6.2.1 Pituitary Gland

The pituitary gland is a small endocrine gland located just below the hypothalamus. It is attached to the hypothalamus by a stalk called the infundibulum. The pituitary gland is divided into three lobes: the anterior, posterior, and median lobes. It is often called the "master gland" because it secretes numerous hormones, many of which regulate the activity of other endocrine glands.

Definition

Pituitary Gland: Pituitary gland is located just below the hypothalamus. It is attached to hypothalamus by a stalk called infundibulum which is composed of blood vessels and the fibres of neurosecretory cells. Pituitary gland is divided into three lobes: the anterior, posterior and the median.

Main Idea

• The pituitary gland is located just below the hypothalamus.
• It is attached to the hypothalamus by a stalk called the infundibulum.
• The infundibulum is composed of blood vessels and the fibres of neurosecretory cells.
• The pituitary gland is divided into three lobes:
• Classically, the anterior pituitary is considered the master gland of the endocrine system because it secretes numerous hormones, many of which regulate the activity of other endocrine glands.
• It secretes six hormones, all of which regulate the secretory action of other endocrine glands.

Core Concept

• Pituitary gland = located below hypothalamus
• Infundibulum = stalk connecting pituitary to hypothalamus
• Three lobes = anterior, posterior, median
• Anterior lobe = master gland; secretes six hormones
• Posterior lobe = stores and releases ADH and oxytocin
• Median lobe = produces melanocyte stimulating hormone (MSH)

Detailed Explanation

Pituitary Gland

• Pituitary gland is located just below the hypothalamus.
• It is attached to hypothalamus by a stalk called infundibulum which is composed of blood vessels and the fibres of neurosecretory cells.
• Pituitary gland is divided into three lobes, the anterior, posterior and the median.

Anterior Lobe of Pituitary

• Classically, the anterior pituitary is considered the master gland of the endocrine system because it secretes numerous hormones, many of which regulate the activity of other endocrine glands.
• It secretes six hormones, all of which regulate the secretory action of other endocrine glands.

Hormones of the Anterior Lobe:

1. Growth Hormone (GH) or Somatotrophic Hormone (STH)

• It is released under influence of hypothalamic growth hormone releasing factor (GHRF) and are inhibited by hypothalamic somatostatin.
• GH has a direct effect on growth and development.
• GH stimulates cell growth and cell division.
• It also stimulates uptake of amino acids into cells and increases rate of protein synthesis.

Deficiency of GH: - Results in Dwarfism in which development is much slower and individual has short stature, however, the body parts stay in proportion and brain development and IQ are unaffected.

• Gigantism is result of over secretion of GH during childhood in which the bones are still capable of growth and person increase in height abnormally.
• Over secretion of GH in adult life causes acromegaly in which bones are no longer capable of increasing in length but grow in thickness.
• Acromegaly is characterised by enlarging the hands, feet, skull, nose and jawbone.

2. Thyroid Stimulating Hormone (TSH)

• Thyrotrophin releasing factor (TRF) from hypothalamus stimulates the synthesis and release of thyroid stimulating hormone (TSH) from the anterior pituitary.
• TSH regulates the endocrine function of the thyroid gland.
• It increases the number of cells and secretory activity of the thyroid gland.
• Over secretion of TSH causes hyperthyroidism i.e., excess of thyroxin and its under secretion causes hypothyroidism i.e., lack of thyroxin.

3. Adrenocorticotropic Hormone (ACTH)

• It is secreted by the release of corticotrophin releasing factor (CRF) from hypothalamus which is controlled by steroid level in the blood and by direct nervous stimulation of the hypothalamus as a result of stress e.g., cold, heat, pain, fright and infections.
• ACTH acts on adrenal cortex and stimulates the secretion of corticosteroids (cortisone and aldosterone).

4. Follicle Stimulating Hormone (FSH)

- Acts upon reproductive system and regulates its function.

5. Luteinising Hormone (LH)

• Also called interstitial cell stimulating hormone (ICSH) in the male.
• Acts upon reproductive system and regulates its function.

6. Prolactin or Leucotrophic Hormone (LTH)

- Acts upon reproductive system and regulates its function.

Note: FSH, LH, and Prolactin are all collectively known as gonadotropic hormones. These hormones act upon reproductive system and regulate its function.

Median Lobe of Pituitary

• In humans, median lobe of pituitary is not very prominent.
• It is a thin layer of cells between the anterior and posterior pituitary.
• It produces melanocyte stimulating hormone (MSH).
• Secretion of MSH is regulated by hypothalamic MSH inhibitory hormone.
• Melanocyte stimulating hormone increases in humans during pregnancy too.
• It stimulates the production and release of melanin by melanocytes in skin and hair.

Posterior Lobe of Pituitary

• Posterior pituitary is not glandular by itself.
• It does not synthesize any hormone.
• It is largely made up of axons of neurosecretory cells of hypothalamus.

Hormones of the Posterior Lobe:

1. Antidiuretic Hormone (ADH)

• Posterior pituitary stores antidiuretic hormone (ADH or vasopressin) and oxytocin.
• These hormones are released in response to nerve impulses from hypothalamus.
• ADH is produced during the state of dehydration, decreased blood volume and low blood pressure.
• Under secretion of ADH causes diabetes insipidus which is characterized by excessive production of diluted urine and frequent thirst.
• Over secretion may leads to the kidney problems.

• Under certain conditions, such as severe blood loss, exceptionally large amounts of ADH are released, causing a rise in blood pressure.
• The alternative name for this hormone, vasopressin, reflects this particular effect.

2. Oxytocin

• It is released during child birth and in nursing women.
• During birth it is released in waves, and results in labour contractions.
• Over secretion causes rupturing of uterine wall while under secretion of oxytocin inhibits normal labour process.
• In lactating women, suckling causes the release of oxytocin.
• During this feeding process it causes the dilation of milk ducts of mother's mammary glands and thus promotes milk ejection.

Summary Table of Pituitary Hormones

Intermediate Level

Anterior Lobe Hormones

Median Lobe Hormone

Posterior Lobe Hormones

Disorders of Pituitary Gland

Formula / Mathematical Form

Not applicable to this topic.

Solved Example

Not applicable to this topic (descriptive topic).

Important Points

• 1. Pituitary gland is located just below the hypothalamus.
• 2. It is attached to hypothalamus by infundibulum.
• 3. Infundibulum is composed of blood vessels and neurosecretory cell fibres.
• 4. Pituitary gland is divided into three lobes.
• 5. Anterior lobe is considered the master gland.
• 6. Anterior lobe secretes six hormones.
• 7. GH stimulates growth and development.
• 8. GH deficiency causes dwarfism.
• 9. GH excess in childhood causes gigantism.
• 10. GH excess in adults causes acromegaly.
• 11. TSH regulates thyroid gland.
• 12. ACTH stimulates adrenal cortex.
• 13. FSH, LH, and prolactin are gonadotropic hormones.
• 14. Median lobe produces MSH.
• 15. MSH stimulates melanin production.
• 16. Posterior lobe stores and releases ADH and oxytocin.
• 17. ADH regulates water retention.
• 18. ADH deficiency causes diabetes insipidus.
• 19. Oxytocin causes labour contractions.
• 20. Oxytocin promotes milk ejection.

Remember

• - Pituitary gland = below hypothalamus
• - Infundibulum = stalk connecting pituitary to hypothalamus
• - Three lobes = anterior, posterior, median
• - Anterior lobe = master gland; six hormones
• - **GH** = growth and development
• - **TSH** = thyroid regulation
• - ACTH = adrenal cortex stimulation
• - FSH, LH, Prolactin = gonadotropic hormones
• - **MSH** = melanin production
• - **ADH** = water retention
• - Oxytocin = childbirth, milk ejection
• - **Dwarfism** = GH deficiency
• - Gigantism = GH excess in childhood
• - Acromegaly = GH excess in adults
• - Diabetes insipidus = ADH deficiency

Common Mistakes

• 1. Confusing the lobes of the pituitary — Anterior, posterior, median.
• 2. Mixing up the hormones — GH, TSH, ACTH, FSH, LH, Prolactin (anterior); MSH (median); ADH, oxytocin (posterior).
• 3. Forgetting the role of the infundibulum — Connects pituitary to hypothalamus.
• 4. Confusing dwarfism and gigantism — Dwarfism = GH deficiency; gigantism = GH excess in childhood.
• 5. Mixing up gigantism and acromegaly — Gigantism = childhood; acromegaly = adults.
• 6. Forgetting the role of ADH — Water retention.
• 7. Confusing ADH and oxytocin — ADH = water retention; oxytocin = childbirth and milk ejection.
• 8. Thinking the posterior lobe synthesizes hormones — It stores and releases hormones.
• 9. Mixing up the gonadotropic hormones — FSH, LH, prolactin.
• 10. Believing the pituitary is not important — It is the master gland.

Quick Revision

Pituitary gland is located just below the hypothalamus. It is attached to hypothalamus by a stalk called infundibulum which is composed of blood vessels and the fibres of neurosecretory cells. Pituitary gland is divided into three lobes, the anterior, posterior and the median. Classically, the anterior pituitary is considered the master gland of the endocrine system because it secretes numerous hormones, many of which regulate the activity of other endocrine glands. It secretes six hormones, all of which regulate the secretory action of other endocrine glands. Growth hormone (GH) or Somatotrophic hormone (STH) is released under influence of hypothalamic growth hormone releasing factor (GHRF) and are inhibited by hypothalamic somatostatin. GH has a direct effect on growth and development. Deficiency of GH results in Dwarfism. Gigantism is result of over secretion of GH during childhood. Over secretion of GH in adult life causes acromegaly. Thyroid stimulating hormone (TSH) regulates the endocrine function of the thyroid gland. Adrenocorticotropic Hormone (ACTH) acts on adrenal cortex and stimulates the secretion of corticosteroids. Follicle stimulating hormone (FSH), luteinising hormone (LH), and prolactin or leucotrophic hormone (LTH) are all collectively known as gonadotropic hormones. In humans, median lobe of pituitary is not very prominent. It produces melanocyte stimulating hormone (MSH). Posterior pituitary is not glandular by itself. It does not synthesize any hormone. It stores antidiuretic hormone (ADH or vasopressin) and oxytocin. Under secretion of ADH causes diabetes insipidus. Oxytocin is released during child birth and in nursing women.

60-Second Revision

• Pituitary gland = below hypothalamus
• Infundibulum = stalk connecting pituitary to hypothalamus
• Three lobes = anterior, posterior, median
• Anterior lobe = master gland; six hormones
• GH = growth and development
• TSH = thyroid regulation
• ACTH = adrenal cortex stimulation
• FSH, LH, Prolactin = gonadotropic hormones
• MSH = melanin production
• ADH = water retention
• Oxytocin = childbirth, milk ejection
• Dwarfism = GH deficiency
• Gigantism = GH excess in childhood
• Acromegaly = GH excess in adults
• Diabetes insipidus = ADH deficiency
• Warning: Anterior lobe is the master gland; posterior lobe stores and releases hormones

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• Chapter:
• 6. Endocrine System of Man

• Topic:
• 6.2.2 THYROID GLAND

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