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Anatomy ICOM > Embryogenesis > Flashcards

Embryogenesis Flashcards

1
Q

Embryonic age

A

Time from fertilization

  1. Hard to know clinically
  2. Gestational -2 weeks
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2
Q

Gestational age

A

Time from 1st day of last menstrual period

  1. About 2 weeks before ovulation
  2. Embryonic + 2 weeks
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3
Q

Carnegie stages

A

First 8 weeks = 23 stages based on embryo appearance on structures
1. Can correlate w/ embryonic age

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4
Q

Week 1: implantation

A
  1. Fertilization
  2. Zygote formation
  3. Morula formation
  4. Blastocyst formation
  5. Implantation
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5
Q

Fertilization

A

Day 1: Secondary oocyte + spermatozoan -> zygote
1. Secondary oocyte
A. Meiosis I completed
B. Zona pellucida - thick gel, prevents polyspermia
C. Corona radiata - signals to attract sperm
2. Capacitated spermatozoa: chem rxn to enable fertilization
3. Phase 3: after membrane fusion
A. Spermatozoan w/ acrosomal enzymes -> thru corona radiata
B. Sperm bind and penetrate zona pellucida
C. Membrane fusion -> sperm to cytoplasm
D. Oocyte changes to prevent polyspermy

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6
Q

Zygote formation

A

Day 1:

  1. Oocyte advances to meiosis II
  2. DNA replicated -> pronuclei fuse
  3. Mitosis
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7
Q

Morula formation

A

Day 2-5:

  1. Cells divide w/o growing
  2. Morula at 16 cells (Day 3)
  3. Outer mass
  4. Inner mass
  5. At uterine cavity
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8
Q

Blastocyst formation

A

Days 5-6:

  1. Fluid in -> swelling
  2. Outer mass -> trophoblast
  3. Inner mass -> embryoblast
  4. Blastocoele - fluid surrounded by trophoblasts
  5. Zona pullucida degenerates
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9
Q

Implantation

A

Days 6-7:

  1. Trophoblasts near pole adhere uterine epithelium -> invade endometrium
  2. Blastocyst burrows into endometrium
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10
Q

Embryonic dev. Days 8

A
  1. Trophoblasts invade and differentiate -> layers
    A. Cytotrophoblast - inner layer, mononucleated cells
    B. Syncytotrophoblast- outer layer, multinucleate mass, no cell boundaries
  2. Embryoblasts differentiate -> 2 layer embryonic disc
    A. Epiblast- columnar cells forming floor of amniotic cavity
    B. Hypoblast - cuboidal cells on ventral side
    • induction of ventral surface of embryo
  3. Amnioblast - squamous cells, form roof of amniotic cavity
    A. NOT part of disc
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11
Q

Embryonic dev. Day 9: lacunar stage

A
  1. Trophoblast derivatives:
    A. Cytotrophoblasts and syncytiotrophoblasts proliferate
    B. Lacunae formation - spaces filled w/ maternal blood and debris
    *nutrients and O2 diffuse thru conceptus
  2. Embryoblast derivatives:
    A. Amnioblasts proliferate - allows inc. amniotic cavity
    B. Epiblasts = unchanged
    C. Hypoblasts migrate -> inner surface of cytotrophoblast => exocoelomic cavity (primary yolk sac)
    *replaces blastocoele
  3. Uterus
    A. Conceptus embedded in endometrium
    B. Fibrin coagulum plug forms
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12
Q

Embryonic Dev. Days 10-12

A
  1. Trophoblast derivatives:
    A. Proliferation and invasion cont.
    B. Trophoblastic lacunae + uterine sinusoids -> primitive uteroplacental circulation
  2. Embryoblast derivatives:
    A. Amnioblasts and epiblasts unchanged
    B. Exocoelomic cells proliferate and migrate -> surround amniotic and exocoelomic cavities => extraembryonic mesoderm
    *multiple cavities form and fuse -> chorionic cavity
    1. Extraembryonic somatic mesoderm - lines inner cytotrophoblast
    2. Extraembryonic splanchnic mesoderm- surrounds amniotic and exocoelomic cavities
    3. Connecting stalk- connects 2 extraembryonic mesoderm layers
    C. Hypobalasts opposite stalk differentiate => anterior visceral endoderm (AVE) - induces cranial dev.
  3. Uterus:
    A. Decidua rxn -> provide nutrients for conceptus
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13
Q

Embryonic Dev. Day 13

A
  1. Trophoblast derivatives:
    A. Primary villi form as columns of proliferating cytotrophoblasts that penetrate syncytoiotrophoblasts
    B. Inc. uteroplacental circulation
  2. Embryoblast derivatives:
    A. Amnioblast + extraembryonic splanchnic mesoderm -> amnion
    B. Epiblasts = little change
    C. Hypoblasts - secondary proliferation and migration -> secondary yolk sac
    D. Chorion cavity contains:
    1. Embryo
    2. Secondary yolk sac (umbilical vesicle)
    3. Amniotic sac (secured by connection stalk)
  3. Uterus:
    A. Decidua rxn continues throughout endometrium
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14
Q

Placenta previa

A

Dev. Placenta bridges internal OS opening of cervix

1. Risk of life-threatening bleeding

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15
Q

Ectopic pregnancy

A

Implantation outside uterine body

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16
Q

Placental dev. Conceptus portion

A
  1. Chorionic plate - thickening of extraembryonic somatic mesoderm
  2. Villi - extension of cytotrophoblasts and extraembryonic somatic mesoderm form between lacunae of syncytiotrophoblasts
    A. Stem villi: chorionic plate to decidual plate
    B. Free villi: branches into intervillous space
  3. Outer cytotrophoblast shell adheres decidua
  4. Extraembryonic vessels form and connect w/ dev. Intraembryonic circulatory system
17
Q

Placental dev. Maternal portion

A
  1. Decidua surrounds conceptus
  2. Decidual plate forms
  3. Uterine vessels into cytotrophoblast and intervillous space
    A. Spiral arteries deliver O2 and nutrient blood -> intervillous spaces
    B. Uterine veins remove waste and CO2
18
Q

Placental Dev from chorion and decidua near pole

A
  1. Chorion frondrosum- growth and expansion of villi

2. Decidual basalis w/ decidual plate and septa

19
Q

Dizygotic twins

A

2 secondary oocyte release and fertilized -> 2 zygotes

  1. Conceptus Ed genetically distinct and sexes mixed or matched
  2. Embryos dev. In own amnion and have own umbilical vesicles
  3. Separate placentas and chorion (may end up fusing)
20
Q

Monozygotic twins

A

One secondary oocyte + one sperm -> one zygote
1. Two blastocysts formed during cleavage
A. Own amniotic cavity and umbilical vesicles
B. Separate placenta and chorion (can fuse)
C. Similar to dizygotic but identical DNA

  1. One blastocyst -> 2 embryoblasts
    A. Own amniotic cavity and umbilical vesicles
    B. Shared placenta and chorionic membrane
  2. One blastocyst -> 2 partially separate embryo
    A. Shared amniotic and umbilical vesicle
    B. Shared placenta and chorion membrane
    C. May be conjoined
    *conceptuses identical and same sex
21
Q

Gastrulation

A
  1. Primitive node and streak form (caudal, dorsal) epiblast
  2. Anterior visceral endoderm (AVE) stops node and streak from dev. On hypoblast
  3. Epiblasts migrate thru streak and node -> mesenchymal -> trilaminar disk
    A. Endoderm - replaces hypoblast, form ventral layer
    B. Mesoderm- notochord, prechordal mesoderm (xs cells from endoderm)
    C. Ectoderm- epiblast cells that don’t migrate thru primitive streak
  4. Early embryonic structures
    A. Oropharyngeal and cloacal membrane at craniotomy/caudal regions -> openings to gut tube
    B. Allantios- invagination of endoderm lining of secondary yolk sac near connecting stalk
    C. Primordial germ cells- from epiblast -> endoderm -> embryo -> progenator gametes
  5. Laterality established by gradient of signaling molecules (variation due to disruption)
    A. Situs solitus: normal left/right symmetry
    B. Situs inversus: mirror image of normal
    C. Situs ambiguous (heterotaxy): some organ reversed or asymmetric
22
Q

Neurulation

A

Signals fro notochord and prechordal mesoderm stimulation -> nervous system 1st to dev.
1. Neural plate along midline folds in on itself - 2 regions
A. Neural groove in midline
B. Neural folds (sides)

  1. Neural tube forms from fusion of lateral edges of neural plate
    A. Cranially caudally
    B. CNS cells derived
    1. All somatic efferent neurons
    2. All presynaptic visceral efferent neurons
  2. Neural crest cells from crests of neural folds
    A. Detach and migrate throughout mesoderm
    B. Gives rise to:
    1. Sensory neurons of PNS
    2. Postsynaptic neurons of ANS
    3. Neuroendocrine cells in adrenal gland medulla
    4. Non-neural tissues: melanocytes, facial bones, dermis of face, pharyngeal arch cartilage
  3. Spina bifida: incomplete neural tube in trunk region
23
Q

Surface ectoderm layer

A
  1. Epidermis of skin and appendages
  2. Epithelial lining
    A. Oral and nasal cavities
    B. Distal anus
    C. Distal vaginal canal
24
Q

Mesoderm differentiation

A

Signaling in gastrulation stimulates:
1. Paraxial mesoderm - lines notochord bilateral -> more differentiation
A. Cranial
1. Mastication skeletal muscles
2. Facial expression and pharyngeal muscles
3. Bones of cranial vault
B. Somatic
1. Somites (dermatome, myotome, scleratome)

  1. Intermediate mesoderm- cords lateral to paraxial in trunk region
    A. Urinary system- kidneys and ureters
    B. Reproductive system - supporting stromatolites of gonads and epithelial lining of genital tracts
  2. Lateral plate mesoderm - extends lateral edges of flat embryo, continuous w/ extraembryonic mesoderm
    A. Splanchnic layer + endoderm = splanchnopleure
    1. Smooth muscle and supporting cells of viscera
    2. Visceral serous epithelium
    3. Primordial heart
    4. Blood and lymph vessels
    5. Spleen
      B. Somatic (parietal) + ectoderm = somatopleure
    6. Lining inner body walls
    7. Fibrous pericardium
      C. Coelomic (intraembryonic) cavity - continuous w/ chorionic cavity
25
Q

Endoderm differentiation

A
  1. Epithelial lining
    A. GI tract, gallbladder, glandular ducts, parenchyma of liver and pancreas
    B. Tracheobronchial tree and parenchyma of lungs
    C. Bladder and urethra (from allantois)
26
Q

Embryonic folding (Midweek 3)

A
  1. Lateral folding - lateral edges of somatopleure and splanchnopleure fuse at midline -> “tube w/in tube”
    A. Primitive gut tube = fusion of left and right splanchopleure
    B. Body wall encloses coelomic cavity by fusion of left and right somatopleure
    C. Vitelli new duct = connection between primordial mid-gut and secondary yolk sac
  2. Cephalocaudal folding- cranial and caudal end folding -> fetal position
    A. Primordial heart moves to cervical region
    B. Septum transversum partially divides coelomic cavity superioinferiorly
    C. Allantois - partially incorporated into embryo - connected to primordial hind-gut
  3. Amniotic sac- amniotic membrane pulled by somatopleure -> surrounds embryo and forms umbilical cord
  4. Coelomic cavity division
    A. After cephalocaudal folding
    1. Primordial heart and septum transversum repositioned
    2. Septum tranversum demarcates thoracic and abdominal cavities
    3. Left and right pericardioperitoneal canals still connected to coelomic cavities
    4. Tracheobronchial diverticulum dev. Off foregut
      B. Pleural and pericardial cavity separation
    5. Pleuropericardial folds dev and carry phrenic n.
    6. Lungs grow to fill in cavity
    7. Pleuropericardial folds grow between lungs and heart
      *fuse at midline and to roots of lungs
      *phrenic nerve between pleural and pericardial sac
      *ventral lung expansion between heart and ventral body wall
      C. Separation of pleural and peritoneal cavities
    8. Septum transversum forms ventral partition
    9. Esophagus and mesentary -> median partition
    10. Pleuroperitoneal folds from posterolateral wall and span canals
    11. Myoblasts from cranial somites 3-5 invade periphery of membrane

Anatomy ICOM (34 decks)

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