SN4
SHORT NOTE
5M
★ High-yield
Describe the development, structure and contents of the umbilical cord.
Definition
The umbilical cord is the connection between the fetus and the placenta, formed by the fusion of the connecting stalk and the vitelline duct, covered by amnion.
| Feature | Detail |
|---|---|
| Length | About 50–55 cm |
| Diameter | 1–2 cm |
| Covering | Amnion — no skin |
| Ground substance | Wharton jelly — mucoid connective tissue that prevents kinking and compression |
| Vessels | Two arteries and one vein |
| Spiral | Usually twisted to the left, about 40 turns |
The Vessels
| Vessel | Number | Carries | Fate after birth |
|---|---|---|---|
| Umbilical arteries | Two | Deoxygenated blood from fetus to placenta | Medial umbilical ligaments (the proximal parts remain as the superior vesical arteries) |
| Umbilical vein | One (the right disappears) | Oxygenated blood from placenta to fetus | Ligamentum teres in the free margin of the falciform ligament |
Contents in Early Development
- Vitelline (omphalomesenteric) duct and vessels — normally obliterated
- Allantois — becomes the urachus, then the median umbilical ligament
- Physiological umbilical herniation — the midgut loop occupies the cord from the 6th to the 10th week, because the abdominal cavity is too small, and then returns
Applied Aspects
- Single umbilical artery — in about 1% of cords; associated with renal, cardiac and chromosomal anomalies in up to a quarter, so the baby must be examined carefully
- Cord prolapse — the cord descends ahead of the presenting part and is compressed; an obstetric emergency requiring immediate delivery
- Nuchal cord — the cord round the neck in about a quarter of deliveries; usually harmless
- True knots occur in about 1%; false knots are merely vascular loops and are of no significance
- Cord blood is used for blood gases at delivery, and is banked as a source of haemopoietic stem cells
- Umbilical vein catheterisation in the newborn gives rapid vascular access in resuscitation, since the vein remains patent for several days
- Delayed cord clamping by 1 to 3 minutes transfers additional blood to the infant and improves iron stores — of real value where anaemia is prevalent
Remnants at the Umbilicus
| Structure | Remnant of | Anomaly if it persists |
|---|---|---|
| Ligamentum teres | Umbilical vein | Recanalises in portal hypertension → caput medusae |
| Medial umbilical ligaments | Umbilical arteries | — |
| Median umbilical ligament | Urachus (allantois) | Urachal fistula, sinus or cyst |
| (Obliterated) vitelline duct | Yolk sac stalk | MECKEL diverticulum, umbilical fistula, sinus, or a fibrous band causing volvulus |
All questions in General Embryology
- Q1Describe gametogenesis. Compare spermatogenesis with oogenesis and add a note on the significance of meiosis. ★
- Q2Describe fertilisation, cleavage and implantation. Add a note on the decidua and ectopic pregnancy. ★
- Q3Describe the events of the second and third weeks of development. Explain gastrulation, the notochord and neurulation. ★
- Q4Describe the derivatives of the three germ layers. Explain the folding of the embryo and add a note on the fetal membranes. ★
- Q5Describe the development, structure and functions of the placenta. Add a note on amniotic fluid. ★
- SN1Define teratogen. Describe the critical periods of development and give important teratogens with their effects. ★
- SN2Describe the types of twinning and their fetal membranes. Add a note on the complications. ★
- SN3Describe the neural tube defects with their causes, diagnosis and prevention. ★
- SN4Describe the development, structure and contents of the umbilical cord. ★
- SN5Describe the chromosomal abnormalities with their mechanisms and clinical features. ★
- SN6Describe the amnion and amniotic fluid with their functions and disorders of volume. ★
- SN7Describe the periods of prenatal development with their milestones. Add a note on the estimation of gestational age.