Lecture 11 - Embryology II Flashcards
What are the pharyngeal arches?
They are a vestige of gills
In humans, they develop into the pharynx, larynx, jaw etc
When are the pharyngeal arches visible?
Only in the embryo
When do limbs start to form?
Fourth to eighth week
Describe limb formation
A bud starts to form out (pulls dermatome with it)
HOX genes set up the various regions of the limb
Describe how HOX genes form the regions of the limb
Hand: HOXd genes 9-13
Wrist: HOX 9-12
Arm: HOX 9-10
Scapula: 9
Which germ layers are involved in limb development?
Initiated by mesoderm, controlled by ectoderm
Describe formation of hands and feet
Start off as flat, symmetrical disks
Apoptosis sculpts the fingers and toes
All derivates of the endoderm are…
Epithelial tissue
Describe how the yolk sac separates from the lumen of the gut
Pinches off like a draw string
However, it remains attached for a long time at the midgut region
How does the trilaminar disk become a hollow tube?
A coelom forms from the split in the lateral mesoderm
The splanchnic mesoderm extends down and meets to form the GIT
The somatic mesoderm extends down and meets, enclosing the GIT and coelom
When do the mouth and anus form?
After three weeks of development
Describe formation of the mouth
Stomadeum separated from forget by the oral plate
The oral plate breaks down to form a continuous tube
Describe formation of the anus
The proctodeum is initially sealed by the cloacal membrane
The urorectal septum extends down, separating the rectum and the allantois
What is in between the allantois and the rectum?
Urorectal septum
What does the allantois give rise to?
Urethra and bladder
From what does the heart develop?
Splanchnic mesoderm
Describe the formation of the heart
Initially as two tubes from the splanchnic mesoderm which fuse to form the myocardium
After fusion, the heart folds
Symmetrically aortic arches develop, and are then remodelled
What is interesting about the time scale of the developing heart?
Organogenesis continues while the heart beats from day 22 onwards
Describe the flow of blood in the developing heart
Unidirectional during development: flow of blood through the fossa ovalis
At birth, the whole needs to close up immediately
This is a very common birth defect
Describe the arterial supply of the regions of the gut
Foregut: coeliac artery
Midgut: superior mesenteric artery
Hindgut: inferior mesenteric artery
Describe growth of the GIT
Quickly starts to lengthening –> herniation out of the body wall
Rotation gives rise to the large intestine
Gut retracts back between week 6-9
What is omphalocoele?
Failure of the gut to retract
What is an umbilical hernia?
Retraction, but failure of the body wall to seal up
Describe formation of viscera
Endodermal outpocketings interacting with mesoderm
Does the genital or urinary system form first?
Urinary
Describe the development of the urinary system
Pronephos - pronephric duct Mesonephros - mesonephric duct Metanephros
What becomes of the neohrostomes?
Degenerate
What becomes of the mesonephric duct?
Vas deferens in males
Degenerates in females
What becomes of the metanephros?
Becomes the kidneys and ureters
What becomes of the Müllerian duct?
Fallopian tube, uterus, distal vagina
What does the somatic mesoderm go on to form?
What about the splanchnic mesoderm?
Somatic:
• body wall
Splanchnic:
• viscera
NB ectoderm and endoderm are involved
Which structure will become the coelom?
The gap in the lateral mesoderm between somatic and splanchnic mesoderm
What does the metanephros consist of?
Kidney and ureters
What does the neural tube go on to form?
The brain and spinal cord
What does the notocord go on to form?
Nucleus pulposus
