Chapter 29: Development And Ingeritance Flashcards
Prenatal Development
Is the time from fertilization to birth and includes the embryonic and fetal periods.
Is divided into periods of 3 calendar months known as trimesters.
Trimesters
Hormonal changes occurs during all 3 of the stages
1st : most critical stage of development. All major organs systems begin to form. Priory when the developing organism is most vulnerable to effects of drugs, etc.
2nd: characterized by the nearly complete development of organ systems. By the end, fetus assumes distinctively human features.
3rd: period of fetal growth in which the weight doubles. Most organs become fully functional.
Embryonic Period
Extend from fertilization through the 8th week.
Major body’s organs and systems develop.
Includes fertilization, cleavage of zygote, blastocyst formation and implantation.
Blastula formation occurs.
Acrosomal Reaction
The release of the contents of acrosome. The acrosome enzymes digest a path through zonal pellucida as the lashing sperm tail pushes the sperm cell onward.
Polyspermy
Fertilization by more than one sperm cell.
Male Pronucleus
Developed from the nucleus in the head of the sperm.
Female Pronucleus
Developed from the nucleus of the fertilized ovum.
Syngamy
The process where a male and female pronuclei form and fuse producing a single diploid nucleus.
Fusion of haploid pronuclei restores the diploid number (2n) of 46 chromosomes/
Zygote
Fertilized ovum
Results from the fusion of the male pronucleus and the female pronucleus.
Dizygotic Twins
Produced from the independent release of 2 secondary oocytes and subsequent oocytes.
Subsequent fertilization of each different sperm.
Monozygotic Twins
Develop from a single fertilized ovum.
Contain exactly the same genetic material and are always the same sex.
Cleavage
After fertilization, rapid mitosis cell divisions of the zygote takes place.
Blastomeres
Progressively smaller cells that are produced by cleavage.
Morula
A solid sphere of cells produced by successive cleavage.
Surrounded by the zonal pellucdia and is about the same size as the original zygote.
Uterine Milk
Fluid, and nutrients that is stored in the cytoplasm, of the blastomeres of the morula.
Provides nourishment for the developing morula.
Blastocyst Cavity
Large fluid filled cavity.
At the 32 cells stage, fluid enters the morula and collects between the blastomeres. They are reorganized in this cavity.
Once the cavity is formed the mass is called a blastocysts.
Blastocyst.
Developing mass that is formed in the blastocyst cavity.
It has hundreds of cells and is about the same size as the original zygote.
During formation 2 distinct cells population arises”
1. Embryo blast
2. Trophoblast
Embryoblast
Or inner mass
Internally located and eventually develops into the embryo.
Trophoblast
Is the outer superficial later of cells that forms the sphere like wall of the blastocyst.
Promotes implantation and produces hCG
Will develop into the outer chorionic sac that surrounds the fetus and the fetal portion of the placenta.
Develops about 8 days after fertilization into 2 layers in the region of contact between the blastocyst and endometrium.
Implantation
Blastocyst remains free with the uterine cavity for 2 days before it attaches.
6 days after fertilization the blastocyst loosely attaches to the endometrium.
Implants is either the posterior portion of fundus or the body of the uterus.
Orients with the inner cell mass towards the endometrium.
Decidua
Following implantation the endometrium becomes this.
Separates from the endometrium after the fetus is delivers much as normal menstruation.
Regions:
Development of Bilaminar Embryonic Disc
Cells of the embryoblast differentiate into 2 layers around 8 days after fertilization.
Amniotic Cavity
A small cavity that appears after development of the bilaminar embryonic disc within the epiblast and eventually enlarges to form the cavity.
Amnion
Developed from the epiblast
Is a profile layer
As the amniotic cavity enlarges a single layer of squamous cell forms this dome like roof above the epiblast cells.
Amniotic Fluid
Fluid that fills the amniotic cavity.
Derived from maternal blood.
The fetus contributes to the fluid by excreting urine into the cavity.
Once baby is delivered the baby can breathe on its own, absorbing the fluid in the lungs.
Functions:
1. Serves as shock absorber for the fetus,
2. helps regulate fetal body temp
3. helps prevent the fetus from drying out
4. prevents adhesions between skin of the fetus and surround tissues.
Development of the Yolk Sac
On the 8th day after fertilization, cells at the edge of the hypoblast migrate and cover the inner surface of the blastocyst wall.
The migrating columnar cells become squamous and form the thin membrane called exocoelomic membrane.
Together with the hypoblast and membrane from the wall of the yolk sac.
Development of Sinusoids
Occurs on the 9th day after fertilization.
Blastocysts becomes complete in GH embedded in the endometrium.
As the syncutiotroblast expands, small spaces called lacunae develop within in.
After 12th day, lacunae fuse to form larger spaces called lacunae networks.
Endometrial capillaries around the developing embryo become dilated as maternal sinusoids.
Extraembryoinc Mesoderm
Develops on about the 12th day after fertilization.
These cells are derived from the yolk sac and form a CT layer around the amnion and yolk sac.
Chorion
Formed by the extraembryonic mesoderm, together with the 2 layers of the trophoblast.
Surrounds the embryo and later the fetus.
Becomes the principle embryonic part of the placenta.
Protect the embryo and fetus from the immune response of the mother.
Chorionic Cavity
When the inner layer of the chorion fuses with the amnion.
Connecting Stalk
The future umbilical cord.
By the end of the 2nd week of development the bilaminar embryonic disc becomes connected to the trophoblast by a band of extraembryonic mesoderm known as the connecting stalk.
Gastrulation
The fist major event of the 3rd week of development.
Occurs about 15 days after fertilization.
The bilaminar embryonic disc transforms into a trilamionar embryonic disc consisting of 3 layers:
1. Ectoderm-inside
2. Mesoderm-middle
3. Endoderm-outside
Primitive Node
A rounded structure that is formed at the head end of the primitive stalk as small group of epiblastic cells.
Notochordal Process
Occurs about 16 days after fertilization.
Mesodermal cells from the primitive node migrate towards the head of the embryo and follow tube of cells in the midline.
Notochord
Notochordal process becomes a solid splinter of cells that occurs by 22-24 days or third week of development.
Nuurulation: the process by which the neural plate, neural fold and neural tubes form.