Nutrients: Ingestion to

Energy Metabolism

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 System

Mouth 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: Digestion

• Mouth– Mastication

(chewing)– Amylase

• Stomach– Churning– Acid

• Small intestine– Sugar enzymes

• Large intestine– Bacteria

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: Digestion

• Mouth– Mastication– Lingual lipase

• Stomach– Gastric lipase

• Small intestines– Bile– Pancreatic lipase– Micelle formation

[Insert Fig. 2.12 here]

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

• Digestion causes release from foods• Absorption occurs in small and large intestines

Vitamins, Minerals, and Water

What is energy?

• It is the entity that enables our bodies to perform work.

• It has no shape.• It has no physical mass.• Our bodies rely on

chemical energy.

Photo © Photodisc

What is the body’s source of energy?

• Macronutrients– Carbohydrates– Fats– Proteins

• Body’s direct energy source– Adenosine

triphosphate (ATP)

Adenosine Triphosphate (ATP)

• Body’s energy source• Two high-energy

bonds• Other phosphates

– ADP– AMP

Cell Structure and Organelles Necessary for ATP Production

What are the three energy systems?

• Phosphagen System

• Anaerobic Energy System

• Aerobic Energy System

Comparison of the Three Energy Systems

Metabolic Pathways

Energy Nutrients

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 Intensity

The small storage pool of ATP is the source of energy whenever instantaneous energy is needed.

Energy System Contributions to Activities of Varying Intensity

During short bursts of intense activity (i.e., 100m run), the phosphagen system is the main energy system that supplies the ATP pool.

Energy System Contributions to Activities of Varying Intensity

During longer lasting sprint activities of lower intensity (i.e., 800m run), the main supplier is the anaerobic system with help from the phosphagen and aerobic systems.

Energy System Contributions to Activities of Varying Intensity

During longer lasting activities of even lower intensity (i.e., mile run), the main supplier becomes the aerobic system with help from the anaerobic system.

Energy System Contributions to Activities of Varying Intensity

During long lasting activities of low intensity (i.e., any sustainable activity), the main supplier becomes the aerobic system with minimal help from the other systems.

Summary:

The Energy Systems Work Together 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.