Establishment of the Digestive System Flashcards
The first indication in the formation of the digestive tract is initiated by the establishment of the ____
endodermal layer of the blastocyst
The mesoderm splits into somatic and splanchnic layers where the splanchnic layer become closely associated with the endoderm as the _____
splanchnopleure
The intraembryonic tube, lined by endoderm and covered by splanchnic mesoderm
Primitive Gut
Gives rise to the epithelial lining of the digestive tract
ENDODERM
Forms connective tissue and smooth muscle components of the digestive tract wall
SPLANCHNIC MESODERM
- The cranial portion lying beneath the head
- The first part of the primitive gut to be definitely incorporated into the embryo
foregut
*foregut
Ends blindly, but has communication with the undifferentiated part of the gut called ____
anterior intestinal portal
*foregut
Closed cranially by the ____ which is lined by endoderm on the inside and covered by ectoderm on the outside.
oro-pharyngeal membrane
*foregut
An ectodermal depression at the location of the oro- pharyngeal membrane, the ____, later develops into the oral cavity.
stomodaeum
- A connecting portion between the foregut and the hindgut
- Opens into the yolk sac
- The last to acquire its floor through the lateral body folds
Midgut
- Formed in similar manner as the foregut beneath the caudal portion of the embryo.
- The posterior intestinal portal is its communication with the rest of the gut.
Hindgut
*hindgut
Also blind, being closed by the _____, similarly lined by endoderm and covered by ectoderm.
cloacal membrane
*hindgut
A depression at the site of the cloacal membrane, the _____, develops into the anus and the opening of the uro-genital system.
proctodaeum
- Extends from the developing pharynx, where it opens dorsal to the larynx, to the spindle-shaped primordium of the stomach.
- Its principal morphogenic development is elongation.
Esophagus
*Species differentiation
Coated by skeletal muscle throughout its
length (____),
to the diaphragm (____),
to the mid-thorax (____),
or not at all (____).
dog, ruminants
pig
cat, horse, human
avian
Develops as a spindle-shaped dilation of the more caudal portion of the foregut, becoming evident during the third week of gestation in the pig.
Stomach
- The ____ develops as an expansion of the fundus, and a caudoventral pocket of the developing rumen forms the ____.
- The _____ develops as a bulge along the lesser curvature.
The rest of the stomach becomes _____.
rumen
reticulum
omasum
abomasum
The liver and the pancreas both develop from ____ and ____ that originate from the most caudal region of the foregut.
dorsal and a ventral endodermal buds
the liver and a minor portion of the pancreas
ventral bud-
the major portion of the pancreas
dorsal bud-
The hepatogenic part of the ventral endodermal bud develops into a ____ and ____
larger cranial and a smaller caudal portion.
develops into the gall bladder and cystic
duct.
caudal or cystic portion (pars cystica)
develops into the liver tissue and the remaining bile ducts.
cranial or hepatic portion (pars
hepatica)
The relatively large endodermal cells
differentiate into ____ and become arranged in column or plates with intervening _____.
hepatocytes (Pars hepatica)
sinusoids
Initially, the liver develops a left and a right lobe , but subsequent outgrowths from the right
lobe form the ____ and ____ . This, in turn, is followed by species-specific division of the lobes.
quadrate and caudate lobes
*SPECIES DIFFERENCES
the liver remains more or less horizontally attached to the diaphragm in the midline
Carnivores and pig-
*SPECIES DIFFERENCES
the intestinal system displaces the liver by 45° to the right
Horse-
*SPECIES DIFFERENCES
the stomach system pushes the liver 90° to the right.
Ruminants-
Develops from dorsal and ventral endodermal buds off the caudal end of the foregut.
pancreas
One diverticulum arises ventrally as a bud of the hepatic diverticulum; it forms the ____ and ____ of the pancreas.
pancreatic duct and right lobe
The other diverticulum arises dorsally from the duodenum (minor duodenal papilla) and forms the ____ and ____
accessory pancreatic duct and the left
lobe of the pancreas.
*SPECIES DIFFERENCES
Accessory pancreatic duct is later obliterated in
cat and small ruminants.
*SPECIES DIFFERENCES
Pancreatic duct is later obliterated in
ox and pig.
*Pancreas
At the termination of the smallest branch, cluster of cells form the secretory ____ (exocrine portion)
pancreatic acini
Scattered between the acini are group of cells, the ____ (endocrine portion).
islet of Langerhans
The haematopoietic liver occupies most of the abdominal cavity, the growing intestinal loop is displaced out of the abdominal cavity into the extra-embryonic coelom.
PHYSIOLOGICAL UMBILICAL HERNIATION
*Intestines
The cranial limb which becomes the ____ returns to the abdomen first
ascending duodenum
The mass of the ____ fills much of the ventral abdomen and the _____ lies on the right side of the abdomen
coiled jejunum
distal jejunum
During the process of passing in and out of the intestine in the abdominal cavity, accompanying rotational mvts occur
along its dorsal mesenteric attachment, thus the twisted part of the mesentery that attached the intestine to the dorsal body wall is called the _____
root of the mesentery
The intestinal loop rotates _____ around a dorso-ventral axis with the cranial mesenteric artery located in the axis.
clockwise
*Intestines
The first phase of rotation, which occurs
when the intestinal loop forms the hernia, accounts for ___.
180°
*Intestines
Later, during the reduction of the hernia,
an additional rotation augments the rotation to about ___.
270°
*Intestines
At the return of the intestinal loop to the abdominal cavity the final species- specific positioning of the intestines occurs; a process that includes yet more rotation bringing the total to about ___.
360°
*SPECIES DIFFERENCES
In ____—the secondary loop coils
into inverted pyramid
pig
*SPECIES DIFFERENCES
-spiral colon is rope-like
Ruminant
*SPECIES DIFFERENCES
In ____—the secondary loop bends on itself; also the cecum enlarges so that the proximal colon is incorporated within the cecum.
horse
