Early Embryology Flashcards
Zygote
Original thing formed after fertilization
Morula
Blastomere at 16 cell stage that forms compact ball of cells
Inner cell mass
Forms embryo and contributes to fetal membranes (amniotic and part of chorionic)
Outer cell mass
Contributes to fetal members (placenta and umbilical cord)
Zona Pellucida
Surrounds blastmere and helps maintain the integrity of the cells
Days 1-5
Morula forms and zona pellucida is destroyed by enzymes from the outer cell mass
Blastocyst
Cells of morula secrete fluid to push inner cell mass to one side
Results in formation of blastocyst cavity
Embryo plants in wall of uterus
Embryoblast
Inner cell mass at one end of blastocyst
Trophoblast
Lines blastocyst cavity and contributes to placenta
Cytotrophoblast
Cellular inner layer lining blastocyst cavity
Syncytiotrophoblast
Invasive multinucleated cells that invade uterine endometrium to allow blastocyst to implant in uterus
Important hormone
HCG - human chorionic gonadotropin secreted by syncytiotrophoblast
Tells corpus luterm to secrete progesterone
Embryoblast differentiates into
Epiblast and hypoblast
Epiblast
Adjacent to embryonic pole of blastocyst
Hypoblast
Cells adjacent to cavity
When embryoblast differentiates, it forms a
Bilaminar disc
How is amniotic cavity formed?
Migration of epiblast cells
Amnion
Cells lining amniotic cavity
How is yolk sac formed?
Migration of hypoblast cells
Exocoelomic membrane
Formed from hypoblast cells and surrounds the primitive yolk sac
Lacunae
Spaces appearing in the embryonic pole of the syncytiotrophoblast and begin to connect to intact uterine vessels to form circulation
Extraembryonic mesoderm and derived from
Derived from exocoelomic membrane
Found in between exocoeleomic membrane and cytotrophoblast layer
Totally separates embryo proper from amniotic cavity and yolk sac
Isolated spaces
Formed when extraembryonic mesoderm begins to die
Chorionic cavity
Isolated spaces in the extraembryonic mesoderm coalesce to form one large space surrounding the mebryo proper, amnion, and primitive yolk sac
Connecting stalk and what does it form?
Portion of the extraembryonic mesoderm that connects embryo to the chorion
Becomes umbilical cord
Chorion comprised of what and what does it become?
Extraembryonic mesoderm and cytotrophoblast
Becomes fetal component of placenta
Secondary/definitive yolk sac formed by
second wave of cells from hyopblast migrate inside exocoelomic membrane to form yolk sac
Buccopharyngeal membrane
Formed between hypo and epi layer near head
Forms mouth
Cloacal mebrane
Becomes anal opening
Primary villi formed from
Cytotrophoblast cells that begin to invade the syncytiotrophoblast
Gastrulation
Formation of three germ layers
Primitive streak
At cadual end
Caused by migrating epiblast cells invaginating into the hypoblast layer
Primitive pit/primitive node
Rostral streak of primitive pit
Primitive streak appears as
Depression in the midline of the epiblast cell layer
Endoderm cells and what they develop to
Epiblast cells that migrate through primitive streak and replace hypoblast cells
Become linings of digestive, resp, urogen, and phyrangeal pouches of head and eck
Mesoderm cells and what they develop to
Migrate through primitive streak and sandwich between endoderm and ecotderm layers
Become skeletal, smooth and cardiac muscle, most cartilage and bone, dermis of skin, portion of kidneys and gonads
Mesoderm layer also called
Intraembryonic mesoderm
Notochord
Midline specialized cells in the region of the endoderm and mesoderm
Ectoderm cells
Remaining epiblast cells once mesoderm and endoderm cells have migrated through
Develop into nervous system and epidermis
All germ layers derived from
Epiblast
Direction of epiblast migration
The more caudal the cells, the more laterally they move
Caudal cells form more lateral structures while cells from the node form more midline structures
What layer doesn’t exist at body cavities?
Mesoderm
Notochord, what it forms and what are remnants
Basis of vertebral column
Mesoderm cells between ecto and endo layers that migrate in cephalic direction
Induces CNS
Nucleus pulposus
Prechordal plate
Head organizer
Neurulation
Results in formation of primitive nervous system
Mechanism of neurulation
Notochord secretes inducing factors which cause the overlying ectoderm to proliferate and thicken into the neural plate
Begins at cranial end
why does Neural groove form?
Forms in midline due to proliferation of cells on lateral edge of neural plate
Neural folds
Continued overgrowth of neural plate results in the neuroectoderm becoming more elevated along laterla margins
Neural crest cells
At the crest of neural folds…will eventually migrate from neural ectoderm to deeper mesoderm
Nerual tube formation
Neural folds approach one another and fuse in the region of the future neck…grow toward both ends
Anterior and posterior neuropores
Cranial and caudal ends of the neural tube still open to the amniotic cavity
Exencephaly and other name
Failure of anterior neuropore to close
Cranioschisis
Spina bifida
Failure of posterior to close
Spina bifida oculta
Absense of portion of the vertebral arch and is covered by skin…midline patch of hair
Spina bifida cystica
More severe…meninges or spinal cord protrude through skin
Meningomyelocele vs. meningocele
Meningomyelocele - Both spinal cord and meninges protude
Meningocele - only the meninges are protruding
Mesoderm specializes into
Paraxial
Intermediate
Lateral phase
Paraxial mesoderm
Most medial
Create somites
Intermediate mesoderm
Least extensively developed
Becomes parts of urogenital system
Lateral mesoderm and splits
Somatic (parietal) portion in contact with ectoderm
Splanchnic (visceral) portion in contact with endoderm
Somatic mesoderm becomes
Serosa of body cavities and long bones and connective tissue of body wall
Splanchnic mesoderm becomes
Smooth muscle of GI and serosa of superfical surfaces of organs
Intraembryonic coelom
Located between somatic and splanchnic mesoderms
Continuous with extraembryonic coelem (chorionic cavity)
What forces transverse folding?
Overgroth of paraxial mesoderm and nervous system
When does mesoderm split?
During transverse folding
Yolk sac becomes
Foregut, midgut, hindgut
Longitudinal folding caused by
Rapid growth of neural plate at both ends
Moves the heart and septum transversum to the caudal side of the body
What becomes digestive system?
Part of yolk sac closest to the embryo
Foregut
Lower respiratory system, pharynx, esophagus, stomach, and initial part of duodenum
Midgut
Remainder of small intestine, much of large
Hindgut
Becomes rectum, anal canal, and portion of urogenital
Allantois
Caudal extension of hindgut that extends into connecting stalk
Decidual rection
Uterine cells fill with lipids and glycogen at implantation site
Primary chorionic villi
Formed by pegs of cytotrophoblast cells that protrude into the syncytiotrophoblast
Secondary villi
When the extraembryonic mesoderm invades the core of the cytotrophoblast
Embryonic vessels form from
Mesodermal cells within cytotrophoblasts pegs of tissue
Tertiary or stem villi
Villi with capillary networks
Intervillous space
Where maternal blood pools
Last thing for cytotrophoblast and syncytiotrophoblast
Syncytiotrophoblast surrounds lacunae to form intervillous spaces
Cytotrophoblast becomes continuous superficially with syncytiotrophoblast…anchors chorion to the decidue basalis of uterus
Splanchnic mesoderm replaces _______ as folding occurs
Extraembryonic mesoderm on the superficial surface of the endoderm-lined yolk sac
