WEEK 7: 7.6 Thyroid and Parathyroid Flashcards
Where is the thyroid gland located?
immediately below the larynx on each side of and anterior to the trachea
What kind of shape is the thyroid gland?
a bow shape
What are thyroid follicles
spherical structures that form the functional units of the thyroid
What are the thyroid follicles composed of, and what is their function
They are composed of follicular cells, which are specialised pubertal epithelial cells that play an important role in the formation & secretion of thyroid hormones
What are thyroid colloid
gelatinous substances that contain protein called thyroid globulin
what are thyroid globulin molecules
they are effectively the protein backbone upon which the thyroid hormones are formed between the follicles, like the power follicular cells
what is calcitonin
it reduces the resorption of bone during times of high calcium demand, such as during pregnancy and breastfeeding. it plays an important role in the everyday regulation of free plasma calcium concentration
What stimulates the production of thyroid hormones?
thyroid stimulating hormone, which is secreted into the bloodstream and circulates/acts on the cells of the thyroid gland to produce thyroid hormones
What is secretion from the anterior pituitary gland regulated by?
hypothalamic hyper physio tropic hormones
What are the two ways in which the effects of thyroid hormones can be broadly classified?
- effect on metabolic pathways- thyroid hormones boost energy metabolism in mitochondria increasing basal metabolic rate- therefore will also influence body temp
- effect on cellular differentiation and development - hormones promote the development and differentiation of many cells including the neurons and supporting cells of the CNS
What does thyrotopin-releasing hormone (TRH) stimulate the release of?
thyroid stimulating hormone (TSH)
What kind of feedback loop maintains a constant supply of thyroid hormones?
a negative feedback loop
how are T3 and T4 transported in the blood?
by carrier proteins
What are non-genomic effects of TSH
-enhances iodide pump activity which increases iodide trapping (iodine is needed to make thyroid hormones)
-increases iodination of tyrosine which increases T3 and T4 synthesis
-increases proteolysis (breakdown) of thyroglobulin which increases release of T3 and T4
what are genomic effects of TSH
it promotes gene transcription for iodide pump, thyroglobulin, T3 and T4 synthesis enzymes, nitric oxide synthase leads to vasodilation which therefore increases blood flow to the thyroid, local growth factors lead to hyperplasia (more cells) and hypertrophy (bigger cells), hence the gland grows
What are non genomic effects
fast, direct changes without altering DNA transcription
What are genomic effects?
slower, through gene transcription and new protein production
How does TSH start its effect on thyroid follicular cells
- it bind to a G protein coupled receptor on the follicular cell
- it activates cAMP inside the cell
- cAMP leads to changes through 2 broad types of effects (genomic and non-genomic)
Where are thyroid receptors found?
within the nucleus of the target cells
What is the overall action of thyroid hormones on the cardiovascular system?
improving cardiac output by increasing excitability and contractility of cardiac muscle, by increasing the no of ca na and k+ pumps and increasing the expression of beta adrenergic receptors, as well as other important G protein coupled receptors
Summarize the effects of thyroid hormone on neural activity
-> alertness, memory, learning, emotional stability, nerve reflexes
Summarize the effects of thyroid hormone on reproduction & growth
-> required for reproductive capabilities
-> enhances effects of growth hormone
Summarize the effects of thyroid hormone on metabolism
-> increased heat prod
-> increased lipolysis, glycogenolysis (breaking down glycogen into glucose)
-> increased glucose absorption from GIT
-> increased mitochondrial size, no and enzymes
-> increased basal metabolic rate (rate of O2 consumption/ energy expenditure at rest)
Summarize the effects of thyroid hormone on oxygen delivery
- increases heart rate, stroke volume, force of contractions, resting resp rate
- increased RBC mass
- up regulates B1 receptors
