Embryology Flashcards
(30 cards)
Overview of Pregnancy - Stages of baby over the course of the weeks, noting level of cell differentiation
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)
Female Reproductive Anatomy (Define ovary, uterine tube, endometrium, myometrium, cervix)
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
Describe the process of ovulation
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
What are the stages of the conceptus during the first week of pregnancy?
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
Describe basis of implantation and sites of ectopic pregnancy
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
Changes to the blastocyst + endometrium during implantation (when does this happen?)
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
Other names for endometrium
Uterine mucosa = uterine decidua
Changes to Blastocyst during Week 2
- invading trophoblast differentiates to syncytiotrophoblast + cytotrophoblast
- inner cell mass differentiates to hypoblast (future endoderm) + cavitates, forming amniotic cavity (differentiates to epiblast, future ectoderm)
- Yolk sac develops, contiguous with hypoblast
- Bilayer embryonic disk (Hypoblast + Epiblast)
- Appearance of extra-embryonic mesoderm: outside embryo, cavitates to form extra-embryonic coelem
- thin coating of extra-embryonic mesoderm results in formation of chorion, yolk sac proper, and amnion proper
3 Compenents of Endometrium during placenta formation
Decidua basalis: maternal component, source of blood, engaged w/villous chorion
Decidua capsularis: “bag w/chorion + amnion”
Decidua parietalis: uninvolved uterine musoca
Three components of Placenta
Placenta: chorionic villi bathed in maternal blood from decidua basalis
- Syncytiotrophoblast: outside lining, directly engages with decidua basalis
- Cytotrophoblast: middle layer
- 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
Changes from early placental membrane to late placental membrane
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
How do DZ and MZ twins form?
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]
What do the Primitive Node and Streak do?
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)
Intraembryonic Mesoderm Condenses to form what?
- Notochord (medial) - vertebral disk pulposis, induces neurulation
- Paraxial Mesoderm - somites for bone, muscle, connective tissue for back/body wall
- Intermediate Mesoderm - small early, forms kidneys/gonads
- 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
What does the absence of amniotic fluid mean?
Amniotic fluid = fetal urine
no amniotic fluid = no kidney formation = no formation of intermediate mesoderm = improper gastrulation
What else occurs during gastrulation besides mesoderm development?
- connection stalk to chorion shifts to caudal end of embryo (umbilical cord)
- allantois forms - vestigial caudal projection of yolk sac (egg laying organisms use for gas exchange)
- cardiogenic plate develops on cranial side b/w endoderm/ectoderm (required to supply nutrients to rapidly growing # cells, diffusion no longer enough)
What is neurulation? When does it occur
Neurulation: immediately following gastrulation (Week 3)
- coelem extends from lateral plate through cardiogenic mesoderm - becomes all body cavities
- Neural plate folds in, becomes neural tube (all neurons with cell bodies in CNS) and neural crest (all neurons with cell bodies outside CNS)
What occurs during week 4 development?
ESTABLISHMENT OF VERTEBRATE BODY PLAN
- Amnion tucks around sides of disc to form cylinder, envelops embryo + neural cord
- 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
- 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* - Heart prominence, somites, limb buds
What is the difference between cell fate specification and pattern formation?
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
What axes are different in embryo?
When does patterning occur?
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
What are the 3 functional classes of genes regulating fly development?
- Maternal Effect Genes (1st body polarity)
- Segmentation genes (i. Gap Genes, ii. Pair Rule genes, iii. Segment Polarity Genes)
- Homeotic genes (give formed segments their unique identity
Genes expressed in order of 1,2,3!
What is the function of HOX genes?
How do different HOX genes have different effects?
- “homeobox” encodes proteins containing DNA-binding motif called “homeodomain”
- Acts as transcription factor, binding similar DNA motifs
- Establishes Anterior-Posterior Axis
- Some homeodomains have more/less binding diversity
- expressing different HOX genes at different regions or during different times can yield different results
What are the types of colinearity seen in pattern formation genes?
- Spatial - order of genes maps an axis in embryo (3’ genes = anterior, 5’ genes = posterior)
- Temporal - order of genes maps times of expression (3’ genes = first, 5’ genes = last)
What are the 5 key features demonstrated by human HOX clusters?
- 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
