Mechanism of formation of urine pdf

In low-pressure states, ANH does not seem to have much effect. ADH is also called vasopressin. Early researchers found that in cases of unusually high secretion of ADH, the hormone caused vasoconstriction vasopressor activity, hence the name. Only later were its antidiuretic properties identified. Synthetic ADH is still used occasionally to stem life-threatening esophagus bleeding in alcoholics.

When blood volume drops 5—10 percent, causing a decrease in blood pressure, there is a rapid and significant increase in ADH release from the posterior pituitary. Immediate vasoconstriction to increase blood pressure is the result. ADH also causes activation of aquaporin channels in the collecting ducts to affect the recovery of water to help restore vascular volume.

A diuretic is a compound that increases urine volume. Three familiar drinks contain diuretic compounds: coffee, tea, and alcohol. The caffeine in coffee and tea works by promoting vasodilation in the nephron, which increases GFR. Alcohol increases GFR by inhibiting ADH release from the posterior pituitary, resulting in less water recovery by the collecting duct. In cases of high blood pressure, diuretics may be prescribed to reduce blood volume and, thereby, reduce blood pressure.

The most frequently prescribed anti-hypertensive diuretic is hydrochlorothiazide. Osmotic diuretics promote water loss by osmosis. An example is the indigestible sugar mannitol, which is most often administered to reduce brain swelling after head injury. However, it is not the only sugar that can produce a diuretic effect.

In cases of poorly controlled diabetes mellitus, glucose levels exceed the capacity of the tubular glucose symporters, resulting in glucose in the urine. The unrecovered glucose becomes a powerful osmotic diuretic. Classically, in the days before glucose could be detected in the blood and urine, clinicians identified diabetes mellitus by the three Ps: polyuria diuresis , polydipsia increased thirst , and polyphagia increased hunger.

Sodium has a very strong osmotic effect and attracts water. It plays a larger role in the osmolarity of the plasma than any other circulating component of the blood. There is an increase in total volume of water, which leads to hypertension high blood pressure. Over a long period, this increases the risk of serious complications such as heart attacks, strokes, and aneurysms.

It can also contribute to system-wide edema swelling. Potassium is present in a fold greater concentration inside the cell than outside the cell.

Chloride is important in acid—base balance in the extracellular space and has other functions, such as in the stomach, where it combines with hydrogen ions in the stomach lumen to form hydrochloric acid, aiding digestion. Practice Exam Questions. Under this category, we will describe the reabsorption of useful materials back into the blood. Reabsorption of glucose, amino acids, vitamins, hormones, chlorides, sodium, potassium, and much water are reabsorbed here.

These are reabsorbed by active and passive transport. Water reabsorption occurs by osmosis. Here the filtrate is isotonic to the blood plasma. Loop of Henle: This part of the loop of Henle consists of its ascending and descending limb. After passing through the PCT, filtrate enters the loop of Henle. Descending limb of the loop of Henle : Here water is reabsorbed when filtrate moves down the loop of Henle and not the solutes like sodium.

This makes the filtrate hypertonic to the blood plasma. Ascending limb of the loop of Henle : Here solutes like sodium, potassium, magnesium, calcium, chloride are reabsorbed. This makes the filtrate hypotonic to the blood plasma. Distal Convoluted Tubule DCT : In this part of the nephron, under the influence of the aldosterone hormone secreted by the cortex of the adrenal gland, sodium ions are reabsorbed.

Under the influence of ADH, water reabsorption occurs here. Chloride ions are reabsorbed too. Again here, filtrate becomes isotonic to the blood plasma. Here more water is reabsorbed under the influence of ADH, which makes the filtrate more concentrated and hypertonic to the blood plasma.

Sodium ions are also reabsorbed. This concentrated filtrate is now called urine. In the renal tubule, with reabsorption, secretion also occurs. Secretion of harmful toxic materials like ammonia, creatinine, urea, hippuric acid, drugs, etc. Mostly, secretion occurs in DCT. Some secretions also occur in the loop of Henle and DCT.

Urea is secreted in the loop of Henle, while in DCT, potassium, ammonia is reabsorbed. Kidneys not only excrete harmful substances out from the body but also maintain the amount of water and salt in the body. Then in the ascending loop of Henle, the filtrate gets hypotonic to the blood plasma. Then again, in DCT, due to the action of aldosterone and ADH, the filtrate becomes isotonic as sodium ions and water are reabsorbed by them, respectively. In the collecting duct, further reabsorption of water takes place which makes filtrate more hypertonic.

Now this filtrate is called urine. This unique mechanism of the nephron helps in making the urine concentrated. In the limbs of the loop of Henle, filtrate flows in the opposite direction, which forms the counter current. The flow of blood in capillaries surrounding the loop of Henle is also in the opposite direction and forms a counter current.

Its function is to increase the concentration of sodium ions in the interstitial fluid and concentrate the filtrate in the collecting duct by allowing more reabsorption of water from it. This concentrates urine. Urine formed in the kidneys comes down to the urinary bladder through ureters and then is expelled out of the body. This expulsion is called micturition.

Diluted urine is excreted in larger volumes a condition called diuresis. Glucose, urea, mannitol and other diuretic substances are administered to such patients. The kidneys excrete these substances and water is automatically excreted out with these.

Caffeine of tea is also diuretic. That is why, urination becomes more frequent when more tea is taken. Contrarily, If secretion of ADH is permanently hampered or blocked in a patient, the urine becomes very dilute and tasteless insipid. This condition is called diabetes insipidus. Intermittent urination at short intervals and thirst are the only discomforts in this condition.

Concentration mechanism Juxtamedullary nephrons During times of low water intake or excessive water loss, for example, due to heavy perspiration, diarrhoea, vomiting, etc the kidneys must conserve water while still eliminating wastes and excess ions.

The kidneys accomplish this by producing concentrated urine. Welcome Back. Continue with Google. Continue with Facebook. Forgot Password? New User? Sign Up. Create your account now. Signup with Email. Gender Male Female. Create Account. Already Have an Account?

The glomerular-capsular membrane through which ultrafiltration occurs comprises three layers, viz 1 endothelium 2 basement membrane of the wall of glomerular capillaries and 3 squamous epithelial layer of the finger-like processes 'foot processes' or pedicels of podocyte cells of capsular wall entwining the walls of capillaries. The effective filtration pressure that causes ultrafiltration is determined by three pressures : 1 glomerular hydrostatic pressure, 2 colloid osmotic pressure of blood and 3 capsular hydrostatic pressure.

This exchange involves 1 a selective reabsorption of useful materials into the the blood from the filtrate and 2 Absorption of remaining unfiltered amount of excretory substance from blood flowing in the peritubular capillaries, by the cells of uriniferous tubules and then subsequent secretion of these substances into the filtrate. Use Coupon Code. Sushil Kumar. Biology Class Join Course.

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