ENDOCRINE SYSTEM

DR.NILESH KATE. M.D.

ASSOCIATE PROFESSOR,DEPARTMENT OF PHYSIOLOGY,

OBJECTIVES

Hormone : definition, classification. Hormones general consideration. Hormone receptors & mechanism of

action. Measurement of hormones.

HOMEOSTASIS & CONTROLS Successful

compensationHomeostasis

reestablished Failure to

compensatePathophysiology ○ Illness○ Death

Figure 1-5: Homeostasis

COMPARISON OF ENDOCRINE AND NERVOUS SYSTEMS.

NERVOUS SYSTEM “WIRED” CHEMICAL SIGNAL AT

TARGET CELL RAPID BRIEF DURATION CLOSE ANATOMICAL

PROXIMITY

ENDOCRINE SYSTEM “WIRELESS” CHEMICAL SIGNAL IN

BLOOD. SLOW LONG DURATION SPECIFIC RECEPTORS

ENDOCRINE SYSTEM

Hormaein-- Greek word means “to execute or to arouse”.

Def:- Secretary product of ductless glands

which are released in catalytic amounts into

blood stream & transported to specific target

cells where they elicit physiologic,

morphologic & biochemical responses.

LOCATION OF DIFFERENT ENDOCRINE GLANDS.

Long Distance Communication: Endocrine Hormones

Signal Chemicals Made in endocrine

cells Transported via

blood Receptors on target

cells

Figure 6-2a: Long distance cell-to-cell communication

TYPES OF HORMONES Functional

ENDOCRINE HORMONES – Travel through the blood to act at a site distant from the secreting cell or gland

PARACRINE HORMONES – Act on cells near the secreting cell

AUTOCRINE HORMONES – Act on the secreting cell

NEUROCRINE HORMONES – Secreted by neural cells○ neurotransmitters ○ neurohormones

Figure 6-2b, c: Long distance cell-to-cell communication

Paracrine and Autocrine Hormones

Local communication Signal chemicals

diffuse to target Example: Cytokines

Autocrine–receptor on same cell

Paracrine–neighboring cells

Figure 6-1c: Direct and local cell-to-cell communication

CHEMICAL CLASSIFICATION OF HORMONES

Depending upon chemical nature Amines or amino acid derivatives: Proteins & Polypeptides: Steroid hormones

Depending upon mechanism of action.

Group I hormones. Group II hormones. : A,B,C,D.

HORMONE : GENERAL CONSIDERATION.

Hormones chemistry, synthesis, storage & release.

1 Amines / amino acid derivatives2 Protein & polypeptide hormones.3 Steroid hormones.

HORMONE TRANSPOT, PLASMA CONC, HALF LIFE.

Hormone transport.Unbound.Bound .

Plasma concentrations.Peptide hormone 10 -12 mol/ L to 10 -14 mol/LEpi / Nor Epi = 2× 10-10 to 13 × 10 -10

Steroid & thyroid 10-9 mol/ L & 10-6 mol/ L. Half life.

Peptide hormone – shortSteroid, & thyroid – long.

FUNCTIONS OF HORMONES.

Regulation of biochemical reactions Regulation of bodily process.

HORMONE DISPOSAL.

Target cell uptake & intracellular degradation. Metabolic degradation / inactivation. Urinary / biliary secretions. Metabolic clearance rate (MCR):-

volume of plasma cleared per unit time.

REGULATION OF HORMONE SECRETION.

Feedback control Neural control. Chronotropic control

FEEDBACK SYSTEM.

Figure 6-26: Negative and positive feedback

Figure 7-14: Negative feedback loops in the hypothalamicanterior

pituitary pathway

NEGATIVE FEEDBACK REFLEXES : LONG , SHORT & ULTRASHORT LOOP.

HORMONES RECEPTORS.

Characteristics Specificity .Location .○ Internal ○External .

Regulation of number.○Down regulation○Up regulation .

STRUCTURE OF RECEPTORS.

Recognition domain. Coupling domain.

CLASSIFICATION OF RECEPTORS.

Receptor kinase Receptor linked kinase. G-protein coupled receptors. Ligand gated ion channels.

MECHANISM OF ACTION OF HORMONES.

Through change in membrane permeability.

Through effect on gene expression. Through second messengers. Through tyrosine kinase activation.

THROUGH CHANGE IN MEMBRANE PERMEABILITY.

Hormones bind with external receptors.

Conformational change in protein of receptors.

Opening of Na, K, Ca channel.

Movement of ions.

THROUGH EFFECT ON GENE EXPRESSION.

Figure 7-7: Steroid hormone action

THROUGH SECOND MESSENGERS SYSTEM.

Adenyl cyclase- cAMP system. Guanyl cyclase –cGMP system. Membrane phosplipase- phoapholipid

system. Calcium- calmodulin system.

ADENYLATE CYCLASE-CAMP (Sutherland 1961)

PHOSPHOLIPASE-C-CA2+ (CONTINUED)

CA2+- calmodulin system (CONTINUED)

THROUGH TYROSINE KINASE ACTIVATION.

MEASUREMENT OF HORMONES.

BIOASSAY.Injecting unknown sample of

plasma in experimental animals & observing specific biological effect.

IMMUNOASSAY.(AG-AB REACTION)RADIOIMMUNOASSAY ○ Mix Unknown sample of plasma

containing hormone + purified specific antibody + purified hormone tagged with radioactive isotopes.

ELISA○ Instead of specific antibody,

stained with suitable dye. & intensity of colour measured by spectrophotometer.

MEASUREMENT OF HORMONES.

CYTOCHEMICAL ASSAY.Endocrine gland cut in

slicesIncubate in ascorbate

enriched culture medium

Genesis of hormone detected.

DYNAMIC TESTS.Suppression type.Stimulation type.

ENDOCRINE REFLEX PATHWAYS: OVERVIEW

Figure 7-9: Hormones may have multiple stimuli for their release

PATHOLOGIES: OVER OR UNDER PRODUCTION

Figure 7-19: Negative feedback by exogenous cortisol

PATHOLOGIES: DUE TO RECEPTORS

Figure 7-20: Primary and secondary hypersecretion of cortisol

Thank you