Download MBBS Physiology Presentations 7 Thyroid Hormones Lecture Notes

Download MBBS (Bachelor of Medicine, Bachelor of Surgery) 1st Year, 2nd Year, 3rd Year and Final year Physiology 7 Thyroid Hormones PPT-Powerpoint Presentations and lecture notes

Develops from evagination of floor of

pharynx

Thyroglossal duct marks the path of

thyroid from tongue to neck

Gland is highly vascularized and has

one of the highest rates of blood flow

per gram of tissue
Thyroxine (T4)- Greater amount

released. Biological activity less

Triiodothyronine (T3)- Lesser amount

released. Biologically more active.

Generated at the site of action in

peripheral tissues by deiodination of

T4.

Reverse

Triiodothyronine (RT3)-

Small amounts
Pendrin (Cl/I exchanger)

Pendred syndrome- Thyroid dysfunction

and deafness

Salivary

glands, Gastric mucosa,

placenta, ciliary body of eye, choroid

plexus, mammary glands and certain

cancers of these tisssues express NIS

but the transprter is not affected by TSH

in these tissues.
T4 and T3 are deiodinated in liver, kidneys

and other tissues

Pituitary and cerebral cortex has high T3/T4

ratio

Three deiodinases: D1, D2 and D3- contain

selenocysteine

D1 ? present in liver, kidneys, thyroid and

pituitary

D2- present in brain, pituitary and brown

adipose tissue

D3- present in brain and reproductive tissues
T4 and T3 increase oxygen consumption

of all metabolically active tissues except :

Adult brain
Testes
Uterus
Lymph nodes
Spleen
Anterior pituitary
o T4 depresses oxygen consumption of

anterior pituitary because it inhibits TSH

secretion

Thyroid hormones increase the activity

of membrane bound Na-K ATPase

Some calorigenic effect is due to

metabolism of fatty acids they mobilize
Nitrogen excretion is increased
Potassium released due to protein

catabolism is excreted in urine

Increased urinary hexosamine and

uric acid excretion

Need for vitamins is increased due to

increased BMR

Thyroid hormones are necessary for

hepatic conversion of carotene to

Vitamin A

Thyroid

hormones increase the

number and activity of mitochondria

Thyroid hormones increase active

transport of ions through cell

membranes.
Stimulation

of

carbohydrate

metabolism

Stimulates rapid uptake of glucose by

cells

Glycolysis is increased
Gluconeogenesis is increased
Increased reabsorption from GIT
Increased insulin secretion

Stimulation of fat metabolism:
Lipid are mobilized rapidly from fat

tissue

Decreases fat stores of the body
Increases free fatty acid concentration

in plasma

Increased thyroid hormones decrease

the concentration of cholesterol,

phospholipids and triglycerides in the

plasma
Increase cholesterol secretion in bile

Increased thyroid hormones increase

LDL receptors on the liver leading to

rapid removal from plasma

Increased requirements of vitamins
Increases basal metabolic rate
Decreased body weight
Increases respiration
Increased gastrointestinal motility
Increased

activation

of

Reticular

Activating system (RAS)

Affects brain development
Cerebral cortex, basal ganglia

and

cochlea are mainly affected

Deficiency causes during development

causes mental retardation, motor

rigidity and deafness.

Exerts effects on reflexes- Reaction time

of reflexes is increased in hypothyroidism

and decreased in hyperthyroidism

In hypothyroidism, mentation is slow

and CSF protein levels increased

Thyroid

hormones revert these

changes

Cerebral blood flow, glucose and

oxygen consumption are normal in

both hypo and hyperthyroidism
Increases blood flow and cardiac

output

Increases heart rate
Increases heart strength
Pulse pressure increases
Increases expression of - MHC,

sarcoplasmic reticulum calcium

ATPase, K- Channels

Inhibits - MHC, Phospholamban,

adenylyl cyclase, nuclear receptors,

Na-Cl exchangers

Increases

rate and force of

contractions