Development 2 Flashcards
Which organs does the endoderm provide epithelial lining for?
GIT tracts, respiratory tract, tonsils, thyroid, parathyroid, thymus, liver, pancreas
What is the coelom?
A hollow tube which surrounds the viscera
How does the coelom form?
The lateral mesoderm splits into two sheets - the somatic mesoderm and the splanchnic mesoderm which curve around and enclose a space - the coelom
What does the somatic mesoderm give rise to?
Muscle and connective tissue
What does the splanchnic mesoderm give rise to?
Viscera
What forms the primitive gut tube?
The space enclosed by the splanchnic mesoderm coming together
What forms the body wall?
The somatic mesoderm coming together
What connects the gut to the yolk sac?
the yolk stalk - which remains persistent for a long time
What is the stomodeum?
A thin layer of ectoderm which covers the mouth end of the gut tube
At what age does the oral cavity form?
3 weeks
What is the proctodeum?
A thin membrane across the rear end of the gut tube
What is the allantois?
A branch off the gut that extends down into the body stalk - branches off at the proctodeum - will form the urogenital tract and bladder
What divides the allatnois from the gut?
The urorectal septum - which will fuse with the cloacal membrane and form two separate openings for the urogenital tract and the gut
What is the heart derived from?
Lateral splanchnic mesoderm
How does the heart develop?
Two separate tubes develop in the thoracic cavity and then fuse in the midline - forms a single atrium and single ventricle each with two inflows and two outflows - then complex folding occurs to result in the two atria and two ventricles
What is the commonest heart defect?
ventricular septal defect - where the left and right ventricles are not sealed off from one another
What is an atrial defect?
Where the foramen ovale doesn’t close
What is omphalocoele?
Failure of the gut to retract back into the coelom - fatal condition
Which organs are derivates of the gut wall?
The lungs, liver, pancreas and thymus gland
What is situs invertus?
mirror image of organ positions
What causes situs invertus?
Failure of the primitive node to develop - no cilia to beat and create a current for the signalling molecules to follow
What is urogenital system (apart from the bladder and urethra) derived from?
The intermediate mesoderm
Which forms first the urinary system or the genitals?
The urinary system
How do the kidneys develop?
First the pronephros and the pronephic duct grow and then the development of the pronephros is aborted, then the mesonephros forms and the pronephric becomes the mesonephric duct - then the mesonephros degenerates and the metanephros forms as bud that grows alongside the mesonephric duct - the metanephros becomes the kidney and ureters and then mesonephric duct becomes the vas deferens
How does the penis form?
by fusion of urogenital folds
What is hypospadiasis?
when partial fusion of the urogenital folds leaves a urethral opening on the base of the penis
When is all major organogenesis completed?
By three months
