Explain the role the kidney has in urine production and osmoregulation.
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The Kidney The kidneys are part of the urinary system along with the ureter, bladder and urethra. They filter the blood plasma and return most of the water and solutes back to the bloodstream. The remaining solutes and water form urine. This is stored in the bladder and then passed out of the body through the urethra. The following information will attempt to explain the role the kidney has in urine production and osmoregulation. The kidneys are two bean-shaped organs. They are located in the middle of your back, just below your rib cage, on either side of your spine (4) The right kidney is lower than the left to make room for the liver. In adults, a kidney is about 10-12cm long, 5-7cm wide and 3cm thick (1). It has a concaved shape which, means it curves inwards. This area is called the hillus and is where the ureter, blood vessels and nerves enter the kidney (2). Although the kidneys are small organs, they receive about 20% of the blood pumped by the heart. This large blood supply enables them to do a number of tasks, which have been put in a table in appendix 1. The protective layer of tissue surrounding the kidney is the renal capsule.
By the time the filtrate has travelled through the PCT, all the materials that need to be reabsorbed, have been reabsorbed. The filtrate that enters the descending limb of the loop of Henle, (LOH) enters at 40-45 ml/min. This is much less than when it entered the PCT. Here, the mixture is very different because there is no longer any glucose, amino acids or nutrients. The osmolarity of the tubular fluid is similar to that of blood. Reabsorption is still taking place in the LOH. 15% of the water is reabsorbed and 20-30% of Na+, K+ and Ca2+; 10-20% of HCO3- and 35% CL-. All the water absorbed in the LOH does so in the descending limb, no water is absorbed in the ascending limb as it differs in permeability. The descending limb is permeable to water and the ascending limb is permeable to sodium ions and chloride ions. The differences enable more tubular reabsorption to occur. The loop is mostly made of simple squamous epithelium, which are slightly fatter than usual but thinner than regular cuboidal epithelium. The epithelium of the descending limb does not allow solutes to pass through because the cells don't have the protein channels here. In the ascending limb, sodium is actively secreted out into the medullary interstitial fluid.
Peritoneal works similar to hemodialysis but the blood is cleaned inside the body rather than through a machine. The abdomen has a peritoneal cavity which is lined by a membrane, called the peritoneum. The peritoneal cavity is filled with dialysis fluid that enters the body through a permanently implanted catheter. Excess water and wastes pass though the peritoneum into the dialysis fluid. This fluid is then drained from the body and disposed of. Appendix 1. Functions of the kidney Function Regulates blood volume By keeping the volume of water in the body constant. An increase in blood volume increases blood pressure and a decrease in blood volume decreases blood pressure. Regulates blood pressure By releasing the enzyme rennin, which activates the renin angiotensin. An increase in renin causes an increase in blood pressure. Maintaining blood osmolarity By regulating loss of water and solutes in the urine, they can maintain a constant blood osmolarity close to 290 mosm/litre. Producing hormones The kidney produces two hormones. Calcitriol, which helps regulate calcium homeostasis and erythropoienetin, which stimulates production of RBCs. Regulating blood glucose levels Releases glucose into the blood to maintain a normal blood glucose level. Excreting waste and foreign substances By forming urine, the kidneys help excrete any substances that are no longer any use to the body. Regulates blood pH The kidneys excrete hydrogen ions into urine and conserve bicarbonate ions. These help regulate blood pH.
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