Gestation: carrying one or more embryos in uterus. Humans: 266 days Rodents: 21 d Dogs: 60 d Cows: 270 Elephant: 600 days
Conception: fertilization of egg by sperm Humans: occurs in oviduct Contact of sperm with egg surface: metabolic rxns within egg that trigger the onset of embryonic development. Enzymes in acrosome of sperm dissolve outer egg membrane. (lock and key fit: sperm to egg) Fast block to polyspermy: change in memb. Potential Slow block: cortical rxn: enzymes released from cortical granules to outside (exocytosis).
Different species differ in the stage of meiosis the egg has reached at fertilization. Some: have completed meiosis at time of release from female Humans: arrested at metaphase of meiosis II. Until fertilized.
Sperm requires about 6 hours in female reproductive tract … before ready to encounter egg. Egg: is cloaked by follicle cells (released with it during ovulation)
HCG: human chorionic gonadotropin: from embryo. Acts like LH Maintain secretion of progesterone and estrogens by the corps luteum. HCG levels so high they go into urine (detected in pregnancy test)
Contains blood vessels of both Mother Embryo
Organisms development determined by Genome of zygote Neighboring cells (who directs the first differentiations?)
Early embryonic cells become different because of Cytoplasmic determinants: maternal substances found in Unfertilized egg: uneven distribution Heterogeneous cytoplasm of polarized egg (mRNA, proteins, mitochondria) Location in embryonic regions with different characteristics. Inner layer or trophoblast Induction: cell stim by nearby cells (gene expression) Diffusible chemicals OR cell surface interactions
An animals spatial organization: where organs and limbs are found Control by induction from nearby tissue
Cell differentiation: through selective control of Gene Expression. Cell signaling: Timely communication of instructions telling cells what to do and when to do it. Morphogenisis: process by which animal takes shape. Differentiated cells end up where they are supposed to.
Cells developmental potential: range of structures it can give rise to. Goes down with cells “age” Mammals: zygote cells are totipotent until the 8 cell stage.
Cleavage : 24 hours post conception: zygote begins to divide (without dbl cytosol) Blastocyst (blastula), sphere of cells containing a cavity: made by cleavage(1 wk. post conception). Implants in uterus. Trophoplast: outer layer Gastrulation : produces 3 layered gastrula Organogenesis: rudimentary organs from which adult structures arise.
Notochord: from dorsal mesoderm: signals the ectoderm to form Neural plate. Neural plate: dorsal ectoderm: becomes nueral tube. Becomes CNS In only vertebrates: have neural crest: become, peripheral nerves, teeth skull bones etc.
After completion of neural tube: Mesoderm is making 2 tissue layer of coelom. Somites are beside notochord: they will become segmented: muscle and vertebrae.
Adaptations are needed to avoid drying out on land (for all amniotes: reptiles and mammals) amniotes: extraembronic membranes (chorion, amnion, yolk sac) 1. shelled egg of birds and reptiles And monotremes (mammals that lay eggs- platypus) 2. uterus (eutherians) Marsupials mammals
Changes in cell Shape and Position Cell shape: ie neural plate forms neural tube Reorganize cytoskeleton. Actin fibers contract. Cell position: Cells “crawl” within the embryo with cytoskeletal fibers extend and retract.
Extracellular matrix: secreted glycoproteins outside the plasma membrane. Direct migrating cells May act as tracks Provide anchorage