Thyroid Gland Flashcards
Where is the thyroid gland located
Just bellow larynx
On anterior and lateral surfaces of trachea
Nape of neck
What hormones are secreted at the thyroid
Thyroid hormone - essential for optimal metabolic activity
Calcitonin - hormone involved in calcium homeostasis
Outline the structure of the thyroid gland
Composed of small spherical sacs called follicles
Each follicle surrounded by follicular cells and is the site of thyroid hormone synthesis
Clear cells (C cells) lie in clusters between follicles and make the hormone calcitonin
What are follicular cells
Simple cuboidal epithelial cells
What class of hormone is thyroid hormone
Lipid soluble hormone
How are thyroid (lipid soluble) hormones stored
Thyroglobulin (TGB) protein is made in thyroid follicles and contains tyrosine (Y)
Iodine enters follicle cell from blood and reacts with tyrosine in TBG
Thyroid hormones detach from iodised TGB as needed
What are the 2 forms of thyroid hormones and their roles
T3 - active form. Goes and targets cells
T4 - more plentiful form. Depository/storage form
Why is iodine a necessary part of our diet
It is required for the production of hydroid hormone
Outline target cells activation by thyroid hormone
Made in advance and stored until required
Travels bound carrier to protein
Detaches from carrier protein and enters target cell
T3 binds to T3 receptor in nucleus (receptor bound to specific DNA site)
Specific genes are activated to transcribe mRNA
mRNA translation occurs in cytoplasm and specific proteins are synthesised
Are the cell activations of thyroid hormones and steroid hormones the same
No
What is the response time of target cell activation by thyroid hormone
45 minutes - days
Outline the control of thyroid hormone secretion
External/internal stimuli lead to CNS input to hypothalamus
Hypothalamus secretes Thyrotropin-releasing hormone TRH
Anterior pituitary secretes Thyroid-stimulating hormone TSH
Thyroid gland secretes thyroid hormones
Thyroid hormone effects: Increase Basel metabolic rate, stimulates growth, nervous system (normal alertness reflexes), inhibits TRH secretion in hypothalamus and TSH secretion in anterior pituitary
How is basal metabolic rate increased
Increases in synthesis and activity of Na+ and K+ pumps
What is basal metabolic rate
BMR is the body’s rate of energy expenditure under basal conditions:
Person in awake, at physical and mental rest, lying down, no muscle movement, at a comfortable temperature, and fasted
What normal functions is thyroid hormone required for
Growth, alertness, metabolism
