[09.09a] Embryology and Fetal Development V2

Uterine endometrium

Where does the blastocyst implant?

Human chorionic gonadotropin (hCG)

Which hormone is used as a basis for pregnancy tests?

Heuser’s membrane/exocoelomic membrane

What is the membrane that lines the primary yolk sac?

True

T/F: The chorionic sac is used to evaluate the early pregnancy outcome development.

Exoembryonic cavity

Which does not refer to chorionic cavity: Gestational sac, Exoembryonic cavity, or Extraembryonic cavity?

True

T/F: The primitive streak marks the start of gastrulation

Association with the development of the urethra

Which of the following is NOT a function of the allantois: Association with the development of the urethra, Involved with early blood formation, Respiratory function, or Reservoir for urine?

False

T/F: The reproductive system is the first organ system to reach a functional state

Allantois

What structure eventually becomes the urachus?

Union of the sperm and egg in the ampulla of the fallopian tube

What process forms the embryo?

Morula

What is the solid ball of cells formed from mitotic divisions of the embryo?

Blastomere

What is each cell of the morula called?

Inner cell mass and trophoblast

What two structures does the blastocoel divide the embryo into?

Inner cell mass

Which of these will develop into the embryo?

Trophoblast

Which of these will develop into the placenta?

Embryonic pole

Which pole of the blastocyst attaches to the uterine endometrium?

Syncytiotrophoblast and cytotrophoblast

Into what two layers does the trophoblast differentiate?

Syncytiotrophoblast

Which layer of the trophoblast is a continuous multinucleated layer of protoplasm with no discernable cell boundaries?

Lactogen, estrogen, progesterone, and human chorionic gonadotropin (hCG)

What hormones does the syncytiotrophoblast secrete?

Cytotrophoblast

Which layer of the trophoblast consists of discrete cuboidal cells with cell boundaries?

Epiblast and hypoblast

The inner cell mass differentiates into what bilaminar embryonic disc?

Amniotic cavity

What cavity starts in the epiblast?

Primary yolk sac (exocoelomic cavity)

What structure forms when cells from the hypoblast proliferate and migrate, enclosing the blastocoel?

Heuser’s membrane (exocoelomic membrane)

What is the lining of the primary yolk sac called?

Chorionic cavity

What cavity is also known as the gestational sac or extraembryonic cavity?

Extraembryonic mesoderm

Cells from the epiblast form a layer of connective tissue called what?

Amniotic cavity, primary yolk sac, and chorionic cavity

What three cavities are present in the embryo during week 2?

Extraembryonic mesoderm, cytotrophoblast, syncytiotrophoblast

What layers form the chorionic membrane from inward to outward?

Secondary yolk sac

What structure forms when extraembryonic endodermal cells from the hypoblast migrate inside the primary yolk sac?

Site of origin of the primordial germ cells and transfer of nutrients to the embryo

What are the functions of the secondary yolk sac?

Epiblast and hypoblast

What two layers does the embryoblast form?

Primary yolk sac, amniotic cavity, chorionic cavity, and secondary yolk sac

What cavities are formed during week 2?

Ectoderm, mesoderm, and endoderm

What three germ layers are established during gastrulation?

Primitive streak

What structure must form before the three germ layers can form?

Gastrula

What is the embryo called once the primitive streak appears?

Notochord

What structure starts to develop in the gastrula?

Caudal to cranial

The primitive streak grows in which direction?

Primitive groove

What groove/canal does the primitive streak acquire?

Primitive node

What rounded area forms at the cephalic end of the primitive streak?

Cranial-caudal, medial-lateral, and left-right axes

What axes of the embryo does the primitive streak define?

Sacrococcygeal teratoma

What can result from the persistence of the primitive streak?

Mass seen at birth in the sacrococcygeal area of neonate, remnant of primitive streak, most common tumor in newborns (especially females), usually benign, requires surgical excision

What are the characteristics of sacrococcygeal teratoma?

Epiblast

Which layer gives rise to all three germ layers?

Prechordal plate

What rounded region is formed by proliferating endodermal cells at the cranial end of the embryonic disc?

Head organizer, induction of the forebrain, and primordium of oropharyngeal membrane

What is the importance of the prechordal plate?

Oropharyngeal and cloacal membranes

In what areas does the ectoderm and endoderm fuse?

Opening of the oral cavity

What does the oropharyngeal membrane become when it ruptures?

Opening of the anus

What does the cloacal membrane become when it ruptures?

Mesenchymal cells

What cells from the primitive node migrate to form the notochordal process?

Mesodermal area

In what area is the notochord found?

Nucleus pulposus of the intervertebral disc

What structure does the notochord persist as?

Induces the overlying ectoderm to thicken and form the neural plate, the primordium of the CNS

What is the most important function of the notochord?

Notochordal canal

What lumen/canal does the notochordal process acquire?

Thickening of the embryonic ectoderm overlying the notochord

What forms the neural plate?

Neural tube

What structure is the primordium of the central nervous system (CNS)?

Neurula

What is the embryo called once the neural tube has formed?

Morula, blastocyst, gastrula, and neurula

What are the four stages of embryonic development?

Small outpouching from the caudal wall of the secondary yolk sac

What is the allantois?

Respiratory function, reservoir for urine, involved with early blood formation, and association with the development of the urinary bladder

What are the functions of the allantois?

Urachus

What structure does the allantois become?

Median umbilical ligament

What does the urachus continue as?

Neural crest cells

What cells detach from the neural tube and migrate to different areas of the body?

Failure of neural crest cells to migrate and reach the hindgut

What causes Hirschsprung’s Disease?

Neural tube defects

What are among the most common congenital anomalies?

Spina bifida

What condition results from non-fusion of the vertebral arch?

Meningocoele

In which condition is the spinal cord still intact, but the meninges and cerebrospinal fluid project through the defect?

Meningomyelocele (Myelomeningocele)

In which condition do the meninges, cerebrospinal fluid, and spinal cord all project through the defect?

Anencephaly

What neural tube defect results in the brain failing to develop?

Paraxial, intermediate, and lateral plate mesoderm

What are the three components of mesoderm?

Somites/somitomeres

What cuboidal bodies does the paraxial mesoderm become?

Axial skeleton and its associated musculature

What do somites give rise to?

7th week of gestation

When does the heart start to beat?

Mesenchyme on each side of primitive streak migrate around prechordal plate

How is the cardiogenic area formed?

Gastrula and neurula

What are the two key developmental stages in the third week?

Primitive streak, three germ layers, and notochord

What three things does the gastrula give rise to?

Neural tube, somites, and cardiovascular system

What three things does the neurula give rise to?

Fertilization, division into a morula, blastocyst formation, and implantation

What processes occur during the first week of development?

Embryoblast forms the epiblast and the hypoblast together with the 4 cavities: primary yolk sac, amniotic cavity, chorionic cavity and the secondary yolk sac. Implantation of the embryo will also be complete and embedded in the endometrium

What processes occur during the second week of development?

Gastrula gives rise to the primitive streak, three germ layers, and the notochord; the neurula gives rise to the neural tube, somites, and the cardiovascular system

What key structures arise during the third week from the gastrula and neurula?

Irregular outline of chorionic sac

What indicates a non-viable pregnancy during an ultrasound evaluation of the chorionic sac?

Hypoblast

Which is not a layer of the chorionic membrane: Extraembryonic mesoderm, Cytotrophoblast, Syncytiotrophoblast, or Hypoblast?

False

T/F: After implantation, the morula differentiates to inner cell mass and trophoblast.

3rd week

During what week is the right-left axis evident?

Meningocoele

In which condition is the spinal cord still intact but the meninges and the cerebrospinal fluid will project through the defect?

Ectoderm

Is the nervous system derived from the ectoderm, endoderm, or mesoderm?

Endoderm

Is the epithelial lining of the respiratory system derived from the ectoderm, endoderm, or mesoderm?

Mesoderm

Are the circulatory and lymphatic systems derived from the ectoderm, endoderm, or mesoderm?

Ectoderm

Are sensory receptors in epidermis derived from the ectoderm, endoderm, or mesoderm?

Mesoderm

Is the notochord derived from the ectoderm, endoderm, or mesoderm?

Endoderm

Is the pancreas derived from the ectoderm, endoderm, or mesoderm?

Ectoderm

Are tooth enamel derived from the ectoderm, endoderm, or mesoderm?

Mesoderm

Is the lining of the body cavity derived from the ectoderm, endoderm, or mesoderm?

Endoderm

Is the thyroid and parathyroid glands derived from the ectoderm, endoderm, or mesoderm?

Ectoderm

Is the adrenal medulla derived from the ectoderm, endoderm, or mesoderm?

Mesoderm

Is the adrenal cortex derived from the ectoderm, endoderm, or mesoderm?

Endoderm

Is the thymus derived from the ectoderm, endoderm, or mesoderm?

Ectoderm

Is the epithelium of the pineal and pituitary glands derived from the ectoderm, endoderm, or mesoderm?

Mesoderm

Is the dermis of the skin derived from the ectoderm, endoderm, or mesoderm?

Endoderm

Is the lining of the urethra, urinary bladder, and reproductive system derived from the ectoderm, endoderm, or mesoderm?

Ectoderm

Is the epidermis of the skin derived from the ectoderm, endoderm, or mesoderm?