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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

A

Gut tube

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
Q

When does the notochord form

Describe its formation

A

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
Q

What is the nucleus pulposus

A

Centre of IV disc

Remnant of notochord

27
Q

What is neurulation

A

Formation of spinal cord and brain begins

Neural plate → neural groove → neural tube

28
Q

How does the process of neurulation progress

What supplement is important in this process

A
  • 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
Q

What do the somites become & when

A

Bones and muscles

By end of WEEK 4

30
Q

Where does the mesoderm differentiate to

When does this happen

A

Lateral to notochord - week 3

Extends cranially and caudally

31
Q

What is the mesoderm divided into

A

SOMITES - 40 pairs of body segments by end of week 4

INTERMEDIATE MESODERM - lateral to somites

LATERAL PLATE - splits to form coelom (cavity)

32
Q

Name the divisions of the mesodermal lateral plate and where they are located

A
  • Somatic mesoderm - apposed to the ectoderm
  • Splanchnic mesoderm - apposed to the endoderm
  • Coelom in between will become the serous cavities of the ventral body cavity: peritoneal, pericardial, pleural
33
Q

What does the coelom (in between the somatic and splanchnic mesoderm) become

A

The serous cavities of the ventral body cavity

Peritoneal

Pericardial

Pleural

34
Q
A
35
Q

When does folding begin

A

Week 4

Lots of growth of ectoderm

36
Q

What happens at day 24

A

Embryo protrudes into amniotic cavity

37
Q

What happens at day 23 of embryonic development

A

Begins to fold

Lateral folds will join ventrally

Spaces appear in mesoderm

38
Q

Cylindrical human body plan @ day 28 VS cross section through abdomen of an adult

A
39
Q

Major derivatives of the embryonic germ layers

A
40
Q

When does the heart start pumping

A

29 days

embryo is 0.5cm in size

41
Q

2 major ways that developmental abnormalities can occur

A
  1. Congenital (inherited or genetic)
  2. Maternal derived abnormalities
42
Q

Trisomy 21

A

Down Syndrome - major chromosome abnormality

43
Q

Trisomy 18 (also 9, 13, 15)

A

Edwards Syndrome

44
Q

Possible reason for increased occurence of chromosomal abnormalities with age

A

The egg has been sitting “stagnant” for a long time

45
Q

Define absolute risk

A

The rate of occurence of an abnormal phenotype among individuals exposed to the agent (e.g. foetal alcohol syndrome)

46
Q

Relative risk

A

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
Q

Overview of embryonic development

A

GGE (33 decks)

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