Human Anatomy & Physiology Chapter 24 - Metabolism & Nutrition

Human Anatomy & Physiology - Chapter 24: Metabolism & Nutrition Part 1

Nutrients

  • Definition: A molecule obtained from food that the body requires for metabolic processes.

Macronutrients

  • Characteristics:

    • Required in large amounts.

    • Make up the bulk of our diet.

    • Includes proteins, carbohydrates, lipids (note: water is not a nutrient).

Summary of Macronutrients

  • Class: Nutrient Type

    • Sources (Examples): Food sources of each macronutrient.

    • Adult Recommendation: Recommended percentage of caloric intake.

    • Carbohydrates: Fruits, rice, pasta, meat, vegetables; should constitute 45-65% of caloric intake.

    • Lipids: Meats, dairy, plant oils; should constitute <30% of caloric intake.

Micronutrients

  • Definition: Vitamins and minerals required in small amounts.

    • Vitamins: Organic compounds necessary for metabolic processes.

    • Minerals: Any element required by living organisms other than C, H, O, N.

Essential Nutrients

  • Definition: Nutrients that must be obtained from the diet as the body cannot synthesize them.

  • Includes:

    • 9 essential amino acids.

    • 2 essential lipids.

    • Most vitamins.

    • All minerals.

Proteins

  • Amino Acids:

    • 11 non-essential amino acids.

    • 9 essential amino acids.

  • Complete Proteins: Supply all essential amino acids.

    • Most animal proteins are complete; notable plant exceptions include soy and quinoa.

    • A vegetarian diet can provide all 9 essential amino acids; sources include nuts and legumes, though these are generally not complete proteins.

Lipids

Saturated Fats

  • Characteristics:

    • All C atoms joined by single bonds (no double bonds).

    • Typically animal lipids.

    • Tend to be solid at room temperature.

    • High levels associated with high blood cholesterol and cardiovascular disease.

Unsaturated Fats

  • Characteristics:

    • C atoms joined by double bonds (monounsaturated or polyunsaturated).

    • Mostly plant oils.

    • Considered healthier than saturated fats; however, overconsumption can lead to obesity and related health issues.

Essential Fatty Acids

  • Types:

    • Linoleic acid.

    • Linolenic acid.

  • Sources: Both are found in most plant oils; linolenic acid is also found in fish oil.

Carbohydrates

Complex Carbohydrates

  • Description: Polysaccharides like starch; includes fiber (both soluble and insoluble).

  • Importance: Significant source of energy and fiber in a healthy diet.

Soluble Fiber

  • Characteristics:

    • Dissolves in water.

    • Digested by intestinal microbes, producing beneficial fatty acids.

    • Delays gastric emptying.

Insoluble Fiber

  • Characteristics:

    • Does not dissolve in water.

    • Provides bulking; absorbs some water.

    • Helps maintain regular bowel movements.

Minerals

Major Minerals

  • List:

    • Calcium ions (Ca++)

    • Phosphorus (P)

    • Sodium ions (Na+)

    • Chloride (Cl-)

    • Magnesium ions (Mg++)

    • Potassium ions (K+)

    • Sulfur (S)

Trace Minerals

  • List:

    • Zinc (Zn)

    • Iron (Fe)

    • Manganese (Mn)

    • Copper (Cu)

    • Fluoride (F)

    • Iodine (I)

    • Molybdenum (Mo)

    • Chromium (Cr)

    • Selenium (Se)

    • Cobalt (Co)

Summary of Minerals

  • Functions:

    • Calcium ions: Required for bone and tooth synthesis/maintenance, important for nerve function and muscle contraction.

    • Phosphorus: Important component of nucleotides and buffers, required for bone/tooth synthesis.

    • Sodium ions: Important cation in physiological processes, participates in maintaining fluid balance.

    • Symptoms of deficiency for each major mineral include osteoporosis, muscle spasms, and others depending on the mineral involved.

Vitamins

  • Total Number: 13 vitamins.

  • Types:

    • Lipid Soluble Vitamins: A, D, E, K are structurally similar to cholesterol and can be stored in adipose tissues.

    • Water Soluble Vitamins: C and B vitamins; not stored in the body.

Summary of Vitamins

  • Fat-Soluble Vitamins:

    • Vitamin A: Important for low-light vision, immune function; sources include leafy green vegetables. Recommended daily allowance (RDA) is 0.7-0.9 mg.

    • Vitamin D: Required for calcium ion homeostasis; synthesized in skin with sunlight exposure is 15-20 µg.

    • Vitamin E: Antioxidant; dietary sources include vegetable oils, RDA 15 mg.

    • Vitamin K: Necessary for synthesis of clotting factors; sources are leafy greens and produced by intestinal bacteria, RDA 90-120 μg.

  • Water-Soluble Vitamins:

    • Include B1, B2, B3, B5, B6, B7, B9, B12, and C; their functions range from acting as coenzymes in metabolism to having roles in the function of the nervous system.

Hypervitaminosis

  • Definition: Abnormally high levels of vitamins in the body most commonly due to excessive consumption of vitamin supplements.

  • Implications: Can lead to irritability and toxicity.

Metabolic States

Absorptive State

  • Duration: Lasts about 4 hours after a meal.

  • Description: A period characterized by the absorption of nutrients from the digestive tract into the bloodstream.

  • Key Features:

    • Includes an abundance of glucose in the blood.

    • Storage of excess energy primarily as glycogen and lipids.

  • Fate of Absorbed Nutrients:

    • Glucose:

    • Cellular respiration.

    • Glycogenesis (glucose to glycogen).

    • Lipogenesis (glucose to lipids).

    • Lipids: Most are stored in adipose tissue; a small amount may be converted to structural lipids (cholesterol and phospholipids).

    • Amino Acids: Primarily used for protein synthesis, also can provide small amounts of energy.

  • Hormonal Regulation: Insulin is the primary hormone influencing this state, stimulating the conversion of excess nutrients into storage forms (triglycerides, glycogen).

Postabsorptive State

  • Duration: Begins about 4 hours after the last meal.

  • Description: Most anabolic processes slow or stop, requiring the body to maintain blood glucose levels through alternative metabolic pathways.

  • Key Features:

    • Cells in the central nervous system primarily depend on glucose.

    • Red blood cells rely solely on glycolysis.

  • Major Metabolic Processes:

    • Liver functions such as glycolysis, gluconeogenesis, and lipolysis release glucose and fatty acids into the bloodstream.

    • Ketogenesis occurs, particularly with prolonged fasting, where fatty acids are converted into ketone bodies.

  • Protein Catabolism: Breakdown of muscle proteins becomes essential for maintaining blood glucose levels during extended fasting.

Metabolic Reactions

  • Definition: Metabolism is the sum total of all chemical reactions in the body, mediated by enzymes. Each reaction forms part of a metabolic pathway.

Four Basic Processes in Metabolism

  1. Energy Production: Most foods are utilized for energy.

  2. Conversion: Transforming some substances from one form to another.

  3. Synthesis of Polymers (Anabolism): Building larger molecules from subunits.

  4. Decomposition of Polymers (Catabolism): Breaking down larger molecules into their components.

Catabolic Reactions

  • Definition: Reactions that break large molecules down into smaller ones, typically releasing energy.

  • Energy Utilization: Approximately 40% of the energy released is converted to work; the remainder is lost as heat.

Anabolic Reactions

  • Definition: Reactions that synthesize large molecules from smaller ones and usually require energy.

  • Examples: Protein synthesis and glycogenesis.

Energy Dynamics

  • Exergonic Reactions: Release energy; key in catabolic processes.

  • Endergonic Reactions: Require energy; typical of anabolic processes.

Role of ATP

  • Energy Transfer: ATP plays a crucial role in transferring energy between catabolic and anabolic reactions.

  • ATP Dynamics: Each cell contains about 1 billion ATP molecules that are rapidly utilized and regenerated.

Electron Carriers

  • Function: Molecules that bind high-energy electrons to safely transfer energy during metabolism; found in mitochondrial membranes.

  • Key Electron Carriers:

    • NAD+ (Nicotinamide Adenine Dinucleotide): First accepts electrons from nutrients during catabolism, reduced to NADH.

    • FAD (Flavin Adenine Dinucleotide): Similar role as NAD+; becomes FADH2 when reduced.

Summary of Cellular Energetics

  • ATP Synthesis: ATP is generated through processes that couple the breakdown of nutrients (catabolism) to the formation of ATP (anabolism).

    • Components of Cellular Respiration:

    1. Glycolysis: Breaks down glucose to pyruvate in the cytosol.

    2. Krebs Cycle: Involves the breakdown of Acetyl-CoA in mitochondria; produces ATP and electron carriers.

    3. Electron Transport Chain: Located on mitochondrial membranes where electrons released provide energy to produce more ATP (up to 34 ATP).

Human Anatomy & Physiology - Chapter 27: Metabolism & Nutrition Part 2

Lipid Metabolism

Transport by Lipoproteins

  • Definition: Lipoproteins are special transport structures for lipids, needed because most lipids are not water-soluble and must be transported in plasma.

  • Composition: Outer shell consists of proteins, phospholipids, and cholesterol; proteins determine function; classified based on density.

Types of Lipoproteins

  • Chylomicrons:

    • Least dense; 6-7% cholesterol; primarily transport lipids from intestines to adipose tissues for storage.

  • Very Low-Density Lipoproteins (VLDL):

    • Formed in the liver; 20% cholesterol; primarily transport liver products to adipose storage.

  • Low-Density Lipoproteins (LDL):

    • 50% cholesterol; 75% of blood cholesterol; a high number increases coronary artery disease risk (commonly referred to as “bad cholesterol”).

  • High-Density Lipoproteins (HDL):

    • 20% cholesterol; transport excess cholesterol to the liver for elimination (often referred to as “good cholesterol”).

Blood Cholesterol Levels

  • Most cholesterol produced in the body from lipids; some comes from diet.

  • Implications of High LDL: Increased risk for coronary artery disease.

  • Ways to Increase HDL: Regular exercise, decrease fat intake, and medication.

Fates of Lipids

  • Triglyceride Storage: Forms 98% of energy reserves, convert to glucose or acetyl CoA for ATP production.

  • Structural Lipids: Include cholesterol and phospholipids within cell membranes.

  • Steroid Hormones: Cholesterol is a precursor.

Protein Metabolism

  • Characteristics: Amino acids are not stored; utilized for protein synthesis or converted to glucose/triglycerides or burned for ATP (following conversion).

  • Essential Amino Acids: 9 out of 20 amino acids are essential and must be included in the diet.

  • Transamination: The amine group must be removed before amino acids can be utilized, resulting in ammonia (NH3, which is toxic) that is converted to urea for excretion.

Carbohydrate Metabolism

  • Simple Carbohydrates: Include glucose, fructose, galactose; fructose and galactose are generally converted into glucose in metabolism.

  • ATP Production: Glucose is the most common cellular energy source.

  • Glycogenesis: Glucose can be stored as glycogen in the liver and skeletal muscle.

  • Triglyceride Synthesis: Glucose can also be converted into triglycerides for storage.

Cellular Respiration

  • Overall Reaction: The breakdown of glucose to produce ATP can be summarized as:
    C6H{12}O6 + O2
    ightarrow H2O + CO2 + ATP

  • Stages of Cellular Respiration:

    1. Glycolysis: Takes place in the cytosol, splitting glucose into two 3-carbon pyruvic acid molecules; consumes 2 ATP and generates 4 ATP (net gain = 2 ATP); does not require oxygen.

    2. Krebs Cycle: Occurs in mitochondrial matrix; involves the breakdown of Acetyl-CoA into CO2, H+, and electrons; produces ATP and electron carriers.

    3. Electron Transport Chain: Takes place at the inner mitochondrial membrane, transferring electrons to produce approximately 32 ATP and combined with O2 to generate H2O.

ATP Synthesis Mechanism

  • Energy Storage in Gradients: Energy is stored in the electrochemical gradient (H+) in the intermembrane space of mitochondria, powering ATP synthase to convert ADP and inorganic phosphate (Pi) into ATP.

ATP Yield Calculations

  • Total yield of ATP from cellular respiration can be summarized as:

    • 2 ATP from Glycolysis

    • 2 ATP from Krebs Cycle

    • 34 ATP from the Electron Transport Chain

    • Total: 38 ATP per glucose molecule.

  • Conclusion: These metabolic processes represent crucial pathways through which our body derives energy from nutrients to maintain essential physiological functions.