Basics Of Embryology 2 Flashcards
What is gastrulation and when does it occur?
Around 16 days, this is when structures start to appear in the embryo
The cranial end of the primitive streak is expanded as the ______________ and it contains a circular depression called the ________________, which is continuous down the midline of the primitive streak with a trough-like depression called the _______________.
Primitive node
Primitive pit
Primitive groove
The primitive pit and groove represent what?
Areas where cells are leaving the primitive streak and moving into the interior of the embryonic disc
During gastrulation, the hypoblast cells become the…
Definitive endoderm
The area between the endoderm and the epiblast contains cells that coalesce to form the…
Intraembryonic mesoderm
After gastrulation is complete, the epiblast is called the:
Ectoderm
Just before the neural tube forms, a mesoderm migration begins to form in 3 areas:
Mouth - prechordal plate
Heart - cardiogenic mesoderm
Amnion, yolk sac, allantois (future placenta) - extraembryonic mesoderm
Order of migration cranial to caudal, mid-gastrulation
- Notochord
- Head mesoderm
- Somites
- Intermediate mesoderm
- Lateral plate mesoderm
The future vertebrae forms from the…
Notochord
How does the notochord form?
It is derived from the primitive node and ends up in the mesodermal layer. Therefore its considered a mesodermal derivitive.
The unsegmented region of the mesoderm becomes the:
Head mesoderm.
The head mesoderm gives rise to the
Face, jaw, and throat.
What is the mesenchyme?
A loosely organized, mainly mesodermal embryonic tissue that develops into connective and skeletal tissue, including blood and lymph.
The bands of cell found in the mesoderm soon segment into these blocklike condensations
Somites
When do the first pair of somites first form?
Day 20 or so. The remainder form at a rate of about 3 or 4 per day.
By about day 30, around 42 to 44 pairs of somites form.
What is the final count of somites, and why?
About 37. Because the caudalmost somites disappear, due to the fact humans dont have tails…idiot
Somites give rise to….
Most of the axial skeleton.
Vertebral column, part of occipital bone
Musculature of the neck, body wall, and limbs
Dermis of the neck
Intermediate mesoderm
Connects the paraxial mesoderm (somites) with the lateral plate mesoderm.
What does the intermediate mesoderm differentiate into?
Urogenital structures. It also helps to develop the excretory units of the urinary system and the gonads.
Lateral plate mesoderm splits into….
Parietal/somatic
-forms the body wall folds
visceral/splanchnic
-forms the walls of the gut tube
What are the four main events of neurulation?
Formation of the neural plate
Shaping of the neural plate
Bending of the neural plate
Closure of the neural groove
During gastrulation, what is the major inductive event that occurs in the embryo?
Neural induction
What happens during neural induction?
The primitive node induces the overlying ectoderm to thicken as the neural plate.
The is the earliest rudiment of the central nervous system?
Neural plate
Around what day does the primitive streak disappear? And what is appearing in its place?
Day 25
Neural plate, and the first expansions of the brain
As the neural plate flattens along its length, the ________ disappears
Primitive streak
During subsequent development, the neural plate will fold up into a what?
Neural tube
During the formation of the neural tube, what arises from the lateral edges of the neural plate?
Neural crest cells
Neural plate, crest, and tube are all part of…
Ectoderm
The development of the ________ ______, _________ ____________, and __________ __________, all happen simultaneously and in synchrony.
Neural tube, mesoderm migrations, and notochord formation
What is the “Tube-Within-a-Tube Body Plan”
The result of body folding during embryonic development.
Consists of an embryo body design composed of two main tubes: an outer ectodermal tube forming the skin and an inner endodermal tube forming the gut.
The space between the two tubes is filled mainly with mesoderm, the lateral plate mesodermal part of which splits to form the body cavity (coelem).
The neural tube, derived from the outer ectodermal tube, becomes internalized during the process of neurulation
The blastocyst contains which 2 parts?
The inner mass cells and the trophoblast
Cells in the ICM differentiate into…?
- Epiblast which gives rise to the embryo proper (dorsal - back)
- Hypoblast which gives rise to the primary (extraembryonic) endoderm that forms the yolk sac (ventral - belly)
What is the primitive streak?
The first marker of the craniocaudal axis.
It occurs on the dorsal side of the epiblast and near the caudal end of the epiblast. The cranial end of the streak proliferates to become the primitive node and results from proliferation and migration of cells.
How do we turn the 2 layer disc into a 3 layer disc?
Through gastrulation.
There is a depression in the primitive streak called the primitive groove, and it is the site along which the cells migrate through the epiblast.
The first cells to migrate through the epiblast form the endoderm.
Later cells form the mesoderm, and non ingressing cells form the ectoderm.
2 populations of cells that migrate through the streak generate the 3 layer disc from 2 layer disc.
What is gastrulation?
Process by which the 3 germ layers are formed through cell migration
What are the 3 ways in which cells can migrate through the epiblast and why is that important?
- Through the node
- Near the node
- Away from the node
This is important because they create different cell fates
How is the neural tube formed?
Dorsal ectoderm becomes the neural plate. Lateral edges become elevated to form neural folds and midregion becomes depressed and form the neural groove. Neural fold moves toward each other and fuse to become the neural tube. Neural tube then detached from the overlying ectoderm.
What does the nonneural ectoderm become?
The skin
What does the neural ectoderm become?
The brain and spinal cord
What germ layer does the notochord derive from?
Mesoderm
What is neurulation?
Formation of the neural tube
How do cells fuse during neurulation?
Cells in the middle of the neural folds fuse first and zippers both anteriorly and posteriorly at the same time
What are cranial and caudal neuropores?
Transient openings at either end of the neural tube after zippering of the neural folds occur
How do birth defects or neural tube defects occur?
When the neuropores do not close correctly
How can women avoid neural tube defects?
Consume more folic acid
What are the functions of the notochord?
Transient structure that defines the body axis
Provides rigidity to the embryo
Functions as a signaling center to, at least, induce neural fates such as which neural cells become dorsal or ventral
Precursor for the axial skeleton
Which germ layer forms the neural crest?
Ectoderm
What are neural crest cells?
Migratory cells that are ectoderm-derived and migrate throughout the body to give rise to a diverse number of cell fates
What are the 4 regions of the mesoderm?
Axial (gives rise to the notochord)
Paraxial (gives rise to somites, adjacent to the neural tube)
Intermediate (kidney/gonads)
Lateral plate (lining of the organ cavities)
What are the derivatives of endoderm?
Gives rise to the GI tract, epithelial lining of lung buds and trachea, liver, gall bladder, and pancreas
