Hormones and absorbtion

Secretin

• Released in response to entry of chyme from the stomach; stimulates the release of bicarbonate and controls the rate of bile release

Cholecystokinin

 Released in response to fat from the chyme; stimulates gallbladder contraction and the release of bile

Ghrelin

• Controls hunger; increases meal frequency but not meal size

These hormones regulate:

• Enzyme release

• Hunger

• Digestive processes

Topic 12: Absorption

Absorption occurs in the small intestine

Active transport →

Amino acids and carbohydrates (monosaccharides)

Passive diffusion →

Water-soluble vitamins
Different carriers exist for different nutrients

Outcome of absorption:

• Amino acids and monosaccharides are transported to the liver

• In the liver:

  • Monosaccharides are converted to glycogen for storage, and some are secreted directly into the circulation

  • Amino acids are released directly into the bloodstream, where they are available to the tissues for absorption into the cells

  • Excess amino acids are converted to either non-essential amino acids or fat for storage

  • Once amino acids are converted to fat, they cannot be used for protein production

Fat Absorption

• The majority of fat digestion occurs in the duodenum by pancreatic lipase and bile acids

Bile salts:

• Create a lipid/water interface to permit lipase digestion of triglycerides

• Produced in the liver from cholesterol and stored in the gallbladder

• End result: Emulsify dietary fat

Micelle formation:

• Done by intestinal contractions mixing fat, lipase, and bile salts

• The emulsion of smaller fat droplets is called micelles

• End result: Micelles are absorbed passively into the enterocytes

Chylomicrons:

• Formed within the enterocyte when fatty acids reform into triglycerides and attach to lipoproteins

• End result: Chylomicrons transport fats (triglycerides and cholesterol) to body tissues and the liver

 The Large Intestine

• Begins at the ileocecal valve and continues to the cecum, ascending, transverse, and descending colon, rectum, and anus

• These divisions are demarcated based on their location

• Feed enters through the ileocecocolic valve

• The cecum is small in cats and dogs — it is just a pocket next to the colon and serves no purpose in non-ruminant herbivores

Primary functions of large intestine

• Water absorption → Ensures the passage of formed feces and prevents dehydration
  

• Electrolyte management
  

• Bacterial fermentation: (take undigested fiber and create beneficial compounds such as vitamin k from fiber to feed bacteria in the gut)
  

• Storage of feces
  

• Limited nutrient absorption because there are no villi or brush border enzymes; however, it does absorb water and electrolytes well