Pituitary gland or Hypophysis is a pea-sized endocrine gland weighing about 0.5gm which is a protrusion at the bottom of hypothalamus, more precisely, below the hypothalamus at base of brain.
It has three lobes: Anterior lobe, Middle lobe and Posterior lobe. These lobes secrete endocrine hormones that control various functions of the body. Most of the hormones are controlled by hypothalamus, which is just overlying it. The mechanism of hormone secretion is often either Positive feedback (more hormone secretion on stimuli) or Negative feedback (less hormone secretion on stimuli).
HORMONES AND FUNCTIONS
Following are the hormones secreted from their respective lobes:
|Pituitary Gland Hormones and their functions|
Anterior lobe hormones
Hypothalamus produces hormones and transfers them to anterior lobe via special capillary system called Hypothalamic-Hypophyseal Portal System. Anterior pituitary gland secretes the following hormones from pituitary gland :
- Prolactin : Also knwon as Lactotrophs, it acts on milk producing cells in breasts (lactocytes) and causes Lactation (milk production).
- Human Growth Hormone: Also known as HGH or Somatotropins, it acts on body cells and causes growth.
- Thyroid Stimulating Hormone: Also known as TSH, it acts on thyroid and causes realease of thyroxine, thereby stimulates growth and metabolism.
- AdrenoCorticotropic Hormone: Also known as ACTH or Corticotropins, it acts on adrenal glands over kidney, and causes adrenaline release which is a FIGHT FLIGHT FEAR Hormone.
- Follicular Stimulating Hormone: It acts on testes in males and causes testicular growth, while in females, it acts on ovaries and causes development of ovarian follicles.
- Lutenizing Hormone: It acts on testes in males and causes testesterone production while in females, it acts on ovaries and causes egg production (ovulation) and estergen and progesterone production.
Middle lobe hormones
Middle lobe or the Intermediate lobe syntehsizes and secretes only one hormone:
- Melanocyte Stimulating Hormone: Also known as MSH, it causes release of melanin pigment, which imparts color to skin and hair.
Posterior lobe hormones
Posterior pituitary gland stores and secretes but doesn’t synthesizes the hormones. Posterior lobe secretes the following hormones from pituitary gland:
- Anti-Diuretic Hormone: It acts on kidneys and maintains regulation of water.
- Oxytocin: It acts on uterus and causes labour contractions.
Mechanism of Hormone Control
Hormones are often under control of hypothalamus or other feedback mechanism. These can be as follows :
Under control of hypothalamus. It is stimulated by Growth Hormone Releasing Hormone (GHRH) and inhibited by Somatostatin.
Under control of hypothalamus. It is stimulated by Thyrotropin Releasing Hormone (TRH) and inhibited by Somatostatin.
It is under negative feedback mechanism and inhibited by reduction of Corticotopin Releasing Hormone (CRH).
It is stimulated by nipple suction by the infants, and is inhibited by Dopamine.
It is again under negative feedback mechanism.
It is under positive feedback mechanism, the more the labour contractions, more the Oxytocin is released causing further contractions.
HORMONES DEFECT: EXCESS OR DEFICIENCY?
Deficiency or Excess of these pituitary gland endocrine hormones can cause following pathological abnormalities:
Human Growth Hormone
Excess: Gigantism before epiphyseal closure and Acromegaly after epiphyseal closure
Excess: Cushing’s disease/Syndrome
Deficiency: ACTH deficiency (Addison’s deficiency)
Thyroid Stimulating Hormone
Follicular Stimulating Hormone
Excess: In males- Premature puberty; In females- Irregular periods, breast development, Infertility
Melanocyte Stimulating Hormone
Excess: Hyperpigmentation, often dark colored skin
Deficiency: Hypopigmentation, often light toned skin
Deficiency: Diabetes Inspidus (Central type)
Excess: Causes Euphoria, social happiness
Deficiency: Causes depression.
Pituitary Hormones at all
- Hypopituitarism: Deficiency of all pituitary hormones
- Hyperpituitarism: Excess of all pituitary hormones
- Panhypopituitarism: Deficiency of most hormones