Thyroid, Parathyroid and Adrenal Gland Flashcards
Primary Endocrine Glands
- Pineal
- Pituitary
- Thyroid
- Parathyroid
- Thymus
- Adrenals
- Islets of Langerhans
- Ovaries
- Testes
Secondary Endocrine Organs
- Heart
- Liver
- kidneys
Effects of hypophyseal hormones on Target Organs
PIC
How many lobes does Throid Gland Have?
2
Thyroid Gland Development
The foramen cecum of the tongue marks where the thyroid diverticulum originates at week 4 and it is formed by week 7(PIC)
What is the functional and structural unit of the thyroid gland?
Thyroid Follicle
____ Is the only endocrine gland that stores the hormone it produces in large quantities extracellular in the colloid of the follicles
The Thyroid
Follicular Cells purpose
In charge of producing thryoid hormone- typical secretory cells that contain microvilli and RER
Parafollicular cells (C Cells) Produce…
Produce Calcitonin
Where do C Cells derive from and where can they be found?
Derived from NEURAL CREST CELLS and can be found within the FOLLICULAR EPITHELIUM or as clusters between follicles
Is Throid highly vascularized?
YES, commonly in secretion organs
T3
Triiodothyronine (thyroid hormones)–more active than T4
T4
Thyrozine (thyroid hormones)–Less Active than T3
T3 and T4
- Produces, stored, absorbed, and secreted by FOLLICULAR CELLS
- Increase basal metabolic rate (mitochondrial number, their cristae density and activity)-Cause OxPhos
- Influence body growth and nervous system development at fetal state
Calcitonin
- Produced and secreted by PARAFOLLICULAR (C CELLS)
- Induced by increases in blood calcium levels
- Lowers blood calcium by inhibiting bone resorption (osteoclasts)
What happens when blood has too much calcium in blood?
Osteoclasts destroy bone locally and adjust calcium availability
What is needed to produce T3 and T4
Follicular cells have IODIDE PUMPS (transporters) that concentrate iodide in the thyroid gland
Radioactive Iodine Scan
After injection of radioactive iodide, 40% is in thyroid gland within 10 MINS
First Step of Synthesis of Thyroid Hormones
Synthesis of THYROGLOBULIN (660 kDA) and secretion into the follicles
Second Step of Synthesis of Thyroid Hormones
Uptake of circulating iodide by follicular cells via Na/I symporter in their basolateral membrane
Third Step of Synthesis of Thyroid Hormones
Oxidation of iodine by THYROID PEROXIDASE and transport of oxidized iodine into the follicle cavity by PENDRIN, an anion transporter
Fourth Step of Synthesis of Thyroid Hormones
IODINATION OF TYROSINE residues of thyroglobulin by thyroid peroxidase generates T4, T3, fiiodotyrosine and monoiodotyrosine
Thyroid Feedback Loop- How Thyroid is regulated
By hypothalamus- which stimulates pituitary gland
- Releasing TSH
- T3 and T4 are released in bloodstream and goes to target cells
- Negative Feedback loop tells hypothalamus to stop releasing hormones
PIC
Thyroid Hormone Secretion First step
upon stimulation by thyrotropin, follicular cells take up colloid by endocytosis
Thyroid Hormone Secretion second step
endocytic vesicles are digested by lysosomal enzymes
Thyroid Hormone Secretion third step
Proteases cleave the bonds between iodinated tyrosine residues and the thyroglobulin molecule
Thyroid Hormone Secretion fourth step
T4 and T3 are liberated to the cytoplasm and secreted basally into the blood
Thyroid Hormone Secretion fifth step
Di- and monoiodotyrosines are NOT secreted; their iodine is recycles after cleavage by iodine halogenase
Thyroid Hormone Secretion sixth step
T4 is most abundant (90%) but most hormone activity is attributed to T3