Kaplan - Endocrinology - Part IV

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What are the secretions of the adrenal medulla?: 80% epinephrine
20% norepinephrine
Where does most circulating epinephrine arise from?: adrenal medulla
Where does most circulating norepinephrine come from?: postganglionic sympathetic neurons
Is the adrenal medulla essential for life?: no, the adrenal medulla is not essential for life because many of the effects of epinephrine and also effects of norepinephrine.
hormonewise, what happens to a person that goes from a lying to a standing position?: plasma norepinephrine levels double when one goes from a lying to a standing position.
The secretion of epinephrine by the adrenal medulla rapidly increases in response to what?: exercise
emergencies
exposure to cold
severe hypoglycemia
What is a stimulus that causes a rise inall stress hormones?: Severe hypoglycemia is a stimulus that causes a rise in all stress hormones.
Epinephrine acts to mobilize what substrates?: carbohydrates and fat
Epinephrine does not break down protein.
What are the metabolic actions of epinephrine on carbohydrates and fat?: -will raise plasma glucose by releasing it from the LIVER
-Will cause glycogenolysis from skelital muscle, but since skeletal muscle cannot dephosphorylate glucose it cannot release free glucose. It
Why is skeletal muscle unable to secrete glucose and what does it do with the glucose for glyocgenolysis?: It cannot secrete glucose because it is unable to dephosphorylate the glucose molecule. Therefore it must metabolize the glucose down to lactate before it can be release into the circulation.
How does epinephrine increase the FFA (free fatty acids) in the blood?: it works on hormone synsitive lipase to cause lipolysis.
What are pheochromocytomas?: Tumors arising from sympathetic chromaffin tissue.
What is the primary secretion of pheochromocytomas? and what are the other possible secretions?: most release norepinephrine but epinephrine or even dopamine can be secreted.
What are the bodily effects of a pheochromocytoma?: 1. Hypertension
2. Hyperglycemia and glucouria are often present.
What proportion of the calcium in the circulation is free calcium?: 50%
What is the biologically active form of calcium?: free form
How do you determine the amount of bound calcium in the plasma?: The amount of bound calcium is equal to the difference between the total amount of calcium in the plasma and the total amount of calcium in the interstitial fluid.
What does bone depostion or reabsorption depend on when concerning calcium and phosphate.: Whether or not the PRODUCT of calcium X phosphate the over or under a certain given value, sometimes called the solubility PRODUCT or ion PRODUCT.
Where is parathyroid released from and what causes it's release?: It is released from the parathyroid and the only important physiological signal regulating release of PTH is free Ca++.
What is the function of PTH?: Function is to raise free Ca++ which it does so by several mechanisms.
What are the fast mechanisms that PTH uses?: -increases Ca++ reabsorption in the distal tubule of the kidney
-decreases phosphate reabsorption in the proximal tubule
-increases the exchange of calcium from ISF pool surrounding bone.
What is the only hormonal action that deals with the proximal tubule?: PTH increases the secretion of phosphate into to the urine in the proximal tubule.
What is the function of osteoblasts and what do they arise from?: osteoblasts deposit bone and arise from osteoprogenitor cells of mesenchymal origin
What do osteocytes arise from?: osteocytes are osteoblasts which become entreaped in meneralized bone
What do osteoclasts do and what are they derived from?: Osteoclasts resorb bone and arise from monocytes which migrate to bone
Where are the receptors for parathyroid hormone located?: Receptors for parathyroid are located on the osteoblasts, not the osteoclasts.
What are the slower actions of Parathyroid hormone?: - PTH slowly increases the formation and activity of osteoclasts which resorb bone Ca++
- PTH increases the formation of 1,25 di-OH D3 (which is active Vitamin D) in the proximal tubules of the kidney, which leads to increased absorption of Ca++ and phosphate from the small intestine.
What type of hormone is calcitonin and what is it secreted by (2names)?: calcitonin is a peptide hormone secreted by the parafollicular cells ("C" cells) of the thyroid.
What is calcitonin released in respons to?: is released in response to elevated free calcium.
What is the result of the release of calcitonin?: calcitonin lowers plasma calcium by decreasing the activity of osteoclasts, thus decreasing bone resorption.
Is calcitonin a significant hormone in humans?: calcitonin is not a major controller of Ca++ in humans.
Where are the receptors to calcitonin located and how does this compare with the receptors for PTH?: The receptors for calcitonin are located on the osteoclasts whereas the receptors for parathyroid hormone are located on the osteoblasts.
What is a marker for osteoblastic activity?: increased serum alkaline phosphatase
which marker is an index for osteoclast activity?: increased urinary excretion of hydroxyproline, a breakdown product of collagen.
What are the consequences of primary hyperparathyroidism?: -increased plasma calcium
-decreased plasma phosphate
what is primary hyperparathyroidism usually do to?: tumor
What is the general rule as to what will determine the plasma phosphate?: the plasma phosphate is determined mainly by process going on in the kidney. for example, the hypersecretion of PTH will cause bone resorption, raising phosphate, the it also stimulates the proximal tubule to dump phosphate with will lower plasma phosphate. overall the kidney wins and plasma phosphate is lowered.
what is the main cause of primary hypoparrathyroidism?: thyroid surgery
what happens to calcium and phosphate in primary hypoparrathyroidism?: increase plasma phosphate and decrease plasma calcium
what is one of the main symptons of hypocalcemia and what is the mechanism?: hypocalcemia increases the excitability of motor neurons, but the skelital muscle fibers themselves
What is a general rule for a primary disorder? and what is the exception to this rule?: it is a primary disorder if the plasma calcium and phosphate are moving in different directions.

the exception to this is chronic renal failure. in this case they are also going in opposite directions but it is not a primary disorder.
What is the only significant signal affecting PTH secretion: free calcium
What will always be the cause of secondary parathyroidism?: changes in plasma calcium
What is Vitamin D required fot?: absorption of calcium from the intestine
What is a good example of something that will cause secondary hyperparathyroidism?: A diet deficient in vitamin D.
What is the cause of secondary hypoparathyroidism? and what is a good example of something that will cause this?: in increase in plasma Ca++

-a good example of something that will cause this is a diet with excessive intake of vitamin D.
what is the golden rule of secondary parathyroidisms?: when the plasma calcium and phosphate are changing in the same direction the origin is usually a secondary disorder.
What are the two different sources of vitamin D?: 1. Dietary intake of vitamin D.
2. Synthesis of vitamin D in the skin in the presence of untraviolet light. if you have enough sunlight on the skin you can synthesize the minimus daily requirement.
What type of vitamin is vitamin D?: it is a fat soluble vitamin and it can be stored for a prolonged period of time.
What is the main circulating form of vitamin D?: 25-hydroxy form of Vitamin D
What does the liver convert vitamin D2 and D3 to?: 25-hydroxy for of vitamin D
Whether is is dietary uptake of synthesized in the skin, where is most of the vitamin D transported?: Most of the vitamin D is transported to the liver to become 25-hydroxy form of vitamin D
Which form of vitamin D is from dietary uptake?: vitamin D2
which form of vitamin D is synthesized in the skin?: vitamin D3
What is the form of vitamin D that is measured clinically: 25-hydroxy form
Although it is the main form, what is the activity level of the 25-hyroxy form of vitamin D.: the 25-hydroxy form has VERY LOW activity.
What form of vitamin D is drawn apon when activation of vit. D is required and what is the site of this activation?: The form drawn upon is the 25-hydroxy form. The site of the activation is in the kidney.
In what part of the kidney does the activation of vitamin D take place?: renal proximal tubule
What enzyme activates vitamin D?: 1-alpha-hydroxylase
1-alpha hyroxylase converts what to what?: converts 25-hydroxy for to 1,25 dihydroxy form
What is the hormonal/active form of vitamin D?: 1,25-dihydroxy form
What is the other form of vitamin D and the 25-hydroxy form can also be converted to and what is it's activity level?: 24, 25-dihydroxy which is an inactive form.
Very important: What regulates the activity of 1-alpha hydroxylase?: this enzyme of activated by low plasma phosphate and it is activated by PARATHYROID HORMONE acting on the renal proximal tubules.
Under normal conditions what does 1,25-dihydroxy D3 do to calcium and phosphate levels?: under normal conditions 1,25-dihydroxy acts to raise plasma calcium and phosphate
Overall what does this rise in plasma calcium and phosphate cause?: bone deposition
What are the three actions of 1,25 dihydroxy D3?: 1. 1,25 dihydroxy D3 increases the absorption of calcium and phosphate from the small intestine.
2. 1,25 dihydroxy D3 increase calcium reabsorption from the renal distal tubules.
3. At extemely high levels 1,25 dihydroxy D3 will cause resorption of calcium and phosphate from bone.
What are the effects of 1,25 di OH D3 deficiency?: secondary hyperparathyroidism which causes bone resorption.
what are the effects of excess 1,25 di OH D3?: excess vitamin D acts directly on bone and causes bone resorption leading to osteoporosis?

**Note that both defieiency and excess 1,25 diOH D3 will cause bone resorption.
What types of hormones are thyroid hormones?: major anabolic hormones
What substance is essential for thyroid hormone secretion and what form must it be in to be absorbed.: Iodine is essential and it must be in the I- form
What is the functional unit of the thyroid gland?: Thyroid follicle
How many follicles make up the thyroid gland?: thousands
What are the two components of each individual follicle?: 1. the interior of the follicle is filled with THYROGLOBULIN - a pink staining protein material
3. Surrounding the lumen are the follicle cells.
How are the thyroid hormones stored?: They are stored covalently bonded to THYROGLOBULIN.
Is the follicle lumen considered to be intra- or extracellular?: extracellular
What is the function of the follicle cells?: synthesize and release thyroid hormones T4 and T3.
What are the two substrates that you need to synthesize thyroid hormones?: I- and thyroglobulin
How does I- get into the cell? What happens if you inhibit this mechanism?: it is actively pumped into the cell from the interstitium, against it's concentration gradient and electrical gradient.
If you inhibit this mechanism it will slow down the production of thyroid hormones.
How does thyroglobunlin get into the follicular cells?: Thyroglobulin is synthesized by the follicular cells themselves
What are the steps involved in thyroid hormone synthesis?: 1. Oxidation of I- to the Io form.
2. This step is the most important, it is the iodinization of tyrosine residues with the Io.
3. Coupling of the MITs and DITs
What converts the I- to Io?: The enzyme peroxidase.
What enzyme plays a part in all three steps?: peroxidase
What is the function of the tyrosine residues on the thyroglobumin and what is each tyrosine residues capacity?: The tyrosine residues bind the Io molecules and store them. Each tyrosine residue has a capacity of 2 Io molecules.
What are the initial products of the iodination of tyrosine.: MIT and DIT mono- and diiodotyrosine.
When iodine is abundant, what is the main product of the iodination of tyrosine?: When iodine is abundant, the main product is diiodotyrosine (DIT).
How much MIT is normally formed?: not very much unless there is a deficiency in iodine.
What is the most common product of coupling?: T4
This is because DIT is normally formed over MIT, when two DIT couple T4 is produced, and when a DIT and MIT couple, T3 is produced.
If iodine becomes scarse, what happens to the production of T4 and T3: T3 increases
Because in iodine deficiency, MIT is formed more and you are more likey to couple an MIT with a DIT
What are the four iodine containing structures attached to the thyroglobulin molecule?: -uncoupled MIT
-uncoupled DIT
-T3
-T4
What is the most active form of thyroid hormone?: T3
What is the differency between T3 and reverse T3?: T3 has 2 iodines on the inner ring and 1 iodine on the outer ring.
Reverse T3 has 1 iodine on the inner ring and 2 iodines on the outer ring.
What is the activity of reverse T3?: Reverse T3 has no activity whatsoever.
How do you regulate the activity of T4?: remove an iodine from the outer ring or the inner ring. This will convert it to T3 or reverse T3, respectively
What are the steps involved in the secretion of thyroid hormone?: 1. Endocytosis of thyroglobulin with thyroid hormone attached in to the follicle cell.
2. Fusion of the endocytosed material with lysosomes.
3. Digestion of the thyroglobulin - Within the lysosomes, the thyroglobulin is broken into free amino acids, some of which are T4, T3, DIT, and MIT. With the digestion of thyroglobulin you release iodine containing compounds.
What enzyme removed the iodine from iodinated tyrosines (DIT and MIT) for recycling.: deiodinase
Why is there 50 times more T4 in circulation than T3: Two reasons:
you release 20 times more T4 than T3 and the T4 binds more strongly to protein in the circulation and thus has a longer half life.
Why is T3 considered the more active form of the hormone?: Although T3 and T4 bind to the same receptor, T3 binds more strongly (has more affinity) than T4
What do many tissues do to locally regulate the activity of thyroid hormone?: Locally many tissues can regulate the conversion of T4 to either T3 or reverse T3.
What enzyme do tissues use to convert T4 to T3?: 5' monodeiodinase
What enzyme do tissues use to convert T3 to reverse T3 (inactive form): 5 monodeiodinase
What is the basic effect of thyroid hormones on metabolism?: thyroid hormones speed up metabolism, but DO NOT affect the metabolic rate of nervous tissue.
What are thyroid hormones absolutely essential for?: Are absolutely essential for normal BRAIN MATURATION
-and essential for normal MENSTRAUL CYCLES.
When will the absence of thyroid production become evident in a newborn?: -The fetal growth rates appear normal in the absence of thyroid hormone production.
-With out thyroid hormones in the perinatal period, abnormalities develop in nervous system maturation.
What is the consequence of not starting thyroid replacement theray soon after birth: IRREVERSIBLE NEURAL CHANGES
What happens to prepubertal growth in the absence of thyroid hormones?: it is retarded
What happens to bone ossification in the absence of thyroid hormones?: it is retarded
Thyroid hormone is requied for the normal synthesis and secretion of what hormone?: growth hormone
In lipid metabolism, what is thyroid hormone required for?: Thyroid is required for the conversion of carotene to Vitamin A
What is the effect of thyroid hormone on the autonomics?: it increases the number and affinity of Beta receptors in the heart.
What is the ratio in circulation of T4 and T3: 50:1
Where does the negative feedback take place for thyroid hormone secretion?: Level of the hypothalamus and anterior pituitary.
Which form the thyroid hormone creates most of the negative feedback?: T4 because there is 50 times for of it.
Which form the thyroid hormone is more potent at creating negative feedback?: they are equally potent
How does T4 create the negative feedback?: Inside the thyrotroph, T4 must be converted to T3 before it creates the negative feedback effect.
What happens in low T3 syndrome?: T3 goes down and thus, because T3 is the more potent of the two, you have less of an effect from thyroid hormone on metabolism of the body and your metabolism decreases. But since negative feedback from T4 is still strong you do not get an increases in secretion of thyroid hormone and the problem is not corrected.
What if you give a large injection of T3?: It will increase the negative feedback and TSH will go down.
If someone had hypothyroid and was overweight would it make more since to give T3 or T4.: T3 because you could give smaller dose and still get the same effect because it is more potent.
What is the effect of TSH on thyroid hormone?: TSH speeds up both the synthesis and degradation of thyroid hormone.
What does increased TSH do to the thyroid gland?: Increases hyroid cell size which leads to hypertrophy of the gland.
What is the correlation between thyroid size and function?: There is NO CORRELATION between thyroid size and function.
What is the most sensitive indicator of hypothyroidism and why?: TSH is a better indicator than thyroid hormone because thyroid hormone is not water soluble and is bound to proteins and is hard to count. Because TSH is water soluble it is easy to count.
What is the mechanism for graves disease?: Graves disease is an autoimmune disease which directly stimulates the thyroid tissue to release more thyroid hormone.
What is the effect of graves disease on TRH, TSH, and T4/T3?: the direct stimulation of thyroid tissue and increase in T4/T3 will increase the negative feedback and decrease both TRH and TSH.
What happens when iodine is deficient but not absent in the diet?: person will be euthyroid but will develop a goiter.
How is it that the euthyroid state is preserved even though the iodine in take is decreased?: more T3 is produced when there is less iodine, and because the T3 is more potent, the function of the thyroid is not compromised.
Why is a goiter formed in an iodine deficiency?: In the iodine deficiency a goiter is formed because with the decreased production of T4 and thus decreased production of the overall amount of thyroid hormone being secreted there is less negative feedback on the secretion of TRH and TSH and the increase in TSH causes the thyroid tissue to hypertrophy , thus creating a goiter.
What are 7 characteristics of hypothyroid adults?: -decreased basal metabolic rate and oxygen consumption
-an elevated TSH is more diagnostic than the decreasae in T4 in primary hypothyroidism.
-decreased mental capacity
-elevated blood lipids (individuals are slightly overweight)
-complex of protein hyaluronic acid, and chondroitin sulfate (mucopolysaccharide) accumulate.
-prolonged relaxation phase of deep tendon reflexes (stretch reflex)
-physiological jaundice (carotene accumulatoin), horse voice, constipation, anemia.
What are the characteristic of hyperthyroid individual?: -increased metabolic rate
-inspite of increased appitite there is generally weight loss, protein wasting and muscle weakness (thyrotoxic myopathy)
-excitability, irritability, restlessness
-tachycardia and increased cardiac output due to the increased B receptor stimulation.
-exopthalamos
What is the most common chief complaint of people who have a thyroid problem?: heart problem

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