K.C.S.E Biology Q & A - MODEL 2006PP2QN07
Describe how human kidney functions
The afferent arteriole which is the branch of renal artery supplies blood to glomerulus; The afferent arteriole has a wider diameter than the afferent arteriole; this causes high pressure; leading to ultra filtration. The walls of the blood capillaries are one cell thick hence glucose, amino acids, (vitamins, hormones) salts, (creatinine) urea and water filter into Bowman’s Capsule to form glomerular filtrate; White blood cells/ red blood cells and plasma proteins such as (Globulin, fibrinogen, platelets) are too large to pass through the capillaries: the filtrate flow into the proximal convoluted tubule; where amino acids (vitamin) and all glucose are selectively reabsorbs back into the blood stream. Many mitochondria provides energy for re- absorption of these substances against concentration gradient/ by active transport. The Glomerular filtrate flow into loop of henle. Water in descending loop moves by osmosis into the blood capillaries; sodium chloride is actively pumped from the ascending arm of loop henle into the blood capillaries. The glomerular filtrate flow into the distal convoluted tubule, water is absorbed from distal convoluted tubule into blood capillaries; the glomerular filtrate flows into collection tube/ duct from where more water is reabsorbed into the blood stream.
Antidiuretic hormone influences the amount of water reabsorbed ( depending on osmotic pressure of blood); The glomerular filtrate from collecting duct now referred to as urine; is emptied into pelvis. The urine passes though pelvis and ureter into bladder out of the body through urethra.