Excretory Products and their Elimination Test 9

Ammonia is produced in cells as metabolic waste. Aquatic animals directly excrete ammonia as it is highly soluble in water. Terrestrial animals convert ammonia to urea to save water. Urea is less soluble in water as compared to ammonia. Urea needs to filter out of blood. Filtration occurs in Bowman's capsule and filtrates initially collects in Bowman's capsule.

The process of urine formation in kidneys include the following steps:
(i) Glomerular filtration
(ii) Tubular reabsorption
(iii) Tubular secretion

(i) Glomerular filtration - Urine formation begins when the fluid portion of the blood is filtered by the glomerulus and enters the Bowman's capsule as glomerular filtrate. The afferent arteriole entering the glomerulous is wider than the efferent arteriole in diameter.This increases the blood pressure within the glomerulous helping in filtration. Glomerular filtrate is formed of all blood constituents except corpuscles and plasma proteins.
(ii) Tubular reabsorption - When the glomerular filtrate comes to the proximal tubule then the nutrients essential for body is reabsorbed from the filtrate. Glucose, amino acids, water, ions like sodium, potassium, chloride, bicarbonate, magnesium, calcium are reabsorbed from the glomerular filtrate as it flows trough the proximal tubule, loop of Henle and distal tubule. When the filtrate finally comes to the collecting duct ADH (anti diuretic hormone) acts and reabsorbes the excess water and decreses the urine volume.
(iii) Tubular secretion - When the glomerular filtrate is in the proximal tubule cretinine, uric acid are secreted in it.When the filtrate goes to the distal part urea, potasium ion and some hydrogen ions are secreted in it.
Therefore, the correct answer is option B.

Mammals including humans excrete urea as the excretory substance. Urea is produced in liver but is filtered from blood in the kidneys. Each kidney has nearly one million complex tubular structures called nephrons, which are the functional units of kidneys. Each nephron has two parts the glomerulus and the renal tubule. The glomerulus is a tuft of capillaries formed by the afferent arteriole, a fine branch of the renal artery. Blood from the glomerulus is carried away by an efferent arteriole. The renal tubule begins with a double walled cup-like structure called Bowman's capsule, which encloses the glomerulus. Glomerulus along with Bowman's capsule is called the malpighian body or renal corpuscle. Thus, Bowman's corpuscle is part of the kidney not the part of heart.

Each kidney has nearly one million complex tubular structures called nephrons, which are the functional units. Each nephron has two parts the glomerulus and the renal tubule. The glomerulus is a tuft of capillaries formed by the afferent arteriole a fine branch of the renal artery. Blood from the glomerulus is carried away by an efferent arteriole. The renal tubule begins with a double walled cup-like structure called Bowman's capsule, which encloses the glomerulus. Glomerulus along with Bowman's capsule is called the malpighian body or renal corpuscle.

Certain invertebrates like some molluscs (Unio, Limnaea) and some echinoderms (Asterias, Paracentrotus) excrete out excess amino acid as such without undergoing any deamination, these animals are called aminotelic. Elimination of nitrogenous waste inthe form of amino acids is called aminotelism.
Anaerobic metabolism results in the accumulation of the amino acids like alanine and glutamate inside the cell. During hypo-osmotic stress (cell have more concentration of salts/solutes than its surrounding) the intracellular concentrations of amino acids decreases by extrusion from the cells followed by deamination and / or excretion. Thus amino acids (when in excess) are directly excreted as a part of osmoregulation in marine molluscs and echinoderms under salinity stress.

Malpighian corpuscles are seen in the cortex of the kidney. They are 0.2 mm in diameter, with each capsule composed of two parts: a central glomerulus and a glomerular capsule. The corpuscles are part of a filtering system through which non-protein components of blood plasma enter the tubules for urinary excretion.

Nitrogenous wastes in aquatic animals are directly excreted as ammonia where as in terrestrial animals they are excreted as urea through urine. One of the major component of urine of terrestrial animals is urea. The urea is produced in liver and is filtered from blood in kidneys. The kidneys comprise of nephrons each having a Bowman's capsule and a tubular part. The fluid that accumulates in Bowmans capsule is called filtrate. This is subjected to absorption and secretion to form the urine which is excreted out.

Ureotelism is a type of excretion, where urea is the main nitrogenous waste material. Animals showing ureotelism are called ureotelic animals. Ureotelism is generally found in land animals, which can afford to excrete sufficient volume of water or to concentrate urea in considerable quantity in the urine. 1 gm of urea needs about 50 ml of water to the expelled out. It is commonly found in man, whales, seals, desert mammals like kangaroo rats, camels, toads, frogs, cartilagenous fishes, aquatic and semi aquatic reptiles like alligator, terrapins and turtles. 

The paired adrenal glands are small, yellow masses of tissue that lie in contact with the upper ends of the kidneys. Each gland consists of a central portion, the adrenal medulla and a larger outer section, the adrenal cortex. The adrenal medulla is a neuro-endocrine gland that is coupled to the sympathetic nervous system. It develops from neural tissue and its secretion is controlled by sympathetic nerves. The adrenal medulla secretes epinephrine and nor epinephrine. Chemically, these hormones are very similar; they are amino acid derivatives that belong to the chemical group known as catecholamines. Most of the hormone output of the adrenal medulla is epinephrine. During a stressful situation, adrenal medullary hormones initiate an alarm reaction that enables us to think more quickly, fight harder or run faster than usual. Metabolic rate increases by as much as 100%. Blood vessels going to the brain, muscles and heart are dilated, whereas those to the skin and kidneys are constricted. Constriction of blood vessels serving the skin has the added advantage of decreasing blood loss in case of hemorrhage (and explains the sudden paling that comes with fear or rage). At the same time, the heart beats faster. Strength of muscle contraction increases. Thresholds in the reticular activating system of the brain are lowered, so we become more alert. The adrenal medullary hormones also raise fatty acid and glucose levels in the blood (through glycogen breakdown), ensuring needed fuel for extra energy.