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83 Cards in this Set
- Front
- Back
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thyroxine
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T4
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triiodothyronine
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T3
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what is thyroid secretion controlled by
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TSH
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where is TSH secreted
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anterior pituitary
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what secreted by the thyroid controls calcium
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calcitonin, decreases serum calcium
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what is the main difference between thyroxine and triiodothyronine
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thyroxine is more abundant, but triodothyronine is more potent and lasts a shorter time
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what is the functional unit of the thyroid gland
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follicle
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what are thyroid follicles lined by
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cuboidal epithelial cells
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what do cuboidal epithelial cells secrete
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colloid
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what is colloid composed of
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thyroglobulins that contain thyroid hormones
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what is required at a rate of 1mg/week to maintain adequate thyroid hormone production
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iodide
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what is the first step in thyroid hormone production
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transport of iodides from blood into thyroid glandular cells
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how is iodide pumped into the interior of the cell
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sodium iodide symporter located on the basal membrane of the thyroid cell
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what is the process of getting iodide into the thyroid cell called
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thyroid trapping
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what stimulates the symporter to pump in iodide
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TSH
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what is iodide transported out of the cells with
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chloride-iodide ion counter transporter - pendrin
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where are t3 and t4 hormones formed
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on the actual thyroglobulin proteins in the colloid
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how is iodide modified once in the cell
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oxidized to iodine which then combines with tyrosine - done by peroxidase
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why is peroxidase being located on the apical membrane important
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right where thyroglobulin comes out from the golgi apparatus
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what is the process of iodine binding with the tyrosines in the thyroglobulin molecule called
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organification
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how is thyroxine formed
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when two molecules of diiodotyrosine combine
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how is T3 formed
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when a monoiodotyrosine and a diiodotyrosine combine
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why are the physiologic effects of a thyroid hormone shortage not seen immediately
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about 2-3 months of hormone are stored at one time
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how are t3 and t4 released from thyroglobulin
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proteases
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what happens to left over mono and diiodotyrosines
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recycled via deiodinase enzyme - if not present can become iodine deficient
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what happens to thyroxine in the blood stream
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slowly converted to triiodothyronine
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what happens to T3 and T4 when enters blood
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combine with thyroxine binding globulin
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why does T3 and T4 last a few days in the bloos stream
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because it is released slowly, T4 is released slower than T3 because of higher affinity
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what lasts longer in muscle cells, T3 or T4
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T4 because it binds tighter
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what is the generalized effect of thyroid hormone on the body
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increased transcription of nuclear genes
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what happens to thyroxine before binding to genes
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loses an iodine to become T3
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what do thyroid hormones bind to on DNA
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retinoid x receptors (RXR) on thyroid hormone response elements
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what happens to metabolic rate under thyroid hormones
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increase 60-100 precent
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what happens to cellular mitochondria under thyroid hormone
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increase in size and multiply in number
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how does thyroid hormone increase body heat
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make membranes leaky to sodium and increases activity of sodium potassium pump, increase metabolic rate, make heat
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growth rate with hypothyroid children
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greatly retarded
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growth rate with hyperthroid child
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grows faster and at a quicker rate, though the epiphyses close sooner so the duration of growth and final height may not be as tall
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what happens to fetus without thyroid hormone
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no brain development
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effect of thyroid hormone on carbohydrate metabolism
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it is all driven by it, even release of glucose
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effect of thyroid hormone on fat metabolism
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increases plasma fatty acid levels and increases levels of fat oxidation in cells
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what happens to cholesterols, phospholipids and triglycerides during increased thryroid levels
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decreases plasma concentration of them
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what is associated with low levels of thyroid hormone
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severe atherosclerosis because of high levels of circulating plasma cholesterol
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what happens to vitamin requirements in a hyperthyroid state
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large increase, can become short very quickly
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what happens to the basal metabolic rate in a complete absense of thyroid hormones
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falls to one half normal
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what happens to cardiac output with hyperthroidism
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can rise up to 60% above normal due to systemic need for more oxygen and need to relieve metabolic heat
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why is heart rate used for determining thyroid production
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because it is highly sensitive to changes in thyroid hormones
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what happens to heart contraction strength with a small elevation in thyroid hormones
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large increase
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what happens to heart contraction with a large increase in thyroid hormone concentration
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can induce myocardial cell death because of increased rates of protein catabolism
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what happens to mean arterial pressure during excess thyroid hormone
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stays more less the same
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why is pulse pressure increased with thyroid hormone excess
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increased blood flow in tissues between heart beats
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why does hyperthyroidism cause diarrhea
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because of increased motility in the GI tract
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what are the neurological consequences of hyperthyroidism
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anxiety, paranoia, psychoneurotic complexes
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what happens to muscles with excess thyroid hormone
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a little increases contraction vigor, too much makes sluggish because of increased protein catabolism
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how is muscle tremor associated with hyperthyroidism
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increased reactivity of neuronal synapses that control muscle tone, tested by piece of paper on finger
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effect on sleep - hyperthyroidism
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makes always tired, but excitable effect of thyroid hormone makes diffcicult to sleep, hypothyroidism makes sleep for 12-14 hours a day
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hyperthyroid affect on ACTH
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increased thyroid hormone inactivates more adrenal glucocorticoids, which leads to increase in ACTH by anterior pituitary which increases glucocorticoids
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efffect of thyroid hormone on men sex drive
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hypo = loss of libido, hyper = ED
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hypothyroid hormone on women sex drive
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monorrhagia, polymenorrea, or even amenorrhea - depending on women
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hyperthyroid woman sex rive
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oligomenorrhea (reduced bleeding) or amenorrhea
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what effect does TSH have on thyroid hormone production
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accelerates all steps of production
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what is the most acute affect of administering TSH to a person
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will increase proteolysis of thyroglobulin releasing T3 and T4, happens in 30 minutes
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how does TSH increase thryroid cell production
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activation of adenyl cyclases and cAMPs
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what regulates TSH
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TRH from hypothalamus
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what does TRH stimulate to produce TSH
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phospholipase second messenger system
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what is the best way to increase TRH and consequently TSH production
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make person cold
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what do thiocyanates do to thyroid production
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competively inhibit iodide transport into the cell, can cause a goiter because of very high TSH levels causing thyroid hypertrophy
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propylthiouracil effect on thyroid
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prevents oxidation of thyrosine and combining iodinated tyrosines to form thyroxine or T3, can cause goiter as well by TSH excess
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iodides in high concentrations
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decreased thyroid activity and size, given to patients before thyroid surgery to make surgery easier
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what happens to TSH levels in graves disease people
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goes to 0 because TSI binds on to TSH receptors in thyroid and binds tighter, in creases T3 and T4 levels and neg feedback shuts off TSH
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what happens to normal thyroid gland cells if an adenoma develops
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release of hormones drops to 0 because adenoma is releasing T3 T4 at a constant rate shutting TSH production off
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most obvious characteristic of hyperthyroidism
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exopthalamos
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TSI levels in hyperthroid cases
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high in thyrotoxicosis and low in thyroid adenoma
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main cause of hypothyroidism
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autoimmune that destroys it rather than stimulate (hashimotos)
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what happens to thyroid with lack of iodine
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no way to make thyroid hormones, but high levels of TSH stimulate thryroglobulin formation and hypertrophy of the thyroid gland - form goiter
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method of goiter development with idiopathic nontoxic colloid goiter
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signs of mild thyroiditis, leads to increase TSH which leads to growth of non inflammed parts of gland
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goitrogenic substances
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food products that act the same way as propylthiouracil anti thyroid activity
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myxedma
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almost complete lack of thyroid production
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how does myxedma cause edema
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increase in haluronic acid in intersitital spaces increases fluid build up
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treatment of hypothyroidism
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take thyroxine pill daily
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congenital cretinism
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lack of thyroid gland in embryo
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lack of iodine in diet
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endemic cretinism
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how to treat cretinism in newborn
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must give thyroxine within a few weeks of birth or permamnent mental retardation takes place
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skeletal growth in cretinism
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slow compared to muscle growth, causes short, obese appearance
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