Mesoderm I

1. Mesoderm I
Embryos, Tissues, Cells
August 25, 2008
Douglas L. Falls, M.D.
1

2. 2
Mesoderm I / II: Reading
Carlson (2004) Human Embryology and Developmental Biology
(3
rd
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)

3. Mesoderm I: Learning objectives
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
–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”.
3

4. 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
4

5. Vocabulary
coelom –
•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: 1681
of 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.
C
5

6. 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
6

7. 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”.
7

8. 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
8
14-15 days
16 days
2 wks

9. 9
Carlson Fig. 5-4 (p86)+ 5-5 (p87)
transverse
section
Human embryo during gastrulation

10. 10
Carlson Fig. 5-1 (p84)
Laminae of
bilaminar
embryo
Derivatives of the bilaminar embryo
Extraembryonic
mesoderm

11. 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?]
11

12. last week #1last week
#2
this lecture
Carlson 6-25 (p125)
•only “embryonic
tissues” in this figure
•No “extraembryonic”
12

13. Development of mesoderm
(visualized in transverse sections)
13
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

14. Major subdivisions of the mesoderm
Sadler 3-4 (p19)
“parietal”
(wall)
layer
“visceral”
(organ)
layer
14

15. From Carlson 6-25 (p125)
Embryonic mesoderm
Intermediate
mesoderm
Urogenital
system
(kidney, ureter,
not bladder
adrenal cortex
gonads
not gametes)
Vagina, uterus,
uterine tubes
Dermis
of skin
Skeleton
(axial, not limb)
Postnatal derivatives of embryonic mesoderm
Lateral
mesoderm
Paraxial
mesoderm
Muscles
(axial & limb)
Splanchnic
mesoderm
Somatic
mesoderm
Skeleton
(not axial, limb)
Parietal
pleura
pericardium
peritoneum
Visceral
pleura
peritoneum
Mesenteries
Blood cells,
blood vessel
endothelium,
endocardium
Respiratory
tract wall
Gut wall
Epicardium
Myocardium
somatic = “parietal” = wall layer. For gut and gut
derivatives, the parietal layer lines body wall.
splanchnic = visceral = organ layer
epicardium
= visceral
pericardium
15

16. Cross section of intestine:
16
• 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

17. 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”.
17

18. 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).
18

19. 19
From Carlson 6-25 (p125)
Embryonic mesoderm
Intermediate
mesoderm
Urogenital
system
(kidney, ureter,
not bladder
adrenal cortex
gonads
not gametes)
Vagina, uterus,
uterine tubes
Dermis
of skin
Skeleton
(axial, not limb)
Mesodermal origin of muscle
Lateral
mesoderm
Paraxial
mesoderm
Muscles
(axial & limb)
Splanchnic
mesoderm
Somatic
mesoderm
Skeleton
(not axial, limb)
Parietal
pleura
pericardium
peritoneum
Visceral
pleura
peritoneum
Mesenteries
Blood cells,
blood vessel
endothelium,
endocardium
Respiratory
tract wall
Gut wall
Epicardium
Myocardium
skeletal
cardiac
smooth

20. 20
Lineage tracing studies demonstrate that limb
muscles derive from somites

21. 21
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

22. 22
Muscle fibers exhibit different functional characteristics reflecting
formation from different myoblast subpopulations
Carlson 9-30 (p201)
muscle stem cells?

23. 23
In contrast to skeletal muscle, cardiac and smooth muscle
myocytes do not undergo fusion, but remain as individual cells
Carlson 9-34 (p205)

24. 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”.
24

25. 25
From Carlson 6-25 (p125)
Embryonic mesoderm
Intermediate
mesoderm
Urogenital
system
(kidney, ureter,
not bladder
adrenal cortex
gonads
not gametes)
Vagina, uterus,
uterine tubes
Dermis
of skin
Skeleton
(axial, not limb)
Mesodermal origin of bone
Lateral
mesoderm
Paraxial
mesoderm
Muscles
(axial & limb)
Splanchnic
mesoderm
Somatic
mesoderm
Skeleton
(not axial, limb)
Parietal
pleura
pericardium
peritoneum
Visceral
pleura
peritoneum
Mesenteries
Blood cells,
blood vessel
endothelium,
endocardium
Respiratory
tract wall
Gut wall
Epicardium
Myocardium

26. 26
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

27. 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”.
27

28. The
End
28

29. 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)
29

30. 30
From Carlson 6-25 (p125)
Embryonic mesoderm
Intermediate
mesoderm
Urogenital
system
(kidney, ureter,
not bladder
adrenal cortex
gonads
not gametes)
Vagina, uterus,
uterine tubes
Dermis
of skin
Skeleton
(axial, not limb)
Postnatal derivatives of embryonic mesoderm
Lateral
mesoderm
Paraxial
mesoderm
Muscles
(axial & limb)
Splanchnic
mesoderm
Somatic
mesoderm
Skeleton
(not axial, limb)
Parietal
pleura
pericardium
peritoneum
Visceral
pleura
peritoneum
Mesenteries
Blood cells,
blood vessel
endothelium,
endocardium
Respiratory
tract wall
Gut wall
Epicardium
Myocardium
somatic = “parietal” = wall layer. For gut and gut
derivatives, the parietal layer lines body wall.
splanchnic = visceral = organ layer
epicardium
= visceral
pericardium

31. 31
From Carlson 6-25 (p125)
Embryonic mesoderm
Intermediate
mesoderm
Postnatal derivatives of embryonic mesoderm
Lateral
mesoderm
Paraxial
mesoderm
Splanchnic
mesoderm
Somatic
mesoderm
Parietal
parietal pleura
parietal pericardium
parietal peritoneum
Visceral
visceral pleura
visceral pericardium
visceral 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

32. 32

33. 33

34. 34

35. 35

36. 36

37. 37
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

38. 38