Introduction to Embryology Questions
and Answers.
Gestational age - Answer age of embryo or fetus from the time point of fertilization
days/weeks after conception
Postmenstrual age - Answer first day of last menstrual period-> used in obstetrics but not in
this embryology course
Gametogenesis - Answer formation of specialized generative cells (gametes) from gamete
precursor cells (diploid with 23 pairs of chromosomes)
Spermatogonia and oogonia undergo meiosis-> result in haploid gametes with 23 chromosomes
(HALVED)
Where does female gametogenesis take place? Result in? - Answer Ovaries (oogenesis)
Formation of oocytes
Where does male gametogenesis take place? Result in? - Answer Testes (spermatogenesis)
Spermatozoa (sperm)
Fertilization - Answer -oocyte released from ovary
-oocyte enter uterine tube
-sperm deposited in vagina move through uterus into uterine tube
-happens in uterine tube
-sperm fuse with oocyte = diploid zygote
Conceptus - Answer all derivates of zygote regardless of its developmental stage
Ovulation - Answer oocyte released from ovary
Cleavage - Answer Starts about 24 hours later fertilization
1. zygote divides by mitosis into two cells, which continue to divide
solid ball of cells = morula
2. At 16 cell stage, cells of the morula differentiate into two groups: embryoblast and
trophoblast
, 3. At 32 cell stage, fluid enters the space between cells, resulting in formation of a blastocystic
cavity = blastocyst
-embryoblast is a condensed cell mass located at one pole of blastocyst and trophoblast is a
single cell layer forming the wall of the blastocyst
Morula - Answer In cleavage, a solid ball of cells
Inner cell mass (Embryoblast) - Answer gives rise to embryo proper and its associated
extraembryonic membranes
Outer cell layer (trophoblast) - Answer forms the placenta and its associated extra embryonic
membranes
Gastrulation
(Week 3) - Answer -cells that form the embryo blast proliferate and change their position to
each other
-disk-shaped embryo with 3 distinctive layers (germ layers):
1. endoderm
2. mesoderm
3. ectoderm
What 3 major axes have been established by the end of gastrulation? - Answer 1. dorsal-
ventral
2. cranial-caudal
3. medial-lateral
Neurulation
(Weeks 3 & 4) - Answer early central nervous system is developed
parts of ectoderm specialize into neuroectoderm to fold to build the neural tube -> later forms
brain and spinal cord
Body Plan Formation/ Embryonic Folding
(Week 4) - Answer -2-D disk-like embryo folds to a cylindric shape
-cranial and caudal regions and lateral parts move ventrally -> look like adult
-several spaces and cavities formed (gut tube and abdominal cavity)
Organogenesis
and Answers.
Gestational age - Answer age of embryo or fetus from the time point of fertilization
days/weeks after conception
Postmenstrual age - Answer first day of last menstrual period-> used in obstetrics but not in
this embryology course
Gametogenesis - Answer formation of specialized generative cells (gametes) from gamete
precursor cells (diploid with 23 pairs of chromosomes)
Spermatogonia and oogonia undergo meiosis-> result in haploid gametes with 23 chromosomes
(HALVED)
Where does female gametogenesis take place? Result in? - Answer Ovaries (oogenesis)
Formation of oocytes
Where does male gametogenesis take place? Result in? - Answer Testes (spermatogenesis)
Spermatozoa (sperm)
Fertilization - Answer -oocyte released from ovary
-oocyte enter uterine tube
-sperm deposited in vagina move through uterus into uterine tube
-happens in uterine tube
-sperm fuse with oocyte = diploid zygote
Conceptus - Answer all derivates of zygote regardless of its developmental stage
Ovulation - Answer oocyte released from ovary
Cleavage - Answer Starts about 24 hours later fertilization
1. zygote divides by mitosis into two cells, which continue to divide
solid ball of cells = morula
2. At 16 cell stage, cells of the morula differentiate into two groups: embryoblast and
trophoblast
, 3. At 32 cell stage, fluid enters the space between cells, resulting in formation of a blastocystic
cavity = blastocyst
-embryoblast is a condensed cell mass located at one pole of blastocyst and trophoblast is a
single cell layer forming the wall of the blastocyst
Morula - Answer In cleavage, a solid ball of cells
Inner cell mass (Embryoblast) - Answer gives rise to embryo proper and its associated
extraembryonic membranes
Outer cell layer (trophoblast) - Answer forms the placenta and its associated extra embryonic
membranes
Gastrulation
(Week 3) - Answer -cells that form the embryo blast proliferate and change their position to
each other
-disk-shaped embryo with 3 distinctive layers (germ layers):
1. endoderm
2. mesoderm
3. ectoderm
What 3 major axes have been established by the end of gastrulation? - Answer 1. dorsal-
ventral
2. cranial-caudal
3. medial-lateral
Neurulation
(Weeks 3 & 4) - Answer early central nervous system is developed
parts of ectoderm specialize into neuroectoderm to fold to build the neural tube -> later forms
brain and spinal cord
Body Plan Formation/ Embryonic Folding
(Week 4) - Answer -2-D disk-like embryo folds to a cylindric shape
-cranial and caudal regions and lateral parts move ventrally -> look like adult
-several spaces and cavities formed (gut tube and abdominal cavity)
Organogenesis
