Exam 3, Day 2 Lecture Flashcards
These are large neuroendocrine cells with cell bodies in the supraoptic nucleus and paraventricular nucleus of the hypothalamus.
Magnocellular neurons
Two main peripheral tissues where large amount of T4 is converted to T3
Liver and kidneys
Symptoms of thyrotoxicosis (3)
Weight loss
Tachycardia
Nervousness
Connective tissue components deposited in SQ tissues (in myxedema) (3)
glycosaminoglycans
hyaluronic acid
mucopolysaccharides
Myxedema probably results from autoimmunity in which _______ binds to and stimulates _____.
Anti-TSH receptor Ig ……. fibroblasts
3 Components of Hypothalamohypophyseal-Thyroid Axis
Hypothalamus
Thyrotrope
Thyroid gland (follicular cells)
Inferior thyroid artery is a branch of ____
thyrocervical trunk
Which thyroglobulins are recycled?
MIT and DIT (dionization)
Most thyroid hormones are bound to which type of transport protein?
Thyroxine-binding globulin (TBG) = 70%
Incidence of congenital hypothyroidism
1 in 3,000 births.
Girls x2 than boys
This is considered as the GOITER BELT
Midwest
Thyroid hormones require ____.
iodine
Which ring is closer to the thyroglobulin molecule?
Inner ring
This is a specific form of cutaneous and dermal edema secondary to increased deposition of connective tissue components in SQ tissue as seen in various form so hypothyroidism and Grave’s disease.
Myxedema
Location of Thyroid receptors ?
Nucleus. They are not found in the cell surface.
Gland that produce PTH
parathyroid
Where does synthesis of thyroid hormones occur?
cytoplasm
Neurons that make oxytocin and ADH
Magnocellular neurons of the paraventricular and supraoptic nuclei of the hypothalamus
T3 has ___x greater biological activity then T4.
10x
What enzyme does cortisol inhibits?
5’/3’-deiodinase (converts t4-t3)
These cells form the wall of the follicle
follicular cells (cuboidal epithelial cells)
Tissue TSH receptor expression (top 3)
- Thyroid
- Fetal thyroid
- Cardiomyocytes
Connection between two thyroid lobes
Isthmus
Arteries that are lateral to the thyroid lobes.
Carotid arteries
Most thyroid hormone in blood is bound to ________ because thyroid hormones are HYDROPHOBIC. Only a very small fraction is free (unbound) and biologically active.
transport protein
Each Magnocellular neuron receives about how many synapses or neurosecretory terminals from afferent neurons?
10,000
Superior thyroid vein drains to the ____
internal jugular vein (largest vein in the neck)
9 Actions of Thyroid Hormones in Metabolism
Increased in:
BMR
Lipolysis
Oxygen consumption
Gluconeogenesis
Glycogenolysis
Glucose absorption
Mitochondria
Na-K Pump
Protein Synthesis
True or False:
In goiter, Thyroid hormone levels can be high or low.
True
Superior thyroid artery is a branch of ___
external carotid artery
Where does binding of thyroid hormones and precursors to Tg occur?
follicular lumen or Colloid
At the apical membrane, the Iodide is converted to diatomic Iodine by ______.
peroxidase
This is an autoimmune thyroid disorder causing decreased T4 and T3.
Hashimoto’s thyroiditis
It inhibits the conversion of T4 to T3.
Cortisol
Iodine content of milk
88 - 168 microgram/ cup milk (1cup = 8 ounces)
Grave’s disease is an autoimmune disease causing overactive thyroid gland which results in serious metabolic imbalance known as ____ and ___.
hyperthyroidism: overactive of tissue within the thyroid gland
thyrotoxicosis: Increase thyroid hormone in the blood
In countries that use iodized salt, ______ is the most common cause of goiter.
Hashimoto’s thyroiditis.
This thyroid level signifies more available, more biologically active T4 to be converted to T3.
Free T4
This is a transport molecule within the magnocellular neuron.
Neurophysin
ALL T4 are secreted by the ____.
Thyroid gland
In the synthesis of thyroid hormones, ioDIDE is taken up, converted to ______.
diatomic ioDINE (I2)
Enzyme responsible for deiodination?
deiodinase
2 Other names of T3
triiodothyronine Liothyronine
Orange peel appearance on the anterior aspect of the lower legs, spreading to the dorsum of the feet, or as a non-localized, non-pitting edema of the skin in the same areas.
Pretibial myxedema
2 reasons why T3 and T4 do not feedback on thyroid gland
- Because follicular cells do not have the ability to get T3 and T4 into the cell
- They lack nucler receptor for T3 and T4
Thyroid gland respond only to TSH and Iodides
This cells are found between follicles, which produce calcitonin (calcium balance)
Parafollicular cells (C cells or clear cells or Calcitonin cells)
Each thyroglobulin (Tg) contains ___tyrosines.
120
5 Actions of Thyroid hormones in CV
Increased:
HR
CO, SV
Tissue Blood flow
Heart strength
Up-regulate catecholamine receptors
What are the 5 tyrosine residues? They make up the colloid!
MIT
DIT
T3
RT3
T4
Type of T4 that has a feedback mechanism to the anterior pituitary gland to secrete more or less of the TSH.
Free T4 in plasma
Neurohypophyseal hormones are transported into the posterior pituitary for storage and release. What kind of transport mechanism is used?
axoplasmic transport (bound to neurophysins)
This is a projection from the isthmus
pyramidal lobe
Minimum Iodine requirement
75 micrograms/day
What stimulates endocytosis of Tg and Na-I symporter?
TSH
Official name for Na-I symporter?
SLC5A5
The most common form of hyperthyroidism is ____.
Grave’s disease
Worldwide, over 90% cases of goiter are caused by _____.
iodine deficiency
Transporter found in the apical membrane of the follicular cells.
Pendrin (SLCA26A4)
Nerve impulses cause ______ of the hormone bound to the neurophysin but they quickly disengage and are absorbed into the capillaries.
exocytosis
What activates (ligand) the TSH receptor in Grave’s disease?
Thyroid stimulating Ig (TSI)
This where precursors of thyroid hormones are stored (good for 2-3weeks use)
colloid (a glycoprotein)
Condition where there is widespread shutdown in T3 binding across the body due to cortisol inhibiting the conversion of T4 to T3.
RT3 Dominance
Enzyme that converts T4 to RT3
5/3-deiodinase
2 Exogenous T3 drugs
Liothyronine
Cytomel
Iodine content of iodated bread
2.2 - 54 microgram iodine per slice
This is an autoimmune disorder that can cause hypothyroidism.
Hashimoto’s thyroiditis
Name 3 Exogenous T4 drugs
Levothyroxine
Synthroid
Levoxyl
First symptom of Grave’s disease
Diffuse goiter
Human proteins mostly start with the first amino acid ___.
Methionine
What cells have the TSH receptor?
follicular cells (cuboidal epithelial cells)
Thyroglobulins with 2 tyrosine rings (3)
T3, RT3, T4
This hormone does not stimulate thyroid hormone receptors. However, it blocks the action of T3.
RT3
Almost all proteins made in the body start synthesis with _____.
Signal peptide
In endemic or colloidal goiter:
Pituitary gland secretes TSH to stimulate thyroid gland to produce Thyroid hormone, but the only result is that the folicles accumulate more and more ______.
unusable colloid (no iodination is happening)
Type of cell found in the posterior pituitary gland.
Pituicytes (glial-like cells)
Hypothalamohypohyseal-thyroid axis
T3 and T4 do have a NEGATIVE feedback on the ____ and ____, but not on the ____.
hypothalamus and anterior pituitary …
but not on the thyroid gland!!!!
Thyroid eye disease which is frequently found especially in smokers.
Grave’s ophthalmopathy
This is a measure hoe much T4 can get inside the cell
RT3 level
Vascular supply and drainage of the thyroid gland
2 pairs of arteries, 3 pairs of veins
What hormones are secreted from the follicular cells (after proteases acted on the colloed droplet)?
T3, T4, RT3 (no transporter needed)
This is the process by which diatomic iodine combines with thyroglobulin.
Iodination and coupling
2 effects of Thyroid Hormones on Oxygen-carrying capacity
- Increase in RBC mass
- Increase oxygen dissociation from Hgb
Most of the T3 and RT3 production comes from
deiodination of T4 in peripheral tissues
Hormones of the posterior pituitary gland is composed of how many amino acids?
9 (referred to as Neurohypohyseal NONApeptide hormones)
Total free thyroid hormones (%)
0.33%
fT4: 0.03%
fT3: 0.3%
The thyroid gland contains numerous follicles, composed of ____ and ____.
cuboidal epithelial cells (follicular cells) and colloids
Name 2 Iodine deficiency disorders
Goiter
Cretinism
T4 is considered as ____, a precursor to T3.
prohormone
Inferior thyroid vein drains to the ___
cephalic vein
What two substances are needed for exocytosis?
Calcium and ATP
What type of cells are stimulated by anti-TSH receptor Ig (TSI)? (2)
follicular cells
Fibroblasts
Process of converting T4 to T3
Deiodination
Type of goiter caused by decreased Iodine resulting in enlargement of thyroid gland.
Endemic or Colloidal goiter
This is the relationship between Hypothalamus, thyrotrope, and thyroid gland.
Hypothalamohypophyseal- Thyroid Axis or
Hypothalamopituitary Thyroid Axis
What cleaves off the colloid droplet thereby producing T3, T4, DIT, MIT?
proteases from lysosomes
Hormones produced by thyroid gland (4)
T4, T3, RT3, Calcitonin
What type of receptor is thyroid hormone receptor?
nuclear receptor
What pump is located at the basolateral membrane of the follicular cell?
Iodide pump/trap or Na-I symporter (2nd active transport)
These are anterior pituitary gland cell type that produces TSH
thyrotrope
Low iodide levels (increase or decrease) iodine transport (Iodide pump) into follicular cells, and vice versa.
increase
Major sources of Iodine (4)
Iodized salt Iodated bread Dairy products Shellfish and fish
Pretibial myxedema occurs in ___ (3)
Non-thyrotoxic Grave’s disease
Hashimoto’s thyroiditis
Stasis dermatitis
This hormone reduce blood calcium level, opposing the effects of Parathyroid hormone (PTH)
Calcitonin (calcium stored in the bones = increased deposition)
T3 inner ring has how many Iodide?
2
Where is TSH produced?
Anterior pituitary gland
This is a medical condition caused by a congenital thyroid hormone deficiency, when untreated results in CRETINISM.
Congenital hypothyroidism
