Okay kiddo, imagine that when a baby is growing inside their mommy's tummy, they are inside something called the amniotic sac. This sac is filled with something called amniotic fluid which helps protect the baby and keeps it healthy.
Now, inside the amniotic sac, the baby is connected to their mommy by something called the umbilical cord. The umbilical cord is kind of like a rope that connects the baby to their mommy so they can get food and oxygen to help them grow.
But the umbilical cord isn't just a rope, it's also a special kind of tissue that helps transport things between the baby and their mommy. This tissue is called the cord lining.
The cord lining has these tiny blood vessels called arteries and veins that help deliver food and oxygen to the baby and also take away waste products from the baby. So basically, the cord lining is like the baby's lifeline to their mommy until they are born and can breathe on their own.