Stomach
What percentage of the horse's GIT volume does the stomach make up?
What is hydrochloric acid (HCl)? What cell produces it?
Acidifies the stomach and creates the acidic environment needed for digestion - parietal cells
Approximately how long is the small intestine in a mature horse?
70-80 ft
What digestive substance in produced by the liver? What organ do horses lack to store this?
Bile, gallbladder
What is the primary function of cecum & large colon? What is the primary function of the small colon?
Cecum & large colon - Microbial fermentation of fiber and production of volatile fatty acids (VFAs).
Small colon - Water reabsorption and fecal ball formation
What are the two primary functions of the stomach?
Chemical and mechanical digestion
What is the function of gastrin?
Stimulates gastric acid secretion (HCl)
Name the three sections of the small intestine
Duodenum, jejunum, and ileum
What is the primary digestive function of bile?
Bile aids fat digestion and absorption, particularly through emulsification and micelle formation
What microbial group is primarily present in the horse's hindgut?
Anaerobic bacteria
What is the margo plicatus? Why is it important to understanding stomach anatomy/issues?
The dividing line between the glandular and nonglandular (squamous) regions - nonglandular region is more susceptible to ulcers because it lacks mucus protection of the glandular region
What is the function of pepsinogen & lipase?
Pepsinogen is activated to pepsin for protein digestion; gastric lipase contributes to fat digestion.
What are the two major functions of the small intestine?
Chemical/enzymatic digestion and nutrient absorption
What does emulsification accomplish during fat digestion?
It breaks large fat globules into smaller droplets, increasing surface area for pancreatic lipase to act on
Name the 3 major VFAs produced through fermentation
Acetate (most), propionate, butyrate
Name the two mechanisms that help protect the glandular stomach lining from acid.
The mucus-bicarbonate barrier and prostaglandin-mediated protection, especially PGE2
What is the function of histamine?
Stimulates/supports HCl secretion by parietal cells.
Why are villi and microvilli important?
They greatly increase the absorptive surface area of the small intestine and support digestive and transport mechanisms needed for efficient nutrient absorption
What hormone plays a major role in stimulating pancreatic enzyme secretion?
Cholecystokinin (CCK)
Name one addition product of microbial fermentation besides VFAs
Methane, B-complex vitamins, heat
Why can horses develop gastric ulcers even when they have not recently eaten?
Horses continue to secrete HCl even when the stomach is empty. Without feed and saliva to help buffer the acid, the nonglandular region can be exposed to damaging acidity
What is the function of somatostatin?
Helps inhibit HCl secretion and suppresses gastrin and histamine release.
Name the digestive aid that breaks down each of the following: Starch, Protein, Fat
Starch - pancreatic amylase and enzymes
Protein - Proteolytic enzymes (trypsin, chymotrypsin, carboxypeptidases)
Fat - bile salts & pancreatic lipase
Name two pancreatic enzymes & the nutrient they digest
Amylase - starch
Lipase - fat
Trypsin, chymotrypsin, carboxypeptidases - protein
Explain how microbial fermentation benefits the horse nutritionally
Microbes ferment structural carbohydrates that the horse cannot digest enzymatically
VFAs are absorbed and used as an important energy source. Microbial activity also contributes products such as B-complex vitamins.