Anatomy and Physiology 2 Chapter 29 - Fertilization and First Trimester

ovulation

secondary oocyte ovulated and is suspened in meiosis II (metaphase II) with 1 polar body; secondary oocyte is surrounded by the corona radiata and zona pellucida

capacitation of sperm

• after insemination, sperm travel to oviducts

• sperm bind to isthmus region to wait for ovulation signal (presence of progesterone) via cilia

• acrosomal proteins undergo change to allow for penetration of corona radiata and zona pellucida

• hyperactive motility

5 steps of fertilization

1. fertilization and oocyte activation: acrosomal enzymes in the sperm digest follicle/granulosa cells (corona radiata) and zona pellucida to reach oocyte membrane

2. pronuclei develop and DNA synthesis occurs: female and male pronuclei form and DNA synthesis occurs in both pronuclei

3. spindle fiber formation begins: pronuclei chromatin condenses into chromosomes and male-donated centrioles duplicate and begin to form spindle fibers

4. amphimixis occurs and cleavage begins: pronuclei membranes dissolve, metaphase occurs, and fusion of gametes occur (amphimixis) forming a zygote

5. first cleavage forms 2 blastomeres: anaphase, telophase, and cytokinesis occur; cell size/volume decreases, while the # of cells increase and 2 blastomeres form

shock (hardening)

prevents polyspermy by an influx in Na+ which causes the following:

• Ca2+ release from ER

• release of enzymes that alter zona pellucida (and corona radiata)

• “hardens” matrix and destroys binding receptors

what is formed/occurs from zygote to blastocyst

• zygote

• blastomere

• morula

• blastulation occurs

• blastocyst which is made of blastocoele (fluid), inner cell mass, and trophoblast (outside cells)

what does the inner cell mass and trophoblast develop into

• inner cell mass: develop different types of membranes/structures

• trophoblast: develop into embryo associated tissue to help with development

what are cytoplasmic determinants

help cells “know” what they should become and usually come from the oocyte; chemicals that float in the cytoplasm and have uneven distribution during mitotic division where different genes are turned on or off

gestation

counted from 1st day of last menstrual period (though first 2ish weeks are follicular phase so no ovulation)

what are the 3 trimesters

1. 1st: pre-embryo > embryo > fetus

2. 2nd: development of organs and systems

3. 3rd: increase in size and mass of offspring

2 stages of the 1st trimester

1. pre-embryonic stage: implantation

2. embryonic phase: embryogenesis and gastrulation

pre-embryonic stage: implantation and what occurs during this

a 10 day post-fertilization period where the following occur:

• blastocyst in uterine cavity at day 6

• blastula moves towards endometrium at day 7

• outer trophoblast cells differentiate into:

  • syncytial (multinucleated) trophoblast: destroy the endometrial and maternal capillary walls to release more nutrients and create lacunae respectively (invade endometrium basically)

  • cellular trophoblast: surround lacunae (villi) to absorb and transfer nutrients to embryo

• yolk sac formation at day 10 and is the site of red blood cell production (erythrocytes) and is the primary source of nutrition for ~2 weeks from the maternal blood supply

embryonic phase: embryogenesis and gastrulation and what occurs during this

occurs from implantation to week 9

• inner cell mass continuing to divide and differentiate into the 3 germ layers

• neuralation occurs later on

what are the 3 germ layers and examples of tissues formed from each layer

1. ectoderm: outer layer

   1. consists of superficial cells that don’t migrate into the interior of the blastodisc

   2. epidermis, neuron of brain, pigment cell

2. mesoderm: middle layer

   1. poorly organized layer of migrating cells between the ectoderm and endoderm

   2. cardiac muscle, skeletal muscle, smooth muscle, tubule cell of kidney, red blood cells

3. endoderm: inner layer

   1. consisting of the cells that face the yolk sac

   2. lung cell, thyroid cell, pancreatic cell

neurulation and what happens with each germ layer

development of the primitive nervous system

• ectoderm folds inward to form a thickened neural plate (forms brain) and central canal (forms spine)

• somites are mesodermal blocks that form muscle and vertebrae

• endoderm develop below mesoderm

what are the 4 membrane types and what germ layers create them

1. yolk sac: mesoderm and endoderm

2. amnion: ectoderm and mesoderm

3. allantois: mesoderm and endoderm

4. chorion: trophoblasts and mesoderm

similarities vs. differences between amniotic egg and placental animal membranes

similarities: all 4 membrane types are present and used in the same way

differences: amniotic egg has a hard shell surrounding it and most of the membranes come together to form the umbilical cord in placental animals