Embryology: Fertilization, Implantation, Fetal and Placental development Flashcards
(27 cards)
Define gametogenesis.
Formation and development of gametes
Define spermatogenesis.
Process by which spermatogonia (diploid germ cells) is transformed into mature sperm or spermatozoa (haploid cells) in males
Define oogenesis.
Process by which oogonia (diploid germ cell) is transformed into mature oocytes (eggs) in females
Where does spermatogenesis occur and what are the 3 major stages of spermatogenesis?
Seminiferous tubules
- Mitotic proliferation
- Meiosis
- Packaging
What changes do spermatids undergo to form spermatozoa?
Cytoplasm reduction, Nuclear Condensation, Flagellum formation, Acrosome Formation
Where do spermatozoa mature?
Epididymis
Briefly describe the process of oogenesis.
Starts in fetal life; ~6–7 million oogonia by 5 months.
Oogonia → Primary oocytes (arrest in Meiosis I, Prophase I).
Primary oocyte + epithelial cells = Primordial follicle.
After puberty: 1 follicle matures each cycle.
Before ovulation: Meiosis I completes → Secondary oocyte.
Meiosis II begins, arrests at Metaphase II.
If fertilized (within 12–36 hrs): Meiosis II completes → Ovum.
What is fertilization?
Fusion of male and female gametes. Occurs in the ampullary region of the uterine tubes.
Define capacitation and acrosome reaction.
Capacitation: removal of glycoprotein coat and seminal plasma proteins from spermatozoon head
Acrosome reaction: release of enzymes to penetrate zona pellucida including acrosin and trypsin substances
What are the 3 phases of fertilization?
a) Penetration of corona radiata
b) Penetration of zona pellucida
c) Fusion of oocyte and sperm cell membranes
What are the 3 stages of prenatal development?
STAGE 1: GERMINAL STAGE(WEEK O-2)
Starts at the time of conception
Zygote begins to divide in order to implant onto the uterine wall
STAGE 2: EMBRYONIC(WEEK 2-8)
Structures and organs like neural tube, head, eyes, mouth and limbs form
STAGE 3: FETAL(WEEK 9-BIRTH)
Fetal growth
Organ systems function
What happens during cleavage?
Begins post-fertilization; 1-cell zygote divides by mitosis.
Resulting cells = blastomeres, enclosed in zona pellucida.
Repeated division forms a morula (solid ball).
Fluid buildup turns morula into blastocyst (early → late stages).
What happens during implantation?
Occurs 6–7 days after fertilization.
Trophoblast differentiates into:
Cytotrophoblast (inner)
Syncytiotrophoblast (outer)
Mention the 3 phases of implantation.
- Apposition – Initial contact with uterus
- Adhesion – Stronger attachment
- Invasion – Trophoblast penetrates uterine wall
What is an ectopic pregnancy?
Fertilized egg implants and grows outside the main cavity of the uterus
What happens in week 2 (week of 2s)?
2 Gem layers-epiblast and hypoblast
2 cavities-aminiotic cavity and yolk sack
2 placental layers-syncytiotroblast and cytotrophoblast
2 extraembryonic mesoderm layers-splanchnopleuric and somatopleuric
What happens during week 3 (week of 3s)?
Gastrulation – formation of 3 germ layers:
Ectoderm
Mesoderm
Endoderm
Development of 3 embryonic cavities:
Amniotic cavity
Yolk sac
Chorionic cavity
Formation of 3 placental villi layers:
Syncytiotrophoblast
Cytotrophoblast
Chorionic mesoderm
What are the derivatives of the ectoderm?
*Neurulation- neural tube forerunner of brain and spinal cord
Mammary glands
Sensory epithelia of eyes, ears and nose
Hair
Nails
Pituitary gland
Teeth enamel
Epidermis
Name and describe 2 neural tube defects?
Anencephaly
Description: Brain end of neural tube fails to close.
Result: Missing brain/skull; not compatible with life.
Spina Bifida
Description: Spinal tube fails to close.
Result: Varies by type (mild to severe):
Occulta: Hidden, usually no symptoms.
Meningocele: Meninges protrude, minor effects.
Myelomeningocele: Spinal cord and meninges protrude, major disability.
Encephalocele
Description: Brain tissue protrudes through skull.
Result: Can cause brain damage or delay.
Craniorachischisis
Description: Entire neural tube remains open.
Result: Fatal.
What are the derivatives of the mesoderm?
Connective tissue
Cartilage
Bones
Ovaries
Testes
Striated and smooth muscles
Blood and lymphatic system
Genital ducts
Spleen
What are the derivatives of the endoderm?
Parathyroid and thyroid gland
Tonsil parenchyma
Thymus
Liver
Pancreas
Epithelial lining of; GI tube, Resp tract, Middle ear
What are the functions of the placenta?
Gas Exchange: Oxygen and carbon dioxide between mother and fetus.
Nutrient & Electrolyte Transfer: Supplies essential substances to fetus.
Immunity: Transfers maternal IgG antibodies for passive immunity.
Protection: Acts as a partial barrier to some diseases and harmful substances.
Hormone Production:
Progesterone: Maintains pregnancy.
Estrogen (estriol): Supports uterine and mammary development.
hCG: Sustains the corpus luteum.
Somatomammotropin: Prepares breasts for lactation.
Define placenta abruptio.
Placenta detaches from the uterus before delivery
What would have developed at 12 weeks gestation?
- Foetus develops recognizable form
- Nails and earlobes are formed
- Eyes almost fully developed
- Foetal heart rate can be heard at 10 weeks with a doppler ultrasound machine
- Most organs and tissues are developed
