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Biology
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17 Nov 2019

What material is stored in the thyroid follicles?

thyroid hormones, ready to be immediately released
enzymes that produce thyroglobulin
iodinated thyroglobulin, from which thyroid hormone can be released
pure iodine, so the thyroid has a constant supply

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20 Jan 2019
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Related questions

Key: A.Increase

B.Decrease

C. Remain thesame

For questions 19-20 use the following information Thyroid-stimulating hormone (TSH) is secreted from the anterior pituitarygland and acts on the thyroid gland to increase the secretion ofthyroid hormones. Thyroid hormones, on the other hand, have anegative-feedback effect on TSH secretion (See Fig. 16.8 in yourtext). For a person having normal thyroid function, the rate atwhich TSH and thyroid hormones are secreted remains within a normalrange of concentrations. In some people, however, the immune systembegins to produce an abnormal substance that functions likeTSH.

Predict what that substance will do to:

19. _____the rate of thyroid stimulating hormone secretion

20. _____ the rate of thyroid hormone secretion.

For question 21 use the following information. Background:Hormones are dissolved in blood plasma and transported either in afree form or bound to plasma proteins. Hormones that are lipidsoluble, such as steroids and thyroid hormone, circulate in theblood in combination with these plasma proteins. Hormones that bindto plasma proteins do so in a reversible fashion according to theequation:

H + BP <-----------> HBP

(Hormone) (BindingProtein) (Hormone bound to binding protein)

An equilibrium is established between the free plasma proteinsand the hormones bound to the plasma proteins. This equilibrium isimportant because only a free hormone is able to diffuse throughcapillary walls and bind to target cells. The combination of ahormone bound to a binding protein reduces the rate at which theydiffuse through the walls of capillaries.

This increases the half-life of the hormone. The half-life isthe length of time it takes to eliminate half a dose of a substancefrom the circulatory system. The half-life of a hormone is astandard measurement used by endocrinologists because it allowsthem to predict the rate at which a given hormone will beeliminated from the body.

21. _____How is the half-life of a hormone affected by adecrease in the concentration of the

specific plasma protein to whichthat hormone binds? Remember if the time to

eliminate a hormone from theblood stream is longer then the half life has increased.

If the time to eliminate ahormone shortens then the half life has decreased

22. _____Consider a hormone that is secreted in large amounts ata given interval, modified

chemically by the liver, andexcreted by the kidney at a rapid rate, making the

half-life of the hormone in thecirculatory system very short. The hormone therefore

rapidly increases in the bloodand then decreases rapidly. Predict the

consequences of liver and kidneydisease on the blood levels of that hormone.

For question 23 use the following background information:Periodic increases in the sensitivity of some tissues to certainhormones is called up-regulation. It results from an increase inthe rate of receptor molecule synthesis. In many tissues the numberof hormone receptors rapidly decreases after exposure to certainhormones. This is called down-regulation.

Problem. Estrogen is a hormone secreted by theovary. It is secreted in greater amounts after menstruation and afew days before ovulation. Among its many effects is causing

up-regulation of receptors in the uterus for another hormonesecreted by the ovary called progesterone. Progesterone is secretedafter ovulation. A major effect of progesterone is to cause theuterus to become ready for the embryo to attach to its wallfollowing ovulation. Pregnancy cannot occur unless the embryoattaches to the wall of the uterus.

23. ______Predict the consequences on becoming pregnant if theovary secretes too little

estrogen?

24. ______ Predict the effect of inadequate dietary intake ofcalcium on PTH secretion

25. ______ Predict the effect of inadequate dietary intake ofcalcium on Calcitriol secretion

1. What happensif the human body makes excess thyroid hormones? What type ofdisorder causes this in Graves’ disease?

2. Parathyroidhormone (PTH) and calcitonin are antagonistic hormones. Describewhat them means with respect to PYH and calcitoninfunction.

3. Explain theaction of insulin and glucagon on blood glucose levels. Are theyantagonistic hormones? 28. In response to low blood glucose levels,which hormone (insulin or glucagon) would be released? Where arethese hormones produced? Glucagon would be realesed,liver

4. What type of cells in thehypothalamus produce hormones?

5. Explain how hormones secreted from theadrenal medulla differ from hormones secreted by the adrenal cortexin response to stress.

2. Let’s consider transport of iodine (I- ) into your thyroid cells. You need iodine in your diet for normal thyroid activity, but dietary iodine concentrations are very low (usually in America we get enough just from what is added to iodized salt). People have been interested for some time in trying to figure out how we can transport iodine so efficiently. One way we can study the transporter is to look for mutations that alter its function, and therefore lead to thyroid problems.

A. The transporter is a rocker-switch type Na+ / Isymport. The pivot of the rocker mechanism is a glycine amino acid, #93 in the primary structure of the transporter. Some people with thyroid problems have a mutation that changes this glycine to an arginine. Define what is meant by “the primary structure” of the transporter. Explain how that change would alter the function of the transporter. (You may consult the structure of arginine on slide 7 of Lecture 3.)

B. There is normally an Arginine at position #124 in the primary structure of the transporter. This Arginine participates in hydrogen bonding with an Asparagine, positioned at #441 in the primary structure. There is evidence that these H-bonds are present in the outward-facing transporter conformation, but are broken when the transporter switches to the inward-facing conformation. People with mutations that replace Arginine 124 with Histidine have difficulty transporting Iodine into their thyroid cells. Copy the structures of Arginine and Asparagine. Label relevant H-bond donor and acceptor atoms between these two amino acids. Explain how replacing Arginine 124 with Histidine could affect the operation of the transporter. (Make a sketch of the transporter in the inward-facing and outward-facing conformations to help you to visualize this.)

C. Recent investigation demonstrated that there are actually TWO Na+ ions symported with the Iion. When a colleague of mine saw this report, he said “Ah ha! So that’s why iodine transport is so efficient!” Explain why it would make a difference whether one or two sodium ions were involved? Why would involving two sodium ions make the transporter more efficient?

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