Early Development I Flashcards
Gametes
. Derived from primordial germ cells
. Male: spermatogonia
. Female: oogonia
Primordial germ cell
. From wall of yolk sac then migrate to developing gonads
. Diploid, carry full chromosomal complement of 46 chromosomes (2N)
. Proliferate via mitosis
Spermatogenesis
. Spermatogonia dormant until puberty
. Begin to multiply
. Enter meiosis I becoming primary spermocytes
. Complete meiosis I yielding 2 secondary spermatocytes
. Undergo meiosis II yielding 4 haploid spermatids (n, 23)
. Morphological changes mature spermatozoa
Oogenesis
. Oogonia multiply w/in ovary via mitosis during embryo phase
. Fetal phase oogonia begin 1st meiotic division becoming primary oocytes occupying primitive follicles
. Arrested in meiosis I until puberty
. After 1st period primary oocytes mature from reproductive hormones
. During ovulation primary oocyte completes meiosis I making secondary oocyte and enters meiosis II
. Arrested in meiosis II until fertilization when it finishes and makes mature ovum (n, 23)
Ovulation occurs on day ___ if 1st day of period is day 1
14
How pregnancy timeline is calculated
. 280 dates (40 weeks) from date of last period
. 366 days (38 weeks) from date of fertilization
Pregnancy trimesters
. 3 trimesters of 13 weeks each
Pre-embryonic period
. Weeks 1-2
. Begins at fertilization
. Initial differentiation of embryonic and extraembryonic tissues and implantation
Embryonic period
. Weeks 3-8
. Establishment of primary germ layers, vertebrate body plan, and organogenesis
Fetal period
. Weeks 9-38
. Organ system maturation and growth
How long is secondary oocyte viable for?
24 hours after ovulation
Fertilization
. Ovum and spermatozoon produce diploid zygote
. Day 1 week 1 of development
Most common site of fertilization
Ampulla of uterine tube
Acrosomal reaction
. Coat of enzymes (acrosome) covers head of sperm
. Binds to and breaks down protein coat of zone pellucida surrounding oocyte
Zygote
. Diploid
. Cytoplasm mostly maternally inherited
Conceptus
. Zygote and it’s derivatives
Blastomeres
. Derived from zygote mitotically dividing as it descends down uterine tube
Morula
. Solid ball of 1620 blastomeres in 2 cell groups
. Inner cell mass: internal cells that become embryo proper
. Trophoblast: surface blastomeres that contribute to placenta and fetal membranes
. Contains ETCHbox genes
ETCHbox genes
. Homeobox genes unique to placental mammals
. Exclusively expressed during 8-cell through morally phase
Blastocyst
. Forms as conceptus enters uterus on day 4
. Has blastocele cavity that separates inner mass (embryoblast) from most of the trophoblast
. Embryoblast occupies one pole
. Trophoblast forms external wall
In terms of differentiating ability, Blastomeres are ___ while embryoblast are ___
. Totipotent (can form complete embryo)
. Pluripotent (can give rise to lost any cell of tissue)
Implantation
. Day 6
. Zone pellucida degenerates
. Blastocyst implants w/in endometrial lining of uterus
. Most common in posterosuperior uterine wall
. Embryoblast oriented toward the wall
. Trophoblast adjacent to embryoblast, releases enzymes that erode into endometrial surface
. Takes several days
. At end blastocyst is surrounded by endometrium
Ectopic implantation
. Common in uterine tube but can also happen in cervix, ovary, and abdominal cavity
. In tubal pregnancies, not viable beyond 2 months
. Leading cause of first trimester bleeding
What occurs on day 8?
. Trophoblast divides into cytotrophoblast (inner layer) and syncytiotrophoblast (outer layer)
. Embryoblast divides into epiblast (cells close to trophoblast) and hypoblast (cells close to blastocele) making blastula (bilaminar disc)
Syncytiotrophoblast
. Multinucleated mass from breakdown of cell membrane
. Produces human chorionic gonadotropin (hCG) to stimulate corpus luteum to produce progesterone
Amniotic cavity
. Develops w/in epiblast
Yolk sac
Hypoblast cells proliferate and migrate to surround blastocele
Extraembryonic mesoderm
Mesenchymal cells derived from epiblast proliferate to surround the amniotic cavity, yolk sac, and embryonic disc
Chorionic cavity
. Develops w/in extraembryonic mesoderm
. Expands to envelop the yolk sac, amniotic sac, and embryonic disc
Chorion
. Membranous wall of chorionic cavity
. Consists of extraembryonic mesoderm and trophoblast
. Contributes to fetal portion of placenta
Amnion
Membraneous wall of amniotic cavity
. Consists of extraembryonic mesoderm and epiblast
Connecting stalk
. Extraembryonic mesoderm connecting bilaminar disc to trophoblast
. Contributes to future umbilical cord
Gastrulation
. Embryonic cell migration that leads to formation of a trilaminar embryonic disc or gastrula
. Controlled by fibroblast growth factor 8 (FGF8)
. Initiated day 15 at caudal end of blastula by formation of primitive streak in epiblast
. Primitive streak elongates to form primitive groove that terminates cranially at primitive node
Primitive node
. Raised rim of epiblast
During gastrulation, epiblast cells proliferate and migrate ____
Through primitive groove moving lat. and ant.
Endoderm
.cells migrate deep to epiblast and displace hypoblast
Intraembryonic mesoderm
. Cells that migrate btw epiblast and endoderm
Ectoderm
Nonmigratory epiblast cells
Prechordal plate
. Mesodermal cells that migrate through primitive pit and move directly ant.
Notochord
. Midline CT rod
. Forms cranial to caudal as primitive pit migrates post.
. Defining characteristic of all vertebrates
. Scaffold of developing vertebral column
. Persists through early childhood as part of the nucleus purposes
At each end of embryo, a depressed region of ectoderm displaces mesoderm and fuses to endoderm forming ____
. Oropharyngeal membrane
. Cloacal membrane
Oropharyngeal membrane
. Located at cephalic end, marking location of future mouth
Cloacal membrane
. Caudal end
. Marking location of future anus and urogenital openings
Allantois
. Fingerlike outpouching yolk sac invades connecting stalk
Neurulation
. Formation of neural tube (precursor to CNS)
. Directed by FGF suppressioni of BMP activity
. Molecular signals secreted by primitive node, notochord, and prechordal plate induce proliferation of ectodermal cells forming midline neural plate (neuroectoderm)
What happens on day 18?
. Neural plate invaginates to form neural groove flanked by neural folds
. Neural groove deepens, folds meet and fuse to make hollow neural tube cranially to caudally from center of disc
. Completed during week 4 and gives rise to brain and spinal cord
Neural crest
. Special cell population in neural folds
. Become mesenchymal cells and migrate throughout developing embryo
. Gives rise to variety of structures throughout body
Neural tube defects
. Failure to close causes CNS issues
. Anencephaly (lethal)
. Spina bifida
. Assoc. w/ maternal folic acid deficiency
What happens starting day 19?
. Mesoderm proliferates and condenses into 3 parallel columns located lat. on notochord bilaterally
. Paraxial mesoderm
. Intermediate mesoderm
. Lateral plate mesoderm
Paraxial mesoderm
. Becomes segmented into somites adjacent to notochord and neural tube
. Cranial to caudal
Somites subdivided into _____
. Dermotome
. Sclerotome
. Myotome
Dermotome
. Contributes to dermis of back and ventrolateral trunk
Sclerotome
Gives rise to vertebrae and ribs
Myotome
. Gives rise to segmental muscles of back and anterolateral body wall
Intermediate mesoderm
. Gives rise to parts of urogenital system
Lateral mesoderm
. Somatic mesoderm (parietal): gives rise to parietal serous membranes, parts of body wall, ventral dermis, and CT of limbs
. Splanchnic mesoderm (visceral): gives rise to visceral serous membranes, smooth muscle of gut, and blood vessels
Intraembryonic coelom
. Space in between somatic and splanchnic mesoderm
. Gives rise to adult body cavities
Cardiogenic region
. Extension of splanchnic mesoderm cranial to oropharyngeal membrane
. Precursor to heart
