Digestion and Absorption of Nutrients Flashcards
describe the digestion of carbohydrates
Salivary Amylase: Secreted by the salivary glands, this enzyme begins breaking down starch (polysaccharides) into maltose - inactivated by stomach acid
Pancreatic Amylase: Produced by the pancreas and secreted into the duodenum, this enzyme continues breaking down starch and glycogen into maltose.
Brush Border Enzymes: Located on the microvilli of the small intestine, these enzymes complete carbohydrate digestion
describe and name the enzymes involved in glucose breakdown
Maltase: Breaks down maltose into two glucose molecules.
Lactase: Hydrolyzes lactose into glucose and galactose.
Sucrase: Splits sucrose into glucose and fructose.
describe the absorption of carbohydrates
Glucose and Galactose: Absorbed via secondary active transport using the sodium-glucose co-transporter (SGLT1). This process relies on the sodium-potassium pump to maintain a concentration gradient.
Fructose: Absorbed by facilitated diffusion through the GLUT5 transporter.
Transport into the Bloodstream: Monosaccharides exit the enterocytes via GLUT2 transporters and enter the capillaries, where they are carried via the hepatic portal vein to the liver for metabolism.
carbohydrates are broken down into what monosaccharides
glucose, galactose, and fructose
what are the Brush Border Enzymes
lactose
sucrose
maltose
what are causes of Diarrhoea
*Excessive small-intestinal mobility
*Excess osmotically active particles
where does protein digestion begin
stomach
describe protein digestion
Pepsin: activated from pepsinogen by hydrochloric acid (HCl). Pepsin breaks down proteins into smaller peptides (polypeptides and oligopeptides). in the stomach
In the intestine: Pancreatic Enzymes break down protein into peptides. Brush Border Enzymes (Located on the microvilli of intestinal epithelial cells)
Aminopeptidase – Cleaves amino acids from the amino end of peptides.
describe absorption of proteins
Amino Acids – Absorbed through sodium-dependent active transport (via Na⁺-amino acid co-transporters).
Dipeptides & Tripeptides – Absorbed via proton-dependent transporters (PepT1) and further broken down into amino acids inside the enterocytes.
Transport to Bloodstream – Amino acids exit the enterocytes through facilitated diffusion and enter the capillaries of the villi, eventually reaching the hepatic portal vein to the liver for metabolism.
name the pancretic enzymes involved in protein digestion
Trypsin – Activated from trypsinogen by enterokinase (a brush border enzyme); further activates other proteases.
Chymotrypsin – Breaks down proteins into smaller peptides.
Carboxypeptidase – Cleaves single amino acids from the carboxyl end of peptides.
Elastase – Breaks down elastin and other proteins.
what does a triglyceride break into
Free fatty acids and Monoglycerides
what are micelles
water-soluble particles that can carry the end products of fat digestion within their lipid-soluble
interiors
describe digestion of fats
Mouth – Lingual Lipase: Secreted by salivary glands, this enzyme begins breaking down triglycerides into diglycerides and free fatty acids
Stomach – Gastric Lipase: Secreted by the stomach, it continues the breakdown of triglycerides
Small intestine:
Bile Salts (from the Liver & Gallbladder): Emulsify fats, breaking large fat droplets into smaller micelles, increasing the surface area for enzymatic action.
Pancreatic Lipase (from the Pancreas): Hydrolyzes triglycerides into monoglycerides and free fatty acids for absorption.
describe absorption of fats
Micelles (small lipid aggregates formed by bile salts) transport lipids to the brush border of enterocytes.
Lipid-soluble contents (monoglycerides, fatty acids, cholesterol, and fat-soluble vitamins A, D, E, K) diffuse into enterocytes.
Inside the Enterocytes:
Reformation of Triglycerides: Once inside, monoglycerides and fatty acids are reassembled into triglycerides.
Chylomicron Formation: Triglycerides, cholesterol, and phospholipids combine with proteins to form chylomicrons, which are lipoprotein carriers.
Chylomicrons enter the lymphatic system via lacteals (lymph vessels in the villi).
They are eventually released into the bloodstream via the thoracic duct, reaching tissues for metabolism or storage.
Short- and Medium-Chain Fatty Acids (unlike long-chain fatty acids) are directly absorbed into the bloodstream via the hepatic portal vein.
