Embryonic Disk and more Flashcards
label the parts of the embryonic disk
drawn out
what is the amniotic cavity
forms the inside inner cell mass and surrounded by layer of cells called the amnion or amniotic sac
what structures form after implantation
embryonic disk
composed of 2 layers - epiblast and hypoblast
- the amniotic cavity eventually covers the developing embryo providing a protective fluid bag
yolk sac
forms inside blastocele from hypoblast
what is the epiblast
its 3 germ layers that becomes the embryo
what is the hypoblast
its extraembryonic memebrane and helps with extra embryonic tissue
explain what happens during day 13-14 (gastrulation) - formation of germ layers
- cephalic end = Becomes head
- caudal end = Becomes base of torso
- epiblast layer multiplies and thickens along primitive streak
These 3 germ layers are gonna form all of the body tissues:
- Ectoderm –> skin and most of nervous system
- Mesoderm –> blood supply, bones and muscles
- Endoderm –> digestive system, lungs
describe the formation of the germ layers
endoderm
- Inner layer
- forms lining of digestive tract and derivatives
mesoderm:
- middle layer
- forms tissues like muscle, bone. blood vessels
ectoderm:
- outer layer
- forms skin and nervous system
what happens at day 16 - formation of notochord
- mesodermal cells are formed
- solid cylinder of cells under the ectoderm –> becomes neural plate at day 18
- notochord is involved in induction of signals from ectoderm to the neural plate and it at the cephalic end (the primitive streak is at caudal end)
what does the oropharngeal membrane becomes?
mouth
what does the cloacal membrane becomes?
anus - end of digestive system
what happens on day 18-26 - formation of neural tube
- Notochord has sent a signal to ectoderm –> thickens it and becomes neural plate
neural plate Forms neural folds and a central indentation called a neural groove
-
Neural folds becomes higher and neural indentations get bigger - Ridges = crest of neural fold
- Crests come together and form an outer layer (becomes skin) at the top and it makes a tube in the middle (neural tube that becomes spinal cord and brain)
- Outside neural tube theres somites thats formed from mesoderm
what does the neural tube form
forms the brain and spinal cord (CNS)
what does the neural crest form?
- sensory and post ganglionic autonomic (cant consciously control) portions of PNS
- general CT of the head
what is a somite formed from and what does it become?
formed from mesoderm adjacent to neural tube
eventually become vertebral column, ribs, and some skeletal muscle
what is the importance of the neural plate and how is it formed?
it becomes the spinal cord and brain
the notochord sends signals from the mesoderm to the ectoderm layer to thicken ectoderm and become neural plate
what are the two types of embryonic folds? explain.
- lateral body fold
- across the length of the neural tube - fold in the median plane
- this forms the ends called the hindgut and foregut
what does the lateral fold produce?
- it forms the gut tube from the endoderm
- coelom within the mesoderm –> body cavities
- ectoderm –> skin
what does the median plane fold produce?
- foregut and hindgut
- allantois
What is the allantois?
a region of the yolk sac that is pinched off and ends up in the connecting stalk and becomes a part of the urinary system.
what happens at day 20 of embryo folding and gut formation?
the amniotic cavity folds around the 3 germ layers into 2 different ways
- longitudinally - forms gut tube
- medially - forms head and tail
what happens at day 25 of embryo folding and gut formation?
- the folds get closer to each other and the midgut is now defined.
- oropharyngeal is in contact with endoderm = mouth opening
- cloacal membrane and region under disappear = anus
- yolk sac is narrowed and celom gets longer
what happens at day 30 of embryo folding and gut formation?
lateral folds fuse to form:
- amniotic cavity is around all germ layers like the whole embryo
- gut tube from oropharyngeal to cloacal membrane
evaginations from gut tube form:
- anterior pituitary, thyroid gland, lungs, liver, pancreas
- branchial arches
coelom:
- fuses around the heart as pericardial cavity
- expands to become the pleural and peritoneal cavities
- cavities become separate entities.
what is evagnation
turning the gut tube inside out?
what is the coelom?
A fluid-filled cavity lined by mesoderm tissue.
what do brachial arches form?
pharynx, auditory tubes, tonsils, thymus and parathyroid glands
when does limb bud development occur?
upper limb = day 24
lower limb = day 28
what is limb bud development?
- limbs grow from proximal to distal
- mesoderm cells are proliferating
what is the apical ectodermal ridge?
thickened ectoderm at distal end of each developing limb that stimulates outward growth
what is the protein for limb bud development called?
sonic hedgehog
what did taking thalidomide cause problems in children?
def: thalidomide = drug given to prego women to reduce sickness
caused:
because it inhibits the formation of blood vessels. if the apical ectodermal ridge doesnt have enough blood supply to grow it wont and the limb will be stunted
where is the skeleton derived from?
mesoderm or neural crest cells
where are muscles derived from?
myoblasts - derived from the somites that develop into skeletal muscle fibers
where is the nervous system derived from?
neural tube and neural crest cells
what is the foregut
oral cavity
what is the hindgut
anus
what is the midgut
mid duodenum
