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58 Cards in this Set

  • Front
  • Back
How do the rapid mitotic divisions of the zygote differ from ordinary cell division?
Cells DO NOT grow in size between divisions
~3 days after fertilization, the zygote becomes what?
Ball of cells called MORULA
The morula enters the uterus and becomes what?
The blastocyst contains what two cellular masses?
Trophoblast (outer cell mass)
Embryoblast (inner cell mass)
What substance allows the trophoblast to become sticky and attach to the uterine epithelium
Following uterine invasion, the trophoblast differentiates into what two layers?
syncytiotrophoblast and cytotrophoblast
How does the syncytiotrophoblast cells proliferate?
Mitosis of cytotrophoblast, and addition of these cells to the syncytiotrophoblast (syncytiotrophoblast cells do not divide on their own)
Give a 5-step summary of the first week.
1. Ovulation
2. Fertilization
3. Cleavage, morula, blastocyst
4. Zona pellucida disappears
5. Trophoblast invades superficial epithelium
The embryoblast becomes differentiated into two distinct layers. Which day does this occur and what are the two layers?
8th day

Epiblast (columnar)
Hypoblast (cuboidal)
What does the bilaminar germ disc consist of? Which week of development is the embryo bilaminar.
Epiblast (columnar)
Hypoblast (cuboidal)

2nd week.
What is the protective membrane that begins forming on the 8th day (and will eventually surround the entire embryo)?
Right after the embryo becomes completely embedded in the uterine endometrium, what is the defect (in the endometrium) closed by?
Fibrin plug (epithelium will eventually close over the plug)
What are lacunae?
Spaces that appear in the syncytiotrophoblast
How is the uteroplacental circulation established?
syncytiotrophoblast erodes away lining of maternal sinusoids and glands, and maternal blood flows into and out of lacunae.
What do the extraembryonic somatic mesoderm and extraembryonic splanchnic mesoderm respectively surround
Amniotic sac and Yolk sac.
Around the 13th day, hypoblast cell proliferation surrounds what new cavity?
Secondary yolk sac.
Explain the initial formation of the prechordal plate.
Thickened hypoblast cells (become columnar)that are firmly attached to overlying epiblast.
What connects the embryo to the trophoblast
Connecting stalk
What will the connecting stalk become?
umbilIcal cord (let's say it together, umbilIIIIcal)
Give a 7-step summary of the 2nd week of development with regards to the extraembryonic regions?
1. Trophoblast differentiates (cytotrophoblast and syncytiotrophoblast)
2. Lacunae develop
3. syncytiotrophoblast erodes maternal sinusoids and endometrial gland
4. Primary chorionic villi form on external surface of chorionic sac
5. Implantation completed and defect closed
6. Amnion forms
7. Secondary yolk sac forms
What are the two main developments of the embryoblast during the 2nd week?
1. Differentiation to epiblast and hypoblast (bilaminar)
2. Prechordal plate develops
What is placenta previa?
Blastocyst implantation in lower segment of uterus. Will lead to severe bleeding during birth.
What is ectopic pregnancy and where do most occur?
Pregnancy outside the uterus occurring mostly in the uterine tube (which will eventually rupture and hemorrhage).
What is the main feature of the 3rd week?
What does gastrulation consist of?
1. Primitive streak formation
2. Notochord formation
3. Germ layers
Explain the movement of the epiblast cells through the primitive streak (what germ layers are created)
Ectoderm = epiblast that does not enter primitive groove

Mesoderm = between epiblast and hypoblast layers]

Endoderm = hypoblast layer
What are the 2 locations between the epiblast and hypoblast layers that mesodermal cells do NOT migrate?
1. Prechordal plate
2. Cloacal Membrane
What happens at the margins of the embryonic disc
intraembryonic and extraembryonic mesoderm become continuous.
The mesoderm that migrates cranially of the prechordal plate becomes what
Cardiogenic area
How is the notochord formed?
Cranial migration of the mesoderm from the primitive node
By day 16, what is the outpouching of the yolk sac?
What do the blood vessels of the allantois become?
umbilical arteries and veins
What is ectodermal neurulation?
Notochord induces overlying ectoderm to become neural plate, which will eventually fold and pinch off, yielding the neural tube (by the end of the 3rd week)
Towards the end of the 3rd week, what causes the primitive streak to shrink and eventually disintegrate?
Cranial pole development
What is sacrococcygeal teratoma?
A tumor that arises from remnants of the primitive streak.
What is caudal dysplasia?
Various syndromes that result from abnormal gastrulation in which migration of mesoderm is disturbed.
About when do the anterior and posterior neuropores of the neural tube close?
25-27th day
What two structures influence one another, eventually forming the lens and optic cup, respectively.
Lens placode and Optic vesicle (outpouch of diencephalon)
What does high levels of BMP-4 cause?
1. Ectoderm to form epidermis
2. mesoderm to form LPM and IM
What 3 secretions from notochord inhibit BMP-4? What fn do they have other than inhibiting BMP-4?
noggin, chordin, and follistatin

These also cause forebrain and midbrain development
What does BMP-4 inhibition result in?
ectodermal neuralization, thus causing ectoderm directly above notochord to become neural plate and eventually pinch off forming the neural tube.
What are WNT-3a and FGF?
Caudal neural plate influencers that form hindbrain and spinal cord.
What do low levels of BMP-4 influence?
Neural crest formation.
Ectodermal derivatives.
1. CNS
2. PNS
3. Sensory epithelium
4. Epidermis (hair, nails, glands)
5. Ant. pituitary gland
6. Enamel of teeth
7. Derivatives of neural crest cells
What gives rise to somites?
Paraxial mesoderm
What do somites give rise to?
1. Dermatome (dermis of skin)
2. Myotome (muscles)
3. Sclerotome (bone, cartilage)
The space between intraembryonic somatic and splanchnic mesoderm form what?
intraembryonic coelom

LPM --> intraembryonic somatic and splanchnic --> intraembryonic coelom
By 8 weeks, what does the intraembryonic coelom develop into?
1. pericardial cavity (heart)
2. pleural cavity (lungs)
3. peritoneal cavity (guts)
Mesodermal derivatives
1. CT, cartilage and bone (except head and neck)
2. striated, smooth, cardiac muscle
3. blood cells, heard, blood and lymph vessels
4. kidneys
5. gonads and ducts
6. cortex of adrenal glands
7. spleen
What germ layer contributes to embryo folding?
Endodermal derivatives
1. Epithelium of gut
2. lining of Resp. tract
3. tonsils, thyroid gland, parathyroids, thymus, liver, and pancreas
4. lining of bladder and urethra
5. lining of tympanic cavity and auditory tube
6. Epithelium and glands of guts
What is the period of maximal sensitivity to abnormal development (which weeks)?
Weeks 3-8
What is vasculogenesis
Vessels arising from blood islands
What is angiogenesis?
Vessels arising from existing vessels
Lateral Plate Mesoderm Derivatives
Intraembryonic somatic: body wall

Intraembryonic splanchnic: wall of gut
Paraxial mesoderm derivatives
somites [which will form dermatome (dermis), myotome (muscles), and sclerotome (CT, bone, and cartilage)]
Neural crest derivatives
1. CT and bones of face and skull
2. Odontoblasts (dentine)
3. Dermis in face and neck
4. Spinal ganglis
5. Adrenal medulla
6. Schwann and glial cells
7. meninges (pia and arachnoid)
8. melanocytes
Intermediate mesoderm derivatives
Gonads and kidneys