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Tissues of body > Session 9: The Pre-embryonic Period and Gastrulation > Flashcards

Session 9: The Pre-embryonic Period and Gastrulation Flashcards

1
Q

Embryogenesis lasts how many weeks?

A

8 weeks

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2
Q

Foetal period lasts how many weeks?

A

32 weeks

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3
Q

Average gestation period in humans is ___ weeks?

A

40 weeks

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4
Q

First trimester?

A

0-12 weeks

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5
Q

What is spermatogenesis triggered by?

A

Testosterone produced by Leydig cells of testis during puberty

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6
Q

Testosterone is produced by what cells?

A

Leydig cells of testis

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7
Q

Testosterone production is under the control of what hormone?

A

Pituitary luteinizing hormone (LH)

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8
Q

Spermatogenesis process?

A

1) Multiplication Phase
- Spermatogonia enter mitotic division to form primary spermatocyte

2) Growth Phase
- Primary spermatocyte enters meiosis 1
- Secondary spermatocyte enters meiosis 2 to form spermatid

3) Maturation Phase
- Spermatid undergoes spermiogenesis to form spermatozoa

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9
Q

Oogenesis process?

A

Foetal Life
- Oogonia enter mitotic division to form primary oocyte
- Primary oocyte enters meiosis 1
- Primary oocytes arrest at prophase 1 stage of meiosis 1 until puberty (beginning of menstrual cycle)

Beginning of Menstrual Cycle
- Primary oocyte becomes a secondary oocyte
- Secondary oocyte arrests at metaphase 2 of meiosis 2 until fertilisation occurs

Fertilisation
- Secondary oocyte undergoes completion of meiosis 2 to form an Ovum

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10
Q

Primary oocytes arrest at what stage of meiosis 1 until beginning of menstrual cycle?

A

Prophase 1

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11
Q

Secondary oocytes arrest at what stage of meiosis 2 until fertilization takes place?

A

Metaphase 2

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12
Q

Sperm vs Ovum?

A

Sperm
- 55µm (smaller)
- Motile (tail)
- Acrosome head full of enzymes for penetrating ovum
- Lots of mitochondria for energy (motility of sperm tail)

Ovum
- Larger (~0.1 mm) - largest cell in human body
- Immotile
- Two protective membranes = corona radiata (outermost) and zona pellucida (innermost)

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13
Q

First (outer) protective membrane of the ovum?

A

Corona radiata - follicular cells

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14
Q

Zona pellucida is made of ___?

A

proteoglycans

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15
Q

Second (inner) protective membrane of the ovum?

A

Zona pellucida - proteoglycans

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16
Q

Corona radiata is made up of ___ cells?

A

follicular

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17
Q

Fertilisation?

A

Fusion of male and female gametes to form a zygote

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18
Q

In order to fertilise the egg, the sperm must undergo ___?

A

Capacitation

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19
Q

Describe the first phase of fertilisation?

A

Penetration of the corona radiata

The enzyme hyaluronidase released from acrosome of sperm penetrates the corona radiata (outermost membrane of ovum) which is made of follicular cells. This process is aided by movements of the tail of the sperm.

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20
Q

Describe the second phase of fertilisation?

A

Penetration of the zona pellucida

Acrosome reaction. Release of proteolytic enzymes including acrosin that causes lysis of the zona pellucida (innermost membrane of ovum). This allows sperm to come into contact with ovum plasma membrane.

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21
Q

Describe the third phase of fertilisation?

A

Fusion of the plasma membrane of ovum and sperm

The fusion of plasma membrane of ovum and sperm leads to the hardening of zona pellucida. This hardening prevents other sperm from entering ovum.

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22
Q

Describe the fourth phase of fertilisation?

A

Completion of second meiotic division of the ovum

Secondary oocyte undergoes completion of Meiosis 2. Formation of two daughter cells which include = second polar body (hardly receives cytoplasm) and one mature definitive ovum. Chromatin material of the mature ovum (22, X) is arranged into the female pronucleus.

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23
Q

Describe the fifth phase of fertilisation?

A

Formation of the male pronucleus

Chromatin material of the sperm is organised into the male pronucleus. Sperm tail detaches, degenerates. Combination of 23 chromosomes in each pronucleus forms a zygote of 46 chromosomes. DNA replication occurs in each pronucleus - in preparation for division of zygote.

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24
Q

Describe the sixth and final phase of fertilisation?

A

Metabolic activation of the ovum

Breakdown of pronuclear membranes and the mixing of maternal and paternal chromosomes. Chromosomes organised onto a spindle in preparation for normal mitotic division.

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25
The first cleavage of the zygote occurs roughly ___ hours after fertilisation?
30
26
What are the consequences of fertilisation process? Describe four consequences.
1) Secondary oocyte completes meiosis 2 producing a second polar body 2) Restoration of normal diploid number of chromosomes (2n = 46 chromosomes) in zygote 3) Variation in human species through mingling of paternal and maternal chromosomes - fertilisation is RANDOM! 4) Determination of the chromosomal sex of the embryo
27
Dizygotic twins?
Fraternal twins ## Footnote These siblings result from two separately fertilized eggs. Two separate placentas. Different genetic material (non-identical).
28
Monozygotic twins?
Identical twins ## Footnote These arise from single fertilisation event. Shared placenta. Identical genetic material.
29
Risk factor in mothers for monozygotic twins?
Older mothers (ageing)
30
What is the cleavage process of the zygote?
Series of repeated mitotic divisions of the zygote which features a rapid increase in the number of blastomere cells (totipotent cells)
31
After the ___ cleavage of the zygote = the compaction process takes place?
After the third cleavage of the zygote = the compaction process takes place
32
Three days after fertilisation - what is the name of the structure formed from dividing zygote?
16-cell morula ## Footnote In the morula - all cells are the SAME and undifferentiated.
33
Four days after fertilisation - what is the name of the structure formed from dividing zygote?
Blastocyst ## Footnote In the blastocyst, cells are not the same - they are differentiated.
34
Structure of a blastocyst?
- Outer = trophoblast surrounding embryo - Inside cavity = blastocoele - Inner cell mass (ICM) = give rise to embryo (embryoblast)
35
The inner cell mass (ICM) is where stem cells are extracted. These embryonic stem cells are ___?
Pluripotent
36
Pluripotent?
Able to give rise to multiple, but not all, cell types.
37
Embryo hatching?
5 days after fertilisation ## Footnote Embryo liberates itself from the zona pellucida shell, leaving it behind.
38
Implantation of the embryo?
6 days after fertilisation - The hatched blastocyst attaches itself to the endometrial epithelium (decidua) - Trophoblast outer layer rapidly proliferates and differentiates into = cytotrophoblasts and synctiotrophoblasts ## Footnote Synctiotrophoblasts erode maternal endometrium, enabling embryo to burrow and implant securely.
39
What feature of synctiotrophoblasts allow them to burrow into the maternal endometrium?
Synctiotrophoblasts produce proteolytic enzymes that erode the maternal tissue which enables the embryo to burrow and implant securely into the endometrium.
40
The second week post-fertilisation is characterised by the formation of what structure?
Formation of the bi-laminar embryonic disc ## Footnote Differentiation of the inner cell mass (ICM) into flat, bilaminar embryonic disc consisting of epiblast and hypoblast cells.
41
Epiblast eventually gives rise to the...?
embryo
42
Day 9-10 post-fertilisation?
Implantation continues with the formation of a fibrin plug. The appearance of vacuoles in the synctiotrophoblasts join to form lacunae. ## Footnote These lacunae soon reach capillaries of maternal tissue and become filled with blood, allowing for the exchange of nutrients/gases. Amnioblast cells separate from the epiblast and organise to form the amnion (a thin membrane that encloses the amniotic cavity). Hypoblast cells proliferate to form the primary yolk sac.
43
Day 11-13 post-fertilisation?
The hypoblast gives rise to extraembryonic mesoderm which splits to form the chorionic cavity. ## Footnote Transformation of the primary yolk sac to the secondary yolk sac. Beginning of utero-placental circulation occurs as the lacunae fill with maternal blood.
44
The chorion eventually gives rise to the fetal part of the ___?
placenta
45
WEEK 2 - The hypoblast becomes...?
46
WEEK 2 - The epiblast becomes...?
47
Name two abnormalities that can occur during week two post-fertilisation in the developing embryo?
Ectopic pregnancy - Abnormal implantation (uterine tube or outside uterus) Molar pregnancy (Hydatidiform Mole) - Occurs when only the trophoblast layers of embryo proliferate and epiblast layer FAILS to proliferate. No embryo forms as a result.
48
Gastrulation occurs during the third week of embryonic development. What is gastrulation?
Gastrulation is the process by which bi-laminar embryonic disc is converted to a tri-laminar embryonic disc which has three germ layers... Ectoderm (outer) Mesoderm (middle) Endoderm (inner)
49
Gastrulation is the beginning of ___?
Morphogenesis
50
The beginning of gastrulation is marked by the formation of a transient structure formed from epiblast cells called the ___ ___ on day 15?
Primitive streak
51
Primitive streak formation?
Primitive streak **begins in caudal end of embryo (butt)** and moves **towards cranial end (head)** elongating to form a primitive groove. ## Footnote At the cranial end - epiblast cells form circular cavity known as the primitive pit.
52
Gastrulation process?
Epithelial cells at the lateral edge of the epiblast undergo epithelial-to-mesenchymal (EMT) transition. ## Footnote Invagination of ingression of mesenchymal cells - cells migrate down into the primitive streak. The first set of cells to move down which integrate into hypoblast layer become the endoderm (innermost). The second set of cells to move down primitive streak become the mesoderm (middle). The last set of cells to move down primitive streak become the ectoderm (outer).
53
The consequence of gastrulation process is the formation of a ___ map?
Fate map
54
All our tissues and structures derive from these three important layers...
Endoderm (inner) Mesoderm (middle) Ectoderm (outer)
55
Derivatives of the three germ layers?
**Endoderm (inner)** - Respiratory tract - Lining of GI tract - Parenchyma of major digestive glands **Mesoderm (middle)** - Muscle - Bone - Urinary system - Vascular system **Ectoderm (outer)** - Nervous tissue - Sweat glands - Epidermis
56
Name TWO abnormalities arising during gastrulation process?
**1) Caudal dysgenesis (sirenomelia)** - **Insufficient mesoderm** in **caudal**-most region of embryo - Abnormalities of lower limbs/urogenital system **2) Sacrococcygeal teratomas** - **Primitive streak persists** and results in **tumour in sacrococcygeal region** - Most common newborn tumour
57
Most common tumour found in newborns arising from persistence of the primitive streak?
Sacrococcygeal teratomas
58
Caudal dysgenesis (sirenomelia)?
Insufficient mesoderm in caudal-most regions of embryo Abnormalities of lower limb and urogenital region
59
Some causes of male infertility?
- Reduced motility of sperm - Having low levels of sperm - Having abnormally shaped sperm ## Footnote Link to previous lecture = Kartagener′s syndrome causes immotile sperm leading men to be sterile.
60
Some causes of female infertility?
- Problems with ovulation - Thickening of cervical mucus - Scarring of ovarian tubes or cervix from surgery - Pelvic inflammatory disease
61
The translucent glycoprotein shell surrounding the oocyte that dissolves prior to implantation?
Zona pellucida
62
What is the outcome of the first cleavage of the zygote?
Two blastomeres of equal size
63
What is the specific name for the embryo at the 16 cell stage?
A morula
64
Each cell is totipotent at the 16 cell stage. What does this mean?
Cells have the potential to become any cell type
65
When does fate become more restricted to many rather than all lineages?
Following compaction (when cell becomes blastocyst)
66
What structure forms following compaction?
The blastocyst
67
What is the fate of the inner cell mass?
It forms the embryo and some extraembryonic structures.
68
The key event following implantation is the transition from
69
The key event following implantation is the transition from histiotrophic to haemotrophic nutrition. How is this achieved?
Establishment of maternal blood flow
70
Name the disorder: Poor growth of foetus due to, for example, poor supply of oxygen and nutrients.
Intra-uterine growth restriction (IUGR)
71
Name the disorder: An obstetric complication arising from implantation in the lower uterine segment.
Placenta praevia
72
Name the disorder: Incomplete differentiation of cytotrophoblast cells into endothelium results in poor blood supply to the embryo, one consequence of which is maternal hypertension.
Pre-eclampsia
73
A potentially life-threatening disorder resulting from implantation outside the womb.
Ectopic pregnancy
74
From which collection of cells does the primary yolk sac form?
Extraembryonic mesoderm
75
How long is the pre-embryonic period?
Two weeks
76
Identify the following structure in a day 9 embryo.
A = Trophoblast lacunae B and C = Enlarged blood vessel D = Synctiotrophoblast E = Cytotrophoblast F = Amniotic cavity G = Epiblast H = Hypoblast I = Exocoelomic membrane J = Fibrin plug K = Primitive yolk sac
77
Identify the structures in this image depicting gastrulation.
A = Epiblast B = Primitive pit C = Primitive streak D = Invaginating mesodermal cells E = Hypoblast
78
Identify the axes marked on this image of the anatomical position.
C-D = Posterior-anterior A-B = Cranial-caudal E-F = Right-left
79
Name a disorder that is routinely detected by pre-implantation screening?
Cystic fibrosis
80
From which cell layer is the notochord derived?
Epiblast
81
Identify the transverse, coronal and sagittal planes.
Coronal = Plane 1 Transverse = Plane 2 Sagittal = Plane 3
82
Cognitive impairment caused by teratogen...
Alcohol
83
Multiple defects including microcephaly, visual impairment, cognitive impairment is caused by the teratogen...
Maternal cytomegalovirus infection
84
Shortened limbs is caused by the teratogen...
Thalidomide
85
Toxoplasmosis from poorly cooked meat leads to what developmental outcome?
Hydrocephalus
86
Most common site for implantation
Stroma of posterior uterine wall
87
Which highly-invasive layer of the embryo interacts with the connective tissue of the endometrium to facilitate implantation?
Synctiotrophoblast
88
Identify the structures in the following diagram showing an embryo at day 13 following fertilisation.
A = Primary chorionic villi B = Amniotic cavity C = Epiblast D = Cytotrophoblast E = Secondary yolk sac F = Remnant of primary yolk sac
89
In the following photomicrograph of a histological section of developing tongue, myotubes are labelled A. What type of tissue is labelled B?
Mesenchymal connective tissue
90
Which of one of the following is not a common source of DNA to allow genetic testing for foetal abnormalities in a pregnant woman? A) Amniocentesis B) Foetal DNA in the mother's blood stream C) A chorionic villus sample D) An isolated cell at the morula stage
An isolated cell at the morula stage
91
What stage of embryogenesis does this image represent?
Embryo hatching
92
What stage of embryogenesis does this image represent?
Implantation of the embryo
93
Day 7-8 post-fertilisation
94
Day 9-10 post-fertilisation
95
Day 11-13 post-fertilisation
96
Formation of the tri-laminar disc during gastrulation
The beginning of gastrulation is marked by formation of transient structure from epiblast cells called the primitive streak (day 15) - Starts at caudal end - Moves to cranial end, elongating to form primitive groove - At cranial end = epiblast cells form circular cavity called primitive pit - Primitive pit cells enlarge to form primitive node
97
What is occurring in this image taken during gastrulation?
Epithelial cells at the lateral edge of epiblasts undergo 'epithelial-to-mesenchymal' (EMT) transition - Invagination or ingression = cells become flask-shaped and move down into the primitive streak - First set to move down = endoderm (innermost) - Second set = mesoderm - Third set = ectoderm (outermost)

Tissues of body (14 decks)

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