Excretory Products and their Elimination Test 20

During the process of urine formation first glomerular filtrate is formed. After the filtrate formation the necessary solutes are reabsorbed from the filtrate and again some metabolites are secreted in that filtrate. thus, ultimately the urine formed.

• Nephron is the structural and functional unit of the kidney. 
• Its chief function is to regulate the concentration of water and soluble substances like sodium salts by filtering the blood, reabsorbing what is needed and excreting the rest as urine. 
• Each nephron is composed of two main structures: the glomerulus and renal (kidney) tubule. There are about 1,000,000 nephrons in each human kidney. 
  
  

Arid environment limits to water availability and organisms exhibit adaptation to preserve more and more water. The loop of Henle consists of a descending limb and an ascending limb which serve to reabsorb most of the water from the filtrate and make the urine concentrated. Thus, to restore most of the water, the animals in the arid environment have long loop of Henle. Thus, the correct answer is D.

The thin ascending limb is impermeable to water but it is permeable to ions. 

• Juxtaglomerular cells secrete the renin which mainly controls the level of sodium in the blood.
• When the concentration of sodium is lower in the blood the juxtaglomerular cells secrete renin which activates  angiotensin.
• Angiotensin constricts the arterioles to increase the blood pressure and stimulates the release of aldosterone from the adrenal cortex which promotes the reabsorption of sodium ions and maintains a constant sodium level and water level in the  blood.

One of the effects of the sympathetic nervous system is to stimulate renin secretion by the juxtaglomerular cells, activating the renin-angiotensin-aldosterone system (RAAS). The RAAS increases extracellular fluid volume by increasing sodium reabsorption which is the fall in glomerular filtration rate.

The image shows nephron, a structural and functional unit of kidneys. Each nephron has a cuplike structure called the glomerular capsule, proximal convoluted tubule (PCT), distal convoluted tubule (DCT) and a loop of the nephron (loop of Henle). Together these structures serve in urine formation. Thus, the correct answer is A.

The renal arteries carry a large portion of total blood flow to the kidneys. Up to a third of total cardiac output can pass through the renal arteries to be filtered by the kidneys.The renal artery, the afferent arteriole, entering the small cup-like space of the Bowman’s capsule as a network of blood capillaries. Thus, the correct answer is the option A.