How Does a Cow Turn Blood Into Milk?
Every litre of milk starts with about 400 litres of blood flowing through the udder. But milk isn't strained out of blood. It's built from scratch. Inside the udder, blood flows past clusters of tiny sacs. The cells lining them pull out glucose, amino acids and fats, and build what blood never held: casein and butterfat, which turn milk white. The cleverest ingredient is a sugar, lactose. Water follows lactose, so the more sugar the cells make, the more milk flows. Then the hormone oxytocin squeezes the sacs, and the milk lets down.
A cow doesn't filter her blood into milk. She rewrites it.
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Transcript
Every litre of milk starts as about four hundred litres of blood. Yet milk isn't strained out of blood. It's built from scratch. Inside the udder, blood flows past clusters of tiny sacs, whose lining cells pull out glucose, amino acids and fats. From them, they build what blood never held: casein and butterfat, which turn milk white.
But the cleverest ingredient is a sugar: lactose. Water always follows lactose, so the more sugar her cells make, the more milk flows. Then the hormone oxytocin squeezes every sac, and the milk lets down. So a cow doesn't filter her blood into milk. She rewrites it.
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