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Development And Ageing Flashcards

1
Q

Describe maternal to zygotic transition

A

Up until 4-8 cell stage, the embryo is fully dependent on the maternal mRNA and proteins for the first few divisions As its genome hasnt been transcribed yet
After the 4-8 cell stage, the embryo needs to become dependent on its own dna
It does this by doing 3 things
- zygomatic genome activation (transcrption of embryonic genes)
-increase protein synthesis
-organelle (mitochondria, Golgi) maturation

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2
Q

Fertilization age vs Gestational age

A

Fertilization age: measured from fertilization date (assumed to be ovulation day + 1)
Gestational age: measured from start of LMP (last menstrual period)

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3
Q

What are the carnegie stages

A

23 stages of embryonic develooment based on embryonic features not time

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4
Q

Describe the 3 main stages of emebyo fetal development

A

1) embryogenic stage: 14/16 days post fertilization, determination of 2 population cell types: pluripotent embryonic cells which contribute to the embryo, extra embryonic cells which contribute to extra embryonic structures eg placenta
2) embryonic stage: 16-50 days post fertilisation, establishment of 3 germ layers and differentiation of cell types, establishment of body plan
3) fetal stage: 50-270 days post fertlization, migration of organ systems to final location, extensive growth and acquisitionof fetal viability (survival outside womb)

Embryogenic and embryonic are in first trimester
Fetal is second and third trimester

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5
Q

Describe the formation of the 2 main cell types in embryonic development

A

At the 8 cell stage (around day 3) the outer cells begin to press against the zona pellucida and they change shaoe from rounded spheres to wedged
The inner cells stay rounded spheres
By day 5 there are two distinct groups of cells - the outer and different,y shaped cells (trophoblast - forms extra embryonic structures) and the inner cells (inner cell mass- forms embryo)
There is also the blastoceol

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6
Q

How is the blastoceol formed

A

Trophectoderm pumps Na+ ions into the cavity, forming the blastoceol by osmotic action

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7
Q

What needs to happen in order for implantation to occur

A

The blastocyst needs to escape the zona pelucida which it does by enxymatic degradation and cellular contraction (“hatching”, day 5/6)

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8
Q

Describe the process of implantation into the urterine surface

A

Day 7-9
Some Trophoblast cells fuse to synciotiotrophoblast which provides interface between mother and foetus
The rest don’t fuse and are called cytotrophoblasts
The inner cell mass splits into hypoblast (forms yolk sac, extra embryonic structure) and epiblast (forms embryo)

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9
Q

What does the syncitiotrophoblast secrete

A

Hcg

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10
Q

What is the bilaminar embryonic disc

A

A disc formed of 2 layers of cells: one layer of epiblast cells, one layer of hypoblast cells
The disc is sandwiched between the blastoceol cavity and the amniotic cavity

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11
Q

What can failure of nerual tube closure cause

A

Failure to close at head end: Anencephaly

Failure to close at tail end: Spina bifida

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12
Q

What is the allantois

A

An outgrowth of the yolk sac
Grows along the connective stalk frommthe embryo to the chorion
Becomes vascularised and coated in mesoderm, forming umbilical cord

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13
Q

Describe how the amniotic sac is formed

A

The amnion expands as it becomes filled with fluid, until it comes in contact woth the chorion
They then fuse to form the amniotic sac which has aminion as inner surface and chorion as outer surface

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14
Q

2 functions of cytotrophoblast

A

Proliferates to provide cells for syncitiotrophoblast
Has finger like projections which form primary chorionic villi - push throgh syncitiotrophoblast into maternal endometrium

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15
Q

3 steps of chorionic villi formation

A

Primary: outgrowth of cytotrophoblast forming finger like projections, and the branching of these projections
Secondary: growth of fetal mesoderm into the villi
Tertiary: growth of umbilical artery and vein into the villi mesoderm, providing vasculature

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16
Q

Describe the structure of the vessels in terminal chorionic villi

A

Vessels are dilated and knotted which slows the blood flow, allowing fir more time for exchange with maternal blood
Whole structure is coated by trophoblast layer which decreases in thickness over the pregnancy (reduced diffusion distance)

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17
Q

Describe the blood flow to the mother’s uterine wall

A

Uterine artery branches to from arcuate arteries which lie in the mesoderm of the uterine surface
Arcuate arteries form radial arteries which penetrate the mesoderm deeper
These branch into basal arteries
Basal arteries branch into spiral arteries during menstrual endometrial thickening, which penetrate the endoderm

Uterine, arcuate, radial, basal, spiral
Under All Rocks Bats Sleep

(Only basal and spiral are in endoderm, arcuate and radial are in mesoderm)

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18
Q

Describe spiral artery remodelling

A

Extra villus trophoblast cells (EVT) which line the villi that project into the placenta invade the maternal mesoderm and coat the inside of the spural arteries, becoming endo vascular EVT
They break down the smooth muscle and endometrium of the arteries , unspiralling them and forming low pressure, high capacity conduits to carrry maternal blood

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19
Q

Describe amino acid transport to the foetus

A

Reduced urea excretion by mother

Actuve transport of amino acids to foetus

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20
Q

Describe electrolytes transport to foetus

A

Across placenta

Diffusion or active energy dependent cotranporters

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21
Q

Describe calcium transport to the foetus

A

Actively transported by the magnesium ATPase calcium channel

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22
Q

Describe changes to maternal O2 transport during pregnancy

A

Increase in cardiac output
Decrease in peripheral resistance
Increase in blood volume
Increase in pulmonary ventilation

23
Q

What is the first stool delivered after birth and how is it made

A

Meconium

Formed as embryo swallows amniotic fluid which contains bile and debris

24
Q

Describe cirulatory system in foetus

A

Placenta is the main site for gas exchange
Ventricles pump in parallel rather than series (drive blood togtehr ariund same circulatory loop)
This is achieved by vascular shunts which bypass pulmonary and hepatic circulation

25
Q

When do stress responses start in the foetus

A

Week 18

26
Q

When does the thalamus-cortex connections form

A

By week 24

27
Q

How is organ maturation coordinated

A

By foetal corticosteroids

28
Q

4 stages of pregnancy in relation to cervix and uterus

A

QASI

QUIESCENCE: cervical softening
ACTIVATION: cervical ripening
STIMULATION: cervical dilation, uterine contraction
INVOLUTION: cervical repair, uterine involution

29
Q

Decsribe the 3 stages of labour

A

1st stage = contractions start, cervical dilation

  • latent phase: slow dilation to 2-3 cm
  • active phase: rapid dilation to 10 cm

2nd stage = delivery of the foetus

  • commences at 10cm dilation
  • maximal myometrial contractions

3rd stage = delivery of placenta

  • delivery of placenta and foetal membranes
  • post partum repair
30
Q

Describe how the structure of the cervix helps with its function

A

Has bundles of collagen embedded in a proteoglycan matrix

This provides it with stretch resistance and rigidity

31
Q

Describe the remodelling of the cervix

A

1) softening: the cervix is made of bundles of collagen embedded in a proteoglycan matrix. Changes to the collagen bundle structures cause softening of the cervix. This decreases the compliance of the cervix but it still stays competent ie still holds baby in
2) ripening: monocyte infiltration, IL6 and IL8 secretion, Hylaluron deposition

3) dilation: increased expression of Hylaluronidase which breaks down HA
MMPs (matrix metallic proteases) break down the collagen therefore increasing elasticity of cervix

4) post partum repair: recovery of tissue integrity and competency

32
Q

How do CRH levels relate to partuition time

A

The fetus uses the CRH levels to determine its partuition time
Towards the end of pregnancy, CRH levels rise exponentially
A decline in CRH binding proteins contributes to this as it makes more CRH bioavailable

33
Q

CRH functions in labour

A

CRH acts on fetal adrenal gland and cause it to release cortisol and ACTH
The cortisol acts on the placenta and causes it to release CRH too, which travels back to fetus in blood and causes the same respone —> positive feedback
The CRH also causes the adrenal cortex to produce DHEAS which are a substitute for oestrogen
DHEAS = dehydroepiandrosterone sulphate

34
Q

What mainatins uterine relaxation throughout pregnancy?

A

High levels of progesterone

35
Q

What happens to progesterone and oestrigen as term approaches

A

Progesterone receptors expressed on the uterus change from active signalling isoforms (PR-A) to repressive isoforms (PR-B and PR-C). The uterus becomes non-responsiveto progesterone —> FUNCTIONAL PROGESTERONE WITHDRAWAL
At the same time, the uterus becomes more sensitive to oestrogen

36
Q

How is oxytocin released and describe its release towards term

A

Relased by stretch receptors —> ferguson reflex
Signals through G coupled oxytocin receptors (OXR/OXTR)
Increase in oxytocin towards the end of pregnancy
- it was inhibited by progesterone throughout pregnancy to make sure the uterus stayed relaxed. But an increase in oestrogen causes an increase in expression of OXR/OXTR on uterine surface

37
Q

3 functions of oxytocin in uterine contraction

A

1) increases connectivity of myocytes in myometrium
2) destabilises membrane potential so lowers the threshold for contraction
2) enhances liberation of intracellular ca2+ stores

38
Q

Decsribe the stretch/ferguson reflex

A

As the embryo pushes down onto and stretches the cervix, stretch receptors signal upto the maternal hypothalamus
The neurones synapse onto paraventricular and supraortic nuclei which then send signal to posterior pituitary causimg it to release oxytocin
Oxytocin then acts on uterus and myometrium causing contraction

39
Q

What are the primary prostaglandins during labour and what do they do

A 
PGE2 = cervix remodelling: leukocyte infiltration, IL8 release and collagen bundle remodelling 
PGF2alpha = myometrium contraction: membrane destabilisation, increasing connectivity of myocytes

PGI2 = myometrium smooth muscle relaxation and lower uterine relaxation

40
Q

Describe 2 ways oestrigen causes Prostgoandin release

A

1) rising oestrogen activates phosphlipase A2 enzyme which forms arachidonic acid needed for PG synthesis
2) oestrogen causes increased oxytocin receptor expression which promotes PG release

41
Q

Describe myometrial contractions

A

Start at top of uterus - the “fundus”
Then extend down to upper segment and lower segment
Contractions are brachystatic which means that the fibres do not return to their original length after contraction
This pulls up the lower segment and cervix, forming the birth canal

42
Q

Describe how baby exits

A 
Head is pressed against pelvic space
Pressure causes chin to press against the chest 
Baby rotates 
Head is pushed out 
Followed by shoulders
Followed by torso
43
Q

Why is the umbilical cord clamped

A

Stops fetal blood flow to the placenta - villi collapse

44
Q

What happens in the embryo around day 5-6

A

Hatching
- to implant, the blastocyst must escape the zona pellucida, it does this by enzymatic degradation and cellular contractions

45
Q

What are the two main cell lineages in the morula around day 6

A

Inner cell mass - forms embryonic structures

Trophoblast (around outside) - forms extra embryonic structures

46
Q

What happens during days 7-9 of embryonic development

A

Some Trophoblast cells fuse to form the syncitiotrophoblast which invades maternal endometrium - provides an interface for exchange
The rest of the trophoblast cells remain individual and are called chytotrophoblast cells

The inner cell mass splits into 2 groups of cells:
The hypoblast = forms the yolk sac (extra embryonic structure)
The epiblast = forms foetal tissues

47
Q

What happens at day 12+ of embryonic development

A

The final stage before gastrulation:
Amniotic cavity forms in the inner cell mass
This causes the formation of a bilaminar embryonic disc (one layer of hypoblast and one layer of epiblast cells)

48
Q

List structures formed from the mesoderm

A 
Blood
Muscles
Bone 
Cartilage
Kidneys 
Adrenal cortex 
Gonads
49
Q

List structures formed from the ectoderm

A

CNS
Neural crest
Skin epithelia
Tooth enamel

50
Q

List structures formed from the endoderm

A 
Liver 
Pancreas
GI tract
Lung 
Thyroid
51
Q

Describe/explain somitogenesis

A 
Bits of mesoderm run alongside the neural tube 
Blocks of paraxial mesoderm condense and bud off in somite pairs 
Forms somites (blocks of mesoderm) on either side of neural tube 
Somitogenesis commences at the head end and progresses down the long axis of the embryo
52
Q

What are the somite derived tissues

A

1) Sclerotome: forms vertebrae and rib cartilage

2) Dermamyotome: composed of dermatome and myotome
Dermatome: forms dermis of skin, some fat and connective tissues of the neck and trunk
Myotome: forms muscles

53
Q

2 types of folding that form the gut

A

Ventral folding

Lateral folding

brs (8 decks)

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