8/12/2019 Goiter Physio (2)

1/17

8/12/2019 Goiter Physio (2)

2/17

PHYSIOLOGY OFTHYROID GL ND

8/12/2019 Goiter Physio (2)

3/17

THYROID GLAND SECRETIONS

Thyroid gland secretes thyroid hormones

Thyroxine or Tetraiodothyronine 93%

Triiodothyronine 7%

Calcitonin: polypeptide hormone.

8/12/2019 Goiter Physio (2)

4/17

REGULATION OF THYROID HORMONE SECRETIONS

8/12/2019 Goiter Physio (2)

5/17

METABOLIC EFFECTS OF THYROID HORMONES

A. Carbohydrate Metabolism Increase absorption of glucosefrom GIT

Enhance glycogenolysis, gluconeogenesis and enhances

diabetogenic effectsof glucagon, cortisol and growth hormone.

Enhancement of glucose utilizationof peripheral tissues.

PHYSIOLOGICAL EFFECTS OF THYROID HORMONES

EFFECT ON TRANSCRIPTION OF GENES

Activates the nuclear transcription of large numbers of genes.The net result is generalized increase in Metabolic activity

throughout the body.

8/12/2019 Goiter Physio (2)

6/17

B. Protein Metabolism

T4 and T3 in physiological dosages stimulates proteinsynthesis, increasing anabolismof protein and causing

positive nitrogen balance .

C. Effect On fat metabolism

Accelerate the oxidationof free fatty acids by cells. Promote synthesisof cholesterol.

Also increase decompositionof cholesterol by liver cells.

Net effect of T3 and T4 is to decrease plasma

cholesterol concentration because the rate ofsynthesis is less than that of decomposition.

8/12/2019 Goiter Physio (2)

7/17

Calorigenic action of thyroid hormones

Increase O2consumption .

Increase in number and activity of mitochondria.

Increasing heat production and BMR ( 60 to 100% above

normal).

Enhances Na+-K+ATPase activity.

Makes cell membrane of most cells to become leaky to Na+

ions, which farther activates Na+pump and increases heat

production.

8/12/2019 Goiter Physio (2)

8/17

EFFECTS OF THE THYROID HORMONES

ON DIFFERENT BODY SYSTEMS

EFFECT ON THE CARDIOVASCULAR SYSTEM

Increased blood flow and cardiac output.

Increases heart rate. Increases heart strength.

8/12/2019 Goiter Physio (2)

9/17

EFFECT ON RESPIRATORY SYSTEM

Increases rateand depthof respiration.

EFFECTS OF THYROID HORMONE ON NERVOUS

SYSTEM:

Increases excitabilityof central nervous system.

These hormones increases the rapidity of cerebration.

These can also stimulate the sympathetic nervous

system.

8/12/2019 Goiter Physio (2)

10/17

EFFECT OF THYROID HORMONES ON GROWTH AND

DEVELOPMENT

Essential for normal growth and development especiallyskeletal growth and development.

Stimulate formation of dendrites, axons, myelin sheath and

neuroglia.

EFFECT ON GASTROINTESTINAL TRACT:

Increase the appetiteand food intake.

Increase both the rate of secretion of the digestive juices and

the motilityof the gastrointestinal tract.

8/12/2019 Goiter Physio (2)

11/17

BIOCHEMISTRY OFTHYROID HORMONES

8/12/2019 Goiter Physio (2)

12/17

CHEMISTRY OF THYROID HORMONESThyroid hormones are derivativesof the the amino acid

tyrosine bound covalently to iodine.

8/12/2019 Goiter Physio (2)

13/17

8/12/2019 Goiter Physio (2)

14/17

MECHANISM OF ACTION OF THYROID HORMONES

8/12/2019 Goiter Physio (2)

15/17

Transport & Protein Binding

Plasma proteins

Thyroxin-binding Globulin

Thyroxin-binding Prealbumin

Albumin

Free T3and T4is the physiologically activeform .

8/12/2019 Goiter Physio (2)

16/17

EXCRETION

Both T3 and T4 also form

glucuronideconjugates in the liver

that are excreted via bile into feces.

8/12/2019 Goiter Physio (2)

17/17