Ch 23 Digestion and Absorption

These flashcards cover key vocabulary and concepts related to the digestive system, specifically focusing on digestion and absorption processes in the small intestine.

Small Intestine

The primary site of nutrient absorption within the human digestive system.

Jejunum

The middle section of the small intestine where most nutrient absorption occurs.

Ileum

The final section of the small intestine, which continues the absorption process but to a lesser extent than the jejunum.

Circular folds

Increases surface area for absorption.

Microvilli

Cellular extensions on the enterocytes that increase surface area for absorption in the small intestine.

Villi

Finger-like projections that line the small intestine

Cellular structures of small intestine

Apical surface and Basolateral membrane

Apical surface

Surface facing the lumen; key site for nutrient absorption.

Basolateral membrane

Surface that interfaces with connective tissue and blood supply

Brush Border Enzymes

Enzymes located on the microvilli of enterocytes that facilitate the final steps of digestion before absorption.

Tight Junctions

Connections between enterocytes that prevent substances from passing between the cells.

Carbohydrate digestion

• Begins in buccal cavity with salivary amylase, minor contribution.

• Most significant breakdown occurs in small intestine via pancreatic enzymes, primarily pancreatic amylase.

• Brush Border Enzymes further reduce complex carbs to monosaccharides.

Carbohydrate absorption

• Transport of Monosaccharides:

• Glucose and Galactose: Absorbed via secondary active transport coupled with sodium (requires energy).

• Fructose: Absorbed via facilitated diffusion (no sodium needed).

• Transported across apical surface, then through the cytosol to the basal side where they enter interstitial fluid.

Protein digestion

• Initiation: Begins in the stomach with pepsin, activated by hydrochloric acid.

• Pancreatic Enzymes: Continue protein breakdown into smaller peptides in the small intestine.

• Brush Border Enzymes: Further break down peptides into mono-, di-, and tripeptides.

Protein absorption

Transport: Similar to carbohydrates, using secondary active transport influenced by sodium gradient for amino acids and some peptides.

Fat digestion

• Fat digestion differs as fats are lipid-soluble and do not require carriers like water-soluble molecules.

• Begins in the buccal cavity with lingual lipase, but this is minimal.

• Digestion process:

  • Gastric lipase continues fat digestion in the stomach.

  • In the small intestine, bile (from gallbladder) emulsifies fats to increase surface area for pancreatic lipases to act on them.

  • Fat digestion produces fatty acids and monoglycerides, which can easily diffuse across the apical membrane into enterocytes.

Fat absorption

• Inside enterocytes, fats are reassembled into triglycerides and packaged into chylomicrons.

• Chylomicrons are then secreted via exocytosis into interstitial fluid and transported through lymphatic and circulatory systems.

Pancreatic Enzymes

Enzymes produced by the pancreas that aid in the digestion of carbohydrates, proteins, and fats.

Monomers

The simplest form of nutrients that can be absorbed, such as amino acids and monosaccharides.

Galactose

A monosaccharide that is absorbed across the intestinal wall during carbohydrate digestion.

Glucose

A simple sugar that is the primary source of energy for the body's cells, absorbed during carbohydrate digestion.

Fructose

A monosaccharide found in many plants, absorbed differently from glucose and galactose, via facilitated transport.

Lipid Digestion

The breakdown of fats, which involves emulsification and action of lipases produced by the pancreas.

Emulsification

The process by which bile breaks down large fat globules into smaller droplets to increase surface area for digestion.

Chylomicron

A lipoprotein that transports lipids from the intestines into the lymphatic system and bloodstream.

Gastric Lipase

An enzyme secreted in the stomach that continues the process of fat digestion.

Micelles

Structures formed during fat digestion that help transport fats in the intestine.