Thyroid Hormonal System Flashcards
Functional unit of the parathyroid gland
Parathyroid Cells (Chief Cells)
Congenital hypothyroidism occurs in _________.
Congenital hypothyroidism occurs in foals.
Percursors of thyroid hormone synthesis
Tyrosine Amino Acids
Iodide
_____________ is synthesized and secreted by parathyroid glands and is stimulated by decreased [calcium]
Parathyroid Hormone (PTH) is synthesized and secreted by parathyroid glands and is stimulated by decreased [calcium]
The primary clearance organs for thyroid hormone are
liver and kidney
_____________ is characterized by decreased thyroid horomone and thus decreased metabolic rate.
Hypothyroidism is characterized by decreased thyroid horomone and thus decreased metabolic rate.
When T3 binds _________ receptors it activates oxidative phosphorylation and ATP synthesis
When T3 binds mitochondrial receptors it activates oxidative phosphorylation and ATP synthesis
______________ blood samples are taken before and after administration of TSH.
TSH Stimulation Test blood samples are taken before and after administration of TSH.
________________
Expect to see increased T4 after administration
Was Gold Standard at one time
____________: located between thyroid follicles, produce calcitonin.
Parafollicular Cells (C Cells): located between thyroid follicles, produce calcitonin.
Cold temperatures (increases/decreases) [T3]
Cold temperatures (increases/decreases) [T3]
Etiology of Hypothyroidism
Lymphatic thyroiditis (autoimmune)
Idiopathic atrophy
Control of Thyroid Hormone homeostasis is maintained by the ____________.
Control of Thyroid Hormone homeostasis is maintained by the Hypothalamic - Pituitary - Thyroid- Axis.
___________ is synthesized and secreted by parafollicular cells and is stimulated by increased [calcium]
Calcitonin is synthesized and secreted by parafollicular cells and is stimulated by increased [calcium]
Calcitonin effects on target tissues
@ Bone - inhibits osteoclast activiyt
@ Kidney - inhibits reabsorption of calcium
@ GI - inhibits absorption of calcium
Increased [T3] and [T4] (increases/decreases) the release of TRH and TSH
Increased [T3] and [T4] (increases/decreases) the release of TRH and TSH
__________: epithelial cells in spherical arrangement that produce thyroid hormones.
Thyroid Follicles: epithelial cells in spherical arrangement that produce thyroid hormones.
____________ disease in which excessive amounts of PTH produced leading to increased blood [calcium]
Hyperparathyroidism disease in which excessive amounts of PTH produced leading to increased blood [calcium]
_____________ binds to anterior pituitary and signals the release of TSH
Thyroid Releasing Hormone (TRH) binds to anterior pituitary and signals the release of TSH
High carbohydrate diet (increases/decreases) [T3] causing an (increased/decreased) metabolic rate.
High carbohydrate diet (increases/decreases) [T3] causing an (increased/decreased) metabolic rate.
___________ are provided by thyroglobulin and secreted into the colloid.
Tyrosine Amino Acids are provided by thyroglobulin and secreted into the colloid.
____________: densely arranged near capillaries and produce parathyroid hormone (PTH)
Parathyroid (Chief) Cells: densely arranged near capillaries and produce parathyroid hormone (PTH)
__________ is the most common feline endocrine disorder.
Hyperthyroidism is the most common feline endocrine disorder.
Diagnosis of Hyperthyroidism
tT4
fT4
tT3 or fT3
TSH Stimulation Test
T3 Suppression Test
______________ test for hyperthyroidism where T3 is administered to inhibit the release of TSH and decrease T4 secretion.
T3 Suppression Test test for hyperthyroidism where T3 is administered to inhibit the release of TSH and decrease T4 secretion.
Thyroid hormones are _______ soluble.
Thyroid hormones are fat soluble.
___________________
Must be bound to protein in order to circulate
Explain the process of secretion of thyroid horomones
Epithelial cells ingest colloid by endocytosis
Endosomes fuse whith lysosomes to liberate thyroglobulin
Free thyroid hormones diffuse out
Explain thyroid hormone mechanism of action
Free T3 and T4 taken up by target cell
In cytoplasm T3/T4 bound to transport proteins
T4 → T3 by deiodinase
T3 binds mitochondrial or nuclear receptors
_____________ : enzyme that brings precursor molecules together
Thyroxoid Peroxidase (TPO) : enzyme that brings precursor molecules together
_____________ disease in which C cell production of calcitonin may be impaired leading to increased blood [calcium]
Thyroid Parafollicular Cell Dysfunction disease in which C cell production of calcitonin may be impaired leading to increased blood [calcium]
________ is the bioactive thyroid hormone.
T3 is the bioactive thyroid hormone.
Hypothyroidism is more common in ______
Hypothyroidism is more common in dogs
______________________
Can occur in cats after bilateral thyroidectomy
Etiology of Hyperthyroidism
Thyroid Adenoma/ Benign Adenomatous Hyperplasia
Thyroid Carcinoma
________ is most abundant thyroid hormone
T4 is most abundant thyroid hormone
DIT + DIT =
T4
When T3 binds _________ receptors it increases mRNA transcription leading to increased protein synthesis.
When T3 binds nuclear receptors it increases mRNA transcription leading to increased protein synthesis.
________ measures only free T4
fT4 measures only free T4
_______________
Used to corraborate tT4
Parathyroid hormone effects on target tissues
@ Bone - stimulate osteoclast activity
@ Kidney - inhibit excertion of calcium, promote reabsorption of calcium
@ GI - stimulate uptake of calcium
Explain the process of thyroid hormone synthesis
Iodide → Iodine
Iodine +Tyrosine → MIT or DIT
Coupling process
Thyroid hormone stored bound to thyroglobulin in colloid until stimulated to be released
__________ disease in which insufficient PTH is produced leading to decreased blood [Calcium]
Hypoparathyroidism disease in which insufficient PTH is produced leading to decreased blood [Calcium]
________ measures both free and bound T4
tT4 measures both free and bound T4
Functional units of the thyroid gland
Thyroid Follicles
Colloid
Parafollicular Cells
T4 undergoes glucuronidation by _________ in order to increase its solubility to bile.
T4 undergoes glucuronidation by T4 UDP-Glucuronyl Transferase in order to increase its solubility to bile.
Endocrine system
Collection of ductless glands that secrete hormones directly into the circulatory system
_______________ stimulates T3/T4 synthesis and secretion.
Thyroid Stimulating Hormone (TSH) stimulates T3/T4 synthesis and secretion.
Diagnosis of Hypothyroidism
tT4
fT4
TSH Stimulation Test
________: intrafollicular fluid rich in thyroglobulin
Colloid: intrafollicular fluid rich in thyroglobulin
T3 has a (higher/lower) affinity for binding protien than T4.
T3 has a (higher/lower) affinity for binding protien than T4.
MIT + DIT =
T3 or reverse T3
___________ is obtained from the diet and secreted into the colloid
Iodide is obtained from the diet and secreted into the colloid
______________________
Process called iodide trapping
__________ binds 70-80% of all circulating thyroid hormones.
Thyroid Binding Globulin (TBG) binds 70-80% of all circulating thyroid hormones.
