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Foundations 2 > Embryology > Flashcards

Embryology Flashcards

1
Q

Overview of Pregnancy - Stages of baby over the course of the weeks, noting level of cell differentiation

A

Weeks 1-2: Blastocyst (Totipotent - 2nd embryo -> Pluripotent - not another embryo)
Weeks 3-8: Embryo - organ systems develop
Weeks 9-36: Fetus (Multipotent - can differentiate only within tissue type)

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2
Q

Female Reproductive Anatomy (Define ovary, uterine tube, endometrium, myometrium, cervix)

A

Ovary: where egg cells (ova) made/stored
Uterine Tube: not physically connected to ovary, where fertilization occurs (at distal third), fimbriae needed to catch ova
Endometrium: inner uterine layer where development occurs (loose connective tissue + epithelium)
Myometrium: smooth muscle layer
Cervix: “neck” of uterus

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3
Q

Describe the process of ovulation

A

30 primordial developing follicles: all will die except the one to be released (becomes most mature - epithelium develops from simple squamous to stratified)
Released ovum one of largest cells in body, released with follicular cells/fluid
Fimbriae @end of uterine tube envelop ovary and help guide ovum to tube for fertilization

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4
Q

What are the stages of the conceptus during the first week of pregnancy?

A

Day 1: Zygote - fertilized egg
2, 4, 8 cell stages as pushed along uterine tube (via SM contraction)
Day 4: Morula: “berry” solid sphere
Day 5: Blastocyst: cavity forms (inner cell mass (will become embryo), blastocyst cavity, trophoblast (outer simple squamous epithelium)
Day 6: reaches uterine cavity and IMPLANTATION BEGINS

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5
Q

Describe basis of implantation and sites of ectopic pregnancy

A

Implantation: blastocyst penetrates + embeds in epithelium of endometrium (back wall ~2/3 up)

Tubal: most common, dangerous b/c tube cannot expand
Abdominal: Fimbriae fail to envelop ovary and catch ovum, placenta may still form and pregnancy may still be viable - HOWEVER organ movement can endanger fetus and fetal growth can cause internal bleeding/damage to mother
Ovarian and Cervical Pregnancies may occur

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6
Q

Changes to the blastocyst + endometrium during implantation (when does this happen?)

A

BEGINNING OF WEEK 2
Uterine glands dilate with glycogen rich fluid to nourish blastocyst via diffusion
Trophoblast of blastocyst INVADES endometrium + differentiates
Syncytiotrophoblast: outer trophoblast, finger-like projections into endometrial wall (synctium - cytoplasmic mass many nuclei)
Cytotrophoblast: inside layer of trophoblast

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7
Q

Other names for endometrium

A

Uterine mucosa = uterine decidua

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8
Q

Changes to Blastocyst during Week 2

A
  1. invading trophoblast differentiates to syncytiotrophoblast + cytotrophoblast
  2. inner cell mass differentiates to hypoblast (future endoderm) + cavitates, forming amniotic cavity (differentiates to epiblast, future ectoderm)
  3. Yolk sac develops, contiguous with hypoblast
  4. Bilayer embryonic disk (Hypoblast + Epiblast)
  5. Appearance of extra-embryonic mesoderm: outside embryo, cavitates to form extra-embryonic coelem
  6. thin coating of extra-embryonic mesoderm results in formation of chorion, yolk sac proper, and amnion proper
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9
Q

3 Compenents of Endometrium during placenta formation

A

Decidua basalis: maternal component, source of blood, engaged w/villous chorion
Decidua capsularis: “bag w/chorion + amnion”
Decidua parietalis: uninvolved uterine musoca

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10
Q

Three components of Placenta

A

Placenta: chorionic villi bathed in maternal blood from decidua basalis

  1. Syncytiotrophoblast: outside lining, directly engages with decidua basalis
  2. Cytotrophoblast: middle layer
  3. Mesenchyme: core, coating that gives rise to connective tissue + blood vessels

Anchoring villi not covered by syntrophoblast (span thickness of placenta), cytotrophoblastic shell anchors villous chorion to decidua basalis

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11
Q

Changes from early placental membrane to late placental membrane

A

Early: Synciotrophoblast, Cytotrophoblast, connective tissue, endothelium of mother’s blood vessels
Late: Synciotrophoblast, endothelium (both share same basal lamina)
cytrotrophoblast disappears as vessels move closer to maternal blood

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12
Q

How do DZ and MZ twins form?

A

DZ - 2 zygotes, 2 fertilizations, 2/3 of all twins DZ (2 chorions, 2 placentas, 2 amnions)

MZ - 65% inner cell mass division in 1 blastocyst (35% earlier division) [1 chorion, 1 placenta, 2 amnions due to shared trophoblast]

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13
Q

What do the Primitive Node and Streak do?

A

Week 3: GASTRULATION
Node/streak originate from ectoderm thickening
Node: contains primitive pit, towards head/cranially
Streak: source of intraembryo mesoderm, contains primitive groove, towards tail/caudal
Both give off cells to make MESODERM!
Gives rise to midline notochord + streak mesoderm elsewhere (doesn’t invade oral/cloacal membrane)

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14
Q

Intraembryonic Mesoderm Condenses to form what?

A
  1. Notochord (medial) - vertebral disk pulposis, induces neurulation
  2. Paraxial Mesoderm - somites for bone, muscle, connective tissue for back/body wall
  3. Intermediate Mesoderm - small early, forms kidneys/gonads
  4. Lateral Plate Mesoderm - future coelem, body wall/cavities/gut wall
    Somatopleure - near ectoderm
    Splanchnopleure - near endoderm
    Additional mesenchyme - loose connective tissue between these epithelial mesoderm columns and ectoderm/endoderm
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15
Q

What does the absence of amniotic fluid mean?

A

Amniotic fluid = fetal urine

no amniotic fluid = no kidney formation = no formation of intermediate mesoderm = improper gastrulation

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16
Q

What else occurs during gastrulation besides mesoderm development?

A
  1. connection stalk to chorion shifts to caudal end of embryo (umbilical cord)
  2. allantois forms - vestigial caudal projection of yolk sac (egg laying organisms use for gas exchange)
  3. cardiogenic plate develops on cranial side b/w endoderm/ectoderm (required to supply nutrients to rapidly growing # cells, diffusion no longer enough)
17
Q

What is neurulation? When does it occur

A

Neurulation: immediately following gastrulation (Week 3)

  1. coelem extends from lateral plate through cardiogenic mesoderm - becomes all body cavities
  2. Neural plate folds in, becomes neural tube (all neurons with cell bodies in CNS) and neural crest (all neurons with cell bodies outside CNS)
18
Q

What occurs during week 4 development?

A

ESTABLISHMENT OF VERTEBRATE BODY PLAN

  1. Amnion tucks around sides of disc to form cylinder, envelops embryo + neural cord
  2. Formation of foregut (extends to oral membrane), midgut (direct comm with yolk sac), hindgut (extends to cloacal membrane), all from endoderm, each fed by main arteries
  3. Intraembryonic coelem from lateral plate forms body cavity
    3a. Splanchnopleure: lateral plate coating endoderm - organs bud off this, form splanchnic nerves
    3b. Somatopleure: lateral plate mesoderm coating ectoderm - somatic nerves
    * Autonomic nerves in both*
  4. Heart prominence, somites, limb buds
19
Q

What is the difference between cell fate specification and pattern formation?

A

CFS: how embryo acquires all different cell types
PF: organization of embryonic cells into 3D body plan, (primary) initiated by establishing axes by (expressing different genes or concentrations of a gene along an axis), (secondary) establishing regional, limb, or organ specific axes (brain/liver), occurs within a specific PLACE and TIME

20
Q

What axes are different in embryo?

When does patterning occur?

A 
Anterior-Posterior = Head-Tail
Ventral-Dorsal = Belly-Back

During Weeks 4-8: during development of tissues and organs in embryo
By week 8, most of patterning is done, embryo looks human, during fetal stage, everything just gets bigger

21
Q

What are the 3 functional classes of genes regulating fly development?

A
  1. Maternal Effect Genes (1st body polarity)
  2. Segmentation genes (i. Gap Genes, ii. Pair Rule genes, iii. Segment Polarity Genes)
  3. Homeotic genes (give formed segments their unique identity

Genes expressed in order of 1,2,3!

22
Q

What is the function of HOX genes?

How do different HOX genes have different effects?

A
  1. “homeobox” encodes proteins containing DNA-binding motif called “homeodomain”
  2. Acts as transcription factor, binding similar DNA motifs
  3. Establishes Anterior-Posterior Axis
  4. Some homeodomains have more/less binding diversity
  5. expressing different HOX genes at different regions or during different times can yield different results
23
Q

What are the types of colinearity seen in pattern formation genes?

A
  1. Spatial - order of genes maps an axis in embryo (3’ genes = anterior, 5’ genes = posterior)
  2. Temporal - order of genes maps times of expression (3’ genes = first, 5’ genes = last)
24
Q

What are the 5 key features demonstrated by human HOX clusters?

A
  • 4 different HOX clusters due to high complexity or need for redundancy*
    1. Temporal + Spatial Colinear Expression
    2. Posterior Prevalence (more genes expressed in posterior regions)
    3. Posterior Dominance (most posterior gene will be expressed in region with multiple genes present)
    4. Redundancy: in function between paralogous groups of HOX genes
    5. Colinear expression along anterior-posterior axis and other axes in limbs, GI tract, and female GU tract
25
Q

Why is identification of target HOX genes so difficult?

How can we best identify target HOX genes?

A
  1. Some regulate other developmental pathways, and others regulate cell function
  2. direct targets: genes the homeodomain binds to; vs indirect targets: genes influenced by genes targeted by homeodomain

Genome wide testing and fruit fly model species to identify downstream targets

26
Q

What is the function of the hedgehog signaling pathway in drosophila and mammals?

A

D: segment polarity gene, patterning of imaginal discs (legs, wings, eyes) + dorsal epidermis (spiny + smooth segments)
M: 3 Hh genes (Shh, Dhh, Ihh) secreted from two organizing centers to establish dorsal-ventral axis in neural tube/somites, and the anterior-posterior axis of limbs

27
Q

How does Shh develop its axis?

A

Develops Dorsal-Ventral Axis
Notochord secretes Shh to signal neurulation + helps paraxial mesoderm form somites
Concentration determines axis polarity
Ventral neural tube: highest Shh - motor neurons and ventral floor plate
Dorsal neural tube: lowest Shh - sensory ganglia/neurons
Ventral-Medial Somites: closer to notochord, high Shh - scleratome (vertebral bodies/ribs)
Dorsal-Lateral Somites: further away - low Shh - dermomyotome (dermis + muscles)

28
Q

What are the 3 different limb axes + how does Shh create one of them?

A 
Proximal-Distal = arm-hand
Dorsal-Ventral = back of hand-palm
Anterior-Posterior = thumb-pinky

Zone of Polarizing Activity (ZPA) secretes Shh from proximal posterior limb bud
High Shh = pinky digit
Low Shh = thumb digit
(establishes anterior-posterior limb axes)

29
Q

How does Shh signaling differ in Drosophila and Vertebrates?

A

D: Hh (+) -| Ptc (-) -| Ci (+/- transcription factor)
V: Ihh, Dhh, Shh (+) –| Ptch1, Ptch2 (-) –| GLI1 (+), GLI2 (+/-), GLI3 (-)

30
Q

List the diseases associated with different mutations in HOX clusters or the hedgehog signalling pathway

A
  1. Synpolydactyly - mutation in HOX-D13
  2. Holoprosencephaly - mutation in Shh
  3. Nevoid Basal Cell Carcinoma Syndrome - mutation in Ptch1
  4. Greig Cephalopolysyndactyly Syndrome - mutation in GLI3
  5. Post-Axial Polydactyly Type A - mutation in GLI3
    all mutations are loss of function mutations

Foundations 2 (12 decks)

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