Pituitary Gland Hormones

Pituitary Gland

• The pituitary gland is a small endocrine gland with a diameter of 1cm and weight of 0.5 to 1g.
• It is situated in the sphenoid bone at the base of the skull in a depression called 'sella turcica'.
• It is connected to the hypothalamus by the pituitary stalk or hypophyseal stalk.

Anterior Pituitary or Adenohypophysis

• The anterior pituitary secretes six hormones:
  • Growth hormone (GH) or somatotropic hormone (STH)
  • Thyroid-stimulating hormone (TSH) or thyrotropic hormone
  • Adrenocorticotropic hormone (ACTH)
  • Follicle-stimulating hormone (FSH)
  • Luteinizing hormone (LH) in females or interstitial cell-stimulating hormone (ICSH) in males
  • Prolactin
• Growth hormone (GH) is responsible for the general growth of the body.
• Hypersecretion of GH causes enormous growth of the body, leading to gigantism.
• Deficiency of GH in children causes stunted growth, leading to dwarfism.

Actions of Hormones

• Thyroid-stimulating hormone (TSH) is necessary for the growth and secretory activity of the thyroid gland.
• Adrenocorticotropic hormone (ACTH) is necessary for the structural integrity and the secretory activity of the adrenal cortex.
• Follicle-stimulating hormone (FSH) acts along with testosterone and accelerates the process of spermeogenesis in males.
• In females, FSH causes the development of graafian follicle from primordial follicle and causes secretion of estrogen.
• Luteinizing hormone (LH) is essential for the secretion of testosterone from Leydig cells in males and is responsible for ovulation in females.
• Prolactin is necessary for the final preparation of mammary glands for the production and secretion of milk.

Posterior Pituitary or Neurohypophysis

• Posterior pituitary hormones are:
  • Antidiuretic hormone (ADH) or vasopressin
  • Oxytocin
• The posterior pituitary does not secrete any hormone.
• ADH and oxytocin are synthesized in the hypothalamus.
• These hormones are transported to the posterior pituitary through the nerve fibers of the hypothalamo-hypophyseal tract.
• In the posterior pituitary, these hormones are stored at the nerve endings.
• When impulses from the hypothalamus reach the posterior pituitary, these hormones are released from the nerve endings into the circulation.

Antidiuretic Hormone (ADH)

• Antidiuretic hormone has two actions:
  • Retention of water
  • Vasopressor action
• The major function of ADH is retention of water by acting on the kidneys.
• It increases the facilitative reabsorption of water from the distal convoluted tubule and collecting duct in the kidneys.
• In large amounts, ADH shows vasoconstrictor action.
• This causes constriction of the arteries in all parts of the body.

Endocrine Glands

• Endocrine glands are the glands which synthesize and release the classical hormones into the blood.
• Endocrine glands are also called ductless glands because the hormones secreted by them are released directly into blood without any duct.
• Endocrine glands are distinct from exocrine glands which release their secretions through ducts.
• Endocrine glands play an important role in homeostasis and control of various other activities in the body through their hormones.

Major Endocrine Glands

• Pineal gland
• Pituitary gland
• Thyroid gland
• Parathyroid glands
• Thymus
• Adrenal gland
• Pancreas
• Ovary (in females)
• Testis (in males)

Hormones Secreted by Major Endocrine Glands

• Anterior Pituitary
  • Growth hormone (GH)
  • Thyroid-stimulating hormone (TSH)
  • Adrenocorticotropic hormone (ACTH)
• Mineralocorticoids
  • Aldosterone
  • 11-deoxycorticosterone

Classification of Chemical Messengers

• Endocrine messengers
• Paracrine messengers
• Autocrine messengers
• Neurocrine messengers

Endocrine Messengers

• These are the classical hormones.
• Examples are growth hormone and insulin.

Paracrine Messengers

• These are the chemical messengers which diffuse from the control cells to the target cells through the interstitial fluid.
• Examples are prostaglandins and histamine.

Autocrine Messengers

• These are the chemical messengers that control the source cells which secrete them.
• Examples are leukotrienes.

Neurocrine or Neural Messengers

• These are neurotransmitters and neurohormones.
• Examples are acetylcholine and dopamine.

Thyroid Gland

• The thyroid gland is an endocrine gland situated at the root of the neck on either side of the trachea.
• It has two lobes, which are connected in the middle by an isthmus.
• The thyroid gland secretes three hormones:
  • Tetraiodothyronine or T4 (thyroxine)
  • Triiodothyronine or T3

Neurocrine or Neural Messengers

• Neurocrine or neural messengers: These are neurotransmitters and neurohormones.
• Neurotransmitter: An endogenous signaling molecule that carries information from one nerve cell to another nerve cell or muscle or another tissue.
• Neurohormone: A chemical substance that is released by the nerve cell directly into the blood and transported to the distant target cells.