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Nutrients: Ingestion to Energy Metabolism
Chapter 2
What happens to nutrients after they are ingested?
Digestion
Mastication
Enzymatic activity
Absorption
Transport
Assimilation and/or energy production
Digestion: Anatomy and Functions of the Digestive System
Mouth (oral cavity)
Esophagus
Stomach
Small intestine
Large intestine
Rectum
Figure 2.1 Anatomy of the digestive system.
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Digestion: Salivary Glands
Salivary glands
Parotid
Sublingual
Submandibular
Secrete saliva
Moistens food
Contains enzymes
Figure 2.3 The salivary glands. The three pairs of salivary glands supply saliva, which moistens and lubricates food.
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Digestion: Stomach
5
Muscular organ
Primary function: digestion
Major secretions
Hydrochloric acid
Mucus
Digestive enzymes
Digestion and Absorption: Small Intestine
Duodenum
Majority of digestion occurs here
Jejunum
Little digestion
Absorption
Ileum
Absorption
Figure 2.4 The small intestine. Secretions from the pancreas, liver, and gallbladder assist in digestion.
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Absorption: Surface of Small Intestine
Convoluted interior
Villi
Microvilli
Result: Increased surface area for absorption
Figure 2.5 The absorptive surface of the small intestine.
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Absorption: Large Intestine
Colon
Ascending
Transverse
Descending
Rectum
Anus
Some absorption
Water – Potassium
Sodium – Vitamin K
Chloride
Figure 2.6 The large intestine. In the large intestine, bacteria break down dietary fiber and other undigested carbohydrates, releasing acids and gas.
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Absorption of Nutrients
Absorption: Mechanisms (1 of 2)
Passive diffusion
Facilitated diffusion
Active transport
Endocytosis
Figure 2.8 Mechanisms for nutrient absorption. (A) and (B)
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Absorption: Mechanisms (2 of 2)
Passive diffusion
Facilitated diffusion
Active transport
Endocytosis
Figure 2.8 Mechanisms for nutrient absorption. (C) and (D)
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Carbohydrates: Digestion
Mouth
Mastication
Amylase
Stomach
Churning
Acid
Small intestine
Sugar enzymes
Large intestine
Bacteria
Figure 2.12 Triglyceride digestion. Most triglyceride digestion takes place in the small intestine.
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Carbohydrates: Absorption
Most absorption occurs in small intestine
Mechanisms
Facilitated diffusion
Fructose
Active transport
Glucose
Galactose
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Carbohydrates: After Absorption
Transport via blood
Cellular uptake
Insulin
Glucose transporters
Fates
Storage
Conversion
Energy
Figure 2.9 Flowchart of glucose and other simple sugars immediately after a meal.
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Fats: Digestion
Mouth
Mastication
Lingual lipase
Stomach
Gastric lipase
Small intestines
Bile
Pancreatic lipase
Micelle formation
Figure 2.12 Triglyceride digestion. Most triglyceride digestion takes place in the small intestine.
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Fats: Absorption
Occurs in small intestine
Mechanism
Passive diffusion
Very little fat makes it to large intestine
Steatorrhea
Crohn’s disease
Cystic fibrosis
Figure 2.13 Summary of lipid absorption.
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Fats: After Absorption
Transport
Lymph
Chylomicrons
Blood
Cellular uptake
Lipoprotein lipase
Fates
Storage
Energy
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Proteins: Digestion
Mouth
Mastication
Stomach
Churning
Acid denaturation
Small intestine
Proteases
Peptidases
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Proteins: Absorption
Occurs in small intestine
Mechanism
Facilitated diffusion
Active transport
Very little makes it to large intestine
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Proteins: After Absorption
Transport
Blood
Become part of amino acid pool
Fates
Body proteins
Conversion
Energy
Figure 2.16 Amino acid pool turnover. Cells draw upon their amino acid pools to synthesize new proteins.
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Cellular Protein Synthesis
Transcription
DNA
mRNA
Translation
Transfer RNA
Amino acids
Figure 2.17 Protein synthesis.
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Vitamins, Minerals and Water
Digestion causes release from foods
Absorption occurs in small and large intestines
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.
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What is the body’s source of energy?
Macronutrients
Carbohydrates
Fats
Proteins
Body’s direct energy source
Adenosine triphosphate (ATP)
Figure 2.19 The ADP–ATP cycle. When extracting energy from nutrients, the formation of ATP from ADP + Pi captures energy.
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Adenosine Triphosphate (ATP)
Body’s energy source
Two high-energy bonds
Other phosphates
ADP
AMP
Figure 2.20 ATP, ADP, AMP, and high-energy phosphate bonds. Your body can readily use the energy in high-energy phosphate bonds.
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Cell Structure and Organelles Necessary for ATP Production
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What are the three energy systems?
Phosphagen System
1
Anaerobic Energy System
2
Aerobic Energy System
3
Comparison of the Three Energy Systems
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Metabolic Pathways
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Energy Nutrients
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Cellular ATP Production: The Metabolic Factory
Figure 2.23 Metabolic factory analogy of energy metabolism.
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Phosphagen Energy System
Stores of high-energy phosphates
ATP
Creatine phosphate (CP)
Also known as:
Immediate energy system
ATP-CP system
Figure 2.24 The ATP–CP energy system.
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Anaerobic Energy System
Involves only carbohydrates
Does not require oxygen
Also known as:
Anaerobic glycolysis
Figure 2.28 Anaerobic glycolysis.
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Aerobic Energy System
Involves all macronutrients
Requires oxygen
Also known as:
Oxidative system
Figure 2.29 Aerobic metabolism of the macronutrients.
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Carbohydrate intake impacts protein metabolism
Carbohydrates are an important energy source for the body.
Low CHO intake can result in muscle protein breakdown and loss of muscle mass.
Gluconeogenesis forms glucose from proteins.
Adequate carbohydrate intake spares muscle mass.
Figure 2.34 Gluconeogenesis.
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Energy System Contributions to Activities of Varying Intensity
Energy System Contributions to Activities of Varying Intensity (1 of 5)
The small storage pool of ATP is the source of energy whenever instantaneous energy is needed.
Figure 2.25 The three energy systems work together to meet the energy demands of any level of physical activity.
Energy System Contributions to Activities of Varying Intensity (2 of 5)
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
Energy System Contributions to Activities of Varying Intensity (3 of 5)
During longer-lasting sprint activities of lower intensity (e.g., 800m run), the main supplier is the anaerobic system with help from the phosphagen and aerobic systems.
Figure 2.25 The three energy systems work together to meet the energy demands of any level of physical activity.
Energy System Contributions to Activities of Varying Intensity (4 of 5)
During longer-lasting activities of even lower intensity (e.g., mile run), the main supplier becomes the aerobic system with help from the anaerobic system.
Figure 2.25 The three energy systems work together to meet the energy demands of any level of physical activity.
Energy System Contributions to Activities of Varying Intensity (5 of 5)
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.
Figure 2.25 The three energy systems work together to meet the energy demands of any level of physical activity.
Summary:
The Energy Systems Work Together to Meet ATP Demand
Reproduced with permission of McGraw-Hill Education LLC from Bowers RW, Fox EL. Sports Physiology, 3rd ed. Dubuque, IA: William C Brown Publishers; 1992, p. 34.
Figure 2.26 ATP contribution of the three energy systems to maximally sustained activities of very short, high-intensity exercise, such as the shot put (i.e., left margin of graph), to low-intensity maximally sustained exercise lasting longer than 3 minutes, such as running a marathon (i.e., right margin).
