This set of Molecular Endocrinology Multiple Choice Questions & Answers (MCQs) focuses on “Renin-Angiotensin System”.
1. Where is the enzyme renin present in the human body?
a) Afferent arteriole of nephron
b) Efferent arteriole of nephron
c) Loop of Henley
d) Medulla
View Answer
Explanation: The nephron afferent arteriole exhibits cytoplasmic granules containing an enzyme called Renin. These granules are secretory vesicles of this enzyme. Renin (etymology and pronunciation), also known as angiotensinogenase, is a kidney-secreted aspartic protease protein and enzyme that is involved in the renin-angiotensin-aldosterone mechanism of the body (RAAS).
2. Which enzyme is released in conditions like hypovolemia?
a) Hydrolase
b) Renin
c) Aldosterone
d) Vasopressin
View Answer
Explanation: A drop in the concentration of sodium, hypovolemia, hypotension and a decrease in intracellular calcium promote the release of “renin” into the blood from JG cells. Often, bradykinin and glucagon induce renin production.
3. In the reaction of renin given below, which product is formed from angiotensin?
a) Angiotensin-III
b) Angiotensin-II
c) Angiotensin-I
d) Angiotensin-IV
View Answer
Explanation: Renin acts on an alpha2-globulin plasma substrate, called angiotensinogen or the hypertensinogen that the liver produces. The enzyme cleaves the “Leucyl-Leucyl” bond to create “Angiotensin I” between 10 and 11 positions from the N-terminal end.
4. Renin is a proteolytic enzyme.
a) True
b) False
View Answer
Explanation: Renin is a proteolytic enzyme with a molecular weight of 35000. Renin isoenzymes or renin-like enzymes have recently been identified in the brain, placenta, submaxillary duct, and at the uterine endometrium and myometrium junction.
5. Cortisol and β-estradiol enhance the reaction of renin on angiotensinogen.
a) True
b) False
View Answer
Explanation: The reaction of renin on angiotensinogen is a rate limiting step. This reaction is intensified by cortisol and β-estradiol, possibly by increasing the hepatic synthesis of angiotensinogen. Renin catalyses the transformation of a plasma protein called angiotensinogen into a decapeptide called angiotensin I (consisting of 10 amino acids).
6. Which enzyme is involved in the formation of Angiotensin II?
a) Hydrolase
b) Converting enzyme
c) Renin
d) Isomerase II
View Answer
Explanation: Angiotensin-I is acted upon by another enzyme namely ‘converting enzyme’ which is a protease enzyme. It cuts-off the terminal “Histidyl-Leucyl” dipeptide by forming ‘Angiotensin II’. The RAS’s main effector molecule is angiotensin II. It causes blood pressure to rise, affects the retention of sodium and water in the renal tubules, and triggers the release of aldosterone from the adrenal gland.
7. Which hormone synthesis is induced by angiotensin II?
a) Aldosterone
b) Vasopressin
c) Oxytocin
d) Insulin
View Answer
Explanation: Angiotensin II is the “active” element that improves aldosterone synthesis by operating on zona glomerulosa cells. It raises the rate in which the hormone is released. Aldosterone is a steroid hormone in the distal tubule and collecting duct of the nephron that induces a rise in sodium reabsorption and potassium excretion.
8. Which enzyme inactivates angiotensin II?
a) Acetylase
b) Hydrolase
c) Renin
d) Angiotensinase
View Answer
Explanation: There is an enzyme called angiotensinase, an amino-peptidase that is found in the blood, intestines, and kidneys. This enzyme, by hydrolysis, inactivates angiotensin II. Angiotensin II is an extremely potent vasoconstrictor but has a very low half-life, degrading to inactive fragments by angiotensinase.
9. From which animal was angiotensin III isolated in the beginning?
a) Rat
b) Human
c) Monkey
d) Mice
View Answer
Explanation: Heptapeptide Angiotensin III has recently been isolated in rats. It is believed to be found in humans as well. In promoting aldosterone secretion, both heptapeptide (angiotensin III) and octapeptide (angiotensin II) are believed to be equipotent.
10. Which hormone can inhibit the enzyme renin?
a) Vasopressin
b) Aldosterone
c) Oxytocin
d) Cortisol
View Answer
Explanation: By “feed-back” inhibition, aldosterone can ‘inhibit’ the enzyme’ renin’. As a result, the formation of angiotensin II is reduced. In controlling blood volume and systemic vascular resistance, the renin-angiotensin-aldosterone system (RAAS) plays an important role, affecting cardiac production and arterial pressure together.
11. Which is the second messenger produced by angiotensin II?
a) Inositol-1, 4, 5-triphosphate
b) cAMP
c) cGMP
d) Cyclin
View Answer
Explanation: Angiotensin II binds to the membrane of zona glomerulosa cells with a particular “receptor.” This causes the formation of ‘inositol-1,4,5-triphosphates’. An inositol phosphate signalling molecule is inositol trisphosphate or inositol 1,4,5-trisphosphate, abbreviated as InsP3 or Ins3P or IP3.
12. Which enzyme is boosted by angiotensin II for the conversion of corticosterone to aldosterone?
a) 20-hydroxylase
b) 19-hydroxylase
c) 18-hydroxylase
d) 21-hydroxylase
View Answer
Explanation: Angiotensin II promotes the conversion of corticosterone to aldosterone by increasing the synthesis of 18-hydroxylase. The successful tubular reabsorption of sodium is improved by the production and secretion of aldosterone.
13. What is the role of angiotensin II in the smooth muscle contraction?
a) Stimulates relaxation
b) Inhibits relaxation
c) Inhibits contraction
d) Stimulates contraction
View Answer
Explanation: Angiotensin II Induces smooth muscle contraction on the walls of the alimentary canal, uterus, arteries/arterioles, but the sphincter muscles do not relax. It presumably responds to a particular “receptor” in the smooth muscle cell membrane, leading to an improvement in intracellular calcium, which then stimulates the contraction of smooth muscle fibers.
14. What is the role of angiotensin II in water homeostasis?
a) Causes water retention
b) Reduces water retention
c) Increases water loss
d) Increases ultrafiltration
View Answer
Explanation: Angiotensin II stimulates the secretion of vasopressin. This in turn causes water retention indirectly. The homeostasis of body water is controlled primarily by ingested fluids, which, in turn, depends on thirst.
15. Which molecule reduces the antidiuretic effect of angiotensin II?
a) Renin
b) Vasopressin
c) Prostaglandins (PG)
d) Aldosterone
View Answer
Explanation: Prostaglandins act against angiotensin II, especially PGE2. This reduces the effects of angiotensin II on renal vasoconstrictors and antidiuretics. Renal function maintenance seems to be accomplished in part by the synthesis within the kidney of two vasoactive factors—angiotensin II and prostaglandins.
Sanfoundry Global Education & Learning Series – Molecular Endocrinology.
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