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EMBRYOLOGY (foundation B) > Intro 28: Gastrulation & formation of Tri-Laminar Disc > Flashcards

Intro 28: Gastrulation & formation of Tri-Laminar Disc Flashcards

1
Q

Anatomic terms for Embryo
Superior=
Inferior=
Anterior=
Posterior=
Sagittal=
Coronal=

A

Superior= =CRANIAL, CEPHALIC
Inferior= CAUDAL
Anterior= VENTRAL
Posterior= DORSAL
Sagittal= MEDIAN
Coronal= FRONTAL

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2
Q

When does GASTRULATION occur

A

WEEK 3
of embryonic development

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3
Q

GASTRULATION is the process by which…

A

Bi-laminar embryonic disc is converted into a TRI-LAMINAR EMBRYONIC DISC

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4
Q

TRI-LAMINAR EMBRYONIC DISC contains 3 GERM LAYERS:

A

ECTODERM
MESODERM
ENDODERM

  • will give rise to
    all specific tissues and organs
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5
Q

Gastrulation is the beginning of

A

MORPHOGENESIS
(development of the form
and structure of various organs and parts of the body)

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6
Q

Gastrulation begins with the formation of a transient structure called…
on what day

A

PRIMITIVE STREAK
- DAY 15

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7
Q

PRIMITIVE STREAK is formed by the THICKENING of…

A

THICKENING of EPIBLAST CELLS

  • first appears at CAUDAL end (cells in median area will start to proliferate at caudal end)
  • elongates into primitive groove
  • MIGRATES towards CRANIAL end (towards prechordal plate)
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8
Q

formation of primitive streak establishes the..

A

cranial/caudal axis of the embryo

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9
Q

At the CRANIAL end of primitive streak EPIBLAST cells ingress at
a greater rate forming a CIRCULAR CAVITY called..

A

PRIMITIVE PIT

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10
Q

cells of the PRIMITIVE STREAK PROLIFERATE and become
ENLARGED to form the…

A

PRIMITIVE NODE
– primary
tissue organiser

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11
Q

EPITHELIAL cells in the lateral edge of the EPIBLAST undergo…

A

EMT
-epithelial to MESENCHYMAL
transition

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12
Q

What happens to the epithelial cells that undergo EMT

A

become flask-shaped,
detach,
MIGRATE DOWN/INTO PRIMITIVE STREAK

(INVAGINATION / INGRESSION)

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13
Q

The FIRST set of epithelial cells of epiblast to move down primitive streak INTEGRATE INTO HYPOBLAST LAYER and REPLACE it to form…

A

ENDODERM

(1st germ layer to be formed)

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14
Q

The SECOND set of epithelial cells to detach and ingress FILL
the SPACE between ENDODERM and EPIBLAST, which forms…

A

MESODERM

(middle layer)

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15
Q

What do the REMAINING epiblast cells that don’t migrate into primitive streak form

A

ECTODERM

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16
Q

How is gastrulation regulated?

A

Through regulation of gene expression

Examples:
- FGF8 secreted by the node and p.s. induce the expression of a
gene called Nodal that is involved in initiating and maintaining the
primitive streak

  • BMP4 (bone morphogenic protein 4) is secreted throughout the
    embryonic disk and together with FGF8 will drive ventralization of
    the mesoderm
  • Chordin, noggin and follistatin antagonise the activity of BMP4
    and as a result cranial mesoderm is dorsalized into notochord,
    somites and somitomeres
  • left-right body axis is established through a signalling cascade and
    differential expression of genes on the left and right side
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17
Q

Examples of Gastrulation Abnormalities

A

Caudal dysgenesis (sirenomelia):
- insufficient mesoderm is formed in the caudalmost region of the embryo
- as a result abnormalities in the lower limbs and urogenital system

Sacrococcygeal teratomas:
- tumours that occur when reminants of the primitive streak persist in the
sacrococcygeal region
(most common tumour in newborns: 1/37000)

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18
Q

What 2 things happen in the 3rd week

A
  • Gastrulation
  • Development of the NOTOCHORD
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19
Q

Day 18 –21 Development of the notochord:
Progenitor mesoderm (mesenchymal) cells from the primitive node and pit migrate to form a..

A

median cellular cord
–the NOTOCHORDAL PROCESS

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20
Q

the NOTOCHORDAL PROCESS soon acquires a lumen called..

A

NOTOCHORDAL CANAL

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21
Q

DAY 18-21
The primitive streak regress…
as the notochordal process advances…

A

caudially
cranially between the ectoderm
and endoderm until it reaches the prechordal plate

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22
Q

day 18-21:
Some mesenchymal cells from the primitive streak migrate cranially and meet to form the CARDIOGENIC MESODERM in the…

A

CARDIOGENIC AREA/PLATE

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23
Q

CARDIOGENIC AREA/PLATE is where the…

A

PRIMORDIUM of the HEART begins to develop
at the END of the 3RD WEEK

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24
Q

day 18-21:
As the hypoblast is replaced by endoderm cells (gastrulation) what happens to the NOTOCHORDAL PROCESS and what is formed?

A

NOTOCHORDAL PROCESS cells PROLIFERATE and DETACH from endoderm to form NOTOCHORDAL PLATE

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25
Q

DAY 18-21
NOTOCHORDAL PLATE will ultimately form a solid cylinder of cells called:

A

NOTOCHORD

26
Q

what is the NOTOCHORD and its functions (4)

A

a transient structure that:

  • provides SUPPORT
  • defines the AXIAL AXIS for the embryo (serves as the basis for the development of the AXIAL SKELETON)
  • induces the overlying embryonic ectoderm to thicken and form the NEURAL PLATE (the primordium
    of the central nervous system)
  • Indicates the future sites of the vertebral bodies
27
Q

Fused layers of ectoderm and endoderm form the…

A

-OROPHARYNGEAL MEMBRANE
(located at the future site of the
oral cavity)
- CLOACAL MEMBRANE
(at the future site of the anus)

28
Q

Specific regions of the epiblast migrate through different parts of the node and primitive streak to form mesoderm:

Cells migrating at the CENTRAL and most CRANIAL part of the node will form the…

A

NOTOCHORD

29
Q

Specific regions of the epiblast migrate through different parts of the node and primitive streak to form mesoderm:

Cells migrating more POSTERIORLY will form

A

PARAXIAL MESODERM
(pm; somitomeres and somites)

30
Q

Specific regions of the epiblast migrate through different parts of the node and primitive streak to form mesoderm:

The next region will form…

A

INTERMEDIATE MESODERM
(im; urogenital system)

31
Q

Specific regions of the epiblast migrate through different parts of the node and primitive streak to form mesoderm:

Cells migrating through the MORE CAUDAL part of the streak will form…

A

LATERAL PLATE MESODERM
(lpm; body wall)

32
Q

Specific regions of the epiblast migrate through different parts of the node and primitive streak to form mesoderm:

Cells migrating through the MOST CAUDAL part will contribute to…

A

EXTRAEMBRYONIC MESODERM
(eem; chorion)

33
Q

Blastomeres differentiate into…

A

Trophoblast
Embryoblast / ICM

34
Q

Embryoblast differentiate into…

A

Epiblast
Hypoblast

35
Q

Epiblast differentiate into…

A

Endoderm
Mesoderm
Ectoderm

36
Q

Derivatives of MESODERM

A

HEAD
PRAXIAL MESODERM
INTERMEDIATE MESODERM
LATERAL MESODERM

see diagram

37
Q

Derivatives of ECTODERM

A

SURFACE ECTODERM
NEUROECTODERM -Neural Crest, Neural Tube

see diagram

38
Q

The placenta is a…

A

materno-foetal organ
(some derived from maternal tissue, some derived from foetal tissue)

39
Q

The placenta provides…

A
  • nutrition
  • gas exchange
  • waste removal
  • source of haematopoietic cells
  • endocrine
  • immune support
40
Q

Stages of PLACENTA DEVELOPMENT
(0,1,2,3,4)

A

0 –Lacunar stage
1 –Primary villus
2 –Secondary villus
3 –Tertiary villus
4 –Free villus and cytotrophoblast layer

41
Q

at DAY 9-10 what appear in syncytiotrophoblasts (which are proliferating and invading)

A

vacuoles appear in syncytiotrophoblasts which fuse to form LANUNAE
(spaces between STs)

42
Q

DAY 9-10
As syncytiotrophoblasts invade further what do they meet

A

meet MATERNAL CAPILLARIES which are eroded by syncytiotrophoblasts

  • syncytiotrophoblasts fill LACUNAE with blood from maternal capillaries
43
Q

At around DAY 13, what is formed

A

PRIMITIVE UTERO-PLACENTAL CIRCULATORY SYSTEM

(1st contact between blood of mother and tissue of embryo)

44
Q

how is the PRIMITIVE UTERO-PLACENTAL CIRCULATORY SYSTEM formed at day 13

A

Cytotrophoblasts grow into the Lacunae as the PRIMARY CHORIONIC VILLI
(small projects of cytotrophoblasts begin to expand into syncytiotrophoblast)

45
Q

What is formed at DAY 16

A

SECONDARY CHORIONIC VILLI

46
Q

how is the SECONDARY CHORIONIC VILLI formed

A

from day 14-16
- Primary chorionic villi begin to BRANCH
- EXTRAEMBRYONIC MESODERM INVADES (grows into primary villi)

47
Q

What happens at the end of the 3rd week / DAY 21 and what is formed

A

EMBRYONIC BLOOD VESSELS (foetal capillaries) begin to form in the extra-embryonic MESODERM of the Secondary Villi
- formed the TERTIARY CHORIONIC VILLI

48
Q

Placental Barrier has 4 layers:

A
  • EXTRA-EMBRYONIC MESODERM
  • CYTOTROPHOBLAST
  • SYNCYTIOTROPHOBLAST
  • FOETAL CAPILLARIES
49
Q

EMBRYONIC BLOOD VESSELS in/invading the tertiary villus:

A

UMBILICAL ARTERIES
- carry the DEOXYGENATED blood from the embryo to the placenta

UMBILICAL VEIN
- returns the OXYGENATED blood to the embryo

(other way round)
embryo

50
Q

by the end of the 4TH WEEK:
a complex vascular network develops in the placenta allowing…

A

maternal-embryonic exchanges

51
Q

Until the beginning of the 8th week, CHORIONIC VILLI will…

A

cover the entire CHORIONIC SAC

52
Q

At 8th week, what happens to CHORIONIC VILLI covering CHORIONIC SAC?

A
  • some will degenerate producing the SMOOTH CHORION

-those in close proximity to the DECIDUA BASALIS will form the VILLOUS CHORION / CHORION FRONDOSUM

53
Q

What is the DECIDUA BASALIS

A

(derived from decidua)
the maternal part of the placenta

54
Q

The UMBILICAL CORD connects what…

A

connects PLACENTA to EMBRYO

55
Q

What does the umbilical cord contain:

A

2 UMBILICAL ARTERIES
1 UMBILICAL VEIN

56
Q

What does the umbilical cord contain:

A

2 UMBILICAL ARTERIES
1 UMBILICAL VEIN

57
Q

When is the PLACENTA and EMBRYO formed

A

at 8 WEEKS

58
Q

4 FUNCTIONS OF PLACENTA

A
  • Exchange of gases
    (eg oxygen, carbon dioxide and
    carbon monoxide)
  • Exchange of nutrients and electrolytes
    (amino acids, free fatty acids,
    carbohydrates and vitamins)

-Transmission of maternal antibodies

-Hormone production

59
Q

Transmission of maternal antibodies at around WEEK 14

A

immunoglobulins consist almost entirely of maternal IgG,
which begins to be transported from mother to foetus at 14 weeks

  • Passive Immunity
60
Q

Hormone production in placenta

A
  • by end of the 4th month the placenta produces
    PROGESTERONE:
    necessary for maintenance of pregnancy
  • Increasing amounts of ESTROGENS:
    stimulate uterine growth and development of mammary
    glands
  • SOMATOMAMMOTROPIN (hPL – human Placental Lactogen) :
    gives foetus priority on maternal blood glucose
    promotes breast development for milk production
61
Q

Examples of Abnormalities related to development of placenta

A

PLACENTA PREVIA
- The placenta overlies internal
os of uterus, covering the birth
canal
- 1/200-250 pregnancies

PLACENTA ACCRETA
- Abnormal adherence, with
absence of decidua basalis
- 3/1000 deliveries

EMBRYOLOGY (foundation B) (4 decks)

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