Digestion and Absorption Flashcards
What is the basic chemical structure, dietary sources and function of carbohydrates?
Monosaccharides (e.g. glucose, fructose, galactose)
Disacharides - 2 monosaccharides joined by glycosidic bond (e.g. sucrose Gl+F, maltose Gl+Gl, lactose Gl+Ga)
Polysaccharides - multipile joined by glycosidic (e.g. starch - amylose and amylopectin, fibre)
Dietary source: potatoes, bread, rice, pasta, cereals
Function: energy source
What is the basic chemical structure, dietary sources and function of protein?
Amino acids joined together by peptide bonds and folded into primary, secondary and tertiary structures
Dietary source: meat, fish, dairy, lentils, nuts, seeds, tofu
Function: repair and growth
What is the basic chemical structure, dietary sources and function of fats?
Triglycerides: 90%, glycerol + 3 fatty acids (sat vs unsat)
Cholesterol
Phospholipids: glycerol + phosphate group + 2 fatty acids
Dietary sources: animal foods such as meat fat, butter, cheese and cream (saturated); from plants (unsaturated) such as olive and rape seed, nuts, cholesterol from plants and animals, dairy products, palm and coconut oil
Function: plasma membrane (c + p), long term energy store, insulation
What are the main features of a balanced diet?
Eat well guide:
1/3 veg and fruit
1/3 wholegrain or higher fibre carbs
Protein (mainly from beans and pulses)
Dairy and alternatives
Oils and spreads
Water
2000 - 2500 kcal per day from all food and drink
Describe the digestive events in the mouth
Mastication: breaks up food and moistens it
Carbohydrates are broken down by alpha amylase to maltotriose, maltose and alpha-limit dextrin
Proteins = no digestion as no protease
Lipids: v small amount broken down by lingual lipase
Describe the digestive events in the stomach
Churning and mixed with gastric juices
Nothing happens to carbohydrates
HCl activates pepsin and denatures proteins
Gastric lipase has minor contribution to lipids
Describe the digestive events in the small intestines
Chyme mixed with pancreatic juice and bile in the duodenum
- Alpha-amylase further digests starch, brush border disaccharidases (maltase, sucrase, lactase) result in monosaccharides
- Proteins cleaved by trypsin, chymotrypsin, elastase, carboxypeptidases to produce increasingly smaller peptides/ dipeptides, brush border peptidases produce dipeptides and amino acids
Lipids: pancreatic lipase digests lipids to monoglycerides and fatty acids, phospholipase digests phospholipids to lysolectithin and fatty acids
Jejunum: completes digestion and some nutrient absorption
Ileum: nutrient absorption
What is the role of the pancreas in digestion?
Exocrine function: makes up majority of pancreas, release pancreatic juices which contain multiple enzymes, releases alkali secretions which neutralise stomach pH making an optimum pH for enzyme activity
Endocrine function: secretion of insulin and glucagon
What is the role of the liver in digestion?
Production and secretion of bile
Bile is then stored in the gall bladder and released into the duodenum after a meal
Bile salts emulsify fat particles and aid in the absorption of fats by forming complexes called micelles, solubilisation and transport of lipids in aq environment
- synthesised from cholesterol, amphipathic (hydrophobic cholesterol part and hydrophilic amino acid part - gives emulsive properties)
Where are digestive enzymes secreted from?
Glandular cells in mouth
Cheif cells in stomach
Excorine cells of pancreas
Enzymes bount to apical membrane of enterocytes
What is a zymogen? Give examples
a pro-enzyme
- Many enzymes are synthesised as inactive peptides that are then activated by cleavage of peptide bonds
- The inactive precursor is called a zymogen
E.g. pepsinogen is the zymogen to pepsin, prothrombin is the zymogen to thrombin
Enzymes involved in digestion of carbohydrates
Alpha amylase (in salivary secretion and duodenum) cleaves alpha 1-4 bond
Maltase, sucrase and lactase (on brush border) break disaccharides into monosacharides
Enzymes involved in digestion of proteins
Pepsin (chief cells produce pepsinogen which is then activated by release of HCl from parietal cells in stomach) - an endopeptidase (forms smaller oligopeptides)
Trypsin, chymotrypsin, elastase, carboxypeptidases produce increasingly smaller peptides/ dipeptides
Brush border peptidases produce dipeptides/ amino acids
Where are most of the enzymes produced? Which ones? Divide into released as zymogens and in active forms
Pancreas
As zymogens:
- trypsin, chymotrypsin, carboxypeptidase, elastase (proteins), phospholipase (phospholipids)
In active form:
Amylase (starch), lipase (triglycerides), ribonuclease (RNA), deoxyribonuclease (DNA)
Enzymes involved in digestion of lipids
Lingual lipase (in mouth - minor contribution)
Gastric lipase (in stomach - minor contribution)
Pancreatic lipase (duodenum) - breaks lipids into monoglycerides and fatty acids
Phospholipase digests phospholipids to lysolecithin and fatty acids
