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Questions and Answers
Why are Gla residues of prothrombin effective in chelating positively charged calcium ions?
What is the role of the prothrombin-calcium complex in blood clotting?
Which foods are rich sources of Vitamin K?
What is a primary reason newborns are at risk for Vitamin K deficiency?
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What dose of Vitamin K is recommended as a prophylactic measure for newborns?
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What are some potential toxic effects of prolonged administration of synthetic Vitamin K (menadione) in infants?
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Study Notes
Prothrombin and Platelet Interaction
- The Gla residues of prothrombin have a strong chelating effect on positively charged calcium ions due to their two adjacent, negatively charged carboxylate groups.
- The prothrombin-calcium complex binds to phospholipids on the surface of platelets, essential for blood clotting.
- Attachment to platelets increases the rate of proteolytic conversion of prothrombin to thrombin.
Vitamin K Distribution and Requirement
- Vitamin K is found in various food sources, including cabbage, kale, spinach, egg yolk, and liver.
- The bacteria in the gut also synthesize vitamin K.
- The recommended daily intake of vitamin K is 120 µg for adult males and 90 µg for adult females.
Vitamin K Deficiency in Newborns
- Newborns have sterile intestines, lacking the bacteria that synthesize vitamin K.
- Human milk provides only about one-fifth of the daily requirement for vitamin K.
- A single intramuscular dose of vitamin K is recommended for newborns as prophylaxis against hemorrhagic disease.
Vitamin K Toxicity
- Prolonged administration of large doses of synthetic vitamin K (menadione) can cause hemolytic anemia and jaundice in infants.
- Toxic effects occur due to damage to red blood cell membranes.
- Synthetic vitamin K is no longer used to treat vitamin K deficiency.
- There is no established upper limit for vitamin K consumption.
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Description
This quiz covers the interaction of prothrombin and platelets, and the role of vitamin K in blood clotting. It explores the binding of prothrombin to calcium and phospholipids, and the conversion of prothrombin to thrombin.
