Excretory system MCQ Quiz in मल्याळम - Objective Question with Answer for Excretory system - സൗജന്യ PDF ഡൗൺലോഡ് ചെയ്യുക

Key Points

• The loop of Henle is a critical structure found in the nephrons of the kidney, which is responsible for maintaining water and electrolyte balance in the body.
• It plays a vital role in the process of urine formation and helps in concentrating urine.
• The loop of Henle is located in the renal medulla, the inner part of the kidney.
• It consists of a descending limb, a thin segment, a thick ascending limb, and a thin ascending limb.
• The loop of Henle is primarily found in the juxtamedullary nephrons, which are responsible for the production of concentrated urine.

Fig 1: Loop of henle

Important Points

• P. Long loop of Henle is associated with greater amount of vasopressin secretion. INCORRECT
  • Vasopressin (also known as antidiuretic hormone or ADH) is a hormone produced by the hypothalamus and released by the pituitary gland.
  • It plays a role in regulating water balance in the body. While vasopressin influences water reabsorption in the kidneys, it is not directly related to the length of the loop of Henle.
  • Vasopressin acts on the collecting ducts rather than the loop of Henle.
• Q. In a long loop of Henle, the counter-current exchanger is more effective. CORRECT
  • The loop of Henle plays a crucial role in concentrating urine and conserving water.
  • It creates a counter-current exchange system, where the descending limb and ascending limb of the loop of Henle run parallel to each other and have different permeabilities to water and solutes.
  • This arrangement sets up a concentration gradient that allows for the reabsorption of water and solutes.
  • By having a longer loop of Henle, desert animals increase the length of the descending and ascending limbs, thereby extending the area of the counter-current exchange system.
  • This results in a more effective concentration gradient and enhances water reabsorption.
  • As a consequence, these animals can produce highly concentrated urine and conserve water more efficiently in their arid environments
• R. A long loop of Henle conserves more water. CORRECT
  • ​As mentioned above, the longer loop of Henle in desert animals allows for a more effective concentration gradient, resulting in increased water reabsorption.
  • This adaptation enables these animals to conserve water in their bodies, which is essential for survival in arid environments where water availability is limited.
  • By conserving water through the extended loop of Henle, desert animals can minimize water loss through urine and maintain proper hydration levels.
  • This adaptation is crucial for their survival in environments with low water availability and helps them thrive in desert conditions.
• S. Long loop of Henle stimulates the production of angiotensin II. INCORRECT
  • Angiotensin II is a hormone involved in the regulation of blood pressure and fluid balance.
  • While the renin-angiotensin system, which includes angiotensin II, does influence renal function, there is no direct relationship between the length of the loop of Henle and the production of angiotensin II.
  • Angiotensin II primarily acts on the blood vessels and adrenal glands rather than the loop of Henle.
• In summary, the correct reasons for desert animals having a longer loop of Henle compared to humans are that it allows for a more effective counter-current exchanger and facilitates the conservation of water in arid environments.

Concept:

• The renal corpuscle is the initial site of blood filtration in the kidney, where blood is filtered to form a fluid called filtrate.
• The filtration occurs in the glomerulus, which is a network of capillaries surrounded by a specialized structure called the Bowman's capsule.
• The podocytes are specialized cells found in the Bowman's capsule that wrap around the glomerular capillaries.
• Podocytes have foot-like projections, called pedicels, that interdigitate with one another to form a filtration barrier in the glomerulus.
• The filtration barrier is made up of three layers:
  • Fenestrated endothelium of the capillaries,
  • Basement membrane,
  • Slit diaphragm between adjacent pedicels of podocytes.
• These three layers act together to prevent the passage of large molecules, such as proteins, into the urine while allowing the passage of smaller molecules, such as water and ions, into the filtrate.
• The podocytes also play a role in maintaining the structural integrity of the glomerulus.
• They secrete extracellular matrix proteins, such as collagen and laminin, that help to form the basement membrane and anchor the podocytes to the glomerular capillaries.
• Podocytes are also involved in signaling pathways that regulate the function of the glomerulus and the overall filtration rate of the kidney.
• In summary, podocytes are specialized cells that wrap around the glomerular capillaries in the renal corpuscle and form a filtration barrier to prevent the passage of large molecules into the urine while allowing the passage of smaller molecules.
• They also play a role in maintaining the structural integrity of the glomerulus and regulating the overall function of the kidney.

Explanation:

• Podocytes are specialized cells that form the inner layer of the Bowman's capsule in the kidney.
• They have foot-like processes called pedicels that wrap around the glomerular capillaries and interdigitate with each other to form a selective filtration barrier.
• The filtration barrier consists of the glomerular endothelium, the basement membrane, and the podocytes' foot processes, and it allows only small molecules such as water and ions to pass through while preventing larger molecules such as proteins from crossing the barrier.
• The interdigitating processes of podocytes have several unique features that contribute to their function in the kidney.
• For example, they are highly flexible and can change shape in response to changes in pressure or flow rate, which helps to regulate filtration.
• Additionally, the processes are covered with negatively charged glycoproteins, which repel negatively charged molecules and help to maintain the barrier's selective permeability.

Concept:

• Filtration is the first step in the production of urine.
• Under pressure, fluid and tiny solutes are forced to flow from the glomerulus into the glomerular capsule's capsular space.
• The glomerulus' filtering unit, the Bowman's capsule, includes microscopic openings that allow filtrate to enter the nephron.
• Filtrable and non-filterable blood components enter the glomerulus.
• Water, nitrogenous waste, and nutrients are all parts of the blood that can be filtered, and these components are transported into the glomerulus to create the glomerular filtrate.
• Blood cells, albumin, and platelets are among the non-filterable blood components that pass via the efferent arteriole to leave the glomerulus.
• The force of the differential between hydrostatic and osmotic pressure leads to glomerular filtration.

​Explanation:

• Renal ultrafiltration is the method by which glomerular filtration takes place.
• Filtrate is pushed out of the capillaries and into the slits in the nephron by the force of hydrostatic pressure in the glomerulus, which is the force of pressure produced from the pressure of the blood artery itself.​
• The force of hydrostatic pressure is larger than osmotic pressure (the pulling force produced by albumins), and the difference between the two defines the effective pressure of the glomerulus, which affects the force by which molecules are filtered.
• These elements, along with a few others, will affect the glomerular filtration rate.

​

 hence the correct answer is option 3

Key Points

Statement A - CORRECT

• Aldosterone plays a key role in the regulation of sodium reabsorption in the kidney.
• In the early portion of the distal tubule, aldosterone stimulates the synthesis and insertion of Na⁺-Cl^- symporters (thiazide-sensitive Na⁺-Cl^- cotransporters) into the apical membrane of the principal cells.
• These symporters facilitate the co-transport of sodium and chloride ions from the tubular fluid into the interior of the principal cells, promoting the reabsorption of sodium.

Statement B - CORRECT

• In the late portion of the distal tubule, aldosterone increases the number of epithelial sodium channels (ENaC) in the apical membrane of the principal cells.
• ENaC channels are responsible for the passive reabsorption of sodium ions from the tubular fluid into the principal cells.
• By increasing the number of ENaC channels, aldosterone enhances the reabsorption of sodium, leading to increased sodium reabsorption in the distal tubule.

Statement C - INCORRECT

• Aldosterone actually has the opposite effect on the synthesis of Na⁺, K⁺-ATPase.
• It stimulates the synthesis and insertion of Na⁺, K⁺-ATPase pumps into the basolateral membrane of the principal cells in the distal tubule.
• Na⁺, K⁺-ATPase pumps actively transport sodium out of the cells and potassium into the cells, creating an electrochemical gradient that facilitates the reabsorption of sodium from the tubular fluid.

Statement D - INCORRECT

• Aldosterone does not directly affect the thick ascending limb of the loop of Henle.
• Its primary effects on sodium reabsorption occur in the distal tubule and collecting ducts of the nephron.
• In the thick ascending limb, sodium reabsorption is primarily mediated by the Na⁺-K⁺ and 2Cl^- symporter, which is not directly regulated by aldosterone.

Therefore, the correct statement is option 1.

The correct answer is Option 1 i.e. A and B

Concept:

• Guanylyl cyclase is the enzyme that catalyses the synthesis of cyclic GMP from GTP in a reaction that is analogous to that of adenylyl cyclase.
• On the basis of their distribution, guanylyl cyclase is divided into two types:

1. Soluble guanylyl cyclase - 
   • It is homologous to the intracellular catalytic domain of the membrane-bound forms of guanylyl cyclase.
   • They are heterodimers consisting of α and β subunits, with both subunits containing a catalytic domain and a heme-binding domain. 
   • This soluble form of guanylyl cyclase is activated by nitrate oxide.
   • Many neurotransmitters like glutamate, acetylcholine, substance P, histamine and bradykinin, are known to activate finally cyclase by the production of NO.
   • Similar to this, all organic nitrate medications used to treat ischemic heart diseases, such as nitroglycerin and nitroprusside, cause vasodilation by activating soluble guanylyl cyclase and raising levels of cGMP.
2. Membrane-bound guanylyl cyclase - 
   • It is a transmembrane protein that consists of the following three parts:
   1. Cell-surface domain - it functions as the neuropeptide receptors
   2. A single transmembrane domain.
   3. Intracellular domains -  it contains the guanylyl cyclase activity.
   • The catalytic domain is activated as a result of ligand binding to the receptor, which also causes the receptor domain to become active.
   • These enzymes also possess another region known as the protein-kinase domain.
   • It is believed that the ATP-binding site in this domain is necessary for guanylyl cyclase action.
   • In fact, the binding of ATP to the site may contribute to the conversion of ligand binding at the receptor domain to enzyme activation at the catalytic domain.
   • This would be similar in function to how GTP-binding to G proteins translates ligand binding to G protein-coupled receptors to control adenylyl cyclase.
   • Three forms of membrane-bound guanylyl cyclase have been identified, out of which,  two are plasma membrane receptors for atrial natriuretic peptide (ANP) and its related peptides.
   • While the third form, found in the intestine, is guanylyl cyclase C, that binds to the peptide guanylin, and is also activated by a bacterial enterotoxin.
   • Activation of these receptors occurs by ligand-mediated dimerization of the receptors.

Explanation:

Statement A: CORRECT

• ANP (Atrial natriuretic peptide) is a peptide with 28 amino acids.
• It is important in regulating sodium excretion and maintaining blood pressure. 
• Guanylyl cyclase A located in the heart is a membrane-bound guanylyl cyclase enzyme and it binds to the ANP, leading to an increase in the cGMP.
• Guanylyl cyclase B is another membrane-bound guanylyl cyclase enzyme, it is located in the brain neuronal tissue and it binds to the C-type natriuretic peptide

Statement B: CORRECT

• Nitroglycerin is known to increase the concentration of cGMP by activation of soluble guanylyl cyclase enzyme.

Statement C: INCORRECT

• Nitroprusside is known to increase the concentration of cGMP by activation of soluble guanylyl cyclase enzyme.

Statement D: INCORRECT

• Atrial natriuretic peptide interacts with membrane-bound guanylyl cyclase enzymes.

Hence, the correct answer is Option 1.