development of GI tracts

Question 1

what is the blastocele ?

Answer 1

refers to the ball of cells containing zygote to uterine wall

Question 2

what is the trilaminar disk ?

what layers make up the disk ?

Answer 2

• cells at the early stage of development
• upper layer = ectoderm
• middle layer = mesoderm
• bottom layer = endoderm

Question 3

where does the trilaminar disc sit between ?

Answer 3

amniotic cavity

yolk sac

Question 4

what is organogenesis ?

Answer 4

the differentiation of the cells into tissues of the body + organs

Question 5

what does the ectoderm become ?

Answer 5

skin + nervous system

Question 6

what does the mesoderm become ?

Answer 6

muscles
vascular system
connective tissue
kidneys

Question 7

what will the endoderm form ?

Answer 7

the gut
the lungs
the liver
the hepatobiliary system

Question 8

what does intrauterine life refer too ?

Answer 8

the interval of life between conception + birth

Question 9

at what point of intrauterine life does the gut begin to develop ?

Answer 9

week 3

Question 10

what does the yolk sac do ?

Answer 10

helps transfer of nutrients to the embryo before placental circulation

Question 11

what triggers the development of the fetal vasculature ?

when does this happen ?

Answer 11

week 3

mesoderm invades the yolk sac

Question 12

what part of the yolk sac gives rise to the gut ?

Answer 12

the dorsal side

Question 13

what is embroynic folding ?

when does this take place ?

Answer 13

4th week of development

embryo changes shape from flat trilaminar disk into cylinder

Question 14

why does folding occur in 2 planes ?

what are these planes ?

Answer 14

• horizontal + median plane

- different rates of growth of the embryonic structures

Question 15

what does folding of the horizontal plane lead to ?

Answer 15

development of the 2 lateral body folds

Question 16

what does folding in the median plane result in ?

Answer 16

development of the cranial + caudal folds

Question 17

what happens to the endoderm during embryonic folding ?

Answer 17

• moves towards the midline + fuses with dorsal part of yolk sac
• this creates the primitive gut tube

Question 18

what 3 parts does the primitive gut tube differentiate into ?

Answer 18

• foregut
• midgut
• hindgut

Question 19

where is the foregut found in early development ?

Answer 19

at head of embryo

Question 20

what temporarily closes the foregut ?

what does rupture of this structure give rise too ?

Answer 20

• oropharyngeal membrane

- forms the mouth

Question 21

where is the midgut found ?

Answer 21

between the fore + hind gut

Question 22

what is the vitelline duct ?

Answer 22

the narrowing of the yolk sac into a stalk

Question 23

where is the hindgut found ?

Answer 23

tail of the embryo

Question 24

what temporarily closes the hindgut ?

what does rupture of this structure lead to ?

Answer 24

• cloacal membrane

- urogenital + anal opening

Question 25

what is the coelomic cavity ? | what does it give rise to ?

Answer 25

trapped space of the gut | - peritoneal cavity

Question 26

where does the gut tube come from ?

Answer 26

posterior + anterior walls by a double folded membrane

Question 27

what are the membranes that hold the gut tube called ?

Answer 27

dorsal + ventral mesenteries | known as dorsal + ventral mesogastrium

Question 28

what supplies the gut tube with blood ? | how does it reach it

Answer 28

the aorta at the back of the abdomen | via arterial branches in the dorsal mesentery

Question 29

what is a function of the yolk sac ?

Answer 29

nutrients are absorbed from its vessels in earlier stages

Question 30

what is vitelline circulation ?

Answer 30

system of blood flowing from embryo to yolk sac + back

Question 31

what happens when vitelline circulation is no longer needed ?

Answer 31

yolk sac regresses | lie in developing umbilical cord

Question 32

what is the allantois ?

Answer 32

sac from the hindgut | nonfunctional in humans

Question 33

what forms the ubilical artery

Answer 33

the blood vessels of the allantois

Question 34

what does the proximal end of the allantois become ?

Answer 34

urinary bladder

Question 35

what does the thoracic part of the foregut give rise to ?

Answer 35

the lower respiratory tract

Question 36

what happens to the foregut in the third week of intrauterine life ?

Answer 36

develops respiratory diverticulum

Question 37

what does the splanchnic mesoderm form ?

Answer 37

- connective tissue of lungs + respiratory tract

Question 38

what develops in the ventral mesogastrium ?

Answer 38

rhe liver

Question 39

what is a distinct feature of the pancreatic development ?

Answer 39

arises as 2 separate buds

Question 40

what part of the pancreas becomes the uncinate process ?

Answer 40

part of pancreas that came from the ventral pancreas

Question 41

what does the midgut become ?

Answer 41

most of the intestines | ends 2/3 of the way along the transverse colon

Question 42

how is the midgut connected to the yolk sac ?

Answer 42

via the vitelline duct

Question 43

where does the midgut get its blood supply from ?

Answer 43

superior mesenteric artery

Question 44

what happens to the midgut during the mid trimester ?

Answer 44

- herniates into the umbilical cord to escape pressure of growing liver

Question 45

what happens to the midgut when it leaves the umbilical cord ?

Answer 45

lost its connection to the yolk saac

Question 46

describe the midgut rotation :

Answer 46

- cranial + caudal limbs elongate + rotate 90 degree counterclockwise as it enters the umbilical - as it leaves the umbilical the midgut rotates 180 degree counterclockwise

Question 47

what does the cranial limb become ?

Answer 47

small bowel

Question 48

what does the caudal limb become

Answer 48

large bowl

Question 49

where is the caecum found ? | what is the start of ?

Answer 49

on the caudal limb | larger bowel

Question 50

what are Mao rotations ?

Answer 50

complications of midgut rotations

Question 51

what is a non-rotation ?

Answer 51

failure of the second phase of midgut rotation | leaves small bowel on right hand side + large bowel on left

Question 52

what is a omphalocele ?

Answer 52

failure of gut to return to abdominal cavity | midgut is outside of the body

Question 53

what is gastroschisis ?

Answer 53

protrusion of gut through anterior abdominal wall | isnt within a sac , intestines are exposed

Question 54

what have gastroschisis been related to ?

Answer 54

- maternal smoking - drug abuse - low birthweight - possible genetic link

Question 55

what does the hindgut give rise ?

Answer 55

bottoms 1/3 of transverse colon descending + sigmoid colon rectum upper 1/2 of anal canal

Question 56

what forms the bottom 1/2 of the anal canal ?

Answer 56

formed by the proctodeum

Question 57

what happens to the embyonic bladder enlarges ?

Answer 57

forms the urachus

Question 58

what is the distal part of the hindgut called ?

Answer 58

the cloaca

Question 59

what partitions the hindgut into 2 compartments ?

Answer 59

the mesenchyme = urorectal septum

Question 60

what does the urorectal septum do ?

Answer 60

pushes the cloaca towards the cloacal membrane | separates urogenital tract from the future rectum + anal canal

Question 61

what becomes the perineal body ?

Answer 61

the site of fusion of the cloacal membrane with the urorectal septum

Question 62

what happens at the 7th week of intrauterine life ?

Answer 62

endoderm meets ectoderm of the proctodeum and the cloacal membrane is divided into the urogenital and anal membrane

Question 63

what leads to a imperforated anus ?

Answer 63

a persistance of anal membrane

Question 64

what is a rectovaginal / rectrourethral fistula ?

Answer 64

- incomplete separation of the cloaca into urogential + anorectal parts

Question 65

what does rectovaginal fistula lead to ?

Answer 65

vagina becomes infected with fecal bacteria

Question 66

what does rectourethral fistula cause ?

Answer 66

feces in the urethra or infections