Pharmacology 3620 Lecture Notes - Lecture 36: Anterior Pituitary, Colloid, Enzyme Inhibitor

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1 May 2018

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10. Drugs used in Thyroid Disease

Learning Objectives

● Recall the function of the thyroid gland in human physiology.

● Explain the biosynthesis and mechanism of action of thyroid hormones.

● Recall the 2 classes of thyroid disorders, and corresponding examples of diseases

● Explain the mechanisms of action for each pharmacologic agent used to treat thyroid

disorders.

● Identify the adverse effects associated with drug treatments for thyroid diseases, and

integrate how these effects relate to the function of the thyroid in normal human

physiology.

The H-P-T Axis is part of the neuroendocrine system

● Thyrotropin-Releasing Hormone (TRH)

○ Peptides hormone released from the hypothalamus

○ Stimulates endocrine cells of the anterior pituitary to secrete Thyroid-

Stimulating Hormone (TSH)

● TSH binds its receptors on the thyroid follicle cells

○ Increase synthesis of thyroid hormone

● Thyroid hormone feedback to reduce production of TRH and TSH

○ Negative feedback regulation

● The thyroid gland is not essential for adult life

○ But it is important

● Thyroid hormone receptors are present in the nuclei of most cells of the body

● Thyroid hormone regulates BMR by:

○ Stimulating Na+/K+ ATPase activity

■ Accounts for 20% of oxygen consumption

○ Stimulating carbohydrate absorption from intestine and release of fatty acids

from adipocytes

○ Upregulation of ฀-adrenergic receptors

■ Heart and nerves system

● Maintaining constant levels of thyroid hormone depends on their negative feedback

○ Inhibit synthesis and secretion of TSH and TRH

Thyroid Gland

● Comprised of follicles

○ A follicle is a colloid surrounded by thyroid follicular cells

○ Colloid:

■ A proteinous “goop”

■ Contains of thyroglobulin

● Provide tyrosine residue critical for production amine hormones

■ Surrounded by a layer of follicular cells

○ Thyroid hormone synthesis occurs in the follicle cells and colloid of the thyroid

gland

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Document Summary

Recall the function of the thyroid gland in human physiology. Explain the biosynthesis and mechanism of action of thyroid hormones. Recall the 2 classes of thyroid disorders, and corresponding examples of diseases. Explain the mechanisms of action for each pharmacologic agent used to treat thyroid disorders. Identify the adverse effects associated with drug treatments for thyroid diseases, and integrate how these effects relate to the function of the thyroid in normal human physiology. The h-p-t axis is part of the neuroendocrine system. Stimulates endocrine cells of the anterior pituitary to secrete thyroid- Tsh binds its receptors on the thyroid follicle cells. Thyroid hormone feedback to reduce production of trh and tsh. The thyroid gland is not essential for adult life. Thyroid hormone receptors are present in the nuclei of most cells of the body. Stimulating carbohydrate absorption from intestine and release of fatty acids from adipocytes. Maintaining constant levels of thyroid hormone depends on their negative feedback.

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

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Pharmacology 3620 Lecture Notes - Lecture 36: Anterior Pituitary, Colloid, Enzyme Inhibitor

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