Differentiation of the Ectoderm and Organ development Flashcards
What does the ectoderm differentiate into?
Non neural ectoderm and neural ectoderm
What does non-neural ectoderm form once fully developed?
Epidermis of the skin and all the components associated with it (e.g. hair, nails, tooth enamel)
What does neural ectoderm form?
Nervous system, neural plate border
What kind of ectoderm is found exclusively in the head? What does it form?
Ectodermal placodes Lens of the eye, ear (structures of the head)
The cells on the ectoderm that are placed along or near the midline become what kind of tissue? How does the cell shape change? What is the tissue that is next to it?
Becomes neural plate Tall columnar cell shape Tissue next to on either side is non-neural ectoderm
What does the neural plate develop into?
Most of the tissue will form the nervous system
How does the neural plate vary along the rostral caudal axis? What different structures does this develop?
It is wider at the rostral end and thinner at the caudal end Forms the brain at the rostral end and the spinal cord at the caudal end
How does the neural plate change as development proceeds? What does it form? What is the process called?
The central area of the neural plate folds downwards (creating a ‘ditch’ in the neural plate) and the outer edges rise and curl upwards and inwards It forms a neural tube Process is called primary neurulation
Is the neural tube a closed cylinder? Explain
No, it has the rostral/anterior neuropores and caudal/posterior neuropores still open (e.g. the top and bottom ends are still open)
What is the condition where the rostral neuropores don’t close? What is its lethality?
Anencephaly It is lethal
What is the condition where the caudal neuropores don’t close?
Spina bifida
What is chance of a neural tube not closing properly?
1 in 1000 live births
Where does the neural tube form in relation to the non-neural ectoderm?
The neural tube is covered over by the non-neural ectoderm
Where is the neural tube located in the embryo?
It runs from the caudal to rostral end
What forms at the rostral end of the neural tube? What will this develop into?
The forebrain, midbrain and hindbrain vesicle Will develop into the brain
What does the neural tube that does not develop into the vesicles develop into?
The spinal chord
What happens to the cells on the edge of the neural plate as the neural plate rises? What do they develop into?
Goes from being epithelial like cells to mesenchymal cells and come out of the forming neural tube, migrating around the entire body form the peripheral nervous system, melanocytes and other neural tissue
What kind of hox gene expression occurs from below the midbrain?
Hox gene patterning
What are hox genes?
A type of transcription factors
What kind of hox gene is expressed in the forebrain and midbrain?
There are no hox genes expressed in these regions
Where does the head start? What determines this?
It is debatable as it could start from the midbrain where hox genes are not expressed OR it could start from the hindbrain where the somites are the beginning on non-brain neural tissue
What does secondary neurulation form?
Forms the neural tube from the caudal end
How does secondary neurulation form a neural tube?
A rod like condensation of mesenchymal cells beneath the dorsal ectoderm (ectoderm on the back of the embryo) in the tail bud forms and a cavity opens up in the centre of the rod
How does primary and secondary neurulation differ?
Primary starts at rostral end and ectoderm folds over itself to form a tube, secondary starts at caudal and is a rod the then develops a central canal throughout he rod
How does the neural tube produced by primary and secondary neurulation combine? Is secondary neurulation a prominent process?
The two central canals in the primary and secondary neural tubes become continuous with each other It is in some species, in humans no but in chickens it forms the spine form the hips backwards and in fish is the main process for neural tube formation
Where does the tissue for the secondary neurulation come from?
The ectoderm from above migrates downwards
What is the significance of the location of the point where the neural tubes from primary and secondary neurulation come together?
It is about the location where spina bifida originates
What is the neural crest? How is it formed?
Small group of cells on the outside edge o the neural plate that becomes the tip of the neural folds As the neural folds rise the cells move to the outside edge
What do the cells in the neural crest form? What do they do?
They give rise to the peripheral nervous system by producing the neurons and also produce the hormone secreting cells of the adrenal gland and melanocytes (melanin cells), in the cranial region they also form cartilage, bone and muscles of the face and neck They become mesenchymal and migrate out of the lateral edges
How does the the brain develop similarly and differently among different vertebrate?
The forebrain, midbrain, hindbrain and spinal chord are all present in early development, however the different species will have disproportionate growth in each of three brain vesicles
What is the relative growth of each of the three vesicles in humans?
Forebrain: most growth Midbrain: very little growth Hind brain: middle growth
What does the forebrain develop into in humans/apes?
The cerebral hemispheres and thalamus
What is the function of the midbrain in humans/apes?
Reflective actions
What does the hindbrain develop into in humans/apes?
Pons, medulla and cerebellum
What is the names of the vesicles that are the precursor for the forebrain, midbrain and hindbrain?
Forebrain = telencephalic vesicle Midbrain = mesencephalic vesicle Hindbrain = rhombencephalic vesicle
Label the diagram
(FYI what do the vessels that connect to)
What does the pharyngeal arches give rise to on fish vs terrestrial animals?
Fish = gills Terrestrial = specific structures on the head and neck
Where do the pharyngeal arches form on a human embryo?
At the level of the future head and neck regions
What does each pharyngeal arch develop into?
A specific head or neck structure with specific blood vessels, muscles and nerves
What are the pharyngeal arches made of?
Derivatives of the three embryonic germ layers
What is each pharyngeal arch covered in? What germ layer is inside them?
On the outside by ectoderm, inside by endoderm and mesoderm and the neural crest (it migrates down into arches) in the middle
How many pharyngeal arches are there in humans?
5
How are the pharyngal arches separated?
By pharyngeal pouches on the inside and pharyngeal clefts on the inside
What structure does the first pharyngeal arch divide into? What function are these involved in? What tissue do these structures form from?
The bones, muscle and nerves of the jaw Mastication (chewing) Formed by the cranial neural crest migrating downwards
Label the diagram of the bones formed by the pharyngeal arch 1
Label the diagram of the muscles formed by the pharyngeal arch 1
Label the diagram of the nerves formed by the pharyngeal arch 1
By the end of the fourth week of development, what does the face of the embryo have on it? What are they formed by?
5 initial swellings called facial prominences Formed b the neural crest and by some mesenchyme that originates from the cranial somitomeres corresponding to the first pharyngeal arch
Label the different types of facial prominences on the diagram and where they go on the embryo as it develops
Where is the eye on the developing embryo at an early stage?
On the side of the head
Are abnormalities in the fusion of facial prominence common? Give an example
Yes e.g. cleft lip occurs in 1 in 1000 births
What does defects in the first pharyngeal arch lead to?
Abnormalities in the outer and middle ear
What is the process shown in this diagram? Label the diagram and what order the process is being undertaken
Heart looping sv = sinus venosus, pA = primitive atrium, pV = primitive ventricle, BC = bulbs cordis, RSV/LSV = right / left sinus ventricle
A challenge for the embryo is to get access to gases and nutrients without functional lungs and intestines, what structures have evolved to get gases and nutrients?
Intraembryonic embryo circuit, vitelline circuit and allantois circuit
Label the diagram
UNLABELLED BLOOD VESSELS OF EMBRYO
What does the intraembryonic circuit do?
Provides nutrients to the tissue of the embryo
What does the vitelline circuit do?
Gathers nutrients from the yolk sac
What does the allantois circuit do?
Gets rid of nitrogenous waste
What structures in the embryo do the aortic arches provide nutrients for? How many aortic arches are in each structure?
The pharyngeal arches One aortic arch in each pharyngeal arch
In mammals, what circuit brings the nutrients into the embryo?
The allantois circuit (aka the umbilical chord FYI)
What does the umbilical vein and artery transport?
The umbilical vein transports oxygen and nutrient rich blood into the embryo The artery transports waste
Where is the embryonic waste transported to?
The placenta
