Lecture 12 - Embryology III Flashcards
What does the paraxial mesoderm become in the head region?
The paraxial mesoderm differentiates into skeleton, muscles and connective tissue of the face and skull.
What does the paraxial mesoderm in the trunk region become?
The paraxial mesoderm forms somites, which gives rise to muscles (myotome), bones (sclerotome), dermis and connective tissue (dermatome) for the rest of the body depending on its position.
What does the intermediate mesoderm give rise to?
The urogenital system which includes:
- kidneys
- gonads
- associated ducts
What is along the mesonephric duct?
There is:
- the pronephros (degenerates first)
- the mesonephros (embryonic kidney, gonads)
- the metanephros (definite kidney)
How does the gonads change according to gender?
An embryo has both the wolffian duct (forms male gonads) and the Müllerian duct (forms female gonads).
Female: wolffian duct degenerates
Male: Müllerian duct degenerates
How is the lateral mesoderm divided?
It is divided into two parts;
- splanchic lateral mesoderm
- somatic lateral mesoderm
Between the two is the coelom
What does the splanchic mesoderm form?
It forms the heart, blood/lymphatic vessels (endothelial cells) and the smooth muscle of the GI tract.
How does the heart form in an embryo?
The heart starts off as two endocardial tubes that fuse together. It then elongates and loops around. Then septation follows to form a four chamber heart.
What does the somatic mesoderm form?
It forms the connective tissue of the body wall and limbs.
What does the endoderm form?
It forms:
- lining of digestive tract (buds off to form liver, gall bladder & pancreas)
- respiratory tube
- pharynx
- epithelial pockets of pharynx (thyroid, thymus and parathyroid)
During which week does the embryo/fetus fold?
During 4th week.
What occurs during the folding of the trilaminar disc?
Embryo grows rapidly (in length) as well as the amnion. Yolk sac remains the same. The developing notochord, neural tube and somites stiffen along dorsal axis. The folding occurs in the cranial and casual as well as the lateral sides.
What does the folding of the disc do?
The folding generates the form of the body.
What is the septum transversum?
It is a group of cranial mesenchyme cells that gives rise to the thoracic diaphragm. It also develops into parts of the ventral mesentery of stomach and duodenum.
How does the development of the gut occur?
It develops in the 4th week. The folding of the disc pushes the endoderm inwards which forms the lining of the gut. The epithelium at the cranial and caudal ends form the primitive mouth and anal pit.
What does the lateral folding do?
The lateral folding of the embryo completed the gut tube.
What are the 3 types of gut?
There is the foregut, midgut and hindgut
What forms part of the foregut?
Pharynx, oesophagus, stomach, proximal duodenum, thyroid, parathyroid, liver, gall bladder, pancreas and lungs (trachea and bronchi)
What forms the midgut?
Distal duodenum and half of the colon
What forms the hindgut?
The other half of the colon to anus (includes urinary bladder)
How is the stomach developed?
Distal part of foregut begins to dilate slightly. It eventually enlarges and broadens ventro-dorsally (dorsal side grows faster) and rotates 90 degrees clockwise.
How is the pancreas developed?
The pancreas develops initially as two separate organs (dorsal and ventral pancreas bud). When the stomach rotates, it brings the dorsal and ventral buds together to form the final pancreas
How did the lungs develop?
The lungs begin to develop at 22 days. Tracheal buds begin to develop along the gut. The stem of diverticulum will separate from the oesophagus and form the trachea. The tracheal bud slowly develop and start to form bronchial buds which form the bronchi. Eventually lungs develop.
What are primordial germ cells? (PGC)
They are precursors of sperm and egg. They were specified early in development when the embryonic disc was two layers.
PGC migration
They migrate along the hindgut, through the dorsal mesentery and coalesce with the left and right genital ridges.
What is the 3 types of mesoderm?
Paraxial mesoderm
Intermediate mesoderm
Lateral mesoderm
