The endocrine system regulates homeostasis, metabolism, growth, development, reproduction, the immune system, and muscle function through hormones. Hormones are produced in glands and travel through the bloodstream to target cells where they bind to specific receptors to cause effects. The pituitary gland located in the sella turcica regulates many other glands through releasing and inhibiting hormones that travel through a hypothalamic-hypophyseal portal system. The anterior pituitary is divided into lobes that secrete hormones like growth hormone, prolactin, thyroid stimulating hormone, and gonadotropins which are regulated by the hypothalamus through negative feedback loops.

1. ENDOCRINE SYSTEM 1
R. Kalliecharan

2. 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

3. 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

4. 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

6. 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 )

7. 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

9. Pars nervosa

11. 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

14. 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

16. • 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

18. 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 )

19. Hypothalamic Regulation
of Pars Distalis
GRH(SRH)---↑GH--- ↑Somatomedin C
•
• Somatostatin---↓ GH
PRH--- ↑ Prolactin--- ↑ milk secretion
•
PIH (dopamine)--- ↓ Prolactin
•

21. Cont.
• Pars Tuberalis--- some cells secrete
FSH and LH
• Pars Intermedia---Area is
rudimentary in Humans

22. Negative Feedback System
• Hypothalamus(CRH)->AntPit(↑ACTH)
↑ ↓
•
• ¦ Adrenal cortex(↑cortisol)
↓
• ¦
---------------------------------- ↓
•

23. ++
Target
Target Tissue Tissue
TSH
T3& T4

25. 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