Flashcards in Third to Eight Weeks- The Embryonic Period Deck (21):
When does the embryonic disc form a head fold, tail ford, and lateral fold?
the 4th week, due to rapid growth
Derivatives of the ectoderm layer
the central and peripheral nervous systems, the sensory epithelium of the eye, ear, and nose, the epidermis and epidermal derivatives
Cells of the neural plate make up the _____.
Between 25 and 27 days the cranial and caudal neuropores close, formed a closed central nervous system consisting of what?
brain vesicles and spinal cord
Derivatives of the mesoderm
by the 17th day the shealth of mesoderm begins to differentiate and form 3 subdivisions, the paraxial, intermediate, and lateral mesoderm
forms the occipital, cervical, throacic, lumbar, sacral, and coccygeal pairs of somites
forms the urogenital organ components
splits into 2 layers, parietal (somatic) and visceral (splanchnic) mesoderm
Mesoderm cells of the parietal layer form what? (from the lateral mesoderm)
mesothelial serous membranes that line the pleural, pericardal, and peritoneal cavities
Mesoderm cells of the visceral layer form what? (from the lateral mesoderm)
thin, serous membrane around the organs
blood islands appear in the mesoderm that surrounds the umbilical vesicle around the 3rd week of development
Blood islands arise from mesoderm that forms hemangioblasts that differentiate into what?
angioblasts, that form blood vessels
once vessels are formed by vasculogenesis, new vessels are added from sprouting from the existing vessels
Blood cell formation
first blood cells arise from hemangioblasts in the center of the blood islands in the umbilical vesicle that form hematopoietic stem cells
Derivatives of the endodermal layer
the GI tract
What does the midgut communicate with?
the umbilical vesicle via the vitelline duct
What is the foregut closed off by?
the oropharyngeal membrane (ruptures in week 4)
What is the hindgut closed off by?
the cloacal membrane (ruptures in week 7)
What does the endodermal germ layer give rise to?
epithelial lining of organs such as the respiratory and urinary tracts, the parenchyma of the thyroid, liver, and pancreas
How is the age of the embryo determined starting in the second month?
the crown-rump length