The Thyroid Gland Flashcards
it has a follicular structure and is the only tissue of the body which is able to accumulate iodine in large quantities and incorporate it into hormones.
Thyroid gland
Thyroid hormones have many functions in the body, in General;
✓ regulate growth
✓ differentiation
✓ metabolism of lipids, proteins and carbohydrates
Thyroid hormones
✓ Triiodothyronine (T3)
✓ Tetraiodothyronine (T4)
two thyroid lobes located on the lateral surfaces of the trachea;
✓ In pigs- midline of the ventral cervical region w/ dorso-lateral projections
✓ In dogs- cranial to the left lobe and almost touches the caudal aspect of the larynx
major supply of blood
cranial thyroid artery
principal venous drainage
caudal thyroid vein
usually enter directly into the cervical lymphatic drunk or internal jugular vein
Efferent lymphatics
has a rich supply of sympathetic nerves associated with blood vessels
thyroid
affect the rate of synthesis of thyroid hormone
Thyrotropin or Thyroid-stimulating hormone (TSH)
originates as a thickened plate of epithelium in the floor of the pharynx
Thyroid Gland
Thyroid gland originates as a thickened plate of epithelium in the floor of the pharynx and in the adult animal consists of;
✓ follicular cells
✓ parafollicular cells or C-cells
✓ colloid
✓ interstitial connective tissue
is common in the dog and may be located anywhere from the larynx to the diaphragm
Accessory Thyroid tissue
is completely lacking in C-cells (parafollicular), which secrete calcitonin
accessory thyroid tissue
in the dog, it is usually are not successful because the accessory thyroids readily respond to an increase in endogenous TSH secretion and undergoes sufficient hypertrophy and hyperplasia of follicular cells to sustain adequate thyroid hormone production
Induced Hypothyroidism
thyroid gland contains follicles ranging from ____________um size and are filled with a __________ produced by the cells lining the follicle.
20-150
filled with COLLOID
is stimulated by TSH and that microfilament integrity and phosphorylation of tyrosine are essential to thyroid cell response
Folliculogenesis
the majority of the epithelial cells and the most important functional cells of the thyroid
follicular cells
the histologic appearance of the thyroid is dramatically influenced by the level of circulating TSH from the?
Adenohypophysis
binds to receptors of thyroid follicular cells
Thyrotropin
what enzymes thyrotropin activates?
Adenylate cyclase
caused by iodine deficiency in the diet
Diffuse thyroid hyperplasia (goiter)
Example of goitrogenic substances include;
- Thiouracil
- Sulfonamides
- Complex anions
- plants from the family Brassicacceae
is a peptide hormone of the mammalian thyroid that has been shown to be secreted by C-cells
Calcitonin (CT)
are distinct from the follicular cells that secrete thyroid hormones (T3 and T4)
C-cells
the assembly of thyroid hormones within the follicular lumen is made possible by a unique protein called?
thyroglobulin
it synthesized by follicular cells
thyroglobulin
is a high molecular weight glycoprotein synthesized in successive subunits on the ribosomes of the endoplasmic reticulum of follicular cells
Thyroglobulin
an essential component of thyroid hormones, is incorporated within the molecular structure of thyroglobulin
Amino acid TYROSINE
iodine if bound to ____________ residues in thyroglobulin at the apical surface of follicular cells to form successively ______________ and ___________.
Tyrosyl
Monoiodotyrosine
Diiodotyrosine
the resulting MIT and DIT combine to form the biologically active iodothyronines;
✓ Thyroxine- T4
✓ Triiodothyronine- T3
