Download MBBS Physiology Presentations 9 Mech Of Hormone Actn Lecture Notes

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Mechanism of Action of hormones

Receptors

Hormones bind with specific receptors to exert

their actions

Receptors may be present :
1. On the cell membrane
2. In the cytoplasm
3. In the nucleus

Earl. W. Sutherland received Nobel prize for his

discoveries on mechanism of hormone action in

1971.
Receptors

Hormone-receptor complex binds activates a

series of signal generating mechanisms via
cascade of enzymatic reactions

Signal molecules increase in each step leading

to manifold increase in the action ? Signal
amplification

Peptide and amine hormones bind to cell

surface receptors

Steroid

and thyroid hormones bind to

intracellular receptor

Mutation of receptors causes diseases

1. Familial hypothyroidism due to mutation

of TSH receptors

2. Color blindness due to mutation of

receptors for cone pigment

3. Nephrogenic diabetes insipidus due to

mutation of V2 vasopressin receptors
Quantity and sensitivity of receptors

Regulated by the hormone concentrations

1. Up-regulation
2. Down ? regulation
3. Desensitization

Types of receptors

Ion channel linked receptors

G-protein coupled receptors

Enzyme linked receptors
G-proteins

Small G ?Proteins:
1. Rab family
2. Rac Family
3. Ras Family

Large G-proteins:
Gs, Gi, Gq, Gt and G13

S.NO. Hormones using receptor

tyrosine kinase signaling

1

Fibroblast growth factor

2

Growth hormone

3

Hepatocyte growth factor

4

Insulin

5

Insulin like growth factor

6

Leptin

7

Prolactin

8

Vascular endothelial growth factor
S.NO.

Hormones using adenylyl cyclase ?Camp
messenger system

1

ACTH

2

Angiotensin II

3

Calcitonin

4

Catecholamines ( receptors)

5

CRH

6

FSH, LH

7

Glucagon

8

HCG

9

PTH

10

Secretin

11

Somatostain

12

TSH

13

Vasopressin (V2 receptor)

S.NO. Hormones using Phospholipase -

C second messenger system

1

Angiotensin II

2

Catecholamines ( receptors)

3

GnRH

4

GHRH

5

Oxytocin

6

TRH

7

Vasopressin (V1 receptor)