mesoderm i
TRANSCRIPT
Mesoderm I
Embryos, Tissues, Cells
August 25, 2008
Douglas L. Falls, M.D.
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Mesoderm I / II: Reading
Carlson (2004) Human Embryology and Developmental Biology (3rd edition)
Reference: • ch 6 p108-118
early mesoderm development including somite development and early circulatory system development
• ch 6 p122-126 overview of structure of 4 wk human embryo)
• ch 6 fig 6-25 (p125) flow chart organ/tissue origin from germ layers)
• ch 9 p193-206, especially p195-196 and 204-206 muscular system development)
• ch 9 p185-193 skeletal development)
Mesoderm I: Learning objectivesStudents should be able to describe: • the origin of the mesodermal germ layer• the early division of the mesoderm into paraxial, intermediate mesoderm, and
lateral mesoderm and the split of lateral mesoderm into splanchnic and somatic mesoderm
• the major fates of the mesoderm
• Re muscle:
– in outline, a lineage tracing method used to determine the developmental origin of limb muscle
– the major steps in development of a skeletal muscle fiber from a mononucleate myoblast
– the developmental basis of slow versus fast twitch muscle
– the difference between skeletal versus cardiac and smooth muscle development with respect to myoblast fusion
• Re bone:
– The two mechanisms of bone formation
Students should be able to define, use in context, and provide examples of• all words on the slides titled “Vocabulary”.
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Embryology education resource:Endowment for Human Development WWW site
• Excellent source of human embryology education materials
• Some available in multiple languages
• http://www.ehd.org/
• DVD: The Biology of Prenatal Development
• In class we will watch Ch2, Ch5-->29 of DVD
• Script can be downloaded: http://www.ehd.org/pdf/BPD%204-26-2006%20English.pdf
• Suggest begin with:
• Prenatal overview (and take the quizzes?)
• Prenatal timeline
• Prenatal slide shows
• Movie theater
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Vocabularycoelom – • Etymology: German, from Greek koilōma cavity, from koilos Date: 1875 :
the usually epithelium-lined space between the body wall and the digestive tract of metazoans above the lower worms
splanchnic • Etymology: New Latin splanchnicus, from Greek splanchnikos, from splanchna, plural, viscera; akin to Greek splēn spleen Date:
1681of or relating to the viscera : visceral
viscus (plural: viscera; adj = visceral) • an internal organ of the body; especially : one (as the heart, liver, or intestine) located in the great cavity of the trunk proper
somatic• of or relating to the wall of the body : parietal
parietal• of or relating to the walls of a part or cavity
axial• relating to or situated in the central part of the body, in the head and trunk as distinguished from the limbs, e.g., axial skeleton.
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Vocabulary
Somite – • Etymology: International Scientific Vocabulary, from Greek sōma body Date: 1869
one of the longitudinal series of segments into which the body of many animals is divided
Names of the 3 paired veins that drain into the tubular heart of a 4 wk embryo
vitelline – • Etymology: Middle English, from Medieval Latin vitellinus, from Latin vitellus egg yolk Date: 15th
century
cardinal • Etymology: Middle English, from Late Latin cardinalis, from Latin, serving as a hinge, from cardin-,
cardo hinge Date: 14th century of basic importance : main, chief, primary <a cardinal principle>
umbilical • Date: 1541
of, relating to, or used at the navel
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Learning objectives: Mesoderm I
Students should be able to describe: • the origin of the mesodermal germ layer• the early division of the mesoderm into paraxial, intermediate mesoderm, and lateral
mesoderm and the split of lateral mesoderm into splanchnic and somatic mesoderm• the major fates of the mesoderm
• Re muscle:
– in outline, a lineage tracing method used to determine the developmental origin of limb muscle
– the major steps in development of a skeletal muscle fiber from a mononucleate myoblast
– the developmental basis of slow versus fast twitch muscle
• Re bone:
– The two mechanisms of bone formation
Students should be able to define, use in context, and provide examples of• all words on the slides titled “Vocabulary”.
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Epiblast cells that do migrate down (ventrally) through the primitive streak during later stages of gastrulation constitute the mesoderm layer(dull red in 16 day image at lower right )
day 16
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14-15 days
16 days
2 wks
9Carlson Fig. 5-4 (p86)+ 5-5 (p87)
transverse section
Human embryo during gastrulation
10Carlson Fig. 5-1 (p84)
Laminae of bilaminar embryo
Derivatives of the bilaminar embryo
Extraembryonic mesoderm
http://www.abdn.ac.uk/langling/resources/usflimgs.html
Though early on you were a quite flat disk, now are a doughnut
[And what is in the middle?]
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last week #1last week #2
this lecture
Carlson 6-25 (p125)
• only “embryonic tissues” in this figure
• No “extraembryonic”
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Development of mesoderm(visualized in transverse sections)
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Paraxial mesoderm• Organizes into somites• Somites give rise to axial skeleton, axial muscles, limb muscles, dermis.
Intermediate mesoderm• Gives rise to urogenital system
Lateral mesoderm• heart (endo, epi, pericardium)• blood• endothelium (lining of blood vessels)• wall of gut• wall of respiratory tract•lining of body cavities
Major subdivisions of the mesoderm
Sadler 3-4 (p19)
“parietal”(wall)layer
“visceral”(organ)layer
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From Carlson 6-25 (p125)
Embryonic mesodermIntermediatemesoderm
Urogenitalsystem
(kidney, ureter, not bladder
adrenal cortex
gonadsnot gametes)
Vagina, uterus, uterine tubes
Dermis of skin
Skeleton (axial, not limb)
Postnatal derivatives of embryonic mesoderm
Lateralmesoderm
Paraxialmesoderm
Muscles (axial & limb)
Splanchnicmesoderm
Somaticmesoderm
Skeleton(not axial, limb)
Parietalpleura
pericardiumperitoneum
Visceralpleura
peritoneum
Mesenteries
Blood cells, blood vessel endothelium, endocardium
Respiratorytract wall
Gut wallEpicardium
Myocardium
somatic = “parietal” = wall layer. For gut and gut derivatives, the parietal layer lines body wall.
splanchnic = visceral = organ layer
epicardium= visceral pericardium
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Cross section of intestine:
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• Endodermally-derived inner lining (a “muscosa”)• Mesodermally-derived muscle layers and outer lining• Ectodermally-derived nerve plexuses
= mesoderm-derived component of intestinal wall
Also mesoderm-derived, but not part of wall
Learning objectives: Mesoderm I
Students should be able to describe: • the origin of the mesodermal germ layer• the early division of the mesoderm into paraxial, intermediate mesoderm, and lateral
mesoderm and the split of lateral mesoderm into splanchnic and somatic mesoderm• the major fates of the mesoderm
• Re muscle:
– in outline, a lineage tracing method used to determine the developmental origin of limb muscle
– the major steps in development of a skeletal muscle fiber from a mononucleate myoblast
– the developmental basis of slow versus fast twitch muscle
• Re bone:
– The two mechanisms of bone formation
Students should be able to define, use in context, and provide examples of• all words on the slides titled “Vocabulary”.
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The 3 Types of muscle (and their developmental origins)
• Skeletal
– Paraxial (somite) derived
• Cardiac (myocardium)
– Splanchnic mesoderm
• Smooth
– Splanchnic
– “Local mesoderm” (for example, muscle elevating hairs of skin when you get cold).
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19From Carlson 6-25 (p125)
Embryonic mesodermIntermediatemesoderm
Urogenitalsystem
(kidney, ureter, not bladder
adrenal cortex
gonadsnot gametes)
Vagina, uterus, uterine tubes
Dermis of skin
Skeleton (axial, not limb)
Mesodermal origin of muscle
Lateralmesoderm
Paraxialmesoderm
Muscles (axial & limb)
Splanchnicmesoderm
Somaticmesoderm
Skeleton(not axial, limb)
Parietalpleura
pericardiumperitoneum
Visceralpleura
peritoneum
Mesenteries
Blood cells, blood vessel endothelium, endocardium
Respiratorytract wall
Gut wallEpicardium
Myocardium
skeletal
cardiac
smooth
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Lineage tracing studies demonstrate that limb muscles derive from somites
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Major steps in developmental progression by which skeletal muscle fibers are formed include:
satellite cell = muscle stem cell?
• Myoblasts leave the cell cycle
• Postmitotic myoblasts fuse to form myotube
• A muscle fiber is a multinucleate syncytium formed by fusion of multiple mononucleate myoblasts
• Assembly of contractile units (sarcomeres). The contractile apparatus pushes nuclei to the edge
• Growth of fiber (“hypertrophy”) involving fusion of satellite cells
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Muscle fibers exhibit different functional characteristics reflecting formation from different myoblast subpopulations
Carlson 9-30 (p201) muscle stem cells?
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In contrast to skeletal muscle, cardiac and smooth muscle myocytes do not undergo fusion, but remain as individual cells
Carlson 9-34 (p205)
Learning objectives: Mesoderm I
Students should be able to describe: • the origin of the mesodermal germ layer• the early division of the mesoderm into paraxial, intermediate mesoderm, and lateral
mesoderm and the split of lateral mesoderm into splanchnic and somatic mesoderm• the major fates of the mesoderm
• Re muscle:
– in outline, a lineage tracing method used to determine the developmental origin of limb muscle
– the major steps in development of a skeletal muscle fiber from a mononucleate myoblast
– the developmental basis of slow versus fast twitch muscle
• Re bone:
– The two mechanisms of bone formation
Students should be able to define, use in context, and provide examples of• all words on the slides titled “Vocabulary”.
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25From Carlson 6-25 (p125)
Embryonic mesodermIntermediatemesoderm
Urogenitalsystem
(kidney, ureter, not bladder
adrenal cortex
gonadsnot gametes)
Vagina, uterus, uterine tubes
Dermis of skin
Skeleton (axial, not limb)
Mesodermal origin of bone
Lateralmesoderm
Paraxialmesoderm
Muscles (axial & limb)
Splanchnicmesoderm
Somaticmesoderm
Skeleton(not axial, limb)
Parietalpleura
pericardiumperitoneum
Visceralpleura
peritoneum
Mesenteries
Blood cells, blood vessel endothelium, endocardium
Respiratorytract wall
Gut wallEpicardium
Myocardium
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Two major types of bone formation
• Endochondral ossification illustrated at R Cartilage model of bone
forms first At specific periods during
embryogenesis, this cartilage is replaced by true bone
Most bones
• Intramembranous bone formation Direct ossification of
mesenchymal cells without an intermediate cartilagenous stage
Superficial bones of face and skull
Learning objectives: Mesoderm I
Students should be able to describe: • the origin of the mesodermal germ layer• the early division of the mesoderm into paraxial, intermediate mesoderm, and lateral
mesoderm and the split of lateral mesoderm into splanchnic and somatic mesoderm• the major fates of the mesoderm
• Re muscle:
– in outline, a lineage tracing method used to determine the developmental origin of limb muscle
– the major steps in development of a skeletal muscle fiber from a mononucleate myoblast
– the developmental basis of slow versus fast twitch muscle
• Re bone:
– The two mechanisms of bone formation
Students should be able to define, use in context, and provide examples of• all words on the slides titled “Vocabulary”.
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The End
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Appendix: formation of the body cavities
• Following slides will be much clearer after you have had anatomy.
• For purposes of ETC quizzes, you don’t need to know anything about body cavities (or their lining membranes): – peritioneal cavity (visceral and parietal peritoneum)
– pleural cavity (visceral and parietal pleura)
– pericardial cavity (visceral and parietal pericardium)
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30From Carlson 6-25 (p125)
Embryonic mesodermIntermediatemesoderm
Urogenitalsystem
(kidney, ureter, not bladder
adrenal cortex
gonadsnot gametes)
Vagina, uterus, uterine tubes
Dermis of skin
Skeleton (axial, not limb)
Postnatal derivatives of embryonic mesoderm
Lateralmesoderm
Paraxialmesoderm
Muscles (axial & limb)
Splanchnicmesoderm
Somaticmesoderm
Skeleton(not axial, limb)
Parietalpleura
pericardiumperitoneum
Visceralpleura
peritoneum
Mesenteries
Blood cells, blood vessel endothelium, endocardium
Respiratorytract wall
Gut wallEpicardium
Myocardium
somatic = “parietal” = wall layer. For gut and gut derivatives, the parietal layer lines body wall.
splanchnic = visceral = organ layer
epicardium= visceral pericardium
31From Carlson 6-25 (p125)
Embryonic mesodermIntermediatemesoderm
Postnatal derivatives of embryonic mesoderm
Lateralmesoderm
Paraxialmesoderm
Splanchnicmesoderm
Somaticmesoderm
Parietalparietal pleura
parietal pericardium parietal peritoneum
Visceralvisceral pleura
visceral pericardiumvisceral peritoneum
Mesenteries
somatic = “parietal” = wall layer.
For example, gut and gut derivatives, the parietal layer lines body wall.
splanchnic = visceral = organ layer
epicardium= visceral pericardium
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mesentery
• mesentery (mes en-ter- ) [TA]
• A double layer of peritoneum attached to the abdominal wall and enclosing in its fold a portion or all of one of the abdominal viscera, conveying to it its vessels and nerves.
• The fan-shaped fold of peritoneum suspending the greater part of the small intestines (jejunum and ileum) and attaching it to the posterior abdominal wall at the root of the mesentery (radix mesenterii). Syn: mesenterium dorsale commune, mesostenium
• Syn: mesenterium TA [Mod. L. mesenterium, fr. G. mesenterion, fr. G. mesos, middle, + enteron, intestine]
Stedman’s
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