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BRS - Development & Ageing > Early Development > Flashcards

Early Development Flashcards

1
Q

What is fertilisation/conceptual age?

A

The time from the point of fertilisation

Assumed to be one day from the last ovulation

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2
Q

What is gestational age?

A

The time from the beginning of the last menstrual period
Fertilisation age +14 days
Can be measured by comparing embryo size charts

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3
Q

What is carnegie stage?

A

This is a measure of 23 stages of embryo development by comparing embryo features (i.e. first heart beat)

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4
Q

State are the 3 stages in embryo development

A

Embryogenic
Embryonic
Fetal

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5
Q

What occurs during the embryogenic stage (give time)

A

2 weeks post fertilisation
This is the establishment of the early embryo
There are 2 cell populations: pluripotent embryonic cells and extraembryonic cells

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6
Q

What is occurs during the embryonic stage (give time)?

A

2-8 weeks after fertilisation

The establishment of the 3 germ layers and the body plan

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7
Q

What occurs during the fetal stage and when?

A

Trimesters 2+3
The formation of organ systems
Migration of organs to final destination
Acquisition of fetal viability

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8
Q

Outline the cell stages of development (include cell numbers)

A 
Ovulated oocyte - 1 cell
Fertilised zygote - 1 cell
Embryo cleavage - 2-8 cells
Morula - 16 cells
Blastocyst - 200-300 cells
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9
Q

What is the maternal to zygotic transition?

A

A shift away from maternal to zygotic RNA at the 4-8 cell stage

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10
Q

What occurs during compaction?

A

Outer cells become compressed and more wedge shaped as the inner cells grow and compress against the zona pellucida
2 cell populations form - inner and outer

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11
Q

Which 2 cell jucntions form during contraction?

A

Desmosomes and tight junctions

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12
Q

Which type of stem cells make up the inner cell mass?

A

Pluripotent stem cells - contribute to final organism

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13
Q

What is contained within the blastoceal?

A

Na+ ions which drive water to follow in

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14
Q

What is the role of the zona pellucida?

A

Protects early embryo

Prevents polyspermy

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15
Q

What occurs during blastocyst hatching?

A

There are cellular contractions and enzymatic digestions - allow embryo to continue to grow

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16
Q

Briefly outline the role and formation of the syncitotrophoblast

A

It arises from the trophectoderm
The fusion of trophectoderm cells froms the syncitiotrophoblast
It invades the maternal endometrium and breaks capillaries to establish a blood supply

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17
Q

What is the role of the cytotrophoblast?

A

They provide a source of syncitiotrophoblast cells

18
Q

What 2 things does the inner cell mass divide into?

A

Epiblast - form the fetal tissue

Hypobalst - forms the yolk sac

19
Q

Which hormone is released from the syncitiotrophoblast?

A

beta hCG

20
Q

Describe bilaminar disc formation?

A

Amniotic cavity separates the cells of the epiblast

The upper layer forms the amnion and cells of epiblast and hypoblast are separated by amniotic cavity

21
Q

What is gastrulation?

A

The formation of the 3 germ layers and establishment of the body axis

22
Q

What occurs during gastrulation?

A

Primitive streak form through the bilaminar disc
Cells from the epiblast move through the streak and it becomes a pit
This forms the definitive endoderm and hypoblast is displaced
Cells in the middle and top become the mesoderm and ectoderm respectively

23
Q

Which organs arise from the endoderm?

A 
Liver
Pancreas
Lung 
GI tract
Thyroid
24
Q

What arises from the ectoderm?

A

Tooth enamel
Skin epithelia
CNS
Neural crest

25
Q

What arises from the mesoderm?

A 
Blood
Muscles
Gonads
Adrenal cortex
Kidneys
Bone and cartilage
26
Q

What is the notochord and where does it develop?

A

It is a rod like structure made from cartilage like cells.
It is the organising centre for neurulation
Develops on the ectoderm

27
Q

Outline what occurs during neurulation?

A

Notochord releases signals which cause the ectoderm to invaginate, forming the neural crest. Neural ridges form and they move over the neural grove and eventually fuse

28
Q

What cells are found in the neural folds?

A

Neural crest cells which eventually migrate from the folds

29
Q

When do the head and tail ends close?

A

Head closes at d23

Tail closes at d 27

30
Q

What 2 conditions arise due to failure of the neural plates to fuse?

A

Anencephaly - failure to close at the head end (born without brain and most of skull)
Spinal bifida - failure to close at the tail end (lower spine)

31
Q

What do neural crest cells migrate into?

A 
Cranial NC
Cardiac NC
Sacral NC
Vagral NC
Trunk NC
32
Q

What defects can arise due to failure to migrate?

A

Deafness
Pigmentation disorders
Cardiac and facial defects
Gut innervation failure

33
Q

What are somites and what is somitogenesis

A

Somitogenesis is the production of somites

Somites are paired blocks of mesoderm

34
Q

What is rate of budding in humans?

A

1/90mins

35
Q

What type of development measuring can somite number be used in?

A

Carnegie staging

36
Q

What 2 types of tissue do somites form initially?

A

Sclerotome - vertebrae and rib cartilage

Dermomyotome - dematome is skin, fat and connective tissue; myotome is muscle

37
Q

What 2 types of folding occur in primitve gut formation?

A

Ventral folding - head and tail end curl together

Lateral folding - the two sides of the embryo roll

38
Q

What is the result of this folding?

A

Pinches off part of the yolk sac which forms the fore/mid/hindgut

39
Q

What are the derivatives of the primitive gut?

A

Foregut - upper duodenum, pancreas, liver, gall bladder, stomach, esophagus
Midgut - lower duodenum, rest of SI, ascending colon, 2/3 of transverse colon
Hindgut - 1/3 of transverse colon, descending colon, rectum and upper anal canal

40
Q

Describe the derivation of the heart

A

From the mesoderm

Heartbeat detectable from 6 weeks

41
Q

Describe the derivation of the lungs

A

Arises from the endoderm - lung bud

Lung bud progressively splits into 2 from 4 weeks

42
Q

Describe the derivation of the gonads

A

Arises from the mesoderm as bipotential - not committed to male or female - forms gonadal ridge
XY embryos - SRY gene triggers sertoli cells to develop into testes and leydig cells from
XX embryos - absence of SRY gene causes granulosa formation and ovary formation - reinforced by FOXL2 gene

BRS - Development & Ageing (3 decks)

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