Excretory Products and Excretory Structures
* Carbon dioxide, ammonia, urea, uric acid, water and excess ions like phosphate, sulphate, sodium, potassium and chloride are some of the excretory products produced in our body.
* The process of elimination of metabolic waste products from the animal body is called excretion.
* Ammonia-excreting animals are called ammonotelic animals and the process is called ammonotelism.
* Excretion in the form of urea is called ureotelism and such animals are called ureotelic animals.
* Animals excreting nitrogenous wastes in the form of uric acid are called uricotelic animals and the process is called uricotelism.
* In mammals, apart from the kidneys, which are the main excretory organs, the skin, liver and lungs also help in excretion.
Human Excretory System
* The human excretory system consists of a pair of kidneys, a pair of ureter, a urinary bladder and the urethra.
* The kidneys are compact, bean-shaped organs on either side of the spinal cord in the lower back.
* Nephrons are the functional units of a kidney.
* Ureters carry urine from the renal pelvis of the kidneys to the urinary bladder.
* The urinary bladder temporarily stores urine till it is released from the body.
* Urine leaves the urinary bladder via the urethra.
Urine Formation
* Urine formation involves three major processes, namely glomerular filtration, reabsorption and secretion.
* The first step in urine formation is filtration of blood, which occurs in the glomerulus.
* The amount of filtrate formed in Bowman’s capsule every minute is called the glomerular filtration rate.
* About 99 percent of the filtrate is absorbed during the process of reabsorption.
* Tubular secretion maintains the ionic and acid base balance of body fluids by secreting ions and ammonia back into the distal convoluted tubule and passing it to the collecting duct.
Kidney Function- Regulation and Disorders
* The hormone feedback mechanisms of the hypothalamus, JGA and heart regulate the functioning of the kidneys.
* The process of disposing urine is called micturition and the mechanism responsible for the process is known as the micturition reflex.
* A urine test helps to diagnose many metabolic disorders in the body and any malfunction in the kidneys.
* Malfunctioning of the kidneys can cause diseases like uremia, renal calculi and glomerulonephritis.
* A life-saving process for uremic patients is hemodialysis, where excess urea in the blood is removed.