Pituitary gland – Master gland “ The conductor of Endocrine Symphony”
Origin: originated from ectoderm of embryo
Location:
– below the hypothalamus in the depression of the sphenoid bone of skull -Connected with the brain by a short, thin stalk called infundibulum
Structure :
- Pinkish, pea sized, about 1.3 cm, weighing 0.5gm.
- 3 lobes : Anterior lobe, intermediate lobe (anterior and intermediate together called as adenohypophysis) and posterior lobe (neurohypophysis).
- Hypothalamus produce releasing and inhibiting hormones which regulate and coordinate the anterior lobe of pituitary gland to initiate the production or suppression of specific hormones.
Hormones of anterior lobe
Somatotrophin or Somatotrophic hormone (STH) or Growth Hormone (GH)
- Stimulates the growth and development of all the tissues by accelerating the protein synthesis and cell division, absorption of calcium and conversion of glycogen to glucose
- Secretion is controlled by hypothalamus
Target cells: Various body cells which undergoes growth
Disorders:
Hypo secretion: Dwarfism
Hypersecretion: Gigantism- overgrowth of skeleton; and Acromegaly- overgrowth of bones of hands, feet and specially cheeks, jaws and face.
Thyrotropin of Thyroid Stimulating Hormone (TSH)
- Regulate the growth of thyroid glands and production of thyroxin therein.
Target cells : Cells of Thyroid
Adrenocorticotrophic hormone (ACTH)
- Cause adrenal cortex to grow and secrete all of its normal hormones.
Target cells : Cells of Adrenal cortex.
Melanocyte stimulating hormone (MSH)
- Stimulates cutaneous (skin) pigmentation by dispersion of melanin granules.
Target cells : Melanocytes in skin
Prolactin hormone (PRL) or Luteotropin hormone (LTH)
- Activates growth of breasts during pregnancy and stimulates milk production and secretion of mammary gland after childbirth.
- Also controls reproduction, osmoregulation, growth and metabolism.
Target cells : Cells of Mammary glands.
Gonadotropins (FSH, LH in female and ICSH in male)
Stimulates gonads ( testis and ovaries ) and controls sexual cycle
i) Follicle stimulating hormone (FSH)
- growth of ovarian follicles up to the point of ovulation in female
- development of seminiferous (sperm carrying ) tubules and maintenance of spermatogenesis (production of sperms) in male
Target cells : Cells of gonads (testis and ovary)
ii) Luteinizing Hormone (LH) or Interstitial cell stimulating Hormone (ICSH)
- Responsible for final maturation of ovarian follicles and ovulation
- Stimulates ovaries to produce estrogen and testis to produce androgens.
- LH alone induces rupturing of follicles and secretion progesterone
- In male, ICSH stimulates interstitial cells of testis and also the secretion of testosterone.
Target cells: Cells of gonads (testis and ovaries)
HORMONES OF NEUROHYPHOPHYSIS (POSTERIOR LOBE)
- Hormones are actually produced by neurosecretory cells of hypothalamus and passed into posterior lobe which later is releases when required.
Oxytocin (OT)
- Released when hypothalamic neurons are stimulated by widening of uterus at the time of delivery or sucking of breast by child.
- Stimulates contraction of uterine muscles during childbirth and contraction of myoepithelial cells of mammary gland during sucking by child. Hence called: birth hormone and milk ejecting hormone.
Antidiuretic hormone (ADH) or Vasopressin
- Stimulates the reabsorption of water in DCT, CT in kidneys and decrease water loss.
- Stimulates contraction of smooth muscles of blood vessels and increases blood pressure.
Deficiency of ADH reduces reabsorption of water and increases urine output causing excessive thirst, this defect is called as diabetes insipidus. No glucose is lost in urine of such patient.
