Attribution: Nephron, CC BY-SA 3.0, via Wikimedia Commons — Small intestinal wall histology
Numbered Label Explanations
| Label | Structure | Function |
|---|---|---|
| 1 | Villus | Finger-like projection of intestinal mucosa; increases absorptive surface area (macro-level amplification) |
| 2 | Microvilli / Brush Border | Dense mat of microscopic projections on each enterocyte's apical surface; further 20–30x surface area amplification; together with villi = ~600-fold total amplification |
| 3 | Brush Border Enzymes | Maltase, sucrase, lactase (carbohydrate completion), aminopeptidase, dipeptidases (protein completion), nucleotidases, nucleosidases — located on the brush border membrane |
| 4 | Enterocyte (Absorptive Cell) | Columnar epithelial cell with brush border on apical surface; absorbs glucose + amino acids (active transport); reassembles fats as chylomicrons (passive diffusion into cell) |
| 5 | Goblet Cell | Interspersed between enterocytes; secretes mucus for lubrication and protection |
| 6 | Blood Capillary | Central blood vessel in villus; receives glucose (via SGLT) and amino acids (via active transport from enterocytes) → drains into portal vein → liver |
| 7 | Lacteal | Blind-ended lymph capillary in villus core; receives chylomicrons (reassembled fats) from enterocytes → drains into mesenteric lymphatics → thoracic duct → left subclavian vein |
| 8 | Lamina Propria | Connective tissue core of villus containing capillary and lacteal |
| 9 | Crypts of Lieberkühn | Intestinal glands between villi; contain stem cells that renew the intestinal epithelium every 3–5 days |
| 10 | Muscularis Mucosae | Thin smooth muscle layer beneath the mucosa; contractions move villi back and forth, mixing contents and improving absorption contact |
Key Relationships
- Every villus = complete micro-absorption unit (enzymes + blood capillary + lacteal)
- Brush border enzymes are membrane-BOUND (not secreted) → final digestion directly adjacent to transport proteins
- Lacteal and blood capillary serve DIFFERENT nutrients in the SAME villus simultaneously