Chapter 35 - Jejunum and ileum Flashcards
What is the average length of the equine small intestine?
The equine small intestine varies from 10 to 30 m in length, with an average length of approximately 25 m.
- Where is the duodenojejunal flexure located, and what does it mark the junction of?
The duodenojejunal flexure is located on the left side of the dorsal abdomen, marking the junction of the duodenum and jejunum.
Describe the location of the jejunum in the equine abdomen.
The jejunum is situated mainly in the left dorsal quadrant of the abdomen, between loops of the small colon.
What provides arterial supply to the jejunum, and what is the structure of the vascular arcades in the mesojejunum?
The cranial mesenteric artery provides arterial supply to the jejunum. Vascular arcades in the long mesojejunum are composed of a major jejunal vessel, an arcuate vessel, and several vasa recta.
How is the length of the ileum marked, and what attaches its antimesenteric side to the dorsal band of the cecum?
The length of the ileum is marked by the distinct ileocecal fold, and its antimesenteric side is attached to the dorsal band of the cecum.
What forms the papilla of the terminal ileum, and where is the ileal orifice located?
Describe the muscle composition of the ileocecal papilla.
The muscle of the ileocecal papilla is composed of 3 layers:
an inner circular layer,
a central longitudinal muscle layer from the ileum,
and an outer layer formed from the circular muscle of the cecum
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Does the ileocecal papilla have a true sphincter?
No, the ileocecal papilla lacks a true sphincter, although the lumen of the ileum appears reduced at the ileocecal junction.
What cells constitute about 90% of the small intestinal epithelial cells, and what is their turnover time?
Columnar absorptive cells or enterocytes constitute about 90% of the small intestinal epithelial cells, and their turnover time is usually 2 to 3 days.
What is unique to the small intestine in adults regarding its epithelial surface?
Unique to the small intestine in adults are fingerlike projections of the epithelial surface called villi, each surrounded by approximately six to nine crypts of Lieberkühn.
What is the primary function of the villi in the small intestine?
Villi in the small intestine function in the digestion and absorption of nutrients.
What are the primary components of the small intestinal epithelial cells, aside from enterocytes?
Aside from enterocytes, small intestinal epithelial cells include mucous (goblet) cells, enteroendocrine cells, Paneth cells, and undifferentiated columnar cells.
How are mature absorptive cells (columnar cells) formed, and what is their turnover time?
Mature absorptive cells migrate onto the villus as mature absorptive cells after at least two divisions within the crypt, and they are extruded at the villous tip with a turnover time of 2 to 3 days.
What structures form the brush border membrane on the apical surface of a mature enterocyte?
Microvilli form the brush border membrane on the apical surface of a mature enterocyte.
What is the function of tight junctions in enterocytes?
ight junctions restrict the transmucosal flux of large molecules but are permeable to water and many low-molecular-weight substances.
What is the primary mechanism for absorption of Na+ and Cl− in the small intestine?
The cotransport of Na+ and Cl− through a carrier mechanism on the luminal membrane is the primary mechanism for absorption of these ions in the small intestine.
How is the release of secretin stimulated, and what is its role in pancreatic secretion?
Secretin is released from S-cells in the duodenal mucosa in response to hydrogen ions in the duodenum. Secretin stimulates the pancreas and liver to secrete bicarbonate (HCO3−) and water.
What is the role of cholecystokinin (CCK) in pancreatic secretion?
Protein and fat in the duodenum stimulate the release of cholecystokinin (CCK) from I-cells in the duodenal mucosa. CCK causes the pancreas to secrete enzymes for the digestion of carbohydrates, fat, and protein.
How do bile salts aid in fat absorption, and what is the fate of bile salts in the small intestine?
Bile salts aid in fat absorption by emulsifying fat in the small intestine.
Approximately 94% of bile salts are reabsorbed by the small intestinal mucosa, pass to the liver, and are resecreted, creating enterohepatic circulation.
Where does the bulk of water absorption in the small intestine occur, and what are the routes for transepithelial movement of ions and water?
The bulk of water absorption in the small intestine occurs in its distal third region, but Na+ and water absorption in the small intestine is important for nutrient absorption. The routes for transepithelial movement of ions and water are through the cells (transcellular) and through the paracellular space (extracellular).
Which hormone stimulates the release of bicarbonate and water from the pancreas and liver?
Secretin.
Which transporter is responsible for D-glucose and D-galactose uptake in the enterocytes?
SGLT1 (sodium-glucose cotransporter type 1).
How does fructose move into the enterocyte?
Through facilitated diffusion via the GLUT5 transporter.
What effect does a dietary increase in soluble carbohydrates have on glucose transport in horses?
It increases glucose transport rates and SGLT1 expression.
What is responsible for the solubilization of lipids in the small intestine?
formation of water-soluble mixed micelles with bile acids.
What are the two basic components of myoelectrical activity in gastrointestinal smooth muscle?
Slow waves and action potentials.
What is the role of the migrating motor complex (MMC) in the small intestine?
Reducing bacterial colonization during the interdigestive state.
Which peptide regulates the interdigestive migrating motor complex?
Motilin.
How is iron stored in the body when combined with an intracellular protein?
As ferritin.
What can decrease calcium absorption in the small intestine?
High concentration of dietary magnesium competing for the calcium transport site.
What are the end products of starch digestion by amylase?
A. D-glucose, D-fructose, and D-galactose
B. Maltose and lactose
C. Sucrose and maltase
D. Amylose and amylopectin
D-glucose, D-fructose, and D-galactose
In horses on a grass-based diet, where is sucrase activity comparable to other nonruminants?
Jejunum
What is the major site of D-glucose uptake by the SGLT1 transporter in grass-fed horses?
Duodenum
How does fructose move from the lumen into the cell in horses?
Facilitated diffusion through GLUT5
What is the primary transporter for D-glucose and D-galactose across the enterocyte membrane?
SGLT1
How does the dietary increase in soluble carbohydrates affect glucose transport along the equine small intestine?
Increases throughout the small intestine
What is the effect of a gradual switch in hydrolyzable carbohydrate in the diet from low to high?
Increases SGLT1 expression
How are small neutral peptides further broken down in the enterocyte?
By brush border oligopeptidases
How do dipeptides and tripeptides enter the portal circulation from the enterocyte?
By facilitated diffusion
What facilitates the movement of lipids through the unstirred water layer to the brush border?
Mixed micelles
What is the primary site for fat digestion in horses?
Jejunum
How is fat digestion in horses affected by the composition of the diet?
Highest for added triglycerides
How is iron transported out of the cell if no binding protein is available?
Through transferrin receptors
What regulates the protein that complexes with absorbed calcium in the enterocyte?
Vitamin D
What percentage of magnesium absorption is approximately observed in growing foals and mature ponies?
40-70%
What cells secrete an almost pure extracellular fluid over the mucosal surface of the small intestine?
Crypts of Lieberkühn
What is the primary determinant of intestinal water and electrolyte secretion?
Chloride secretion
What plays an important role in reducing bacterial colonization in the small intestine during an interdigestive state?
MMC (Migrating Motor Complex
Which receptors mediate sympathetic relaxation of ileal smooth muscle in horses?
α1-adrenergic receptors
What are the non-strangulating lesions in the SI?
Ileal impaction
Proximal enteritis
Ileal muscular hypertrophy
What are the strangulating lesions in the SI?
Pedunculated lipoma
Epiploic foramen entrapment
Volvulus
Volvulus (foals)
Inguinal/scrotal hernia
Intussusception (all types)
Intussusception (ileocecal)
Mesenteric rent
Gastrosplenic ligament entrapment
Umbilical hernia
What is the prevalence range of small intestinal diseases among colic cases treated at veterinary hospitals?
A. 25% to 34%
B. 34% to 58%
C. 58% to 85%
D. 85% to 100%
C. 58% to 85%
What is the most common cause of nonstrangulating obstruction of the equine small intestine?
A. Ileal impaction
B. Muscular hypertrophy
C. Ascarid impactions
D. Duodenitis–proximal jejunitis
Ileal impaction
In which region of the United States is ileal impaction more prevalent, and what may be related to its high prevalence in that area?
Ileal impaction is more prevalent in the Southeast region of the United States, and its high prevalence may be related to feeding coastal Bermuda grass hay.
What is the primary medical treatment for ileal impaction, and what are the key components of this treatment?
The primary medical treatment for ileal impaction includes a balanced electrolyte solution administered intravenously and flunixin meglumine, along with mineral oil if gastric reflux has ceased.
How is ileal impaction diagnosed, and what can be palpated per rectum in cases of ileal impaction?
Ileal impaction is diagnosed through rectal palpation and ultrasonographic examination. The impacted ileum can be palpated per rectum as a smooth, tubular obstruction.
What complications may arise if the diagnosis of ileal impaction is delayed, and what is the prognosis for horses treated surgically versus medically?
Complications include ileus, gastric rupture, mucosal necrosis, perforation of the ileum, and laminitis. The prognosis is favorable, with a higher success rate for medical treatment compared to surgery.
What is the cause of muscular hypertrophy of the ileum, and how is it different from muscular hypertrophy proximal to a chronic obstruction?
Muscular hypertrophy of the ileum is considered idiopathic. It causes marked luminal constriction and is different from muscular hypertrophy proximal to a chronic obstruction.
What are the clinical signs and diagnostic methods for detecting muscular hypertrophy of the ileum?
Clinical signs include recurrent colic.
Diagnostic methods include rectal palpation and abdominal ultrasonography, which can show severe annular thickening in the muscle wall
How do Parascaris equorum infections contribute to small intestinal obstructions in foals, and what are the recommended treatments?
P. equorum infections can cause impactions, intussusception, abscessation, and rupture in foals.
Recommended treatments include enterotomy or resection if the bowel is devitalized.
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Figure 35-5. Removal of impacted ascarids through an enterotomy
in the jejunum. Note that small intestine on the left is dimpled at sites where ascarids remain attached as they are drawn through the incision.
What is the prevalence of duodenitis–proximal jejunitis (DPJ) among small intestinal colics, and how does it manifest clinically?
The prevalence of DPJ is 3% to 22% among small intestinal colics. Clinically, it manifests as nasogastric reflux of a large volume of fluid, signs of pain, and subsequent depression.
Describe the diagnostic hallmarks of DPJ, including clinical signs, rectal examination findings, and laboratory parameters.
Diagnostic hallmarks include:
nasogastric reflux,
tachycardia,
prerenal azotemia,
dehydration,
hypotension,
electrolyte abnormalities,
fever,
leukocytosis,
and higher liver enzyme activities.
How does medical treatment differ from surgical treatment for DPJ?
Medical treatment involves frequent gastric decompression, correction of water and electrolyte disturbances.
DPJ is considered sx in how % of cases? Prognosis factors?
Surgery is considered in 6% of cases. Prognosis is influenced by factors like anion gap, abdominal fluid total protein, and gastric reflux volume.
What are the complications and risks associated with surgery in DPJ cases, and how do survival rates compare between medical and surgical treatments?
Surgical complications include lower survival rates and a higher likelihood of diarrhea.
Survival rates are similar between medical and surgical treatments.
What are the potential causes of liver damage in horses with DPJ, and how is this damage manifested?
Liver damage causes may include reflux of duodenal contents, ascending infection, endotoxin absorption, or hepatic hypoxia.
Manifestations include congestion, vacuolization, periportal fibrosis, and necrotizing hepatitis
What preventive measures are recommended for avoiding ascarid impactions in foals, and what is the significance of anthelmintic resistance?
Prevention involves a sound deworming program using effective anthelmintics and monitoring with fecal egg counts. Anthelmintic resistance is significant, emphasizing the importance of proper deworming practices.
How can ultrasonographic examination be useful in diagnosing ascarid impactions, and what are the possible postoperative complications?
Ultrasonography can show ascarids in the small intestine.
Postoperative complications include focal necrotizing enteritis, peritonitis, abscess formation, and adhesions.
In the context of ileal impaction, what medical treatment is recommended, and what criteria indicate the need for surgery?
Medical treatment involves balanced electrolyte solution, flunixin meglumine, and mineral oil. Surgery is indicated if there’s persistent pain, gastric reflux, or peritoneal fluid abnormalities.
what feeding practices are associated with an increased risk of DPJ?
eeding practices associated with an increased risk include more concentrate and grazing on pasture.
IIn the case of DPJ, what factors are associated with death, and what complications may necessitate euthanasia in protracted cases?
Factors associated with death include anion gap, abdominal fluid total protein, and gastric reflux volume.
Complications leading to euthanasia include laminitis and the considerable cost of prolonged medical treatment.
FIGURE 2 Start of digital dissection at the caudal edge of the
foramen. a = Caudate lobe, b = right dorsal colon, and
c = approximate location of the portal vein
FIGURE
FIGURE 3 Completed dissection to enlarge the epiploic
foramen (EF) at necropsy of a healthy horse, not included in the
study. a = pancreas, b = caudate lobe, and c = right dorsal colon.
The right arrow indicates the approximate location of the portal
vein and the cranial end of the EF. The white dot represents the
caudal end of the EF initially and the point from which the
dissection starts in a caudal direction (to the left). The two short
arrows indicate the extent to which the EF can be opened by fascial
separation, exaggerated beyond clinical relevance to demonstrate
what is possible
FIGURE 1 Anatomy of epiploic foramen (EF) relevant to
enlargement. a = right kidney, b = caudate lobe, c = duodenum
and d = the right dorsal colon. The broken line is the line of
dissection to separate the caudate lobe from its attachments. The
arrow indicates the approximate location of the portal vein, remote
to the line of dissection. Cranial is to the right, dorsal to the top
FIGURE 4 Necropsy image from a clinical case, horse
1, showing partial spontaneous closure of the EF at the caudal edge
(arrow) at 30 days after surgery but leaving an opening sufficient to
accommodate a finger. a = right kidney, b = caudate lobe,
c = duodenum, and d = right dorsal colon beneath the
mesoduodenum. Cranial is to the right, dorsal to the top
Figure 35-10. Small intestinal volvulus. (A) Diagram. (B) Intraoperative presentation. Note the typical appearance of numerous coils of distended and ischemic small intestine stacked one on another.
Figure 35-12. Dissected vaginal tunic in a foal with a congenital scrotal hernia, demonstrating the jejunum and the testicle above it and to the left. The cremaster muscle is evident on the left side.
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Figure 35-11. Direct inguinal hernia in a foal, with massive preputial and scrotal swelling from loops of small intestine beneath the skin. The tunic ruptured, allowing bowel to escape into a subcutaneous position.
Figure 35-19. The mesodiverticular band is evident as a thin fold extending to the antimesenteric surface of the jejunum. The jejunum was strangulated in a mesenteric rent at the point of attachment of the band and mesentery.
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Figure 35-20. Meckel diverticulum that was knotted around the jejunum in a 5-month-old Clydesdale foal. The diverticulum was resected and the linear defect in the jejunum was oversewn.
