Animal Physiology How is water handled in the urinary system

Animal Physiology

How is water handled in the urinary system? start with the glomerulus and end with urine. Include all volumes

How is sodium handled in the urinary system? start with the glomerulus and end with urine.

How is glucose handled in the urinary system? start with the glomerulus and end with urine.

Solution

The step in making urine is to separate the plasma of blood from the blood cells.The process takes place in the glomerulus of the nephron of kidney.Blood enters the glomerulus by afferent arteriole and leaves the glomerulus through efferent arteriole at a low pressure.While in the glomerulus,the blood is filtered in the capillaries.The capillaries do not allow proteins and blood cells to filter out while the plasma contents i.e water, ions such as Na,K,Cl,HCO3-, glucose,aminoacids and small proteins are filtered out.

Water: Water is filtered out of the glomerulus filtrate.The rate at which glomerulus filters the blood is called glomerular filtration rate.The outward pressure of the blood as it enters the glomerulus is counteracted by inward pressure due to the hydrostatic pressure of the fluid within the urinary space.The pressure generated by the proteins left in the capillaries pull water back into the circulatory system and this pressure is known as colloidal osmotic pressure. The net filtration pressure is given as : outward pressure minus the inward pressure and this helps to remove water from the glomerulus.The water that comes out is again reabsorbed along the tubules of the nephron i.e in proximal convoluted tubule via osmosis,in the loop of henle and in collecting duct via ADH hormone regulation.The remaining is excreted as urine. It has ben estimated that 180 litres of water enters the glomerulus per day and out of that 178-179 litres is reabsorbed while 1-2 litres comes out in urine.

Sodium:Sodium is filtered out of the glomerulus filtrate.As the sodium ions comes out of the glomerulus,they are reabsorbed along the entire length of the tubules of nephron.65% of reabsorption takes place in the proximal tubules via isosmosis,25% of reabsorption takes place in the loop of henle via sodium-potassium-chloride symporter ,5% of reabsorption takes place in distal tubules via sodium chloride symporter and 5% of reabsorption takes place in the collecting tubules via hormone aldosterone regulation.The rest excess sodium is excreted out in the urine.It has ben estimated that 579 g of sodium ions enter the glomerulus per day and out of that 575 g is reabsorbed while 2-4 g comes out in urine.

Glucose:Glucose is filtered out of the glomerulus filtrate.As the glucose comes out of the glomerulus, they are reabsorbed along the tubules of the nephron.The reabsorption of glucose takes place in the proximal convoluted tubules and this is 100%.The reabsorption takes both passively and actively via sodium glucose transport proteins and glucose transporters.Therefore no glucose should be present in urine under normal conditions.It has ben estimated that 162 g of glucose enters the glomerulus per day and entire 162 g is reabsorbed and so no glucose comes out in urine.