Lower Extremity Anatomy > General Embryology 1 > Flashcards

General Embryology 1 Flashcards

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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
Syncytiotrophoblast is located
- At the embryonic pole | - Adjacent to embryoblast)
26
Syncytiotrophoblast on day 8
- Begins invading into the endometrium
27
(~Day 10) Blastocyst/embryo becomes
- Completely embedded within the endometrium
28
Synctytiotrophoblast contacts uterine vessels and glands, creating
- Primitive uteroplacental circulation - Lacunae filled with maternal blood - Lacunae fuse creating a lacunar network
29
Cytotrophoblast forms extensions that grow into overlying synctiotrophoblast to form
- Chorionic villi - Villi become penetrated by extraembryonic mesoderm - Eventually form blood vessels (week 2 and 3)
30
By day 8, the embryoblast differentiates into
- 2 epithelial cell layers - Epiblast - Hypoblast
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Epiblast
- Columnar cells adjacent to amniotic cavity | - Dorsal side of embryo
32
Hypoblast
- Small cuboidal cells adjacent to exocoelomic cavity | - Primitive yolk sac
33
Epiblast + Hypoblast
- Forms into a bilaminar embryonic disc | - Located between amniotic cavity and the primary umbilical vesicle
34
Amniotic cavity
- Forms within the epiblast | - Epiblast cells migrate forming the amnion (which encloses the amniotic cavity)
35
Hypoblast migration
- Lines the blastocystic cavity | - Forms the exocoelomic membrane
36
Blatocystic cavity
- Referred to as the primary umbilical vesicle (primary yolk sac)
37
Extraembryonic mesoderm
- Located outside the embryo - Produced by hypoblast and cytotrophoblast - Proliferates and develops spaces within
38
Spaces within the extraembyronic mesoderm
- Fuse to form the extraembryonic coelom (chorionic cavity)
39
Extraembryonic coelom (chorionic cavity)
- Fluid filled cavity - Surrounds the umbilical vesicle and amnion - Except at connecting stalk (precursor to the umbilical cord)
40
Week 3: days 14-21
- Appearance of primitive streak - Development of the notochord and neural induction - Differentiation of 3 germ layers (gastrulation)
41
Gastrulation
- Process where the bilaminar embryonic disc is converted into a trilaminar embryonic disc - Beginning of morphogenesis
42
Morphogenesis
- Development of the form and structure of organs and parts of the body
43
3 germ layers developed in gastrulation
- Ectoderm - Endoderm - Mesoderm
44
Ectoderm
- Outside layer | - Gives rise to skin and nervous tissue
45
Mesoderm
- Middle layer | - Generates most of the muscle, blood and connective tissue
46
Endoderm
- Epithelial lining and glands of the gut, lung, urogenital tract
47
Onset of gastrulation
- Beginning of the 3rd week with the formation of the primitive streak
48
Primitive streak location
- Appears caudally in the medial plane | - Dorsal aspect of embryonic disc
49
Primitive streak formation
- Epiblast proliferates and migrate toward the median plane of the embryonic disc
50
Epiblast dives within the primitive streak
- Pushes away hypoblast, forms definitive endoderm - Forms mesoderm in between ectoderm and endoderm - Remaining epiblast form the ectoderm
51
Elongation of primitive streak
- Addition of cells to the caudal end
52
Appearance of primitive streak allow identification of
- Cranial/caudal - Dorsal/ventral - Left/right - Medial/lateral
53
Cell proliferation at the cranial end
- Forms the primitive node | - Primitive node functions as a signaling center
54
Mesoderm is patterned based on
- 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
Notochordal process
- Cellular rod - Formed by cell migration cranially from the primitive node/pit - Formed by day 20
56
The notochord
- Defines embryo axis and provides support | - Serves as an important signaling center in the development of the gut, vertebral column and CNS
57
Notochord degeneration
- Degenerates as the vertebrae form | - Part persist as the nucleus pulposus
58
Neurulation
- Formation of the neural tube
59
Neurulation process
- 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
Folding and closure of the nueral plate
- Closure first begins in the cervical region | - “Zips” up toward the head and down toward the tail
61
2 openings of the neural plate upon closure
- Anterior neuropore (closes day 25) | - Posterior neuropore (closes day 28)
62
Errors in neurulation
- Raschischisis - Anencephaly - Spina bifida
63
Raschischisis
- Failure of neural tube folding
64
Anencephaly
- Failure of anterior neuropore closure
65
Spina bifida
- Failure of posterior neuropore closure (other causes)
66
Neural crest cells
- 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
Neural crest cells contribute to many structures
- 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
Neurons of the spinal ganglia, ANS ganglia, cranial nerve ganglia (contributed to by neural crest cells)
- Pseudounipolar sensory neurons and post-synaptic neurons of ANS
Lower Extremity Anatomy
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