Week 1: fertilization to implantation Flashcards
Name the two divisions of human developmental periods
1.Prenatal development
-Germinal period
-Embryological period
-Foetal period
2.Postnatal period
-Infancy
-Childhood
-Puberty
-Adulthood
How long is the germinal period?
It consists of the first 2 weeks
How long is the embryonic period?
The embryonic period is 6 weeks, from Week 3-8.
-Most visible development occurs
How long is the foetal period?
Week 9 till birth
-Differentiation and growth of tissues and organs occurs
-Rate of body growth increases
How many stages of embryologic development?
23 stages
Stage 1: Begins at fertilization
Stage 23: Embryonic development ends
When is the most critical stage of development? (Which trimester)
Critical stages of development occur during the first trimester.
How long does the process of fertilization take?
24hrs
_____________ secreted by the oocyte and follicular cells guide sperm cells to the oocyte for fertilization
Attractant chemical
When does the secondary oocyte undergo the second meiotic division?
After the sperm penetrates the oocyte
How is variation of the human species achieved
Achieved by the mingling of the maternal and paternal chromosomes
What helps the sperm pass through the corona radiata? (3)
-The sperm acrosome releases an enzyme called hyalurodinase, which causes dispersal of follicular cells that make up the corona radiata
-Tubal mucosal enzymes also helps with dispersal of follicular cells
-The tail of the sperm performs propelling movements that help with penetration.
What helps the sperm move through the zona pellucida?
-Acrosome releases esterase, acrosin, and neuraminidase
- Cause lysis of zona pellucida, forming a path for the sperm to enter the oocyte
What is the zona reaction?
-When the sperm penetrates the zona pellucida, the properties of the zona pellucida changes, thus hindering the other sperm cells from penetrating the oocyte. This is called the zona reaction.
What parts of the sperm enters the cytoplasm of the oocyte, and what parts are left behind?
-Sperm head and tail enter oocyte cytoplasm
-Sperm cell membrane and mitochondria remain behind
How is the female pronucleus formed?
-After penetration by the sperm, the 2ndary oocyte undergoes meiosis II to form a mature oocyte and a polar body.
The mature oocyte becomes the female pronucleus after the maternal chromosomes have decondensed.
How is the male pronucleus formed?
The sperm nucleus enlarges to form the male pronucleus, and the tail of the sperm degenerates.
True or false: You can’t distinguish the male pronucleus from the female one
TRUE
Male and female pronuclei are morphologically
indistinguishable
Describe zygote cleavage
Repeated mitotic divisions of zygote
* Occurs as zygote passes along uterine tube toward uterus
* Results in rapid increase in cell numbers - Blastomeres
* Blastomeres become smaller with each successive cleavage division
- Lie within zona pellucida
- Eventually change shape and become tightly packed (compaction)
When does zygote cleavage start?
- Begins around 30 hours after fertilization
How many blastomeres make up the morula? And when does it form?
12-32 blastomeres (compacted)
Forms around day 3 after fertilization, as it enters the uterus
When does blastocyst formation occur?
Around 4 days after fertilization
Describe blastocyst formation
Begins with formation of blastocystic cavity (fluid-filled space) inside morula
- Fluid passes from uterine cavity through zona pellucida. It separates blastomeres into two parts
What are the two parts of the blastocyst? Describe them.
1.Trophoblast
- Thin, outer cell layer (Forms wall of blastocyst)
- Gives rise to embryonic part of placenta.
2. Embryoblast
- Group of centrally located cells
- Gives rise to the embryo
How long does the blastocyst float in the uterus?
2 days
When does implantation occur?
day 6 post fertilization
Explain the process of iimplantation
Blastocyst attaches to endometrial epithelium
- Usually adjacent to embryonic pole
- Trophoblast immediately proliferates rapidly and forms two layers
Name the layers of the trophoblast?
Cytotrophoblast (inner layer)
2. Syncytiotrophoblast (outer layer)
- Multinucleated protoplasmic mass (no cell boundaries)
- Lies adjacent to embryoblast/ embryonic pole
- Extends into endometrium to embed blastocyst
The _______________ is formed by the blastomeres of the embryoblast, and lies on embryoblast surface facing blastocystic cavity
Hypoblast
Phases of fertilization
- Passage through corona radiata
2.Passage through zona pellucida - Fusion of cell membranes of oocyte and sperm
- Completion of the 2nd meiotic division
- Formation of male pronucleus
- Zygote
What does the trophoblast give rise to
Embryonic part of placenta
What is the endometrium adjacent to
Embryonic pole
