DIMS Lectures Embryology PDF

Here is the complete pdf lecture of embryology

Embryology

Embryology is the branch of biology that studies the formation, growth, and development of the embryo from fertilization to birth.

Occurs in the testes within the seminiferous tubules.
Begins at puberty and continues throughout life.
Steps:
- Spermatogonia (2N) → Primary Spermatocyte (4N) → Secondary Spermatocyte (2N) → Spermatids (N) → Spermatozoa (N)
Clinical Relevance:
- Oligospermia (low sperm count) and azoospermia (absence of sperm) can cause male infertility.
- Klinefelter syndrome (XXY) results in defective spermatogenesis.

Occurs in the ovaries; begins before birth and completes at puberty.
Steps:
- Oogonia (2N) → Primary Oocyte (4N) → Arrests at Prophase I until puberty → Secondary Oocyte (2N) → Ovum (N) after fertilization
Clinical Relevance:
- Turner Syndrome (45, X0) results in ovarian dysgenesis and infertility.
- Polycystic Ovarian Syndrome (PCOS) leads to ovulatory dysfunction.

Occurs in the ampulla of the fallopian tube.
Sperm binds to the zona pellucida, triggering the acrosomal reaction.
Zygote formation (diploid 2N) marks the beginning of development.
Clinical Relevance:
- Ectopic pregnancy: Implantation occurs outside the uterus, most commonly in the fallopian tube.
- Failure of fertilization leads to infertility, managed via IVF (In-Vitro Fertilization).

Day 1-3: The zygote undergoes rapid mitotic divisions (cleavage) forming the morula.
Day 4-5: Morula develops into a blastocyst.
Day 6-7: Blastocyst implants in the endometrium.
Clinical Relevance:
- Implantation failure leads to early pregnancy loss.
- Hydatidiform mole: Abnormal trophoblastic proliferation leading to a non-viable pregnancy.

Formation of three germ layers:
- Ectoderm (skin, nervous system, eyes, ears)
- Mesoderm (muscles, bones, heart, kidneys, blood)
- Endoderm (lungs, liver, GI tract)
Clinical Relevance:
- Spina bifida: Failure of neural tube closure.
- Sirenomelia: Defective mesodermal development causing lower limb fusion.

Neural plate folds into the neural tube.
Forms brain and spinal cord.
Clinical Relevance:
- Anencephaly: Failure of cranial neuropore closure.
- Folic acid deficiency increases neural tube defects risk.

Heart begins beating by day 22.
Cardiac looping (Week 4) establishes heart chambers.
Clinical Relevance:
- Tetralogy of Fallot: Combination of pulmonary stenosis, VSD, right ventricular hypertrophy, and overriding aorta.
- Transposition of great arteries: Aorta and pulmonary artery are switched.

Week 4-8: Limb buds form.
HOX genes regulate limb growth.
Clinical Relevance:
- Phocomelia: Abnormal limb formation due to thalidomide exposure.
- Polydactyly: Extra fingers or toes.

Foregut, midgut, and hindgut differentiation.
Rotation of the intestines (Week 6-10).
Clinical Relevance:
- Omphalocele: Failure of midgut to return to abdominal cavity.
- Hirschsprung disease: Absence of ganglion cells in the colon.

Organs develop further in 2nd and 3rd trimesters.
Clinical Relevance:
- Prematurity (<37 weeks) increases risk of respiratory distress syndrome (RDS).
- Intrauterine Growth Restriction (IUGR) due to placental insufficiency.

Folic acid deficiency increases the risk of neural tube defects.
Ectopic pregnancy should be suspected in women with lower abdominal pain and positive pregnancy test but no intrauterine gestational sac.
Congenital heart diseases (e.g., Tetralogy of Fallot, Transposition of Great Arteries) require early diagnosis and intervention.
Omphalocele and gastroschisis are abdominal wall defects requiring surgical correction.
Hirschsprung disease presents with failure to pass meconium and requires surgical resection of the aganglionic segment.