blood. Nephrons accomplish urine formation.V. There are three basic processes in urine formation: glomerular filtration by the renal corpuscle, tubular reabsorption by the renal tubule, and tubular secretion by the renal tubule.VI. The principle of filtration is to remove wastes from the blood. Blood hydrostatic pressure is the driving force of filtration. Filtrate consists of all blood components except formed elements and plasma proteins. You would not want these to be filtered because you would have to continuously make more. The average person makes about 180 liters of filtrate per day. Obviously, you would not want plasma proteins and formed elements to be in this because there would be a lot. Filtrate is reabsorbed so that you do not urinate 180 liters a day. Normal amounts of urine are 1-2 liters per day. Therefore, 178-179 liters are reabsorbed. There are a few renal corpuscle adaptations that enhance filtration. Glomerular capillaries are long, which decreases velocity, so that the fluid flows slowly to be reabsorbed. The endothelial-capsular membrane is porous (remember the fenestrations) which helps filtration. Lastly aiding in filtration, glomerular blood hydrostatic pressure is higher than normal blood pressure. VII. Net filtration pressure of the kidneys is determined by glomerular blood hydrostatic pressure (outward force), capsular hydrostatic pressure (inward force), and blood colloid osmotic pressure (inward force). The equation is as follows: NFP = GBHP – (CHP + BCOP) = 60 – (18+32) = +10 mmHg. The filtration fraction (10%) represents the proportion of the fluid reaching the kidneys which passes into the renal tubules. 25% cardiac output = 1250 ml/min1250 mL/min x 0.1 (10%) = glomerular filtration rate (GFR)GFR = 125 mL/minSo, 125 mL/min is the proportion of fluid reaching the kidneys. VIII. GFR = 125 mL of filtrate is produced every minute. The glomerular filtration rate is directly related to the net filtration pressure similar to the pressures we learned earlier this semester. Homeostasis requires a relatively constant GFR. Glomerular blood flow depends on two factors: systemic blood pressure (this controls a lot) and afferent and efferent arteriole diameters. Thesetwo factors are regulated by three mechanisms. The first is renal autoregulation (why someone’s kidney functions in another person). It is a myogenic (muscle originating) mechanismthat uses tubuloglomerular feedback to regulate it. Secondly, hormonal regulation which is controlled by the renin-angiotensin-aldosterone system. Lastly is the neural regulation which are the sympathetic nerve fibers mentioned previously.IX.X.XI. The tubular reabsorption of solutes has a tubular maximum (Tm). It can occur via active or passive transport. Receptors (carriers) and ATP are involved with active transport. Glucose and amino acids are reabsorbed 100% of the time; therefore, neither should be found in urine. The amount of sodium and magnesium that is reabsorbed is controlled by aldosterone. Calcium reabsorption is controlled by parathyroid hormone (PTH) and calcitonin (CT). Passive transport occurs by diffusion or through an electrochemical gradient. Cl- and HPO4- help this