Topic 5: early human development Flashcards
how long is the pre-embryonic period?
-2 weeks
what starts off the pre-embryonic period?
-zygote
-1 cell that is diploid
-sperm has one set and
ovum has one set
where does the zygote form? what does a zygote undergo?
-forms in the uterine tube
-rapid mitotic divisions
-called cleavage
divisions
-short lived interphase
what does a zygote change into?
-morula
what is a morula
-solid ball of 16-32 cells
-these cells are called blastomeres
-same size as an ovum/zygote
what does a morula change into?
-blastocyst
what are the features of a blastocyst?
-fluid filled cavity that develops
-blastocoel/blastocyst
cavity
-embryoblast - the inner cell mass
-trophoblast - made of trophoblast cells
what forms the embro?
-the division and differentiation of cells within the embryoblast
what is the chorion?
-provides nutrients to the developing embryo
-surrounds all embryonic membranes
-contains chorionic villi
what forms the chorion?
-the division and differentiation of trophoblast cells
where does the blastocyst move and attach to? when does this occur?
-moves from the uterine tube
-attaches to the endometrium (uterine wall)
-5-7 days after fertilization
what happens after implantation?
-embryoblast forms a bilayer
-called the embryonic disc
-extraembryonic membranes start to form
what is the embryonic disc composed of?
-epiblast
-hypoblast
what does the epiblast form?
-undergoes mitosis
-forms the amnion
-fluid filled cavity
(amniotic cavity)
-3 germ layers of the embryo
what does the hypoblast form?
-undergoes mitosis
-forms a sac that sits under the embryo and the epiblast (yolk sac)
what are germ layers
-groups of cells that form layers from differentiation of epiblast cells
-contributes to the formation of an embryos organs and tissues
what is the embryonic period?
-3rd week to the 8th week
-germ layers are present and can now help form the embryo
what are the 3 germ layers called?
-ecotoderm (outside)
-mesoderm (middle)
-endoderm (inside)
what does the ectoderm control?
-formation of the nervous system
-the epidermis of the skin
what does the mesoderm control?
-formation of muscles, cardiovascular system, dermis, and most bones
what does the endoderm control?
-formation of epithelial linings of the digestive, reproductive, respiratory, and urinary systems plus their associated glands
what occurs during the embryonic phase
-major organ systems are almost fully formed
-heart begins to beat
-limb buds differentiate
-embryonic membranes form
what are the embryonic membranes that develop?
-chorion
-amnion
-yolk sac
-allantois
what are chorionic villi?
-projections of the chorion that contain blood vessels
-these vessels will form the fetal part of the placenta
what is the amnion?
-derived from epiblast
-forms the amniotic cavity
-surrounds the embryo/fetus with amniotic fluid
what is the purpose of amniotic fluid?
-shock absorption
-temperature regulation (keeps the embryo warm)
what is the yolk sac for?
-forms part of the gut
-gastrointestinal tract
-source of reproductive germ cells and embryonic blood cells
what is the allantois?
-projection off of the yolk sac
-forms the umbilical cord and urinary bladder
what is the fetal period?
-9th to 40th week
-growth and maturation of organs occurs
