Flashcards in Embryology Deck (50)
How long does the embryonic period last?
The rapid growth and production of cells
The process of developing and changing to become specialised
The adaptation of a cell to carry out a particular function
Cell death as a normal and controlled process of cell growth and development
The biological process that causes a cell to develop its shape
Name 2 conditions that arise from ineffective proliferation/ apoptosis
Excessive proliferation = Polydactyly
Failed apoptosis = Syndactyly
Describe the process of fertilisation
Sperm cell --> Corona radiata of egg --> Acrosome releases enzymes --> Sperm cell penetrates zona pellucida --> Sperm cell's membrane fuses with egg cell's membrane
Outline what occurs just after fertilisation takes place
- Oocyte completes meiosis II
- Cumulus oophorus cells surround the oocyte
- Theca cells form the corpus luteum
- Corpus luteum secretes progesterone which prepares and sustains the uterine wall for implantation
Describe the fertilised ovum
- 12-24 hours after fertilisation
- Sperm must get through corona radiate and zona pellucida
- Zona becomes specialised once a sperm has traversed it, blocking others from entering
- Oocyte completes meiosis II and 2 pronuclei form
- Male and female pronuclei fuse to form zygote (2n)
What are the stages of embryonic development?
1. Fertilised ovum
2. Cleavage (30 hrs - day 3, mitosis increases cell number)
3. Morula (day 3-4, solid ball of cells)
4. Blastocyst (day 5, trophoblast, blastocoel and inner cell mass form)
5. Implantation (blastocystic stage, day 7-8, syncytiotrophoblast secretes enzymes that allow implantation)
6. Gastrulation (end of week 2, primary germ layers form)
What is a blastocoel?
Cavity in blastocyst
When are the discs formed?
Week 2 = Bilaminar disc
Week 3 = Trilaminar disc
How does the bilaminar disc form?
Differentiation of the embryoblast (inner cell mass)
What are the 2 parts of the bilaminar disc?
Describe the formation of the epiblast
- Cells cavitate to form the amnion
- Cells from the epiblast will also eventually form the body of the embryo
- Located above amniotic cavity
Describe the formation of the hypoblast
- Future cranial region
- Cells of hypoblast migrate along inner surface of cytotrophoblast and form primary yolk sac
- Primary yolk sac reduces in size and becomes secondary yolk sac
- Transfers nutrients between foetus and mother
What is the yolk sac?
Origin of blood cells and vessels
What are the 2 types of trophoblast?
Describe the cytotrophoblast
- Divides mitotically into syncytiotrophoblast to form primary chorionic villi
- Cells from these villi can be removed for chorionic villus sampling
- Have membranes
Describe the syncytiotrophoblast
- Acellular (no membranes or mitosis)
- Produces hCG
- Invades endometrium
- As it comes in contact with blood vessels, it forms lacunae which fuse to form lacunar networks
- Blood flows in and out of these networks, exchanging nutrients and waste products with the foetus
What are lacunae?
Spaces filled with maternal blood
What is gastrulation?
A phase in the early stages of embryonic development in which the single-layered blastula becomes a multi-layered gastrula
What is a primitive streak?
- Raised groove on dorsal surface
- Region of cell migration from the epiblast layer, forming 2 germ cell layers (endoderm and mesoderm)
What causes the formation of the trilaminar disc?
What are the 2 cavities in the gastrula?
1. Yolk sac
2. Amniotic cavity
What is the notochord?
- A flexible rod similar to cartilage
- Defining structure in all chordate embryos
- Neural tube (beginning of CNS) and neural crest (beginning of PNS) development
- Neural tube closure which begins at week 3 and ends in week 4
- Folic acid can be used as 'therapy' to prevent occurrence of neural tube defects
Name 3 other developments that occur during gastrulation
- Primordial mouth and anus
- Primordial cardiovascular system
- Secondary and tertiary chorionic villi