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Lower Extremity Anatomy > General Embryology 1 > Flashcards

General Embryology 1 Flashcards

1
Q

Oocytes

A
  • 2 million at birth
  • 40,000 at puberty
  • 400 ovulated
  • LH surge causes changes within the ovary and egg for it to rupture
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2
Q

Egg is surrounded by

A
  • Zona pelucida

- Corona radiate

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3
Q

Zona pelucida

A
  • Layer of glycoproteins
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4
Q

Corona radiate

A
  • Granulosa cells

- Surround the ovary after ovulation

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5
Q

Early egg development

A
  • Egg swept into oviduct (uterine tube)
  • Fertilization
  • Begins process of cellular division (cleavage)
  • Enters uterus (day 4)
  • Implantation into uterine wall
    begins 6th embryonic day
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6
Q

Week 1 (days 1-6) of oocyte development

A
  • Fertilization, day 1
  • Cleavage, day 2-3
  • Compaction, day 3
  • Blastocyst formation, day 4
  • Implantation begins, day 6
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7
Q

Fertilization usually occurs in

A
  • Ampulla of the uterine tubes
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8
Q

Fertilization steps (8)

A
  • Multiple sperm bind to corona radiate
  • Sperm passes through the corona radiata
  • Sperm binds to a ZP protein in the zona pellucida
  • Cell membrane of 1 sperm fuses with cell membrane of oocyte
  • Initiates calcium influx causing the release of cortical granules (cortical reaction)
  • Completion of 2nd meiotic division of the oocyte
  • Male and female pronuclei form fuse
  • Arrangment of the chromososmes for mitotic cell division
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9
Q

Sperm binds to a ZP protein in the zona pellucida, causing

A
  • Release of enzmes

- Allow it to burrow through ZP (acrosome reaction)

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10
Q

Initiation of calcium influx by fusion causes

A
  • Release of cortical granules (cortical reaction)

- Blocks other sperm from fertilizing egg

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11
Q

Zygote

A
  • Result of the union of the male/female gametes
  • Restores 46
  • Maternal/paternal chromosomes are mixed
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12
Q

Cleavage of zygote

A
  • Repeated mitotic cell division

- Results in an increase in cell number (not size)

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13
Q

Blastomere

A
  • A cell formed by cleavage of a fertilized ovum
  • Becomes smaller with division
  • Early blastomeres are totipotent (capable of giving rise to any cell type)
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14
Q

8 cell stage

A
  • Compaction begins
  • Blastomeres tightly align by increased cell adhesion
  • Segregate inside vs. outside
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15
Q

Blastomere cell segregation (inside vs. outside)

A
  • Outer cells become trophoblast (will form placenta)

- Inner cell mass will form embryo

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16
Q

Morula

A
  • Conceptus with 16-32 blastomere
  • Inner cells and outer cells
  • Enters uterus ~ 4 days after fertilization
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17
Q

Blastocytic cavity

A
  • Created by sodium and water being pumped into embryo
  • Mostly separates the embryoblast and trophoblast
  • Embryo is called a blastocyst
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18
Q

~ 6 days after fertilization

A
  • Blastocyst attaches to endometrium

- Blastocyst “hatches” from zona pellucida prior to implantation

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19
Q

Blastocyst “hatches” from zona pellucida by

A
  • Enzymatically bores a hole and squeezes out
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20
Q

Implantation in the wrong location (ectopic pregnancy) can be caused by

A
  • Early ZP shedding

- Delayed zygote transport

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21
Q

Week 2: days 7-14

A
  • Embryo becomes more deeply embedded within endometrium
  • Development of trophoblast into placenta precursor
  • Formation of bilaminar embryo, amniotic cavity
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22
Q

(~Day 7) Trophoblast proliferates and differentiates into

A
  • Cytotrophoblast

- Syncytiotrophoblast

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23
Q

Cytotrophoblast

A
  • Stem cell population that adds cells to the syncytioblast
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24
Q

Syncytiotrophoblast

A
  • Derived from cytotrophoblast proliferation

- Cells lose membranes and form a syncytium

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25
Q

Syncytiotrophoblast is located

A
  • At the embryonic pole

- Adjacent to embryoblast)

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26
Q

Syncytiotrophoblast on day 8

A
  • Begins invading into the endometrium
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27
Q

(~Day 10) Blastocyst/embryo becomes

A
  • Completely embedded within the endometrium
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28
Q

Synctytiotrophoblast contacts uterine vessels and glands, creating

A
  • Primitive uteroplacental circulation
  • Lacunae filled with maternal blood
  • Lacunae fuse creating a lacunar network
29
Q

Cytotrophoblast forms extensions that grow into overlying synctiotrophoblast to form

A
  • Chorionic villi
  • Villi become penetrated by extraembryonic mesoderm
  • Eventually form blood vessels (week 2 and 3)
30
Q

By day 8, the embryoblast differentiates into

A
  • 2 epithelial cell layers
  • Epiblast
  • Hypoblast
31
Q

Epiblast

A
  • Columnar cells adjacent to amniotic cavity

- Dorsal side of embryo

32
Q

Hypoblast

A
  • Small cuboidal cells adjacent to exocoelomic cavity

- Primitive yolk sac

33
Q

Epiblast + Hypoblast

A
  • Forms into a bilaminar embryonic disc

- Located between amniotic cavity and the primary umbilical vesicle

34
Q

Amniotic cavity

A
  • Forms within the epiblast

- Epiblast cells migrate forming the amnion (which encloses the amniotic cavity)

35
Q

Hypoblast migration

A
  • Lines the blastocystic cavity

- Forms the exocoelomic membrane

36
Q

Blatocystic cavity

A
  • Referred to as the primary umbilical vesicle (primary yolk sac)
37
Q

Extraembryonic mesoderm

A
  • Located outside the embryo
  • Produced by hypoblast and cytotrophoblast
  • Proliferates and develops spaces within
38
Q

Spaces within the extraembyronic mesoderm

A
  • Fuse to form the extraembryonic coelom (chorionic cavity)
39
Q

Extraembryonic coelom (chorionic cavity)

A
  • Fluid filled cavity
  • Surrounds the umbilical vesicle and amnion
  • Except at connecting stalk (precursor to the umbilical cord)
40
Q

Week 3: days 14-21

A
  • Appearance of primitive streak
  • Development of the notochord and neural induction
  • Differentiation of 3 germ layers (gastrulation)
41
Q

Gastrulation

A
  • Process where the bilaminar embryonic disc is converted into a trilaminar embryonic disc
  • Beginning of morphogenesis
42
Q

Morphogenesis

A
  • Development of the form and structure of organs and parts of the body
43
Q

3 germ layers developed in gastrulation

A
  • Ectoderm
  • Endoderm
  • Mesoderm
44
Q

Ectoderm

A
  • Outside layer

- Gives rise to skin and nervous tissue

45
Q

Mesoderm

A
  • Middle layer

- Generates most of the muscle, blood and connective tissue

46
Q

Endoderm

A
  • Epithelial lining and glands of the gut, lung, urogenital tract
47
Q

Onset of gastrulation

A
  • Beginning of the 3rd week with the formation of the primitive streak
48
Q

Primitive streak location

A
  • Appears caudally in the medial plane

- Dorsal aspect of embryonic disc

49
Q

Primitive streak formation

A
  • Epiblast proliferates and migrate toward the median plane of the embryonic disc
50
Q

Epiblast dives within the primitive streak

A
  • Pushes away hypoblast, forms definitive endoderm
  • Forms mesoderm in between ectoderm and endoderm
  • Remaining epiblast form the ectoderm
51
Q

Elongation of primitive streak

A
  • Addition of cells to the caudal end
52
Q

Appearance of primitive streak allow identification of

A
  • Cranial/caudal
  • Dorsal/ventral
  • Left/right
  • Medial/lateral
53
Q

Cell proliferation at the cranial end

A
  • Forms the primitive node

- Primitive node functions as a signaling center

54
Q

Mesoderm is patterned based on

A
  • Where the epiblast pass through the primitive streak
  • Closer to primitive node the more axial in location
  • Notochord
  • Paraxial mesoderm
  • Intermediate mesoderm
  • Lateral mesoderm
55
Q

Notochordal process

A
  • Cellular rod
  • Formed by cell migration cranially from the primitive node/pit
  • Formed by day 20
56
Q

The notochord

A
  • Defines embryo axis and provides support

- Serves as an important signaling center in the development of the gut, vertebral column and CNS

57
Q

Notochord degeneration

A
  • Degenerates as the vertebrae form

- Part persist as the nucleus pulposus

58
Q

Neurulation

A
  • Formation of the neural tube
59
Q

Neurulation process

A
  • Forming the neural plate
  • Neural plate inviginates to form neural groove with lateral neural folds
  • Neural folds fuse forming the neural tube (week 4)
  • Neural tube separates from overlying ectoderm (week 4)
60
Q

Folding and closure of the nueral plate

A
  • Closure first begins in the cervical region

- “Zips” up toward the head and down toward the tail

61
Q

2 openings of the neural plate upon closure

A
  • Anterior neuropore (closes day 25)

- Posterior neuropore (closes day 28)

62
Q

Errors in neurulation

A
  • Raschischisis
  • Anencephaly
  • Spina bifida
63
Q

Raschischisis

A
  • Failure of neural tube folding
64
Q

Anencephaly

A
  • Failure of anterior neuropore closure
65
Q

Spina bifida

A
  • Failure of posterior neuropore closure (other causes)
66
Q

Neural crest cells

A
  • Group of cells that arise in the ectoderm at the margins of the neural plate
  • Form a flattened mass on the dorsolateral aspect of neural tube
  • Detach from the neural tube and become migratory
67
Q

Neural crest cells contribute to many structures

A
  • Neurons of the spinal ganglia, ANS ganglia, cranial nerve ganglia
  • Enteric ganglia (gut)
  • Melanocytes
  • Schwann cells
  • Adrenal chromaffin cells
  • Pia and arachnoid
  • Parafollicular cells of thyroid gland
  • Also contribute to heart and face development
68
Q

Neurons of the spinal ganglia, ANS ganglia, cranial nerve ganglia (contributed to by neural crest cells)

A
  • Pseudounipolar sensory neurons and post-synaptic neurons of ANS

Lower Extremity Anatomy (35 decks)

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