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Embryology
Fall 2012 Post-Bac Embryo
76
Biology
Post-Graduate
09/09/2012

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Term
Notochordal Process
Definition
The midline cellular code tha forms when mesenchymal cells migrate cranially from the primitive node
Term
Notochordal Process grows cranially between the _______ and _______ until it reaches the _________
Definition
endoderm and ectoderm; prechordal plate
Term
Transitory neurenteric canal
Definition
Cell of Notohordal process that fuse with the embryonic ectoderm to connect the amniotic cavity with the yolk sac
Term
Definitive notochord
Definition
forms when cells from transitory neurenteric canal separate
Term
Notochord
Definition
solid rod of cells in the midline between the embryonic ectoderm and endoderm
Term
What 4 things do inductive signals from the notochord do?
Definition
1) Stimulates a: conversion of overlying surface ectoderm into neural tissue b: the earliest steps in the development of the dorsal pancreas 2) Specify the identity of certain cells within early nervous system 3) Transfom certain mesodermal cells of somites into vertebral bodies.
Term
Cloacal membrane
Definition
The circular area that is caudal to the primitive streak and covers cloaca
Term
What is extraembryonic mesoderm derived from?
Definition
Cytotrophoblast and sometimes the primitive streak
Term
Proctodeum
Definition
Shallow depression outside cloacal membrane
Term
Cardiogenic area
Definition
future site of the heart
Term
Describe the migration of the cells from the primitive streak into the cardiogenic area.
Definition
Cells from primitive streak migrate craniallyon each side of the notochordal process around the prechordal plate, where they meet cranially in the cardiogenic area
Term
At what 2 sites does the embryonic disc remain bilaminar?
Definition
The cloacal membrane and oropharyngeal membrane.
Term
Why does the embryonic disc remain bilaminar at specific sites?
Definition
The embryonic ectoderm and endoderm are fused at these sites, thus preventing migration of mesenchymal cells between them
Term
Intraembryonic mesoderm separates th ectoderm and endoderm everywhere except?
Definition
1) Oropharyngeal membrane cranially 2)Cloacal membrane caudally 3) In the midline cranial to the primitive node, where the notochordal process extends
Term
Where does the notochord extend?
Definition
From the oropharyngeal membrane to the primitive node
Term
When does the notochord degenerate and disappear?
Definition
As the bodies of vertebrae form
Term
Nucleosis pulposis
Definition
Notochord that persists inside of each intervertebral disc.
Term
Allantois
Definition
tiny, finger-like outpouching or diverticulu from the caudal wall of the yolk sac
Term
What 2 functions does the allantois serve in embryos of reptiles, birds, and some mammals?
Definition
1) Respiratory function 2) Storage place for urine during embryonic life
Term
Allantois is involved in early ____ ______
Definition
blood formation
Term
Where do blood vessels come from in the allantois?
Definition
Mesodermal walls
Term
Blood vessels from allantois become what?
Definition
Umbilical arteries
Term
Urachus
Definition
Urinary bladder to umbilicus (belly button)
Term
The urachus in adults is represented as the ____ _____ ________
Definition
Median umbilical ligament
Term
Neuralation
Definition
Formation of the neural plate, the neural folds, and their closure to form the neural tube
Term
When is neuralation complete?
Definition
At the end of the 4th week when closure of caudal neuropore occurs
Term
What is the embryonic ectoderm of neural plate called?
Definition
neuroectoderm
Term
What happens to the neuroectoderm as the notochord develops?
Definition
It thickens to form the neural plate
Term
What is neural plate formation induced by?
Definition
The developing notochord
Term
What main thing does the neuroectoderm give rise to?
Definition
Central nervous system (consists of brain and spinal cord)
Term
How does the neural plate first appear?
Definition
Cranial to the primitive node
Dorsal to the notochordal process and the mesoderm adjacent to it
Term
How far does the neural plate extend as the notochord forms and elongates?
Definition
To the oropharyngeal membrane
Term
What happens to the neural plate on the 18th day?
Definition
It invaginates along its central axis to fom a neural groove (neural folds on each side)
Term
What fuses to form the neural tube?
Definition
Neural folds
Term
Explain how the surface ectoderm becomes continuous with the back of the embryo?
Definition
The neural tube separates from the surface ectoderm and the fre edges of surface ectoderm fuse
Term
What happens to some neuroectodermal cells as neural folds fuse?
Definition
They lose their epithelial affiniites and attachments to neighboring cells.
Term
What happens to neuroectodermal cels as the neural tube separates from surface ectoderm?
Definition
These neural crest cells migrate ventrolaterally on each side of the neural tube
Term
What is the neural crest?
Definition
An irregular flattened mass between the neural tube and the overlying surface ectoderm
Term
What does neura crest come from?
Definition
neuroectoderm
Term
Neuropore
Definition
region where neural folds haven't fused into a tube; they eventually close (if not, defect happens like spina bifida)
Term
What 5 types of ganglia does the neural crest give rise to?
Definition
1) dorsal root ganglia 2) sympathetic ganglia 3) enteric ganglia 4) parasympathetic ganglia of CN V11, 1X, X 5) Part of sensory ganglia of cranial nerves
Term
Other than ganglia, what does the neural crest give rise to?
Definition
1) Schwann cells 2) melanocytes 3) satellite cells of peripheral ganglia 4) cartilage of pharyngeal arches 5) chromafin cell of adrenal medulla 6) pia and arachnoid membranes
Term
what are placodes?
Definition
specialized epidermal cells that join neuralcrest to form sensory ganglia of cranial nerves V V11-X
Term
paraxial mesoderm
Definition
a longitudinal column of intraembryonic mesoderm that forms on each side of the notochord and neural tube
Term
When is the paraxial mesoderm formed?
Definition
As the notochord and neural tube forms
Term
What is the paraxial mesodem continuous with?
Definition
The intermediate mesoderm which gradually things into the lateral mesoderm
Term
What does the intermediate mesoderm produce?
Definition
produce the urinary system and part of the genital system
Term
What is the lateral mesoderm continuous with?
Definition
The extraembryonic mesoderm covering the yolk sac and amnion
Term
Somitomeres
Definition
A series of regular pairs of segments thatare sometimes confused with closely packed mesenchymal cells
Term
What do somitomeres #1-7 do?
Definition
contribute mesoderm to pharyngeal arches; don't form somites
Term
What is head mesenchyme derived from?
Definition
Head mesoderm, ectodermal neural crest and (in the most cranial midline) the prechordal plate
Term
Mesoderm from somitomeres 1-7 give rise to what type of mesenchyme?
Definition
Head mesenchyme
Term
What happens to the remaining somitomeres (apart from 1-7)?
Definition
condense in a craniocaudal sequence to form 22-44 pairs of somites
Term
Somites
Definition
paired cuboidal bodies that are derived from the paraxial mesoderm
Term
What do somites give rise to?
Definition
Most of the axial skeleton and associated musculature; adjacent dermis of the skin
Term
where are somites located?
Definition
on each side of the developing neural tube
Term
dermatome
Definition
dermis and subcutaneous tissue of back
Term
myotome
Definition
muscles of back (epimeric and hypomeric muscles)
Term
sclerotome
Definition
1)bones of vertebra 2) cartilage of vertebra
Term
What can somites be used in determining?
Definition
an embryos age by counting them
Term
Where does the intraembryonic coelem first appear?
Definition
lateral mesoderm and the cardiogenic mesoderm
Term
What 2 layers does intraembryonic mesoderm divide lateral mesoderm into?
Definition
1) somatic (parietal) 2) Splanchic (visceral)
Term
What is somatic (parietal) layer continuous with?
Definition
Extraembryonic mesoderm covering the amnion
Term
What is splanchic (visceral) layer continuous with?
Definition
Extraembryonic mesoderm covering the yolk sac
Term
Somatic (parietal) gives rise to what?
Definition
Inner lining o body wall and parts of the limbs
Term
Splanchic (visceral) gives rise to what?
Definition
Mesothelial covering of visceral organs and part of the wal of the viscera
Term
What do the somatic mesoderm and overlying embryonic ectoderm form?
Definition
Embryonic wall or somatopleure
Term
What does splanchic mesoderm and embryonic ectoderm form?
Definition
Embryonic gut wall or splanchnopleure, or wall of primitive gut
Term
Which body cavities is the intraembryonic coelem divided into during the 2nd month?
Definition
1) pericardial cavity 2) pleural cavities 3) peritoneal cavity
Term
When do primary chorionic villi began to branch?
Definition
Shortly after they appear at the end of the second week
Term
What grows into primary chorionic villi early in the third week?
Definition
Mesenchyme
Term
Secondary chorionic villi
Definition
primary chorionic villi plus the mesenchymal core
Term
Tertiary chorionic villi
Definition
villi plus mesenchymal core plus blood vessels
Term
What forms the arteriocapillary venous networks?
Definition
Mesenchymal cells that differentiate nto blood capillaries
Term
Stem/anchoring villi
Definition
Villi that are attached to the maternal tissue vi the cytotrophoblastic shell
Term
Branch villi
Definition
Villi that grow from the side of the stem villi
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