Enterocyte
Also known as: absorptive cell, intestinal absorptive cell
Enterocytes are the tall columnar absorptive cells of the intestinal epithelium. Their microvillous brush border carries digestive enzymes and nutrient transporters.
Overview
Enterocytes are strongly polarised. The apical membrane forms a brush border of tightly packed microvilli, each about 1 µm long. It is covered by a glycocalyx that anchors brush-border enzymes: maltase-glucoamylase, sucrase-isomaltase, lactase, aminopeptidases, dipeptidyl peptidases, alkaline phosphatase, and, in the duodenum, enteropeptidase. Tight junctions seal the apical pole. The basolateral membrane carries Na⁺/K⁺-ATPase. By keeping intracellular Na⁺ low, this pump powers most secondary active nutrient uptake.
The cytoplasm has abundant smooth ER, where absorbed fatty acids and monoglycerides are re-esterified into triglycerides, and a large Golgi, where chylomicrons are assembled with apolipoprotein B-48. Enterocytes live only about 3–5 days before being shed at the villus tip.
Parts & subdivisions
- Apical transportersSGLT1 (2Na⁺:glucose/galactose), GLUT5 (fructose), PepT1 (H⁺:di- and tripeptides), Na⁺-coupled amino acid carriers, DMT1 (Fe²⁺), NPC1L1 (cholesterol), NHE3 (Na⁺/H⁺) and, in the ileum, ASBT (bile salts) and the cubilin receptor (B12–IF).
- Basolateral transportersGLUT2 (monosaccharide exit), ferroportin (iron exit), amino acid exporters and the Na⁺/K⁺-ATPase.
- Microvilli with an actin core and a digestive glycocalyx.
- Seal the paracellular route. They are "leaky" in the jejunum and "tight" in the distal colon.
Anatomy
- Histology
Tall columnar cell with a basal oval nucleus. With routine stains the brush border appears as a PAS-positive striated border.
Function
- Terminal (contact) digestion by brush-border hydrolases.
- Absorbs monosaccharides, amino acids, peptides, lipids, vitamins, minerals and water.
- Re-synthesises triglycerides and assembles chylomicrons.
- Barrier function, with tight junctions and mucus.
Clinical significance
Lactose intolerance
Lactase activity declines after weaning in most of the world's adults (lactase non-persistence). Undigested lactose causes osmotic diarrhoea, and its colonic fermentation causes bloating and flatus. The hydrogen breath test is positive. Secondary lactase deficiency follows gastroenteritis or coeliac disease.
Inherited transport defects
Glucose–galactose malabsorption (SGLT1 mutation) causes severe neonatal diarrhoea that resolves on a fructose-based formula. Hartnup disease (B⁰AT1) causes neutral aminoaciduria and pellagra-like features. Abetalipoproteinaemia (MTP deficiency) prevents chylomicron formation.
Test yourself
Which transporter is responsible for apical uptake of glucose by enterocytes?
- GLUT2
- GLUT5
- PepT1
- SGLT1
Answer: SGLT1
SGLT1 co-transports 2 Na⁺ with each glucose or galactose molecule (secondary active transport). GLUT5 takes up fructose. GLUT2 carries all three monosaccharides out across the basolateral membrane. PepT1 carries di- and tripeptides. Oral rehydration therapy depends on SGLT1.
Dietary long-chain triglycerides leave the enterocyte mainly as:
- Free fatty acids bound to albumin in portal blood
- Chylomicrons entering the central lacteals
- Micelles entering villous capillaries
- VLDL secreted into the hepatic sinusoids
Answer: Chylomicrons entering the central lacteals
Inside the enterocyte, fatty acids and monoacylglycerol are re-esterified and packaged with apoB-48 into chylomicrons. These are too large for blood capillaries, so they enter the lacteals and reach the blood via the thoracic duct. Micelles never cross the epithelium; they only carry lipids to the brush border.
Compiled from standard anatomy and physiology references — see the Digestive System sources. For education only; not medical advice.