Topic: Embryology: Placenta and placental barrier
Question: Write short notes on,a.Formation and structure of umbilical cord. b.Anatomical basis of claw hand.
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a) Formation and structure of umbilical cord
– The umbilical cord forms during fetal development and connects the fetus to the placenta, allowing passage of oxygen and nutrients.
– Formed from the umbilical vessels that arise from the fetus:
– Two umbilical arteries – carry deoxygenated blood from fetal iliac arteries to the placenta.
– One umbilical vein – carries oxygenated blood back from placenta to the fetus. Enters the fetus at the umbilicus and connects to the hepatic portal system.
– These vessels are surrounded by gelatinous connective tissue called Wharton’s jelly, composed of myofibroblasts and mucopolysaccharide matrix. Protects vessels from compression and twisting.
– External covering is single layer of amniotic epithelium.
– Normally 32–60 cm long and 1–2 cm in diameter at birth.
– Cord inserts centrally into the placenta at the umbilical ring. Insertion into fetus is at umbilicus.
– Also contains remnant of yolk sac and allantois from embryonic development.
b) Anatomical basis of claw hand
– Claw hand deformity occurs due to paralysis of intrinsic hand muscles from lower motor neuron damage.
– Most commonly caused by ulnar nerve injury at the C8-T1 spinal cord levels or in the lower brachial plexus.
– Ulnar nerve supplies the ulnar 1.5 digits, as well as ulnar wrist flexors and intrinsic hand muscles.
– Injury causes paralysis of the lumbricals, palmar and dorsal interossei, 3rd and 4th lumbricals, hypothenar muscles, and ulnar wrist flexors.
– Unopposed action of extensor digitorum and extensor carpi radialis longus leads to hyperextension at MCP joints and flexion at IP joints.
– Gives the hand a ‘clawed’ appearance.
– Median nerve injury can contribute by paralysing the thenar muscles.
– Causes include trauma, compression, neuralgic amyotrophy, polio, neuropathy (e.g. leprosy), motor neuron diseases.
