Mineralocorticoids – Functions & Regulation

MINERALOCORTICOIDS – FUNCTIONS & REGULATION

Q. 1

Mineralocorticoid receptors are present in all of thefollowing sites, Except:

 A

Hippocampus

 B

Kidney

 C

Colon

 D

Liver

Q. 1

Mineralocorticoid receptors are present in all of thefollowing sites, Except:

 A

Hippocampus

 B

Kidney

 C

Colon

 D

Liver

Ans. D

Explanation:

Liver [Ref Molecular and cellular pediatric endocrinology By Stuart Handwerger p219; http://en.wikipedia.orgAviki/Mineralocorticoid_receptor%5D

Mineralcorticoid receptors are expressed at high levels in renal distal tubules and cortical collectiong ducts and in other mineralocorticoid target tissues such as salivary glands and the colon. It is also found in multiple sites in the brain (hippocampus), myocardium, peripheral vasculature, brown adipose tissue and sweat glands. Mineralcorticoid receptors are located mainly in the cytoplasm.


Q. 2 Aldosterone receptors are present in all except
 A liver
 B colon
 C hippocampus
 D distal nephron
Q. 2 Aldosterone receptors are present in all except
 A liver
 B colon
 C hippocampus
 D distal nephron
Ans. A

Explanation:

liver [Ref. : http://en.wikipedia.org/wiki/Mineralocorticoidreceptor;
http://www.lib.bioinfo.pl/meid..35592]

  • The aldosterone receptor, also called mineralocorticoid receptor (or MR, MLR, MCR), is officially labelled nuclear receptor subfamily 3, group C, member 2, (NR3C2). It belongs to the steroid hormone receptor family where the ligand diffuses into cells, interacts with the receptor and results in a signal transduction affecting
  • expression in the nucleus
  • MR is expressed in many tissues, such as the kidney, colon, heart, central nervous system (hippocampus), brown adipose tissue and sweat glands. In epithelial tissues, its activation leads to the expression of proteins regulating ionic and water transports (mainly the epithelial sodium channel or ENaC, Na+/K+ pump, serum and glucocorticoid induced kinase or SGKI) resulting in the reabsoprtion of sodium, and as a consequence an increase in extracellular volume, increase in blood pressure, and an excretion of potassium to maintain a normal salt concentration in the body.
  • The receptor is activated by mineralocorticoids such as aldosterone and deoxycorticosterone as well as glucocorticoids, like cortisol and cortison. It also responds to some progestins.

 


Q. 3

Increased Aldosterone leads to all of  the following, except:

 A

Hypokalemia

 B

Hypertension

 C

Hypernatremia

 D

Metabolic acidosis

Q. 3

Increased Aldosterone leads to all of  the following, except:

 A

Hypokalemia

 B

Hypertension

 C

Hypernatremia

 D

Metabolic acidosis

Ans. D

Explanation:

Increased Aldosterone is associated with metabolic alkalosis and not metabolic acidosis. Other findings associated with it includes hypokalemia (potassium excretion), hypernatremia (sodium conservation) and hypertension (characteristically diastolic).

Ref: Endocrine Physiology, 3rd Edition, Chapter 6; CURRENT Diagnosis and Treatment in Family Medicine, 3rd Edition, Chapter 36


Q. 4

Which of the following actions does aldosterone secretion from the adrenal gland regulate in the kidney?

 A

Exchange of K+ for Na+ in the distal convoluted tubule

 B

Exchange of Na+ for K+ in the distal convoluted tubule

 C

Exchange of K+ for Na+ in the proximal convoluted tubule

 D

Exchange of Na+ for K+ in the proximal convoluted tubule

Q. 4

Which of the following actions does aldosterone secretion from the adrenal gland regulate in the kidney?

 A

Exchange of K+ for Na+ in the distal convoluted tubule

 B

Exchange of Na+ for K+ in the distal convoluted tubule

 C

Exchange of K+ for Na+ in the proximal convoluted tubule

 D

Exchange of Na+ for K+ in the proximal convoluted tubule

Ans. B

Explanation:

The distal convoluted tubule (DCT) in the kidney cortex functions to reabsorb Na+ and secrete K+. This is regulated by the adrenal hormone, aldosterone, as stimulated by angiotensin II, which will increase reabsorption of Na+ and secrete K+. The DCT also functions in the continuation of bicarbonate ion reabsorption with hydrogen ion secretion. The terminal portion of the DCT is sensitive to antidiuretic hormone (ADH) from the neurohypophysis, which acts to increase the permeability of the tubule to water, resulting in concentrating the urine. 

Ref: Barrett K.E., Barman S.M., Boitano S., Brooks H.L. (2012). Chapter 20. The Adrenal Medulla & Adrenal Cortex. In K.E. Barrett, S.M. Barman, S. Boitano, H.L. Brooks (Eds), Ganong’s Review of Medical Physiology, 24e.

 


Q. 5

Which of the following inhibits aldosterone synthesis in the adrenal cortex?

 A

Adrenocorticotropin (ACTH)

 B

Atrial natriuretic peptide (ANP)

 C

Angiotensin I

 D

Angiotensin II

Q. 5

Which of the following inhibits aldosterone synthesis in the adrenal cortex?

 A

Adrenocorticotropin (ACTH)

 B

Atrial natriuretic peptide (ANP)

 C

Angiotensin I

 D

Angiotensin II

Ans. B

Explanation:

Atrial natriuretic peptide (ANP) inhibits the synthesis of aldosterone in the adrenal cortex. ANP is secreted by atrial cardiocytes and it stimulates the excretion of Na+, accompanied by an increase in water excretion. The inhibitory effect on aldosterone synthesis is partially responsible for the physiological effects of ANP, however other mechanisms (e.g. increase in glomerular filtration rate) are also important in the natriuretic action of ANP. Adrenocorticotropin (ACTH), angiotensin II, and the increase of plasma K+ level are the major physiological stimuli of aldosterone biosynthesis. Angiotensin I, the prohormone form of angiotensin II does not influence directly the aldosterone synthesis in the adrenal cortex.
 
Ref: Molina P.E. (2013). Chapter 10. Endocrine Integration of Energy and Electrolyte Balance. In P.E. Molina (Ed), Endocrine Physiology, 4e. 


Q. 6

Aldosterone regulates extracellular volume and potassium homeostasis by binding to its receptors present in all, EXCEPT:

 A

Liver

 B

Colon

 C

Hippocampus

 D

Distal nephron

Q. 6

Aldosterone regulates extracellular volume and potassium homeostasis by binding to its receptors present in all, EXCEPT:

 A

Liver

 B

Colon

 C

Hippocampus

 D

Distal nephron

Ans. A

Explanation:

Aldosterone regulates extracellular volume and potassium homeostasis by binding to renal cortical collecting duct principal epithelial cell mineralocorticoid receptors.

The mineralocorticoid receptor — a member of the nuclear receptor family and also found in the heart, colon, and hippocampus — is localized to the cytoplasm prior to activation, undergoes a conformational change on binding to aldosterone, and translocates into the nucleus where it functions as a transcription factor.

Aldosterone is rapidly inactivated to tetrahydroaldosterone in the liver.
 
Ref: Young, Jr W.F. (2011). Chapter 10. Endocrine Hypertension. In D.G. Gardner, D. Shoback (Eds), Greenspan’s Basic & Clinical Endocrinology, 9e.  

 


Q. 7

Predict the effect of aldosterone hypersecretion on body fluid pH and electrolytes ?

 A

pH decreased, K+ decreased, Na+ increased

 B

pH increased, K+ decreased, Na+ increased

 C

pH decreased, K+ increased, Na+ decreased

 D

pH increased, K+ increased, Na+ decreased

Q. 7

Predict the effect of aldosterone hypersecretion on body fluid pH and electrolytes ?

 A

pH decreased, K+ decreased, Na+ increased

 B

pH increased, K+ decreased, Na+ increased

 C

pH decreased, K+ increased, Na+ decreased

 D

pH increased, K+ increased, Na+ decreased

Ans. B

Explanation:

Aldosterone increases the rate of sodium absorption and potassium secretion by the kidneys, but in high concentrations aldosterone also stimulates hydrogen ion secretion. Therefore elevated aldosterone levels such as occur in patients with Cushing’s syndrome can elevate body fluid pH above normal (alkalosis). The major factor that influences the rate of hydrogen ion secretion, however, is pH of the body fluids.
 
Ref: Barrett K.E., Barman S.M., Boitano S., Brooks H.L. (2012). Chapter 20. The Adrenal Medulla & Adrenal Cortex. In K.E. Barrett, S.M. Barman, S. Boitano, H.L. Brooks (Eds), Ganong’s Review of Medical Physiology, 24e.

Q. 8

Several hormones regulate the tubular reabsorption of water and electrolytes at different sites in the nephron. Which of the following combination is correct?

 A

Angiotensin in distal tubule

 B

Aldosterone in collecting ducts

 C

ADH in proximal tubule

 D

ANP in loop of Henle

Q. 8

Several hormones regulate the tubular reabsorption of water and electrolytes at different sites in the nephron. Which of the following combination is correct?

 A

Angiotensin in distal tubule

 B

Aldosterone in collecting ducts

 C

ADH in proximal tubule

 D

ANP in loop of Henle

Ans. B

Explanation:

B i.e. Aldosterone in collecting duct

Hormones

Site of action in kidney

Angiotensin 11

Constricts afferent arterioles, helps to reduce GFR.

Aldosterone

Cortical collecting duct & Distal tubulesQ.

ADH

Medullary collecting ductQ.

ANP

Collecting duct.


Q. 9

Excess secretion of aldosterone causes all except

 A

Increased ECF

 B

Very High Na+ in plasma

 C

Increased BP

 D

Natriuresis

Q. 9

Excess secretion of aldosterone causes all except

 A

Increased ECF

 B

Very High Na+ in plasma

 C

Increased BP

 D

Natriuresis

Ans. B

Explanation:

B i.e. Very High Na+ in plasma

Hyperaldosteronism (excess mineralocorticosteroid) leads to potassium (K+) depletion/ hypokalemia and sodium (Na+) retention, usually without edema but with weakness tetany, polyuria, hypertension and hypokalemic mild metabolic alkalosisQ.

Hyperaldosteronism does not cause metabolic acidossQ. And plasma Na+ level is elevated only slightly if at allQ because water is retained with osmolically active Na+ ions.


Q. 10

Most potent mineralocorticoid is

 A

Aldosterone

 B

DOCA

 C

Dexamethasone

 D

Betamethasone

Q. 10

Most potent mineralocorticoid is

 A

Aldosterone

 B

DOCA

 C

Dexamethasone

 D

Betamethasone

Ans. A

Explanation:

Ans. is ‘a’ i.e., Aldosterone

o Glucocorticoid with max. mineralocorticoid activity —> Hydrocortisone (cortisol) o Glucocorticoid with min. glucocorticoid activity -4 Hydrocortisone

o Glucocorticoid with no mineralocorticoid activity —> Betamethasone, Paramethasone, Dexamethasone, Triamcinolone.

o Mineralocorticlid with no glucocorticoid activity DOCA

o Maximum mineralocorticoid activity —> Aldosterone.

o Maximum glucorticoid activity -4 dexamethasone, Betamethasone.


Q. 11

Increased Aldosterone leads to all except:

 A

Hypernatremia

 B

Hypokalemia

 C

Hypertension

 D

Metabolic acidosis

Q. 11

Increased Aldosterone leads to all except:

 A

Hypernatremia

 B

Hypokalemia

 C

Hypertension

 D

Metabolic acidosis

Ans. D

Explanation:

Answer is D (Metabolic acidosis):

Increased Aldosterone is associated with metabolic alkalosis and not metabolic acidosis.

Hypokalemia (potassium excretion), Hypernatremia (sodium conservation) and hypertension (characteristically diastolic) may all be seen with increased aldosterone.


Q. 12

Aldosterone acts chiefly on which of the following cells: 

September 2011

 A

DCT

 B

PCT

 C

Loop of Henle

 D

Glomerulus

Q. 12

Aldosterone acts chiefly on which of the following cells: 

September 2011

 A

DCT

 B

PCT

 C

Loop of Henle

 D

Glomerulus

Ans. A

Explanation:

Ans. A: DCT

Aldosterone acts on the principal (P) cells of DCT and collecting tubules

Aldosterone

  • It increases the reabsorption of sodium ions and water and the secretion of potassium ions in the collecting ducts and distal convoluted tubule of the kidneys’ functional unit, the nephron.
  • This increases blood volume and, therefore, increases blood pressure.
  • Drugs that interfere with the secretion or action of aldosterone are in use as antihypertensives.
  • One example is spironolactone, which lowers blood pressure by blocking the aldosterone receptor.
  • Aldosterone is part of the renin-angiotensin system.
  • Aldosterone is a yellow steroid hormone (mineralocorticoid family) produced by the outer-section (zona glomerulosa) of the adrenal cortex.
  • The overall effect of aldosterone is to increase reabsorption of ions and water in the kidney. Its activity is reduced in Addison’s disease and increased in Conn’s syndrome.

Q. 13

Aldosterone secretion is maximally stimulated by‑

 A

Hyperkalemia

 B

ACTH

 C

Hypernatremia

 D

Exogenous steroids

Q. 13

Aldosterone secretion is maximally stimulated by‑

 A

Hyperkalemia

 B

ACTH

 C

Hypernatremia

 D

Exogenous steroids

Ans. A

Explanation:

Ans. is ‘a’ i.e., Hyperkalemia

Mineralocorticoid secretion is stimulated by hyperkalemia, angiotensin-H, ACTH and hyponatremia, in reducing order of efficacy.

1) Aldosterone secretion in response to hyperkalemia is the most important and forms the basis for renal regulation of body potassium balance.

2) Stimulation of aldosterone by angiotensin II (through renin-angioensin system) is important for the correction of hypovolemia and hypotension in conditions like salt depletion or renal ischemia.

3) Stimulation of aldosterone secretion by ACTH results in diurnal variation of aldosterone secretion. However, ACTH is not an important physiological regulator for aldosterone secretion.

4) Hyponatremia is a weak stimulator of aldosterone secretion.



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