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Body log > Embryology > Flashcards

Embryology Flashcards

1
Q

How does one cell become a multicellular body?

A

Growth
Morphogenesis - development in form and structure
Differentiation - specialisation for function

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2
Q

What occurs in the pre embryonic period?

A

First 2 weeks of pregnancy
Cleavage - forms morula
Compaction - forms blastocyst with subprocess of cavitation
Implantation begins - once blastocyst forms implantation occurs

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3
Q

What is cleavage and when does it occur?

A

Cleavage which means splitting and it is the first mitotic division
Cleavage begins 30hrs after fertilisation and results in two blastsomeres of equal size
The mitotic division continues, the cells are smaller than the first mitotic division, every single cell is identical to the original zygote.

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4
Q

What is Totipotent and which cell is totipotent ?

A

The cell had capacity to become any cell type, the morula in the first week

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5
Q

What occurs in assisted reproductive techniques ?

A

Oocytes is fertilised in vitro and allowed to divide to the 4- or 8 cell stage
The morula is transferred to the uterus

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6
Q

What is PGD?

A

Pre-implantation genetic diagnosis, this is when a cell can be safely removed from the morula and tested for serious heritable disease before being transferred into the mother

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7
Q

What is compaction and when does it occur ?

A

Compaction is the first week and along side cavitation it forms the blastocyst and a cavity within the blastocyst.

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8
Q

What is the blastocyst

A

Blasto means primitive and undifferentiated
Cyst means fluid filled

The blastocyst contains the trophoblast (outer cell mass), embryoblast (inner cell mass).

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9
Q

What is embryoblast, trophoblast and blastocyst cavity?

A

Embryoblast is the inner cell mass - it is the group of cells that become the embryo and it is pluripotent

Trophoblast is the outer cell mass- it becomes the supporting cell, tissue and goes on to become the placenta and membranes that support normal human development.

Blastocyst cavity - cavity/space filled with small amount of tissue fluid

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10
Q

What type of cell is produced before compaction and after compaction?

A

Before compaction - totipotent :capacity to become any type of cell.

After compaction - pluripotent: capacity to become one of many cell types.

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11
Q

What is hatching and when does it occur?

A

Hatching occurs at week one is the point where the blastocyst hatches from the zona pellucida (thick glycoproteins shell which prevents further expansion and growth)

The blastocyst is now free to expand and interact with the uterine surface, as the cells of the blastocyst can now communicate with the cells of the uterine lining

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12
Q

How many cells does the conceptus have?

A

The blastocyst has approximately 100 cells and 8 makes the embryo and the rest develop into the fetal membrane.

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13
Q

What happens in fertilisation?

A

The ovary releases the oocyte and the oocyte travels through the Fallopian tube.

The sperm fertilises the oocyte at the ampulla and now the fertilised oocyte is known as a zygote.

Oocyte is viable for 12-24 hrs
Sperm 3-5 days

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14
Q

What occurs in week 2 and why is it known as the week of twos ?

A

Differentiation as Two distinct cellular layers occur from the inner and outer cell mass

The outer cell mass forms the
syncytiotrophoblast
Cytotrophoblast

The inner mass forms the bilaminar disk
Epiblast - produces the embryo
Hypoblast - produces the

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15
Q

By the end of the 2 week how does the structure look

A

Two cavities the yolk sac and the amniotic cavity
Suspended - connecting stalk
Supporting sac - chorionic cavity

Check pg 20 of lecture 1

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16
Q

When is implantation complete

A

Implantation is when the blastocyst breaches the uterine epithelium and the conceptus implants within the uterine stroma

Mechanical implantation is complete around day 9-10

Implantation isn’t absolutely complete until the 1st trimester

  • implantation establishes maternal blood flow within the placenta
  • established the basic structural unit of the materno-fetal exchange - the chorionic villus
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17
Q

What condition is linked to implantation defects ?

A

IUGR
Pre-eclampsia

Ectopic pregnancy
Placenta praevia

Last two are more important as the first two are complex

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18
Q

What is an ectopic pregnancy

A

Implantation at the site other than the uterine body (most commonly the Fallopian tube)

Can be peritoneal or ovarian

Can very quickly become life threatening emergency

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19
Q

What is Placenta Praevia?

A

Implantation in the lower uterine segment
Can cause haemorrhage in pregnancy
Requires C-section

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20
Q

What is the embryonic Pole and the Abembryonic pole?

A

Embryonic pole - rapid development of the syncytiotrophoblast

Abembryonic pole
The primitive yolk sac formed and the hyper blast is lining it

The yolk sac membrane is also in contact with the cytotrophoblast

These all occur at week 2 day 9

Check pg 29

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21
Q

What occurs at week 2 day 11?

A

The primitive yolk sac membrane is pushed away from cytotrophoblast layer by an acellular embryonic reticulum to create more space

The reticulum later converted to extrembryonic mesoderm by cell migration.

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22
Q

What occurs Week 2 day 12?

A

The synctiotrophoblast invades the maternal sinusoids (blood vessels) - this allows the conceptual to be bathed in the maternal blood.

Leading to the beginning of uteroplacental circulation

Lacuna becomes continuous with sinusoids

Uterine stoma prepares for support of the embryo

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23
Q

What occurs at week 2, Day 13

A

The formation of the secondary yolk sac (definitive yolk sac

Pinches off from primitive yolk sac

Check pg 32

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24
Q

How is the chorionic cavity formed and when ?

A

Spaces within the extraembryonic mesoderm merge to form the chorionic cavity

Week 2 day 14

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25
Q

What is the embryo and its cavities suspended by?

A

By the connecting stalk, this is the

Column if mesoderm
Future umbilical cord

26
Q

Why may bleeding occur at week 2, day 14?

A

Due to implantation, this is highly vascular and the capillaries within the endometrium are producing and soiling a lot of blood around the conceptus.

The point at which the conceptus penetrated the endometrium has not fully sealed off and can lead to a little bit of spotting and bleeding which can be confused for a menstrual cycle.

27
Q

What are the different cavities, coelom, sacs and spaces that occur in the pre-embryonic stage?

A

Blastocoele
• first cavity, formed as a result of compaction

Amniotic sac
• formed from spaces within the epiblast

Primitive yolk sac
• a.k.a exocoelomic cavity
• formed by hypoblast lining blastocoele

Secondary yolk sac
• a.k.a definitive yolk sac
• formed within primitive YS

Extraembryonic coelom
• a.k.a chorionic cavity
• formed from spaces within extraembryonic reticulum & mesoderm

28
Q

What is the percentage of zygotes lost in the first 2-3 weeks ?

What percentage of diagnosed pregnancies will miscarry?

What percentage of women suffer recurrent miscarriages?

A

approximately 50% of all zygotes are lost in the first 2 - 3 weeks

15% diagnosed pregnancies will miscarry

1% women suffer from recurrent miscarriage (miscarriage in 3
consecutive pregnancies)

29
Q

When does the embryonic period occur and what happens in this period?

A

Weeks 3-8

Period of the greatest change

All major structures and systems are formed

Greater risk of major congenital malformation (teratogenesis) due to environmental exposure or drug therapy

30
Q

What are some examples of teratogens?

A

Teratogenic viruses e.g. rubella

Ionising radiation is a mutagen and can interrupt DNA during the embryonic period, this is why women don’t have X-rays.

Drugs and chemicals- Thalidomide is the drug given to pregnant women that lead to to babies coming out with catastrophic congenital malformation of the limbs

31
Q

What are the effects of teratogenesis at the different stages?

A

Pre-embryonic period - lethal effects - the effect is loss of pregnancy.

Embryonic period - increased sensitivity to particular systems of the body for congenital malformations, it tends not to be Lethal.
Significant effects to particular systems.

Fetal period - the plain and the cardiovascular system are first vulnerable systems.
The limbs will be sensitive but destructive later on in the embryonic period.

After the embryonic period, risk of structural defects are low.
Except in the CNS, as it continues to grow, the CNS is sensitive throughout pregnancy.

32
Q

What are the key events/processes in early development?

A 
Fertilisation & Implantation 
Gastrulation 
Neurulation 
Segmentation 
Folding
33
Q

What is the bilaminar disk?

A

The disk in the blastocyst consisting of the epiblast and the hypoblast.

The epiblast is facing towards the amniotic sac

34
Q

What happened to the epiblast of the third week?

A

At the end of the second week the epiblast is a uniform disk

In the third week, on the dorsal surface of the epiblast the primitive streak shows up and indicates that development is proceeding and the process of gastrulation has started.

Pg 7-8 lecture 2

35
Q

What occurs during gastrulation?

A

It is simple the migration and invagination of cells

The cells of the epiblast layer increases in number and piles up towards the edges of the primitive streak.

Then push through the epithelium, squeezing through the intracellular junctions.

Then they push through and migrate across the embryonic disc.

Gastrulation occurs in week 3

36
Q

What happens to the hypoblast during gastrulation?

A

The hypoblast layer is responsible in establishing the yolk sac, as it’s done its job it is removed (displaced and degenerated)

37
Q

What are is the trilaminar disc ?

A

Disc formed during gastrulation from the bilaminar disc

Three layers are
Ectoderm - outside tissue
Mesoderm - middle tissue
Endoderm - inside tissue

38
Q

What is the derivatives of the ectoderm ?

A

Organs and structures that maintain contact with outside world

E.g. nervous system and epidermis

39
Q

What are the derivative of mesoderm ?

A

Supporting tissue

E.g muscle, cartilage, bone, vascular system (including heart and vessels)

40
Q

What are the derivatives of the endoderm?

A

Internal structures

E.g. epithelial lining of the GI tract, respiratory tract; parenchyma of glands

41
Q

What is situs inversus?

A

Complete mirror image viscera

Pg 14

42
Q

What is the primitive node and what does it do?

A

A node that is a part of the primitive streak.

It is responsible for ensuring that left and right asymmetry is established,

There are ciliates cells at the primitive node that wafts leftward signals to the left and right wards signals to the right.

Pg 16

43
Q

What occurs in neurulation ?

A
  • Notochord is found during neurulation
  • Notochord is found in the mesoderm
  • Notochord direct conversion of overlying ectoderm to neuroectoderm

Pg 20 lecture 2

44
Q

How is the neurectoderm form?

A
  • Ectoderm is the upper layer and the notochord is just beneath it and causes the ectoderm to thicken and become the neurectoderm
45
Q

How is the neural plate and neural tube produced?

A
  • The neural plate develops as it thickens and the edges of the disc curl and creates the neural tube
  • The edges rise up off the plane of the ectoderm
  • this is running the entire length of the ectoderm from head end to tail end
  • neural tube causes large physical presence along the midline of the embryonic body

Pg 21

46
Q

What happens to the mesoderm during neurulation ?

A

The mesoderm starts to organise itself into different zones which have different functions.

Intermediate mesoderm
Paraxial mesoderm - transformed into a structure called a simile
Somatic mesoderm - acts as the axis of embryo , somatic always means to do with body
Splanchnic mesoderm - acts as axis of embryo, splanchnic means to do with the viscera, so the organs of the body.

Pg 22

47
Q

What is the intraembryonic coelom?

A

A space between the somatic and splanchnic mesoderm inside of the embryo, it is a cavity into which the organs of the body can grow.

48
Q

What are somites ?

A
  • Somites are different to somatic, as they are embryonic structures.
  • Somites are severest derived from the paraxial mesoderm.
  • The embryonic body arranges the paraxial mesoderm into little segmental clumps of tissue.

There are 44 pairs present by the end of the 5th week and some disappear to leave just 31

Occurs in segmentation

Pg 24

49
Q

What do somites do?

A
  • They appear as regular blocks of mesoderm cells arranged around cavity.
  • followed by organised degeneration, the ventral wall of somite breaks down, leading to the formation of sclerotome
  • somites go on to form the basis of the musckeloskeletal system
  • further organisation of the dorsal portion forms the combined dermomyotome.
  • myotome proliferates and migrates and the dermatome disperses
50
Q

What is the meaning of Dermatome, myotome and scleratome ?

A

They are derivatives of somites

  • Dermatome - skin section - dermis
  • Myotome - muscle section - muscles
  • Scleratome - hard tissue section - bones
51
Q

What are the implications of segmentation?

A

Organisation of the mesoderm into somites gives rise to repeating structures such as :

  • Vertebrae
  • Ribs
  • intercostal muscle
  • spinal cord segments
52
Q

How many somites and spinal nerves are there?

A

31 segments - 31 pairs of spinal cords

Pg 30

53
Q

What does gastrulation ensure?

A
  • Gastrulation ensures that we can begin the process of the development of the neural tube (neurulation)
  • Also ensures that we begin development of our body segments (segmentation)
54
Q

What is the buccopharyngeal membrane and the cardio genie area and where are they found?

A
  • The Buccopharyngeal membrane is the future mouth it is part of the trilaminar embryonic disk at the head end of our embryo where the mouth is suppose to be.
  • The Cardiogenic area is the future mouth it’s also at the top of the buccopharyngeal membrane.

Check pg 33

55
Q

What is the problem with where the cardiogenic area is ?

A

The heart is not suppose to be cranial (superior/top) to the mouth.

  • the embryonic disc needs to change its configuration.
  • the change of the configuration is driven by the expansion of the neural tube and also the size of the developing segments.
56
Q

How does folding start ?

A
  • As the neural tube grows, it becomes massive and it is running down the midline.
  • it causes the edges of the disc to curve under at the head and the tail end.
57
Q

What are the two types of folding?

A
  • Cephalocaudal folding - head folding (cephalo) and tail folding (caudal)
  • in addition with lateral folding (folding at the edges.
  • a opening is seen in the middle of the yolk sac
  • after folding ectoderm is presented to the surface

Pg 34-35

58
Q

Understand the images

A

Pg 36-39

59
Q

What does folding accomplish?

A
  • Draws together the margins of the disk
  • creates a ventral body wall
  • Pulling amniotic membrane around the disk - so the embryo becomes suspended within the amniotic sac
  • pulling connecting stalk ventrally
60
Q

What occurs at the end of the 4th week?

A
  • The nervous system has started to form
  • Segments have appeared, assigning specific tasks to specific cells.
  • The embryo has folded, putting everything in the right place.

Body log (13 decks)

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