Early Development and Disorders

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Testis development:
• Sry gene on Y chromosome.
• Testosterone (Leydig cells).
• MIF (Sertoli cells).

Meiosis I:
• Synapsis; crossing over; disjunction.

Meiosis II:
• No synapsis or crossing over.
• Disjunction with centromere splitting.

Spermatogenesis:
• Type A spermatogonia form Type B spermatogonia.
• Type B spermatogonia form primary spermatocytes after meiosis I.
• Primary spermatocytes form secondary spermatocytes.
• Secondary spermatocytes form 2 spermatids.
• Spermatids form sperm after spermiogenesis.

Oogenesis:
• Primordial germ cells form oogonia.
• Oogonia form primary oocytes after meiosis I.
• Primary oocytes arrested in prophase of meiosis I until puberty.
• Primary oocytes become secondary oocytes at puberty.
• Secondary oocytes arrested in metaphase of meiosis II and ovulated.
• Secondary oocyte forms mature oocyte and polar body after fertilization.

Ectopic tubal pregnancy:
• Blastocyst implantation in ampulla.
• Risk factors: endometriosis, PID, tubular pelvic surgery, diethylstilbestrol (DES) exposure.
• Uterine bleeding; abdominal pain; delayed menses; positive hCG test.

hCG:
• Urine pregnancy test.
• Low: ectopic pregnancy or spontaneous abortion.
• High: multiple pregnancy; hydatidiform mole; gestational trophoblastic neoplasia.

Sacrococcygeal termaoma:
• Arises from remnants of primitive streak.

Chordoma:
• Arises from remnants of notochord.

Caudal dysplasia (sirenomelia):
• Abnormal gastrulation; disturbed migration of mesoderm.
• Causes: VATER (vertebral defects, anal atresia, tracheoesophageal fistula, renal defects.)
• Also causes: VACTERL (vertebral defects, anal atresia, tracheoesophageal fistula, renal defects, upper limb defects.)

Additional Readings:

Basic Embryology

1. Early Development and Disorders
2. Differentiation and Anatomy of a Blastocyst

Related Topics

1. Genetic and Developmental Disorders

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Page accessed on: July 29, 2010, 10:59 am.

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