Vitamin K: Absorption and Deficiency

Questions and Answers

What was the primary discovery made by Dr. Henrik Dam regarding vitamin K?

It prevents infections.

It reduces cholesterol levels.

It is essential for vision.

It plays a role in blood coagulation. (correct)

What distinguishes vitamin K1 from vitamin K2?

K1 is more abundant in the body than K2.

K1 is found in plant sources while K2 is in animal products. (correct)

K1 is synthetic while K2 is natural.

K1 is more effective in absorption than K2.

Why were chicks used to quantify vitamin K content in foods?

They easily develop vitamin deficiencies. (correct)

They lack an immune system.

They are a common food source.

They have longer lifespans than other animals.

What percentage of total dietary vitamin K intake is constituted by vitamin K2?

10% Signup and view all the answers

Which types of vitamin K are considered synthetic?

K3, K4, and K5 Signup and view all the answers

What role did Edward A. Doisy play in the discovery of vitamin K?

He uncovered its structure and chemical nature. Signup and view all the answers

Why might vitamin K2 form a significant portion of the total vitamin K absorbed despite its lower intake percentage?

It has better absorption and longer biological half-life. Signup and view all the answers

In what year did Dr. Henrik Dam and Edward A. Doisy receive the Nobel Prize in Medicine?

1943 Signup and view all the answers

What is Vitamin K3 also known as?

Menadione Signup and view all the answers

Where is phylloquinone absorbed in the body?

Jejunum Signup and view all the answers

What enhances the absorption of Vitamin K?

Bile salts and pancreatic juice Signup and view all the answers

What is a primary function of Vitamin K in the body?

Carboxylation of proteins Signup and view all the answers

Which of the following tissues is known to store Vitamin K?

Adrenal glands Signup and view all the answers

What percentage of phylloquinone is typically recovered in urine after being injected?

20 percent Signup and view all the answers

What must fibrinogen be converted into for blood to clot?

Fibrin Signup and view all the answers

Which form of Vitamin K has the most potent gamma-carboxylation activity?

Vitamin K2 Signup and view all the answers

What is a potential consequence of Gas6 production interference?

Decreased clot formation Signup and view all the answers

What symptom is NOT typically associated with overt vitamin K deficiency?

Excessive sweating Signup and view all the answers

Why is vitamin K deficiency uncommon in healthy adults?

Adults have a fully functional vitamin K cycle Signup and view all the answers

Which group is at a greater risk for vitamin K deficiency?

Individuals with liver damage Signup and view all the answers

What is a reason why breastfeeding infants may be at risk for vitamin K deficiency?

Low liver storage of vitamin K in infants Signup and view all the answers

What is commonly administered to protect infants from vitamin K deficiency?

Vitamin K injections Signup and view all the answers

What is a limitation in confirming vitamin K deficiency?

Unavailability of screening tests Signup and view all the answers

Which vitamin K form is synthesized by bacteria in the gut?

Menaquinones Signup and view all the answers

What does an increase in under-carboxylated vitamin K-dependent proteins in the blood indicate?

Vitamin K deficiency Signup and view all the answers

Which protein is specifically mentioned as being secreted by osteoblasts in response to vitamin K deficiency?

Osteocalcin Signup and view all the answers

What alternative measure is used to assess vitamin K sufficiency besides the detection of under-carboxylated proteins?

Plasma levels of phylloquinone Signup and view all the answers

How is urinary Gla related to vitamin K status?

It decreases in vitamin K deficiency Signup and view all the answers

What is one reason under-carboxylated species of coagulation proteins are significant in diagnosing vitamin K deficiency?

Their levels correlate with vitamin K deficiency severity Signup and view all the answers

What initiates the intrinsic pathway of blood clotting?

Exposure to endothelial collagen Signup and view all the answers

What is the role of calcium in the coagulation process?

It mediates the binding of Gla proteins to phospholipid membranes Signup and view all the answers

What is the main difference between the intrinsic and extrinsic pathways of blood coagulation?

Intrinsic pathway is activated by internal trauma, whereas extrinsic is triggered by external trauma Signup and view all the answers

Which factor is activated first in the intrinsic pathway?

Factor XII Signup and view all the answers

What enzyme is produced from the conversion of prothrombin during the coagulation cascade?

Thrombin Signup and view all the answers

What characterizes the common pathway in blood clotting?

It leads to the formation of an insoluble clot Signup and view all the answers

What does the cross-linking of fibrin result in?

Creation of an insoluble clot Signup and view all the answers

Which vitamin is essential for the activation of certain coagulation factors in the intrinsic pathway?

Vitamin K Signup and view all the answers

Study Notes

History of Vitamin K

Discovered in 1929 by Dr. Henrik Dam while studying cholesterol and its related bleeding issues in chicks.
Named "Vitamin K" from the Germanic word "Koagulations vitamin" relating to its role in blood coagulation.
Edward A. Doisy furthered the research, uncovering Vitamin K's structure, leading to a Nobel Prize in Medicine in 1943 for both researchers.
Early quantification of Vitamin K in foods was done using a model of Vitamin K-deficient chicks.

Types of Vitamin K

Composed of fat-soluble 2-methyl-1,4-naphthoquinones, primarily categorized into K1 (Phylloquinone) and K2 (Menaquinone).
Vitamin K1 sourced from green leafy vegetables, algae, and vegetable oils.
Vitamin K2, primarily found in meat, fermented foods, and certain dairy products.
K2 is absorbed more efficiently and has a longer biological half-life than K1.
Synthetic forms include K3 (menadione, a provitamin), K4, and K5.

Absorption and Transport

Phylloquinone is absorbed in the jejunum through an energy-dependent mechanism; menaquinones via passive diffusion.
Bile salts and pancreatic juice enhance Vitamin K absorption.
Transport occurs through chylomicrons into the lymphatics and blood, with significant storage in the liver and extrahepatic tissues like lungs and kidneys.

Vitamin K Cycle

Functions as a cofactor for converting glutamate into gamma-carboxyglutamate, essential for calcium binding in proteins.
Predominantly in oxidized form in the body.
Vitamin K2 exhibits stronger gamma-carboxylation activity compared to other forms.

Excretion

Metabolized in the liver with about 20% of phylloquinone recovered in urine and 40-50% in feces.

Role in Blood Clotting

Essential for converting fibrinogen into fibrin, forming a clot during bleeding.
Activated through intrinsic (trauma within the vascular system) and extrinsic (external trauma) pathways, involving Vitamin K-dependent factors II, VII, IX, and X.
Calcium ions play a critical role in the binding of Gla proteins to phospholipid membranes for clotting.

Deficiency

Overt deficiency leads to impaired blood clotting, symptoms include bruising, nosebleeds, and serious internal bleeding in infants.
Rare in healthy adults due to dietary availability, bacterial synthesis in the gut, and conservation via the Vitamin K cycle.
At-risk groups: people on Vitamin K antagonists, individuals with liver damage, or fat malabsorption disorders.
Breastfed newborns are particularly vulnerable due to limited placental transfer and low breast milk content.

Assessment of Vitamin K Status

Conventional coagulation assays can detect overt deficiencies, while under-carboxylated Vitamin K-dependent proteins signify milder deficiencies.
Measurement of under-carboxylated osteocalcin (ucOC) helps assess bone Vitamin K status.
Indicators of sufficiency also include plasma phylloquinone levels and urinary Gla excretion, which decreases in Vitamin K deficiency.

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Description

This quiz explores the essential nutrient Vitamin K, focusing on its absorption, functions, and the effects of deficiency. Learn about the historical discovery of this fat-soluble vitamin and its critical role in health. Test your knowledge on Vitamin K's importance and impact on the body.