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GGE > Embryos - Embryology Basics > Flashcards

Embryos - Embryology Basics Flashcards

1
Q

What is the average foetal age

A

38 weeks from conception to birth is the average foetal age

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2
Q

What is the gestational age

A

Last menstrual period (2 weeks before ovulation) to birth = 40 weeks

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3
Q

What happens in the embryonic period

A

1st 8 weeks - all major organs are formed

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4
Q

What is the foetal period

A

The remaining 30 weeks - organs grow larger and become more complex

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5
Q

Fertilisation to implantation

A
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6
Q

Define ovulation

Where does the egg then travel

A
  • Egg released into the peritoneal cavity
  • Travels down fallopian tube in which fertilisation occurs
  • At conception in fallopian tube, maternal and paternal genetic material join to form a human life - zygote
  • Cell division occurs while travelling down the tube and into uterus
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7
Q

What happens to the zygote as it moves down the tube towards the uterus

When does this process occur

A

Divides repeatedly as it moves down the tube towards the uterus (cleavage)

WEEK 1 POST-CONCEPTION

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8
Q

Name the daughter cells of the zygote

A

Blastomeres

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9
Q

Define morula

A

The solid cluster of 12-16 blastomeres at about 72 hours

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10
Q

What happens on day 4 post-conception

A

60 cell morula enters uterus, taking up fluid & becoming BLASTOCYST

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11
Q

Describe the 2 distinct types of cells that make up the blastocyst

A

INNER CELL MASS - forms the embryo

TROPHOBLAST - layer of cells sorrounding the cavity which helps form the placenta

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12
Q

What happens to the blastocyst after conception

A

Floats for about 3 days

Implantation on about day 6 post-conception

  • trophoblast eordes uterine wall
  • takes 1 week to complete
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13
Q

How are monozygotic (identical) twins formed - at blastocyst level

A

If inner cell mass of a single blastocyst divides in the first week

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14
Q

Describe the events of week 2

A
  1. Inner cell mass divides into epiblast and hypoblast
  2. 2 fluid filled sacs form

Amniotic sac from epiblast

Yolk sac from hypoblast

  1. Bilaminae embryonic disc = area of contact - gives rise to the whole body

** only 2 layers of cells in week 2

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15
Q

What does the epiblast give rise to

A

Amniotic sac

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16
Q

What does the hypoblast give rise to

A

Yolk sac

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17
Q

Describe the events of week 3

A
  • Bilaminar disc becomes a trilaminar disc
  • 3 primary germ layers - all body tissues develop from these
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18
Q

Ectoderm

A

Skin

Nervous system

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19
Q

Mesoderm

20
Q

Endoderm

A

Connective tissue

21
Q

How are the 3 germ layers formed

A
  1. Primitive streak (groove) on dorsal surface of epiblast
  2. Gastrulation - invagination of epiblast cells
  3. Days 14-15 - they replace hypoblast, becoming the endoderm
  4. Day 16 - mesoderm formed in between
  5. Epiblast cells remain on surface, forming the ectoderm
22
Q

What do the ectoderm and endoderm have in common

A

Epithelial tissues

23
Q

What sort of tissue is the mesoderm

A

Mesenchyme tissue

24
Q

Describe mesenchyme cells

A

Star shaped - do not attach to one another => migrate freely

25
When does the notochord form Describe its formation
days 16-18 Primitive node epiblast cells invaginate and migrate anteriorly with some endoderm cells Rod defining the body axis is formed Future sight of the vertebral column
26
What is the nucleus pulposus
Centre of IV disc Remnant of notochord
27
What is neurulation
Formation of spinal cord and brain begins Neural plate → neural groove → neural tube
28
How does the process of neurulation progress What supplement is important in this process
* Closure of neural tube begins at the end of wk 3 and complete by end of wk 4 * Folic acid is important for this step * Extends cranially - brain, and caudally - spinal cord * Neural crest, lateral ectodermal cells, pulled along and form sensory cells and other structures
29
What do the somites become & when
Bones and muscles By end of WEEK 4
30
Where does the mesoderm differentiate to When does this happen
Lateral to notochord - week 3 Extends cranially and caudally
31
What is the mesoderm divided into
SOMITES - 40 pairs of body segments by end of **week 4** INTERMEDIATE MESODERM - lateral to somites LATERAL PLATE - splits to form coelom (cavity)
32
Name the divisions of the mesodermal lateral plate and where they are located
* Somatic mesoderm - apposed to the ectoderm * Spla**_n_**chnic mesoderm - apposed to the e**_n_**doderm * Coelom in between will become the serous cavities of the ventral body cavity: peritoneal, pericardial, pleural
33
What does the coelom (in between the somatic and splanchnic mesoderm) become
The serous cavities of the ventral body cavity Peritoneal Pericardial Pleural
34
35
When does folding begin
Week 4 Lots of growth of ectoderm
36
What happens at day 24
Embryo protrudes into amniotic cavity
37
What happens at day 23 of embryonic development
Begins to fold Lateral folds will join ventrally Spaces appear in mesoderm
38
Cylindrical human body plan @ day 28 VS cross section through abdomen of an adult
39
Major derivatives of the embryonic germ layers
40
When does the heart start pumping
29 days embryo is 0.5cm in size
41
2 major ways that developmental abnormalities can occur
1. Congenital (inherited or genetic) 2. Maternal derived abnormalities
42
Trisomy 21
Down Syndrome - major chromosome abnormality
43
Trisomy 18 (also 9, 13, 15)
Edwards Syndrome
44
Possible reason for increased occurence of chromosomal abnormalities with age
The egg has been sitting "stagnant" for a long time
45
Define absolute risk
The rate of occurence of an abnormal phenotype among individuals exposed to the agent (e.g. foetal alcohol syndrome)
46
Relative risk
Ratio of the rate of the condition among the exposed and the non-exposed (e.g. smokers risk of having a low birth weight baby compared to non-smokers) \* A high relative risk may indicate a low absolute risk if the condition is rare
47
Overview of embryonic development

GGE (33 decks)

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