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Old 10-17-2011
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Question The physiology behind tetanic contractions

Leading stars of soap operas are prone to enter fits of hysteria associated with hyperventilation. In real life, when that happens it usually leads to muscle cramping (tetanic contractions). What is the physiological concept that explains what happens in that situation?
A. Decreased protein-bound calcium
B. Hypercalcemia secondary to PTH-mediated bone resorption
C. Increased dissociation of protein-bound calcium
D. Decreased ionized plasma calcium levels
E. Increased renal calcium excretion
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D. Decreased ionized plasma calcium levels
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D
hyperventilation --->decreased PH ----> hydrogen ions leave its place on proteins and free calcium take its place and get bounded--->hypocalcemia
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Originally Posted by dr.muhamad View Post
D
hyperventilation --->decreased PH ----> hydrogen ions leave its place on proteins and free calcium take its place and get bounded--->hypocalcemia
hyperventilation causes an increase pH because it causes hypocapnia (less CO2, less H2CO3, pH goes up) that's why hydrogen ions leave it's place on proteins to get the pH down.
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Correct Answer

Hyperventilation cause a reduction in blood CO2 and thereby alkalinization of blood. This alkalinization of the blood causes vessels to constrict (vasoconstriction); it is theorized that myofibrillar calcium sensitivity is increased in the presence of high pH value.
The high pH value resulting from hyperventilation also reduces the level of available calcium (hypocalcemia), which affects the nerves and muscles, causing constriction of blood vessels and tingling. This occurs because alkalinization of the plasma proteins (mainly albumin) increases their calcium binding affinity, thereby reducing free ionized calcium levels in the blood. Therefore, low levels of carbon dioxide can cause tetany by altering the albumin binding of calcium such that the ionised (physiologically influencing) fraction of calcium is reduced.
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Quote:
Originally Posted by dr.muhamad View Post
D
hyperventilation --->decreased PH ----> hydrogen ions leave its place on proteins and free calcium take its place and get bounded--->hypocalcemia
i meant increase PH sorry
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good explanation


Hyperventilation cause a reduction in blood CO2 and thereby alkalinization of blood. This alkalinization of the blood causes vessels to constrict (vasoconstriction); it is theorized that myofibrillar calcium sensitivity is increased in the presence of high pH value.
The high pH value resulting from hyperventilation also reduces the level of available calcium (hypocalcemia), which affects the nerves and muscles, causing constriction of blood vessels and tingling. This occurs because alkalinization of the plasma proteins (mainly albumin) increases their calcium binding affinity, thereby reducing free ionized calcium levels in the blood. Therefore, low levels of carbon dioxide can cause tetany by altering the albumin binding of calcium such that the ionised (physiologically influencing) fraction of calcium is reduced.
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