Thyroid Function and Disorders: Impact on Hormone Secretion and Calcium Regulation | Assignments Physiology

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largeamountsofan

abnormalsubstancethatfunctionslikeTSH.Predictwhatthesubstancewilldotothe

rateofTSHsecretionandtherateofthyroidhormonesecretion.Whatisonename

foradisorderofthistype?



ThesubstanceshouldslowtherateofTSHsecretionbecausethelevelsofT3andT4will

becomesufficientlyhightoinhibitthepituitarygland.Obviously,thismeansthatit

wouldincreasetherateofthyroidhormonesecretion–thissituationbreaksthe

negative‐feedbackmechanism.



AcommonnameforadisorderofthistypeisGraves’Disease.



Ofmembrane‐boundreceptorsandintracellularreceptors,whichisbetteradaptedfor

mediatingaresponsethatlastsaconsiderablelengthoftimeandwhichisbetterfor

mediatingaresponsewitharapidonsetandashortduration?Explainwhy.



Intracellularreceptorswouldbebettersuitedtomediatearesponsethatlastsa

relativelylongtime.Membrane‐boundreceptors,inturn,arebettersuitedtomediate

responseswitharapidonsetandshortduration.



Thedifferenceisduetothehalf‐lifeofthetypeofhormonethatbindstoeachtypeof

receptor.Lipid‐solublehormonesusuallybindtointracellularreceptorswhilewater‐

solublehormonesbindtomembrane‐boundreceptors.



Lipid‐solublehormonesareboundtoaproteincarrierandarelesseasilyremovedby

theliverorkidneyandthereforecirculatethroughthebloodstreamalongerperiodof

timethanwater‐solublehormones.Thismeansthatthedurationofactionoflipid‐

solublehormonesislongerthanthatofwater‐solublehormones.



Also,Iwouldthinkthattheinteractionofalipid‐solublehormoneandDNAtoproduce

proteinswouldinherentlyhavealonger‐termeffectthantheinteractionofawater‐

solublehormone.



Apatientdiagnosedwiththyroidcancerlaterhadtheirthyroidglandremoved.

Explainwhythisindividualwasprescribedcalciumandhormonesupplementation.In

otherwords,whyarethethyroidglandanditsassociatedtissueslinkedtocalcium

regulation?



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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 large amounts of an abnormal substance that functions like TSH. Predict what the substance will do to the rate of TSH secretion and the rate of thyroid hormone secretion. What is one name for a disorder of this type? The substance should slow the rate of TSH secretion because the levels of T 3 and T 4 will become sufficiently high to inhibit the pituitary gland. Obviously, this means that it would increase the rate of thyroid hormone secretion – this situation breaks the negative‐feedback mechanism. A common name for a disorder of this type is Graves’ Disease. Of membrane‐bound receptors and intracellular receptors, which is better adapted for mediating a response that lasts a considerable length of time and which is better for mediating a response with a rapid onset and a short duration? Explain why. Intracellular receptors would be better suited to mediate a response that lasts a relatively long time. Membrane‐bound receptors, in turn, are better suited to mediate responses with a rapid onset and short duration. The difference is due to the half‐life of the type of hormone that binds to each type of receptor. Lipid‐soluble hormones usually bind to intracellular receptors while water‐ soluble hormones bind to membrane‐bound receptors. Lipid‐soluble hormones are bound to a protein carrier and are less easily removed by the liver or kidney and therefore circulate through the bloodstream a longer period of time than water‐soluble hormones. This means that the duration of action of lipid‐ soluble hormones is longer than that of water‐soluble hormones. Also, I would think that the interaction of a lipid‐soluble hormone and DNA to produce proteins would inherently have a longer‐term effect than the interaction of a water‐ soluble hormone. A patient diagnosed with thyroid cancer later had their thyroid gland removed. Explain why this individual was prescribed calcium and hormone supplementation. In other words, why are the thyroid gland and its associated tissues linked to calcium regulation?

Hormone supplementation is needed because the thyroid produces thyroid hormones which regulate the metabolism and affect the growth and rate of function of most of the systems in the body. The thyroid produces the hormone calcitonin, which plays a definite role in calcium homeostasis. Calcitonin stimulates the movement of calcium into bone, in opposition to the parathyroid hormone which serves to increase blood level concentrations of calcium by bone resorption. The parathyroid hormone affects the activity of 1 ‐alpha‐hydroxylase in the kidney, which in turn stimulates the production of the active hormone 1,25‐ dihydroxycholecalciferol. The parathyroid hormone stimulates the release of calcium from bone by targeting osteoclasts. Essentially this means that calcium homeostasis is maintained at the expense of bone. To prevent this, to some degree, a dietary calcium supplementation is given to provide a new/different source of calcium. Since the production of vitamin D will be decreased to some extent by the removal of the thyroid gland, a supplement of vitamin D is also given. The reason for the vitamin D supplement is to stimulate reabsorption of calcium in the intestines. If the supplement isn’t given, the calcium supplement isn’t absorbed at all efficiently. The thyroid gland and parathyroid glands produce the hormones necessary to maintain calcium homeostasis. In their absence, the hormones are not produced and must be supplemented somehow. Predict the consequence if pre‐synaptic action potentials in an axon could not release sufficient acetylcholine to cause depolarization to threshold in a skeletal muscle fiber. A probable consequence is muscle weakness or even paralysis. If the skeletal muscle is not depolarized to threshold, it will not fire an action potential and the muscle will not

Thyroid Function and Disorders: Impact on Hormone Secretion and Calcium Regulation, Assignments of Physiology

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