Exercise 39A

Digestive Physiology

The Digestive Process

IngestionPropulsionMechanical DigestionChemical DigestionAbsorptionDefecation

Motility vs. MixingThe difference between peristalsis and segmentation:

Peristalsis moves food along the tract. Segmentation is mixing and part of the mechanical digestion

process.

Absorption of Nutrients• Nearly all occurs in the small intestine.

– 80% of the electrolytes and virtually all food

• Most nutrients are absorbed by active transport.– Glucose, amino acids, & nucleic acids are absorbed

by secondary active transport with sodium.– Iron and calcium require transport proteins (ferritin) or

cofactors (vitamin D).– Anions follow Na+.

• Vitamins -– Fat soluble (A, D, E & K) vitamins are carried with

micelles. Much of the K is absorbed in the colon.– Water soluble vitamins diffuse with the exception of

B12, which requires intrinsic factor.

Hormonal regulation of bile release

Exocrine tissues of the pancreas

Activation of pancreatic proteases in the duodenum

Regulatory mechanisms for release of pancreatic juice

Chemical Digestion Carbohydrates & proteins

Chemical Digestion Lipids & Nucleic acids

Protein digestion in the small intestine

Bile salts emulsify fats

Absorption of lipid

Dietary fats are absorbed into the “lacteals” of the lymphatic system before being transferred to the circulatory system.

Lacteals

The End