Lecture Notes under Development (notice removed when completed)
This lecture is an introduction to the events during the third week of development that relate to early mesoderm development, the embryonic connective tissue layer. This topic introduces the early patterning and segmentation of the mesoderm (notochord, somites, lateral plate) and and the later differentiation of the major body cavities and early heart.
If you are interested in further reading, I have also included below links to more detailed textbooks with further information and images. Please note this additional information is not necessarily examinable, but may be useful if you have not previously studied biology.
The early developing somites
(More? Carnegie Stages)
Lectopia Audio Link to the audio recording of this lecture will be added here when available.
The following text is extracted and modified from lecture slides and should be used as a "trigger" to remind you of key concepts.
Lecture Overview - Mesoderm
The following links are to UNSW Embryology additional resources that provide further background information on the Lecture topics. Note that not all information found on these additional links is considered examinable and the lecture slides and laboratory classes should be used as your initial guide for course theory content.
Links: Timeline - Embryonic Week 3 | Carnegie Stages | Neural Notes | Folic Acid and Neural Tube Defects | Neural System - Abnormal Development | Neural Crest | Week 3 | Carnegie stage 13/14 Embryo Serial Sections (Pig) | Carnegie stage 22 Embryo Serial Sections (Human) | Selected Carnegie stage 22 Highpower Sections (Human) | Limb Development | Axial Skeleton Development | Bone Development | Skull Development
The search window below allows a search within the UNSW Embryology website.
During the 3rd week of human development the trilaminar embryo layers are patterned by genes which is then followed by morphological structural changes in each of the layers. This lecture will introduce the concept of tissue patterning in relation to differentiation of the neural tube that will form the entirecentral nervous system.
These lecture pages are being updated for the current course, so it is worth coming back again later to see if any changes have occurred. Please let me know by email of broken links or content that is not clearly covered in this supporting online material.
Developmental Biology 6th ed. Gilbert, Scott F. Sunderland (MA): Sinauer Associates, Inc.; c2000.
Below are listed links that relate to this Lecture from the textbook "Developmental Biology" which is available free online. You can either click the provided links or do your own search using the search link.
Neuroscience Purves, Dale; Augustine, George J.; Fitzpatrick, David; Katz, Lawrence C.; LaMantia, Anthony-Samuel; McNamara, James O.; Williams, S. Mark. Sunderland (MA): Sinauer Associates, Inc. ; c2001
Molecular Biology of the Cell 4th ed. Alberts, Bruce; Bray, Dennis; Lewis, Julian; Raff, Martin; Roberts, Keith; Watson, James D. New York and London: Garland Publishing; c2002.
Below are listed links that relate to this Lecture from the textbook "Molecular Biology of the Cell" which is available free online. You can either click the provided links or do your own search using the search link.
Blue Histology - Nervous Tissue |
Lecture 05 - Ectoderm, Early Neuralation Wed 13:00 - 14:00 Australian School Business 119 (K-E12-119)
A simplified description of terms more detailed definitions are available from the Glossary link above.
cytotrophoblast "cellular" trophoblast layer surrounding (forming a "shell") the early implanting conceptus. Beginning at uterine adplantation, proliferation and fusion of these cells is thought to form a second outer trophoblast layer, thesyncytiotrophoblast. The cytotrophoblast layer contributes to formation of the placental villi, the functional component of the fetal placenta. (More? Week 2 Notes | Placenta Notes)
gastrulation - the process of forming a gastrula. Term means literally means "to form a gut" but is more in development, as this process converts the bilaminar embryo (epiblast/hypoblast) into the trilaminar embryo (endoderm/mesoderm/ectoderm) and establish the initial body axis. These 3 germ layers will form all the future tissues of the entire embryo. (More? Gastrulation)
hypoblast - epithelium that forms during week 2 of human development that lines the blastoceol, and forms part of the bilaminar embryo (epiblast/hypoblast) from the inner cell mass. During trilaminar embryo development, the process of gastrulation replaces the hyoblast layer within the embryo with endoderm germ layer. (More? Week 2 Notes)
neural crest - cell region at edge of neural plate, then atop the neural folds, that remains outside and initially dorsal to the neural tube when it forms. These paired dorsal lateral streaks of cells migrate throughout the embryo and can differentiate into many different cell types (= pluripotential). Those that remain on the dorsal neural tube form the sensory spinal ganglia (DRG). Neural crest cells also migrate into the somites. (More? Neural Crest Notes)
neural tube - The third stage in early development of the central nervous system. In the trilaminar embryo (ectoderm, mesoderm, endoderm) the central region of the ectoderm (in the midline above the mesodermal notochord) initially forms a columnar epithelium described as the neural plate. This epithelium will fold dorsally to form the neural groove, which then fuses to form an initially open at either end hollow neural tube. The neural tube forms the central nervous system (brain and spinal cord). Developmental sequence: neural plate -> neural groove -> neural tube -> Central Nervous System -> brain and spinal cord. (More? Neural Notes)
neuroenteric canal - canal or opening existing early in trilaminar embryo development that provides transient communication between the amnion and the yolk sac. Canal forms as part of axial process development, which is the precursor to the notochord (axial mesoderm). (More? Neural Notes)
neurogenesis - the process of formation of the neural system. This begins with segregation of the neural plate from the ectoderm of the trilaminar embryo by folding to form initially the neural groove, which then fuses to form the neural tube (the central nervous system progenitor, brain and spinal cord) and associated neural crest. (More? Neural Notes)
neuropore - the initial two openings at either end of neural tube are the neuropores: cranial=rostral=anterior, caudal=posterior. The cranial neuropore closes (day 25) approx. 2 days (human) before caudal. The developmental abnormality classed as Neural Tube Defects (NTDs) are mainly dure to failure of these two neuropores to developmentally close. (More? Neural Notes | Neural Abnormalities)
nidation - means implantation within the uterus. (More? Week 2 Notes)
notochord - (= axial mesoderm) rod of cells lying in the midline of the trilaminar embryo mesoderm layer ventral to the neural tube. Two roles: 1. Mechanical, influencing the folding of the early embryo; 2. Morphogenic, secreting sonic hedgehog a protein which regulates the development of surrounding tissues (neural plate, somites, endoderm and other organs). (More? Mesoderm Notes | Neural Notes)
syncytiotrophoblast a multinucleated cell currently thought to form by the fusion of cytotrophoblasts (trophoblasts) within the trophoblast layer (shell) of the implanting conceptus. In early development, these cells mediate implantation of the conceptus into the uterine wall and secrete the hormone (human Chorionic Gonadotrophin, hCG) responsible for feedback maintainance of the corpus luteum (in maternal ovary) and therefore maintaining early pregnancy. (More? Week 2 Notes | Placenta Notes | human Chorionic Gonadotrophin)
trophoblast - (Greek "trophe" = nutrition) the trophoblast cells have an important contribution to extraembryonic tissues of the fetal placenta and membranes. Week 1 blastocyst formation the outer layer of cells (adjacent to the zona pellucida) form a flat squamous epithelial layer of cells, the trophoblast layer. Week 2 following blastocyst hatching the trophoblast layer is involved with initial adhesion to the uterine wall and subsequent implantation within the wall. During this period the trophoblast layer differentiates into two distinct layers (syncitiotrophoblast, cytotrophoblast). (More? Week 2 Notes | Week 3 Notes | Placenta Notes)
These references are background reviews and research article readings and is not examinable.