2010 BGD Lecture - Development of the Embryo/Fetus 2

Introduction

--Mark Hill 20:54, 3 May 2010 (EST) I am currently updating the notes that will appear here for 2010. Previous 2008 Lecture

This lecture covers the period of Embryonic development, in Humans from week 3 to week 8 and is divided into 23 Carnegie stages of embryonic development. There will also be a brief introduction to fetal development.

This period of development will also be covered in your Practical, which is currently being updated for 2010 and will be available online. Note, the period from week 9 to week 38 is considered Fetal development and will be covered in detail in the Laboratory 11.

Embryonic Development
Organ and System formation (Functioning / Not Functional)
Dynamic changes internal and external
Carnegie stages illustrate external development

First 8 Weeks

Week 3

Mesoderm means the "middle layer" and it is from this layer that nearly all the bodies connective tissues are derived. In early mesoderm development a number of transient structures will form and then be lost as tissue structure is patterned and organised. Humans are vertebrates, with a "backbone", and the first mesoderm structure we will see form after the notochord will be somites.

Facts: Week 4, 22 - 23 days, 2 - 3.5 mm, Somite Number 4 - 12

View: This is a dorsal view of the human embryo, the amniotic membrane has been removed. Top embryo is an early stage 10, bottom is late stage 10.

Early stage 10
Late stage 10
Labeled stage 10

trilaminar embryo
mesoderm regions
somite coelom
neural tube and neural crest

Mesoderm organization: lateral plate - intermediate mesoderm - paraxial mesoderm - axial mesoderm - paraxial mesoderm - intermediate mesoderm - lateral plate

Stage 7 paraxial mesoderm
Stage 7 intermediate mesoderm
Stage 7 lateral plate

Axial Mesoderm

notochord

mechanical role in embryonic disc folding
molecular role in patterning surrounding tissues

Stage 7 embryonic disc
Stage 7 primitive-streak-node
Stage 7 cloacal-oral-membranes
Stage 7 notochord

Adult - contributes to the nucleus pulposis of the intervertebral disc

Paraxial Mesoderm

Stage 7 paraxial mesoderm

differentiates rostro-caudally (head to tail)
remains unsegmented in the head region.
segments in the body region to form pairs of somites along the length of the embryo.

Adult - contributes vertebral column (vertebra and IVD), dermis of the skin, skeletal muscle of body and limbs

Intermediate Mesoderm

named by position (between paraxial and lateral plate)
differentiates rostro-caudally (head to tail)
forms 3 sets of "kidneys" in sequence

pronephros
mesonephros
metanephros

Adult - metanephros forms the kidney

Lateral Plate Mesoderm

a "horseshoe shaped" space forms in the middle
somatic mesoderm - closest to ectoderm
space - forms the 3 body cavities (pericardial, pleural, peritoneal)
splanchnic mesoderm - closest to endoderm

Adult - body connective tissues, gastrointestinal tract (connective tissues, muscle, organs), heart

Somite Development

Somite initially forms 2 main components

ventromedial- sclerotome forms vertebral body and intervertebral disc
dorsolateral - dermomyotome forms dermis and skeletal muscle

paraxial mesoderm
early somite
sclerotome and dermomyotome
dermatome and myotome
epaxial and hypaxial muscles

Sclerotome

sclerotome later becomes subdivided
- rostral and caudal halves separated laterally by von Ebner's fissure
half somites contribute to a single vertebral level body
other half intervertebral disc
therefore final vertebral segmentation “shifts”

Myotome

Body - epaxial and hypaxial muscles
Limbs - flexor and extensor muscles

Dermatome

connective tissue underlying epidermis
begins as a dorsal thickening
spreads throughout the body

Week 4

Heart

Head

Upper and Lower Limb

Limb development occurs at different times for forelimbs and hindlimbs. In the mid-4th week, human upper limb buds first form and lower limbs about 2 days later. The limbs form at vertebra segmental levels C5-C8 (upper limbs) L3-L5 (lower limbs).

Glossary Links

Glossary: A | B | C | D | E | F | G | H | I | J | K | L | M | N | O | P | Q | R | S | T | U | V | W | X | Y | Z | Numbers | Symbols | Term Link

2010 BGD: Lecture 1 | Lecture 2 | Practical 3 | Practical 6 | Practical 12

Cite this page: Hill, M.A. (2024, May 17) Embryology 2010 BGD Lecture - Development of the Embryo/Fetus 2. Retrieved from https://embryology.med.unsw.edu.au/embryology/index.php/2010_BGD_Lecture_-_Development_of_the_Embryo/Fetus_2

What Links Here?