Thyroid

Follicles of the thyroid gland:
- Follicular Cells: produce T3 and T4 hormones
- Colloid (Fluid)
- Thyroglobulin gets iodized
C cells (parafollicular cells)
- Produce Calcitonin

Thyroid Hormones

Triiodothyronine (T3) and Thyroxine (T4)
- Produced by follicular cells
- T4 can be converted to T3
- Receptors have higher affinity for T3
- Regulated by TSH
Targets all cells in the body
Increase basal metabolic rate: overall oxygen consumption, heart rate, heat production, ATP generation
- Increases adrenergic receptors in the heart (and other muscles)
Calorigenic action: increased metabolism of carbohydrates and lipids
Important for growth and development, particularly in young animals
- Hypothyroid animals have abnormalities in the skeletal and nervous system

Production and storage
- Follicle cells take up amino acids (AA) from circulation
- Synthesis of Thyroglobulin
- Thyroglobulin secreted into colloid, where it is iodinated
Release
- Endocytosis of colloid and iodinated thyroglobulin
- Vesicle fuses with lysosome
- Lysosomal enzymes break down thyroglobulin into T3 and T4
- T3/T4 diffuse into blood

Image credit: Greene Xue

Produced by C Cells (parafollicular cells)
Peptide hormone that lowers blood calcium levels
Inhibits the action of osteoclasts and promotes retention of calcium in bones
- 💡"Calcibonin" : puts calcium IN bones
Regulated directly by serum calcium concentrations
Function is minimal compared to the parathyroid hormone

Image credit: Lectures 33, 34

A: TSH (Thyroid Stimulating Hormone)

A: Thyroglobulin secreted into colloid, where it is iodinated

A: Lowers blood calcium levels, Inhibits the action of osteoclasts and promotes retention of calcium in bones

Page updated

Report abuse