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Digestive Sys Exam 3 > Physiology of the Normal Equine GI Tract (Hostnik) > Flashcards

Physiology of the Normal Equine GI Tract (Hostnik) Flashcards

1
Q

What is the name of the junction between the glandular and non-glandular regions of the equine stomach?

A

Margo plicatus

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2
Q

What is the acid-secreting region of the equine stomach?

A

Glandular
- ulceration are more common

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3
Q

What is the approximate volume of ingesta the equine cecum can hold (in the typical, adult, light-breed horse)?

A

30 liters

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4
Q

(T/F) Except for its origin and termination, most of the equine ascending colon is freely movable within the abdominal cavity

A

True

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5
Q

Which of the following are points of decrease in diameter within the large colon?

A
  • Pelvic flexure
  • Right dorsal colon transverse colon transition
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6
Q

List other hindgut fermenters:

A
  • Rabbit
  • Chinchilla
  • Koala
  • Elephant
  • Rhinoceros
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7
Q

Oral Cavity:
- Mechanical breakdown of plant cell walls

A

Mastication

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8
Q
  • Mostly water (99%) -> hypotonic
  • Also contains calcium, chloride, bicarbonate, sodium
  • Secrete 35-40 liters/day
  • pH 8.6-9.1
  • Very little digestive enzymes (amylase)
  • Acts as a lubricant and buffer
  • Forage intake stimulates a larger volume of salivary secretion
A

Saliva

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9
Q

Esophagus/Lower Esophageal Sphincter:
- In the cranial 2/3 of the esophagus

A

Skeletal muscle

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10
Q

Esophagus/Lower Esophageal Sphincter:
- In the caudal 1/3 of the esophagus

A

Smooth muscle

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11
Q

(T/F) Muscle bundles increase towards the cranial esophagus

A

False, towards the caudal esophagus

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12
Q

Esophagus/Lower Esophageal Sphincter:
Thickened inner circular muscle = ______________

A

Lower esophageal sphincter

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13
Q

What structures make it extremely difficult for horses to vomit?

A
  • Thickened inner circular muscle = lower esophageal sphincter
  • Oblique angle at the junction with cardia
    (gastric rupture is a major concern in horses showing signs of abdominal pain (colic))
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14
Q

How are Gastric decompression done?

A
  • Nasogastric intubation – very important in horses with abdominal pain to prevent fatal gastric rupture
    - Should be prioritized in horses with significant tachycardia (> 60 bpm) or severe pain
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15
Q

What separates the oral cavity from the upper airway/esophagus?

A

Positioning of the epiglottis over the caudal rim of the soft palate

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16
Q

(T/F) Horses are obligate nasal breathers

A

True

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17
Q

What is the approximate capacity of ingesta the equine stomach can hold ( adult horse)?

A

8-10 liters
(can be more with distention)

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18
Q

Where is the horse stomach located?

A

Within the Left abdomen, just caudal to the diaphragm/liver between the 9th and 15th ribs

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19
Q

Equine Stomach:
- More susceptible to acid damage
- Protective Factors:
- Tight junctions between cells
- Hydrophobic phospholipid bilayer
- Saliva (buffer)

A

Dorsal Fundus = Nonglandular + stratified squamous epithelium

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20
Q

Equine Stomach:
Contains:
- Parietal cells (acid-secreting)
- Chief cells (pepsinogen-secreting)
- Enterichromaffin cells (histamine-secreting)
- D cells (somatostatin secreting)

A

Ventral (body, fundus) of the stomach; Proper gastric gland region = glandular

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21
Q

Equine Stomach:
Contains:
- Goblets cells (mucus/mucin-secreting cells)
- G cells (gastrin-secreting)
- Enteroendocrine cells

A

Antrum & Pyloric gland region of the stomach = glandular

22
Q

Protective factors:
Bicarbonate-rich and phospholipid-rich mucus layer

A
23
Q

Equine Stomach:
Horses have continuous secretion of what?

A

Gastric Acid
- even when not actively eating (evolved to continuously graze) = “basal secretion”

24
Q

Equine Stomach:
Who is more prone to gastric ulcerations and why?

A

Foals/Neonates may be more susceptible because they have thinner squamous mucosa and gastric acid secretion occurs early in life

25
Q

Equine Stomach:
When forage is available, the area just beyond the lower esophageal sphincter carries a (lower/higher)__________ pH

A

higher

26
Q

Equine Stomach:
The lower, glandular region, containing mostly liquid, remains at a (lower/higher) __________ pH

A

lower

27
Q

Equine Stomach: Protective Mechanisms within the Glandular Mucosa
What is expressed when the enteric nervous system senses a drop in pH?

A

Prostaglandin E2 (PGE2)
- Promotes an increase in mucosal blood flow, increased mucus, and bicarbonate secretion (these maintain pH near neutral at the mucosa within the glandular region)
- PGE2 also directly inhibits acid secretion by parietal cells

28
Q

What digestive enzymes are included in the Equine stomach?

A
  • Pepsin (pepsinogen converted to pepsin in an acidic enviroment)
  • Lipase (also produced by zymogen cells in the fundus)
    Relative importance of these enzymes in digestion in horses is unknown
29
Q

Equine Stomach:
- Large, diverse bacterial community present within the equine stomach
- Similar numbers of anaerobic bacteria in cecum and colon
- High proportion of amylolytic bacteria (starch digesting)
- Negligible cellulolytic bacteria
- Some volatile fatty acids (VFAs) are produced here – how much is absorbed through the gastric wall is unclear

A

Microbial Fermentation

30
Q
  • 50-70 feet in length in adult horses
  • about 50 liters
  • Digestion/absorption -> primarily in the proximal half
  • Intestinal villi -> perform digestive/absorptive functions
  • Crypts -> secretory function, contain intestinal epithelial stem cells (for self-renewal)
A

Equine Small Intestine

31
Q

Equine Small Intestine:
On what side of the horse can the duodenum be visualized ultrasonographically?

A

On the right side
- Ventral to the right kidney
- Between the right liver lobe and the right dorsal colon (12th - 14th ICS)

32
Q

Equine Small Intestine:
Hydrogen ions stimulate the duodenum to release _____ from S cells

A

Secretin
- stimulates bicarbonate secretion from the pancreas and liver (neutralize acid, a protective mechanism, maintain appropriate pH for digestion)

33
Q

Equine Small Intestine:
Protein and fats that appear within the duodenum stimulate the release of ____________

A

Cholecystokinin (CCK)
- stimulates the release of digestive enzymes from the pancreas
- Trypsinogen (activated by enterokinase in the brush border to trypsin)

34
Q

Definition:
Activates other pancreatic enzymes for digestion/absorption

A

Trypsin

35
Q

(T/F) Pancreatic secretions are continuous, but increase rapidly within feeding

A

True

36
Q

Equine Small Intestine:
Bile duct and pancreatic duct open into duodenum at ____________

A

major duodenal papilla

37
Q

Equine Small Intestine: Carbohydrate digestion & absorption
What is breaking down Polysaccharide -> Disaccharide?

A

Pancreatic amylase

38
Q

Equine Small Intestine: Carbohydrate digestion & absorption
Disaccharides -> monosaccharides

A

Brush border enzymes:
- Sucrase (horses have a decent amount in the proximal small intestine)
- Maltase (evenly distributed, high activity)
- Lactase (horses’ lactase activity decreases with time)

39
Q

Equine Small Intestine: Protein digestion & absorption
Protein -> Polypeptide

A
  • Trypsin
  • Others (activated by trypsin)
    • Chymotrypsin
    • Carboxypeptidase
    • Elastase
40
Q

Equine Small Intestine: Protein digestion & absorption
Peptide -> amino acids, di- and tri-peptides

A

Brush border oligopeptidases

41
Q

Equine Small Intestine:
With damage to intestinal villi (from disease), what can happen?

A

Brush border enzymes may be destroyed:
- Maldigestion
- Malabsorption
-» leading to Osmotic Diarrhea

42
Q

What is a major site of glucose absorption?

A

The proximal small intestine

43
Q

SGLT1 expression increases in response to what?

A

Increased glucose exposure in the small intestine

44
Q

(T/F) Sodium-dependent and independent absorption of monosaccharides

A

True

45
Q

(T/F) Fructose does not require sodium

A

True

46
Q

Equine Small Intestine:
(T/F) The small intestine does the majority of the water absorption

A

False, Large intestine does the majority

47
Q

Where do most of the water absorption occur in the small intestines?

A

Distal third

48
Q

Equine Small Intestine:
Water absorption is ______(a)______ (primarily paracellular) and follows ____(b)_____

A

(a) passive
(b) electrolyte transport

49
Q
  • Water content about 86-95%
  • pH 6-7.3 (higher in the ileum)
    • higher than in the stomach because it is buffered
  • Bacteria present (lactobacilli, streptococci, and lactate-utilizing bacteria)
  • Liquid transit through the small intestine about 60-90 minutes
  • Solid transit between 4-7 hours
A

Equine Small Intestine

50
Q

Equine large intestine:
What two structures appear gas-filled on abdominal ultrasound?

A
  • Cecum
  • Colon (large colon)
    generally only distinguishable by location
51
Q

Is especially adapted (large ascending colon & cecum) for hindgut fermentation, providing a large portion of energy from the horse’s diet
Functions:
- Fermentation
- Volatile Fatty Acid (VFA) production & absorption
- Water and electrolyte absorption

A

Equine Large Intestine

52
Q

(T/F) Rabbits are similar to horses but primarily utilize the cecum for fermentation and the ascending colon to a lesser extent

A

True

Digestive Sys Exam 3 (7 decks)

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