Embryology: Digestive System

Front 1

epithelium and glands

Back 1

-primary tissues
- derived from the endoderm

Front 2

CT and muscular tissue

Back 2

-splanchnic mesoderm

Front 3

primitive gut origin

Back 3

portion of the endoderm-lined yolk sac cavity is incorporated in the embryo as a result of longitudinal and transeverse folding

Front 4

foregut and hindgut origin

Back 4

cephalic and caudal part of the primitive gut, respectivelly

Front 5

midgut origin

Back 5

middle part of the primitive gut which remains temporarily connected to the yolk sac by means of the vitelline duct or yolk stalk

Front 6

stomodeum origin

Back 6

an external ectodermal depression that develops at the cranial most end of the foregut

Front 7

buccopharyngeal membrane origin

Back 7

bilaminar membrane produced by the contact of endoderm of the cranial end of the foregut and ectoderm of the stomodeum

Front 8

proctodeum origin

Back 8

ectodermal depression at the caudal end of the hindgut

Front 9

cloacal membrane origin

Back 9

bilaminar membrane produced by the contact of the ectoderm of the caudal end of the hindgut and the proctodeal ectoderm

Front 10

stomodeum

Back 10

-extends from the oral opening to the buccopharyngeal membrane
-develops into the mouth

Front 11

foregut

Back 11

-extends from the buccopharyngeal membrane to the cranial intestinal portal
- develops into the pharynx, esophargus, stomach and cranial part of the duodenum

Front 12

midgut

Back 12

-between the cranial and caudal intestinal portal which is later reduced to vitello-intestinal duct
-develops into the caudal part of the duodenum, jejunum, ileum, cecum and cranial part of the colon

Front 13

hindgut

Back 13

-extends from the caudal intestinal portal to the cloacal membrane
- develops into the caudal part of the colon and rectum

Front 14

proctodeum

Back 14

-extends from the cloacal membrane to the external opening
- develops into the anal canal and anus

Front 15

rupture of buccopharyngeal and cloacal membranes

Back 15

forms the continuity of the digestive tube from the mouth to the anus

Front 16

stomach position

Back 16

-originally develops as a spindle shaped dilatation of the foregut in the future neck region
-later descends with further development of neck and thorax

Front 17

greater and lesser curvatures of stomach

Back 17

-developed when the dorsal side grows faster than the ventral
- after rotations:
1. greater: directed L and caudoventrally
2. lesser: directed R and craniodorsally

Front 18

rotations of stomach

Back 18

1. cranio-caudal axis: shifts greater curvature to the left
2. dorso-ventral axis: shifts caudal end of the stomach to the R and cranially

Front 19

fundus

Back 19

arises as a bulge near the cranial end

Front 20

greater and lesser omentum

Back 20

dorsal and ventral mesogastrium

Front 21

spleen

Back 21

-mesoderm of the dorsal mesogastrium
- gastro-splenic ligament also formed by this part of mesoderm: connects spleen and greater curvature of stomach

Front 22

ruminant stomach

Back 22

develops from primordium similar to the simple stomach, except greater and lesser curvatures are dorsal and ventral curvatures, respectively

Front 23

rumen

Back 23

-develops as an outgrowth of the dorsal surface of the fundus, extending first dorsally, cranially and to the left
- free end divides into future caudodorsal and caudoventral blind sacs
- later tubular rumen primordium turns caudally and grows back dorsal to the rest of the stomach

Front 24

reticulum

Back 24

develops as a left ventral bulge at the origin of the rumen

Front 25

omasum

Back 25

develops from the lesser curvature

Front 26

abomasum

Back 26

formed by the rest of the primordium corresponding to the lower part of the corpus and pyloric part of the simple stomach

Front 27

gastric groove

Back 27

central axis from which the four compartments of the ruminant stomach develop

Front 28

newborn calf stomach

Back 28

-rumen and reticulum:
1. together have about half the capacity of the abomasum
2. remain collapsed and functionless while the diet is restricted to milk

Front 29

8 week calf stomach

Back 29

combined capacity of the rumen and reticulum is equal to that of the abomasum

Front 30

12 week calf stomach

Back 30

rumen and reticulum together have twice the capacity of the abomasum

Front 31

development of calf omasum

Back 31

grows very slowly
- at 1 1/2 years old, the omasal capacity is approximately equal to the abomasal capacity

Front 32

proportion of four chambers of stomach in large ruminants

Back 32

-rumen: 80%
- reticulum: 5%
- omasum: 8%
- abomasum: 7%

Front 33

proportion of four chambers of stomach in small ruminants

Back 33

- rumen: 75%
- reticulum: 8%
- omasum: 4%
- abomasum: 13%

Front 34

midgut communication and suspension

Back 34

-suspended from the dorsal abdominal wall by a short mesentery
- communicates with the yolk sac by a vitelline duct or yolk stalk

Front 35

midgut development

Back 35

-rapid elongation of the gut and mesentery, resulting in formation of the primary intestinal loop
-loop enters the extraembryonic coelem in the umbilical cord because of insufficient space in the abdominal cavity

Front 36

caudal limb of primary intestinal loop of midgut

Back 36

develops into:
1. lower part of the ileum
2. cecum
3. ascending colon
4. part of transverse colon

Front 37

cranial limb of primary intestinal loop of midgut

Back 37

develops into:
1. distal part of the duodenum
2. jejunum
3. part of the ileum

Front 38

rotation of the intestinal loop of midgut

Back 38

-cranial elongates more rapidly than caudal: loop rotates 290 degrees, around the cranial mesenteric artery
- during rotation:
1. herniated intestinal loop begins to return to the abdominal cavity
2. fusion occurs between the parts of the mesentery suspending the ascending duodenum and descending colon

Front 39

colon of carnivores

Back 39

ascending is a short, straight tube
-followed by transverse and descending colon

Front 40

colon of ruminants gen

Back 40

ascending colon develops into elongated loop which grows and coils to form the proximal, spiral and distal loops of the colon

Front 41

colon of cattle

Back 41

spiral loop develop two centripetal turns, the central flexure and two centrifugal turns

Front 42

colon of small ruminants

Back 42

spiral loop is more variable
-usually 3 centripetal and 3 centrifugal turns

Front 43

colon of horses

Back 43

-ascending colon forms two limbs: ventral and dorsal
- each limb differentiates into:
1. R ventral
2. R dorsal
3. L ventral
4. L dorsal

Front 44

colon of pigs

Back 44

ascending colon develops into centripetal and centrifugal coils

Front 45

urorectal septum gen

Back 45

-thickening of endoderm and surrounding mesenchyme at the junction of the hindgut and allantois

Front 46

development of urorectal septum

Back 46

-grows caudally, separating the cloaca into the dorsal rectum and ventral urogenital sinus
-separation continues until it contacts the clocal membrane, dividing the dorsal anal membrane and ventral urogenital membrane

Front 47

perineal body and perineum

Back 47

-perineal body: tissue between the two thin dorsal anal and ventral urogenital membranes
-perineum: external surface

Front 48

bladder

Back 48

enlarged proximal part of the allantois and adjacent cranial portion of the urogenital sinus

Front 49

urachus

Back 49

remainder of the allantois
-slowly degenerates

Front 50

fate of anal and urogenital membranes

Back 50

degenerate and form continuity with derivates of the proctodeum

Front 51

blood supply to foregut

Back 51

celiac a

Front 52

blood supply to midgut

Back 52

cranial mesenteric a

Front 53

blood supply to hindgut

Back 53

caudal mesenteric a

Front 54

intestinal stenosis and atresia

Back 54

-stenosis: narrowing
-atresia: closure
- pups, kittens, foals and calves

Front 55

atresia ani

Back 55

-imperforate anus (failure of anal membrane to breakdown)
-calves and pigs

Front 56

counter-rotation of gut

Back 56

organs develop opposite to their normal position
- eg d. duodenum on the L and d colon on R

Front 57

urorectal fistula

Back 57

-calves
- abnormalities in development of the urorectal septum that permits communication between rectum and urogenital sinus

Front 58

Meckel's diverticulum

Back 58

persistance of vitello-intestinal duct which leads to a diverticulum
-horses and pigs

Front 59

omphalocele

Back 59

failure of retraction of midgut loop produces a congenital hernia

Front 60

patent urachus or urachal fistula

Back 60

urachus remains open and urine is excreted from this tube at the umbilicus

Front 61

hepatic bud or diverticulum

Back 61

ventral outgrowth from the gut endoderm at the terminal part of the foregut
- consists of rapidly proliferating cells

Front 62

pars hepatic and cystica

Back 62

-hepatic diverticulum develops into two parts:
1. pars hepatica: liver parenchyma (liver cords) and hepatic ducts
2. pars cystica: gall bladder and cystic duct, absent in horses

Front 63

hepatic sinusoids

Back 63

-formed by epithelial liver cords intermingling with the vitelline veins

Front 64

liver cords

Back 64

develop into hepatocytes

Front 65

Kupffer cells and CT cells

Back 65

-derived from mesoderm of the septum transversum

Front 66

hepatic lobules

Back 66

created by regularity of the proliferating and branching liver cords

Front 67

bile duct

Back 67

-joined cystic duct and hepatic duct
- opens into duodenum at major duodenal papillae

Front 68

hepatic diverticulum development

Back 68

-from ventral side of foregut
-as duodenum differentiates, unequal growth in the duodenal wall brings hepatic diverticulum to the dorsal surface of the duodenum

Front 69

liver capsule and ligaments of liver

Back 69

splanchnic mesoderm

Front 70

pancreas

Back 70

-formed by two buds which originate from the gut endoderm on the opposite side of the duodenum at the terminal end of the foregut

Front 71

left lobe of pancreas

Back 71

from dorsal pancreatic bud which arises dorsally and grows into dorsal mesentery

Front 72

accessory pancreatic lobe

Back 72

duct which enters the duodenum at the site of the dorsal pancreatic diverticulum

Front 73

right lobe of pancreas

Back 73

from ventral pancreatic bud which arises from the hepatic diverticulum near its origin

Front 74

pancreatic duct

Back 74

duct of the ventral pancreatic diverticulum which opens into the duodenum on the major duodenal papilla, along with the bile duct

Front 75

secretory pancreatic acini

Back 75

-endodermal epithelium of pancreatic diverticulum proliferates and branches
- at ends of branches, clumps of cells form sp acini

Front 76

pancreatic islets (endocrine part)

Back 76

groups of cells derived from pancretic diverticulum which are scattered between secretory pancreatic acini

Front 77

development of pancreatic diverticulum

Back 77

-two pancreatic diverticulum partially fuse, forming a common body where they fuse
- duct systems anastamose so pancreatic secretions can pass by either the pancreatic or accessory pancreatic duct into the duodenum

Front 78

size of accessory pancreatic duct in different animals

Back 78

- original dorsal duct
1. dogs: large
2. ox/pig: large
3. horse/ cat: small
4. sheep/goat: absent

Front 79

size of pancreatic duct in different animals

Back 79

-original ventral duct
1. dogs: small
2. ox/ pig: absent
3. horse/cat: large
4. sheep/goat: large