CBSE Questions for Class 11 Medical Biology Excretory Products And Their Elimination Quiz 5 - MCQExams.com

• Excretion is the removal of waste products of metabolism (means that the waste product has been made by the body itself) from the body. If allowed to accumulate, these would prevent the maintenance of a steady state. 
• In vertebrates this is primarily carried out by the lungs (CO$$_2$$), kidneys (urine), and skin (sweat). 
  
• Egestion or defecation is the removal of undigested food from the gut and is not regarded as excretion because the material taken into the gut through the mouth is not made by the body itself.

• Homeostasis is the tendency to resist change in order to maintain a stable and constant internal environment.
• The internal environment should contain the optimum concentration of gases, nutrients, ions, water, optimal temperature and has an optimal pressure for the health of the cells. 
  
• For example, the concentration of various ions in the blood must be kept steady, along with pH and the concentration of glucose.

• 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. 
  
  

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.

• The process of ultrafiltration occurs in the glomerular capsule also known as Bowman's capsule. 
• The Bowman's capsule contains a dense capillary network called the glomerulus. Blood flows into these capillaries through the afferent arterioles and leaves through the efferent arterioles.
• The blood that enters into the glomerulus is under very high pressure from the afferent renal arteriole and contains urea, glucose, various salts and proteins of plasma and large quantities of water. 
• The filtration occurs across the membrane made up of the glomerular capillary wall and the inner membrane of the Bowman's capsule. The pores of this filtering membrane are impermeable to large molecules like blood cells and proteins.
• But smaller molecules like glucose, urea, creatinine, amino acids, and mineral salts are filtered into the Bowman's capsule. The insufficient filtration in Bowman's capsule results in an increased concentration of urea in the blood.