Umbilical cord: what is it, what is it for, what does it contain?

By Cristiano Antonino On Dec 31, 2022

The umbilical cord, also called the umbilical cord, is an anatomical formation that connects the foetus to the placenta

It is a deciduous, i.e. temporary, conduit that contains the blood vessels connecting the placenta and the fetus, allowing the latter to survive.

In English, the umbilical cord is called ‘navel string’, ‘birth cord’ or ‘funiculus umbilicalis’.

Anatomical characteristics of the umbilical cord

In the final stages of pregnancy, the umbilical cord is approximately 50 to 60 cm long and 2 cm wide and has about fifteen swirls around its long axis.

It is pearly in colour, ‘twisted’ in appearance, smooth to the touch, shiny, semi-rigid, flexible and very strong, being able to bear more than 5 kg of weight.

Its surface reveals the umbilical blood vessels inside.

Generally, it is inserted in the centre of the placenta, but sometimes it is eccentric, or it is inserted on the margin, configuring a situation known as a racket.

It is also possible for it to insert on the ovular membranes, running a short distance over these before reaching the placenta (velamentous insertion).

The umbilical cord begins to form in the fifth week of gestation, functionally replacing the yolk sac, which ensured nutritional supplies in the early stages of the embryo’s development before the formation of the cord.

What does the umbilical cord contain?

The umbilical cord contains the three umbilical blood vessels: one umbilical vein and two umbilical arteries (clearly visible in the photo at the top of this article).

The three umbilical vessels are immersed in a gelatinous substance called Wharton’s jelly, consisting of mature mucous connective tissue, which is irregularly distributed and can create concretions called false knots, as they can give the impression of a knot.

These knots have no pathophysiological role.

Sometimes true knots also form (about 1% of births), which are rarely fatal because Wharton’s jelly usually prevents total occlusion of the vessels.

What is the umbilical cord for?

The umbilical cord connects the placenta with the foetus, allowing the foetus to survive by enabling the transfer of gases and other substances between the mother and foetus, without there being a direct exchange between the blood of the two organisms: the so-called ‘placental barrier’ thus prevents the passage of many harmful substances present in the blood of the future mother, although some can still cross it and harm the foetus, which is why a pregnant woman cannot take drugs, alcohol and other substances lightly.

The passage of gases and substances in the blood passes between the placenta and the foetus through three blood vessels:

the umbilical vein carries oxygenated and nutrient-rich blood from the placenta to the foetus;
the two umbilical arteries carry catabolites from the foetus to the placenta.

We remind the reader that in the systemic circulation, on the contrary, the veins carry non-oxygenated blood and the arteries oxygenated blood.

The three blood vessels, via the umbilical cord, enter the abdomen of the foetus

Inside the abdomen:

the umbilical vein continues to the transverse fissure of the liver, where it divides into two. One of these branches joins the hepatic portal vein (which connects to its left branch), which carries blood from the liver; the second branch of the umbilical vein (known as the ductus venosus) bypasses the liver and flows into the inferior vena cava, which carries blood to the heart;
the two umbilical arteries branch off from the internal iliac arteries and pass either side of the urinary bladder into the umbilical cord, completing the circuit back to the placenta.

To simplify:

the umbilical vein carries arterial and oxygenated blood to the heart;
the umbilical arteries surround the bladder and transport venous and non-oxygenated blood to the outside.

After birth, inside the baby, the umbilical vein and the ductus venosus close and degenerate into fibrous remnants known as the round liver ligament and the venous ligament, respectively.

Part of each umbilical artery closes (degenerating into what are known as the medial umbilical ligaments), while the remaining sections are retained as part of the circulatory system.

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What is the placenta?

The placenta is a temporary vascular organ typical of the female reproductive system; located in the uterus, it consists of tissue originating from the embryo on one side and tissue originating from the mother on the other.

The placenta connects the circulatory system of the conceived and the pregnant woman and acts as a ‘barrier’ (placental barrier) separating the amniotic environment of the foetus from the environment of the uterine cavity.

It is also an endocrine organ in that it produces hormones and releases them into the mother’s circulatory stream, such as human chorionic gonadotropin.

The placenta is destined for elimination with childbirth.

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