Presentation on theme: "Excretion of Nitrogenous Waste"— Presentation transcript:
1Excretion of Nitrogenous Waste WALTTo recap types of nitrogenous wasteTo identify the ultrastructure of the kidneyTo explain ultrafiltration
2Some definitions..Excretion is the process by which waste products of the organism’s metabolism are eliminated from the body.Secretion is the production by the cells substances useful to the body.Egestion is the removal of undigested food & other substances which have never been involved in metabolism.
3Excretory ProductsThere are three main waste products of nitrogenous metabolism:AmmoniaUreaUric acid
4AmmoniaAmmonia is derived from the breakdown of proteins and nucleic acids in the body.It is very toxic and is never allowed to accumulate within the body tissues or fluids.It is extremely soluble and diffuses readily across cell membranes.It is the main excretory product of marine invertebrates & all fresh water animals.
5Uric AcidThe synthesis of uric acid spends more energy than urea, but it is advantageous to many animals.It is insoluble, non-toxic and requires very little water for its removal from the body -- a suitable product for animals in desert places.
6Urea Carbon dioxide + ammonia urea + water CO NH3 (NH2) 2CO + H2OUrea is produced by the ornithine cycle with expenditure of some energy.It is much less toxic than ammonia, less water is needed for its elimination because the tissues can tolerate higher concentrations of it.
7The Mammalian Kidney The kidney has two main functions: It removes metabolic waste from the body through the process of excretion as urineIt regulates the water and ion content of the blood. This keeps the water potential of the blood constant.
12The functions of the kidney Ultrafiltration – filtering blood unbder pressureSelective reabsorption – reabsorbing the useful substancesProduction of an ion gradient in the medulla – to allow production of hypertonic urine if necessaryAdjustment of the water and ion content of the blood – to maintain homestasis
13The Structure of the kidney Each kidney is made of millions of tiny tubules called nephrons, each of which consists of a Bowman's capsule and a uriniferous tubule joining to a collecting duct.A branch of the renal artery enters the Bowman's capsule as the glomerulus, then splits up into capillaries which spread out and wrap around the tubule. Finally, these capillaries join up to the renal vein.
19Cells of Bowman's capsule There are inner podocytes and outer squamous epitheliumThe glomerular filtrate contains water, amino acids, glucose, minerals and urea; blood cells & proteins are too large to pass throughUltrafiltration is a passive process and selection of substances passing from the blood into the glomerular filtrate is made entirely according to the relative molecular mass
20Cells of Bowman's capsule The walls of the glomerulus have 3 layers:The inner layer of flat endothelial cells that make the capillary walls.The basement membrane of the capillariesThe podocytes of the Bowmans capsule: