Chapter 29 - Development and Inheritance PART 1 Flashcards
What is Embryonic Period?
Embryonic Period:
Extends from fertilization through 8th week of development
What is Fertilization?
Fertilization:
Merging of genetic info from Haploid Sperm and Haploid Secondary Oocyte
Sperm swim from Vagina to Cervix
Sperm pass through Uterus and Uterine Tubes mainly due to contraction of walls of these 2 structures
For Fertilization to occur:
Sperm must penetrate the Corona Radiata and the Zona Pellucida
What is Path of Sperm?
1- Corona Radiata
2- Zona Pellucida
3- Plasma membrane of Secondary Oocyte
4- Cytoplasm of Secondary Oocyte
How can Sperm Penetrate into Oocyte?
Enzymes on sperm’s Acrosome, along with Tail movement, allow sperm to penetrate Corona Radiata
Glycoprotein ZP3 in Zona Pellucida is a receptor for the sperm
Membrane proteins in the sperm Head bind to ZP3, and Acrosomal enzymes are released to digest a path in the Zona Pellucida
What is Male Pronucleus?
The Haploid Nucleus in the Head of the sperm becomes the Male Pronucleus
What is Female Pronucleus?
The Haploid Nucleus of the fertilized Ovum becomes the Female Pronucleus
What is Syngamy?
Syngamy:
When Male and Female Pronuclei merge
Form a Diploid Zygote
What is Day 1 Cleavage?
Cleavage:
Day 1
Zygote begins Mitotic Division after fertilization (about 24 hours)
Fist division takes about 6 hours
Successive divisions take less time
What Happens on Day 2 after Fertilization?
A second Cleavage is completed
Yielding 4 cells
What Happens on Day 3 after Fertilization?
By end of Day 3:
There is 16 cells
Blastomeres:
Each division yields smaller and smaller cells called Blastomeres
What Happens on Day 4 after Fertilization?
Day 4:
Morula:
The cluster of cells resembles a mulberry and is called Morula
Morula:
Still surrounded by Zona Pellucida
Still the size of the Zygote
What Happens on Day 4 or 5 after Fertilization?
Morula:
Enters Uterine Cavity
Nourished by Uterine Milk, a Glycogen-rich secretion from Endometrial Glands, in addition to stored nutrients from the Cytoplasm
What is Blastocyst?
Blastocoel:
At the 32-Cell Stage, the fluid now inside the Morula rearranges the Blastomeres into a large, fluid-filled Blastocyst Cavity
Blastocyst:
The mass is now called a Blastocyst
Still same size as original Zygote
As Blastocyst is formed:
Two different cell populations arose:
1- Embryoblast:
Inner cell mass
Will develop into the Embryo
2- Trophoblast:
Outer cell mass
Will develop into Outer Chorionic Sac surrounding the Fetus, and Fetal portion of Placenta
What is Implantation?
Blastocyst remains free in Uterine Cavity for about 2 days and then implants by attaching to the Endometrium at around 6 days after Fertilization
Implantation:
Usually occurs in either the posterior portion of the Fundus or the Body of the Uterus
The Inner Cell Mass orients toward the Endometrium
What happens after Implantation?
After Implantation:
The Endometrium is called Decidua
Decidua:
Separates from the Endometrium after the Fetus is delivered
Has different regions named based on their positions relative to the site of the implanted Blastocyst
1- Decidua Basalis
2- Decidua Capsularis
3- Decidua Parietalis
What happens on Day 8 after Fertilization?
About 8 days after Implantation:
a- Trophoblast develops into the:
1- Syncytiotrophoblast
2- Cytotrophoblast
b- Embryoblast develops into 2 layers:
1- Hypoblast (Primitive Endoderm)
2- Epiblast (Primitive Ectoderm)
Cells of these structure form a flat disc called the Bilaminar Embryonic Disc
Amniotic Cavity forms the Epiblast
What is Yolk Sac?
Also on 8th day:
Exocoelomic Membrane forms
Hypoblast and Exocoelomic Membrane together form the Yolk Sac
What is Amnion and Amniotic Cavity?
Amnion forms the roof of the Amniotic Cavity
Eventually, it surrounds the entire embryo and fills with Amniotic Fluid
What happens on Day 9 after Fertilization?
Lacunae:
Small spaces called Lacunae form
What happens on Day 12 after Fertilization?
Lacunae fuse to form Lacunar Networks
Extraembryonic Mesoderm develops:
1- The cells form a connective tissue layer around the Amnion and Yolk Sac
2- Large cavities develop that fuse and form the Extraembryonic Coelom
What is Chorion?
Chorion:
Extraembryonic Mesoderm and Trophoblast together form the Chorion
Chorion surrounds the embryo, and later the Fetus
Chorion:
Blocks antibody production by the mother
Promotes production of T Lymphocytes to suppress the immune response in the Uterus
Produces Human Chorionic Gonadotropin (hCG)
What is Gastrulation?
Gastrulation:
First major event of the 3rd week of development
The 2-layered embryonic disc transforms into a Trilaminar Embryonic Disc:
1- Ectoderm
2- Mesoderm
3- Endoderm
Gastrulation is associated with the rearrangement and migration of cells from the Epiblast
What are the Steps of Gastrulation?
1- Formation of the Primitive Streak:
Primitive Streak establishes the Head and Tail ends of the embryo
2- Cells of the Epiblast move inward below the Primitive Streak and undergo invagination
3- Following that, the 3 Germ Layers form:
Endoderm
Mesoderm
Ectoderm
What are the Structures produced by Endoderm?
1- Epithelial lining of GIT (except Oral Cavity and Anal Canal)
And Epithelium of its glands
2- Epithelial lining of Urinary Bladder, Gallbladder, and Liver
3- Epithelial lining of Pharynx, Eustachian Tubes (auditory tubes), Tonsils, Tympanic Cavity (middle ear), Larynx, Trachea, Bronchi, and Lungs
4- Epithelium of Thyroid Gland, Parathyroid Gland, Pancreas, and Thymus
5- Epithelial lining of Prostate and Bulbourethral Glands (Cowper’s Glands), Vagina, Vestibule, Urethra, and associated glands such as Greater Vestibular Glands (Bartholin’s Glands), and Lesser Vestibular Glands
6- Gametes (Sperm and Oocytes