University:
Western Sydney University
Course:
MEDI 2003 | Clinical Sciences 2
Academic year:

2024
Views:

370

Pages:

4
Author:

Mariam A. A.

Process of gastrulation Week 3 - Gastrulation 1. There is already a bilaminar disc ● The blue layer is the epiblast (forms future ectoderm) ● The yellow layers is the hypoblast (forms future endoderm) 2. Formation of the primitive streak ● The primitive streak is a thickened structure that forms in the middle of the epiblast ● It appears at the caudal end of the embryo and grows cranially ● It establishes: ○ Left and right ○ Cranial (head) and caudal (tail) ○ Dorsal and ventral surfaces 3. Ingression (inward migration of cells) of the epiblast into the primitive streak 4. Formation of the trilaminar disc (blast → derm) ● The hypoblast is replaced = endoderm ● Epiblast cells that are just in the middle = mesoderm ● Remaining cells of epiblast = ectoderm ○ During gastrulation, epiblast continues to grow from the cranial to caudal end Week 4 - Folding ● Transverse (lateral) ○ Folds like a cannoli = endoderm, mesoderm and ectoderm layers ○ Yolk sac is no part of the embryo but the other yellow part is the primitive gut, which later develops into the digestive tract ○ Future trunk region ● Cephalocaudal ○ Occurs in the head and tail regions ○ Future head and buttocks ○ Forms the C shaped fetus position Organogenesis (ectoderm, mesoderm, endoderm) ● After folding ● Three germ layers differentiate into organs and organ systems ● In week 3, the nervous system and heart form because they are important in the further development of the embryo ● Folding happens in week 4 → the organs are recognisable but not functional ● Organogenesis is complete in week 8 ● Teratogens (agent that can affect the development of the embryo) are most harmful during this time Embryonic development of the nervous system (neurulation) ● First major event in embryonic development → development of the CNS (brain and spinal cord) ● Ectoderm cells thickens to form the neural plate ● The plate folds inwards and the edges fuse to form the neural plate ● Anterior part of the neural tube = brain, the rest = spinal cord ● The brain then differentiates into the forebrain, midbrain and hindbrain → the colours correspond with what they turn into Embryonic development of the heart ● First organ to develop in week 3 ● Forms from the mesoderm - lateral plate ● Cephalocaudal folding determines where the heart will be located → thoracic cavity 1. Two tubes form (endocardial tubes) 2. Transverse folding fuses the bilateral tubes (primitive heart tube) 3. Primitive heart forms five distinct regions Embryonic development of the gastrointestinal system ● Derived from the endoderm ● Transverse folding of the germ layers and a part of the yolk sac (in the left photo) remains on the ventral (under) side of the embryo → this will become the primitive gut which will then form the gastrointestinal system ● ● The primitive gut differentiates into the foregut, midgut and hindgut Each gives rise to specific gut and gut-related structures (in the right photo)