Excretory Products and their Elimination Test 14

The bowman's capsule has a tuft of capillaries having the diffrent diameter at their opening which creates a hydrostatic pressure, which helps in the ultrafiltration which pushes the blood plasma into the kidney tubules through intervening epithelial and basement membranes that act as a filter. The filtrate, which is the primary urine, is almost identical to blood plasma in its composition, except that it lacks high-molecular-weight solutes such as plasma proteins.

Nitrogenous wastes include ammonia, uric acid, and urea. Some aquatic animals excrete ammonia into the surrounding water before it can build up to toxic concentrations in their tissues. A few terrestrial animals, including some snails and wood lice, vent it directly into the air. But many animals, humans included, convert ammonia to some less toxic nitrogenous waste such as uric acid or urea. Uric acid is produced both from ammonia and by the break down of nucleotides from nucleic acids. Uric acid is insoluble in water and forms crystals that are excreted as a crystalline paste, so little fluid loss results. This is an important water-conserving adaptation in many terrestrial animals, including insects, certain reptiles, and birds. Urea, the principal nitrogenous waste product of amphibians and mammals, is synthesized in the liver from ammonia and carbon dioxide by a sequence of reactions known as the urea cycle. Urea is the major excretory substance in urine of mammals.

Correct option: A

A comparison of the volume of the filtrate formed per day (180 liters per day) with that of the urine released (1.5 liters) suggest that nearly 99 per cent of the filtrate has to be reabsorbed by the renal tubules. This process is called reabsorption. The tubular epithelial cells in different segments of nephron perform this either by active or passive mechanisms. For example, substances like glucose, amino acids, Na+, etc., in the filtrate are reabsorbed actively whereas the nitrogenous wastes are absorbed by passive transport. Reabsorption of water also occurs passively in the initial segments of the nephron.

Urine is mainly formed in the kidney. The amino acid is deaminated to form urea in the liver by ornithine cycle which is further filtered by the kidney. Urine is formed by the following three steps namely, glomerular filtration, reabsorption, and secretion, that takes place in different parts of the nephron. The first step in urine formation is the filtration of blood, which is carried out by the glomerulus and is called glomerular filtration. The tubular epithelial cells in different segments of nephron perform absorption (reabsorption) either by active or passive mechanisms. Tubular secretion is also an important step in urine formation as it helps in the maintenance of an ionic and acid-base balance of body fluids.

A. A loop of Henle- The loop of Henle helps to produce concentrated urine, by reducing the volume of water and solutes within the urine but without changing the concentration by using a counter current multiplier.
B. Rental artery- Each kidney receives its blood supply from a single renal artery from dorsal aorta and is drained off by a single renal vein, which opens into the inferior vena cava.
C. Proximal convoluted tubule- The epithelial cells of this region are specialized for transport of salts and other substances from the lumen to the interstitial fluid. The tubule lumen has numerous microvilli (Brush Borders) which increase the surface area for absorption. Also near its basolateral surface, the mitochondria are concentrated, to allow reabsorption of salts by active transport.
D. Glomerulus- Within the bowman's capsule, a tuft of capillaries is present, which is called as the glomerulus. The diameter of afferent arteriole bringing the blood into the glomerulus is greater than efferent arteriole, which takes away the blood from glomerulus. This builds up pressure within the glomerulus resulting into ultrafiltration through the fenestrated endothelium of glomerular capillaries.
E. Distal convoluted tubule - $${Na^{+}}$$ ions and $${H_{2}O}$$ is reabsorbed under the influence of hormone in DCT along with which Urea, uric acid creatine hippuric secreted into the tubule.

Collecting ducts can be traced in medullary pyramids. The reabsorption of the collecting duct is regulated by ADH and the hormones of adrenal cortex. These are long tubules which traverse through the medulla in the pyramids and open in the papilla of the medulla (in rabbit) or papilla of the individual medullary pyramid (in human). Several adjacent collecting ducts converge to open into a common short and thick duct of Bellini (present in papilla of medulla). All ducts of Bellini then open at the tip of the papillae into the pelvis.

"Uriniferous tubule" or "nephron" are the structural and functional unit of kidney. It is present in the outer firm region of kidney, the renal cortex. It consist of renal corpuscle and a long renal tubule. 

Nitrogenous wastes include ammonia, uric acid, and urea. The amino acids and nucleic acids contain nitrogen. During the metabolism of amino acids, the nitrogen-containing amino group is removed (in a process known as deamination) and converted to ammonia. Urea, the principal nitrogenous waste product of amphibians and mammals, is synthesised in the liver from ammonia and carbon dioxide by a sequence of reactions, known as the urea cycle.