thyroid glands Flashcards
What is the thyroid gland?
Bi-lobed gland that sits at the base of the neck in front of the trachea.
What hormones are produced and secreted by the thyroid gland?
10% is tri-iodothyronine (T3) and 90% is tetra-iodothyronine (T4).
What controls the synthesis and secretion of thyroid hormones?
Thyroid-stimulating hormone (TSH) from the anterior pituitary.
What is the role of the hypothalamopituitary axis in thyroid hormone regulation?
It regulates the secretion of TSH, which in turn controls thyroid hormone synthesis.
How are thyroid hormones formed?
Thyroid hormones are formed from iodinated tyrosine residues in a protein called thyroglobulin.
Where are thyroid hormones stored?
Stored as thyroglobulin in colloid.
What process allows the thyroid gland to concentrate iodide from the blood?
The thyroid gland transports iodide to the colloidal space where thyroglobulin is stored.
What happens to thyroglobulin when thyroid hormones are needed?
Thyroglobulin is removed from colloid and degraded, releasing T3 and T4.
What is the function of the enzyme deiodinase in the thyroid hormone process?
It recycles amino acids and iodine.
What is one effect of T3 on growth hormone secretion?
Appropriate T3 activity is required for secretion of growth hormone from the anterior pituitary.
How does T3 affect the basic metabolic rate?
T3 increases basic metabolic rate by increasing activity of Na/K-ATPase.
List some metabolic effects of T3.
- Increases glucose uptake in skeletal muscle
- Increases lipolysis from adipose tissue
- Increases hepatic glycogenolysis and gluconeogenesis
- Increases gastrointestinal motility
- Increases LDL receptors and cholesterol synthesis
- Increases heart rate.
What is the role of calcitonin produced by the thyroid gland?
To reduce the amount of calcium in the blood.
What stimulates the secretion of calcitonin?
Rising levels of calcium in the blood.
How does calcitonin lower blood calcium levels?
- Driving calcium from blood into bone
- Reducing absorption of dietary calcium
- Increasing excretion of calcium in urine.
What are the three hormones that interact to maintain calcium homeostasis?
- Calcitonin
- Parathyroid hormone
- Vitamin D.
What is the function of parathyroid hormone?
To increase the amount of calcium in the blood.
What stimulates the secretion of parathyroid hormone?
Falling levels of calcium in the blood.
How does parathyroid hormone increase blood calcium levels?
- Driving bone resorption
- Decreasing excretion of calcium in urine
- Stimulating renal activation of vitamin D.
What is the normal range of calcium in the blood?
8.5-10 mg/dL or 2.2-2.6 mmol/L.
What is the active form of vitamin D and its role in calcium homeostasis?
Increases intestinal absorption of dietary calcium and evidence of negative feedback control of PTH secretion.
What happens to calcium homeostasis when there is a loss of estrogen?
It may compromise bone health and increase fracture risk.
True or False: Parathyroid hormone is essential for long-term calcium homeostasis.
False.
