Embryology Lecture 3

Cranial Placodes

thickening of the cephalic embryonic ectoderm

vison hearing and olfaction

what sensory organs does cranial placodes contribute to

Invagination

curve of the cranial placode that contains the lens, otic, olfactory, and the adenohypophyseal placode

Delamination

leads to the trigeminal and epibrachial

Adenohypophysis placode

invovled in an invagination of the oral ectoderm in the mouth

it develops directly from Rathke’s pouch

lens placode

part of cranial placode that leads to vision

invagination

in orange

otic placode

part of cranial placode, invagination, that leads to inner ear

hearing/balance

In RED

Olfactory placode

cranial placode that leads to olfactory epithelium (smell)

in blue

Rathke’s pouch

the embryonic precursor of the adenohypophysis

Trigeminal Placode

comes from delamination of the placode

corresponds to 2 regions

• opththalmic

• maxillomandibular

• top two in green

• Gives rise to Cranial Nerve V (5)

Stomodeum

future opening of the mouth

Epibranchial placode

comes from delamination of cranial placode

Corresponds to 3 regions

1. Geniculate

2. Petrosal

3. Nodose

In purple

Geniculate

of the epibranchial placode that is associated with distal ganglion central nerve VII (7)

Petrosal

of the epibranchial placode that is associated with distal ganglion central nerve IX (9)

Nodose

of the epibranchial placode that is associated with distal ganglion central nerve X (10)

Gastrulation

allows the mesoderm to regionalize

Notochord

cells that migrate through the node, passing through the primitive streak

Paraxial mesoderm

the layer of mesoderm that is closes to the notochord since it is next to the primitive node

the lighter blue color

Intermediate mesoderm

the purple section

Node and Primitive Streak

Fate mapping analyses indicated that mesodermal tissue regionalization depends on the positive and the timing of cell passage through the _____ and the _______ in an anterior to posterior direction

Lateral plate mesoderm

in green

extraembryonic mesoderm

in the yellow, doesn’t directly help with the devlopment of the mesoderm proper

Chordamesoderm

the future notochord

Paraxial mesoderm

Gives rise to

• Head mesenchyme (bones in the skull)

• Somites

  • Sclerotome (cartilage, bones)

  • Myotome (skeletal muscle)

  • Dermatome (dermis)

  • Syndetome (tendons)

Large blocks in red

Sclerotome

direct derivative of the somites which are a derivative of the paraxial mesoderm

cartilage and bones, vertebrae

ventral cells migrating

Myotome

direct derivative of the somites

skeletal muscle

Dermatome

direct derivative of the somites

dermis, dorsal, located in between the primaxial and abaxial

Syndetome

direct derivative of the somites

tendon progenitors, the last compartment to form

forms at the boundary between the sclerotome and the myotome

Intermediate mesoderm

gives rise to the

• kidneys

• gonads

Lateral Plate Mesoderm

gives rise to

• Splanchnic (visceral) mesoderm (circulatory system)

• Somatic (parietal) mesoderm (body wall)

Splanchnic mesoderm

visceral, that is involved in the circulatory system

Ventral component

covering of the abdominal organs, lungs, hearts

it is a derivative of the lateral plate mesoderm

the thin red layer on the bottom half surrounding the yellow endoderm

Somatic mesoderm

parietal, body wall,

Mesodermal components of the limbs, like bone(except muscles)

It is the top layer of the lateral plate mesoderm/ Dorsal

it is a derivative of the lateral plate mesoderm

the red layer on the top half that is surrounding the amnion and the the future blue neural tube

Somite

the derivative the paraxial mesoderm that has now developed

the large red blocks

Intermediate mesoderm

the brown blocks that are surrounding the somites

This generates the urinary and genital systems

Coelom

the space between the somatic mesoderm (top) and splanchnic mesoderm

forms the body cavity

• abdominal

• thoracic

yolk sac

What is the area within the yellow endoderm

gut, parietal mesoderm, embryonic body cavity, surface ectoderm, dorsal mesentary, visceral mesoderm

1. what is the yellow tube

2. what is the outer red layer

3. what is the space under the yellow tube

4. what is the blue layer surrounding

5. what is the thick red column above the yellow tube

6. what is the red layer that is directly surrounding the yellow tube

Somatopleure

Somatic (pareital) mesoderm + ectoderm

forms ventral and lateral body wall

forms the membranes that line the peritoneal, pleural and pericardial cavities

Splanchnopleure

Splanchnic (visceral) + endoderm

Form the wall of the gut and the thin serous membrane around each organ

Intermediate mesoderm

which mesoderm generates the urinary and genital systems?

Urinary system

formed sequentially from 3 overlapping kidney systems

• Pronephros

• Mesonephros

• Metanephros

Pronephros

non-functional kidney, degenerate at the end of the 4th week

the most anterior, red color on the diagram

Mesonephros

functional kidney for a short time

during fetal period, then regresses

The blue on the diagram

Metanephros

Permanent Kidney

appears in the 5th week and becomes functional around the 12th week

form in the most posterior region of the embryo

comes from the Metanephric blastema

Ureteric bud

gives rise to the collecting system

the bright yellow structure in the photo

Metanephric blastema

the black structure in the image

gives rise to the excretory system

Ascent

The kidneys at the posterior region near the kidneys will go which way as a result of a decrease in the body curvature

Aorta, glomerulus, dorsal mesentary, genital ridge, excretory tube, mesonephric duct

This is a cross section of the developing gonad

1. big red ball

2. small ball at the end of red

3. thin grey column

4. black thing under the orange

5. blue tube

6. end of the blue tube

Treacher collins syndrome

includes hypoplasia of the facial bones and dental malocclusion

Wolffian duct

another name for the mesonephric duct

• in males, this duct forms an epididymis, vas deferenes, and seminal vesicles

• In females, this duct degenerates

Mullerian duct

another name for the Paramesonephric duct

• in males, this ducts degenerate

• In female, this duct forms the fallopian tubes, uterus, cervix, and vagina

Somites

The number of this is a good indicator of the age of an embryo

Primaxial dermamyotome

derivative of the paraxial mesoderm

closer to the neural tube that gives rise to the muscles of the back

Abaxial dermamyotome

derivative of the paraxial mesoderm

further away from the main axis of the embryo/further from the neural tube and notochord

muscles of the body wall

Location

What determine cell fate within the somite?

Resegmentation

the sclerotome portion of each somite undergoes this process.

A single sclerotome from one single somite will be further divided into cranial and caudal region.

Each vertebrae is formed from the fusion of the caudal half of one somite and the cranial half of its neighbor

Nucleus pulposus

what the notochord will become

surrounded by the circular fibers of the annulus fibrosus

Intervertebral disc

Annulus fibrosus + nucleus Pulposus

Annulus fibrosus

the circular fibers that surround the nucleus pulposus (what use to be the notochord)

limb bud

protrusion of the ectoderm

derived from the mesoderm of somites (muscle precursors) and somatic lateral plate (skeletal precursors)

Apical ectodermal ridge

organizing center in the limb bud

signals to the progress zone to continue to divide and multiply, once the zone gets out of the range of this, it develops into something else

Progress zone

the zone immediately adjacent to the apical ectodermal ridge

participates in the establishment of the proximal-distal axis of the limb

Phocomelia

condition in which the limbs are missing the proximal elements and you see the hand attached to the level of the shoulder

• long bones are shorter than normal and the more proximal elements are lost

ZPA

secrets sonic hedgehog which acts as a gradient. This has an influence on the development of the digits in the hand.

ZPA is posterior (pinky side)