Embryology I Flashcards
Gestational/obstetric calendar vs. Ovulatory calendar
Gestational/obstetrical calendar includes 2 weeks prior to fertilization, while Ovulatory does not.
Acrosome reaction
Occurs approximately 7 hours post sex. Sperm enters corona radiata via hyaluronidase.
Zone reaction
Sperm penetrates the ZP by releasing acrosin, esterases, and neuramidases.
Cleavage overview
Occurs about 30 hours post sex.
Increase in cell number, but decrease in cell size,
Results in morula development on day 3.
Day 5
Day 6
Day 7
Day 5: Fluid pours in creating a blastocyst cavity. Creates early blastocyst.
Day 6: Implantation on the posterior uterus.
Day 7: Creation of a late blastocyst.
By Day 7, the ZP should be gone.
Summary of Week 1
Fertilization Cleavage Formation of the blastocyst ICM (embryoblast) created Implantation
Trophoblast
Give rise to placenta.
Releases EPF in first 10 days.
Gives rise to cytotrophoblast and syncytiotrophoblast.
Cytotrophoblast
Mitotically active stem cell layer. Replaces trophoblast cells.
Syncytiotrophoblast
Provides nutrients for the embryo.
Release hCG and alerts the body that it is pregnant.
Epiblast gives rise to:
Ectoderm
Amnion and amniotic cavity
Hypoblast gives rise to:
EE Endoderm –> EE Mesoderm, prechordal plate and umbilical vesicle.
EE Mesoderm
EE coelom
EE somatic mesoderm: lines trophoblast and covers amnion.
EE splanchnic mesoderm: lines umbilical vesicle.
Summary of Week 3
Gastrulation occurs.
CNS development
Heart development
Saccrococcygeal teratoma
Remnant of primitive streak.
Oralpharyngeal teratoma
Abn migration of germ cells.
Notochord
Mesoderm.
Provides longitudinal axis for embryo.
Provides the framework for the vertebral column.
Induces the formation of the neural plate and CNS.
Chordoma
Believed to be formed from remnants of notochord.
Allantois
Diversion from UV and made of endoderm.
Template for umbilical arteries and veins.
Becomes urachus.
Paraxial Mesoderm
Somites
- Myotome (muscle)
- Sclerotome (skeleton)
- Dermatome (dermis)
Intermediate Mesoderm
Urogenittal
-kidneys, gonads.
Lateral Plate Mesoderm
Somatic or Splanchnic.
-CT (blood, lymph, mesenteries, CV.)
Induction on the neural plate
Notochord release SHH and causes neural groove to dip into the mesoderm and pinch off the neaural tube. Two small remnants of neural crest cells remain.
Neural tube closure
Occurs at rostral and caudal NP.
Primary - brain to lumbar
Secondary - sacrum to coccyx.
Spina bifida is a result of:
Failure of the caudal NP to close.
Neural crest cells
Only sensory Ns. ex: Dorsal root ganglia Schwann cells Melanocytes Chromaffin cells Bones of the face
Spina bifida occulta
Benign (10% of population have it).
-Failure of spinal processes to close.
Meningocele
Dura mater creates cyst filled w/ CSF.
Absence of vertebral arches.
May or may not cause defects.
Meningomyelocele
SC exists in a cyst outside of the spine.
Patient will have sensory and motor defects.
Myelocele
SC is opened and exposed. Opening must be closed or patient is at a high risk for infection.
Failure of rostral neural pore to close causes:
Anencephaly: not compatible with life (top of head is open).
Encephalocele: growth on head. Can contain brain tissue.
Meninges develop from:
Meninx primitiva and is mesoderm origin (sclerotome)
Pachymeninx gives rise to:
Dura mater (mesoderm)
Leptomeninges gives rise to:
Arachnoid mater and pia mater (neural crest cells).
Mesenchyme
Embryonic CT.
Intramembranous ossification
Mesenchyme –> bones
ex: skull and facial bones
Endochondrial ossification
Mesenchyme –> cartilage –> bone
ex: everything else
Production of the vertebral column
From the scleratome.
Caudal dense and cephalic loose fuse to form a vertebra.
Intervertebral disk
Nucleus pulposis: from notochord.
Annulus fibrosis: Fibrous tissue from sclerotome.
Sternum
From somatic lateral plate mesoderm.
Ribs
From sclerotome.
Caudalization
Gain of function. Will look like section below.
Cephalization
Loss of function. Will look like section above.
Myotome gives rise to:
Epimere and hypomere.
Epimere - epaxial muscles (back)
Hypomere - hypaxial muscles (C, T, L, S myotomes)
Poland Syndroma
Hypomere cells do NOT migrate to chest.
Absence of Pect Major and Minor.
Missing 2-4 ribs.
Associated with syndactyly.
Prune Belly Syndrome
Partial or complete absence of of abdominal musculature.
Mostly in males.
Problems with testes to descend (crytorchidism)
Poor formation of UT and bladder.
