ENDOCRINE SYSTEM 1

R. Kalliecharan

Hormonal Effects

Hormones regulate :1) Homeostasis– chemical comp and

volume2) Metabolic Activities3) Growth and Development4) Reproduction5) Immune System6) Smooth and Cardiac Muscles

Location of Glands

• 1) Specific Hormones affect SpecficTARGET Cells by binding to `Specific RECEPTORS

• For e.g. TSH binds to receptors on surface of Thyroid Follicular cells but not to Adrenals

• Receptors are constantly synthesized and broken down

Hormone TransportCirculating Hormones ( Endocrine

secretion) - hormones in blood act on distant target cell e.g. LH or ACTH

Paracrine secretion – act within short distance e.g. Gastrin H of G-cells in pylorus act on parietal cells of fundic glands

Juxtacrine secretion-- act at very short distance e.g. somatostatin inhibits insulin

Autocrine secretion-act on themselves e.g. interleukin-2

Mechanism of Hormone Action

• 1) Steroid and Thyroid Hormones—activation of intracellular

receptor• 2) Protein Hormones—activation of

plasma membrane –1st messenger –adenyl cyclase activation followed by 2 nd messenger (c AMP )

Pituitary Gland (Hypophysis)• Location: Sella Turcica of Sphenoid bone• Gland is attached to Hypothalamus by

infundibulum• Lobes:1) Adenohypophysis- oral ectoderm

and (2) Neurohypophysis-neural ectoderm• 1)Adeno—consists of pars distalis (Ant

pit) , pars tuberalis and pars intermedia• 2)Neuro—consists of pars nervosa (Post

pit) , infundibular stem and median eminence

Pars nervosa

Hypophyseal Portal System

• 1) Hypothalamus secretes releasing and inhibiting hormones into primary capillary plexus (pcp) at Med Eminence

• 2) Int Carotid A—superior hypophysealartery---PCP---hypophyseal portal veins ---secondary CP in pars distalis— hormones go out via Ant hypophyseal veins

Ant Pit (pars distalis)

• 1) Cells are ÷ into chromophils and chromophobes

• Chromophils are ÷ into acidophilsand basophils

• 2) Acidophils and secretions :a) somatotrophs → GH (somatotropin)b) mammotrophs → prolactin

• 3) Basophils and secretionsa) thyrotrophs → TSHb) corticotrophs → ACTH, LPH, MSH,

endorphins and enkephalinsc) gonadotrophs → LH and FSH

4) Chromophobes → no cytoplasmicstaining

Hypothalamic Regulation of Pars Distalis

• Hypothalamus secretes Releasing and Inhibiting Hormones

• TRH--- ↑ TSH --- ↑ T 4 + T 3

• CRH--- ↑ ACTH--- ↑ glucocorticoids(Adrenals)

• GnRH--- ↑ FSH--- ovary (↑ estrogens) , -- Sertoli cells (↑ABP and inhibin)

• --↑ LH maturation,ovulation, and corpus luteum

• --Leydig cells (↑ testosterone )

Hypothalamic Regulationof Pars Distalis

• GRH(SRH)---↑GH--- ↑Somatomedin C• Somatostatin---↓ GH• PRH--- ↑ Prolactin--- ↑ milk secretion• PIH (dopamine)--- ↓ Prolactin

Cont.

• Pars Tuberalis--- some cells secrete FSH and LH

• Pars Intermedia---Area is rudimentary in Humans

Negative Feedback System

• Hypothalamus(CRH)->AntPit(↑ACTH)• ↑ ↓• ¦ Adrenal cortex(↑cortisol)• ¦ ↓• ---------------------------------- ↓

Target Tissue Target Tissue

T3& T4

+

TSH

+

Neurohypophysis• Pars nervosa (post pit)---has no secretory

cells. It has pituicytes and unmyelinated axons of neurosecretory neurons.

• Herring bodies contain hormones. These are Oxytocin from paraventricular N.-uterine m

• And ADH (vasopressin )from supraoptic N• -- increases water permeability of kidneys