1. Oneofthefactorstowhichliedetectorsrespondisanincreaseinskinconductivityduetothe

presenceofmoisture.Explainthephysiologicalbasisfortheuseofthisindicator.



Sweatglandsaredistributedovertheentirebody–exceptforthelips,nipplesandexternal

genitalorgans.Nervecellsfromthesympatheticnervoussystemconnecttothesweatglands.

Whenpeoplearenervous,anxiousorafraid(oftenaphysiologicalresponsewhenlying),the

sympatheticnervoussystembecomesmoreactive.



Duringthisarousalstate,neuronsreleaseacetylcholine–achemicalmessenger.Inresponseto

this,otherneuronsreleasenoradrenalin(norepinephrine)–anotherchemicalmessenger.Also,

theadrenalglandsecretesepinephrineaspartofthefight‐or‐flightresponse.Bothepinephrine

andnorepinephrinebindtoadrenergicreceptorstocausetheeffectsseenduringthefight‐or‐

flightresponse.



However,it’sthebindingofacetylcholinetothecholinergicreceptorsofthesweatglandsthat

producesthestress‐inducedsweatresponse.Whenacetylcholinebindstothecholinergic

receptorsofthesweatgland,itopensligand‐gatedsodiumchannelsinthecellmembrane.

Sodiumionsenterthemusclecell,stimulatingmusclecontraction.Thismusclecontractionis

essentiallythesecretoryresponse.



2. Whileplayingonherswingset,10‐year‐oldSallyfallsandbreaksherrightleg.Atthe

emergencyroom,thedoctortellsherparentsthattheproximalendofthetibiawherethe

epiphysismeetsthediaphysisisfractured.Thefractureisproperlysetandeventuallyheals.

Duringaroutinephysicalwhensheis18,Sallylearnsthatherrightlegis2cmshorterthanher

left,probablybecauseofheraccident.Whatmightaccountforthisdifference?



Thisareafeaturestheepiphysealline.WhenSallyfracturedhertibia,sheseparatedthe

epiphysisanddiaphysisandthereforedisruptedthelongbonegrowthprocessattheepiphyseal

line.Inlongbonegrowth,theepiphysisispushedawayfromthediaphysisbyquickly‐dividing

cartilagecells.Thiscausesanincreaseinbonelength.



Thetimeittookforherfracturetohealcompletelyandrestorelongbonegrowthfunction

probablyaccountedforthe2cmofgrowththatshewouldhaveotherwiseexperienced.Also,as

shewasapproachingtheageof18,shewasundergoingtheprocessofepiphysealplateclosure.

Thisisthefusionoftheboneoftheepiphysisanddiaphysisandgraduallyinhibitsandeventually

ceasesgrowthinbonelength.



3. Toddbrokehislegplayingfootballandneededtousecrutchesfor4weeks.Afollow‐upbone

densityscanrevealedthatthebonesinhisbrokenlegwheresomewhatlessdensethan

beforetheinjury.Explain.



Partofthebonehealingprocessistheresorptionofbonebyosteoclasts.Duringtheremodeling

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1. One of the factors to which lie detectors respond is an increase in skin conductivity due to the presence of moisture. Explain the physiological basis for the use of this indicator. Sweat glands are distributed over the entire body – except for the lips, nipples and external genital organs. Nerve cells from the sympathetic nervous system connect to the sweat glands. When people are nervous, anxious or afraid (often a physiological response when lying), the sympathetic nervous system becomes more active. During this arousal state, neurons release acetylcholine – a chemical messenger. In response to this, other neurons release noradrenalin (norepinephrine) – another chemical messenger. Also, the adrenal gland secretes epinephrine as part of the fight‐or‐flight response. Both epinephrine and norepinephrine bind to adrenergic receptors to cause the effects seen during the fight‐or‐ flight response. However, it’s the binding of acetylcholine to the cholinergic receptors of the sweat glands that produces the stress‐induced sweat response. When acetylcholine binds to the cholinergic receptors of the sweat gland, it opens ligand‐gated sodium channels in the cell membrane. Sodium ions enter the muscle cell, stimulating muscle contraction. This muscle contraction is essentially the secretory response. 2. While playing on her swing set, 10 ‐year‐old Sally falls and breaks her right leg. At the emergency room, the doctor tells her parents that the proximal end of the tibia where the epiphysis meets the diaphysis is fractured. The fracture is properly set and eventually heals. During a routine physical when she is 18, Sally learns that her right leg is 2cm shorter than her left, probably because of her accident. What might account for this difference? This area features the epiphyseal line. When Sally fractured her tibia, she separated the epiphysis and diaphysis and therefore disrupted the long bone growth process at the epiphyseal line. In long bone growth, the epiphysis is pushed away from the diaphysis by quickly‐dividing cartilage cells. This causes an increase in bone length. The time it took for her fracture to heal completely and restore long bone growth function probably accounted for the 2cm of growth that she would have otherwise experienced. Also, as she was approaching the age of 18, she was undergoing the process of epiphyseal plate closure. This is the fusion of the bone of the epiphysis and diaphysis and gradually inhibits and eventually ceases growth in bone length. 3. Todd broke his leg playing football and needed to use crutches for 4 weeks. A follow‐up bone density scan revealed that the bones in his broken leg where somewhat less dense than before the injury. Explain. Part of the bone healing process is the resorption of bone by osteoclasts. During the remodeling

process, after trabecular bone replaces all of the woven bone and cartilage of the fracture callus, osteoclasts substitute the trabecular bone with compact bone. The trabecular bone is resorbed by the osteoclasts while the osteoblasts deposit compact bone within the resulting pit. This deposition results in a product that closely duplicates the bone’s original strength and shape – but not exactly. The bone would appear less dense because material/minerals were “borrowed” from adjacent bone tissue to make the necessary repairs. The repaired bone resembles the original bone in that it responds to the same mechanical stressors.

4. 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. As a side note, people who are taking thyroid hormones, calcium and vitamin D supplements often take them all at the same time. Calcium actually prevents the absorption of the thyroid hormones to a significant extent when they’re taken together. Usually, we recommend that the patient wait 2 ‐ 3 hours after the dose of their thyroid hormone before taking their supplements. Synthroid, Levothroid, Armour Thyroid and Levothyroxine are all best absorbed when taken on an empty stomach.

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