recent posts

01. General Endocrinology

Endocrine glands

Coordination of body functions by chemical messengers

Neural
Neurotransmitters at synaptic junction
Endocrine
Glands/Specialized cells secreate “hormones”
Neuroendocrine
Neurons secreta “neurohormones”
Paracrine
cells secrete substcnces to ECF-affect adjacent cells
Autocrine
cells secrete substance affecting the same cell



Endocrine glands

secrete “hormones “ : Internal secretions that are transported in blood and control metabolism in organs and tissues

Has widespread interrelated effects
  • long term , Slow acting effects : physical and sexual growth
  • Short term ,Rapid acting adaptive function : e.g. Insulin , adrenalin
Function of hormones

1. Homeostasis
  • Via metabolism : Insulin , Glucogan , Thyroxine , Cortisol
  • Via antistress action : Thyroxine , Cortisol , Adrenalin , ATCH , ADH
  • Via water & mineral regulation : ADH, Aldosterone , PTH
2. Growth
  • IGF
  • Thyroxine
  • Testosterone
3. Reproduction
  • Testicular / Ovarian steroids
  • Steroid
  • Gonadotropins
4. Combating emergency
  • Adrenaline
  • Noradrenalin

Endocrine system

Physically separated but functionally related glands
  • Normal endocrine state depend on a balance functioning of endocrine glands
  • hormone may have widespread effects (e.g. Growth hormone ,Thyroxin ) ,Self effects (e.g. ACTH on renal cortex )
  • Usually more general manifestation than local effects seen in endocrine disorders
A. Hormone synthesis

1. Peptide
  • usually synthesized as longer precursors
  • stored in cells
  • secreted by exocytosis on stimulation
  • act on cell membrane receptor
2. Steroid
  • usually synthesized from cholesterol
  • very little storage
3. Amine
  • derived from Tyrosine
B. Hormone Secretion

1. Different hormones has different onset of secretion after stimulus also different duration of action
e.g.
  • Norepinephrine/Epinephrine : Secrete within second of stimulation ,full action within second / minutes
  • Thyroxin / GH : Slower action / may need months for full action 
2. Control hormone secretion  by

Feedback control

(+) Feed Back
(-) Feed Back
  • Increase in target tissue activity leads to further increase in [ Hormone ]
  • E.g. LH surge due to oestrogen
  • Prevent over activation [ Hormone ]
  • Regulation can occur at all form gene transcription to release


Biological Rhythms

  • Circadian rhythm : Cortisol
  • Menstrual Cycle : Oestrogen, Progesteron ,LH,FSH


Other Stimuli

  • Stress : GH,Prolactin
  • Sexual activity : Prolactin, oestrogen
  • Sucking : Prolactin, Oxytocin
  • Fasting Feeding : Insulin ,Glucagon
  • Sleep : Prolactin
C. Hormone Transport in Blood


[ Hormone ] = ( Rate of secretion <-----> Rate of removal )

  • Water Soluble hormones , Usually dissolved : peptide ,Catecholamine
  • Steroids & Thyroid hormones : mainly bound to plasma proteins
  • Protein bound hormones >>> Free hormones : e.g 99% of thyroxine in blood is protein bound

    • Free hormones = active  hormones
    • Protein bound hormones = Reservoir /Slow clearance
D. Mechanisms of action

  • Steroid hormones -----> Cytoplasmic  Receptors-----> Activate protein transcription & Stimulate Protein Synthesis 
  • Thyroid hormone ----> Nuclear Receptors-----> Activate protein transcription & Stimulate Protein Synthesis 
  • Peptide hormone ----> Cell surface Receptors-----> 2 type of action

    • via 2nd messenger ( e.g. ACTH,FSH,GnRH,HCG,TSH,Adrenalin,Calcitonin)
    • Direct (  Tyrosine kinase activity e.g. Insulin , IGF)
E. Clearance

Several Mechanism

  1. Destruction by enzymes in blood /Tissues
  2. Tissue binding
  3. Excretion by liver
  4. Excretion by liver 
  • Most peptide hormones & catecholamines : rapidly declared
  • Protein bound hormones : Slow clearance
01. General Endocrinology 01. General Endocrinology Reviewed by Radiology Madeeasy on August 14, 2010 Rating: 5
Powered by Blogger.