The Kidnesys its Endocrine Functions.pptx

The kidneys its functions structure

1. The Kidneys Kidneys are bean shaped organs, two in number, located at the rear of the upper portion of the abdominal cavity. They sit opposite each other in both sides of the spine. The right kidney sits a little lower than the left to accommodate the liver. Lecture Notes (Physiology): Tariq Bahir Sipra

2. Lecture Notes (Physiology): Tariq Bahir Sipra

3. THE KIDNEYS FUNCTIONS Renal Functions: Renal means, pertaining to the kidneys. Kidneys, process the plasma portion of blood by removing substances from it and by adding substances to it. In doing so kidneys perform a variety of functions. First Function: Kidneys play central role in ; Regulating the water concentration Inorganic ion composition This is done by excreting just enough water and inorganic ions to keep the amounts of these substances in the body relatively constant. For example, if you start eating a lot of salt (sodium chloride), the kidneys will increase excretion of the salts. Alternatively, if there is not enough salt in the body, the kidneys will excrete very little salt or none at all. So the first function of kidneys is the “ REGULATION OF WATER AND INORGANIC ION BALANCE” Physiology MLT Lecture notes by Teacher, Tariq Bashir Sipra

4. Second Function. Metabolic waste products must be removed from the body, otherwise these can be toxic if accumulate in the body. These waste products are; Urea. From the catabolism of proteins. Uric acid. From the catabolism of Nucleic Acids. Creatinine. From the muscle creatine . End products of haemoglobin breakdown (which give urine its colour ) So, second function of kidneys “ REMOVAL OF METABOLIC WASTE PRODUCTS FROM THE BLOOD AND THEIR EXCRETION IN THE URINE ” Kidneys excrete metabolic waste products into the urine as fast as they are produced. Physiology MLT Lecture notes by Teacher, Tariq Bashir Sipra

5. Third Function. Foreign chemicals such as drugs, pesticides and food additives and their metabolites must be removed. So third function is “ REMOVAL OF FOREIGN CHEMICALS FROM THE BLOOD AND THEIR EXCRETION IN THE URINE ” Fourth Function. During prolonged fasting, glucose from carbohydrate source is not available, then kidneys synthesize glucose from amino acids and release into blood. “ Gluconeogenesis” Fifth Function. Maintenance of blood pH. Physiology MLT Lecture notes by Teacher, Tariq Bashir Sipra

6. Sixth function. Kidneys also act as Endocrine glands, releasing; Erythropoietin that controls erythrocyte production. Renin, enzyme/hormone that controls the formation of angiotensin and influences blood pressure and sodium balance. 1,25-dihydroxyvitamin D, which influences calcium balance. Physiology MLT Lecture notes by Teacher, Tariq Bashir Sipra

7. Sixth function. Kidneys also act as Endocrine glands, releasing; Erythropoietin that controls erythrocyte production. Renin, enzyme/hormone that controls the formation of angiotensin and influences blood pressure and sodium balance. 1,25-dihydroxyvitamin D, which influences calcium balance. Physiology MLT Lecture notes by Teacher, Tariq Bashir Sipra

8. The Formation of Urine The fundamental unit for the formation of urine is the nephron. There are about one million nephrons in each kidney. Each nephron consists of; Renal corpuscle, an initial filtering component. Tubule that extends from the renal corpuscle. Anatomy of the Renal corpuscle: Each renal corpuscle contains a compact tuft of 6-8 capillary loops called glomerulus or glomerular capillaries. The glomerulus protrudes into a capsule called Bowman’s capsule. The combination of glomerulus and Bowman’s capsule constitutes a Renal corpuscle. Each glomerulus is supplied with blood by an afferent arteriole. The blood vessel which leaves the glomerulus is efferent arteriole. Lecture Notes (Physiology): Tariq Bahir Sipra

9. Anatomy of the tubule. The renal tubule is continuous with a Bowman’s capsule. The tubule is divided into the; a ) proximal convoluted tubule. b) the loop of Henle consisting descending limb and the ascending limb. c) Distal convoluted tubule. Several tubules lead to each collecting duct which leads to the bladder via the ureter. The urine is voided from the bladder via the urethra. FIG Physiology MLT Lecture notes by Teacher, Tariq Bashir Sipra

10. Urine is formed by the process of: Glomerular Filtration Tubular Reabsorption Tubular Secretion Lecture Notes (Physiology): Tariq Bahir Sipra

11. Glomerular Filtration The glomerulus acts as a filter between blood and tubule. About 1/10 th of the water in the blood flowing through the glomerulus, and its essential small constituents (molecular Wt. less than 67000) are filtered and pass into the tubule. The large constituents including the blood cells. plasma proteins are not filtered. One reason, their high molecular weight. A second reason is that the filtration pathways in the corpuscular membranes are negatively charged, so they oppose the movement of proteins , as most of the proteins are negatively charged. Half of the plasma calcium and all of the plasma fatty acids are bound to plasma proteins and so are not filtered. The filtrate passing into tubule will contain the inorganic salts, food substances like glucose, Amino acids and waste products like urea, uric acid and creatinine. This process of filtration is entirely non-selective . The substances filtered are those of small size and there is no modification at this stage, whatsoever the body’s requirements are. Lecture Notes (Physiology): Tariq Bahir Sipra

12. The volume of fluid filtered from the glomeruli into Bowman’s space per unit time is known as Glomerular Filtration Rate (GFR). All the nephrons working together filter 125 ml water per minute. This is Glomerular Filtration Rate (GFR). About 180 liters/day. Calculations ? Physiology MLT Lecture notes by Teacher, Tariq Bashir Sipra

13. 2) Tubular Reabsorption From about 125 ml/min filtered water about 124 ml/min is reabsorbed as the filtrate passes along the tubule and only 1 ml/min passes to the collecting duct to the ureter to the bladder and become urine. About 1500 ml/day Calculations ? The efferent arteriole leaving the glomeruli form second capillary net work surrounding the tubules. These care called peritubular capillaries. This 2 nd network allows reabsorption to take place. The reabsorption is selective and varies according to the body’s need for each substance. If there is a surplus of a substance, the excess is allowed to continue down the tubule without reabsorption and to pass to the collecting ducts, ureter and the bladder. Glucose is an example of a substance that is reabsorbed completely under normal conditions. Lecture Notes (Physiology): Tariq Bahir Sipra

14. 3) Tubular Secretion The 3 rd process involved in the production of urine is tubular secretion. Tubular secretion is the transfer of substances from peritubular capillaries to tubular lumen of the nephrons. Secretion is a mechanism to improve the efficiency of the kidneys to dispose of further substances. Lecture Notes (Physiology): Tariq Bahir Sipra

15. Average values for some components that undergo Filtration and Reabsorption Substance Amount filtered Amount % per day Excreted per day Reabsorbed Water, L 180 1.8 99 Sodium, g 630 3.2 99.5 Glucose, g 180 0 100 Urea, g 54 30 44 Physiology MLT Lecture notes by Teacher, Tariq Bashir Sipra

16. WATER EXCESS Let us see how body maintains water equilibrium . If you have taken surplus water, this water will adopt the rout; Drinking water -----> small intestine ---> Blood(3 liter plasma) --> Tissue fluid(12liters) -- > cells (30 liters). The dilution of the blood affects the osmoreceptors in the region of the hypothalamus and the amount of the posterior pituitary hormone ADH (antidiuretic hormone) is reduced. This hormone normally facilitates the reabsorption of water in the distal tubule. As a result of the reduction in the ADH level, less water will be reabsorbed and there will be diuresis (increase in urine volume). This increase in the urine volume will continue until the water balance has been restored to normal. Lecture Notes (Physiology): Tariq Bahir Sipra

17. Rate of tubular reabsorption of water GFR is a constant i.e 125 ml/mint. The tubular reabsorption under the influence of a normal level of ADH is initially 124 ml/mint. Thus 1ml/mint urine is passing to the bladder. At the height of the diuresis (urine formation) the ADH level will fall almost to zero and the tubular reabsorption will fall to 110ml/mint. Tubular reabsorption does not fall below 110ml/mint because 7/8 th water is reabsorbed in the proximal tubule and this reabsorption is not under the control of ADH. Diabetes Insipidus The condition of diabetes insipidus is a condition in which the posterior pituitary gland fails to produce ADH. As a result a very large volume of urine is produced each day (it may be upto 20 litres ), and the subject becomes extremely thirsty. Lecture Notes (Physiology): Tariq Bahir Sipra

18. Water Lack On a hot summer days when a large amount of water is being lost by sweating , the ADH level is increased, consequently the tubular reabsorption increases , it may increases to 124.75 ml/mint and the volume produced, drops to 0.25 ml/mint and the urine becomes very concentrated. This volume is equivalent to 375 ml/day, which is the minimum obligatory volume for the excretion of the urea and other waste products. Lecture Notes (Physiology): Tariq Bahir Sipra

19. GFR Tubular Reabsorption Urine/min Urine/day ml Hot Day, Sweating, ADH level High 125 ml/min 124.75 ml/min 0.25 ml 375 Normal 125 ml/min 124 ml/min 1 ml 1500 NO ADH 125 ml/min 110 ml/min 15 ml 22500 Lecture Notes (Physiology): Tariq Bahir Sipra