ENDOCRINE GLANDS AND HORMONES :
- Endocrine glands lacks ducts and are hence, called duct less glands.
- The chemicals secreted by endocrine gland is called hormone.
- Hormones are the chemical synthesized in the endocrine gland, acts as chemical messengers, transported in blood to distance place, where it acts on specific cells/tissue/organs, called target organ.
- Current specific definition of hormone is- hormones are non-nutritional chemicals which act as intercellular messengers and are produced in trace amount.
The hypothalamus :
- It is the basal part of the diencephalon, fore brain.
- It contains several groups of neurosecretory cells called nuclei which produce hormones.
- These hormones regulate the synthesis and secretory activity of pituitary gland.
- Hormones produced by it are two types –
- Releasing hormone (which stimulate secretion of pituitary hormone)
- Inhibiting hormone( which inhibit secretion of pituitary hormone)
- GnRH (gonadotrophins releasing hormone) from hypothalamus stimulate the pituitary gland to release gonadotrophins)
- Somatostatin from the hypothalamus inhibits the secretion of growth hormone from pituitary gland.
- Hormones secreted from the hypothalamus reach the pituitary gland through a portal circulation and regulate the anterior pituitary gland.
- Posterior pituitary is under the direct neural regulation of the hypothalamus.
The pituitary gland :
- Pituitary gland is located in a bony cavity called sella tursica and is attached to the hypothalamus by a stalk.
- Anatomically pituitary gland divided into two parts –
- Adenohypophysis.
- Neurohypophysis.
- Adenohypophysis consists of two portions –
- Pars distalis
- Pars intermedia.
- Pars distalis commonly called anterior pituitary produce following hormones –
- Growth hormone (GH)
- Prolactin (PRL)
- Thyroid stimulating hormone (TSH)
- Adrenocorticotrophic hormone (ACTH)
- Luteinizing hormone (LH)
- Follicle stimulating hormone (FSH)
- Pars intermedia secrete one hormone called melanocyte stimulating hormone.
- Neurohypophysis (pars nervosa) also known as posterior pituitary store and release two hormone called Oxytocin and vasopressin, which are actually synthesized by the hypothalamus and are transported to neurohypophysis.
Growth hormone :
- Regulate normal growth of the body.
- Over secretion of GH leads to overgrowth called gigantism.
- Hypos-secretion of GH leads to dwarfism.
Prolactin :
- Regulates the growth of mammary gland.
- Stimulates formation of milk in the mammary gland.
Thyroid stimulating hormone (TSH) :
- Stimulates the synthesis and secretion of thyroid hormone from thyroid gland.
Adrenocorticotrophic hormone (ACTH) :
- Stimulates the synthesis and secretion of hormones from adrenal cortex called glucocorticoids and mineralocorticoids.
Luteinizing hormone (LH) :
- In male LH stimulate the synthesis and secretion of hormone called androgens from testes.
- In female LH induces ovulation of fully mature follicles (Graafian follicle).
- Maintain the corpus luteum formed from the remnants of Graafian follicle after ovulation.
Follicle stimulating hormone (FSH) :
- In male FSH along with androgen regulate spermatogenesis.
- FSH regulates the development of ovarian follicle.
Melanocyte stimulating hormone :
- MSH acts on the melanocyte (melanin containing cell)
- Regulates the pigmentation of the skin.
