Tag: regulation of urine formation

About $0-80%$ of the glomerular filtrate is reabosrbed in the proximal convoluted tubule (PCT). Glucose, amino acids, vitamins, hormones, sodium, potassium, chlorides, phosphates, bicarbonates, much of water and some urea are reabsorbed from the filtrate. 

A comparison of the volume of the filtrate formed per day ($180$ litres per day) with that of the urine released ($%1.5$ litres). suggests that nearly $99%$ of the filtrate is reabsorbed by the renal tubules into the blood. 

The main driving force favouring fluid filtration from the glomerular capillary to Bowman's space is glomerular capillary blood pressure($P _{GC}$). 

Antidiuretic hormone (ADH) is a hormone that helps your kidneys manage the amount of water in your body. 

Tubular reabsorption is the process by which solutes and water are removed from the tubular fluid and transported into the blood. It is called reabsorption. Reabsorption is a two-step process beginning with the active or passive extraction of substances from the tubule fluid into the renal interstitium, and then the transport of these substances from the interstitium into the bloodstream. These transport processes are driven by Starling forces, diffusion, and active transport. Some key regulatory hormones for reabsorption include: aldosterone, which stimulates active sodium reabsorption; antidiuretic hormone, which stimulates passive water reabsorption. Both hormones exert their effects principally on the collecting ducts.

ADH targets nephrons in the kidney to increase water reabsorption and thereby decreasing water content in urine. The inability of the neurohypophysial system to produce ADH causes excess urine production with resultant ion loss from the blood. This condition is known as diabetes insipidus (watery urine). This makes option A correct and option B incorrect. Since ADH regulates the urine volume, not its pH, option C is incorrect. Urochrome is the yellow pigment, derived from the breakdown of heme, which is deposited in blood and then is excreted by kidney with urine. This makes option D incorrect. The correct answer is A.

Juxtaglomerular cells are the specialized smooth muscle cells present in the walls of the afferent arterioles that go to the glomerulus. Their function is to produce an enzyme called renin when the osmolarity of blood changes. Renin converts angiotensin secreted by the liver into angiotensin$I$. This is later converted into angiotensin$II$ by an enzyme released by lungs. Angiotensin$II$ acts on adrenal glands to stimulate the release of aldosterone. Aldosterone helps in reabsorption of na+ and water from distal convoluted tubule and the concentration of Na$^+$ ions decreases in the filtrate. 

A fall in GFR can stimulate the JG cells to release renin which can stimulate the glomerular blood flow and thereby the GFR comes back to normal.