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Embryology, Pregnancy & Birth > Lecture #1 > Flashcards

Lecture #1 Flashcards

1
Q

Give the 4 fundamental developmental processes within embryology & define each.

A

-Cell division = growth
-Patterning = how cells know from the genome what to become
-Cell differentiation = SCs & progenitors turn into specific cell types - cell specialisation
-Morphogenesis = development of the forms in living organisms

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2
Q

What is oogenesis?

A

Growth process in which the primary egg cell (or ovum) becomes a mature ovum

–> oogonia develop from primordial germ cells in the forming ovaries

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3
Q

When does oogenesis begin in embryology?

A

-Before birth - week 8 of life in utero - in the ovaries of the unborn embryo
-Then is paused/suspended until puberty & ovulation - arrest @ prophase I of meiosis
-Is then paused again @ metaphase II until fertilisation

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4
Q

What is fertilisation?

A

= Union of a sperm nucleus, of paternal origin (haploid), with an egg nucleus, of maternal origin (haploid), to form the primary nucleus of an embryo - a zygote (diploid)
-Accomplishes both the recombination of genetic material
-Initiates events that begin embryonic development

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5
Q

Where does fertilisation occur?

A

Ampulla of the oviduct
–> ampullary-isthmic junction - ovum & sperm transported simultaneously to this junction of fallopian tube
–> so fertilisation occurs in ampullary region of fallopian tube or oviduct

Oviducts = fallopian tubes

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6
Q

What is involved in the process of fertilisation?

A

-Sperm must find way to egg
-Sperm & egg must contact, recognize one another, & fuse
-After sperm-egg fusion -> intracellular signalling cascade occurs in egg = two major consequences:
1 = allows egg to regulate sperm entry so only 1 sperm can fuse with egg = prevents polyspermy
2 = “wakes up” the metabolically quiescent egg so it can resume meiosis & begin embryonic development –> = egg activation

*Sperm must undergo sperm capacitation in female reproductive tract = modifies sperm - so can fertilise egg
–> sperm which successfully undergo capacitation = capacitated sperm

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7
Q

What are capacitated sperm then able to do?

A

Fertilise the egg

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8
Q

What stages are involved in sperm capacitation?

A
  1. Altered memb fluidity due to removal of cholesterol from sperm memb
  2. Removal of prots & carbs from memb - may otherwise block sites that bind to egg
  3. Change in memb pot that may permit Ca2+ to enter sperm = to facilitate acrosome reaction*** (MOST IMPORTANT STAGE WE NEED TO KNOW!)
  4. Phosphorylation of numerous proteins
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9
Q

What 3 barriers must sperm breach in order to penetrate the egg?

A
  • Expanded cumulus (cumulus cell matrix = mostly hyaluronic acid - so v. acidic)
  • Zona pellucida
  • Plasma membrane of egg (= oolemma)

–> egg is surrounded by its expanded cumulus cells in the ampulla of oviduct

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10
Q

Explain the acrosome reaction.

A

Ca2+ dependent event
-Sperm plasma memb fuses w/ outer acrosomal memb to release the contents of the acrosomal vesicle
-Lytic enzymes are released from acrosomal vesicle –> digest zona pellucida - so sperm can contact plasma memb of egg
*Acrosomal reaction occurs whilst sperm is in contact w/ cumulus cells - & can be enhanced by binding to zona pellucida prots

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11
Q

What day of the menstrual cycle does fertilisation typically occur?

A

Day 15 or 16

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12
Q

What is the morula?

A

Ball of cells resulting from cleavage (cell division) of zygote
-Image of morula = bottom right

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13
Q

When (days) is the morula formed?

A

2 days after fertilisation -> here embryo is in oviduct/fallopian tube still

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14
Q

How many cells are in the morula?

A

16 cells

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15
Q

When (days) does the morula become a blastocyst?

A

Days 3-5 after fertilisation -> here embryo has entered uterus

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16
Q

How does the blastocyst form?

A

-Outer cells of morula become tightly adhesive to each other & start to transport fluid into embryonic mass
-This fluid transport forms a cavity = blastocyst
–> hollowing out of morula by morphogenic reorganisation

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17
Q

What is the blastocyst composed of - what 2 subpopulations of cells?

A

-(Eccentric) inner cell mass = embryoblast -> contacts endometrium to facilitate implantation & formation of placenta
-Outer - ep-like layer of trophoblasts = trophectoderm -> forms embryo itself
–> this layer immediately adjacent to inner cell mass is called embryonic pole = this is where blastocyst attaches to uterine endometrium (implantation)

-Primitive endoderm (mentioned as a component too in slides!)

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18
Q

What happens to the blastocyst before implantation?

A

Blastocyst ‘hatches’ from zona pellucida (protective coating)

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19
Q

When does blastocyst ‘hatching’ occur?

A

Around day 5 (post-fertilisation)

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20
Q

How does implantation of blastocyst into uterine endometrium occur?

A

-L-selectin receptors of blastocyst bind to oligosaccharides in uterine wall -> this interaction is stabilised by integrin heterodimers (= cell adhesion molecules
-Trophoblast cells of blastocyst - proliferate & secrete MMPs (Matrix MellaoProteinases)
-MMPs digest ECM (by lysing extracellular prots) & invade endometrium
-So villi of trophoblast can penetrate endometrium - pulling blastocyst (now called embryo) into endometrium until is fully covered by endometrial epithelium

–> SO BLASTOCYST IMPLANTS INTO UTERUS!!!

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21
Q

Summarise the stages from fertilisation to implantation in a diagram - include relevant timings, cell names & locations.

A
22
Q

Explain the morphogenesis occurring simultaneously to implantation.

A

*Epiblast = 1 of 2 layers arising from inner cell mass of blastocyst
–> so cellular morphogenesis gives rise to epiblast
*Other cell layer = hypoblast

–> bilaminar embryonic disc = epiblast + hypoblast

23
Q

What does epiblast (& hypoblast) give rise to?

A

-Future embryo
-& will gastrulate to produce the germ layers:
ectoderm, mesoderm, endoderm

24
Q

What are spontaneous abortions, how are they recognised & why do they occur?

A

1 = Natural pregnancy loss before 20 weeks gestation
2 = often unrecognized or reflected in heavy/late menstruation
3 = frequently characterized by chromosomal abnormalities

25
Q

What is an ectopic pregnancy?

A

Pregnancy that occurs outside uterine cavity - often in fallopian tubes
–> i.e., blastocyst has implanted in incorrect place - not into uterine endometrium

26
Q

Symptoms of ectopic pregnancies.

A

-Possible missed period
-Lower abdominal pain
-Vaginal bleeding, or abnormal discharge
-Referred pain to shoulder
-Sudden sharp pain, dizziness, fainting, pallor

27
Q

Diagnosis of ectopic pregnancy?

A

-Pregnancy test
-Vaginal ultrasound
-Laparoscopy

28
Q

Treatment of ectopic pregnancy?

A

-Laparoscopic surgery to terminate pregnancy
-In case of rupture -> abdominal surgery

29
Q

Summarise the order of cells.

A

-Zygote
-Morula = 16 cells
-Blastula
-Blastocyte
Gastrulation process
-Gastrula
-Embryo?

30
Q

What is gastrulation?

A

Process by which the 2 cell layers (epiblast & hypoblast) = bilaminar disc become 3 germ cell layers = trilaminar disc & the bodily axes observed in mature adult are created

31
Q

When does gastrulation occur post-fertilisation?

A

Week 3

32
Q

Where does gastrulation occur?

A

Primitive streak
(or could say Hensen’s node)
–> at ant. end of primitive streak is Hensen’s node = accumulation of cells

33
Q

What occurs during gastrulation?

A

Gastrulation = process by which bilaminar disc differentiates into trilaminar disc - up of 3 primary germ layers: ectoderm, mesoderm, & endoderm

Day 15
-Bilaminar embryonic disc (epiblast + hypoblast) differentiates throughout week 3 = x3 primary germ layers
-Primitive streak forms near caudal end of bilaminar embryonic disc
-Formation of primitive streak defines the major body axis -> cranial end towards head & caudal end towards tail & left & right sides of embryo
-@ cranial end of embryonic disc - primitive streak expands -> forms primitive node (contains circular depression = primitive pit)
-Primitive pit continues along midline of epiblast towards caudal end of streak - forms primitive groove
-Once formed - epiblast cells migrate inwards into primitive streak - detach from epiblast & split beneath into interior of embryo = invagination
-1st cells to invaginate through primitive groove - invade the hypoblast & displace hypoblast cells
-Hypoblast cells will eventually be replaced by new proximal cell layer = definitive endoderm

Day 16
-Most of hypoblast cells now replaced
-Remaining cells of epiblast now = ectoderm - forms most exterior distal layer
-Some of invaginated epiblast cells remain in space between ectoderm & definitive endoderm -> these cells form mesoderm
-Once definitive endoderm & mesoderm formation = complete - epiblasts cells no longer migrate to primitive streak

-Throughout gastrulation -> ectoderm continues to form from cranial to caudal end of embryo
= 3 distinct primary germ layers throughout embryonic disc

= gastrulation now complete

34
Q

What is an integral component of gastrulation?

A

EMT -> epithelial to mesenchymal transition
–> epithelial cells transform into mesenchymal cells
= so acquire these mesenchymal characteristics - increased cell motility & migration

35
Q

Where else is EMT seen?

A

Cancer cell metastasis - ep cells acquire mesenchymal characteristics = enhanced cell motility & migration

36
Q

What forms in the midline of the mesoderm - critical for neurulation?

A

-Notochord forms in midline of mesodermal layer
-Notochord induces neurulation
–> look at neurology anatomy!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!

37
Q

Which part of the ectoderm undergoes neurulation?

A

= Dorsal part of ectoderm (outer part) - specify as neuroectoderm
-Neurulation produces neural tube - with central canal (containing CSF!!!)

38
Q

Summarise what gastrulation produces?

A

-In animals - forms gut
-In humans (& other vertebrates) - blastopore forms anus & mouth breaks through ant. end to create a through-gut

39
Q

Describe how the endoderm is formed.

A

By epiblast cells that migrate through primitive pit & displace hypoblast cells

40
Q

Describe how the mesoderm is formed.

A

By epiblast cells that migrate through primitive pit & lie between epiblast layer & newly created endoderm

41
Q

Describe how the ectoderm is formed.

A

By epiblast cells that remain in position

42
Q

What does each of the 3 germ layers become/what do they give rise to?

A
43
Q

What is the ‘4th germ layer’?

A

Neural crest

44
Q

What is the neural crest?

A

Progenitors - move out CNS (crest of developing brain) & give rise to PNS & other tissues

45
Q

What does the neural crest form in the head?

A

Musculoskeletal tissues

46
Q

What is segmentation?

A

Separate embryo into segments

47
Q

Where is the embryo segmented?

A

-Spinal cord
-Mesodermal somites
-Medulla = ect
-Pharyngeal arches = ect, mes, endo

48
Q

What is embryonic patterning?

A
49
Q

What occurs during embryonic patterning?

A

Hox genes (members of homebox superfamily of TFs) are found in clusters in genome
-Found that these genes are found in the same order to which their action is exerted in the developing embryo –> this is called collinearity (their order in genome is reflected in their expression along anterior-posterior axis)

50
Q

What hox clusters are found in humans?

A

x4
Hox clusters A,B,C & D

51
Q

What do hox genes do?

A

Specify regions of the body plan of an embryo along the head-tail axis (anterior-posterior axis) of animals
-Different clusters work together to establish the identity of body segments along the head-tail axis
-Towards start of cluster these hox genes act specifically in the development of the head, neck, then middle = thorax/torso/mid-region?, then towards end of the gene cluster - these hox genes act in development of vertebrate limbs (arms, legs or wings)
e.g., Hox6 expresses thoracic vertebrae

–> so these hox genes = TFs (so bind to DNA - have DNA binding region called homeodomain) which ensure the right genes are expressed & the unneeded genes are turned off during development

52
Q

What happens if a hox gene for lumbar vs thoracic vertebrae is expressed throughput the body axis?

A

Lumbar = no ribs form
e.g., Hoxa10 expressed throughout body axis = all vertebrae are lumbar

Thoracic = ribs form
e.g., Hoxb6 expressed throughout body axis = all vertebrae are thoracic

Embryology, Pregnancy & Birth (9 decks)

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