Nutrients:Ingestion to EnergyMetabolism Chapter 2
What happens to nutrients after they are ingested?• Two types of digestion – Mechanical: includes chewing, peristalsis – Chemical: includes digestion enzymes• Absorption• Transport• Assimilation and/or energy production
Digestion: Anatomy and Functions of the Digestive SystemMouth to anus is 25 ft!• Mouth (oral cavity)• Esophagus• Stomach• Small intestine• Large intestine• Rectum
Digestion: Salivary Glands• Salivary glands – See figure to right• Secrete saliva – Moistens food – Contains enzymes
Digestion: Stomach• Muscular organ• Primary function: digestion• Major secretions – Hydrochloric acid to unravel proteins – Mucus to protect stomach tissue from acid. – Digestive enzymes
Digestion and Absorption: Small Intestine• Duodenum – Majority of digestion occurs here• Jejunum – Little digestion – Absorption• Ileum – Absorption
Absorption: Surface of Small Intestine• Convoluted interior• Villi• Microvilli• Result: Increased surface area for absorption
Absorption: Large Intestine• Colon – Ascending – Transverse – Descending• Rectum• Anus• Some absorption – Water – Sodium – Chloride – Potassium – Vitamin K
Absorption: Mechanisms• Passive diffusion – move from high to low concenration• Facilitated diffusion- move from high to low concentration carried by protein carrier.• Active transport – Concentration gradient not a factor.• Endocytosis
Absorption: Mechanisms • Passive diffusion • Facilitated diffusion • Active transport • Endocytosis
Absorption of Nutrients Review this figure to see where along the GI tract individual nutrients are absorbed.
Carbohydrates: Absorption• Most absorption occurs in small intestine• Mechanisms – Facilitated diffusion • Fructose – Active transport • Glucose • Galactose
Carbohydrates: After Absorption• Transport via blood• Cellular uptake – Insulin – Glucose transporters• Fates – Storage in liver or muscles as glycogen. – Conversion to adipose tissue (fat). – Energy
Fats: Absorption• Occurs in small intestine• Mechanism – Passive diffusion• Very little fat makes it to large intestine – Steatorrhea – Crohn’s disease – Cystic fibrosis
Fats: After Absorption• Transport – Lymph • Chylomicrons – Blood• Cellular uptake – Lipoprotein lipase• Fates – Storage – Energy
Proteins: Digestion• Mouth • Mastication• Stomach • Churning • Acid Denaturation: acid unravels proteins so peptide bonds can be cleaved by enzymes. Very important function of the stomach.• Small intestine • Proteases • Peptidases
Proteins: Absorption• Occurs in small intestine• Mechanism – Facilitated diffusion – Active transport• Very little makes it to large intestine
Proteins: Absorption AMINO ACID SUPPLEMENTATION CAUTION• Carrier proteins are responsible for facilitating absorption of amino acids.• Similar amino acids share the same active transport systems and protein carriers.• Taking amino acid supplements containing large amounts of single amino acids can affect the absorption of other amino acids if they share the same transport carrier.• If an athlete takes a large amount of a single amino acid this may result in overabsorption of that amino acid at the expense of another amino acid.
Proteins: After Absorption• Transport – Blood• Become part of amino acid pool• Fates – Body proteins such as muscle, enzymes, hormones. – Conversion to body fat. – Energy : Used for energy only when carbohydrate is not available fuel source. Not preferred fuel source as it has more important and essential roles in body.
Cellular Protein Synthesis• Transcription – DNA – mRNA• Translation – Transfer RNA – Amino acids
Vitamins, Minerals, and Water• Digestion causes release from foods• Absorption occurs in small and large intestines
Cellular ATP Production: The Metabolic Factory
Phosphagen Energy System• Stores of high-energy phosphates – ATP – Creatine phosphate (CP)• Also known as: – Immediate energy system – ATP-CP system
Anaerobic Energy System• Involves only carbohydrates• Does not require oxygen• Also known as: – Anaerobic glycolysis
Aerobic Energy System• Involves all macronutrients• Requires oxygen• Also known as: – Oxidative system
Energy System Contributions to Activities of Varying IntensityThe small storage poolof ATP is the source ofenergy wheneverinstantaneous energy isneeded.
Energy System Contributions to Activities of Varying IntensityDuring short bursts ofintense activity (i.e.,100m run), thephosphagen system isthe main energy systemthat supplies the ATPpool.
Energy System Contributions to Activities of Varying IntensityDuring longer lastingsprint activities of lowerintensity (i.e., 800mrun), the main supplieris the anaerobic systemwith help from thephosphagen and aerobicsystems.
Energy System Contributions to Activities of Varying IntensityDuring longer lastingactivities of even lowerintensity (i.e., mile run),the main supplierbecomes the aerobicsystem with help fromthe anaerobic system.
Energy System Contributions to Activities of Varying IntensityDuring long lastingactivities of lowintensity (i.e., anysustainable activity), themain supplier becomesthe aerobic system withminimal help from theother systems.
Summary: The Energy Systems WorkTogether to Meet ATP Demand
How does carbohydrate intake impact protein metabolism?• Carbohydrates are an important energy source.• Low CHO results in muscle protein breakdown.• Gluconeogenesis.