Gastrulation Flashcards
Gastrulation
Week 3
- trilaminar disc
1.) Ectoderm
2.) Mesoderm
3.) Endoderm
-multipotent
Movement of cells for gastrulation
1.) Preview of main events
2.) Steps at epiblast; cell replication and cell movement
3.) Primitive streak
4.) Cells diving to form Endoderm
5.) Celling diving to form Mesoderm
6.) Mouth and anus
7.) Notochord development and SHH
8.) First Mesoderm’s (3 types)
week 2 development
within the endometrium
- amniotic cavity and chorionic cavity
- extraembryonic membranes
Bilaminer disc
epiblast
hypoblast
Epiblast
ectoderm
Hypoblast
endoderm
Mesoderm
develops between due to invagination and the primitive streak
The upper epiblast layer and upper hypoblast layer migrate upward toward ventral pole creating 2 cavities
1.) Amniotic cavity
2.) Umbilical vesicle
Amniotic cavity
houses embryo
Umbilical vesicle
becomes umbilical (or yolk if not human)
Trophoblast
develops into Chorion and Placenta
Following cytotrophoblast
- cells move out, enzyme digestion, cells break open, fuse together and this forms “syncytium”
~These pools will eventually meet up with endometrial mother blood vessels and the cytotrophoblast cells will move into the pools and form chorionic villi and thus the PLACENTA
syncytium
- collection of cytoplasm with lots of nucleus
- this is synctiotrophoblast
What are cells with well defined margins and nuclei called?
Cytotrophoblast
Chorionic villi
“Two deliveries”
Placenta (CV) arteries
carry deoxygenated blood while the veins carry oxygenated blood (it is opposite of what red and blue color suggest!)
Chorionic villi arteries
carry poorly oxygenated fetal blood and waste products from the fetus
Chorionic villi veins
carries oxygenated blood and nutrients to the fetus
The placental membrane, composed of extra fetal tissues, separates the maternal blood in the intervillous space from the fetal blood in the capillaries in the villi
- note that the placental membrane becomes very thin at full term
Hofbauer cells are thought to be what?
Phagocytic
The intervillous space of the placenta
- maternal blood bathes the villous trees, which are covered by syncytiotrophoblasts (SYN) that are underlaid by a population of progenitor cells called Cytotrophoblasts (CTB)
- the syncytial knots are formed on these villi, and trophoblast-derived material is transferred into the maternal circulation
- EVT indicates extravillous trophoblasts
Fetal-maternal interface and immune cells at term pregnancy
- the placenta serves to ensure exchange of nutrients and gases between the maternal and fetal blood circulation
- the fetal part of the fetal-maternal interface consists of chorionic villi that extend from the chorionic plate into the intervillous space and bathe in maternal intervillous blood
- on the maternal side, the decidua parietals and decidua basalis are in direct contact with fetal membranes (amniochorion) and the invading fetal extravillous trophoblasts, respectively
-the intervillous blood enters the intervillous space through spiral arteries and leads this compartment through uterine veins - maternal immune cells in the intervillous blood are in direct contact with the fetal syncytiotrophoblast and decimal immune cells can interact with extravillous trophoblasts, decimal stromal cells, Hofbauer cells, mucosal associated invariant T cells, macrophages, uterine natural killer cells
- the pink cells in the intervillous space depict erythrocytes
Normal placental development
1.) Extravillous cytotrophoblasts proliferate in anchoring columns to successfully invade through the decidua
2.) And transform the distal spiral arteries
3.) These changes mediate high volume flow at low pressure into the intervillous space
4.) The placental villi are covered by the villous trophoblast compartment, compromising cytotrophoblasts that proliferate to generate the outer syncytiotrophoblast in direct contact with maternal blood
Uteroplacental vascular insufficiency
1.) Extravillous cytotrophoblasts are less successful in invading the maternal decidua and may be removed by the maternal immune system
2.) Consequently, the distal spiral arteries are narrower and diseased
3.) Accompanied by atherosis or local fibrin deposition
4.) And reduced endo-vascular invasion
5.) Hypoxia or hypoxia-deoxygenation injury
6.) Has direct effects on the villous trophoblast compartment, reducing syncytial function
7.) That may trigger the formation of syncytial knots
8.) These accumulate but may fragment and shed into maternal blood
9.) Whereas areas deficient in syncytial fusion may exhibit focal necrosis
Purpose of gastrulation: Bilaminar disc is converted to _________
trilaminar disc
Gastrulation is the process of_____ _____ formation
germ layer
3 germ layers formed during gastrulation
1.) Ectoderm (external)
2.) Mesoderm (middle)
3.) Endoderm (inner)
The pattern of gastrulation is similar in mammals and __________
avian species (birds)
During gastrulation, a ______ is formed
body axis
After gastrulation, the embryo is now called a ________
gastrula
Animals that have only 2 initial cell layers
diploblastic
1.) ectoderm
2.) endoderm
- simple body plan
- few cell types
- sponges, jellyfish, corals, sea anemones
Animals have 3 initial cell layers
triploblastic
1.) ectoderm
2.) mesoderm
3.) endoderm
- complex body plan
- more cell types
- humans, annelids, arthropods, Mollusca, echinoderms, chordates
Ectoderm (outside skin)
- epidermis:
- sweat glands
- hair follicles
- mouth and anus linings
- nervous and sense organs
- jaws and teeth (and enamel)
- pituitary gland, adrenal medulla
- germ cells (sperm, egg)
Mesoderm (connective tissue)
- skeletal system
- muscle (3 types)
- circulatory (blood and vessels)
- Connective Tissue (CT)
- lymphatic
- excretory
- reproductive (not germ cells) but gonads
- skin dermis (CT)
- adrenal cortex
Endoderm (lines tubes)
- epithelial linings:
- GI
- Respiratory
- Excretory
- Reproductive
- Ducts
- liver and pancreas
- thymus, thyroid, parathyroid
Ectoderm
body surface
Mesoderm
stuff inside and between
Endoderm
lines GI
Formation (slide 21) of the three primary germ layers occurs during the first ______ weeks of development
2
- the embryo at this stage is only a few millimeters in length
Preview of main events in movement of cells for gastrulation
- Caudal groove
- Primitive streak
- movement of cells and pseudopodia
- trilaminar disc (3 germ layers)
- Notochord development
- 3 types of mesoderm development
Primitive streak
- primitive groove (narrow depression)
- primitive pit (dimple)
- primitive node (small mound of tissue)
- Steps at epiblast: cell replication and cell movement (day 14)
- 1st caudal groove, starts at tail (caudal) and moves toward head (cranial)
- this creates the cranial caudal axis!
- either side of the groove begins BILATERAL symmetry
- Medial and Lateral are also arranged
- groove forms on the back (dorsal)
- Primitive streak steps (Day 14)
- 2nd groove elongates and cells MOVE (guitar pic)
- primitive groove (narrow depression)
- primitive pit (dimple)
- primitive node (small mound of tissue)
- Cells diving to form Endoderm
- 3rd cells of Epiblast
~ migrate to primitive groove, bottom of groove and DIVE IN
These epiblast cells that get through groove form __________ and differentiate into new cells
NEW CELL LAYERS
Deep Dive
and form deeper embryonic ENDODERM LAYER (Gut)
**REPLACING ventral hypoblast layer
- Cells Diving to form Mesoderm
Shallow dive
Shallow Dive
Embryonic MESODERM LAYER
MESODERM layer
1.) Parietal mesoderm (outside)
2.) Visceral mesoderm (organ)
Cells that do NOT dive
ECTODERM
NOW a ____ (after Mesoderm)
Trilaminar Disc
Tissues of Trilaminar disc (Day 14)
1.) Embryonic endoderm
2.) Embryonic mesoderm
3.) Embryonic ectoderm
Embryonic endoderm REPLACES_______
Trophoblast
Trilaminar disc: All these cells are NOW______
Multipotent
- Mouth and Anus Steps (Day 15)
- cranial end
- caudal end
Cranial end
Ectoderm pushes down to fuse with endoderm
- this becomes the oropharyngeal membrane (and disintegrates)
- at week 4, becomes the MOUTH
Caudal end
Ectoderm pushes down to fuse with endoderm
- this becomes the cloacal membrane (and disintegrates)
- at week 7, becomes the ANUS and GENITOURINARY tracts
Cranial bilaminar region–> oropharyngeal membrane–> mouth
True
Caudal bilaminar region–> cloacal membrane–> anus and genitourinary tracts
True
- Notochord development (Day 17)
Mesoderm forms into a solid shaft or tube
- This becomes Notochord
- This later becomes “nucleus pulposus” of vertebral column
Function of Notochord
- influences how embryo folds early on
- secretes SHH diffuses out through the disc
SHH
Sonic Hedge Hog
What does SHH do?
Tells cells how to differentiate and where to go
Notochord
- transient (future nucleus pulposus)
- influences embryo folding
- secretes SHH protein (cell awareness in space)
- First Mesoderm’s –> three types (Day 20)
1.) Paraxial mesoderm
2.) Intermediate mesoderm
3.) Lateral mesoderm
Day 20- Neurulation
- Notochord stimulates this
- stimulates ectoderm cells to thicken and form the neural plate
- neural plate dips down and forms groove
- the sides of the groove are called neural folds
- the neural folds rise up and meet each other and fuse forming the neural tube
- neural tube will become brain and spinal cord
- this sits between the ectoderm and mesoderm
Secondary villi
villous capillary system –> link to blood and oxygen from mom
- a more dense network of chorionic vessels are established with the endometrium anchoring the embryo to the uterus
Human development: Week 3
1.) Primitive streak
2.) Germ layers
3.) Notochord, SHH, and Neurulation
4.) Villous capillary system
Gastrulation Quick Review
- upon arrival in the region of the streak, cells become flask-shaped, detach from the epiblast, and slip beneath it
- this inward movement is known as INVAGINATION
- once the cells have invaginated, some displace the hypoblast, creating the endoderm, and others come to lie between the epiblast and newly created endoderm to form mesoderm
- cells remaining in the epiblast then form ectoderm
- the EPIBLAST, through the process of gastrulation, is the source of ALL of the germ layers, and cells in these layers will give rise to ALL of the tissues and organs in the EMBRYO
Gastrulation
process of germ layer formation
three germ layers formed during gastrulation
1.) ectoderm
2.) mesoderm
3.) endoderm
Body axis is formed during______
Gastrulation
In mammals, the hypoblast and epiblast are divided from what?
Inner Cell Mass (ICM)
What acts as the initiation site for gastrulation?
Primitive streak
Cells of the epiblast migrate to the primitive streak and move into the space between the ________ and _________
epiblast; hypoblast
A proportion of these cells displace the hypoblast , forming endoderm, the _________
inner germ layer
The _______ will form the primitive gut
endoderm
Mesoderm, the middle germ layer, develops from migrating epiblastic cells which lie between the ______ and the _______
epiblast; primordial endoderm
The remainder of the cells of the epiblast differentiate into what?
Ectoderm
