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Flashcards in Embryology development Deck (20):
1

What is involved in fertilisation?

-Fusion of the oogonium ( 3 polar bodies and 1 ovum) and the spermatogonium (4 sperm bodies)
-Sperm carries through pronucleus. Leaves behind organelles
-Ovum released by the ovary. Fertilised in fallopian tube
-ZYGOTE carried to uterine cavity by cilia

2

What happens in week 1

1-Zygote multiplies by mitosis to form MORULA
2-MORULA becomes BLASTULA
3- BLASTULA made up of inner cell mass, blastocystic cavity, TROPHOBLAST

3

What happens in week 2

1- blastula reaches endocrine cavity
2-TROPHOCYTE become CHORION
3-inner cell mass become flattened- BILATERAL DISC: EPIBLAST and HYPOBLAST.
4-Epiblast separated AMNIOTIC CAVITY
5-Hypoblast separates YOLK SAC

4

What is It and the function of the Chorion

Rearrangement of trophocyte
Mushy-no visible cell membrane
finger like projections

Function:
-implantation
-forms part of placenta
-release of HMC hormone-used to detect pregnancy

5

Differences between fraternal and identical twins

fraternal-dizygote:
-2 sperm-2 ovum
-usually females release 1 ovum per month-in some cases more than 1

Identical-monozygote:
-1 ovum-1 sperm
-division occurs at a later date
- can share placenta and amniotic cavity

6

Role and appearance of the placenta

-develops in 18-24 weeks
-smooth upper foetal surface, contains umbellical cord
-rough maternal surface
role:
-nutrition
-supply of gases + removal of waste
-immune

7

What happens in week 3 - general

1-Primitive streak forms from Epiblast
cells from primitive streak move in between epiblast and hypoblast
Forms axis of embryo.
2-Formation of trilaminar disc- specialised cells

8

What happens to the Ectoderm

1-Notochord formation
Dipping of cells from ectoderm-forms solid tube
2- Notochord releases chemicals which lead to formation of NEURAL TUBE

9

What happens when STI occurs

Cilia function impaired.
Zygote cannot be carried to endocrine cavity
Ectopian pregnancy

10

Where does the foetus get mitochondrial DNA from?

All organelles inherited from mother so all mDNA from mum- including possible diseases.

11

What happens to the mesoderm?

It separates into 3 layers:
-Lateral- forms the peritoneum, pleura and body cavities
-Intermediate- forms the urogenital system
-Paraxial

Paraxial segments into somites- innervated by a pair of spinal nerves.
Somites then develop into:
-Dermatomes-move under the epidermis to form the dermis
-Myotomes- form muscles
-Sclerotomes: form bones and vertebrae

12

What happens in weeks 4-8?

-Heart starts beating on day 24
-Gut formation from the endometrium
-Tube folding
-43 pair of somites
-Urogenital system

13

What is teratogenesis and what does it involve?

Abnormalities during development which can be due to:
ENVIRONMENTAL: e.g. tobacco, drugs, infections
GENETIC: e.g. chromosome number/structure

14

When and what can increase the risk of teratogenesis?
How can it be prevented?

When:
week 1-2: very high risk-will usually end in death
week 3-8 : highest sensitivity to teratogens
Week 9-32: risk decreases
what?
-Dosage
-Exposure during critical periods
-genetic conditions of the embryo
Tests:
-Prenatal:
blood
ultrasound
invasive
-Postnatal:
hearing
breathing

15

What does the gut give rise to (general)

Gut divides into foregut, mid gut and hindgut.
Ventral section of the foregut gives rise to the Lung buds and trachea in week 4.

16

How do the trachea, oesophagus and lung buds develop

-Starts off as laryngotracheal grove or Diverticulum
-Become surrounded in mesoderm
-Lung buds enlarged
-Tracheooesophageal septum separates trachea anteriorly to oesophagus

17

How do the pleura develop

-Splanchic mesoderm gives rise to visceral pleura
-Somatic mesoderm gives rise to parietal pleura
-Pleuroperitoneal canal present in space between them
-Pleuropericardial folds separate heart from lungs

18

How does the diaphragm develop

Shelf depends which is made up of 4 components:
-Septum transversum- central tendon
-Pleuroperitoneal membrane-primitive diaphragm
-Dorsal mesentery of the oesophagus- crura + median portion
-muscular ingrowth of lateral bodies-peripheral part

19

Congenital abnormalities

Fistula: A passage abnormal or surgical which forms between a hollow organ and a body surface or between 2 organs e.g. tracheooesophageal
Atresia: A condition where a passage becomes shut
RDS: Inadequate production of surfactant- detergent used to decrease surface tension
Pulmonary hypoplasia: incomplete development of lungs
Incomplete closure of the diaphragm
Hernia: protrusion of an organ through a muscle which is supposed to contain it

20

Morphogenesis of lung buds

Embryonic
Pseudoglandular ( 5-17 weeks): development of major airways, acinus, bronchial tree
Canalicular (16-26 weeks): specialisation of epithelium-cuboidal
Saccular (24-38 weeks): release of surfactant, alveolar separation
Alveolar (36-2-3years): further separation + increase in size of alveoli. 200-600 mill alveoli by 8 years.