REGULATION OF KIDNEY FUNCTION :
Regulation by ADH :
- Osmoreceptors present in the hypothalamus are activated by the change of blood volume, body fluid volume and ionic concentration.
- An excessive loss of body fluid activates the Osmoreceptors of hypothalamus to release antidiuretic hormone (ADH) or vasopressin from the neurohypophysis.
- ADH facilitates active reabsorption of water from the DCT, preventing dieresis.
- An increase in body fluid volume can switch off the Osmoreceptors and suppress the release of ADH, promoting dilute urine formation.
- ADH also constricts the afferent renal arteriole in increase the blood pressure in the other hand to maintain the GFR.
Regulation by JGA (Juxta Glomerular Apparatus) :
- A fall in glomerular blood flow/glomerular blood pressure/GFR can activate the Juxta Glomerular cells to release renin.
- Renin converts angiotensinogen in blood to angiotensin I and further to angiotensin II.
- Angiotensin II constricts afferent renal arteriole to increase glomerular blood pressure and thereby GFR.
- Angiotensin II also stimulates adrenal cortex to release aldosterone.
- Aldosterone cause active reabsorption of Na+ and water from the distal part of the tubule, this increase in blood volume and GFR.
- This complex mechanism is called RAAS (Renin angiotensin aldosterone system).
Regulation by ANF :
- An increase in blood flow to the atria of the heart due RAAS cause the release of Atrial Natriuretic Factor (ANF).
- ANF can cause vasodilation (afferent renal arteriole) and thereby decrease the blood pressure.
- ANF also stop the release of renin hence stops RAAS.
MICTURITION :
- The expulsion of urine from the urinary bladder. It is a reflex process but can be controlled voluntarily to some extent in grown up children and adults.
- The CNS (Central Nervous System) sends the signal which causes the stretching of the urinary bladder when it gets filled with urine.
- In response, the stretch receptors on the walls of the bladder send signals to the CNS. The CNS passes on motor massage to initiate the contraction of smooth muscles of the bladder and simultaneous relaxation of the urethral sphincter causing the release of urine.
- An adult human excretes on an average 1 to 1.5 liters of urine per day.
- On an average 25-30 gram of urea is excreted out per day.
- Presence of Glucose is called Glycosuria.
- Presence of Ketone bodies in urine called Ketoneuria.
- Glycosuria and Ketoneuria are the indication of Diabetes mellitus.
Role of other organs in excretion :
- Lungs - removes CO2 (18L/day) and water.
- Liver - secretes bilirubin, biliverdin etc. helps to eliminate these substances along with cholesterol, vitamins, drugs and degraded steroid hormones through digestive wastes.
- Sweat and sebaceous glands - These glands of skin help to eliminate small amount of urea, NaCl and lactic acid etc. through sweat while sebaceous glands help to eliminate some substances like steroids, hydrocarbons and waxes through sebum.
- Saliva - It can help to eliminate small amount of nitrogenous wastes.
Disorders of Excretory system :
- Uremia - The accumulation of urea in blood due to malfunctioning of kidney.
- Hemodialysis - The process of removal of urea from the blood artificially. In this process the blood from an artery is passed into dialysing unit after adding an anticoagulant like heparin. The blood passes through coiled cellophane tube surrounding by dialysing fluid. The nitrogenous wastes from the concentration gradient and the blood become clear. This blood is pumped back to the body through vein after adding anti-heparin to it.
- Renal calculi - The formation of insoluble mass of crystallised salts (oxalates or phosphates of calcium.
- Glomerulonephritis - Inflammation of glomeruli of kidney.
