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Esa1 > Session 3: Early embryology > Flashcards

Session 3: Early embryology Flashcards

1
Q

define the pre-embryonic, embryonic and fetal periods of human development

A
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2
Q

discuss the changes taking place as the fertilised human ovum (zygote) travels down the Fallopian (uterine) tube towards the uterus

A

1) Cleavage occurs producing 2 equal size blastomeres within Zona Pellicuda and this continues.
2) After 3rd cleavage blastomeres maximise contact and form compact ball. This process, compaction, segregates inner cells, which communicate extensively by gap junctions, from the outer cells. This process creates a ball of cells known as the morula.

(The inner cell mass gives rise to tissues of the embryo proper, and the outer cell mass forms the trophoblast, which later contributes to the placenta)

3) Morula reaches uterus

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3
Q

describe the meaning of the following terms: zygote

A

A single cell, the product of fertilisation of an ovum by a sperm, produced by fusion of the male & female pronuclei.

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4
Q

describe the meaning of the following terms: cleavage

A

Splitting of zygote into 2 blastomeres, mitotic divisions continue

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5
Q

describe the meaning of the following terms: zona pellucida

A

glycoprotein shell, surrounds oocyte, morula and early blastocyst, barrier to any further sperm

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6
Q

describe the meaning of the following terms: morula,

A

The “mulberry”: a solid ball of cells resulting from cleavage of the cells of the zygote.

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7
Q

describe the meaning of the following terms: ovary, Fallopian tube, uterus

A

Ovary: female reproductive organ where ova/eggs are produced

Fallopian tube:Oocyte fertilised in ampulla of tube and travels along to uterus

Uterus: Ideal site of implantation

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8
Q

discuss the formation of the blastocyst and the initial stages of implantation

A

About the time the morula enters the uterine cavity, fluid begins to penetrate through the zona pellucida into the intercellular spaces of the inner cell mass. Gradually, the intercellular spaces become confluent, and finally, a single cavity, the blastocele, forms. At this time, the embryo is a _blastocyst_.

The inner cell mass becomes the embryo itself, whilst the outer cells collectively become the trophoblast, which is the major component of the fetal membranes, especially the placenta, that surround and sustain the developing embryo and fetus, respectively, until birth. The zona pellucida has disappeared, allowing implantation to begin. In the human, trophoblastic cells over the embryoblast pole begin to penetrate between the epithelial cells of the uterine mucosa on about the sixth day (Fig. 3.10C). New studies suggest that L-selectin on trophoblast cells and its carbohydrate receptors on the uterine epithelium mediate initial attachment of the blastocyst to the uterus.

The trophoblastic placenta develops a special cell layer, the syncytiotrophoblast, which first adheres to, and then invades, the modified (decidualised) endometrium. This process is known as implantation. The preimplantation stages of pregnancy are the most hazardous for life, with up to 30% of zygotes failing to develop to the blastocyst stage.

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9
Q

describe the meaning of the following terms: blastocyst

A

Hollow sphere of cells formed from the morula whereby fluid is pumped in to create the blastocoele, leaving an inner cell mass and an outer cell mass

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10
Q

trophoblast?

A

outer cell mass forms the trophoblast, which later contributes to the placenta

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11
Q

inner cell mass?

A

The inner cell mass (also called embryoblast,) gives rise to tissues of the embryo proper (embryo itself)

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12
Q

implantation?

A

The zona pellucida has disappeared, allowing implantation to begin. In the human, trophoblastic cells over the embryoblast pole begin to penetrate between the epithelial cells of the uterine mucosa on about the sixth day (Fig. 3.10C). New studies suggest that L-selectin on trophoblast cells and its carbohydrate receptors on the uterine epithelium mediate initial attachment of the blastocyst to the uterus.

The trophoblastic placenta develops a special cell layer, the syncytiotrophoblast, which first adheres to, and then invades, the modified (decidualised) endometrium. This process is known as implantation. The preimplantation stages of pregnancy are the most hazardous for life, with up to 30% of zygotes failing to develop to the blastocyst stage.

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13
Q

describe the meaning of the following terms cytotrophoblast, syncytiotrophoblast

A

The trophoblast has differentiated into two layers: (1) an inner layer of mononucleated cells, the cytotrophoblast, and (2) an outer multinucleated zone without distinct cell boundaries, the syncytiotrophoblast

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14
Q

describe the formation of the embryonic disc in the inner cell mass and initial cell differentiation within it

A

Cells of the inner cell mass or embryoblast also differentiate into two layers: (1) a layer of small cuboidal cells adjacent to the blastocyst cavity, known as the hypoblast layer, and (2) a layer of high columnar cells adjacent to the amniotic cavity, the epiblast layer

Layer of Hypoblast cells and layer of Epiblast cells form bilaminar disc.

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15
Q

define the terms: bilaminar disc, germ layer, ectoderm and mesoderm

A

Bilaminar disc: Two-layered embryonic disc consisting of epiblast & hypoblast derived from the inner cell mass.

Germ layer: The three primary tissue layers of the trilaminar disc, ectoderm, mesoderm & endoderm that arise through gastrulation and subsequently give rise to all the tissues of the body

Ectoderm: The outermost layer of the three embryonic germ layers of the trilaminar disk formed during gastrulation.

The middle layer of the three embryonic germ layers of the trilaminar disk formed during gastrulation.

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16
Q

Describe stages to reach this: (end of second week)

A
  • Blastocoele; first cavity, formed as a result of compaction
  • Amniotic sac; formed from spaces within the epiblast
  • Primitive yolk sac; a.k.a exocoelomic cavity, formed by hypoblast lining blastocoele
  • Secondary yolk sac a.k.a definitive yolk sac, formed within primitive YS
  • Extraembryonic coelom a.k.a chorionic cavity, formed from spaces within extraembryonic reticulum & mesoderm
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17
Q

define the terms: primitive streak, gastrulation, trilaminar embryonic disc

18
Q

list the important ectodermal, mesodermal and endodermal derivatives

A

Ectoderm: epidermis, nervous system

Mesoderm: muscle, bones, connective tissue

Endoderm: other organs, e.g GIT, respiratory tract

19
Q

Important dates:

Day 6: implantation begins

Day 9: blastocyst embedded in endometrium, lacunae formation

Day 15 gastrulation

A

-

20
Q
A

-

21
Q

Gastrulation?

A

The process occurring during the third week of development resulting in the formation of the three germ layers of the trilaminar disc from epiblast migrating through the primitive streak

22
Q

Primitive streak?

A

Begins as a thickened region of epiblast at the caudal end of the bilaminar disc and is the site from which gastrulation proceeds.

23
Q

Trilaminar disk

A

The three-layered germ disc produced by gastrulation consisting of the three germ layers, ectoderm, mesoderm & endoderm.

24
Q
A
25
Q

Gastrulation then neurulation (during third week, about same time)

A
26
Q

Whats the role of the notochord in neurulation

A

https://www.youtube.com/watch?v=qzib8bdtK74

After the picture: • Notochord signals cause overlying ectoderm to thicken
• Slipper-shaped neural plate
• Edges elevate out of the plane of the disk and curl towards each other, creating the neural tube

27
Q

describe the differentiation of mesoderm into the notochord, somites, intermediate mesoderm, and lateral plate.

[Somatic mesoderm (parietal mesoderm) and splanchnic mesoderm (visceral mesoderm)] = lateral plate

A
28
Q

Neurulation

A

The process through which a neural tube is formed initiated by the notochord signalling to ectoderm to form the neural plate.

29
Q

Paraxial mesoderm become ….

A

Somites

30
Q

list the derivatives of each region of the mesoderm.

A

Intermediate mesoderm, which temporarily connects paraxial mesoderm with the lateral plate (Figs. 6.8D and 6.9), differentiates into urogenital structures. (gonads and kidneys)

The somatic layer of lateral plate mesoderm then forms the dermis of the skin in the body wall and limbs, the bones and connective tissue of the limbs, and the sternum.

The splanchnic layer of lateral plate mesoderm, together with embryonic endoderm, forms the wall of the gut tube. (serous membranes, which will line the peritoneal, pleural, and pericardial cavities) Muscles of internal organs

Paraxial mesoderm to somites; forms muscular skeletal system and dermis of back.

31
Q

describe the formation of the intra-embryonic coelom.

A

Lateral plate mesoderm splits into (somatic) and (splanchnic) layers, which line the intraembryonic coelom and surround the organs, respectively

32
Q

describe the formation and fate of the neural plate and outline the development of the neural tube.

A

Notochord-induced thickening of the ectoderm overlying the notochord to produce neurectoderm that has a characteristic key-hole or shoe-print shape, wider cranially than caudally. (neural plate)

(neural folds) Longitudinal ridges at the lateral margins of the neural plate that rise out of the plane of the embryonic disc.

The rudiment of the brain & spinal cord formed by folding of the neural folds of the neural plate towards midline and subsequent fusion. (neural tube)

Overall gives rise to CNS

33
Q

describe the formation of the head fold, tail fold and lateral body folds.

A

https://www.youtube.com/watch?v=yXUv4MPuNTA

Sagittal plane= (median plane, in this case)

Transverse plane = horizontal plane

34
Q

describe the differentiation of somites into dermatome, myotome and sclerotome and the fate of each of these in later development

A

Each somite separates into

a dermatome, which gives rise to an area of skin,

a myotome, which gives rise to a block of skeletal muscle

and a sclerotome, which gives rise to a vertebra and rib.

35
Q

explain the use of the terms “dermatome” and “myotome” in describing the innervation of skin and muscles in the adult.

A

Spinal nerve roots growing out from the neural tube enter and innervate the dermatomes and myotomes. The sclerotomes are rearranged to lie between the nerve roots and become the vertebrae.

The terms ‘ dermatome’ and ‘ myotome’ are used clinically to define an area of skin or muscle supplied from a single spinal nerve root, and the spinal cord is described as having ‘ segments’, each of which gives rise to a nerve root.

36
Q

Somite?

A

Paraxial mesoderm that forms regular segmented blocks on either side of the neural tube. Divided into three components: dermatome, myotome & sclerotome.

37
Q

Dermatome

A

The most lateral of the three components of the somite, contributing to the dermis. In neurology (and clinically applied anatomy), this term is used to describe the strip of skin innervated by a single spinal root.

38
Q

gastrulation, neurulation, segmentation, folding

A

order: gastrulation, neurulation, segmentation, folding

39
Q

Left lung has 2 lobes

A
40
Q

End of fourth week…

A

The nervous system has started to
form
• Segments have appeared, assigning
specific tasks to specific cells
• The embryo has folded, putting
everything in the right place

41
Q

What does folding achieve?

(end of 4th week amniotic sac fully envelopes)

A

Draws together the margins of the disk
• Creating a ventral body wall
• Pulling amniotic membrane around
the disk
• embryo becomes suspended
within the amniotic sac
• Pulling connecting stalk ventrally

Also creates the primordium of the gut,
puts the heart and the primordium of the
diaphragm in the right place & creates a
new cavity within the embryo

42
Q

Nucleus pulposus?

A

Of the intervertebral disc - the vestigial remnant of the notochord in the adult.

(not part of spinal chord)

Esa1 (4 decks)

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