Excretion – Human Excretory System: NEET MCQs with Answers

Explanation: The figure shows a tuft of glomerular capillaries enclosed by the double-walled cup-shaped Bowman's capsule. Together, the glomerulus and Bowman's capsule form the Malpighian body (renal corpuscle). Glomerulus or Bowman's capsule alone is only one part, and 'renal capsule' is the fibrous covering of the whole kidney.

Explanation: The proximal convoluted tubule, lined by brush-border cuboidal epithelium, is the main site of reabsorption: nearly all essential nutrients such as glucose and amino acids and about 70-80 percent of electrolytes and water are reabsorbed here.

Explanation: The proximal convoluted tubule is present in the cortex, is about 12–24 mm long and is lined by brush-bordered cuboidal epithelium with numerous microvilli that greatly increase the surface area for reabsorption. These cells also have numerous mitochondria to power active transport.

Explanation: The nephron is the structural and functional unit of the kidney and is also called the renal or uriniferous tubule. It is formed of two parts — Bowman's capsule, and the nephric tubule, which comprises the proximal convoluted tubule, loop of Henle and distal convoluted tubule.

Explanation: Glucose is a high-threshold substance, meaning that it is totally or almost totally reabsorbed from the nephric filtrate into the blood capillaries. The renal threshold for glucose is about 180 mg/100 mL of nephric filtrate; above this level, sugar begins to appear in the urine.

Explanation: The glomerulus does not belong to the uriniferous tubule. Each nephron is divided into the nephric or uriniferous tubule and the glomerulus; the latter is a tuft of about 50 capillaries whose walls have numerous minute pores, making the glomerular membrane 100–500 times as permeable as a usual capillary. Henle's loop, the DCT and the collecting tubule are all parts of the uriniferous tubule.

Explanation: Each human kidney consists of about one million structural and functional units called nephrons. Each nephron has two main parts — the Malpighian body (glomerulus and Bowman's capsule) and the renal tubule. Nephridia, by contrast, are the excretory tubules of flatworms and annelids.

Explanation: In humans the principal nitrogenous excretory compound is urea. It is synthesised in the liver by the ornithine cycle and is then transported by the blood to the kidneys, through which it is eliminated.

Explanation: The convoluted tubules are not part of the renal pyramid; they lie in the cortex of the kidney. The medulla is divided into a number of conical areas called medullary or renal pyramids, and the peritubular capillaries, loop of Henle and collecting ducts all lie within the medulla.

Explanation: Podocytes, or visceral epithelial cells, are the cells of Bowman's capsule that wrap around the glomerular capillaries and create minute slit pores through which blood is filtered. The others need correction: afferent arterioles bring blood to the glomerulus; reabsorption in Henle's loop is minimal; and in the DCT the reabsorption of Na⁺ and water is conditional.

Explanation: The Assertion is correct, but the Reason reverses the facts. Juxtamedullary nephrons have a long loop of Henle extending deep into the renal medulla, whereas cortical nephrons have a shorter loop that only reaches the outer section of the medulla.

Explanation: Juxtamedullary nephrons have a long loop of Henle that extends deep into the renal medulla — the key feature enabling the counter-current mechanism. They are not present in the columns of Bertini, their renal corpuscle lies in the inner cortical region, and they are fewer in number than cortical nephrons.

Explanation: With carbohydrate exhausted, the body turns to stored fat, and the liver oxidises fatty acids faster than the resulting acetyl CoA can be handled by the Krebs cycle. The excess is converted into ketone bodies, which accumulate in the blood and spill over into the urine.

Explanation: The collecting ducts run through the renal medulla, converging on the papillae of the pyramids from which urine drains into the pelvis. Bowman's capsules, both convoluted tubules and the peritubular capillary network surrounding them all lie in the cortex.

Explanation: The glomerulus is a tuft of blood capillaries, so it belongs to the vascular system rather than to the tubule itself. The uriniferous tubule comprises Bowman's capsule and the tubular segments that follow it, with the glomerulus merely lying within the cup of the capsule.