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Constantine’s Conundrum Constantine is a 51-year-old university professor has never had any significant health issues. He exercises...

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Medical Sciences

  1. Constantine’s Conundrum

Constantine is a 51-year-old university professor has never hadany significant health issues. He exercises regularly, doesn’tsmoke or drink alcohol, and keeps his weight within normal range.Recently, however, he’s been experiencing generalized weakness,frequent muscle cramps (tetanic contractions) and tingling in hisfingers. On physical examination, he appeared healthy. However, hisblood pressure was significantly elevated at 180/100, both in thesupine and in the standing positions. His blood and urine analysisrevealed the following:

Table 1: Laboratory Values

Blood analysis

Serum Na+

149 mEq/L

Serum K+

2.0 mEq/L

Serum creatinine

Normal

Serum renin

Low (normal)

Urinalysis

Na+ excretion

Below normal

K+ excretion

Above normal

Urinary catecholamines

Normal

Urinary cortisol

Normal

  1. Provide a tentative etiology (i.e. underlyingpathology) that is consistent with all of Constantine’s blood andurine values. Refer to specific values above to support your answer(or to rule out other pathologies).

  1. Explain the difference between a tetanic contractionand a muscle twitch. Why is Constantine susceptible to tetaniccontractions in his current condition? Explain the underlyingmechanism.

Answer & Explanation Solved by verified expert
4.1 Ratings (562 Votes)
Diagnosishypokalemic muscle twitchSkeletal muscles respond to a single electric shock ofsufficient magnitude by rapid intense contractions called phasiccontractions If the ends of a frog sartorius muscle at 0 C arefixed to prevent shortening the tension increases for about 200milliseconds and then begins to decrease at first rather rapidlyand then more slowly More happens during this mechanical responseto a single stimulation called a twitch than the tension recordsuggestsThe mechanical response to repeated stimulation depends on therate of the stimulation Muscle like other excitable tissues hasa period following its action potential during which the membranewill not respond to stimulation regardless of the strength Thisabsolute refractory period in the frog sartorius at 0 C lastsabout 10 milliseconds after stimulation Therefore a second pulsewithin that time span will not elicit any response If howeverthe pulses are 300 milliseconds apart the muscle will be relaxingwhen the second pulse is given and the tension will appear inwaves in phase with the stimulation causing an unfused tetanus Itis possible to stimulate the muscle at a frequency between theseextremes so that the tension developed by the muscle remainsconstant This latter type of contraction is called a fusedtetanus and the rate of stimulation that produces it is called thefusion frequency The exact rate depends upon the particular muscleand the temperatureUsually the maximum tetanus tension is from 12 to 18 timesgreater than the maximum tension during a twitch Within themuscle many elastic structures connected in series with thecontractile elements are stretched during contraction Theattachment of the muscle fibres to the tendons at the end of themuscle and the attachment of the thin filaments to the Z linecontribute to this elastic component In single fibres howevermost of the elasticity of the series of elastic elements iscontributed by the actinmyosin cross bridges themselves Fullmaximum tension is not apparent at the end of the muscle until thecontractile elements have shortened enough to stretch the elasticelementssomewhat like taking up the slack in a rope before a pullon one end can be felt at the other end In a twitch the activityof the muscle is so brief that the contractile elements cannotextend the elastic elements completely before relaxation begins asa result the tension at the ends of the muscle does not reach themaximum possible level During a tetanus on the other hand theactivity of the contractile elements is maintained and they caneventually shorten enough to extend fully the series of elasticelements When this has been accomplished the maximum tension isapparent at the ends of the muscleLOAD PREVIOUS PAGETwitch and tetanus responsesSkeletal muscles respond to a single electric shock ofsufficient magnitude by rapid intense contractions called phasiccontractions If the ends of a frog sartorius muscle at 0 C arefixed to prevent shortening the tension increases for about 200milliseconds and then begins to decrease at first rather rapidlyand then more slowly More happens during this mechanical responseto a single stimulation called a twitch than the tension recordsuggestsThe mechanical response to repeated stimulation depends on therate of the stimulation Muscle like other excitable tissues hasa period following its action potential    See Answer
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