2. Human Body
Introduction to Human Body and Functional Foods
The Greek physician Hippocrates stated, "Let food be thy medicine and medicine be thy food," a principle central to understanding the connection between dietary choices and overall health.
Functional foods are defined by the Academy of Nutrition and Dietetics as whole foods and fortified, enriched, or enhanced foods that have potentially beneficial effects on health when consumed as part of a varied diet on a regular basis at effective levels.
Probiotics serve as prime examples of functional foods:
Kefir reduces symptoms of lactose intolerance and can ward off virally caused diarrhea.
Additional probiotic foods include yogurt, kimchi, kombucha, and sauerkraut, many of which are produced through fermentation.
Probiotic supplements positively influence intestinal microbial flora (gut microflora), which directly enhances immune system function and aids in illness prevention.
Cell Theory, Cellular Structure, and Macromolecules
A living organism conducts self-sustaining biological processes, with the cell defined as the smallest and most basic form of life.
The Cell Theory incorporates three fundamental principles:
Cells are the most basic building units of life. All living things are composed of cells, and new cells arise from preexisting cells that divide in two. Human development begins when two cells containing complete genetic information (DNA) unite in the womb, subsequently dividing and differentiating into blood, blood vessels, bones, tissues, skin, and organ systems, resulting in trillions of cells in an adult.
Independent single-celled organisms must perform all essential biological processes of life: energy capture (nutrient intake), waste excretion, environmental detection and response, movement, respiration (breathing), growth, and reproduction.
Structurally and functionally complex, a cell operates as a mini-organism composed of functional subunits called organelles.
Macromolecules and Chemical Structure:
Oxygen and hydrogen atoms bond to form water molecules.
The carbon atom is known as the backbone of life due to its ability to readily bond with four other elements to form long chains and complex macromolecules.
Four primary macromolecules form all structural and functional cell units: carbohydrates, lipids, proteins, and nucleic acids.
Animal Cell Organelles:
Nucleus: Houses genetic material (DNA).
Mitochondria: Generate cellular energy.
Ribosomes: Synthesize proteins.
Endoplasmic Reticulum: Serves as a packaging and transport facility.
Golgi Apparatus: Distributes macromolecules.
Lysosomes and Peroxisomes: Act as digestive pouches that break down macromolecules and destroy foreign invaders.
Cytoskeleton: Anchors organelles within the cell cytoplasm.
Plasma Membrane: Isolates organelles from the surrounding environment.
Levels of Biological Organization
Cells represent the basic structural and functional units of life (e.g., red blood cells, nerve cells). Although all cells in an individual contain identical DNA, each cell expresses only the genetic codes relevant to its specific structure and function.
Tissues consist of groups of cells sharing a common structure and function working together. The four basic human tissue types are:
Connective Tissue: Connects other tissues.
Epithelial Tissue: Lines and protects organs.
Muscle Tissue: Contracts to provide movement and structural support.
Nerve Tissue: Responds and reacts to environmental signals.
Organs consist of groups of tissues arranged in a specific manner to support a common physiological function (e.g., brain, liver, heart).
Organ Systems consist of two or more organs working together to support specific physiological functions. The human body contains distinct organ systems.
Organisms represent the complete living system capable of conducting all biological processes of life.
Anatomy and Physiology of the Digestive System
The digestive system is composed of hollow, tube-shaped organs: mouth, pharynx, esophagus, stomach, small intestine, large intestine (colon), rectum, and anus.
The digestive tract is lined with mucosal tissue that secretes digestive juices and protective mucus, facilitating the propulsion of food. Smooth muscle tissue surrounding the tract undergoes involuntary contractions known as peristalsis to move food along.
Digestion operates across two functional levels: mechanical (moving and mixing ingested food) and chemical (breaking down large molecules).
The Four Steps of Digestion:
Ingestion: Intake of food into the digestive tract. Cephalic responses (sight and smell) trigger brain signaling to initiate salivation prior to consumption.
Mechanical and Chemical Breakdown: Begins in the mouth. Chemical digestion utilizes enzymes such as salivary amylase to break large starch molecules into smaller components.
Nutrient Absorption (Stomach to Small Intestine):
In the stomach, peristaltic contractions turn food into chyme (a semi-liquid mass of partially digested food mixed with gastric juices containing hydrochloric acid and the enzyme pepsin for protein breakdown).
High-fat or high-protein meals require longer breakdown times than carbohydrate-rich meals before emptying into the small intestine.
Step 3 occurs predominantly in the small intestine (ileum), which features a massive surface area expanded by circular folds, villi, and microvilli.
Water-soluble nutrients (amino acids, short-chain fatty acids, monosaccharides) pass through absorptive cells via diffusion or transport proteins directly into capillaries.
Lipid-soluble nutrients (larger fatty acids, fat-soluble vitamins, other lipids) pass first into lymphatic vessels before entering the bloodstream.
Incomplete breakdown accounts for less than of consumed food, which then passes into the large intestine.
Elimination: Indigestible food components and fiber enter the large intestine (colon) through a connecting valve.
Transit time spans a few hours in the stomach, in the small intestine, and approximately in the large intestine.
Resident colonic bacteria break down remaining contents without further organ-driven mechanical or chemical digestion.
Feces consists of indigestible food matter and gut bacteria (which makes up almost of fecal mass), stored in the rectum until expulsion through the anus via defecation.
Nutrient Absorption, Transport, and Liver Functions
Water-soluble nutrients enter the bloodstream and travel directly to the liver via the hepatic portal vein.
Metabolic homeostasis occurs when consumed and absorbed nutrients match the energy required for biological processes ().
Lipid transport utilizes the lymphatic system—a one-way system of vessels carrying lymph (a fluid rich in white blood cells and lipid-soluble substances). Lymph travels slowly through lymphatic vessels and empties into blood vessels in the upper chest area for body-wide delivery.
The liver is the sole organ capable of exporting nutrients for energy production to other tissues:
Fasted State (between meals): The liver exports stored nutrients into circulation.
Fed State (post-meal): The liver stores incoming nutrients within its tissue.
Adipose tissue stores fat during the fed state and mobilizes fat components to deliver energy to other body regions when needed.
Energy-supplying macronutrients—carbohydrates, fats, and proteins—fuel all organ systems.
Cardiovascular System and Blood Physiology
Primary Function: Transports nutrients to cells and removes metabolic wastes from cells.
Nutrient Vascular Route: Small intestine Hepatic portal vein Liver Inferior vena cava Heart Lungs (oxygenation) Arteries Capillaries (where reduced vessel diameter dramatically slows blood flow, permitting nutrient harvest and waste exchange with tissues).
Physical Properties of Blood:
Volume: Approximately (), comprising roughly of total human body weight.
Composition: water and solids by volume.
Plasma: Liquid portion containing water alongside proteins, ions, glucose, lipids, vitamins, minerals, waste products, gases, enzymes, and hormones.
Albumin: High-concentration plasma protein that maintains fluid balance between blood and tissues and stabilizes blood pH.
Temperature Regulation: High water content distributes heat throughout the body; specialized nasal capillary networks warm frigid air to body temperature before it reaches the lungs.
Cellular Components of Blood:
Red Blood Cells (Erythrocytes): Most abundant cellular component. Contain approximately hemoglobin proteins bound to iron, which turns red when oxygenated. Transport oxygen from lungs to cells for energy production via aerobic metabolism. Lifespan is approximately .
White Blood Cells (Leukocytes): Part of the immune system; survey tissues for pathogens. Represent roughly of blood volume. Lifespan ranges from to or longer.
Platelets: Cell fragments that initiate clotting at sites of vessel injury. Lifespan is approximately .
Blood components are continuously synthesized from stem cells located in bone marrow.
Central Nervous System
Composed of the brain, spinal cord, and nerve bundles, with neurons serving as the primary structural units.
Function: Senses environmental changes and initiates physiological reactions.
Neurotransmitters are chemical messengers built from dietary amino acids that allow neuronal communication.
Energy Fuel: Glucose is the brain's primary fuel source, utilized almost exclusively except under conditions of extreme starvation.
High Blood Glucose Risks: Chronically elevated blood glucose levels cause cognitive impairment, damage brain cells, and substantially increase the risk of developing Alzheimer's disease.
Respiratory System
Primary Functions: Supplies oxygen for cellular respiration, removes carbon dioxide, and assists in maintaining acid-base balance. Non-vital functions include olfaction, speech production, and straining (coughing, childbirth).
Functional Zones:
Conducting Zone: Provides a conduit for incoming and outgoing air, removes debris and pathogens, and warms/humidifies air. Includes the nose, pharynx, larynx, trachea, and bronchi.
Respiratory Zone: Direct site of gas exchange. Begins where terminal bronchioles join respiratory bronchioles, continuing to alveolar ducts and clusters of alveoli (grape-like air sacs).
Lung Anatomy and Pulmonary Circulation:
Paired, pyramid-shaped organs situated in the thoracic cavity above the dome-shaped diaphragm muscle.
Total surface area available for gas exchange across the permeable pulmonary epithelium is approximately 70\,\text{m}^2$.\n - Right lung contains three lobes (superior, middle, inferior); left lung contains two lobes (superior, inferior).\n - Deoxygenated blood travels via the pulmonary artery, branching into capillaries surrounding alveoli where \text{CO}_2\text{O}_2 is absorbed. Oxygenated blood returns to the heart via pulmonary veins.\n\n# Endocrine System\n\n- Regulates appetite, nutrient absorption, storage, usage, and reproductive processes.\n- Primary Endocrine Glands: Pituitary, thyroid, parathyroid, adrenals, thymus, pineal, pancreas, ovaries, and testes.\n- Pathophysiology of Type 2 Diabetes:\n - Chronic overconsumption of high-fat and high-sugar foods induces insulin resistance in muscle, fat, and liver cells.\n - Resistant cells fail to respond to insulin signaling, resulting in persistent elevations of blood glucose and fatty acids.\n - Sustained hyperglycemia and hyperlipidemia cause systemic vascular and tissue damage, raising risks for cardiovascular disease, kidney disease, nerve damage, and ocular pathology.\n\n# Urinary System\n\n- Functions: Cleanses blood, excretes metabolic waste products, regulates blood pH (alongside lungs and blood buffers), regulates blood pressure (alongside heart and blood vessels), regulates erythrocyte concentration, and performs the final synthesis step of active vitamin D.\n- Stores urine in the bladder prior to voluntary neurological release and anatomical excretion.\n- Hydration Status: Reflected by urine color and odor; high activity or sweating concentrates urine, resulting in darker color and distinct odor despite fluid intake.\n\n# Muscular System\n\n- Controls voluntary movement and involuntary tissue contractions (e.g., cardiac contraction, GI peristalsis, vascular smooth muscle constriction).\n- Composed of over 600 skeletal muscles, cardiac muscle, and smooth muscle layers throughout the alimentary canal and arterial walls.\n- Energy Storage and Fuel Flexibility:\n - Muscle stores glucose as the carbohydrate polymer glycogen.\n - Unlike the liver, muscle tissue cannot export glucose into circulation and uses its glycogen reserves exclusively for internal cellular work.\n - Muscle tissue readily utilizes alternative fuel sources, such as fatty acids and amino acids, when blood glucose levels fall.\n\n# Skeletal System and Bone Remodeling\n\n- Composed of 206 bones linked by connective tissues:\n - Ligaments: Connect bone to bone.\n - Tendons: Connect muscle to bone.\n - Cartilage: Provides joint cushioning and structural flexibility.\n- Key Functions: Supports structural integrity, protects organs (cranium protects brain/eyes/ears; rib cage protects heart/lungs), synthesizes blood cells within marrow, and acts as a mineral reservoir for calcium, phosphorus, and magnesium.\n- Bone Matrix Composition:\n - Inorganic Portion (65\%): Mineralized crystal matrix providing structural rigidity.\n - Organic Portion (35\%): Fibrous collagen protein network offering strength and flexibility.\n- Structural Tissue Types:\n - Trabecular (Spongy/Cancellous) Bone: 50\text{ to }90\%20\% of the adult skeleton; located at long bone ends, vertebral cores, and the pelvis.\n - Cortical (Compact) Bone: Highly dense (10\%80\% of the adult skeleton, forming the exterior layer of bones and the entire shaft of long bones.\n- Membrane and Marrow Organization: Surrounding outer membrane (periosteum) contains connective tissue, blood vessels, and nerves, overlying cortical bone, trabecular bone, and internal bone marrow.\n- Bone Dynamics Across Life Stages:\n - Growth and Modeling: Occurs in infancy, childhood, and adolescence (bone tissue dismantled at one site and built at another). In the first year of life, nearly 100\% of skeletal tissue is replaced.\n - Remodeling: In adulthood, growth ceases, but remodeling persists (degradation and rebuilding at the exact same site). Approximately 10\% of adult bone tissue is remodeled annually.\n - Wolff's Law: Bones adapt their architecture to withstand mechanical strain; weight-bearing exercise directly enhances bone mineral density and strength.\n - Essential Bone Nutrients: Calcium, phosphorus, magnesium, fluoride, vitamin D, and vitamin K.\n - Bone Mineral Density (BMD): Quantitative measure of calcified tissue expressed in \text{g/cm}^2, clinically evaluated via Dual-Energy X-ray Absorptiometry (DEXA) to predict fracture risk.\n\n# Immune System and Nutrition\n\n- Defense Mechanisms: Composed of circulating white blood cells, physical skin barriers, entrapment mucus, and intestinal flora that prevent pathogen colonization.\n- Malnutrition Impact: World's leading cause of acquired immune deficiency. Deficiencies in iron, zinc, selenium, copper, folate, and vitamins A, B6, C, D, and E significantly impair immunity and elevate infection and mortality risks.\n- Specific Role of Zinc: Deficiency damages skin cells, compromises physical barrier functions, and reduces circulating white blood cell counts. Supplemental zinc demonstrates therapeutic efficacy in treating leprosy, tuberculosis, pneumonia, and the common cold.\n- Overnutrition Impact: Obesity elevates systemic inflammation and increases susceptibility to immune disorders, including asthma, rheumatoid arthritis, and specific malignancies.\n- Dietary Fats and Immunity: High saturated and trans fat intakes suppress immune function, whereas omega-3 fatty acids (found in salmon and oily fish) suppress inflammatory responses and reduce autoimmune disease severity (e.g., rheumatoid arthritis).\n\n# Health Indicators: Body Mass Index, Fat Composition, and Fat Distribution\n\n- Diagnostic Definitions:\n - Overweight: Excess body weight relative to height stemming from water, muscle, or fat mass.\n - Obesity: Excess accumulation of body fat specifically.\n- Body Mass Index (BMI):\n - Formula utilizing mass and height measurements to categorize risk:\n - Underweight: \text{BMI} < 18.5\n - Overweight: \text{BMI} > 25\n - Obese: \text{BMI} > 30\n - Health Risk Variances: Health risks associated with equivalent BMI values vary by ethnicity, with Asians exhibiting highest risk, followed by Caucasians, and African Americans.\n - Limitations: BMI does not measure actual body fat percentage or fat distribution. Muscle tissue is significantly denser than fat tissue (equal weights occupy vastly different volumes).\n- Optimal Body Fat Ranges:\n - Females: 20\text{ to }30\% total body weight as fat (required for reproductive physiology and driven by endocrine profiles).\n - Males: 12\text{ to }20\% total body weight as fat.\n- Methods for Assessing Body Composition:\n 1. Skinfold Test: Health professionals use calipers to measure subcutaneous fat thickness at specified sites; simple, low-cost, and noninvasive.\n 2. Underwater (Hydrostatic) Weighing: Measures volume displacement based on density; bone and muscle weigh more in water than fat tissue.\n 3. Bioelectrical Impedance Analysis (BIA): Measures resistance to low-voltage electrical currents; fat tissue impedes electrical speed more than lean tissue.\n 4. Dual-Energy X-Ray Absorptiometry (DEXA): Emits two low-dose X-ray beams to quantify bone, lean mass, and fat mass.\n- Fat Distribution and Visceral Adiposity:\n - Visceral Fat: Fat stored within the abdominal cavity around organs; secretes inflammatory factors and hormones that substantially increase chronic disease risk.\n - High-Risk Waist Circumferences: Men > 40\,\text{inches}> 35\,\text{inches}.\n - Waist-to-Hip Ratio: Calculated by dividing waist circumference by hip circumference. Apple-shaped fat distribution (abdominal dominance) carries significantly greater disease risk than pear-shaped fat distribution (hip dominance).\n - WHO Abdominal Obesity Cutoffs: Waist-to-hip ratio > 0.90> 0.85$$ for females.