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140 Cards in this Set
- Front
- Back
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Development of the embryo from the trilaminar embryonic disk during the 3rd week is characterized by?
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Appearance of the primitive streak
Development of the notochord Differentiation of the three germ layers |
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What does the third week of development coincide with?
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It is the week following the first mist menstrual period.
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What time frame can a woman detect pregnancy with ultrasonography?
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5 weeks after the last normal menstrual period.
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What is gastrulation?
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Process where three germ layers are formed from the bilaminar embryonic disc and axial orientations are established.
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What is gastrulation the beginning of?
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Morphogenesis - development of body form
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What molecules play a role in gastrulation?
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Bone Morphogenic proteins
FGFs Shh (sonic hedgehog) Tgifs Wnts |
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What does embryonic ectoderm give rise to?
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Epidermis, CNS, PNS, Eyes, Internal ears
Neural crest cells that migrate to CT of head |
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What does embryonic endoderm give rise to?
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Epithelial linings of respiratory and digestive tracts.
Glands in the GI tract. Glandular cells of accessory digestive organs. |
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What does embryonic mesoderm give rise to?
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All skeletal muscles, blood cells and the lining of blood vessels.
Smooth muscle. Serosal linings of all body cavities. Reproductive and excretory linigns. Cardiovascular system. Connective tissues, ligaments, dermis, stroma of organs - in trunk |
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What is the first morphologic sign of gastrulation?
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Formation of the primitve streak on the surface of the epiblast.
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When and where does the primitive streak appear?
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Beginning of the 3rd week
Appears caudally in the median plane of the dorsal aspect of the embryonic disc |
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What is the primitive streak?
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Proliferation and movement of cells of the epiblast to the median plane of the embryonic disc.
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What does the cranial end of the primitive streak proliferate into?
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Primitive node
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What is continuous with the primitive node?
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Primitive groove and pit.
Result from the invagination of epiblastic cells. |
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What is important about the appearance of the primitive streak?
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As soon as it appears, it is possible to identify the embryo's craniocaudal axis, cranial and caudal ends, dorsal and ventral surfaces, and right and left sides.
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What doe the cells from the deep surface of the primitive streak form?
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Mesenchyme - spindle shaped cells with sparse collagen fibers.
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What does mesenchyme form?
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Supporting tissues of hte embryo, CT of body and CT of glands. Some forms the mesoblast - enbryonic mesoderm
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What forms in the roof of the umbilical vesicle?
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Embryonic endoderm, the hypoblast cells get displaced.
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What factors induce formation of mesoderm?
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Nodal factors of the transforming growth factor (Beta) superfamily.
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What factors participate in specifying germ cell layer fates?
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Wnt3a, Wnt5a, FGFs
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What factors are involved in specification of the endoderm?
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Transforming growth factor Beta nodal, T-box transcription factor (veg T), and Wnt signaling pathway.
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How is mesoderm formed from the primitive streak?
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Ingression of cells until the early part of the 4th week.
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Where does the remnant of the primitive streak end up?
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In the sacrococcygeal region of the embryo.
It should disappear by the end of the 4th week. |
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What happens if remnants of the primitive streak persist?
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A sacroccygeal teratoma can develop.
Tissues from all three germ layers, at different stages of differentiation. |
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What is a sacrococcygeal teratoma?
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Most common tumors in newborns.
1:35,000 80% affected are female Most are benign and diagnosed in ultrasound. Surgical excision, might cause bowel or urinary obstruction in newborn. |
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What is the notochordal process?
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Mesenchymal cells that have migrated cranially from primitive node and pit forming a median cellular cord.
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What does the notochordal process become?
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Acquires a lumen and becomes the notochordal canal.
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What is the prechordal plate?
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Small circular area of columnar endodermal cells where ectoderm and endoderm are fused.
Mesenchymal population of neural crest origin rostral to notochord. Gives rise to endoderm of the oropharyngeal membrane. |
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What controls the development of cranial structures including the forebrain and eyes?
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Shh and PAX6 from teh prechordal plate.
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What does the notochordal process grow between?
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Ectoderm and endoderm
Grows cranially until it reaches prechordal plate. |
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What are the mesenchymal cells from the primitive streak and notochordal process continuous with?
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Extraembryonic mesoderm covering the amnion and umbilical vesicle.
Some migrate around the prechordal plate and form cardiogenic mesoderm. |
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What is the cardiogenic area?
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Where heart primordium begins to develop at the end of the third week.
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What is caudal to the primitive streak?
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The clocal membrane - future site of the anus. Endoderm and ectoderm are fused.
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At the middle of the third week what has occured?
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Intraembryonic mesoderm has separated the ectoderm and endoderm.
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Ectoderm and endoderm are separated everywhere EXCEPT?
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Oropharyngeal membrane
Median plane cranial to primitive node - where notochordal process is located. Cloacal membrane |
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What factors induce the notochord precursor cells to form the notochord?
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Shh signaling from the floor plate of the neural tube
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What is the function of the notochord?
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Defines the primordial longitudinal axis of the embryo
Gives rigidity Provides signals for development of axial musculoskeletal structures and CNS Contributes to the intervertebral discs |
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What does the notochord process come from?
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Invagination of the cells from the primitive pit.
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What forms the notochordal canal?
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The primitive pit extends into the notochordal process.
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What does the notochordal process span?
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From primitive node to prechordal plate.
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What are the mesenchymal cells from the primitive streak and notochordal process continuous with?
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Extraembryonic mesoderm covering the amnion and umbilical vesicle.
Some migrate around the prechordal plate and form cardiogenic mesoderm. |
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What is the cardiogenic area?
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Where heart primordium begins to develop at the end of the third week.
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What is caudal to the primitive streak?
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The clocal membrane - future site of the anus. Endoderm and ectoderm are fused.
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At the middle of the third week what has occured?
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Intraembryonic mesoderm has separated the ectoderm and endoderm.
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Ectoderm and endoderm are separated everywhere EXCEPT?
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Oropharyngeal membrane
Median plane cranial to primitive node - where notochordal process is located. Cloacal membrane |
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What factors induce the notochord precursor cells to form the notochord?
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Shh signaling from the floor plate of the neural tube
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What is the function of the notochord?
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Defines the primordial longitudinal axis of the embryo
Gives rigidity Provides signals for development of axial musculoskeletal structures and CNS Contributes to the intervertebral discs |
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What does the notochord process come from?
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Invagination of the cells from the primitive pit.
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What forms the notochordal canal?
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The primitive pit extends into the notochordal process.
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What does the notochordal process span?
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From primitive node to prechordal plate.
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How does the notochordal canal communicate with the umbilical vesicle?
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Fused layers of ectoderm and endoderm undergo degeneration forming openings in the floor of the process.
Eventually they will become confluent and the floor of the canal will disappear. |
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What do the remains of hte notochordal process become?
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A flattened groove called the notochordal plate
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What does the notochordal plate infold into?
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The notocord - this begins at the cranial end as a proliferation of cells.
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What does the proximal part of the notochordal canal persist as?
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Neurenteric canal - usually obliterates when development of the notochord is complete.
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What is the neurenteric canal?
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Transitory communication between the amniotic and umbilical vesicle cavities.
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What layer does the notochord detach from?
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Endoderm of the umbilical vesicle
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When does the notochord degenerate?
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As teh bodies of hte vertebrae form
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What is the remnant of the notochord?
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Nucleus pulposus of each intervertebral disc
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What is the primary inductor in the early embryo?
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The notochord
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What does the developing notochord induce the overlying ectoderm to become?
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Thickens into the neural plate (CNS primordium)
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What may form from the vestigial remnants of notochordal tissue?
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A chordoma
Can be both benign and malignant. 1/3 occur at the base of the cranium and extend to the nasopharynx. Grow slowly, malignant infiltrate bone. |
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What is the allantois?
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Appears on day 16
Small diverticulum from caudal wall of the umbilical vesicle that extends to the connecting stalk. Endodermal sac that has a respiratory function or acts as a reservoir for urine. |
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What does allantoic mesoderm become?
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Expands beneath the chorion and forms blood vessels that will serve the placenta.
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What is the urachus?
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The proximal part of the allantois that persists throughout much of development as a stalk.
Extends from the bladder to the umbilical region. |
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What is the urachus represented by in adults?
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Median umbilical ligament.
The blood vessels become the umbilical arteries. |
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Where are allantoic cysts most commonly found?
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In the proximal part of the umbilical cord, near its attachment to the anterior abdominal wall.
Asymptomatic until childhood when they can become inflamed. |
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What constitutes neurulation?
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Process involved in the formation of the neural plate and neural folds.
Closure of the folds to form the neural tube |
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When is neurulation completed?
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By the end of the 4th week.
When closure of the caudal neuropore occurs. |
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What does the notochord induce the ectoderm to become?
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Ectoderm adjacent to the midline is induced to thicken and form an elongated neural plate of thickened epithelial cells.
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What does neuroectoderm give rise to?
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Neural plate - CNS
Retina |
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Where does the neural plate begin and end?
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At first - corresponds to notochord, rostral to primitive node and dorsal to the notochord and mesoderm.
Eventually it extends cranially as far as the oropharyngeal membrane, and beyond the notochord. |
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What occurs on the 18th day?
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Neural plate invaginates along its central axis to form a longitudinal median neural groove, which has neural folds on each side.
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What are the neural folds?
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Are prominent at the cranial end of the embryo and are the first signs of brain development.
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When does the neural plate get converted into the neural tube?
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End of the third week.
Neural crest celsl also undergo an epithelial to mesenchymal transition and migrate away as the folds meet. |
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What does the neural tube give rise to?
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Primordium of brain vesicles and spinal cord.
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What does surface ectoderm differentiate into?
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epidermis
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Where is non-neural ectoderm found?
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The free edges of the neural folds that fuse to be a continuous tube over the dorsal surface of the embryo.
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As the neural tube separates from the surface ectoderm what forms?
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Neural crest cells form a flattened irregular mass, the neural crest between the neural tube and overlying surface ectoderm.
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What factors are essential for the development of the neural crest?
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Wnt/ B-catenin --> activate Gbx2 homeobox gene
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What does the neural crest give rise to?
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Separates into right and left parts that shift the dorsolateral aspect of the neural tube.
Give rise to the sensory ganglia of spinal and cranial nerves, ganglia of autonomic nervous system. CN: V, VII, IX, X Form neurolemma sheaths of peripheral nerves. Leptomeninges of arachnoid and pia Pigment cells, suprarenal medulla, CT components in the head Move into and over the somites. |
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What factors regulate the differentiation and migration of neural crest cells?
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By genes:
FoxD3 Snail2 Sox9 Sox10 Also signaling molecules and transcription factors |
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What interactions are required to establish the boundaries of the neural plate?
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Interactions within the surface epithelium and between it and underlying mesoderm.
Also establishes boundaries of the neural plate. Specifies the sites where epithelial-mesenchymal transformation will occur. |
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What factors are required to establish neural plate boundaries, and to specify mesenchymal transformation?
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BMP's
Wnt Notch FGF signaling systems. Ephrins - migrating NC cells |
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What can happen if there is a disruption in neurulation?
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Neural tube defects = most common congenital anomalies.
Meroencephaly - partial absence of brain (most severe) Teratogenic drugs = affects cell fates, cell adhesion, mechanism of tube closure. Failure of formation of neural tube. Sometimes secondary, linked to lesions that affect the degree of folding of the neural plate. |
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What is the paraxial mesoderm formed from?
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Cells from the primitive node
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What are the columns of paraxial mesoderm continuous laterally with?
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Intermediate mesoderm which thins into lateral mesoderm
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What is the lateral mesoderm continuous with?
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Extraembryonic mesoderm covering the umbilical vesicle and amnion.
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What happens to the paraxial mesoderm during the third week?
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Differentiates, condenses, and begins to divide into paired cuboidal bodies: somites.
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What sequence do the somites form in?
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Cranio-caudal
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How many pairs of somites form during the somite period of human development?
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38
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When is the "somite period of human development?"
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Days 20-30
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When are 42 to 44 pairs of somites present?
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By the end of the 5th week. These are triangular in transverse sections.
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Where do somites first appear?
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In the future occipital region of the embryo.
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What do the somites give rise to?
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Axial skeleton, associated musculature, adjacent dermis of the skin.
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Where does the first pair of somites appear?
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A short distance caudal to the site at which the otic placode forms.
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What genes are required for somite formation from the paraxial mesoderm?
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Notch, Hox, other signaling factors
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What transcription factors are required for somite formation from the paraxial mesoderm?
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Forkhead transcription factors:
Fox C1 and Fox C2 |
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What is the craniocaudal segmental pattern of the somites regulated by?
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Delta-notch signaling.
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Where do the coelomic spaces appear?
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Lateral mesoderm, cardiogenic mesoderm.
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What do the coleomic spaces come together to form?
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Intraembryonic coleom.
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What two layers does the coleom divide the lateral mesoderm into?
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1) somatic or parietal layer of lateral mesoderm
2) Splanchnic or visceral layer of lateral mesoderm |
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What is the somatic layer of lateral mesoderm continuous with?
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Extraembryonic mesoderm covering amnion, located below the ectodermal epithelium
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What is the splanchnic layer of lateral mesoderm continuous with?
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Extraembryonic mesoderm covering the umbilical vesicle.
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What forms the somatopleure?
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Somatic mesoderm and overlying embryonic ectoderm
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What forms the splanchnopleure?
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Splanchnic mesoderm and underlying embryonic endoderm (forms gut)
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What is the intraembryonic coleom divided into during the second month?
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1) pericardial
2) pleural 3) peritoneal |
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How is embryonic nutrition obtained in the second week?
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From maternal blood by diffusion through the extraembryonic coleom and umbilical vesicle.
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What occurs at the beginning of the third week?
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Vasculogenesis and angiogenesis begins in the extraembryonic mesoderm of the umbilical vesicle, connecting stalk, and chorion.
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When do embryonic blood vessels begin to develop?
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Two days after vasculogenesis and angiogenesis
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When does the primordial uteroplacental circulation develop?
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During the third week.
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What is vasculogenesis?
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Formation of new vascular channels by assembly of individual cell precursors called angioblasts.
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What is angiogenesis?
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Formation of new vessels by budding and branching from preexisting vessels.
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What occurs during vasculogenesis in the 3rd week?
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1)Angioblasts differentiate --> form blood islands
2) Cavities appear in the blood islands 3) Angioblasts flatten to form endothelial cells --> form around cavities and make endothelium 4) Cavities fuse to form endothelial channels 5) Vessels sprout via endothelial budding and fuse with other vessels 6) Mesenchyme surronding endothelial BVs differentiate into muscular and CT elements |
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What cells are the precursors of angioblasts?
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Mesenchymal cells
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What are blood islands associated with?
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Umbilical vesicle or endothelial cords
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What are the cavities in the blood islands formed by?
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Confluence of intercellular clefts
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What do blood cells develop from?
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Endothelial cells of vessels as they grow on the umbilical vesicle and allantois at the end of the 3rd week.
Later they grow on specialized sites along the dorsal aorta. |
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When does blood cell formation begin?
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(Hematogenesis)
5th week |
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Where does blood formation occur?
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Along the aorta then in various parts of hte embryonic mesenchyme, liver, spleen, bone marrow, and lymph nodes.
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What are erythrocytes derived from?
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Different hematopoetic progenitor cells
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Where do the heart and great vessels form from?
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Mesenchymal cells in the cardiogenic area
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What are the endocardial heart tubes?
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Paired, longitudinal endothelial-lined channels that develop during the third week.
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What do the endocardial heart tubes fuse to become?
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Primordial heart tube
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What comprises the primordial cardiovascular system?
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Tubular heart, BV's, connecting stalk, chorion, umbilical vesicle
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When is blood circulating?
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End of the 3rd week
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When does the heart beat begin?
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21st-22nd day
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What is the first organ system to reach a functional state?
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Cardiovascular system
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When can the embryonic heartbeat be detected?
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During the 5th week via ultrasound (doppler)
7 weeks after last normal menstrual period |
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When do primary chorionic villi appear?
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End of second week
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When does the mesenchyme grow into the primary villi?
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Early in the third week - forms a core of mesenchymal tissue
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What are the secondary chorionic villi?
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Cover the entire surface of the chorionic sac
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When are the villi called tertiary?
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When blood vessels are visible in them
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What do the capillaries in the chorionic villi fuse to form?
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Arteriocapillary networks - become connected with heart through BVs in the chorion & connecting stalk
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When does blood begin to flow through the capillaries in the villi?
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By the end of the 3rd week.
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What forms the cytotrophoblastic shell?
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cytotrophoblastic celsl of villi proliferate and enter the syncytiotrophoblast to form the exttravillous structure that surrounds the chorionic sac and attaches it to the endometrium.
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What are the villi that attach to the maternal tissues through the shell called?
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Stem chorionic villi
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What are branch chorionic villi?
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Villi that grow from the sides of the stem villi.
Where main exchange of material between the blood of mom and fetus takes place. Bathed in continually changing maternal blood in intervillous space. |
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What do degenerating villi form if the embryo dies?
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Cystic swellings = hydatidiform moles
Produce excessive HCG |
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What is a malignant hydatidiform mole called?
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Malignant trophoblastic lesions - choriocarcinomas
Metastazie - lungs, vagina, liver, bone, intestine, brain |
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How does a hydatidiform mole form?
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Fertilization of an empty oocyte - absent pronucleus (monospermic mole)
Fertilization of an empty oocyte by to sperms (dispermic mole) |
