Anatomy Unit: Umbilical Cord & Twins

Umbilical Cord Development and Structure

• Connects fetus to placenta, approximately 50-60 cm in length and 1 cm in diameter.
• Twisted shape due to the left umbilical vein being shorter than the arteries; features false knots.
• Amniotic membrane covers both surfaces, with central attachment to the placenta.
• Composed of two umbilical arteries (non-oxygenated blood) and one left umbilical vein (oxygenated blood).
• Additional structures: Wharton's jelly (gelatinous substance), remnant of vitello intestinal duct (disappears by the 3rd month), and definitive yolk sac (disappears by the 5th month).

Umbilical Cord Anomalies

• Variants in number: possible to have double or triple cords.
• Length anomalies: very short or very long cords can lead to complications.
• Types of knots: false knots have no clinical significance, while true knots can tighten and potentially cause fetal death.
• Attachment issues: marginal (away from center), velamentous (attached to amnion).
• Structural anomalies may include absent artery due to agenesis or degeneration, associated with cardiovascular abnormalities (15-20% incidence).

Definition and Incidence of Twins

• Twins defined as delivery of more than one fetus, occurring in 1 in every 85 pregnancies.
• Incidence for triplets and quadriplets is 1 in every 90 pregnancies.
• Causes include hereditary factors and medical interventions like gonadotrophins or in vitro fertilization.

Types of Twins

• Identical twins (monozygotic): arise from one fertilized oocyte, occur in 30% of twins, genetically identical.
• Non-identical twins (dizygotic): result from fertilization of two oocytes by two sperms, making up 70% of twins, can be of the same or different sex.

Monozygotic Twins Detailed

• Separation in the 2-cell stage results in two placentas, chorions, and amnions.
• Separation in the inner cell mass produces one placenta, one chorion, but two amnions.
• Bi-laminar disc division yields equal or unequal embryos, leading to one placenta and one chorion with one or two amnions.

Conjoined Monozygotic Twins

• Result from incomplete division of the embryonic disc.
• Types include thoracopagus (most common, united at the thoracic region), craniopagus (united at the head), and pygopagus or ventral body wall joins.

Case Scenario Quiz

• Queries about placental components of dizygotic twins:
  • Correct answer is (D) Two placentas, two amniotic sacs, and two chorions.

This quiz explores key concepts related to the anatomy of the umbilical cord and the characteristics of twins. Participants will learn about the development, structure, and anomalies of the umbilical cord, as well as the definitions and differences between types of twins. Test your understanding of this fascinating subject matter in human anatomy.