Flashcards in Exam #3 Deck (74):
Primitive gut closed at ends by?
oropharyngeal membrane and cloacal membrane (made of endo and ectoderm)
Primitive gut suspended to body wall by?
dorsal mesentery (double fold) and ventral mesentery
Primitive gut temporarily connected to what?
primitive gut supplied blood by?
ventral branches of the aorta
digestive system is the main organ system derived from embryonic?
Parts of the dorsal mesentery?
stomach: greater omentum (dorsal mesogastrum)
descending colon: ascending mesocolon
Lesser omentum: heptogastric and hepatoduodenum
remnant of fetal ventral mesentery and connects liver to body wall
4 divisions of the primitive gut:
1. Pharynx (to GI and respiratory tract)
Components of the foregut?
esophagus, stomach, descending duodenum, liver and pancreas
Components of the midgut?
ascending duodenum ---> transverse colon
Components of the hindgut?
descending colon (distal 1/3), rectum and anal canal
- cervical part not surrounded by coelom
- not suspended by mesentery
- maintains initial shape and position (above trachea, slight left from thoracic inlet to diaphragm)
Arteries to foregut, midgut, and hindgut?
1. Foregut: celiac a.
2. Midgut: cranial mesenteric a.
3. Hindgut: caudal mesenteric a., internal pudendal, and femoral in some
Stomach begins as a fusiform dilation of the?
differential growth of the walls results in changes in position and appearance of?
- Differential growth of walls also leads to compartments
dilations becoming curvatures?
dorsal dilation --> greater curvature
ventral dilation --> lesser curvature
Positional changes of the stomach
rotates 90 degrees clockwise along its axis and dorsal dilation shifts to the left (liver growing further pushes left and caudoventral)
Order of differentiation of compartments of ruminant stomach
1. Rumen: expansion of fundus
2. reticulum: as caudoventral pocket of fundus
3. omasum: expansion of lesser curvature
4. abomasum: dilation of the pyloric region
Adult size of stomach reached after?
1 year of age
- compartments change shape and relative capacities during growth (milk --> grasses)
Liver = the largest
GLAND of the body
Liver begins as?
hepatic diverticulum = ventral outgrowth of foregut
Formation of liver sinusoids?
endodermal cells proliferate into cords that anastomose around vitelline and umbilical veins
Formation of the common hepatic duct?
expansion of the liver narrows the connection with the foregut and the hepatic ducts merge
diverticulum of liver bud - cystic duct joins the hepatic duct to form the bile duct (opening at origin of liver bud)
No gallbladder in?
Horse, rat and birds - forms but quickly regresses
liver expands temporarily - forms the centrum tendineum of diaphragm
Liver remains connected to caudal vena cava by? and to the centrum tendineum by?
caudal vena cava -> coronary ligament
centrum tendineum --> triangular ligaments
Ventral mesentery divided by liver into 2 things?
lesser omentum and falciform ligament
Parts of the lesser omentum?
hepatogastric ligament and hepatoduodenal ligament
origin of the hepatic diverticulum shifted dorsally by?
differential growth of duodenum
Pancreas dual origin: left lobe
dorsal diverticulum from duodenum forms left lobe & accessory duct
Pancreas dual origin: Right Lobe
ventral diverticulum around greater curvature from hepatic diverticulum forms right lobe (along descending duodenum) with pancreatic duct
Species with both pancreatic and accessory ducts?
dog and horse
species with only a pancreatic duct?
cat and small ruminants
species with only an accessory pancreatic duct?
pig and ox (opens at minor duodenal papilla)
forms greater part of digestive tract, suspended by dorsal mesentery and temporarily connected to yolk sac
Physiological herniation of midgut causes?
rapid elongation in a small abdominal cavity
Result of physiological herniation?
herniation into umbilical cord in a U shaped loop with cranial (descending) and caudal (ascending) limbs
Rotation of the midgut?
loop rotates around the axis of the cranial mesenteric A. - determined by connection to yolk sac and uneven growth
- full rotation: 270 degrees counterclockwise around artery forming root of mesentery (180 than 90 during withdrawal)
withdrawal of loop:
sequence of withdrawal determines the final placement of intestines
Cranial limb of the midgut
returns first and passes to the L caudal to artery - forms duodenum and jejunum
Caudal limb of the midgut:
passes to right in from of cranial mesenteric A.
formation of secondary loop of ascending colon
1. spiral colon: pig and ruminants
2. bend colon: horse
common chamber for digestive and urogenital systems (persists in adult birds, reptiles and amphibians)
anal canal and urogenital sinus
diverticulum of the hindgut with yolk sac from the umbilical cord -> forms part of the urinary bladder and urachus
Physiological Gut Atresia
temporary occlusion of the gut by epithelial proliferation - recanalization occurs by degeneration of the central epithelium
- not simultaneous events and anomalies occur at any level
product of fetal digestion (amniotic fluid/embryonic debris) - sticky semisolid green feces
When should meconium be completely eliminated?
by day 4 postnatally - should start 6-8 hrs post birth
common cause of colic in equine neonates (treat with enema)
4 possible causes of gut atresia/stenosis
1. fetal vascular accidents: vessels dont form/regress
2. lack of re-canalization
3. gut rotation defects (clockwise or lack of rotation)
4. other causes: cattle rough manipulation of fetal membranes during preg Dx)
Gut atresia/stenosis genetic condition in?
horses, jersey cows and some dog breeds
rare in domestic animals - commonly due to hypertrophy of wall
- due to persistent anal membrane - Tenesmus (distension/straining)
- surgical corrected
Urorectal septal defects - fistulas
errors in separating cloaca - ectopic anal opening (named for site of communication)
Types of Urorectal Septal defects (7)
1. persistent cloaca
2. anal stenosis
3. persistent anal membrane
4. anoperineal fistula
5. rectovaginal fistula
6. Rectourethral fistula
7. rectal atresia
neural reflex defect - lack of motor function - absent peristalsis
Result: lack of relaxation of sphincter, esophageal distension throughout
Symptoms of megaesophagus
postprandial regurgitation of undigested food
Incidence and management of megaesophagus
breed predilection in dogs
symptomatic tx: bailey feeding chair or PEG tube
most common cause of regurge in cats and dogs
- can also be caused by vascular ring anomalies (persistent right aortic arch)
lack of motor function due to absence of myenteric ganglia
result: hypertrophic dilation of gut cranial to constricted area (compaction)
symptoms of congenital megacolon:
tenesmus (strain), constipation, abdominal distension
- genetic defect
- white foals with overo parents (painted and pinto ponies)
- Mx: surgery difficult (manx cats)
- predisposing factors: stenotic pelvic canal, foreign bodies, tumors, lumbosacral cord inj.
Mega conditions involve lack of migration of what embryonic cells and is absence of what type of innervation?
- Neural crest cells
- Autonomic ganglia
Congenital umbilical hernia
- incomplete closure of abdominal wall at umbilicus
result: herniation of viscera under skin - can be genetic or not - pigs highest incidence - sugical correction
Vitelline duct anomalies
persistent patent ductus - intestinal-umbilical communication (horses) - fecal material evacuated through umbilicus (or meckel's diverticulum/ vitelline cyst)
Urinary and repro systems develop from?
intermediate mesoderm (kidneys, gonads and genital duct system)
Urinary and genital ducts share a common cavity
Urinary system formation:
intermediate mesoderm migrates ventrally and proliferates - forms nephrogenic cords (cranial portion segmented and caudal portion not)
clusters of cells connected to the pronephric duct - transitory and non-functional
- its duct is taken over by the mesonephros
consists of excretory tubules and mesonephric duct (renal corpuscle) - temporary function in some species (birds and reptiles) - becomes adult kidney in fish and amphibians
- dual origin
- ureteric bud: arises from dorsal evagination of mesonephric duct
- forms the collecting system when distal end expands to form renal pelvis, calyces, collecting tubules and proximal part of ureters
- from intermediate mesoderm surrounding ureteric bud - forms excretory system
Nephrogenesis stops when?
At birth (kidney cannot regenerate) - grow postnatally due to growth in tubule size
- migrate from sacral to lumbar region
- metanephric kidney begins to function in fetal stage