Test 6 Endo Thyroid Slides 128-186 Flashcards
What gland has a butterfly shape and is the largest of the “pure” endocrine glands?
Thyroid Gland
What is the location of the Thyroid Gland?
- Lateral lobes on ea. side of trachea projecting upward.
- Inferior to larynx
- Lobes connected by isthmus
- 3rd lobe: extends superior from isthmus, called pyramidal lobe (50% of people have)
What are the functional units of the thyroid?
Follicle
What is the shape of the wall of the follicle and what does it consist of?
Sphere shape
Consists: Follicular cells
What is the inside of the follicle called?
Colloid
What is the name of the cells that reside in between the follicular spheres and produces calcitonin and has no direct action on thyroid hormones?
Parafollicular Cells
What is the inactive form of thyroid hormone and is much more abundant but less potent?
Tetraiodothyronine (Thyroxine, T4)
What is the active form of thyroid hormone and is much more potent but less abundant?
Triiodothyronine (T3)
What is hormone is produced by the parafollicular cells in the thyroid gland and helps regulate calcium?
Calcitonin
The Thyroid is the only endocrine gland that stores its hormones in large quantities, how many days worth does it store?
100 days worth
Follicular cells pull what ions from the blood stream?
Iodide ion
Follicular cells produce what?
Thyroglobulin (TGB): (Glycoprotein-carbon chain of tyrosine)
Where is TGB produced in the Follicular cell?
Endoplasmic reticulum
Where is the TGB packaged and is released by what means into what space of the Follicular cell?
- Packaged: Golgi apparatus
- Released: Exocytosis into lumen (colloid)
What oxidizes the iodide to create the useable form for thyroid hormone synthesis? What is this form?
Perioxidase Oxidizes Iodide (2I-) into Iodine (I2)
The Tyrosine (on TGB) and iodine in the colloid of the Follicular cells react forming bonds, What does the reaction create?
- Monoiodotyrosine (MIT): One iodine to one Tyrosine
- Diiodotyrosine (DIT): Two iodines to one Tyrosine
The MIT and DIT molecules form bonds between each other, what do they form?
- T3 (3 iodine molecules): MIT + DIT
- T4 (4 iodine molecules): DIT + DIT
What stimulates TSH secretion from the Anterior Pituitary Gland?
TRH (Thyroid Releasing Hormone)
What effect does increased demand for ATP have on T3/T4 production?
Increases production of T3/T4
- Cold Environment
- Hypoglycemia
- High Altitude
- Pregnancy
The colloid is pulled back into the follicular cells by pinocytosis, what is contained in the colloid?
T3 and T4
What occurs within the follicular cell once the colloid is inside?
- Lysosome engulf colloid
- Digest TGB
- Cleaves T3 and T4
After the T3 and T4 are cleaved from the TGB what occurs to the hormone?
- Secreted out of the follicular cell into interstitial space and into the bloodstream
- Lipid soluble- easy diffusion
More than 99% of T3 and T4 are bound to what so it may travel through the blood stream?
Thyroxine-Binding Globulin (Transport Proteins)
What actions do the Thyroid Hormones have within the body?
- Increase basal metabolic rate (BMR)
- Stimulates synthesis of additional Na+/K+ pumps
- Helps regulate metabolism
- Enhance actions of catecholamines (some)
- Works w/hGH and insulin to accelerate body growth
What is Basal metabolic rate (BMR)?
Rate of oxygen consumption under normal conditions
-When increased, BMR causes metabolism of carbohydrates, proteins, and lipids
The action of Thyroid Hormones to stimulate synthesis of additional Na+/K+ pumps results in what?
- Increased ATP production and consumption by constant turnover of Na+ and K+
- Reactions release heat as byproduct
- Heat helps raise and maintain body temperature
Thyroid Hormones help regulate metabolism in what ways?
- Stimulates protein synthesis
- Increases use of glucose and FA for ATP production
- Increases lipolysis and enhances cholesterol excretion
What catecholamines does Thyroid Hormone have an enhancing effect on?
Epinephrine and Norepinephrine
-T3 and T4 upregulate beta receptors in the presence of epi and norepi
(upregulation explains hyperthyroid patients experiencing increased heart rate and BP)
What systems does Thyroid Hormones, working w/ hGH and Insulin to accelerate body growth, mainly affect and deficiency of T3/T4 results in what for fetal growth?
Systems: Nervous system and Skeletal Systems
Fetal Growth: infancy or childhood causes severe mental retardation and stunted bone growth