Module 2 Lecture 2 Part 2
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What happens in the process of digestions?
Digestion breaks down ingested food into chemical building blocks (monomers) which are now small enough to be absorbed across the small intestine wall
What does the mechanism of digestion involve? (LABEL)
Mechanism of digestion involves enzymatic breakdown Mechanisms of absorption involve materials passing through enterocytes (via passive or active transport)
What do humans use for growth, maintenance and repair?
humans use food for growth, maintenance and repair,
What are macronutrients?
nutrients which are requires in large amounts i.e. carbs, proteins and lipids
What are micronutrients?
vitamins and minerals, nutrients that your body requires in small amounts
How is energy measured?
Energy is measured in kilojoules, kJ
Energy measured for nutrients (INFO)
Carbohydrates (excl. unavailable carbohydrates) = 17 kJ per gram Proteins = 17 kJ per gram Lipids = 37 kJ per gram Alcohol = 29 kJ per gram
What do carbs account for?
Carbohydrates account for 45-50% of our total energy intake. Sugars: monosaccharides (glucose, fructose, galactose) & disaccharides (sucrose, lactose, maltose) – Polysaccharides (starch, non-starch)
What does amylase act on?
Amylase acts on polysaccharies and disaccharides
What is the amylase source?
Amylase source include salivary glands and exocrine pancreas
What is the site of action of amylase?
mouth stomach –> small intestine lumen
What do disaccharides act on?
Disaccharidases act on disaccharides (maltase, sucrase, lactase)
Source of disaccharides
small intestine cells
Site of action for dissacharides?
Small intestine apical brush border
What must occur in polysaccharides?
Polysaccharides must be digested into monosaccharides before they can be absorbed
Steps?
1) Amylase digests polysaccharides into disaccharides 2) Disaccharidases digest disaccharides into monosaccharides 3) Monosaccharides are transported across the apical brush border membrane (secondary active transport or facilitated diffusion) 4) Monosaccharides exit across basolateral membrane (facilitated diffusion) & enter capillary via intercellular pores
What about carbs makes it different?
Indigestible carbohydrates (fibre) cannot be absorbed but help to move food along the GI tract & feed bacteria in our large intestine
What do proteins account for?
Proteins account for 15-20% of our total energy intake – Dietary proteins – Enzyme proteins secreted into GI tract – Sloughed & disintegrated intestinal cells
What acts on proteins?
Pepsin acts on proteins from stomach
What acts on protein fragements
Pancreatic proteases act on protein fragments from the exocrine pancreas in the small intestine lumen
What acts on also acts on protein fragements?
Aminopeptidases act on protein fragments from the small intestine cells, in the small intestine apical brush border
What must happen to proteins?
Proteins must be digested into small peptides or amino acids before they can be absorbed
Protein digestion and absorption process?
1) Pancreatic proteases digest proteins and protein fragments into smaller peptides and amino acids 2) Aminopeptidases digest protein fragments into amino acids 3) Amino acids are transported across the apical brush border membrane (secondary active transport) 4) Amino acids exit across basolateral membrane (facilitated diffusion) & enter capillary via intercellular pores
What does fat digestion account for?
Fats account for ~30% of our total energy intake – Triglycerides – Sterols – Short-chain fatty acids