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Excretory Products and their Elimination, , , , , , ‘The component structural and functional units of the bodies of, all organism are cells which have been looked as "miniature, chemical factories" because of continuous metabolism taking place, in these. It yields certain waste products which are, not only, useless, but harmful to the cells and the body. Cells, therefore,, throw out these wastes, by diffusion, into their surrounding, medium. Finally, these wastes are eliminated by the body into its, external environment. This is, thus an important vital activity of all, ‘organism. It is called excretion,, , Excretory organs of different organism, , (1) Protozoans : In protozoans like Amoeba and Paramecium, carbon dioxide and ammonia are mostly excreted out by diffusion, through general body surface. It is considered that the contractile, vacuoles also play some role in the removal of excretory products., , (2) Sponges : In sponges, the nitrogenous metabolic waste, (ammonia) leaves the body in the outgoing water current by, diffusion,, , Most of the sponges are marine and have no problem of, surplus water in their cells. A few sponges lie in hypotonic fresh, water and have contractile vacuoles in most of their cells., , Network of, spongiome tubules, Spongiome 2, tubules Bes sf, sper, , , , ag’ ¢, DED > Zz — Spongiome, fed f ., xy ie ft ‘5 Tubules and vesicles, , ‘Spongiome vesicles Te, Fig: 5.4-1 Contractile vacuole in sponge, , (3) Coelenterates : Hydra also lacks special excretory, ongans. The nitrogenous waste products like ammonia are, removed through the general surface of the body by diffusion., Some nitrogenous waste products are also thrown along with, indigestible matter through the mouth., , (4) Platyhelminthes = Planaria, liverfluke and tapeworm, Possess a large number of excretory cells called the flame cells, (solenocytes) or protonephridia and long excretory ducts (also, called canals of vessels). The flame cells open into the ductules, which in tum open into the excretory duct., , Nucleus, , , , , ‘Cell body or flame bulb, , Flagella, Intracellular canaliculus, , a) excretory capillary, , ‘Globules of excretion, ‘Basal granules, , , , , , (a) Fasciola (b) Pla

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882 Excretory Products and their Elimination, , , , , , (5) Nematoda : The round worms such as Ascaris have Hshaped excretory system. It is made up of a single Renette cell, in, entire length of body. It consists of two longitudinal excretory, canals connected anteriorly by a network of transverse canals. A, short terminal duct opens outside via excretory pore. Ascaris, excretes both amnionia and urea., , , , Excretory pore, Terminal duct me, , , , , , , , , Posterior lateral, longitudinal excretory canals, , Fig : 5.4-3 Renette cell of Ascaris, , (6) Annelids (Earthworm) : In earthworm excretory system, is known as nephridial system, which consist of 3 types of nephridia, pharyngeal, septal, and integumentary nephridia. All nephridia, commonly called micronephridia. Earthworm excrete 40% urea,, 20% ammonia, 40% amino acids, Earthworm is mainly ureotelic., Chloragoaen cells found in coelomic fluid are also excretory in, nature. Blood gland in earthworm found in 4, 5, 6 segment, serves, for excretion, manufacture of blood corpuscles and Hb., , Ducts of pharyngeal nephridia, , Blood glands, Pharyngeal nephridia, , Oesophagus, Gizard, , Integumentary nephridia, , Stomach, , Septal nephridia, , Intestine, , Fig: 5.4-4 Various types of nephridia and their, arrangement in Pheretima, (7) Arthropods : The excretory system of the adult Prawn, (crustacean) consists of a pair of antennary or green glands, a pair, of lateral ducts and a single renal sac., , Insects, centipedes, millipedes and arachnids like scorpion and, spider posses Malpighian tubules as their principal excretory organs., In the Malpighian tubules bicarbonates of potassium and sodium,, water and uric acid are formed. A large amount of water and, bicarbonates of potassium and sodium are reabsorbed by the cells, ‘of Malpighian tubules and then transferred to the blood, (haemolymph). Uric acid is carried to the alimentary canal of the, insect and is finally passed out through anus. Spiders and scorpions, ‘possess Malpighian tubules and coxal glands both for excretion., Renal, , , , pores Bladder, , Lateral duct, Transverse connective, , Renal sac, , eae, (a), Saccule, corvessicle Labyrinth, , Diaphragm, , , , , , , , Excretory pore, (b), , Fig : 5.4-5 (a) Antennary gland of Prawn, (b) Coxal gland of Scorpion, , (8) Molluses : They have one or two pairs of kidneys or, ‘organs of bojanus and keber's organ for excretion in unio., , Afferent renal vei, , , , JY) Posterior el chamber, Efferent renal vein, , Anterior renal sinus“, ‘Aperture into posteriot / =, renal chamber be, , Reno-pericardial aperture ahs ~ 3, Pericardium “Aortic ampulla, Ventricle, , Fig : 5.4-6 Organ of Bojanus (Pila ~ mollusca)

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Excretory products in different organisms, , (1) Waste products of protein metabolism, , {i) Amino acids : These are end products of protein, digestion absorbed into the blood from small intestine, Certain, invertebrates, like some molluscs (eg Unio, Limnae, etc.) and some, echinoderms (eg Asterias) excrete excess amino acids as such. This, is called aminotelic excretion or aminotelism., , {ii) Ammonia (NH; orNHg) : In most animals, excess amino, acids are deaminated, i.e. degraded into their keto and ammonia, groups. The keto groups are used in catabolism for producing ATP,, whereas ammonia is excreted as such or in other forms. Ammonia, is highly toxic and highly soluble in water. Its excretion as such,, therefore, requires a large amount of water. That is why, most of, the aquatic arthropods, bony and freshwater fishes, amphibian, tadpoles, turtles, ete excrete ammonia. This type of excretion is, called ammonotelic excretion or ammonotelism., , (ii) Urea CO (NH), This is less toxic and less soluble in, water than ammonia, Hence, it can stay for some time in the body., Many land vertebrates (adult amphibians, mammals) and such, aquatic animals which cannot afford to lose much water (eg., clasmobranch fishes) marine bony fish, adult frog, earthworms,, nematodes, turn their ammonia into urea for excretion. This type, of excretion is called urectelic excretion or ureotelism., , (iv) Uric acid : Animals living in dry conditions, such as land, gastropods, most insects, land reptiles (snakes and lizards), birds, and Kangaroo rat (mammal) etc have to conserve water in thelr, bodies. These, therefore, systhesize crystals of uric acid from their, ammonia, For the formation of uric acid xanthine oxidase enzyme, is necessary. Uric acid crystals are nontoxic and almost insoluble in, water. Hence, these can be retained in the body for a considerable, time before being discharged from the body. Uric acid is the main, nitrogenous excretory product discharged in solid form. This, excretion is called uricotelic excretion or uricotelism., , (v) Trimethylamine oxide : Certain marine molluscs,, crustaceans and teleost fishes first form trimethylamine from their, ammonia by a process known as methylation. Then, the, trimethylamine is oxidised to trimethylamine oxide for, excretion. This oxide is soluble in water, but nontoxic., , (vi) Guanine : Spiders typically excrete their ammonia in the, form of guanine. Some guanine is also formed in unio, penguin,, birds and it is insoluble in water. Hence, no water is required for its, excretion., , (2) Waste products of nucleic acid metabolism, , ‘Asa result of nucleic acid digestion, nitrogenous organic bases, = purines (adenine and guanine) and pyrimidines (cytosine,, thymine and uracil) ~ are absorbed from intestine into the blood., Most of these are excreted out. About 5% of the total excretion of, body accounts for these substances, In man, purines are changed, to uric acid for excretion. In most other mammals, nitrogenous, organic bases are excreted in the form of allantoin. Insects,, amphibians, reptiles and birds also excrete these bases in the form, of utic acid. Some freshwater molluscs and crustacean arthropods, excrete these in the form of ammonia,, , , , 884 Excretory Products and their Elimination, , J, , (3) Some sundry excretory substances (Others, , excretory products), , () Hippuric and ornithuric acids : Sometimes food of, rabbit and other mammals may contain traces of benzoic acid, or, this acid may be formed in small amounts during fat metabolism. It, is highly toxic. As it is absorbed in blood, it Is combined with, alycine and changed into less toxic hippuric acid for excretion. In, birds, benzoic acid is combined with omithine and changed into, ornithuric acid for excretion., , (ii) Creatine and creatinine : Muscle cells contain, molecules of creatine phosphate, which are high energy molecules, and serve for storage of bioenergy like ATP. It is synthesised by 3, amino acids (G.A.M,) (Glycine, Argenine and Methionine). Excess, amount of this phosphate is, however, excreted out as such, or, afier being changed into creatinine., , Excretory system of man, , Mammalian (human) urinary system consists of a pair of, kidneys, a pair of ureter, a urinary bladder and a urethra., , (1) Kidneys : The kidneys are dark-red, bean-shaped organs, about 11 cm long, 5 em wide and 3.cm thick, each weight about, 150 gm in an adult male and about 135 gm in adult female. They, are placed against the back wall of the abdominal cavity just below, the diaphragm, one on either side opposite the last thoracic and, first three lumbar vertebrae. The 11* and 12" pairs of ribs protect, them., , Inferior vena cava Dorsal aorta, , , , Fig : 5.4-7 Human urinary system, , The kidneys are covered by peritoneum on the front (ventral), side only. thus, they are retroperitoneal. The right kidney is, attached more anterior than the left in rabbit. This asymmetry is, just the reverse of that found in man., , In man left kidney occurs at a slightly higher level than the, right one, because right side has prominent right liver lobe. In, rabbit the condition is litle differ due to quadropedilism ie. left, kidney is in normal position while the right kidney shift ahead to, provide place for stomach below it.

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In mammals, the kidney is concavo convex. The center of, concave inner surface is called as hilum or hilus which gives out a, ureter. From this hilus surface the renal artery enters into the kidney,, the renal vein comes out and the renal nerves enter into the kidney., , (i) Structure of kidney : The kidneys are metanephric in, mammals, The kidney is divisible into two parts outer-cortex and, inner-medulla. Three layers of tissue surround each kidney., , (a) The innermost, renal capsule made up of fibrous, connective tissue,, , (b) The intermediate layer, adipose capsule of fatty tissue., , (c) The outermost, renal fascia of dense connective tissue., , Renal pyramids or medullary pyramids : The medulla is, subdivided into 8 to 18 conical masses ~ the renal pyramid, each, having broad base towards the cortex and a narrow end called, renal papilla towards the pelvis,, , Nephron, Collecting duct, , Papillary duct in, , renal pyramid, , Minor calyx., , , , , , , , , , , , Renal cortex, Renal medulla”, , , , Renal papills, Fat in renal sinus Ureter, Renal capsule—, Urinary bladder, , Fig : §.4-8 LS. of human kidney, , Path of urinary drainage : Collecting duct — Papillary duct, in renal pyramid + Minor calyx —> Major calyx —> Renal pelvis >, Ureter + Urinary bladder, , Renal columns of bertini : Between the pyramids, the, cortex extends into the medulla or renal columns of bertini., , Calyx : Each renal papilla projects into the cavity of a minor, calyx, minor calyx join to form major calyx. The major calyx open, into a wide funnel like structure, the pelvis. The latter leads into the, ureter. In rabbit, the pelvis is unbranched hence, itis without calyx., , In frog ventral surface of each kidney has many ciliated, funnels called nephrostomes. They drain wastes from body cavity, {coelom) and connect to renal veins in frog or to uriniferous, tubules in tadpoles, , (il) Histology of kidney : Histologically a kidney is made of, innumerable thin, long, much convoluted tubular units called, uriniferous tubule or nephron,, , Nephron is the structural and functional unit of kidney. One, human kidney may contain about one million (10 lac nephron), nephron (In rabbit each kidney bear about 2 lac nephron). In frog, each kidney bears about 2 thousand nephron., , (a) Structure of nephron : A nephron or uriniferous tubules, consist of two parts, , Excretory Products and their Elimination 885., , , , Malpighian body / Renal Corpuscles : The proximal end, of each nephron forms a blind or closed, enlarged and double, walled cup, the Bowman's:capsules in the cortex. (name Bowman's, capsule is based on English physiologist and histologist William, Bowman)., , Each capsule contains a network of blood capillaries the, glomerulus which receives blood through afferent arteriole and the, blood comes out through the efferent arteriole .The diameter of the, efferent arteriole is comparatively lesser. Bowman's capsule and, glomerulus receives about 20 ~ 25% of the cardiac out put (blood), at rest, , ‘The composite structure of Bowman's capsule and glomerulus, is known as Malpighian body or Malpighian corpuscles after the, Traian microscopst Mareello Malpighi., , Tubule : The tubule is differentiated into 3 parts P.C.T.,, Henle's loop and D.C.T., , ‘The Bowman's capsule opens into a proximal convoluted, tubule (P.C.T.) the anterior part of the P.C.T. is more coiled where, as its posterior part is almost straight. The P.C.T. opens into a, Henle’s loop. The Henle’s loop is a U- shaped structure or makes, hair pin turn, which has a distinct descending limb and an ascending, limb. The ascending limb opens into the distal convoluted tubule., The D.CT. is a coiled structure. Many D.C.T. unite to form a, collecting duct. The collecting ducts of one pyramid unite to form a, duct of Bellini. The duct of Bellini lead into the pelvis part., , (b) Arrangement of nephron : The malpighian body and, most of the P.C.T. and D.C.T. are situated in the cortex. Henle's, loop and collecting ducts are found in the medulla., , , , Distal convoluted tubule __Renal capsule, , , , , , , Peritubular, Capillary net work, , Renal cortex, , , , , Conta!, Vasa recta FRAY fa nephron, Branch of renal uxtaglomerular, artery | nepiron, Pyramid of, Branch ofa vein fenal medulla, Collect, Thick segment of Blecing, ‘econtin Web ol J ], henles Io, are =< J __ “Branch of eolectng, Vasa recta” 7 tbl, Duct of bei, Thin segment of ascoing fe eect iri, , limb of henie's loop, Descending limb of, henle'sloop Pelvis, , Fig : 5.4-9 Position, structure and blood supply of cortical and, juxtamedullary nephrons in. a mammalian kidney, , , , Renal papilla