The Embryo: Early Development Flashcards
(32 cards)
In males, what cells stay dormant until puberty?
Primordial germ cells (PGCs)
What changes occur in spermiogenesis?
Formation of acrosome
Condensation of nucleus
Formation of neck, middle piece and tail
Shedding of cytoplasm
Events that take place in 4th week and 5th month of oogenesis?
4th week - PGCs arrive and differentiate into oogonia
5th month - all oocytes are formed (meiosis I) and arrested in prophase of meiosis I until puberty
What occurs after puberty in oogenesis?
Each monthly cycle, primary oocyte completes meiosis I to form secondary oocyte and polar body
Secondary oocyte enters meiosis II, 3 hours after ovulation but arrests at metaphase of meiosis II
Only if fertilized will it complete meiosis II to form a mature oocyte and a second polar body
If no fertilization, cell degenerates after 24 hours
What and where (oocyte penetration)
Where: Ampulla of uterine tube
Determination of sex
Initiation of cleavage
When do cleavage form and what is important about morula?
Cleavage: 30 hours after fertilization
Morula: divided into inner cell mass (tissues of embryo) and outer cell mass (trophoblase [placenta formation])
Develops 72 hours from fertilization
What happens after morula enters uterus?
Fluid accumulates and form blastocyst
How are inner/outer cell mass and blastocyst related?
- outer cell mass is trophoblast - forms placenta
- Innter cell mass is embryoblast - forms embryo
- At the end of week 1, trophoblast differentiate into cytotrophoblast and syntiotrophoblast
- Implantation begins
What is the progestational/secretory phase?
phase in menstrual cycle where implantation of blastocyst occurs
What are the important factors in implantation?
Layer of endometrium: functional layer (compact and spongy)
Normal site of implantation: anterior or posterior wall of uterus
Zone pellucida must degenerate for implantation to occur
Embryonic pole implants first
What are the clinical signs for abnormal implantation/ectopic pregnancy?
Abnormal uterine bleeding
Sudden abdominal pain with missed period
Partial Mole vs Complete Mole
Partial mole:
one oocyte fertilized by 2 sperm cells
Complete mole:
enucleated ovum fertilized by normal sperm cell
Moles produce high levels of hCG
Which germ layers are partially formed on 8th day of development?
Partial Endoderm (hypoblast) Partial Ectoderm (epiblast)
Importance of hCG?
Produced by syncytiotrophopblast
stimulates progestorone by corpus luteum
Causes endometrium to grow and proliferate
Too low: spontaneous abortion or ectopic pregnancy
Too high: multiple pregnancies, mole pregnancy
What occurs in week 3 and week 4?
Week 3: Gastrulation and formation of 3 germ layers
Week 4: Neurulation
What is gastrulation?
Early development of nervous and cardiovascular system
Appearance of primitive streak
Forms endoderm, mesoderm, ectoderm
These cells will give rise to all tissues and organs in embryo
Importance of prechordal plate?
Cranial end of embryonic disc
Establishes bilateral symmetry
Induces forebrain development
Becomes oropharyngeal membrane which gives rise to opening of oral cavity (mouth)
Importance of notochord?
Days 16-18
Future site of vertebral column
Induces formation of neural plate - primordium of CNS
Remnants of notochord in adults are nucleus pulposus
How is notochord formed?
Prenotochordal cells migrate through primitive streak
Imbed in endoderm to form plate
What occurs during neuralation?
week 4
neural plate to neural groove to neural tube
Caudal dysgenesis / sirenomelia
Think problems with caudal region (lower limbs)
Insufficient mesoderm (contributes to formation of lower limbs)
Causes fusion of limb buds
Holoprosencephaly
High doses of alcohol kill anterior midline of the germ disc
Forebrain is small, fails to develop 2 hemispheres
eyes are closer together
Neural tube defects
At cranial region - anencephaly
At lumbosacral region - spina bifida cystica
Can be prevented by taking folic acid
sclerotome, myotome, dermatome (somite differentiation)
Scleratome - forms cartilage and bone component
Myotome - segemental muscle component
dermatome - segmental skin component
