[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) › Protein digestion and absorption [Physiology](https://durgical.com/en/physiology/) · [Gastrointestinal](https://durgical.com/en/physiology/#s-gi) # Protein digestion and absorption - Mechanism - Exam priority: medium Proteins are cut in the stomach and duodenum down to amino acids and short peptides, which the gut absorbs with its own transporters. Updated 2026-11-01 Also called: Proteases, PepT1 **See it in 3D:** [Stomach](https://durgical.com/en/anatomy/stomach/) · [Pancreas](https://durgical.com/en/anatomy/pancreas/) · [Duodenum](https://durgical.com/en/anatomy/duodenum/) · [Jejunum](https://durgical.com/en/anatomy/jejunum/) ## Key points - Pepsin (from chief cells; pepsinogen is activated at pH - Endogenous proteins (enzymes, shed cells) add up to as much as dietary protein and are digested the same way. - In the newborn, a small amount of intact protein (antibodies in breast milk) can cross the mucosa. - Glutamine is the enterocyte's main fuel. ## How it works, step by step - In the stomach, HCl denatures proteins and activates pepsinogen to pepsin. - Pepsin cuts internal bonds and yields polypeptides; it is inactivated when chyme is neutralized in the duodenum. - Enteropeptidase activates trypsin, which activates the rest of the pancreatic proteases. - Endopeptidases cut within the chain, and carboxypeptidases release amino acids from the C-terminal end. - Brush-border aminopeptidases and dipeptidases leave amino acids, dipeptides and tripeptides. - Amino acids enter with Na⁺ (or by exchange) and short peptides enter with H⁺ via PepT1. - Cytosolic peptidases complete hydrolysis; amino acids leave across the basolateral membrane into portal blood. ## Clinical notes - Pancreatic insufficiency: creatorrhea (undigested meat fibres in stool) alongside steatorrhea. - Kwashiorkor: protein deficiency with relatively preserved calories → edema from low albumin and fatty liver. - Hartnup: neutral aminoaciduria, photosensitive dermatitis and ataxia, which improve with dietary niacin. - Protein-losing enteropathies cause hypoalbuminemia even when absorption is normal. ## Memory aid 'Pepsin starts, trypsin runs the show, the brush border finishes.' ## Test yourself Think of the answer, then tap the question to see it. ## Why does a total gastrectomy not prevent protein digestion, while pancreatic insufficiency does? Pepsin contributes only a small share and pancreatic proteases can do all the work. Without pancreatic enzymes, however, protein passes nearly undigested. ## What advantage does short-peptide absorption via PepT1 offer? It is faster and more efficient than free amino acid uptake, and it preserves absorption when a specific amino acid transporter fails, as in Hartnup disease or cystinuria. ## Why can Hartnup disease look like pellagra? The defective neutral amino acid transporter absorbs tryptophan poorly in the gut and fails to reabsorb it in the kidney; with less tryptophan, less niacin is made. ## What links cystinuria to intestinal amino acid absorption? The same transporter for dibasic amino acids and cystine sits in the gut and the proximal tubule; its defect causes urinary loss of cystine, which precipitates into stones. [Add to my cards (4)](https://durgical.app/estudiar/?add=/en/physiology/protein-digestion-and-absorption/) ## See it in 3D The structures of Durgical's 3D anatomy where it happens. - [Stomach](https://durgical.com/en/anatomy/stomach/) - [Pancreas](https://durgical.com/en/anatomy/pancreas/) - [Duodenum](https://durgical.com/en/anatomy/duodenum/) - [Jejunum](https://durgical.com/en/anatomy/jejunum/) ## Related topics - [Exocrine pancreatic secretion](https://durgical.com/en/physiology/exocrine-pancreatic-secretion/) - [Gastric acid secretion](https://durgical.com/en/physiology/gastric-acid-secretion/) - [Carbohydrate digestion and absorption](https://durgical.com/en/physiology/carbohydrate-digestion-and-absorption/) - [Patterns of malabsorption](https://durgical.com/en/physiology/patterns-of-malabsorption/) - [Nitrogen balance and body protein](https://durgical.com/en/physiology/nitrogen-balance-and-body-protein/) - [Functions of the liver](https://durgical.com/en/physiology/functions-of-the-liver/) ## Related conditions - [Hartnup disease](https://durgical.com/en/conditions/hartnup-disease/) - [Cystinuria](https://durgical.com/en/conditions/cystinuria/) - [Kwashiorkor](https://durgical.com/en/conditions/kwashiorkor/) - [Chronic pancreatitis](https://durgical.com/en/conditions/chronic-pancreatitis/) - [Coeliac disease](https://durgical.com/en/conditions/coeliac-disease/) - [Pellagra (niacin deficiency)](https://durgical.com/en/conditions/pellagra/) ## In Biochemistry - [Tryptophan](https://durgical.com/en/biochemistry/molecules/tryptophan/) - [Niacin (vitamin B3)](https://durgical.com/en/biochemistry/molecules/niacin/) - [Amino acids: structure, charge and pKa](https://durgical.com/en/biochemistry/topics/amino-acids-structure-charge-and-pka/) - [Membrane transport](https://durgical.com/en/biochemistry/topics/membrane-transport/) - [Protein structure and folding](https://durgical.com/en/biochemistry/topics/protein-structure-and-folding/) [← 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); [Hartnup disease: MedlinePlus Genetics](https://medlineplus.gov/genetics/condition/hartnup-disease/) (MedlinePlus, US National Library of Medicine, 2024); [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/protein-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/protein-digestion-and-absorption/