Excretory Products and their Elimination Test - 16

In mammals, urea is produced from ammonia in five enzymatic steps. The urea cycle begins inside liver mitochondria but three of the subsequent steps takes place in the cytosol; the cycle thus spans two cellular compartments. In the last reaction of the urea cycle, the cytosolic enzyme arginase cleaves arginine to yield urea and ornithine. Ornithine is transported into the mitochondria to initiate another round of the urea cycle.

Each nephron has two parts glomerulus and renal tubule. Glomerulus is a tuft of capillaries formed by afferent arteriole. The renal tubule begins with a double walled cup-like structure called Bowman's capsule, which encloses glomerulus. Glomerulus along with Bowman's capsule, is called Mapighian body or renal corpuscle. The tube continues further to form PCT, loop of Henle and DCT. The first step in urine formation is the filtration of blood which is carried out by the Malpighian body.
So, the correct answer is 'Malpighian body'.

The blood in the glomerulus is filtered through minutes pores called filtration slits present in the wall of Bowman's capsule. This phenomenon is called glomerular filtration and the filtrate is called as glomerular filtrate. The relatively larger molecules like blood proteins cannot pass through the minute pores hence ultrafiltration. The filtrate is collected by the cavity of Bowman's capsule and passed to the tubule. Hence liquid which collects in the cavity of Bowman's capsule is plasma minus blood proteins.

Descending limb is the first part of the loop of Henle. It helps to maintain the concentration of urine. It is highly permeable to water thus water is readily reabsorbed from the descending limb by osmosis. It is impermeable to sodium and chloride ions.

Organisms that cannot easily and safely remove nitrogen as ammonia convert it to a less toxic substance such as urea or uric acid. The urea cycle mainly occurs in the liver. The urea produced by the liver is then released into the bloodstream where it travels to the kidneys and is ultimately excreted in urine.

The glomerular filtrate when passes through the convoluted tubules, the useful components present in the filtrate is reabsorbed by tubular reabsorption. It occurs via three mechanisms they are osmosis, diffusion, and active transport. Most of the volume of the filtrate is reabsorbed in the proximal convoluted tubule (PCT). This includes some water and most/all of the glucose (except in the case of diabetics).
So, the correct answer is option B.

One of these forces is called hydrostatic pressure. In our case, this is the pressure exerted by fluid on the capillary walls of the glomerulus or the walls of the Bowman's capsule. The hydrostatic pressure in the glomerular capillaries is essentially the blood pressure in the glomerulus.

If glucose is not reabsorbed by the kidney, it appears in the urine, in a condition known as glucosuria. This is associated with diabetes mellitus. Firstly, the glucose in the proximal tubule is co-transported with sodium ions into the proximal convoluted tubule walls via the SGLT2 co-transporter.

So, the correct option is 'PCT'.

The principle nitrogenous excretory compound in humans is urea. Urea is produced in a series of reactions (urea cycle) which take place in the mitochondrial matrix and cytosol of liver cells. Urea cycle (ornithine cycle) is the series of biochemical reactions that converts ammonia, which is highly toxic, and carbon dioxide to the much less toxic urea during the excretion of metabolic nitrogen derived from the deamination of excess amino acids. The urea is ultimately excreted in solution in urine.

The nitrogen compounds through which excess nitrogen is eliminated from organisms are called nitrogenous wastes or nitrogen wastes. They are ammonia, urea, uric acid, and creatinine. All of these substances are produced from protein metabolism. ​