PNLU - intro to embryology

oocyte

developing egg, immotile, all 23X chromosome

where deos fertilization occur

in the ampulla of the uterine tube for 30min - 6 days

what does the sperm do before fertilization

capacitation and acrosome reaction

capacitation

glycoproteins and seminal plasma proteins removed from the acrosome and eat at the wall of the oocyte

acrosome reaction

binding to and release of enzymes to penetrate oocyte

Phase 1 of fertilization

penetration of corona radiata where the sperm’s acrosome releases enzymes to facilitate penetration to reach the zona pellucida (site of acrosome reaction)

phase 2 of fertilization

penetration of zona pellucia, glycoprotein shell that facilitates sperm binding and acrosome reaction

phase 3 of fertilization

oocyte and sperk cell membranes fuse that results in cortical and zona reactions, 2nd polar body, and definitive oocyte

cortical and zona reactions

lysosomal enzymes from cortical granules cause zona reaction that prevents sperm binding and polysperm

what follows cortical and zona reactions

resumption of second meiotic division forming the 2nd body and definitive oocyte with a female pronucleus (22+X)

what does the male pronucleus become

the 22+X/Y becomes 22+X (female pronucleus) and lose the nuclear envelope to form a diploid cell

what does phase 3 of fertilization result in

1. metabolic activation of egg

2. each pronucleus replicates to generate diploid # of chromosomes

3. chromosomes organize at spindle, undergoing normal mitotic division

4. sister chromatids move to opposite pole and the cytoplasm develops a furrow and divides into two cells to form a zygote

embryonic period

fertilization to 8 weeks (56 days) of development — developing all major structures and establishment of all organ systems

fetal period

occurs 9 weeks (57 days) to term (38 weeks) — differentiation and frowth of organs and tissues

explain the series of mitotic divisions that the zygote undergoes

blastomeres develop from the first and second MD — the 3rd cleavage creates 8 cells, causing compaction, where theres a compact ball of cells delineating inner from outer cells — a 16-cell morula forms 3 days after fertilization with a define inner cell mass and outer cell mass

what does the inner cell mass give rise to

embryoblasts

what does the outer cell mass give rise to

trophoblast, THEN placenta

explain the formation of the blastocyst

fluid enters the inner cell mass to form a single cavity called the blastocele, resulting in the formation of the definitive blastocyst

explain implantation

the blastocyst attaches to the uterine wall and reciprocal interactions between invading trophoblast cells and endometrial cells to the uterine epithelium result in implantation — now the blastocyst is partially embedded in the endometrial stroma of the uterus to gain nutrient from the mother

layers of the trophoblast

2 layers: cytotrophoblast and syncytiotrophoblast

layers of the embryoblast

2 layers: hypoblast and epiblast

what does the blastocyst develop into

the yolk sac, differentiating from the hypoblast and epiblast

describe the formation of the amniotic cavity

the amnion fills with amniotic fluid, eventually growing to surround the embryo

what happens during week 3

development of the allantois, a finger-like outpocketing of the yolk sac that later becomes part of the urinary bladder

gastrulation

formation of 3 embryonic germ layers: ectoderm, mesoderm, endoderm

epiblast forms what

forms all three germ layers

primitive steak

indentation along the dorsal surface of the epiblast in the embryo when it’s flat, oval, disc shaped

node at caudal of primitive steak

releases growth factors that direct cells to multiple and migrate out of the primitive steak to create two new layers of cells

stages of placental development

1. primary villi

2. secondary villi

3. tertiary villi

primary villi

central core of cytotrophoblast cells that form outer cytotrophoblast shell, firmly attaching chorionic cavity to maternal endometrium

secondary villi

core of mesodermal cells

tertiary villi

villous capillaries develop connecting embryo to placenta — villi extends from chorionic plate to outer cytotrophoblast shell to join decidual plate of the endometrium to form the placenta — connection of embryo to placenta (connecting stalk) becomes the umbilical cord

maturation of pharyngeal arches

develops into the head and neck

examples of what the endoderm layers become

1. digestive system

2. liver

3. pancreas

4. lungs (inner layers)

examples of what the mesoderm becomes

1. circulatory system

2. lungs (epithelial layers)

3. skeletal system

4. muscular system

examples of what the ectoderm layer becomes

1. hair

2. nails

3. skin

4. nervous system