49 - Motility of the small intestine: types of movement and regulation; secretion, digestion and absorption

sections

regulation and mobility of small intestines

secretions in small intestines

digestion in small intestines

chemical digestion

absorption

regulation and mobility of small intestines

• Regulation and mobility of small intestine

  • Normal peristalsis-wave like contractions

  • Segmental movements- ➢ closely spaced contractions of the circular smooth muscle ➢ with short periods of relaxation

• Regulation- enteric nervous system – myenteric plexus and submucosal plexus

  • Parasym- stimulate and Symp- inhibit Gastrin, CCK and secritin

secretions in small intestines

• Secretions come from within the crypts of Lieburkhun- Paneth cells:

1. Secretions into the enterocytes

2. Secretions into the blood

• Secretions are fluid and mainly compose of water, electrolytes and mucus

• Mucus: Protect lining of small intestine from digestive enzyme and HCl

digestion in small intestines

• Proteins are broken down to peptides and amino acids before absorption

• Enterocytes - for absorption

• Goblet cells - for mucus production

• Enteroendocrine cells - for hormone release

• Paneth cells - for secretion of microbial antibodies

chemical digestion

• When chyme (partially digested food) enters the small intestine, it contains:

  • Partially digested carbohydrates

  • Partially digested proteins

  • Lipids

• Pancreatic amylase is secreted into the small intestine.

• It breaks down complex carbohydrates → disaccharides → monosaccharides (e.g., glucose), which can then be absorbed.

• Proteolytic enzymes (e.g., trypsin, chymotrypsin, carboxypeptidase) are secreted by the pancreas.

• These enzymes break partially digested proteins → peptides → amino acids for absorption.

• Bile (from the liver, stored in the gallbladder) emulsifies fats—breaking large fat droplets into smaller ones, increasing the surface area.

• Pancreatic lipase then acts on the emulsified fats, converting them into fatty acids and monoglycerides, which are absorbed.

absorption

• Digested food is now able to pass into the blood vessels in the wall of the intestine through either diffusion or active transport.

• The small intestine is the site where most of the nutrients from ingested food are absorbed:

  • Iron is absorbed in the duodenum.

  • Vitamin B12 and bile salts are absorbed in the terminal ileum.

  • Water and lipids are absorbed by passive diffusion throughout the small intestine.

  • Sodium bicarbonate is absorbed by active transport and glucose and amino acid symport.

  • Fructose is absorbed by facilitated diffusion.