Embryology

By the beginning of 4th month,cytotrophoblastic cells and some connective tissue cells disappear.the syncytium and endothelial wall of the blood vessels are then the only layers that separate the maternal and fetal circulation.

The structures representing all three components of embryonic disc is Tympanic membrane

Reference: Langman’s 13th; P-47

Reference: Langman’s 13th; P-43

Meckel's diverticulum is a remnant of Vitello intestinal duct

Rathke's pouch and anterior pituitary develop from stomatodaeum (surface ectoderm) 

Primary oocyte is produced during prenatal period.

Explanation-
Lesser omentum, Falciform ligament, Coronary ligament from ventral mesogastrium.

Reference: Langman’s 13th; P-47

Septum transversum gives rise to central tendon of the diaphragm & fibrous pericardium.

Thyroxine is not teratogenic. Thyroxine replacement is given during pregnancy if there is hypothyroidism.

45XO- Turner's syndrome
47 XXY- Klinefelter's syndrome
47 XX/XY+18- Edward's syndrome (Trisomy 18)
47 XX/XY+13- Patau's syndrome (Trisomy 13)

Down's syndrome:
Also known as Trisomy 21 is the most common numerical chromosomal abnormality.

Cause :
- Non disjunction (94%)- 47 XX/XY+21 (Trisomy 21)
- Mosaicism (2%)
- Transloation (4%)

Criteria of ovum at the time of ovulation:
• Ovum at the stage of secondary oocyte arrested at Metaphase of Meiosis-II 
• 120-150um in diameter
• Surrounded by cumulous oophorus/granulosa cell
• Completes 1st meiotic division 3 hours before ovulation
• Expulsion of 1st polar body just occurred
• Completes 2nd meiotic division after fertilization
• Ovulation process may last 12-48 hours
• Ovulation occurs after 36 hours of LH peak
• Inj. HCG causes ovulation after 38-40 hours

Normal site of Implantation- Anterior or posterior wall of body of uterus

Reference: Langman’s 13th; P-39

Mesoderm showing segmentation is - Paraxial

Explanation: The portal vein forms when an anastomotic network around the duodenum forms one vessel. This anastomotic network is from the veins of the gut,the vitelline veins.

Birth defect, congenital malformation, and congenital anomaly are synonymous terms used to describe structural, behavioral, functional, and metabolic
disorders present at birth.

Susceptibility to teratogens varies with the developmental stage at the time of exposure. The most sensitive period for inducing birth defects is the third to eighth weeks of gestation, the period of embryogenesis. 

Number of blastomeres in Morula – 16

Cheeks & Lateral portion of upper lip are developed from maxillary prominence.

Reference: Langman’s 13th; P-40

Pons & Cerebellum are formed from metencephalon

Human placenta is - Hemochoreal

** Vitamin-D resistant rickets: X-linked dominant
** Thalassaemia & Homocystinuria: Autosomal recessive

X linked Recessive Disorders

Blood:
 Hemophilia A & B
 Glucose-6-P dehydrogenase deficiency
 Chronic granulomatous disease

Musculoskeletal:
 Duchene muscular dystrophy

Immune:
 Agammaglobinemia

Metabolic:
 Nephrogenic diabetes insipidus

Nervous:
 Fragile X syndrome

CNS development does not require influence of notochord for development.

Only IgG can cross placenta

Fate of notochord -Nucleus pulposus of intervertebral disc

Explanation: Capacitation involves removing the glycoprotein coat and seminal plasma proteins from the head of the sperm, exposing the acrosome and allowing the acrosome reaction to occur. Capacitation occurs within the female genital tract, and without its occurrence, fertilization could not occur.

Explanation: also transverse mesocolon, sigmoid mesocolon.

The barriers of an oocyte are
1. First barrier is formed by cells of corona radiata
2. Second barrier is formed by zona pellucida made of glycoproteins, ZP1, ZP2, and ZP3.
3. Third barrier is formed by vitelline membrane of oocyte itself

Septum transversum gives rise to central tendon of the diaphragm & fibrous pericardium.