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
