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Scientific Basis of Midwifery > Embryology > Flashcards

Flashcards in Embryology Deck (50)
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How long does the embryonic period last?

3-8 weeks


Define proliferation

The rapid growth and production of cells


Define differentiation

The process of developing and changing to become specialised


Define specialisation

The adaptation of a cell to carry out a particular function


Define apoptosis

Cell death as a normal and controlled process of cell growth and development


Define morphogenesis

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?

1. Cytotrophoblast
2. Syncytiotrophoblast


Describe the cytotrophoblast

- Inner
- 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

- Outer
- 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?

Cell migration


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


Describe neurulation

- 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


What are the 3 layers of the trilaminar disc?

1. Ectoderm
2. Mesoderm
3. Endoderm