Exam 1 9/27 Davenport Flashcards
Week 4 to 8 of development is known as:
Organogenic period
_____ constitutes most of the embryonic period
Organogenic period
What happens during the organogenic period?
- all major internal and external structures are established
- Main organ systems have begun to develop - CV is the only one with more function
- shape of embryo changes and has distinctly human appearance by 8th week
When do you start to hear the fetal heartbeat?
Week 4-6
During organogenic period, tissues and organs are differentiating rapidly so exposure to teratogens can cause?
major congenital anomalies
What is the fate of the primitive knot and primitive streak?
Nothing; we don’t know where the underlying hypoblast cells go
What remnants of the notochord do we see?
Nucleus pulposis between the intervertebral discs
Between days 26-32, what starts to appear in the embryo?
Somites
How many pairs of somites develop?
38-39
Where do the somites appear?
Occipital region
What happens to the mesoderm around the notochord?
Divides into paraxial mesoderm, intermediate, and lateral plate mesoderm
Which mesoderm is continuous with the extraembryonic mesoderm?
Lateral plate mesoderm
What tissue is responsible for the formation of somites?
paraxial mesoderm
____ gives rise to spinal ganglia, which contributes to _____
neural crest cells; dermatomes
(nerves that come from the spinal ganglia will innervate the structures of those somites; as those somites grow they will form the dermatomes)
True or false: dermatomes and nerves cross the midline
False
Fate of somites
most of axial skeleton and associated muscles, UG system (kidneys and gonads)
Fate of intermediate mesoderm
UG system
Fate of lateral plate mesoderm
heart and CV system; blood; portions of the kidneys, smooth muscle, skeleton of the limbs
Fate of ectoderm
- epidermis
- CNS and PNS
- eyes
- internal ear
- neural crest
- CT of head and neck
Fate of mesoderm
- all skeletal muscles
- blood cells
- lining of blood vessels
- all visceral smooth muscle
- lining of all body cavities
- ducts and organs of the reproductive and excretory systems
- most of CV system
Exceptions to fate of mesoderm - what is derived from neural crest?
CT, cartilage, bones, tendons, ligaments, dermis, stroma of organs of the head
Fate of embryonic endoderm
- epithelium of the respiratory system and digestive system
- ducts of glands
- glandular cells of the liver and pancreas
Teratogens can act between which weeks?
weeks 3-16 (highly sensitive period)
What folds occur when embryo folds?
1 head fold, 2 lateral folds, 1 tail fold
Folding of embryo causes:
- trilaminar embryo changes into cylindrical tube
- change in symmetry from mid axial to bilateral
Folding is a result of differential growth because:
disc cannot keep up with growth in length as a result of developing nervous system
What happens to the yolk sac as the embryo folds?
some is incorporated into embryo (foregut, midgut, hindgut –> GI tract)
Direction of movement during embryo folding
Dorsal to ventral
What eventually happens to the prechordal and cloacal plate?
They rupture so as to form a continuous tube in the embryo
Some of the yolk sac stays ____ outside of the embryo - what is the significance?
herniated; gut is forming and rotates around the superior mesenteric artery, allows 32 ft of intestine to form in relation to SMA
Why is the head fold important?
Puts everything where they need to be
When the heart gets into place, we see the formation of:
2 dorsal aorta (branch of this supplies the pharyngeal arches)
Stomodeum
primitive oral cavity
How is embryonic age estimated?
determined from external characteristics and length measurements
Methods of measuring embryonic age
- during week 3-4, measuring GL (greatest length)
- sitting height (crown-rump length) for older embryos
- standing height or crown heel length - week 8
