biology mcqs
Excretory Products & Their Elimination: MCQs
Test your understanding of excretory products, human excretory system, and kidney function with these multiple-choice questions.
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Showing questions 41 - 60 of 169
41. The smallest functional unit of kidney is
The nephron, also known as the uriniferous tubule, is explicitly identified as the structural and functional unit of the kidney. Each kidney contains about 1 million nephrons, and they are responsible for the entire process of urine formation.
42. Henle's loops are found in those animals which excrete hypertonic urine. One of the following does not have Henle's loop
The presence and length of the Loop of Henle are crucial for the ability of a kidney to concentrate urine. Animals that produce highly concentrated (hypertonic) urine, such as mammals and birds (terrestrial vertebrates adapted for water conservation), possess well-developed Loops of Henle. However, amphibians like frogs, which typically excrete large volumes of dilute urine and can absorb water through their skin, generally lack a well-developed Loop of Henle, or have very short ones, limiting their ability to produce hypertonic urine.
43. The thin segment of descending limb of Loop of Henle is lined by
The Loop of Henle consists of a descending limb and an ascending limb. The thin segment of the descending limb, which lies in the medulla, is specifically lined by flat epithelial cells. These cells have sparse microvilli and few mitochondria, indicative of passive water movement.
44. Collecting tubes or duct combine to form
After receiving filtrate from nephrons, the collecting tubules open into still wider collecting ducts. As these collecting ducts descend into the medulla, they merge to form larger ducts known as the ducts of Bellini, which then run through the renal pyramids and ultimately lead to the renal papilla and calyces.
45. Brush border surface can be taken as the characteristics feature of
The Proximal Convoluted Tubule (PCT) is lined by cuboidal epithelium that possesses prominent brush borders due to the presence of numerous long microvilli. These microvilli significantly increase the surface area for absorption by approximately 20 times, making the PCT highly efficient in reabsorbing essential substances from the filtrate.
46. The first, fourth-fifth portion of the descending limb is lined by
The descending limb of the Loop of Henle has two parts: a thick segment and a thin segment. The thick segment constitutes about four-fifths of the descending limb and is lined by cuboidal cells. These cells have sparse microvilli and fewer mitochondria, indicating that active absorption and secretion are largely absent in this portion.
47. Which of the following statement is not true w.r.t. nephron?
Let's analyze the statements: * Cortical nephrons are more common: Correct. They constitute about 85% of total nephrons. * Cortical nephrons lack vasa recta: Correct. Vasa recta are absent or highly reduced in cortical nephrons. * The glomeruli of juxtamedullary nephrons are placed close to the inner margin of the cortex: Correct. They are present at the junction of the cortex and medulla. * In juxtamedullary nephrons, the blood first passes through vasa recta and then through the capillaries of glomerulus: This statement is not true. Blood always enters the kidney via the renal artery, which leads to afferent arterioles that form the glomerulus. After filtration in the glomerulus, blood exits via the efferent arteriole, which then forms the peritubular capillaries and the vasa recta around the Loop of Henle. Therefore, blood passes through the glomerulus *before* the vasa recta.
48. Which of the following defines the net filtration pressure (NFP)?
The glomerular filtration pressure (GFP), also known as the net filtration pressure (NFP), determines the rate of fluid movement from the glomerulus into Bowman's capsule. It is calculated by taking the glomerular hydrostatic pressure (GHP) and subtracting the sum of the opposing pressures: blood colloidal osmotic pressure (BCOP) and capsular hydrostatic pressure (CHP). The formula given in the source is GFP = GHP - (BCOP + CHP). For example, 60 mmHg (GHP) - (30 mmHg (BCOP) + 20 mmHg (CHP)) = 10 mmHg GFP.
49. Which of the following is correct?
In the glomerulus, blood is supplied by the afferent arteriole and drained by the efferent arteriole. A key anatomical feature is that the efferent arteriole is narrower than the afferent arteriole. This difference in diameter creates resistance to blood outflow, which is crucial for maintaining a high blood pressure inside the glomerulus, driving the process of ultrafiltration.
50. The glomerular filtration rate is
The Glomerular Filtration Rate (GFR) represents the volume of filtrate formed by the kidneys per unit time. The source states that it produces a glomerular or nephric filtrate of about 125 ml/min. This rate translates to approximately 180 liters per day (125 ml/min * 60 min/hr * 24 hr/day = 180,000 ml/day = 180 L/day). Therefore, both options (1) and (2) are correct representations of GFR.
51. If the GFR is 125 ml min-1 and the renal plasma flow is 700 ml min-1, the filtration fraction is
The filtration fraction is the ratio of glomerular filtration rate (GFR) to renal plasma flow (RPF), usually expressed as a percentage. Filtration Fraction = (GFR / Renal Plasma Flow) * 100% Given GFR = 125 ml/min and RPF = 700 ml/min: Filtration Fraction = (125 / 700) * 100% ≈ 0.1785 * 100% ≈ 18%. *The formula for filtration fraction is a standard physiological concept not explicitly detailed in the provided sources, but the calculation is based on the given values.*
52. Which of the following mechanism will operate mainly to check variation in flow to the glomerulus in case of fluctuation in blood pressure?
The kidneys possess intrinsic autoregulatory mechanisms to maintain a relatively constant glomerular filtration rate (GFR) despite fluctuations in systemic blood pressure. The myogenic mechanism is a primary intrinsic autoregulatory response of the afferent arteriole to changes in blood pressure. When blood pressure increases, the smooth muscle in the afferent arteriole stretches and contracts, leading to vasoconstriction and reducing blood flow to the glomerulus, thereby maintaining a stable GFR. Conversely, a drop in pressure leads to vasodilation. *This explanation draws on general biological knowledge as this specific mechanism is not detailed in the provided sources.*
53. One of the following is impermeable to water
The ascending limb of the Loop of Henle is a crucial segment for creating the osmotic gradient in the medulla. Unlike the descending limb which is permeable to water, the ascending limb is specifically impermeable to water. Instead, it actively or passively transports solutes, primarily NaCl, out of the filtrate, contributing to the increasing osmolarity of the medullary interstitium.
54. Active reabsorption of Na+, K+ takes place in
Active reabsorption of ions like Na+ and K+ occurs in multiple segments of the nephron: * Proximal Convoluted Tubule (PCT): Actively reabsorbs Na+ and K+. * Ascending limb of Henle's loop: The thick segment actively transports NaCl out, and also some K+. * Distal Convoluted Tubule (DCT): Na+ is actively reabsorbed under the influence of hormones like aldosterone. Therefore, active reabsorption of these ions takes place in all of these listed parts of the nephron.
55. Tubular secretion helps to maintain a proper acid-base balance by removing one of the following from blood
Tubular secretion involves the active transfer of waste products from the peritubular capillaries into the nephric filtrate in the PCT and DCT. While the provided source generally mentions waste products are secreted, in the context of acid-base balance, the kidneys secrete substances like hydrogen ions (H+) and ammonia into the filtrate to regulate blood pH. This helps to eliminate excess acid from the body. *This explanation draws on general biological knowledge as the specific link between H+ and ammonia secretion and acid-base balance is not explicitly detailed in the provided sources.*
56. Concentration of sodium and chloride ions is lowest
The osmolarity of the filtrate changes significantly as it passes through the nephron. As the filtrate moves up the ascending limb of the Loop of Henle, NaCl is actively transported out, making the filtrate progressively more dilute. By the time the filtrate reaches the distal convoluted tubule (DCT) and then the collecting ducts in the cortical region, its concentration of solutes, including Na+ and Cl–, becomes hypotonic to blood plasma, hence lowest near the cortex.
57. Which statement is wrong?
Let's evaluate each statement: * The counter-current mechanism, involving the Loop of Henle and vasa recta, does create a concentration gradient (due to NaCl and urea) in the medullary interstitium, which helps in concentrating the filtrate (urine) from an initial isotonic state to a hypertonic one. (Correct) * The collecting ducts' walls become permeable to water in the presence of ADH, allowing water reabsorption. The ascending limb of Henle's loop is indeed impermeable to water. (Correct) * Water reabsorption in the DCT is facultative, meaning it is regulated and dependent on the presence of ADH (vasopressin). (Correct) * The thick segment of the ascending limb of Henle's loop actively transports NaCl into the outer interstitial fluid. Therefore, stating that sodium is transported passively in the ascending thick segment is wrong.
58. Which one of the following is produced in the kidneys?
The Juxtaglomerular Apparatus (JGA), a specialized structure within the kidney, releases the enzyme renin into the bloodstream. Renin is a key component of the Renin-Angiotensin-Aldosterone System (RAAS), which plays a critical role in regulating blood pressure and fluid balance.
59. Angiotensin -II increases the blood volume by
Angiotensin II is a powerful hormone that significantly contributes to increasing blood volume and pressure. The sources explicitly state that it works in two ways: 1. By signalling the proximal convoluted tubules (PCT) to reabsorb more NaCl and water. 2. By stimulating the adrenal gland to release aldosterone, which further induces the distal convoluted tubule (DCT) to reabsorb more Na+ and water. Additionally, Angiotensin II is also known to stimulate the release of ADH (vasopressin), which directly increases water reabsorption in the collecting ducts, further contributing to blood volume increase. Therefore, all of these mechanisms contribute to the increase in blood volume by Angiotensin II. *The direct stimulation of ADH release by Angiotensin II is common physiological knowledge, even though this specific source emphasizes the PCT and aldosterone pathways.*
60. Reabsorption of Na+ is controlled by
The reabsorption of sodium ions (Na+) in the distal parts of the nephron, particularly the distal convoluted tubule, is primarily controlled by the hormone aldosterone. Aldosterone, released from the adrenal gland, induces the reabsorption of more Na+ and water, thereby increasing blood volume and pressure.