8. Because of the countercurrent multiplier system in the loop of Henle and medu

Question

8. Because of the countercurrent multiplier system in the loop of Henle and medullary collecting duct

A. isoosmotic urine is generated by alternating active sodium reabsorption through membranes impermeable to water, and variable diffusion of water through ADH-responsive membranes

B. hyperosmotic urine is generated by alternating active sodium reabsorption through membranes impermeable to water, and variable diffusion of water through ADH-responsive membranes

C. hypoosmotic urine is generated by alternating active sodium reabsorption through membranes impermeable to water, and variable diffusion of water through ADH-responsive membranes

D. hyperosmotic urine is generated by active sodium secretion into the loop of Henle and the medullary collecting duct.

9. Cytotoxic T cells act by

A.             secreting antibodies which attack invaders

B.             attaching to antigens on invaders and secreting antibodies

C.              attaching to antigens on invaders and secreting chemicals toxic to the invaders

D.            secreting cytokines toxic to invaders into the blood to seek out and kill invaders

E.             producing interferons that stop invading viruses from entering cells

10.          In order for a helper T cell to interact with a macrophage or B cell and become activated

A.             the antigen must be complexed with MHC I protein and presented to the cell surface

B.              the antigen must be complexed with MHC II protein and presented to the cell surface

C.             IL-1 must be produced by the helper T cell

D.            the antigen must be complexed with MHC I protein and presented to lymphocytes

11.          Transfusion of an incorrect blood type into a person will cause a form of tissue rejection mediated by

A.             antigens

B.              antibodies

C.             cytotoxic T cells

D.            NK cells

E.             macrophages

12.          When AIDS develops

A.             B cells cannot perform adequately

B.             cytotoxic T cells cannot perform adequately

C.             T cells cannot perform adequately

D.             macrophages cannot perform adequately

E.             a, b, and c

13.          One distinction between B cells and T cells is that

A.             B cells directly attack an invader while T cells secrete antibodies that attack the invader

B.             T cells produce antibodies

C               T cells directly attack an invader while B cells become plasma cells that secrete antibodies that attack the invader

D.            both cell types attack invaders directly but some B cells differentiate into plasma cells that also simultaneously secrete antibodies

Explanation / Answer

Because of the countercurrent multiplier system in the loop of Henle and medullary collecting duct

A. isoosmotic urine is generated by alternating active sodium reabsorption through membranes impermeable to water, and variable diffusion of water through ADH-responsive membranes

B. hyperosmotic urine is generated by alternating active sodium reabsorption through membranes impermeable to water, and variable diffusion of water through ADH-responsive membranes

C. hypoosmotic urine is generated by alternating active sodium reabsorption through membranes impermeable to water, and variable diffusion of water through ADH-responsive membranes

D. hyperosmotic urine is generated by active sodium secretion into the loop of Henle and the medullary collecting duct.

Answer Option B :

Counter current multiplier system produces hyperosmotic urine. In the loop of henle different mechanisms work inorder to make the urine hyperosmotic.

Descending loop : This is permeable to water. It has aquaphonis . water moves from the descending loop to the medulla through these aquaporins and makes the urine more hyperosmotic.

Ascending loop : It is deficient in aquaporins and hence impermeable to water .It has active pump of Na/K/Cl which help in pumping out/ secreting Na ions into the medullary interstitium . This eventually makes the urine more hyperosmotic .

Collecting Ducts : Absobtion of water takes place in this region under the influence of ADH making the urine even more concentrated..

Option A : Wrong as the urine formed is hyperosmotic and not isoosmotic

Option C : Incorrect as the urine formed is hyperosmotic and not hypoosmotic

Option D : Hyperosmotic urine is formed as a result of action of both ADH and active sodium secretion and not just by sodium secretion

9. Cytotoxic T cells act by

A.             secreting antibodies which attack invaders

B.             attaching to antigens on invaders and secreting antibodies

C.              attaching to antigens on invaders and secreting chemicals toxic to the invaders

D.            secreting cytokines toxic to invaders into the blood to seek out and kill invaders

E.             producing interferons that stop invading viruses from entering cells

Correct Answer C :

Cytotoxic T cells helps in killing the cells which are most commonly infected with viruses. For them to act they need to be actively presented by an antigen presenting cells .

Once the antigen presenting cells presents the cells to a cytotoxic T cell . It will become activated after recognisign the antigens. It then secretes various cytoxic chemicals like perforins, granzymes which will trigger the death of the cell.

Incorrect answers A,B , E : Antiibodies and interferon secretion is doen by B lymphocytes and not by cytotoxic cells

Incorrect answer D : For the cytokines to be secreted they need to be presented by an antigen presenting cell and wont be secreted in to the blood.

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