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Getting Introduced To Endocrine Physiology Neelambikai.N

General Principles of Endocrinology

Cell-to-cell signaling Local mol. Local mol.. Neurohormone Cell-to-cell signaling

Nervous Vs endocrine systems Control Of secretion Nervous system ?? Typical nerve cell Neuro-endocrine cell Typical endocrine cell axon Blood hormone neurotransmitter Target tissue To target tissues Which tissues?

First Chemical Messengers Neurotransmitter Neurohormone Hormone Released: On target tissues In blood Carry: To all tissues Affect only tissues which………..!

The two major regulatory systems Nervous system Endocrine system What are the characteristics Of responses? What are the characteristics Of responses? Rapid and precise Prolonged Give examples Give examples

Solely endocrine function Mixed function Complete function uncertain Pineal Hypothalamus Pituitary Parathyroid Thyroid Thymus Testes in male Heart Stomach Adrenal gland Pancreas Duodenum Kidney Skin Ovaries in female Placenta in pregnant female

Overall functions of the endocrine system Regulate metabolism Regulate water& electrolyte balance Homeostasis Adaptive changes To cope with stress Regulate growth Control reproduction Regulate RBCs production Regulate CVS and GIT functions

Targets other endocrine Hormones Tropic Non-tropic Targets other endocrine Glands Targets other tissues

Tropic hormones _ _ deficiency of tropic hormone Endocrine gland Anterior pituitary gland _ _ Thyroid stimulating hormone Tropic hormone Endocrine gland Thyroid gland hormone Thyroid hormone deficiency of tropic hormone 1- secretion from target gland decreases 2- target gland atrophy

Endocrine gland Hormone Binding with receptor (Target cell) Binding of hormone with receptor triggers one of the following intracellular events: Acting on pre-existing proteins (channel, enzyme..etc) or 2. Activates specific genes to cause formation of new proteins Physiologic response

H R HR + # of HR in target cell depends on: Hormone receptor interaction hormone receptor Hormone receptor complex H R HR + Final effect of hormone depends on: # of HR in target cell # of HR in target cell depends on: {H} free in blood # of receptors in target cell affinity of receptors to H

General properties of endocrine function Single gland Single hormone Single cell May affect >one type of cell May be secreted By > one gland May be affected By > one hormone May produce > One hormone Anterior pituitary gland ADH Somatostatin hepatocyte

Patterns of hormone secretion Cyclical Non-cyclical (steady) Temporal coordination Of function Thyroid hormone Menstrual cycle

Peptides Amines Steroids Chemical structures of hormone catecholamines Thyroid hormone Water soluble (hydrophylic) Fat soluble (lipophylic) Dissolve in plasma Bind to plasma proteins Receptors on cell membranes Why? Receptors inside cells

Hdrophylic hormone lipophylic hormone free hormone receptor Second messenger Gene

Typical synthesis/secretion of peptide hormones signal Large molecule Rapid response

Biosynthesis of steroid hormones In ester form Synthesized by cell Derived from food Rate of secretion totally controlled by rate of synthesis (Delayed onset) Once synthesizedReleased immediately from the cell by diffusion Transported in blood bound to plasma proteins Biosynthesis of steroid hormones

17 11 15 14 9 1 10 5 3 7

Transport of hormones in blood Hhydrophilic hormones lipophylic hormones Bound to plasma proteins Dissolved in plasma

Dynamic equilibrium Protein bound hormone Free Hormone (active) Gland Factors affecting concentration of free hormone Dynamic equilibrium Protein bound hormone Free Hormone (active) Target tissue Activation Degradation in Liver etc … (inactivation) Excretion (urine) Question: what will happen if the concentration of the binding increases?

second messengers!

The cell membrane phospholipid second messenger system by which some hormones exert their control of cell function

Epinephrine can act through two second –messenger systems

The mechanism of action of a steroid hormones on the target cells

Receptors for Steroid hormones

Mechanism of action of thyroid hormones on the target cells

Receptor for insulin

Enzyme-linked receptor-the leptin receptor

Mechanisms of interaction of lipophilic hormones

Receptors & Down stream effectors of Peptide hormones

Possible fates and actions of a hormone following its secretion by an endocrine cell. Not all paths apply to all hormones

General regulation of hormone secretion Cortisol as an example Regulation of hormone secretion Maintain basal levels of hormones Negative feedback Diurnal or circadian rhythm Neuroendocrine reflexes Response to stress

Negative feedback Anterior pituitary Thyroid-stimulating hormone Thyroid hormone Thyroid gland

Circadian rhythm N = noon M = midnight Light Dark

Endocrine disorders Hormone excess Hormone deficiency

Response of a target cell to a hormone may be varied by: The hormone it self 1- down regulation 2- up regulation or Other hormones 1- permissiveness 2- synergism 3- antagonism

Permissiveness Basic mechanism Example Epinephrine Hormone 1 Thyroid Makes cell responsive to Hormone 1 Target cell Target cell Epinephrine/cortisol Is another example

(uterine smooth muscle) Antagonism Basic mechanism Example estrogen Hormone 1 Makes cell less responsive to Hormone 1 progesterone Hormone 2 Target cell Target cell (uterine smooth muscle)

Synergism testosterone Follicle stimulating hormone Hormone 1 Target cell Spermatogenesis Precursor cells Combined action > sum of actions Combined action > sum of actions

Basic principles of the enzyme-linked immunosorbent assay (ELISA) for measuring the concnetration of a hormones

Principles of Radioimmunoassay

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