THYROID GLAND

Question 1

Thyroid gland consists varying sized follicles, bounded by a single layer of ____ epithelial cells (follicular cells).

Answer 1

cuboidal

Question 2

These cells of thyroid gland secrete calcitonin.

Answer 2

C-cells / Parafollicular cells

Question 3

Describe the thyroid gland of dog and horse.

Answer 3

Consists of two lobes, one on each lateral side of the cranial trachea

Question 4

What are the importance of thyroid hormones in humans ?

Answer 4

• Protein synthesis; fetal and childhood tissue development and growth
• Nervous system normal development
• Contributes to reproductive health - affects libido, fertility, etc.
• Increases the body’s sensitivity to catecholamines by upregulation of receptors in blood vessels
• T3 & T4 excessive - accelerates heart rate, strengthens the heartbeat, increases blood pressure

Question 5

Discuss the synthesis of hormones in thyroid gland.

Answer 5

1. Binding of TSH to its receptors in the follicle cells of the thyroid gland.
   * The cells will actively transport iodine ions across their cell membrane, from the bloodstream into the cytosol
   * The concentration of iodine ions are trapped in the follicular cells is much higher than the concentration in the blood stream.
2. Iodine ions then move to the lumen of the follicle cells that border the colloid.
   * The ions undergo oxidation meaning their negative charged electrons are removed
   * The oxidation of two iodine ions (2 I-) results in iodine (I2) , which passes through the follicle cell membrane into the colloid.
3. Linking of peroxidase enzymes to the tyrosine amino acids in thyroglobulin, producing 2 intermediaries
   * 2 intermediaries –> a tyrosine attached to 1 iodine and a tyrosine attached to 2 iodines
   * When one of the two intermediaries is linked by covalent bonds –> triiodothyronine (T3) as resulting compound
   * T3 has 3 iodine, T4 has 4
   * When 2 copies of the intermediaries bond will result –> thyroxin )T4)

Question 6

The apical surface of the cell membrane of the thyroid gland has microvilli. True or False?

Answer 6

True

Question 7

Describe the thyroid gland of cattle.

Answer 7

Particularly wide isthmus, the thyroid glands are located adjacent to the cranial trachea, close to the recurrent laryngeal nerve, carotid sheath and sternohyoid and sternothyroid muscles

Question 8

Thyroid gland is also consists of basement membrane, surrounding a central lumen with a homogenous protein rich _____.

Answer 8

colloid (thyroglobulin)

Question 9

Describe the thyroid gland of pig.

Answer 9

Connected by the isthmus with a small central pyramidal lobe