Mesoderm I

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.

C

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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:




• Re bone:



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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




• Re muscle:




• Re bone:



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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)


Urogenitalsystem


adrenal cortex

gonadsnot gametes)


Dermis of skin


Mesodermal origin of muscle

Lateralmesoderm

Paraxialmesoderm


Splanchnicmesoderm

Somaticmesoderm


Parietalpleura


Visceralpleura

peritoneum

Mesenteries



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)




• Re muscle:




• Re bone:



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Urogenitalsystem


adrenal cortex

gonadsnot gametes)


Dermis of skin


Mesodermal origin of bone

Lateralmesoderm

Paraxialmesoderm


Splanchnicmesoderm

Somaticmesoderm


Parietalpleura


Visceralpleura

peritoneum

Mesenteries



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




• Re muscle:




• Re bone:



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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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Urogenitalsystem


adrenal cortex

gonadsnot gametes)


Dermis of skin



Lateralmesoderm

Paraxialmesoderm


Splanchnicmesoderm

Somaticmesoderm


Parietalpleura


Visceralpleura

peritoneum

Mesenteries



Gut wallEpicardium

Myocardium

somatic = “parietal” = wall layer. For gut and gut derivatives, the parietal layer lines body wall.






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.



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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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Technology

Mesoderm I