development of GI tracts Flashcards
what is the blastocele ?
refers to the ball of cells containing zygote to uterine wall
what is the trilaminar disk ?
what layers make up the disk ?
- cells at the early stage of development
- upper layer = ectoderm
- middle layer = mesoderm
- bottom layer = endoderm
where does the trilaminar disc sit between ?
amniotic cavity
yolk sac
what is organogenesis ?
the differentiation of the cells into tissues of the body + organs
what does the ectoderm become ?
skin + nervous system
what does the mesoderm become ?
muscles
vascular system
connective tissue
kidneys
what will the endoderm form ?
the gut
the lungs
the liver
the hepatobiliary system
what does intrauterine life refer too ?
the interval of life between conception + birth
at what point of intrauterine life does the gut begin to develop ?
week 3
what does the yolk sac do ?
helps transfer of nutrients to the embryo before placental circulation
what triggers the development of the fetal vasculature ?
when does this happen ?
week 3
mesoderm invades the yolk sac
what part of the yolk sac gives rise to the gut ?
the dorsal side
what is embroynic folding ?
when does this take place ?
4th week of development
embryo changes shape from flat trilaminar disk into cylinder
why does folding occur in 2 planes ?
what are these planes ?
- horizontal + median plane
- different rates of growth of the embryonic structures
what does folding of the horizontal plane lead to ?
development of the 2 lateral body folds
what does folding in the median plane result in ?
development of the cranial + caudal folds
what happens to the endoderm during embryonic folding ?
- moves towards the midline + fuses with dorsal part of yolk sac
- this creates the primitive gut tube
what 3 parts does the primitive gut tube differentiate into ?
- foregut
- midgut
- hindgut
where is the foregut found in early development ?
at head of embryo
what temporarily closes the foregut ?
what does rupture of this structure give rise too ?
- oropharyngeal membrane
- forms the mouth
where is the midgut found ?
between the fore + hind gut
what is the vitelline duct ?
the narrowing of the yolk sac into a stalk
where is the hindgut found ?
tail of the embryo
what temporarily closes the hindgut ?
what does rupture of this structure lead to ?
- cloacal membrane
- urogenital + anal opening
what is the coelomic cavity ?
what does it give rise to ?
trapped space of the gut
- peritoneal cavity
where does the gut tube come from ?
posterior + anterior walls by a double folded membrane
what are the membranes that hold the gut tube called ?
dorsal + ventral mesenteries
known as dorsal + ventral mesogastrium
what supplies the gut tube with blood ?
how does it reach it
the aorta at the back of the abdomen
via arterial branches in the dorsal mesentery
what is a function of the yolk sac ?
nutrients are absorbed from its vessels in earlier stages
what is vitelline circulation ?
system of blood flowing from embryo to yolk sac + back
what happens when vitelline circulation is no longer needed ?
yolk sac regresses
lie in developing umbilical cord
what is the allantois ?
sac from the hindgut
nonfunctional in humans
what forms the ubilical artery
the blood vessels of the allantois
what does the proximal end of the allantois become ?
urinary bladder
what does the thoracic part of the foregut give rise to ?
the lower respiratory tract
what happens to the foregut in the third week of intrauterine life ?
develops respiratory diverticulum
what does the splanchnic mesoderm form ?
- connective tissue of lungs + respiratory tract
what develops in the ventral mesogastrium ?
rhe liver
what is a distinct feature of the pancreatic development ?
arises as 2 separate buds
what part of the pancreas becomes the uncinate process ?
part of pancreas that came from the ventral pancreas
what does the midgut become ?
most of the intestines
ends 2/3 of the way along the transverse colon
how is the midgut connected to the yolk sac ?
via the vitelline duct
where does the midgut get its blood supply from ?
superior mesenteric artery
what happens to the midgut during the mid trimester ?
- herniates into the umbilical cord to escape pressure of growing liver
what happens to the midgut when it leaves the umbilical cord ?
lost its connection to the yolk saac
describe the midgut rotation :
- cranial + caudal limbs elongate + rotate 90 degree counterclockwise as it enters the umbilical
- as it leaves the umbilical the midgut rotates 180 degree counterclockwise
what does the cranial limb become ?
small bowel
what does the caudal limb become
large bowl
where is the caecum found ?
what is the start of ?
on the caudal limb
larger bowel
what are Mao rotations ?
complications of midgut rotations
what is a non-rotation ?
failure of the second phase of midgut rotation
leaves small bowel on right hand side + large bowel on left
what is a omphalocele ?
failure of gut to return to abdominal cavity
midgut is outside of the body
what is gastroschisis ?
protrusion of gut through anterior abdominal wall
isnt within a sac , intestines are exposed
what have gastroschisis been related to ?
- maternal smoking
- drug abuse
- low birthweight
- possible genetic link
what does the hindgut give rise ?
bottoms 1/3 of transverse colon
descending + sigmoid colon
rectum
upper 1/2 of anal canal
what forms the bottom 1/2 of the anal canal ?
formed by the proctodeum
what happens to the embyonic bladder enlarges ?
forms the urachus
what is the distal part of the hindgut called ?
the cloaca
what partitions the hindgut into 2 compartments ?
the mesenchyme = urorectal septum
what does the urorectal septum do ?
pushes the cloaca towards the cloacal membrane
separates urogenital tract from the future rectum + anal canal
what becomes the perineal body ?
the site of fusion of the cloacal membrane with the urorectal septum
what happens at the 7th week of intrauterine life ?
endoderm meets ectoderm of the proctodeum and the cloacal membrane is divided into the urogenital and anal membrane
what leads to a imperforated anus ?
a persistance of anal membrane
what is a rectovaginal / rectrourethral fistula ?
- incomplete separation of the cloaca into urogential + anorectal parts
what does rectovaginal fistula lead to ?
vagina becomes infected with fecal bacteria
what does rectourethral fistula cause ?
feces in the urethra or infections
