Key: A. Increase B. Decrease C. Remain the same For questions 19-20 use the foll
ID: 55151 • Letter: K
Question
Key: A. Increase
B. Decrease
C. Remain the same
For questions 19-20 use the following information Thyroid -stimulating hormone (TSH) is secreted from the anterior pituitary gland and acts on the thyroid gland to increase the secretion of thyroid hormones. Thyroid hormones, on the other hand, have a negative-feedback effect on TSH secretion (See Fig. 16.8 in your text). For a person having normal thyroid function, the rate at which TSH and thyroid hormones are secreted remains within a normal range of concentrations. In some people, however, the immune system begins to produce an abnormal substance that functions like TSH.
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 a free form or bound to plasma proteins. Hormones that are lipid soluble, such as steroids and thyroid hormone, circulate in the blood in combination with these plasma proteins. Hormones that bind to plasma proteins do so in a reversible fashion according to the equation:
H + BP <-----------> HBP
(Hormone) (Binding Protein) (Hormone bound to binding protein)
An equilibrium is established between the free plasma proteins and the hormones bound to the plasma proteins. This equilibrium is important because only a free hormone is able to diffuse through capillary walls and bind to target cells. The combination of a hormone bound to a binding protein reduces the rate at which they diffuse through the walls of capillaries.
This increases the half-life of the hormone. The half-life is the length of time it takes to eliminate half a dose of a substance from the circulatory system. The half-life of a hormone is a standard measurement used by endocrinologists because it allows them to predict the rate at which a given hormone will be eliminated from the body.
21. _____How is the half-life of a hormone affected by a decrease in the concentration of the
specific plasma protein to which that hormone binds? Remember if the time to
eliminate a hormone from the blood stream is longer then the half life has increased.
If the time to eliminate a hormone shortens then the half life has decreased
22. _____Consider a hormone that is secreted in large amounts at a given interval, modified
chemically by the liver, and excreted by the kidney at a rapid rate, making the
half-life of the hormone in the circulatory system very short. The hormone therefore
rapidly increases in the blood and then decreases rapidly. Predict the
consequences of liver and kidney disease on the blood levels of that hormone.
For question 23 use the following background information: Periodic increases in the sensitivity of some tissues to certain hormones is called up-regulation. It results from an increase in the rate of receptor molecule synthesis. In many tissues the number of hormone receptors rapidly decreases after exposure to certain hormones. This is called down-regulation.
Problem. Estrogen is a hormone secreted by the ovary. It is secreted in greater amounts after menstruation and a few days before ovulation. Among its many effects is causing
up-regulation of receptors in the uterus for another hormone secreted by the ovary called progesterone. Progesterone is secreted after ovulation. A major effect of progesterone is to cause the uterus to become ready for the embryo to attach to its wall following ovulation. Pregnancy cannot occur unless the embryo attaches to the wall of the uterus.
23. ______Predict the consequences on becoming pregnant if the ovary secretes too little
estrogen?
24. ______ Predict the effect of inadequate dietary intake of calcium on PTH secretion
25. ______ Predict the effect of inadequate dietary intake of calcium on Calcitriol secretion
Explanation / Answer
19. Decreases the rate of thyroid stimulating hormone secretion. The abnormal substance (from immune system) will increase the thyroid harmone secretion which by feedback mechanism will inhibit/ decrease TSH secretion.
20. Increases the rate of thyroid hormone secretion. This is because the abnormal substance (from immune system) will mimic the function of TSH i.e. to stimulate/increase thyroid secretion.
21. The half life of hormone in the blood will decrease when there is a decrease in the concentration of specific plasma protein to which that hormone binds. Since the concentration of specific plasma protein is low, more amount of free hormone will be present. As mentioned in the question, the free hormone (not bound to the plasma protein) can diffuse more efficiently through the capillaries and hence, there will be an increased elimination of hormone through kidneys. Therefore, decreasing half-life of hormone.
22. A hormone chemically modified by liver is rapidly eliminated from the kidneys. Therefore, decreasing the half-life of the hormone. In case of kidney and liver diseases, this hormone will not be chemically modified in liver and will not be eliminated by kidneys. Hence, the amount of hormone in the blood will increase, thereby increasing the half-life of hormone in blood.
23. If the levels of estrogen are too low, there will be low levels of progesterone receptors. If the level of progesterone receptors is low, the progesterone will not be able to induce the attachment of embryo to the uterus after ovulation. If the embryo fails to bind to uterus, it will not result in a viable pregnancy.
24. Inadequate dietary intake of calcium will upregulate Parathyroid harmone (PTH). This will result in increase the serum calcium levels by dissolving the bones, where most calcium is stored and decrease the elimination of calcium in urine through kidneys.
25. Inadequate dietary intake of calcium will upregulate Calcitriol secretion. When the calcium levels in the blood decreases, PTH increases the synthesis of Calcitriol. Calcitriol increases calcium absorption in the intestine, thereby increasing blood calcium levels.
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