AssessmentsRole of Vitamin K in coagulation
Role of Vitamin K in coagulation
USMLE® Step 1 style questions USMLE
USMLE® Step 2 style questions USMLE
A previously healthy, breast-fed, 4-week-old girl presents to the emergency department with blood in her diaper and difficulty feeding. She was born full-term to a healthy gravida 2, para 1 24 year-old-woman who received standard prenatal care. Physical exam shows a lethargic infant with widespread bruising. Her muscle tone is decreased on the right. Her vital signs are normal. The parents decided to take a natural approach and have a home birth. They refused routine injections. A complete blood count indicates normocytic anemia. Other studies are pending. The patient's condition is most likely due to which of the following?
Contributors:Evan Debevec-McKenney, Marisa Pedron, Jake Ryan, Ursula Florjanczyk, MScBMC, Sean Watts, MD
Without vitamin K, our bodies would be unable to control clot formation.
Imagine being unable to form blood clots effectively--that would mean that we would lose all of our blood volume from something as simple as a pinprick!
To prevent this extreme scenario - vitamin K must be ingested, metabolized, and utilized to create mature coagulation factors.
Now, to understand the regulation of clot formation, we first need to talk briefly about hemostasis--hemo referring to blood, and stasis meaning to halt or stop.
Hemostasis is divided into two phases: primary and secondary hemostasis.
Primary hemostasis involves the formation of a platelet plug around the site of an injured blood vessel, and secondary hemostasis reinforces the platelet plug with the creation of protein mesh called fibrin.
To get to fibrin, a set of coagulation factors, each of which are enzymes, need to be activated.
These enzymes are activated via a process called proteolysis- which is where a portion of the protein is clipped off.
In total, there are twelve coagulation factors numbered factors I-XIII, there’s no factor VI.
Most of these factors are produced by liver cells, and it turns out that producing coagulation factors II, VII, IX, and X requires an enzyme that uses vitamin K.
Vitamin K is found in abundance in green leafy foods—things like spinach, kale, and chard which all have high concentrations of vitamin K.
It’s a fat-soluble vitamin, along with vitamins A, D, and E, meaning that it can be stored in fat cells instead of being excreted by the kidneys.
Vitamin K is also synthesized by bacteria in our gastrointestinal tract as a byproduct of their metabolism, which further contributes to overall intake.
Now, when vitamin K is mobilized from fat cells or the digestive tract to the liver, it’s in its dietary form and it’s called vitamin K quinone.
An enzyme, called quinone reductase, takes electrons from NADPH, and donates them to vitamin K quinone, converting it into the reduced form which is called vitamin K hydroquinone.
Then, vitamin K hydroquinone acts as a cofactor by donating its electrons to an enzyme called gamma glutamyl carboxylase, which converts the non-functional forms of coagulation factors II, VII, IX, and X into their functional forms.
Gamma glutamyl carboxylase adds a carboxyl group, a chemical group made up of one carbon, two hydrogens, and one oxygen, onto the end of glutamic acid residues on the proteins.
- "Medical Physiology" Elsevier (2016)
- "Physiology" Elsevier (2017)
- "Human Anatomy & Physiology" Pearson (2018)
- "Principles of Anatomy and Physiology" Wiley (2014)
- "The role of vitamins in hemostasis" Thromb Diath Haemorrh (1975)
- "Vitamin K--dependent clotting factors" Semin Thromb Hemost (1977)