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Principles > Embryology > Flashcards

Embryology Flashcards

1
Q

What is the embryonic period?

A

First 8 weeks after fertilisation

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2
Q

What is the correct term for a baby from fertilisation to the end of Week 3?

A

Conceptus

Rarely used, so embryo also works

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3
Q

What is the correct term for a baby from Week 4 to Week 8?

A

Embryo

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4
Q

What is the correct term for a baby from Week 9 to Birth?

A

Foetus

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5
Q

What are the six phases of embryogenesis?

A 
Gametogenesis 
Fertilisation 
Cleavage 
Gastrulation 
Morphogenesis 
Organogenesis
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6
Q

What occurs during gametogenesis?

A

Germ cell formation
Oogenesis = Oocyte (egg)
Spermatogenesis = Spermatoza (sperm)

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7
Q

What occurs during fertilisation?

A

Formation of the zygote

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8
Q

What is cleavage?

A

Period of rapid cell division

Formation of morula then blastocyst inside the zone pellucida

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9
Q

What occurs during gastrulation?

A

Formation of the germ layers
Ectoderm, mesoderm and endoderm formed
Body axes established

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10
Q

What occurs during morphogenesis?

A 
Formation of the body plan
Embryonic folding (tube within a tube)
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11
Q

What occurs during organogenesis?

A

Primordial of all organ systems

All organs begin and continue to develop at the sam time

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12
Q

What occurs during the foetal period?

A

Growth and weight gain
Tissues mature and become functional
Overt sexual differentiation (at roughly 10 weeks)
Bone laid down, connections made in CNS

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13
Q

How does the zygote develop all the cells that make up the human body, despite using only a relatively small number of processes?

A

The processes interact with each other, producing more complex outcomes

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14
Q

What are the six Primary Processes?

A 
Cell Division 
Apoptosis 
Differentiation
Cell Attachment 
Induction 
Cell Migration
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15
Q

What occurs during cell division?

A

There is an increase in cell number

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16
Q

What occurs during apoptosis?

A

Programmed cell death
Allows cells to act as a scaffold for further growth before dying off when they are no longer needed (e.g. webbing between fingers)

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17
Q

What occurs differentiation?

A

Change in appearance/structure

Adoption of new functions (specialisation)

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18
Q

What occurs during cell attachment?

A

Physical/functional linkages between cells creating coherent assemblies (tissues)

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19
Q

What occurs during induction?

A

Ability of one cell type to cause another to differentiate

Some cells release proteins which react with the surrounding cells in a specific manner

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20
Q

What occurs during cell migration?

A

Movement form one location to another

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21
Q

What are the three Secondary Processes?

A

Axis formation/Polarity
Folding/Rotation
Changes in mass/dimension

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22
Q

Why is axis formation/polarity important?

A

Determines which way is up Cells need to know where they are in relation to each other and the embryo as a whole

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23
Q

Why is folding/rotation important?

A

Gives the embryo its 3D form

allows the formation of complex organ structures (e.g. heart, gut)

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24
Q

What changes in mass/dimension can occur?

A

Hypertrophy = Increase in dimension with no increase in cell number
Hyperplasia = Increase in cell number with an increase in dimension
Compaction =
Decrease in cell mass with decrease in dimension
OR
Increase in cel number with no increase in dimension

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25
Q

Which three factors control development?

A

Genetic
Epigenetic
Environment

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26
Q

How do genetics control development?

A

Through gene expression

Tightly regulated in time and space

27
Q

How do epigenetic control development?

A

Some genes show preferential expression for either the maternal or paternal copy

28
Q

How does environment control development?

A

Placenta will pass on anything from the mother to the embryo
(e.g. alcohol in mother may lead to foetal alcohol syndrome)

29
Q

What occurs during Phase 1 of fertilisation?

A

Sperm travels through a layer of corona radiata cells which pose no barrier
Binds in a human specific interaction with the zone pellucida glycoproteins

30
Q

What occurs during Phase 2 of fertilisation?

A

Acrosomal enzymes are released from the sperm head which break down the zone pellucida
The sperm digests its way through and into the egg

31
Q

What occurs during Phase 3 of fertilisation?

A

Egg and sperm plasma membranes fuse, and the nucleus of the sperm is released into the oocyte

32
Q

What two things does sperm entry into the oocyte trigger?

A

Completion of Meiosis II

Release of cortical granules by the oocyte, causing zone pellucida hardening and prevents further sperm from entering

33
Q

Where does fertilisation occur?

A

Ampulla

34
Q

What specifically happens to the zygote during cleavage?

A

Zygote undergoes a series of mitotic divisions which subdivide the fertilised egg into many smaller daughter cells called blastomeres

35
Q

Up to what stage are blastomeres thought to be totipotent?

A

Up to the 8 cell stage

36
Q

Why does compaction of the zygote occur during cleavage?

A

The cells are rapidly dividing in an enclosed space (due to the zone pellucida)

37
Q

What are the four parts of the blastocyst and what do they give rise to?

A

Zona pellucida = Protective outer shell which degenerates
Trophoblast = Placenta
Inner cell mass (embryoblast) = Embryo proper
Blastocyst cavity

38
Q

At which point does the blastocyst generally attach to the uterine cavity?

A

6 days

39
Q

What is the zone pellucida’s role in blastocyst travel along the uterine tract?

A

Prevents attachment to the walls
Provides protection
Holds everything together

40
Q

At what stage does the zoo pellucida break down?

A

After sperm implantation in the oocyte
Generally occurs once the blastocyst reaches the uterus
Allows the blastocyst to attach to the uterine cavity

41
Q

Where are the normal sites for blastocyst implantation?

A

Middle or upper dorsal uterine wall

42
Q

What is an eptopic pregnancy?

A

when the blastocyst implants in a region which is not designed to support growth
When a blastocyst implants, it will send out signals for a blood supply; in abnormal sites, there is not the muscle to support this
May result in rupturing of cells and sever blood loss if undiagnosed

43
Q

Where are the abnormal sites for blastocyst implantation?

A 
Ovary 
Ampulla 
Uterine tube 
Lower part of the uterus 
Cervix or peritoneum
44
Q

How does blastocyst implantation occur (6 days)?

A

Trophoblast sends out signal to the uterine epithelium and begins to work its way in

45
Q

How does blastocyst implantation occur (7.5 days)?

A

Trophoblast basically turns into a syncytiotrophoblast
The leading edge acts as a membrane for this cell, and the cells inside will loose their individual membranes
The embryo blast will develop in two: epiblast and hydroblast

46
Q

How does blastocyst implantation occur (9 days)?

A

Complete
A coagulation plug forms, enclosing the embryo within the uterine wall
Syncytiotrophoblast covers the entire embryo
Production of cells occurs at the hypobast end, spreading out to form a layer of primary yolk sac around the cavity

47
Q

What is the appearance of the implanted embryo (9-12 days)?

A

The syncytiotrophoblast has extended and by erosion contacts maternal blood supply
The amniotic cavity is present above the bilayers embryonic disc and the definitive yolk sac below
The chorionic cavity develops and encircles the entire embryo

48
Q

What would you see in the dorsal view of the embryo at week 2?

A

Oropharyngeal membrane = Site of the future mouth

Primitive streak = Driving force behind gastrulation

49
Q

How do the three layers form during gastrulation?

A

Movement of epiblast cells through the primitive streak
Hypoblast is replaced to become definitive endoderm
Intraembryonic mesoderm layer formed between endoderm and epiblast
Epiblast becomes ectoderm

50
Q

What is the fate of ectoderm?

A

Epidermis of skin

Nervous system

51
Q

What is the fate of the mesoderm?

A

Becomes sub divided into three regions either side of the notochord:
Paraxial = Axial skeleton, parts of dermis, voluntary muscle
Intermediate = Urogenital system
Lateral Plate = Somatic part becomes lining of body wall, most of dermis and parts of limbs. Visceral part becomes mesothelial covering of organs and the cardiovascular system

52
Q

What is the fate of the endoderm?

A

Lining of gut tube

Lining of respiratory tract

53
Q

What occurs during lateral folding?

A

Converts open coelom into a closed cavity, creating thoracic and abdominal cavities and closing fore, hind, then mid gut

54
Q

What occurs during cranial folding?

A

Forms the foregut ad defines the thoracic cavities

Developing heart tube displace into thoracic cavity

55
Q

What occurs during caudal folding?

A

Cloacal membrane and connecting stalk are displaces ventrally alongside the neck of the yolk sac, forming the hindgut, anus and umbilical cord

56
Q

What occurs during the third month of foetal development?

A

Eyes and ears position and face becomes more human looking
Limbs lengthen
Primary ossification centres in long bones and skulls
Sex can be determined by external genitalia

57
Q

What occurs during the fourth and fifth months of foetal development?

A

Rapid increase in length

58
Q

What occurs between the six month of foetal development and birth?

A

Rapid increase in weight

59
Q

What are the main causes of congenital abnormalities?

A

Unknown
Genetic factors
Environmental (inc. infectious agnates, radiation, deficiencies, maternal disease)
Multifactorial

60
Q

When is the embryo most at risk of defects forming?

A

Weeks 1 -2 = Loss
Weeks 3 -7 = Major abnormalities
Weeks 8 - 36 = Functional and minor abnormalities
Generally, specific structures are at most risk when they are developing - the timing of this varies from structure to structure

61
Q

What is an Atrial Septal Defect, and what are some examples?

A

Defects of one or both of the atrial septae
Excessive Resorption of Septum Primum = Opening is too large for septum scandium to fully cover
Absent Septum Secundum = Communication between the two atria is not blocked after birth
Probe Patent Formamen Ovale = Septum primum and secundum fail to fuse, but mixing of blood is prevented by pressure difference (increased RA pressure can result in blood mixing)

62
Q

What two things can cause Ventricular Septal Defects?

A

Muscular defect = most common, least severe

Membranous defect = relatively uncommon, very severe

63
Q

What is Transposition of the Great Vessels?

A

Aorta exits right ventricle
Pulmonary trunk exits left ventricle
Deoxygenated blood pumped around the body
Due to failure of the septum of the outflow tract to spiral as it grows

64
Q

What are the four component of the Tetralogy of Fallot?

A

Pulmonary stenosis
Hypertrophy of right ventricle
VSD
Over-riding aorta

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