Lecture 13 - Differentiation of the Endoderm + Mesoderm Flashcards
What tubes does the endoderm form? (2)
Digestive tube - extends entire length of body
Respiratory tube - forms as an outgrowth of the digestive tube
What are the digestive and respiratory tubes initially closed by?
The presence of the oropharyngeal and cloacal membranes
What will the oropharyngeal and cloacal membranes be replaced by?
The openings of the mouth and anus, respectively.
What associated glands bud off from the digestive tube? (3)
Liver
Gallbladder
Pancreas
List two structures of endodermal origin
Digestive tube
Respiratory tube
How is the mesoderm formed?
Formed by cells migrating through the primitive streak that place themselves between the ectoderm and endodermis
Describe the initial structure of the mesoderm
Disorganised and loosely packed (mesenchymal)
What does mesenchymal mean?
Loosely packed mesodermal cells
List the four types of mesoderm
Chordamesoderm
Paraxial (somatic) mesoderm
Intermediate mesoderm
Lateral plate mesoderm
What does the chordamesoderm form?
A rod like structure known as the notochord along the midline of the embryo up to the hindbrain.
What is the function of the chordamesoderm?
Forms the notochord which plays an important role in the development of the nervous system; eventually disappears
Describe the paraxial mesoderm and where it can be found
Paired segmented structures known as somites on both sides of the embryo near the midline.
Describe the process of somite creation
Somites start of as loosely packed cells called somitomeres and become compacted to become somites
What structures will somites form? (5)
Cartilage of vertebrae and ribs
Muscles of trunk and limbs
Tendons that connect muscles and bones
Dermis of dorsal skin
Structures of the circulatory system
How many regions can be identified once somites have formed?
Four regions
True or false: each region of the somite gives rise to a different mesodermal structure
True
List the four regions of a somite and where they are found in relation to one another
Sclerotome - closest to the neural tube and notochord (innermost part of somite)
Syndetome - between the sclerotome and the myotome
Myotome - found between the syndetome and the dermatome
Dermatome - region lying beneath the ectoderm (outermost part of somite)
What do the four somite regions give rise to? How does this happen?
Sclerotome - cells become mesenchymal and migrate towards midline - cartilage of vertebrae (becomes bone) and large part of each of the ribs
Syndetome - gives rise to tendons that attach muscles to bones
Myotome - cells migrate out - gives rise to all skeletal muscles of the body (except head muscles)
Dermatome - cells migrate underneath the ectoderm - contributes to the connective tissue of the dermis of the dorsal skin
Do somitomeres become compacted in the cranial (head) region?
No, they remain unpacked and combine with chordamesoderm to form the head mesoderm.
What is the function of the head mesoderm?
Gives rise to the connective tissues and muscles of the head and neck that aren’t derived from the neural crest
Do all somites give rise to the same structures?
No, each pair of somites give rise to specific structures in the embryo
What does the intermediate mesoderm give rise to?
The urogenital system
- kidneys
- gonads
- associated ducts
What does the lateral plate mesoderm give rise to?
Heart
Blood vessels
Blood cells
Lining of the body cavities
Bones of limbs
What happens to the lateral plate mesoderm around 3 weeks post fertilisation?
It splits into two sheets
Name the two sheets that the lateral plate mesoderm gives rise to and where it is found
Visceral (splachnic) lateral plate mesoderm - nearest to endoderm
Parietal (somatic) lateral plate mesoderm - next to endoderm
What does the visceral lateral plate mesoderm give rise to?
Heart
Smooth muscle
Connective tissue of the gut
What does the parietal lateral plate mesoderm give rise to?
Forms smooth layer of tissue that lines the inside of the body wall (parietal peritoneum)
At level of limbs, cells proliferate and migrate to form skeletal structures and limbs
Which sheet of lateral plate mesoderm forms limbs?
Parietal lateral plate mesoderm
Which lateral plate mesoderm gives rise to the connective tissue of the wall of the gut?
The visceral plate mesoderm
Which lateral plate mesoderm gives rise to the smooth layer of tissue that lines the inside of the body wall?
The parietal lateral plate mesoderm gives rise to the parietal peritoneum
What is the parietal peritoneum?
A smooth layer of tissue that lines the inside of the body wall
What does the space between the visceral and parietal lateral plate mesoderm become?
The body cavity or coelomic cavity (coelom)
What does the coelomic cavity eventually convert to?
A series of separate cavities:
- pericardial coelomic cavity
- 2 pleural coelomic cavities
- peritoneal cavity
