Urinary and Renal system.docx

Urinary system Kidneys Ureters- from kidney to bladder Bladder Urethra- from bladder to the outside of body The kidneys Filters the blood therefore needs good blood supply. Blood enters the kidney from aorta via renal arteries. Filtered blood leaves from kidney to inferior vena cava via real vein...

Urinary system Kidneys Ureters- from kidney to bladder Bladder Urethra- from bladder to the outside of body The kidneys Filters the blood therefore needs good blood supply. Blood enters the kidney from aorta via renal arteries. Filtered blood leaves from kidney to inferior vena cava via real veins. Produces Urine that drains from nephrons into collecting ducts. Collecting ducts merge into the renal pelvis which goes on to the ureter. The nephron- functional unit of the kidney Neophron contains 2 parts to it: a tubular part and a vascular part Glomerulus Efferent and afferent arteriole Bowman’s capsule PCT Loop of Henle DCT Collecting duct Vasa recta Renal pelvis Nephron has 2 distinct regions. Renal cortex Renal medulla There are 2 types of nephrons. Glomerulus- bundle of capillaries Blood enters the glomerulus via afferent arteriole which has a larger diameter to allow more blood in compared to the efferent arteriole via which the blood leaves the glomerulus to increase its pressure to allow for efficient filtration. 3 layers in the glomerulus that filters the blood. Capillary wall- made of flat single layer of endothelial wall making it more permeable compared to other capillaries. Lots of gaps and pores in the capillary wall. Larger proteins are filtered out as they can’t pass through the pores. Basement membrane- made up of collagen and glycoproteins. Collagen provides structural strength whilst the glycoproteins discourage the filtration of small plasma proteins. Glycoproteins are negatively charged meaning it repels plasma proteins such as albumin. Podocytes of bowman’s capsule- the cell body produces primary processes which then produces secondary processes. The processes from one side interdigitate which forms filtration slits another barrier. PCT Filtered fluid passes into the PCT which lies within the cortex. Site of tubular reabsorption Nutrients such as glucose, amino acids Electrolytes Highly selective process Waste products remain, to be excreted in urine. Transepithelial transport in the PCT. To be able to be reabsorbed, a substance must go through 5 distinctive barriers. Luminal epithelial cells (cells in the tubular component) connected with tight junctions so the substance can’t go between cells but must go through the cell. Must pass through the cytosol. Must cross the basolateral membrane. Must diffuse through the interstitial fluid. Must penetrate the capillary wall to enter blood plasma. This means it is very selective process. 2 main ways transeptheitial transport can take place are: Active transport Na+ transport into the ECF via Na+/K+ pump. Passive transport Na+ transport into the luminal cells due to concentration gradient set by Na+/K+ pump. Sodium reabsorption Reabsorption of sodium in the PCT plays a role in reabsorbing glucose, amino acids, and water etc. Na+/K+ pump located in the basolateral cells pumps Na+ meaning low concentration inside the cell so Na+ moves passively from area of high concentration in the filtrate to an area to low concentration in the cell via a sodium channel. Na+ is then pumped out into the interstitial fluid creating a high concentration in the cell but lower concentration in the blood so Na+ moves passively from the cell to the blood. Water reabsorption Concentration gradient set up by the Na+/K+ pump gives high concentration of Na+ outside the cell and low concentration inside the cell therefore water leaves the filtrate via osmosis through the AQP-1 water channels in the lumen. Loop of Henle ONLY Juxtamedullary nephrons set up a vertical osmotic gradient in the interstitial fluid. The gradient allows controlled water reabsorption in the PCT and collecting duct. Loop of Henle sets the concentration gradient for the water to be reabsorbed later in the DCT and collecting duct. Descending limb Contains AQP-1 channels meaning its permeable to water. Contain NO Na+/K+ ATPase. Ascending limb Lots of Na+/K+ ATPase Contains a channel called NKCC2 which is a cotransporter and transports 1x Na+, 1x Cl- and 2x K+ NO AQP-1. As filtrate comes down from the PCT to the descending limb, water leaves through the aquaporins channels into the interstitial fluid. Na+ stays within the filtrate so as the filtrate goes down, it becomes very concentrated inside the tubule. As the filtrate goes up the ascending limb, NKCC2 channel use energy from the Na+/K+ pump to transport NaCl out in the interstitial fluid. Water can’t leave through the ascending limb. Vasa recta Blood vessel with the same shape as the loop of Henle. Crucial shape to maintain the osmotic gradient. Setting up the osmotic gradient is called counter current multiplication. Osmotic gradient is set up by counter current multiplication in the loop of Henle but its maintained by counter current exchange in the vasa recta. DCT Remaining 20% of water is under hormonal control. Posterior pituitary gland releases vasopressin (ADH) Vasopressin has 2 key roles; acts on arteriole to cause vasoconstriction to raise blood pressure and in the kidney, it increases permeability of DCT and collecting duct to reabsorb more water. Osmoreceptors in the hypothalamus detect increase in osmolarity in the blood (dehydration) ADH is released via posterior pituitary gland. ADH acts on the V2 receptors on DCT and CD. AQP-2 channels inserted into luminal membrane. Water diffuses into cell via AQP-2 and out into blood via AQP-3/4 Urine is concentrated and osmolarity decreased. All of this happens due to concentration gradient set up before hand in loop of henle and the aquaporin channels.