Chapter 29: Development and Inheritance Flashcards
Define capacitation during fertilization
A series of functional changes that cause the specs tail to beat even more vigorously and prepare its plasma membrane to fuse with the oocyte’s plasma membrane
For fertilization to occur a sperm cell must first penetrate which two layers?
- Corona radiata - the granulose cells that surround the secondary oocyte
- Zona pellucida - the clear glycoprotein layer between the corona radiata and the oocyte’s plasma membrane
Define acrosomal reaction
Triggered by the binding of sperm to sperm receptor (glyocyprotein ZP3) the acrosome of the sperm releases its contents which digest a path through the the layers to reach the oocytes plasma membrane and fuse with it
Differentiate between fast and slow blow block to polyspermy
Polyspermy - fertilization by more than one sperm cell
Fast block - within a few seconds cell membrane of oocyte depolarizes which makes it unable to fuse with another sperm and trigger exocytosis of secretory vesicles from oocyte
Slow block - molecules released by exocytosis inactivate ZP3 and harden the Mona pellucida
Describe the male and female pronuclei
The nucleus in the head to the sperm develops into the male pronucleus
The nucleus of the fertilized ovum develops into the female pronucleus
Once formed, they fuse, producing a single diploid nucleus, a process known as syngamy and the fertilized ovum is now called a zygote
Difference between DZ, MZ, and conjoined twins
DZ twins - independent release of two secondary oocytes and the subsequent fertilization by different sperm
MZ twins - develop from a single fertilized ovum that separates into two embryos
Conjoined - separations that occur later than 8 days are likely to cause twins to share some body structures
Describe the cleavage of zygote
Following fertilization, rapid mitotic cell divisions of the zygote called cleavage take place
The 1st division begins ~24 hours after fertilization and is completed about 6 hours later resulting in smaller cells referred to as blastomeres
The 2nd cleavage occurs on day 2 resulting in 4 cells
By the end of the 3rd day there are 16 cells
These cleaves eventually produce a solid sphere of cells called the mould which is still surrounded by the zona pellucida and is about the same size as original zygote
Describe the layers of a blastocyst and their eventual fates
Once the blastocyst cavity is formed in the morula it becomes a blastocyst - 2 distinct cell populations arise:
The embryo blast is located internally and eventually develops into the embryo
The trophoblast is the outer superficial layer of cells that forms the sphere like wall of the blastocyst that eventually develops into the outer chorionic sac that surrounds the fetus and the fetal portion of the placentas
Describe implantation, decidua basalis, and decidua capsularis,
Implantation - 6 days after fertilization, blastocyst loosely attaches to the endometrium that eventually results in the during into the endometrium and becoming completely surrounded
Decidua is the term for the endometrium following implantation that have different names depending on their positions:
- Decidua basalis: between the embryo and the stratum basal of uterus; provides glycogen and lipids for the developing embryo
- Decidua capsularis: between the embryo and the uterine cavity
Define etopic pregnancy
Development of embryo or fetus outside the uterine cavity, such as becoming stuck in uterine tube due to scar tissue
Define amnion and amniotic fluid
amnion - a single layer of squamous cells that forms a domelike roof above the epiblasts in an enlarging amniotic cavity
amniotic fluid - initially derived from maternal blood but later the fetus contributes to the fluid by excreting using into the amniotic cavity; serves as a shock absorber, regulates body temp, helps prevent fetus from drying out, and prevents adhesions between skin of fetus and surrounding tissues
Describe the development of the yolk sac
8 days after fertilization, cells at the edge of the hypoblast migrate and cover the inner surface of the blastocyst wall , forming a thin membrane referred to as the exocolomic membrane
Together with the hypoblast, the exocoelemic membrane forms the wall of the yolk sac, the former blastocyst cavity during earlier development
This is the source of blood cells from the third to sixth week
Describe the development of the chorion
The extra embryonic mesoderm together with the two layers of thetrophoblast forms the chorion
It surrounds the embryo and later the fetus - eventually it becomes the principal embryonic part of the placenta, the structure for exchange of materials between mother and fetus
It also protects the embryo/fetus from immune system of mother by 1) secreting proteins that block antibody production by mother and 2) promotes the production of T lymphocytes that supress the normal immune response in uterus
Describe the process of gastrulation
First major event of third week development that occurs about 15 days after fertilization
The bilaminar (two-layered) embryonic disc, consisting of epiblast and hypoblast, transforms into a trilaminar (3-layered) embryonic disc consisting of 3 layers: ectoderm, mesoderm, endoderm
These primary germ layers are the major embryonic tissues from which the various tissues and organs of the body develop
by the end of 22-24 days the notochord process development from mesodermal cells becomes a solid cyndrical of cells called the notochord that plays an extremely important role in induction, the process by which one tissue stimulates the development if adjacent specialized tissues
What structures are are produced by the 3 primary germ layers?
Endoderm - epithelial lining of GI tract, glands, urinary tract, respiratory system, thyroids glands, prostate, and gametes
Mesoderm - all skeletal and cardiac tissue and most smooth muscle tissue
Ecoderm - all nervous tissue
