Trilaminar Flashcards
Cells from which layer of the bilaminar embryonic disk migrate through the primitive streak and pit. What 3 layers do these cells form?
Epiblast; ectoderm, intraembryonic mesoderm, and endoderm.
What layers form the buccopharyngeal and cloacal membranes and where are they located?
These are membranes where the ectoderm and endoderm come into direct contact.
Buccopharyngeal- upper boundary of digestive tract (future mouth)
Cloacal- lower boundary of digestive tract (future anus)
What does the notochord induce?
Induces overlying ectoderm to differentiate into neuro ectoderm to form neural plate.
Induces formation of vertebral bodies.
What are the adult remnants of the notochord?
Nucleus pulposes in adult intervertebral discs.
What is a sacrococcygeal teratoma and how does it arise.
Remnants of he primitive streak in the sacrococcygeal area that lead to a tumor containing tissue derived from all 3 germ layers. Most common tumor in newborns
Briefly describe the process of neurulation
Notochord induces overyling ectoderm to form neural plate.
Neural plate invaginates to form median neural groove flanked by neural folds.
Neural folds fuse to form neural tube which separates from surface ectoderm.
Fusion proceeds in a cranial to caudal direction and is completed by week 4.
What are the 3 types of mesoderm and how are they related anatomically?
Paraxial mesoderm- located on each side of midline; most medial
Intermediate mesoderm- between paraxial and lateral
Lateral- continuous with extraembryonic mesoderm along lateral edges of embryo.
What do somites form?
Scleretome- cartilage and bone of vertebral column
Myotome- skeletal muscle
Dermatome- dermis of skin
How are somites related to notochord
Line the notochord on both sides
What type of mesoderm forms the kidneys
Intermediate mesoderm
From what type of mesoderm does the visceral pleura develop
Splanchnic mesoderm from the lateral layer
What is septum transversum, where is it located, and what does it form in the adult?
Thickened bar of mesoderm that arises early in week 4 rostral to cardiogenic area. Forms diaphragm in adults.
What does embryonic folding accomplish?
Changes the shape of the embryo from 2 dimensional to 3 dimensional cylinder that has an anterolateral body wall and inner gut tube.
How does the head fold reposition the developing heart, diaphragm, and mouth?
Repositions cardiogenic region ventrally toward future chest.
Folds buccopharyngeal membrane ventrally toward region of future mouth.
Shifts the septum transversum ventrally until it wedges between the future hear and yolk sac.
What germ layer forms the allantois and what does it form in the adult?
Endoderm; forms the liamentous urachus which becomes the median umbilical ligament in adult.
With what does the midgut communicate
Yolk sac
What 3 things does the process of gastrulation accomplish?
Transforms the bilaminar disk into a trilaminar disk
Establishes the 3 definitive germ layers
Establishes the body axes (anterior-posterior, dorsal-ventral, left-right)
Development of the uteroplacental circulation begins when
Trophoblastic lacunae form within the synctiotrophoblast
Maternal capillaries near the synctiotrophoblast expand to form __ which anastomose with the lacunae
Maternal sinusoids
As anastomoses develop, the cytotrophoblast proliferates to form __ that grow into the synctiotrophoblast
Primary villi
Primary villi grow out into the __ with a covering of __
Lacunae; synctiotrophoblast
Gastrulation is first indicated by the appearance of the
primitive streak on the surface of the epiblast
The primitive streak consists of the
primitive groove, primitive node, and primitive pit
The primitive streak disappears when
Gastrulation is over
Conjoined twins result from partial splitting of the
primitive node and primitive streak
What is sirenomelia?
mermaid syndrome. insufficient mesoderm is formed in the caudal region of the embryo. Kidney and bladder are underdeveloped so many babies afflicted die within a few days of birth.
What is a cordoma
Tumor that arises from remnants of notochord. Intracranially or sacrally; more common in adult men in their 50s
What is neurulation?
formation of the neural tube
Large spaces develop within the lateral mesoderm to form
the intra-embryonic coelom (which will form pleural, pericardial and peritoneal cavities in adult)
What are the 2 layers that the intraembryonic coelom split the lateral mesoderm into
Somatic mesoderm and splanchnic mesoderm
What does the somatic and splanchnic mesoderm form?
Somatic- forms the parietal serous linings of body cavities
Splanchnic- forms the visceral serous coverings of the organs and some forms the cardiogenic area
What forms the initial partition between the thoracic and abdominal cavities
Septum transversum
Folding of the embryo occurs in what 2 planes
cranio-caudal (head-tail)
Transverse (lateral)
Ectoderm covers the entire embryo except
the future umbilical region where the yolk sac and connecting stalk emerge
Fusion of the lateral edges of the yolk sac endoderm creates the
gut tube
What causes a gastroschisis
Embryonic folding fails to occur
What is gastroschisis
abdominal wall defect where there is an opining in the wall. intestines and other abdominal organs herniate through the opening and spill out into the amniotic fluid.
The cranial portion and caudal portion of the ingot form what?
Cranial- foregut
caudal- hindgut
