Published on July 8, 2007
ENDOCRINE SYSTEM 1 R. Kalliecharan
Hormonal Effects Hormones regulate : 1) Homeostasis– chemical comp and volume 2) Metabolic Activities 3) Growth and Development 4) Reproduction 5) Immune System 6) Smooth and Cardiac Muscles
Location of Glands • 1) Specific Hormones affect Specfic TARGET 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 Transport Circulating 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
Hypophyseal Portal System • 1) Hypothalamus secretes releasing and inhibiting hormones into primary capillary plexus (pcp) at Med Eminence • 2) Int Carotid A—superior hypophyseal artery---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 acidophils and basophils • 2) Acidophils and secretions : a) somatotrophs → GH (somatotropin) b) mammotrophs → prolactin
• 3) Basophils and secretions a) thyrotrophs → TSH b) corticotrophs → ACTH, LPH, MSH, endorphins and enkephalins c) gonadotrophs → LH and FSH 4) Chromophobes → no cytoplasmic staining
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 Regulation of 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 Target Tissue Tissue TSH T3& T4
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
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