[Durgical](https://durgical.com/en/) › [DurgiPedia](https://durgical.com/en/durgipedia/) › [Physiology](https://durgical.com/en/physiology/) › [Gastrointestinal](https://durgical.com/en/physiology/#s-gi) › Fat digestion and absorption [Physiology](https://durgical.com/en/physiology/) · [Gastrointestinal](https://durgical.com/en/physiology/#s-gi) # Fat digestion and absorption - Mechanism - Exam priority: high Bile disperses fat, lipase cuts it, micelles carry it to the wall, and it leaves the gut packed into chylomicrons through the lymph. Updated 2026-11-01 Also called: Micelles, Chylomicrons **See it in 3D:** [Duodenum](https://durgical.com/en/anatomy/duodenum/) · [Jejunum](https://durgical.com/en/anatomy/jejunum/) · [Pancreas](https://durgical.com/en/anatomy/pancreas/) · [Gallbladder](https://durgical.com/en/anatomy/gallbladder/) · [Cisterna chyli](https://durgical.com/en/anatomy/cisterna-chyli/) ## Key points - Pancreatic lipase (with colipase, which anchors it to the droplet when bile salts are present) does nearly all triglyceride digestion → 2-monoglyceride + 2 free fatty acids. - Bile-salt micelles carry the products across the unstirred water layer to the brush border; bile salts stay in the lumen and are reabsorbed in the ileum. - In the enterocyte, triglycerides are re-made (smooth ER) and packed with apoB-48 into chylomicrons. - Chylomicrons are too big for capillaries: they enter lacteals → cisterna chyli → thoracic duct → left subclavian vein, so fat does not pass through the liver first. - Medium- and short-chain fatty acids are absorbed without micelles and go straight to the portal vein (useful in malabsorption). - Steatorrhea with A, D, E and K deficiency: think pancreas (lipase), bile (bile salts) or mucosa (surface). ## What it is Fat does not dissolve in water, so its digestion needs teamwork: bile salts that emulsify it, pancreatic lipase with colipase that hydrolyses it, and micelles that ferry the products to the enterocyte. Inside the cell, triglycerides are rebuilt and leave in chylomicrons into the lymphatic lacteals. Vitamins A, D, E and K travel the same route. ## How it works, step by step - Lingual and gastric lipases start digestion (important in infants), and antral mixing forms a coarse emulsion. - In the duodenum, bile salts and lecithin coat the droplets and greatly increase their surface (emulsification). - Colipase displaces bile salts from the surface and anchors lipase, which cuts triglycerides; phospholipase A2 and cholesterol esterase handle the other lipids. - Fatty acids, monoglycerides, cholesterol and fat-soluble vitamins join mixed micelles. - Micelles cross the unstirred water layer; at the brush border the lipids are released and enter the enterocyte by diffusion and transporters. - In the endoplasmic reticulum, triglycerides and cholesterol esters are rebuilt; MTP loads them onto apoB-48. - Chylomicrons leave by exocytosis into the lamina propria and enter the villus lacteals. - In the blood, endothelial lipoprotein lipase frees fatty acids for muscle and fat tissue; the remnants go to the liver. ## Reference values | Parameter | Value | Note | | --- | --- | --- | | Normal fecal fat | 93–95% | healthy adult | | Lipase reserve | Steatorrhea appears when it falls below 10% of normal | pancreatic insufficiency | Approximate values for a healthy adult at rest; each laboratory sets its own ranges. ## Clinical notes - Chronic pancreatitis and cystic fibrosis: lipase is missing → steatorrhea with bulky, greasy, foul-smelling stools. - Abetalipoproteinemia: MTP defect → no chylomicrons form; enterocytes fill with fat, with acanthocytes and vitamin E deficiency. - Vitamin K deficiency from fat malabsorption → prolonged INR; vitamin D deficiency → hypocalcemia and osteomalacia. - Chylous ascites or effusion: injury to the thoracic duct or lymphatics, with milky, triglyceride-rich fluid. ## Memory aid 'Bile opens, lipase cuts, the micelle carries, the chylomicron leaves by the lymph.' ## Test yourself Think of the answer, then tap the question to see it. ## Why do absorbed lipids reach the systemic circulation before the liver? They are packed into chylomicrons, too large to enter villus capillaries; they enter the lacteals and travel in lymph to the thoracic duct and the subclavian vein. ## What does colipase do in triglyceride digestion? Bile salts coat the fat droplet and keep lipase off; colipase binds that surface and anchors lipase so it can hydrolyse the triglycerides. ## Why are medium-chain triglycerides used in fat malabsorption? Their fatty acids are more water-soluble: they are absorbed without micelles, are barely re-esterified and go straight to the portal vein, with no need for chylomicrons. ## A patient with steatorrhea has a prolonged INR. How is that related to fat? Vitamin K is fat-soluble and absorbed with micelles; with fat malabsorption vitamin K runs short and the liver makes fewer functional factors II, VII, IX and X. [Add to my cards (4)](https://durgical.app/estudiar/?add=/en/physiology/fat-digestion-and-absorption/) ## See it in 3D The structures of Durgical's 3D anatomy where it happens. - [Duodenum](https://durgical.com/en/anatomy/duodenum/) - [Jejunum](https://durgical.com/en/anatomy/jejunum/) - [Pancreas](https://durgical.com/en/anatomy/pancreas/) - [Gallbladder](https://durgical.com/en/anatomy/gallbladder/) - [Cisterna chyli](https://durgical.com/en/anatomy/cisterna-chyli/) ## Related topics - [Bile and the enterohepatic circulation](https://durgical.com/en/physiology/bile-and-the-enterohepatic-circulation/) - [Exocrine pancreatic secretion](https://durgical.com/en/physiology/exocrine-pancreatic-secretion/) - [Patterns of malabsorption](https://durgical.com/en/physiology/patterns-of-malabsorption/) - [How the lymphatic system works](https://durgical.com/en/physiology/how-the-lymphatic-system-works/) - [Gastrointestinal hormones](https://durgical.com/en/physiology/gastrointestinal-hormones/) ## Related conditions - [Chronic pancreatitis](https://durgical.com/en/conditions/chronic-pancreatitis/) - [Coeliac disease](https://durgical.com/en/conditions/coeliac-disease/) - [Abetalipoproteinemia (Bassen–Kornzweig syndrome)](https://durgical.com/en/conditions/abetalipoproteinemia/) - [Crohn disease](https://durgical.com/en/conditions/crohn-disease/) - [Familial chylomicronemia syndrome (lipoprotein lipase deficiency)](https://durgical.com/en/conditions/familial-chylomicronemia-syndrome/) ## In Biochemistry - [Chylomicron](https://durgical.com/en/biochemistry/topics/chylomicron/) - [Lipoprotein lipase (LPL)](https://durgical.com/en/biochemistry/enzymes/lipoprotein-lipase/) - [Apolipoprotein B (ApoB-100 and ApoB-48)](https://durgical.com/en/biochemistry/enzymes/apolipoprotein-b/) - [Lipoprotein metabolism](https://durgical.com/en/biochemistry/topics/lipoprotein-metabolism/) - [Bile acid synthesis](https://durgical.com/en/biochemistry/topics/bile-acid-synthesis/) - [Lipid chemistry](https://durgical.com/en/biochemistry/topics/lipid-chemistry/) - [Lipase as a lab test](https://durgical.com/en/biochemistry/topics/lipase-as-a-lab-test/) - [Vitamin A (retinol)](https://durgical.com/en/biochemistry/molecules/vitamin-a/) - [Vitamin D (calcitriol)](https://durgical.com/en/biochemistry/molecules/vitamin-d/) - [Vitamin E (α-tocopherol)](https://durgical.com/en/biochemistry/molecules/vitamin-e/) - [Vitamin K (phylloquinone)](https://durgical.com/en/biochemistry/molecules/vitamin-k/) [← All of physiology](https://durgical.com/en/physiology/) Educational physiology content; not a diagnostic or treatment guide and no substitute for a health professional's advice. Values are approximate references. No doses are given. Sources: [23.7 Chemical Digestion and Absorption: A Closer Look](https://openstax.org/books/anatomy-and-physiology-2e/pages/23-7-chemical-digestion-and-absorption-a-closer-look) (OpenStax (Rice University), 2022); [23.6 Accessory Organs in Digestion: The Liver, Pancreas, and Gallbladder](https://openstax.org/books/anatomy-and-physiology-2e/pages/23-6-accessory-organs-in-digestion-the-liver-pancreas-and-gallbladder) (OpenStax (Rice University), 2022); [Chronic Pancreatitis](https://www.ncbi.nlm.nih.gov/books/NBK482325/) (StatPearls (NCBI Bookshelf), 2024); Hall JE. Guyton and Hall Textbook of Medical Physiology, 13th ed. (ch. 66). Reference book used to check facts; its text and figures are not reproduced (Elsevier, 2016). ## **Spotted a mistake?** We are always improving for the community. Tell us what is wrong and our team will review it. Report a mistake Representative model, for educational purposes only. --- Source: https://durgical.com/en/physiology/fat-digestion-and-absorption/ License: CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). Cite as: DurgiPedia (durgical.com), https://durgical.com/en/physiology/fat-digestion-and-absorption/