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The kidney is supplied by blood by renal artery,a branch of aorta.The blood is at a high pressure; The unit of excretion is the nephron.Each nephron consists of a cup shaped renal capsule/Bowman's capsule; arteriole(branch of renal artery) the afferent vessels;enters the depression of the renal/Bowman's capsule and breaks into a network of capillaries of glomerulus;blood leaves the glomerulus by an efferent vessel;whose diameter is narrower than that of a blood vessel that enters glomerulus. Narrow diameter of capillaries;further ensures blood flows through capillaries at a high pressure. This brings about pressure/ultrafiltration; water and all dissolved substance;glucose,amino acids, mineral salts and urea diffuse out of endothelium of capillary through the many tiny pores to form glomerula filtrate;blood proteins and red blood cells are too large to pass through hence blood leaving of glomerulus in efferent vessel as it breaks into capillaries that surround the renal/convoluted tubule.
Glomerula filtrate passes through the wall of renal(Bowman's capsule)into capsular space;pores in wall of Bowman's capsule allow for passage of glomerula filtrates;As the filtrate flows through the first part that is proximal convoluted tubule where reabsorption of all glucose,all amino acids;vitamins,hormones,water and mineral salts into capillary surrounding tubule takes place.The much branched tubule provides a large surface area to reabsorption ;wall of renal tubule has to allow for diffusion of particles;and many mitochondria for respiration to provide energy for active transport which is also involved in movement of glucose and amino acids into blood.Presence of microvilli increase surface for reabsorption .From the proximal convoluted tubule filtrate flows through the U-shaped loop of Henle ;with ascending and descending limb through which water and mineral salts are reabsorbed ;As filtrate flows in descending limb mineral salts are actively removed and concentrated in ascending limb;This ensures that a concentration gradient us maintained; for reabsorption of water along the loop.In this way the loop of Henle acts as a counter-current multiplier;the longer the loop,the more the water reabsorbed. From the loop of Henle the fluid passes through the distal convoluted tubule which is coiled to ensure slow movement of fluid.Here,reabsorption of water takes place fluid in tubule has less water,mineral salts and a lot of urea;it flows through collecting duct to pelvis of kidney and into bladder from where its excreted as urine.
Belan answered the question on February 24, 2019 at 09:10
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