kidney

• The kidney consists of two kidneys, two ureters, urinary bladder and urethra.
• The functions of kidneys include excretion of waste products, homeostatic function, and endocrine function.
• The nephron is the structural and functional unit of kidney, each kidney contains one million nephron, and it consists of the glomerulus and renal tubules.
• The glomerulus consists of glomerular capillaries and Bowman’s capsule, they arise from afferent arteriole and drain into the efferent arteriole.
• The renal tubules consist of proximal convoluted tubule (PCT), loop of Henle (LH), distal convoluted tubule (DCT), and collecting duct.
• Urine passes from the collecting duct to the ureter and finally to the urinary bladder.
• Glomerular filtration is the process where plasma is filtered through pores of capillaries to Bowman’s capsule, the filtered fluid is called glomerular filtrate, it contains all constituents of the blood except blood cells and plasma proteins because they are larger than the pores.
• Glomerular filtration rate (GFR) is the volume of fluid filtered by glomerular capillaries/minute, it equals 125 ml/minute (180 L/day), and renal tubules reabsorb 99% of the filtrate and the remaining 1% is excreted as urine.
• Renal tubular reabsorption is the process by which essential substances pass from tubular filtrate to peritubular capillaries (H2O, glucose, Na+ & Ca++).
• Renal tubular secretion is the process by which harmful substances pass from peritubular capillaries to tubular filtrate (urea, H+, NH3, drugs).
• Filling of bladder with urine, stimulation of bladder receptors, micturition centre, contraction of bladder wall and relaxation of internal sphincter, evacuation of the bladder are the steps involved in micturition reflex.
• Micturition reflex is involuntary in infants and with growth, cerebral cortex acquires control on micturition reflex.
• In adult, cerebral cortex can inhibit the reflex if the conditions are unsuitable and can facilitate it if the conditions are suitable.
• Micturition reflex is a process that starts when the wall of urinary bladder contains receptors which sense bladder distension, then send signals to micturition centre in the spinal cord (S2,3,4).
• Micturition is the natural evacuation of bladder through urethra.
• Renal failure is due to reduction in number of working nephrons leading to accumulation of waste products, these toxic substances can be removed by dialysing the blood in a machine called artificial kidney (hemodialyser) in a process called hemodialysis.
• Normal pH of blood is 7.4, pH ˃ 7 is considered alkalosis, pH ˂ 7 is considered acidosis.
• Glucosuria is the presence of increased amounts of glucose in urine.
• Renal failure is the inability to remove waste products from blood, as long as about half of one kidney remains functional, survival is possible.
• Normal metabolism of body releases waste products which cause blood pH to decrease, blood pH is kept constant by chemical buffers, respiratory system, and kidneys.
• Glucosuria can occur in Diabetes mellitus due to increased blood glucose level, and in Renal glucosuria due to decreased number of carrier for glucose in the kidney.
• There are two sphincters around the inlet of urethra: Internal urethral sphincter, made of smooth muscle fibers, its contraction is involuntary, and External urethral sphincter, made of striated muscle fibers, its contraction is voluntary.
• Excreation of waste products includes removal of toxins or waste products
• 1. Homeostatic function:Regulation of water.b- Regulation of acid-base balance
• Endocrine Functiona- Secretion of erythropoietin.b- Production of active vit D3
• 1-Glomerulus 2-Bowman's capsule

  
• Steps of formation of urine 1-Glomerular Filtration 2Tubular reabsorption 3-Tubular secreation