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23 Cards in this Set
- Front
- Back
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How can a pituitary adenoma affect the hypothalamus and optic chiasm?
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Macroadnomas can press on optic chiasm causing tunnel vision.
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What are the positive & negative regulators of prolactin?
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Positive: TRH, Prolactin releasing factor
Negative: dopamine |
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What is the prolactin negative feedback?
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Negative feedback on hypothalamus to restrain its own secretion.
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What are the factors that stimulate prolactin release?
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Stress
Hypoglycemia Exercise Drugs External stimuli-breast feeding |
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Why is prolactin unique among the pituitary hormones if you were to cut the pituitary stalk (containing the portal vessel system)?
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All the pituitary hormones (TSH, ACTH, GH) would go down except prolactin which would increase no more dopamine to inhibit prolactin secretion
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What do these do to prolactin?
1. Pregnancy 2. Estrogen 3. Nursing-breast stimulation 4. Sleep 5. Stress 6. TRH 7. Dopaminergic antagonists |
Stimulate prolactin secretion
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What do these do to prolactin?
1. Dopamine (main regulator of prolactin secretion) 2. Dopamine agonists 3. Prolactin |
Inhibits prolactin secretion
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What happens if there is excess prolactin?
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1. Galactorrhea-when lactation not associated with pregnancy
2. Interferance with hypothalamic GnRH secretion which leads to amenorrhea, lossof menses 3. In men, hyperprolactinemia which can cause impotence or infertility |
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If prolactin excess is confirmed, the patient needs?
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1. Visualization of the pituitary by MRI scan
2. Visual field examination 3. Pituitary surgery, radiation, and/or treatment with dopamine agonist (bromocriptine) |
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What is the structure of the thyroid?
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Spheres lined with follicular cells.
If active, then columnar and if inactive then cuboidal Colloid made of thyroglobulin |
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What happens if the thyroglobulin is stimulated by TSH?
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The thyroid cells take up the thyroid hormone and let it into the blood stream.
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rT3
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Reverse T3 is the inactive form of T3.
The iodine molecules are in different positions |
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T4 is a pro-hormone that has to be converted to?
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T3 via 5'-deiodinase
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Process of iodide coming into the thyroid follicular cells?
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Iodide trapping
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Iodide oxidation followed by iodination of tyrosine residues of thyroglobulin, mediated by thyroid peroxidase
Iodination of tyrosine residues done by thyroid peroxidase to form MIT and DIT |
Iodide organification
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What are the steps taking for thyroid hormone synthesis?
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1. Iodide trapping
2. Iodide organification-formation of MIT and DIT 3. Coupling of residues (thyroid peroxidase) 4. Under influence of TSH, thyroglobulin is taken up by follicular cells by endocytosis 5. Proteolysis by lysosomal enzymes cleaves T3 & T4 and is secreted into blood 6. Deiodination of MIT and DIT to recycle the iodine |
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Thyroid peroxidase
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Responsible for iodination of tyrosine residues to form MIT and DIT
Coupling of residues: MIT & DIT = T3 and DIT + DIT = T4 |
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Radioactive Iodine test
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Used to evaluate if the patient's thyroid is taking up iodine.
Radioactive Iodide is given to patient, mixes with body's total iodine pool, see how much of the radioactive iodine is taking up by the thyroid |
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Which is secreted more by the thyroid T3 or T4?
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T4 with a ratio of 10:1
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What happens to the thyroid hormones during fasting?
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1. Conversion of T4 to T3 is reduced.
2. T4 levels do not change 3. T3 levels drop off, but rT3 increases 4. T4 does not build up because it converts to rT3 with enzyme 5-deiodinase |
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How are the thyroid hormones transported in the blood?
By attaching to these plasma proteisn |
1. Thyroid binding globulin (TBG)
2. Cortisol Binding Globulin (CBG) 3. Sex Hormone Binding Globulin (SHBG) |
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An equilibrium exists between the free and bound states of the thyroid hormones
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Free hormone + Plasma protein-only free is active bc can enter cells, interact with receptors and produce biolgical effects
Hormone-protein complex-while bound hormone not metabolized or excreted so its half-life is prolonged by protein binding. |
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Thryoid Binding Globulin has more affinity for T3 or T4?
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T4 therefore more T4 is bound than T3
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