ENDOCRINE SYSTEM

DR.NILESH KATE.M.D.

ASSOCIATE PROFESSOR,DEPARTMENT OF PHYSIOLOGY,

ESIC MEDICAL COLLEGE& HOSPITAL,GULBARGA.

OBJECTIVES

Hormone : definition, classification.

Hormones general consideration.

Hormone receptors & mechanism of action.

Measurement of hormones.

HOMEOSTASIS & CONTROLS

Successful

compensation

Homeostasis

reestablished

Failure to

compensate

Pathophysiology

○ 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 derivatives

2 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/L

Epi / Nor Epi = 2× 10-10 to 13 × 10 -10

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

Half life.

Peptide hormone – short

Steroid, & 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- phoapholipidsystem.

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 slices

Incubate in ascorbateenriched 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