Excretory Products and their Elimination Test 57

Correct Option: E

Kidneys of desert animals have a longer loop of Henle to make the animal's urine as concentrated as possible and limit the amount of water and salt they lose. This helps desert animals live for long periods of time on minimal amounts of water. 

The excretory organs of insects are malpighian tubules. They collect water and uric acid from surrounding haemolymph (blood) and empty it into the gut.

Correct option: (D)

Explanation for correct option: (D)

The function of the kidney is to filter unwanted substances from the blood and produce urine which is excreted from the body. The nephron is the functional unit of the kidney. It filters blood and forms urine by following steps.

• Filtration of blood occurs in the glomerulus and the filtrate consists of water, wastes and useful solutes like glucose, amino acids, smaller proteins and ions.
• The filtrate now passes through proximal convoluted tubule, the loop of Henle and distal convoluted tubule present in nephron where the nutrients, ions and water from the filtrate are reabsorbed back into the blood.
• The filtrate finally becomes hypertonic to blood plasma and is termed as urine.
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Explanation for incorrect options:

Option (A): The major calyces of the kidney open into the renal pelvis. It acts as a funnel for urine to flow into the ureter.

Option (B): Sweat is made majorly of water, with tiny amounts of other chemicals like ammonia, urea, salts, and sugar. It is secreted by sweat glands.

Option (C): Urinary bladder stores the 1 % filtrate that has to be excreted as urine.

The convoluted tubules are the highly convoluted segments of the nephron in the renal labyrinth of the kidney. It is made up of proximal tubule leading from the Bowman's capsule to the descending of the Henle's loop and distal tubules leading from the ascending part of the Henle's loop to a collecting tubule.

The water in the marine environment is saltier than the water inside a fish, both bony and cartilaginous. The less salty water inside a fish tends to rush out of the body to reach an equilibrium with the saltier seawater, which can leave a fish quite dehydrated. Cartilaginous fish have evolved the ability to reabsorb the urea created by the breakdown of protein back into their tissue, which helps level out the concentration differences so, they do not lose as much water. 

Filtration, which takes place at the renal corpuscle, is the process by which cells and large proteins are filtered from the blood to make an ultrafiltrate that eventually becomes urine. The kidney generates 180 liters of filtrate a day while reabsorbing a large percentage, allowing for the generation of only approximately 2 liters of urine.

The kidney plays an important role in the filtration of the blood. These are located at the posterior end of the abdominal cavity. Organs are retroperitoneal if they have peritoneum on their anterior side only. Structures that are not suspended by mesentery in the abdominal cavity and that lie between the parietal peritoneum and abdominal wall are classified as retroperitoneal. The retroperitoneal space (retroperitoneum) is the anatomical space in the abdominal cavity behind (retro) the peritoneum. 

A - renal artery; B - proximal tubule; C - loop of Henle; D - collecting tubule. The ability to concentrate urine depends on upon the generation of a hyperosmolar environment in the medulla. The loops of Henle are set up so as to concentrate osmolarity in the deepest part of the medulla. This occurs because the ascending and descending limbs have different permeabilities to salt and water. The loop of Henle has three distinct regions, the thin-walled descending limb, the thin-walled lower portion of the ascending limb and the thick-walled upper portion of the ascending limb. The descending limb of the loop is highly permeable to water but almost completely impermeable to solutes. As the filtrate travels down the descending loop, water will flow from the loop into the surrounding medium via osmosis. When the filtrate reaches the hairpin turn, it is isotonic with the surrounding medium (about 1200 most/L). The lower portion of the ascending branch of the loop of Henle is highly permeable to Na+ and Cl-, moderately permeable to urea, and almost completely impermeable to water. As it travels up into the less concentrated regions of the medulla, Na+, and Cl- will passively diffuse across the membrane. As, the filtrate continues up the thick portion of the loop of Henle, Na+, and Cl- are actively pumped out of the filtrate into the surrounding medium. This requires energy but helps to maintain the osmotic concentration gradient in the medulla. 

Proximal convoluted tubule (PCT) is a part of the kidney leading from the Bowman's capsule to the loop of Henle. It is lined by simple cuboidal brush border epithelium, which increases the surface area for reabsorption.