105 - Development 2 Flashcards
What does thalidomide do to embryos?
Causes amelia and meromelia (lacking entire limb, or part of a limb)
When is thalidomide prescribed?
Complications of leprosy. Multiple myeloma.
When is thalidomide able to affect development?
Between 20-36 days post-conception
How does endoderm line organs in development?
Forms organ along with mesodermal tissue
Coelom
Hollow space around viscera
How does coelom form? 1 2 3 4 5 6 7
1) Lateral mesoderm splits. 2) Upper part become somatic mesoderm, joins to ectoderm 3) Lower part becomes splanchnic mesoderm, joins to endoderm. 4) Becomes continuous with extra-embryonic space 5) Edges of embryo fold in laterally to form coelom. 6) Most medial layer of splanchnic mesoderm/endoderm forms wall of the gut, dorsal and ventral mesentaries. 7) Somatic mesoderm joins to seal off coelom
*Coelom formation
Relationship between developing coelom and yolk sack
For a while the developing midgut is continuous with the yolk sack.
Stomadeum
A pit where the mouth will form
Proctadeum
A pit where the anus will form
How is the stomadeum opened?
At ~3 weeks of age, oral plate that separates foregut from stomadeum breaks, oral cavity forms. Ectoderm and endoderm meet here
How are anal and urogenital openings formed?
1) Anus is sealed by cloacal membrane (ectoderm and endoderm) 2) Allantois forms as branch of the hind gut 3) Between allantois and hindgut is urorectal septum (mesoderm) 4) Urorectal septum extends to divide rectum from the urogenital tract
Allantois 1 2
1) Lies within the body stalk 2) Stores nitrogenous waste in some species, vestigial in humans (but very important in human development)
What does the allantois give rise to in humans?
Bladder
Pharyngeal arches 1 2 3
1) Prominent arches near head. 2) Resemble some of the structures of gills (but aren’t gills) 3) Modified for other purposes (EG: jaw, blood vessels, muscles of face, middle ear, Eustachian tube, hyoid, larynx and pharynx, parathyroid gland)
Pharyngeal pouches
Structure between pharyngeal arches. Endodermal lining of pharyngeal pouches forms distinct structures.
Germ layer derivation of heart
Splanchnic mesoderm (lateral mesoderm)
Initial formation of heart
Forms tubes bilaterally
Stage in cardiac development, after the formation of the two endocardial tubes
Fusion of endocardial tubes.
*Arrangement of heart once fusion of endocardial tubes has taken place
Stages of heart development 1 2 3
1) Splanchnic mesoderm forms endocardial tubes 2) Fusion of endocardial tubes 3) Folding of heart 4)
Features of congenital heart defects 1 2
1) Often of no consequence to the foetus. 2) An issue immediately after birth
Most common cardiac developmental defect
Ventricular septal defect (~25%)
Ventricular septal defect aetiology 1 2 3
1) Initial single ventricle is divided partly by ventricular septum. 2) Leaves intraventricular foramen 3) Filled by membranous part of intraventricular septum
Atrial septal defects 1 2 3
1) Patent hole in atrial septum to allow bypass of pulmonary circulation (formen ovalae) 2) Valve on formen should shut once baby begins breathing (increases left atrial pressure) 3) If valve is defective, won’t close on first breath
Aspect of heart contributed to by neural crest
Outflow tract of the heart. If malformed, results in an issue with atrial outflow of heart
GIT at one month
At around one month, GIT consists of foregut and hindgut and a midgut still connected to the yolk sac by yolk stalk
*Folding of GIT in a foetus
Folding of GIT in a foetus 1 2 3 4 5 6
• Initially GIT only as long as the foetus • Quickly lengthens • Begins to buckle in midgut around yolk stalk • Rotates around axis of yolk stalk and superior mesenteric a. • Folds large intestine across small intestine • Further elongation of large intestine gives characteristic folding
Developmental herniation of GIT 1 2 3
1) Week 6-7 - Growing gut is too big for body cavity. 2) Pushes into body stalk. 3) Week 9 - Body cavity is larger, but retracts back.
Name for failure to retract gut back into body cavity
Omphalocoele
Name for retraction of gut but failure to seal abdominal wall
Umbilical hernia
Development of viscera 1 2
• Trachea, lungs, liver and pancreas initially appear as endodermal out-pocketings • Endoderm in out-pocketings is interacting with mesoderm
Name for when organs are in mirror image to normal
Situs invertus
Situs invertus prevalence
1:10000
How is anterior-posterior axis determined?
By first division of zygote.
How is dorsal-ventral axis set?
Blastocyst
What sets left-right asymmetry?
Primitive groove. Patch of cilia, which normally beat counter-clockwise. Leads to concentrations of factor on the left
How does situs invertus come about?
Cilia in primitive groove beat in clockwise direction, or don’t beat at all
Three stages of kidney development
Pronephros, mesonephros, metanephros
Development of the definitive kidney 1 2 3 4
• Kidney is from mesoderm not endoderm • Mesonephros induces metanephros • Mesonephros degenerates (leaving mesonephric duct) • Mesonephros connects to developing testes in male, degenerates completely in females. Separate mesodermally-derived duct (Mullerian) survives in females, becomes fallopian tubes
Migration of kidneys in development
Develop quite low in body cavity, ascend.
Development of external genitalia 1 2 3 4
1) Initial development is identical between sexes 2) When cloaca is present, genital tubercle overlies urogenital folds and cloacal membrane 3) Once anus splits from urogenital tract, males and females become different. 4) Shaft of penis forms from urogenital folds fusing (urethral groove can fail to fuse)
Name for failure of fusion of male urethral groove
Hypospadiasis (1:300)
