Physiology Of Pituitary Gland

PHYSIOLOGY OF PITUITARY GLAND

Q. 1

Commonest functional tumor of pituitary gland is?

 A Gonodotroponoma
 B ACTH secreting tumour
 C TSH secreting tumour
 D

Prolactinoma

Q. 1

Commonest functional tumor of pituitary gland is?

 A Gonodotroponoma
 B ACTH secreting tumour
 C TSH secreting tumour
 D

Prolactinoma

Ans. D

Explanation:

Prolactinoma REF: Sabiston textbook of surgery, 18th ed, chapter 72

Pituitary adenomas arise primarily from the anterior pituitary gland and are classified as either functional (secreting) or nonfunctional (non-secreting) tumors, with the former presenting earlier with symptoms caused by physiologic effects and the latter presenting when of sufficient size to cause neurologic deficits by mass effect on the chiasm with consequent bitemporal hemianopsia.

Tumors smaller than 1 cm in diameter are called microadenomas, and the rest are considered macroadenomas; 50% of pituitary tumors are smaller than 5 mm at the time of diagnosis. Their incidence is increased in multiple endocrine neoplasias. They occur commonly in the third and fourth decades of life and affect both sexes equally.

“The most common functional tumor is the prolactinoma, which causes amenorrhea and galactorrhoea in women”


Q. 2

All are associated with pituitary apoplexy except :

 A >Hyperthyroidism
 B >Diabetes mellitus
 C >Sickle cell anemia
 D >Hypertension
Q. 2

All are associated with pituitary apoplexy except :

 A >Hyperthyroidism
 B >Diabetes mellitus
 C >Sickle cell anemia
 D >Hypertension
Ans. A

Explanation:

Hyperthyroidism /Ref. Harrison 17th/e 2198-2199 & 16thie p 2078]

Pituitary apoplexy

  • Acute intrapituitzuy hemorrhagic vascular event causing substantial damge to pituitary.

Symptoms of pituitary apoplexy

  • Endocrinal emergency
  • Severe hypoglycemia
  • Hypotension
  • Central nervous system hemorrhage and death.

Acute symptoms

  • Severe headache with signs of meningeal irritation
  • B/L visual changes
  • Ophthalmoplegia
  • Cardiovascular collapse and loss of consciousness (in severe cases)

Causes of pituitary apoplexy

  • Preexisting adenoma (spontaneously)
  • Pospartum (sheehan’s syndrome)
  • Diabetes mellitus
  • Hypertension
  • Sickle cell anemia
  • Acute shock

Diagnosis

  • CT or MRI reveal signs of intratumoral or cellar hemorrhage with deviation of pituitary stalk and compression of pituitary tissue.

Treatment

  • Patient with no evidence of visual loss or impaired consciousness – Managed conservatively with high dose glucocorticoid
  • Patient with significant visual loss and loss of consciousness

– Require urgent surgical decompression

– Visual recovery is inversely correlated with the length of the time after the acute event


Q. 3

How many hormones are produced by the anterior pituitary gland?

 A

1

 B

2

 C

3

 D

5

Q. 3

How many hormones are produced by the anterior pituitary gland?

 A

1

 B

2

 C

3

 D

5

Ans. D

Explanation:

There are 5 hormones produced by the anterior pituitary. Those hormones are luteinizing hormone (LH), growth hormone (GH), follicle stimulating hormone (FSH), prolactin (PRL) and thyroid stimulating hormone (TSH).
 
Ref: Molina P.E. (2013). Chapter 3. Anterior Pituitary Gland. In P.E. Molina (Ed),Endocrine Physiology, 4e.

Q. 4

The hypothalamus produces several releasing peptides. Which releasing peptide is responsible for the release of adrenocorticotropin (ACTH) from the pituitary?

 A

CRF (corticotropin releasing factor)

 B

ACF (ACTH releasing factor)

 C

Corticosterone

 D

Cortisol

Q. 4

The hypothalamus produces several releasing peptides. Which releasing peptide is responsible for the release of adrenocorticotropin (ACTH) from the pituitary?

 A

CRF (corticotropin releasing factor)

 B

ACF (ACTH releasing factor)

 C

Corticosterone

 D

Cortisol

Ans. A

Explanation:

Corticotropin releasing factor (CRF) released from the hypothalamic paraventricular nucleus is responsible for release of ACTH. The cell type within the paraventricular nucleus is termed the parvicellular or small neurons. These neurons project their axons into the tuberohypophyseal tract to be released into the hypothalamo hypophyseal portal system to act on the pituitary.
 
Ref: Javorsky B.R., Aron D.C., Findling J.W., Tyrrell J.B. (2011). Chapter 4. Hypothalamus and Pituitary Gland. In D.G. Gardner, D. Shoback (Eds),Greenspan’s Basic & Clinical Endocrinology, 9e.

 


Q. 5

Basophilic cells of pituitary secretes:

 A

Prolactin

 B

GH

 C

LSH

 D

All

Q. 5

Basophilic cells of pituitary secretes:

 A

Prolactin

 B

GH

 C

LSH

 D

All

Ans. C

Explanation:

B i.e. TSH


Q. 6

Posterior pituitary secretes:

 A

Oxytocin

 B

Prolactin

 C

ADH

 D

a & c

Q. 6

Posterior pituitary secretes:

 A

Oxytocin

 B

Prolactin

 C

ADH

 D

a & c

Ans. D

Explanation:

A i.e. Oxytocin; C i.e. ADH


Q. 7

A/E are caused by accidental transection of pituitary stalk:

 A

Diabetes mellitus

 B

Polyuria

 C

Galactorrhea

 D

Diabetes insipidus

Q. 7

A/E are caused by accidental transection of pituitary stalk:

 A

Diabetes mellitus

 B

Polyuria

 C

Galactorrhea

 D

Diabetes insipidus

Ans. A

Explanation:

A i.e. Diabetes mellitus

–                            ADH is formed primarily in supraoptic nucleiQ, whereas oxytocin is formed mainly in paraventricular nucleiQ of hypothalamus. Both hormones are secreted in free form or loosely bound to neurophysin (II & I respectively but then immediately gets detached) to circulate in blood as free hormone formsQ.

–                            Hyperosmolarity is the greatest stimulator for ADH secretionQ. So injection of hyperosmolar (concentrated) electrolyte solution in artery supplying hypothalamus (supraoptic nucleus mainly) cause release of ADH.

–                            Neurosecretion of posterior pituitary hormone ADH (antidiuretic hormone or vaspression) mainly from supraoptic nuclei of hypothalamus is increased with increased plasma osmolality (hyperosmolality) and is decreased with decreased plasma osmolality. Surgery, exercise, stress, pain also increaseADH secretionQ. ADH increases the permeability of distal tubule & collecting ducts to waterQ therefore retaining water in excess of solute.

–                            Vasopressin (ADH) has 3 receptor – VIA receptor in vascular smooth musclesQ, (causing vasoconstriction), liver (glycogenolysis) and area postrema of brain (decreasing cardiac output); V113 or V3 receptor in anterior pituitaryQ (increasing ACTH secretion); and V2 receptor in principal cells of collecting ductsQ (augmenting movement of water through water channel aquaporin-2).

–                            Milk secretion (ejection or let down) a neuroendocrinal reflexQ is caused by oxytocin secreted from posterior pituitaryQ. Oxytocin, whose secretion is affected by emotionsQ & genital stimulation, cause contraction of myoepithelial cellsQ that lie outside the alveoli and hence lit milk ejection.

–                            Diabetes mellitus results from complete or absolute lack of insulin d/t reduction in )3 -cell mass of pacreaseQ. It has nothing to do with pituitary.


Q. 8

Posterior pituitary secrets-

 A

CH

 B

TSH

 C

ADH

 D

FSH

Q. 8

Posterior pituitary secrets-

 A

CH

 B

TSH

 C

ADH

 D

FSH

Ans. C

Explanation:

Ans. is ‘c’ i.e., ADH

Anterior pituitary has two types of cells : ‑

1. Acidophilic cells

o Somatotrophs            –>         Secrete growth hormone

o Lactotrophs               –>          Secrete prolactin

2. Basophilic cells

o Corticotrophs            –>           Secrete ACTH, POMC, MSH

o Thyrotrophs             –>            Secrete TSH

o Gonodotrophs          –>            Secrete FSH, LH Posterior pituitary secretes ADH and oxytocin.


Q. 9

Which of the following is true about pituitary adenoma

 A

Accounts for 10% of brain tumors

 B

Erodes the sellar and extends into surrounding area

 C

Prolactinoma is least common

 D

a and b

Q. 9

Which of the following is true about pituitary adenoma

 A

Accounts for 10% of brain tumors

 B

Erodes the sellar and extends into surrounding area

 C

Prolactinoma is least common

 D

a and b

Ans. D

Explanation:

Ans. is ‘a’, ‘b’

  • Pituitary adenomas constitute approximate 10% of all primary intracranial neoplasms and about 1/3 to 1/2 of all suprasellar/juxtasellar masses [Pituitary adenomas are most common sellar tumors in adults. Most common sellar tumor in children is craniopharyngioma]
  • Pituitary adenomas are classified on the basis of hormone(s) produced by the neoplastic cells detected by immunohistochemical stains.
  • Most common pituitary adenomas are prolactinomas.
  • Pituitary adenomas can be differentiated from hyperplasia by reticulin stain (Absence of reticulin network is seen in adenoma)
  • Pituitary adenomas are sellar lesions but larger adenomas can extend through the diaphragm sella into the suprasellar region and compress the optic chiasm (causing visual field abnormalities) and other cranial nerves. Large adenomas can also erode the sellar turcica and extend into surrounding region (k/a invasive adenomas)

More about Pituitary adenomas

  • It is the most common cause of hyperpituitarism.
  • Pituitary adenomas can be functional (i.e. associated with hormone excess and their clinical manifestations) or silent (i.e. without clinical symptoms of hormone excess. May or may not produce hormone) 
  • Prolactinomas are the most common adenomas
  • Some pituitary adenomas can secrete two hormones – Growth hormone and prolactin being the most common combination
  • Rarely adenomas are plurihormonal
  • Age : usually found in adults
  • Gender

Prolactinomas have 4-5 : 1 female/male ratio

GH secreting adenomas have 2:1 male predominance.

  • Clinical signs & symptoms – occur due to hormone excess or mass effect (visual field disturbances, elevated intracranial pressure or occasionally hypopitutarism – d/t silent adenomas compressing normal pituitary)
  • Acute hemorrhage into an adenoma causes rapid enlargement of mass and sudden clinical deterioration k/a pituitary apoplexy.
  • Prolactinomas have a propensity to undergo dystrophic calcification, ranging from isolated psanunoma bodies to extensive calcification of entire tumor mass (k/a pituitary stone)

Q. 10

Which of the following is the most common type of pituitary adenoma?

 A

Thyrotropinoma

 B

Gonadotropinoma

 C

Prolactinoma

 D

Corticotropinoma

Q. 10

Which of the following is the most common type of pituitary adenoma?

 A

Thyrotropinoma

 B

Gonadotropinoma

 C

Prolactinoma

 D

Corticotropinoma

Ans. C

Explanation:

Answer is C (Prolactinoma):

`Prolactinomas (Lactotroph Adenomas) are the most frequent type of hyperfunctioning pituitary adenomas, accounting for about 30% of all clinically recognized pituitary adenomas’ – Robbins


Q. 11

All are associated with pituitary apoplexy except:

 A

Hyperthyroidism

 B

Diabetes mellitus

 C

Sickle cell anemia

 D

Hypertension

Q. 11

All are associated with pituitary apoplexy except:

 A

Hyperthyroidism

 B

Diabetes mellitus

 C

Sickle cell anemia

 D

Hypertension

Ans. A

Explanation:

Answer is A (Hyperthyroidism):

Hyperthyroidism is not mentioned as a cause of pituitary apoplexy.

Pituitary Apoplexy

Pituitary Apoplexy refers to the clinical syndrome arising from hemorrhage or infarction of the pituitary gland.

Causes/Predisposing factors for Pituitary Apoplexy

  • Pre existing Pituitary Adenoma
  • Pregnancy
  • Postpartum (Sheehan’s syndrome)
  • Diabetes
  • Hypertension
  • Sickle cell anemia
  • Acute shock
  • Others (Internal Medicine 5th/1778)

Trauma, Carotid Angiography, Bleeding/Clotting disorders, Anticoagulant therapy, Radiation to pituitary tumor, Artificial Respiration.


Q. 12

Anterior pituitary develops from ‑

 A

Infundibulum

 B

Neuroectoderm

 C

Rathke’s pouch

 D

None

Q. 12

Anterior pituitary develops from ‑

 A

Infundibulum

 B

Neuroectoderm

 C

Rathke’s pouch

 D

None

Ans. C

Explanation:

Ans. is ‘c’ i.e., Rathke’s pouch

Pituitary gland (hvpophvsis cerebri)

  • Pituitary gland lies within hypophyseal/pituitary fossa or sella turcica of sphenoid bone which is roofed by diaphragm sellae.
  • It is suspended from tuber cinereum of hypothalamus by infundibulum (pituitary stalk).
  • It is related anterosuperiorly to optic chiasma, laterally to cavernous sinus and inferiorly to sphenoid air sinuses in the body of sphenoid.
  • Pituitary gland is oval in shape, measures 8 12 mm, and weighs about 500 mg.
  • Pituitary gland has two main subdivisions:- (i) Adenohypophysis (anterior lobe), and (ii) Neurohypophysis (posterior lobe).
  • Adenohypophysis (anterior lobe) include (i) pars anterior or pars distalis or pars glandularis or anterior lobe proper, (ii) pars intermedia (intermediate lobe); and (iii) tuberal lobe (pars tuberalis).
  • It develops from an upward growth (Rathke’s pouch) from the ectodermal roof of stomodeum. 
  • Neurohypophysis (posterior lobe) include (i) pars posterior or pars nervosa or neural lobe or posterior lobe proper; (ii) infundibulum (infundibular stem); and (iii) median eminence.
  • It develops from a downgrowth from the 3rd ventricle/diencephalon (neuroectoderm) called infundibulum. 
  • Anterior lobe contains many hormone secreting cells: chromophils (acidophils, basophils), chromophobes and follicullostellate cells.
  • Posterior pituitary contain neuroglia like pituicytes which do not secrete any hormone.
  • The posterior pituitary hormones (ADH and oxytocin) are synthesized in hypothalamus and transported to posterior lobe by hypothalamohypophyseal nerve fiber tract and stored in the axon terminals of neurohypophysis in Herring bodies before their release.


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