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Embryology > Lecture 1 > Flashcards

Lecture 1 Flashcards

1
Q

Divides the body into left and right parts

A

Sagittal plane

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2
Q

Divides the body into superior and inferior parts

A

Transverse plane

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3
Q

Divides the body into anterior and posterior parts

A

Frontal (coronal) plane

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4
Q

Vertical plane, divides the body into right and left

A

Sagittal plane

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5
Q

Midsagittal plane - sagittal plane exactly at midline

A

Median plane

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6
Q

Set off from midline

A

Parasagittal plane

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7
Q

The study of the origin and development of an organism

A

Embryology

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8
Q

Prenatal period

A

Before birth

38 weeks from conception to birth

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9
Q

Embryonic period

A

First 8 weeks

All major organs formed

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10
Q

Fetal period

A

Remaining 30 weeks

Organ grow larger and become more complex

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11
Q

Major embryological event in embryonic period

A

Organs form three primary germ tissues called the ectoderm mesoderm endoderm.

Emergence of the basic body plan.

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12
Q

Germ cells become gametes

A

Gametogenesis

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13
Q

Explain primordial germ cells (PGCs)

A

From where gametes come from

  1. Male gamete = sperm
  2. Female gamete = oocyte
  3. Gametogenesis meiosis and mitosis
  4. Cytodifferentiation maturation

They’re formed in the epiblast, 2nd week.

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14
Q

Somatic cells

A

23 homologous pairs of chromosomes

22 autosomes 1 sex chromosomes

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15
Q

Meiosis I

A

Duplication of 46 chromosomes into sister chromatids (diploid number)

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16
Q

Meiosis II

A

Haploid number of chromosomes

Each gamete = 23 chromosomes

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17
Q

Results of meiosis

A
  1. Genetic variy
    1. 1 cross over
    2. 2 random distribution of homologous chromosomes to daughter cells
  2. Haploid number of chromosomes
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18
Q

Critical events in meiosis

A
  1. Crossover
  2. Formation of polar bodies
Females = 1 mature 3 polar bodies
Male = 4 mature
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19
Q

Oogonia become mature oocytes

A

Oogenesis

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20
Q

Maturation of oocytes begins before birth

A

PGC - gonad of a genetic female - oogonia - several mitotic division - end of 3rd month - primordial follicle - primary oocytes some arrested at meiosis 1, prophase

5th mo = 7m germ cells - cell death - atresia
7th mo = majority of oogonia have degenerated

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21
Q

Maturation of oocytes continues at puberty

A

Near time of birth = all primary oocytes have started prophase 1 entering diplotene (resting) stage

Arrested state of primary oocytes - due to presence of oocyte maturation inhibitor (OMI)

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22
Q

Oocytes from birth to puberty

A

At birth = 600k - 800k
Childhood = 40k at the beginning of puberty
Puberty = 500

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23
Q

Females at puberty

A
  1. Meiosis I resumes shortly before ovulation
  2. Meiosis 2 happens before the nucleus of the secondary oocyte returns to its resting stage (meiosis 2, metaphase 2) - prior to ovulation
  3. Meiosis 2 is complete when the oocyte is fertilized
    • fertilization = cell degeneration 24hrs after ovulation
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24
Q

Males at puberty

A
  1. Spermatogenesis
  2. Spermatogonia to spermatozoa
  3. Meiosis I - secondary spermocytes
  4. Meiosis 2 - spermatids
  5. Spermiogenesis - spermatids to spermatozoa
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25
Q

Events on the first week of development

A
  1. Ovulation
  2. Fertilization
  3. Implantation
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26
Q

Events on the first week of development

A
  1. Ovulation
  2. Fertilization
  3. Implantation
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27
Q

Phases of fertilization

A
  1. Penetration of the corona radiata
  2. Penetration of zona pellucida
  3. Fusion of oocyte and sperm cell membranes
    1. 1 cortical and zonal rxns - 1 sperm penetrates ovume.
    2. 2 resumption of 2nd meiotic div - oocyte finishes meiosis
    3. 3 metabolic activation of the egg
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28
Q

Main results of fertilization

A
  1. Restoration of the diploid number of chromosomes
  2. Sex determination of the new individual
    XX = female
    XY = male
    = Chromosomal axe
  3. Initiation of cleavage

**Without fertilization, oocyte usually degenerates 24 hrs after ovulation.

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29
Q

Cleavage facts

A
  1. Begins 12 hour post fertilization
  2. Zygote divides into 2 cells - series mitosis ensue
    = 46 chromosomes in zygote = 46 chromosomes in both daughter cells
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30
Q

Each cleavage division

A

Divided cells = blastomeres

16 cell stage (3 days after fertilization)
=Morula (mulberry)
= Enters the uterus after 3 days in the oviduct

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31
Q

Morula

A

2 cell masses

  • inner cell mass - embryo proper
  • outer call mass - trophoblast - placenta
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32
Q

Blastocyst

A

Morula - entering the uterine cavity, floats freely

Morula begins to accumulate fluid (penetrate the ZP) and forms a cavity (blastocele) between its inner cells

Once the cavity appears it is now called a blastocyst

Blastocyst has fluid filled inner cavity

Evolves from morula on day 5

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33
Q

Day 6 events

A
  1. Trophoblasts over the embryoblast pole begin to penetrate between the epithelial cells of the uterine mucosa
  2. hCG secreted by the trophoblasts
  3. Implantation
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34
Q

hCG is produced

A

Human chorionic gonadotropin

  1. Produced by the trophoblasts starting on day 6
  2. A hormone
  3. Causes endometrium of uterus to grow and proliferate
  4. Prevents the menstrual cycle from occurring
  5. Why a female misses her periods when she is pregnant
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35
Q

Week 2

A
  1. Implantation continues
  2. Erosion of maternal blood vessels
  3. Complete immersion into endometrium of uterus
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36
Q

Day 8

A
  1. Blastocyst partially embedded in the endometrial stroma
  2. Trophoblast differentiates into two layers
    = Inner layer of mononucleated call
    A. Cytotrophoblast
    B. + Mitotic figures
    C. Migrate into the syncytiotrophoblast - fusion - individual cell membranes are lost= Outer multinucleated cells
    A. Syncytiotrophoblast
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37
Q

Embryoblast

A

Differentiates into 2 layers

1. Small cuboidal cells adjacent to cavity
         = Hypoblast

2.  High columnar cells adjacent to the amniotic cavity (within the epiblast
         = epiblast  Forming a bilaminar germ disc

Amnioblasts - epiblast adjacent to the cytotrophs

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38
Q

Day 9

A
  1. Blastocyst more deeply embedded
  2. Trophoblast development progresses - at the embryonic pole with the appearance of vacoules in the syncytium - fusion - forms large lacunae - lacunar stage
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39
Q

Abembryonic pole

A
  1. Formation of Heuser’s membrane (exocoelomic) lines inner surface of cytotrophoblast
  2. Heuser’s membrane with the hypoblast forms the lining of the primitive yolk sac (exocoelomic cavity)
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40
Q

Day 11 and 12

A
  1. Blastocyst completely embedded, producing a slight protrusion into the uterine lumen
  2. Establishment of the uteroplacental circulation
    • trophoblast continues to erode more and more sinusoids, maternal blood begins to flow through the trophoblastic system
      * Formation of the extramebryonic mesoderm (EEM)
  3. Formation of large cavities in the EEM - confluence of cavities - EE coelom or chorionic cavity = surrounds the primitive yolk sac and amniotic cavity
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41
Q

Lines the cytotrophoblast and amnion

A

EE somatopleuric mesoderm

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42
Q

Lines the yolk sac

A

EE splanchopleuric mesoderm

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43
Q

Day 13

A
    • Of villous structures in the trophoblast
  2. Formation of primary villi
  3. Formation of secondary yolk sac or definitive yolk sac (proliferation of the hypoblast)
    • Exocoelomic cysts found in the chorionic cavity
  5. Expansion EE coelom forming chorionic cavity
  6. EEM lining the inside of the cytotrophoblast called the chorionic plate
  7. Connecting stalk is traversed by the EEM

= With development of blood vessels = umbilical cord

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44
Q

End of week 2

A

Two apposed cell discs: epiblast (floor of the amniotic cavity); hypoblast (roof of the secondary yolk sac)

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45
Q

Cephalic region of the hypoblastic disc

A

Buccopharyngeal membrane or oropharyngeal membrane

46
Q

Week 2 events - week of twos

A
  1. Trophoblast - differentiates into cyto and syncytio
  2. Embryoblast - into epiblast and hypoblast
  3. EEM - splits into somatopleure and splanchnopleure
  4. 2 cavities - amniotic and yolk sacs
47
Q

Establishment of all germ layers. Ecto, meso, endo.

A

Gastrulation

48
Q

Week 3 events

A
  1. Appearance of primitive streak
  2. Formation of the notochord
  3. Cloacal membrane formation
  4. Allantois (16th day)
  5. Primary villi with mesenchymal core where small capillaries arise
  6. Establishment of the body axes
49
Q

After invagination, some displace the hypoblast

50
Q

Lie between epiblast and new endoderm

51
Q

Cells remaining in the epiblast

52
Q

Controls cell migration and specification from streak cells

  1. 1 down - regulating E-cadherin (binds epiblast)
   1. 2 into the mesoderm by regulating BRACHYURY (T) expression
A

Fibroblast growth factor 8

53
Q

Inhibit nodal activity; establishing cranial end of embryo

A

Cerberus and Left 1

54
Q

Absent in caudal end; + nodal expression =

A

Establish and maintain primitive streak

55
Q

Primitive streak is formed…

A
  1. Nodal upregulates genes responsible for :
    A. Dorsal and ventral mesoderm formation
    B. Formation of head and tail structures
56
Q

BMP4 with FGF

A
  1. Mesoderm is centralized

2. Antagonized by CHORDIN, noggin and follistatin = dorsal mesoderm

57
Q

Maintains node, induces regional specificity in the forebrain and midbrain

58
Q

Activates inhibitors of BMP4, regulate head dev’t

59
Q

It’s expression is induced by FGF8; restricted to left side by accumulation of serotonin (activate MAD3 - restricts Nodal to left)

60
Q

Establish midline; prevent Nodal from crossing over to right

A

Midline genes - SHH, lefty 1, ZIC3

61
Q

Upregulated by Lefty2, HB gene establish left sidedness

62
Q

Restricted right LPM; probably regulate effector genes for establishing right handedness

63
Q

Once this is formed, genes regulate formation of dorsoventral mesoderm and head and tail structures

A

Once primitive streak is formed

64
Q

By cascade of genes

Heart, spleen, main lobe of liver on the right

A

Left-right asymmetry

65
Q

What period is in the 3rd to 8th week

A

Embryonic period

66
Q

This period is characterized by development of structures (organs)

A

Embryonic period

67
Q

Characterized by growth of those structures

A

Fetal period

68
Q

Formation of the 3 germ layers

A
  1. Primitive streak (groove) on dorsal surface of epiblast
  2. Gastrulation: invagination of epiblast cells
  3. Days 14-15: they replace hypoblast becoming endoderm
  4. Day 16: mesoderm (a new third layer) formed in between
  5. Epiblast cells remaining on surface: ectoderm
69
Q

Are epithelial tissue (form sheets of tissue)

A

Ectoderm and endoderm

70
Q

Is a m mesenchyme tissue

71
Q

Are star shaped and do not attach to one another, therefore migrate freely

A

Mesenchyme cells

72
Q

Beginning of 3rd week

A
  1. Disk shaped ectodermal germ layers - broader ciphalic part
  2. Appearance of notochord and prechordal mesoderm - overlying ectoderm thickens
    = Neural plate
    = It’s cells - neuroectoderm
    = Initial process of neurulation
73
Q

Notochord

A
  1. Days 16-18
  2. Primitive node epiblast cells invaginate and migrate anteriorly with some endoderm cells
  3. Rod defining the body axis is formed
  4. Future site of the vertebral column
74
Q

Neural plate forms the neural tube

A

Neurulation

75
Q

Neurulation process

A
  1. lengthening of the neural plate NP and body axis thru convergent extension
    - lateral to medial movement of cells in ectodermal and mesodermal plan
  2. As the NP lengthens, it’s lateral edges elevate forming neural folds, the depressed midregion is the neural groove.
  3. Neural folds fuse in the midline, beginning at the cervical region (5th somite), then cranial and caudal directions forming neural tube.
  4. Communication between cranial and caudal ends of NT with amniotic cavity is via anterior and posterior neuropores
  5. Cranial neuropore closed at day 25 (18-20 somite stage)
  6. Caudal neuropore closed at day 28 (25 somite stage)
  7. Neurulation is complete
76
Q

Neurulation 3rd to 8th week

A
  1. Notochord signals overlying ectoderm
  2. Neurulation - when complete, the CNS is represented by a closed tube with narrow caudal end, the spinal cord; broader cephalic end; the brain vesicles
  3. Closure of neural tube: begins at end of the week 3; complete by end of week 4 (folic acid important for this step)
  4. Extends cranially (eventually brain) and caudally (spinal cord)
  5. Neural crest, lateral ectodermal cells, pulled along and form sensory nerve cells and other structures.
77
Q

Mesoderm begins to differentiate

A
  1. Lateral to the notochord week 3

2. Extends cranially and caudally (from head to tail or crown to rump)

78
Q

Division of mesoderm into three regions

A
  1. Somites: 40 pairs of best segments (repeating units, like building blocks) by end week 4
  2. Intermediate mesoderm: just lateral to somites
  3. Lateral plate: splits to form coelom (cavity)
79
Q

Divisions of the mesodermal lateral plate

A
  1. Somatic mesoderm: apposed to the ectoderm
  2. Splanchnic mesoderm: apposed to the endoderm
  3. Coelom in between will become the serious cavities of the ventral body cavity:
    A. Peritoneal
    B. Pericardial
    C. Pleural
80
Q

About what months are all major organs are in place in at least a rudimentary form

81
Q

BMP 4 regulating factors: ectoderm

A
  1. It’s inactivation induces neural plate formation

2. It’s inactivation in the hindbrain and spinal by: WNT3a and FGF

82
Q

Cranially inactivation is caused by

A

Noggin
Chordin
Follistation

83
Q

Regulating factors mesoderm

A

SHH
WNT proteins, BMP4, FGF
NT3

84
Q

Produced by notochord and floor plate of the neural tube induces sclerotome

A

Since Hedgehog SHH

85
Q

Muscle forming regions

A

WNT proteins
BMP4
FGF

86
Q

Secreted by dorsal ntube

87
Q

Regulating factors endoderm

A

Homeobox genes (Drosophila)

88
Q

Homeobox genes Drosophila

A
  1. Craniocaudal patterning

2. HOXA, HOXB, HOXC, HOXD

89
Q

Gut tube and body cavities end of 3rd weej

A
  1. Ntube - elevates and closes dorsally
  2. Gut tube - rolls and closes ventrally

Tube on top of a tube

90
Q

It holds the tubes together

LP - visceral (splanchnic), parietal (somatic)

91
Q

Space between visceral and parietal layers

A

Primitive body cavity

92
Q

Parietal layer + ectoderm

A

Lateral body wall folds

Meet in the midline at the end of the 4th week and fuse closing the ventral let wall aided by growth of head and tail regions

93
Q

Curving of the embryo

A

Fetal position

94
Q

Parietal layer of the peritoneum, pleura, pericardium

A

Parietal mesoderm

95
Q

Visceral layer of p p p

A

Visceral mesoderm

96
Q

Peritoneum doubles

97
Q

Pathway for vessels, nerves, and lymphatics

98
Q

Divides the body cavity into thoracic and peritoneal cavity

99
Q

Diaphragm is developed from:

A
  1. Septum transversum (central tendon)
  2. Pleuroperitoneal membranes
  3. Dorsal mesentery of the esophagus
  4. Muscular components from somites At C3-5

Phrenic nerve also arise from C3-5

100
Q

Components of placenta

A
  1. Fetal - from the chorion frondosum or villous chorion

2. Maternal portion - from decidua basalis

101
Q

Functions of placenta

A
  1. Exchange of gases
  2. Exchange of nutrients and electrolytes
  3. Transmission of maternal Abs, providing the fetus with passive immunity
  4. Production of hormones: progesterone, estradiol, hCG, somatomammotopoin
  5. Detoxification of drugs
102
Q

Umbilical cord surrounded by amnion containd

A
  1. 2 umbilical arteries
  2. 1 umbilical vein
  3. Wharton jelly - protection for the vessels
103
Q

2 amnions 2 chorions 2 placentas

A

Dizygotic or fraternal twins

104
Q

2 amnions 1 chorion 1 placenta

A

Monozygotic or identical twins

105
Q

1 amnion 1 chorion 1 placenta

A

Conjoined twins

106
Q

Where epiblasts (flask shaped) invaginate to form Endo and mesoderms

A

Primitive streak

107
Q

Steps of the formation of notochord

A
  1. From the prenotochordal cells and hypoblast (later replaced endodermal cells)
  2. Further forms a midline axis = basis of axial skeleton
  3. Underlies the neural tube
  4. Prechordal plate (PP) forms between the tip of the notochord and bp membrane
    * Pp = induction of forebrain
108
Q

Where is the cloacal membrane formed

A

End of the embryonic disc

109
Q

End of 3rd week

A
  1. Ecto, meso, endodermal established in the head region.

2. Tissue and organ differentiation begins in cephalocaudal direction

110
Q

Establishment of the body axes

A
  1. Anteroposterior (AP), dorsoventral, left-right
  2. Prior to and during gastrulation

Ap = signaled by cells at the posterior margin of embryonic disc (posterior marginal zone PMZ)

PMZ- induces primitive streak formation, establishes cranial to caudal axis in embryo

111
Q

Small diverticulum extending into the connecting stalk; posterior wall of the yolk sac

Embryology (4 decks)

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