Tissues of the gut
The wall of the digestive tract is built from layers of tissue. The innermost layer, the mucosa, is lined by epithelial tissue, a sheet of cells that covers surfaces. The type of epithelium depends on the job.
| Epithelium | Where | Role |
|---|---|---|
| Stratified squamous | Mouth, oesophagus | Protects against rubbing by food |
| Columnar with goblet cells | Stomach, small intestine | Secretes mucus and enzymes; absorbs |
| Columnar with microvilli | Small intestine (villi) | Absorption with a large surface area |
| Glandular | Gastric glands, pancreas | Make digestive enzymes and acid |
The villus
The small intestine is lined with villi. The wall of a villus is a single layer of cells with microvilli, and inside it are blood capillaries and a lacteal. The folds, villi and microvilli together increase the surface area for absorption.
Digestive enzymes
| Enzyme | Made in | Digests | To make |
|---|---|---|---|
| Amylase | Salivary glands, pancreas | Starch | Maltose |
| Pepsin | Stomach | Protein | Peptides |
| Trypsin | Pancreas | Protein | Peptides |
| Lipase | Pancreas | Fats | Fatty acids and glycerol |
| Maltase | Small intestine | Maltose | Glucose |
Try itSurface area of the intestine
A flat tube has a certain surface area. Villi and microvilli multiply it. Choose the multiplying factors.
Key terms
- Epithelium
- A sheet of cells that covers a surface.
- Villus
- A finger-like fold of the small intestine.
- Microvilli
- Tiny projections on the cells of the villus.
- Peristalsis
- Waves of muscle contraction that push food along.
Summary
- The gut is lined with epithelial tissue, with different types for different jobs.
- Villi and microvilli give a large surface area for absorption.
- Amylase, pepsin, trypsin and lipase digest starch, protein and fat.
- Digested food is absorbed into blood capillaries and the lacteal.