An Introduction to the Human Body

Fundamentals of Anatomy and Physiology

• Anatomy Defined: Anatomy is the study of structure and the relationships among structures within the body.

• Subdivisions of Anatomy:

  • Surface Anatomy: The study of anatomical landmarks on the exterior surface of the body, accessible by visualization and palpation.
  • Gross Anatomy: The investigation of structures that can be examined without a microscope (macroscopic structures).
  • Systemic Anatomy: The study of the structure of specific organ systems (e.g., cardiovascular or respiratory system).
  • Regional Anatomy: The study of all structures (muscles, nerves, blood vessels, bones) within a specific physical region of the body (e.g., head, chest, or neck).
  • Radiographic Anatomy: The study of body structures using radiographic imaging techniques such as X-rays.
  • Developmental Anatomy: The study of structural changes occurring from fertilization to the adult state.
  • Embryology: A subdiscipline of developmental anatomy focusing on the first eight weeks of development following fertilization of a human egg.
  • Cytology: The microscopic study of individual cellular structures.
  • Pathological Anatomy: The study of structural changes (macroscopic to microscopic) associated with disease.

• Physiology Defined: Physiology is the study of how body structures and organ systems function.

• Subdivisions of Physiology:

  • Cell Physiology: The study of the chemical and molecular functions of individual cells.
  • Systems Physiology: The study of the functional characteristics of specific biological organ systems.
  • Pathophysiology: The study of functional updates or alterations associated with disease and aging.
  • Exercise Physiology: The study of functional changes in cell and organ activities resulting from muscular exertion.
  • Neurophysiology: The study of functional properties of nerve cells and the nervous system.
  • Endocrinology: The study of hormones and how they control body functions via chemical messengers.
  • Cardiovascular Physiology: The study of the functions of the heart and blood vessels.
  • Immunophysiology: The study of how the body defends itself against disease-causing agents.
  • Respiratory Physiology: The study of the functions of the air passageways and lungs.
  • Renal Physiology: The study of kidney functions and urine formation.
  • Reproductive Physiology: The study of reproductive organs and hormonal control of reproduction.

Levels of Structural Organization

• Structural Hierarchy: The human body is organized hierarchically across six distinct levels:
  1. Chemical Level
  2. Cellular Level
  3. Tissue Level
  4. Organ Level
  5. System Level
  6. Organismal Level

• Progression of Organization:   $\text{Chemical Level} \rightarrow \text{Cellular Level} \rightarrow \text{Tissue Level} \rightarrow \text{Organ Level} \rightarrow \text{System Level} \rightarrow \text{Organismal Level}$

Detailed Breakdown of Structural Levels

• Chemical Level:
  • Represents the most basic level of structural organization.
  • Atoms: The smallest units of matter that participate in chemical reactions. Essential biological elements include Carbon ($C$), Hydrogen ($H$), Oxygen ($O$), Nitrogen ($N$), and Phosphorus ($P$).
  • Molecules: Two or more atoms joined together by chemical bonds. Examples include Glucose ($C_6H_{12}O_6$), Molecular Oxygen ($O_2$), and Water ($H_2O$).
  • Macromolecules: Large complex molecular structures formed by combining smaller units. Examples include nucleic acids, proteins, and carbohydrates.

• Cellular Level:
  • Composed of macromolecules combined to form subcellular components and functional structures.
  • A cell is defined as the basic structural and functional unit of life.
  • Specialized internal structures within cells are called organelles.
  • Cell organelles and structural components include:
  • Plasma Membrane: Outer bounding membrane regulating passage of materials into and out of the cell.
  • Nucleus: Cellular control center containing chromatin, nuclear envelope, nuclear pores, nucleoplasm, and the nucleolus.
  • Cytoplasm and Cytoskeleton: Internal fluid medium containing microfilaments and microtubules that provide structural support.
  • Endoplasmic Reticulum (ER):
    • Rough Endoplasmic Reticulum: Studded with fixed ribosomes for protein synthesis.
    • Smooth Endoplasmic Reticulum: Lacks ribosomes; involved in lipid synthesis and metabolic processes.
  • Ribosomes: Free ribosomes, fixed ribosomes, and polyribosomes involved in protein translation.
  • Golgi Apparatus: Modifies, sorts, and packages proteins into secretory vesicles and exocytotic vesicles.
  • Mitochondrion: Powerhouse of the cell, generating ATP through aerobic cellular respiration.
  • Lysosomes and Peroxisomes: Membrane-bound vesicles containing digestive and oxidative enzymes.
  • Centrioles: Specialized structures involved in spindle fiber formation during cell division.
  • Surface Extensions: Cilia and microvilli for cellular movement and fluid handling.
  • Specific cell types in tissues include gastric chief cells (producing digestive enzymes), parietal cells (producing hydrochloric acid), erythrocytes (red blood cells), leukocytes (neutrophils, lymphocytes, monocytes), and platelets.

• Tissue Level:

  • Tissue Defined: Groups of cells and the materials surrounding them that work together to perform specific shared functions.
  • Histology: The scientific study of tissues.
  • Four Primary Tissue Classes:
  1. Epithelial Tissue: Covers body surfaces, lines hollow organs and cavities, and forms glands.
  2. Connective Tissue: Connects, protects, supports, and binds organs together while insulating and transporting fluids.
  3. Muscular Tissue: Contracts to generate physical force and movement.
  4. Nervous Tissue: Detects changes inside and outside the body and transmits nerve impulses to coordinate body activities.

• Organ Level:

  • Organ Defined: Anatomical structures composed of two or more different tissue types that have specific functions and recognizable shapes.
  • Examples of Human Organs:
  • Brain: Primary organ of the central nervous system.
  • Lungs: Primary organs of gas exchange.
  • Stomach: Organ composed of epithelial tissue, smooth muscle tissue layers, and a serous membrane working together to digest food.
  • Heart: Muscular pump propelling blood through the cardiovascular system.

• System Level:

  • System Defined: A collection of related organs that share a common function.
  • An individual organ can belong to more than one system (e.g., the pancreas functions in both the digestive and endocrine systems).

• Organismal Level:

  • The highest structural level, encompassing all functional parts and systems working in coordination.
  • An organism is defined as a complete living being.

Overview of Human Organ Systems

• The 11 Major Human Organ Systems:
  1. Integumentary System:
  • Components: Skin and associated structures including hair, fingernails, toenails, sweat glands, and oil glands.
  • Functions: Protects the body, helps regulate body temperature, eliminates waste, synthesizes vitamin D, detects sensations.

2. Skeletal System:
   • Components: Bones, joints, and associated cartilages.
   • Functions: Supports and protects the body, provides surface area for muscle attachments, aids body movements, houses cells that produce blood cells, stores minerals and lipids.

3. Muscular System:
   • Components: Skeletal muscle tissue and tendons.
   • Functions: Participates in body movements, maintains posture, produces heat.

4. Nervous System:
   • Components: Brain, spinal cord, nerves, and special sense organs.
   • Functions: Generates nerve impulses to regulate body activities, detects changes in internal and external environments, interprets changes, and responds by causing muscular contractions or glandular secretions.

5. Endocrine System:
   • Components: Hormone-producing glands including the pineal gland, pituitary gland, thyroid gland, thymus, adrenal gland, pancreas, ovaries, and testes.
   • Functions: Regulates body activities by releasing hormones (chemical messengers transported by blood to target organs).

6. Cardiovascular System:
   • Components: Blood, heart, and blood vessels (arteries and veins).
   • Functions: Heart pumps blood through blood vessels; blood carries oxygen and nutrients to cells and carbon dioxide/wastes away from cells; helps regulate acid-base balance, temperature, and water content of body fluids.

7. Lymphatic System and Immunity:
   • Components: Lymphatic fluid, lymphatic vessels, spleen, thymus, lymph nodes, tonsils, thoracic duct.
   • Functions: Returns proteins and fluid to blood; carries lipids from gastrointestinal tract to blood; includes structures where lymphocytes mature and proliferate to protect against disease-causing microbes.

8. Respiratory System:
   • Components: Lungs and air passageways including the pharynx, larynx (voice box), trachea (windpipe), and bronchus.
   • Functions: Transfers oxygen from inhaled air to blood and carbon dioxide from blood to exhaled air; helps regulate acid-base balance of body fluids; produces sound via vocal cords.

9. Digestive System:
   • Components: Organs of gastrointestinal tract including mouth, pharynx, esophagus, stomach, small intestine, large intestine, anus; accessory organs including salivary glands, liver, gallbladder, and pancreas.
   • Functions: Achieves physical and chemical breakdown of food; absorbs nutrients; eliminates solid wastes.

10. Urinary System:
    • Components: Kidneys, ureters, urinary bladder, and urethra.
    • Functions: Produces, stores, and eliminates urine; eliminates wastes and regulates volume and chemical composition of blood; maintains body mineral balance and acid-base balance.

11. Reproductive Systems:
    • Female Components: Ovaries, uterine (fallopian) tubes, uterus, vagina, and mammary glands.
    • Male Components: Testes, epididymis, ductus (vas) deferens, seminal vesicles, prostate, and penis.
    • Functions: Gonads produce gametes (sperm or oocytes) that unite to form a new organism; gonads release hormones regulating reproduction and other body processes; associated organs transport and store gametes; mammary glands produce milk.

Basic Life Processes

• Metabolism:

  • The sum of all chemical processes that occur in the body.
  • Catabolism: The breakdown of complex chemical substances into simpler components (e.g., breaking down proteins into amino acids).
  • Anabolism: The building up of complex chemical substances from smaller, simpler components (e.g., synthesizing new proteins from amino acids).

• Responsiveness:

  • The ability to detect and respond to changes in the external or internal environment.
  • Examples include muscle contraction or nerve impulses responding to environmental stimuli.

• Movement:

  • Includes motion of the whole body, individual organs, single cells, or organelles inside cells.

• Growth:

  • Refers to an increase in size and complexity.
  • Achieved by an increase in the number of cells, an increase in the size of cells, or both.

• Differentiation:

  • The change in a cell from an unspecialized state to a specialized state.
  • Primitive unspecialized stem cells differentiate into specialized cells such as red blood cells or muscle cells.

• Reproduction:

  • Refers to either:
  1. The formation of new cells for growth, repair, or replacement.
  2. The production of a new individual organism.

Principles of Homeostasis

• Homeostasis Defined: Homeostasis is a condition of equilibrium in the body’s internal environment produced by the ceaseless interplay of all the body’s regulatory processes.
• Disruptive Factors:
  • External Stimuli: Intense heat, extreme cold, and lack of oxygen.
  • Internal Stimuli: Psychological stresses and physical exercise.
• Nature of Disruptions: Disruptions are usually mild and temporary.
• Regulatory Control: Homeostasis is regulated by the nervous system and endocrine system, acting together or independently via feedback loops.
• Pathological Outcome: If homeostasis is not maintained, death may result.

Feedback Systems and Regulatory Mechanisms

• Components of a Feedback Loop:
  • Receptor: Monitors a controlled condition and sends input (nerve impulses or chemical signals) to a control center.
  • Control Center: Receives input, evaluates it, determines the next action, and provides output (nerve impulses or chemical signals) to effectors.
  • Effector: Receives directions from the control center and produces a response that changes the controlled condition.

• Negative Feedback Systems:
  • A negative feedback system reverses a change in a controlled condition.
  • Homeostasis of Blood Pressure (BP):
  1. Stimulus: A disruption increases blood pressure.
  2. Controlled Condition: Blood pressure.
  3. Receptors: Baroreceptors in certain blood vessels send nerve impulses (input) to the control center.
  4. Control Center: Brain interprets input and sends nerve impulses (output) to the effector.
  5. Effector: Heart.
  6. Response: A decrease in heart rate decreases blood pressure.
  7. Outcome: The activity of the effector produces a result (drop in blood pressure) that opposes the initial stimulus, bringing blood pressure back to normal.

• Positive Feedback Systems:
  • A positive feedback system reinforces or intensifies a change in a controlled condition.
  • Example: Normal Childbirth:
  1. Stimulus/Initial Event: Contractions of wall of uterus force baby's head or body into the cervix.
  2. Controlled Condition: Stretching of cervix.
  3. Receptors: Stretch-sensitive nerve cells in cervix send nerve impulses (input) to control center.
  4. Control Center: Brain interprets input and releases oxytocin (output) into blood.
  5. Effectors: Muscles in wall of uterus contract more forcefully.
  6. Response: Baby's body stretches cervix more, reinforcing the stretching.
  7. Interruption of Cycle: Birth of baby decreases stretching of cervix, breaking the positive feedback cycle.
  • Positive feedback loops are less common than negative feedback loops.

Anatomical Position and Common Regional Terminology

• Standard Anatomical Position:
  • The standardized method of observing or imaging the body that allows precise and consistent anatomical references.
  • Body is standing upright, facing forward, feet flat on the floor, and upper limbs at sides with palms facing forward.
  • Prone Position: Body lying face down.
  • Supine Position: Body lying face up.

• Common Regional Terms:
  • Cephalic (Head):
  • Cranial: Skull
  • Facial: Face, including:
    • Frontal: Forehead
    • Orbital: Eye
    • Otic: Ear
    • Buccal: Cheek
    • Nasal: Nose
    • Oral: Mouth
    • Mental: Chin
  • Occipital: Base of skull
  • Cervical: Neck
  • Trunk:
  • Thoracic: Chest (sternal/breastbone, mammary/breast)
  • Abdomen: Abdominal area (umbilical/navel)
  • Pelvis: Pelvic area (coxal/hip, inguinal/groin, pubic/pubis)
  • Dorsal (Back): Back (scapular/shoulder blade, vertebral/spinal column, lumbar/loin, sacral/between hips, gluteal/buttock)
  • Upper Limb:
  • Axillary: Armpit
  • Brachial: Arm
  • Antecubital: Front of elbow
  • Olecranal: Back of elbow
  • Antebrachial: Forearm
  • Carpal: Wrist
  • Manual: Hand (palmar/palm, digital or phalangeal/fingers, dorsum/back of hand)
  • Lower Limb:
  • Femoral: Thigh
  • Patellar: Anterior surface of knee
  • Popliteal: Hollow behind knee
  • Crural: Leg
  • Sural: Calf
  • Tarsal: Ankle
  • Pedal: Foot (digital or phalangeal/toes, dorsum/top of foot, plantar/sole, calcaneal/heel)

Directional Terms

• Purpose: Directional terms are used to precisely locate one part of the body relative to another and to reduce length of explanations.
• Common Directional Definitions:
  • Superior (Cranial / Cephalic): Toward the head or upper part of a structure.
  • Inferior (Caudal): Away from the head or lower part of a structure (e.g., the stomach is inferior to the heart).
  • Anterior (Ventral): Nearer to or at the front of the body.
  • Posterior (Dorsal): Nearer to or at the back of the body (e.g., the brain is posterior to the forehead).
  • Medial: Nearer to the midline (an imaginary vertical line dividing the body into equal right and left sides).
  • Lateral: Farther from the midline (e.g., the thumb is lateral to the pinky).
  • Proximal: Nearer to the attachment of a limb to the trunk; nearer to origination (e.g., the elbow is proximal to the wrist).
  • Distal: Farther from the attachment of a limb to the trunk; farther from origination.

Anatomical Planes and Sections

• Anatomical Planes: Used to divide the body or organs into definite areas.
• Types of Planes:
  • Midsagittal Plane (Medial Plane): A vertical plane passing longitudinally through the midline, dividing the body or organ into equal right and left halves.
  • Parasagittal Plane: A vertical plane dividing the body or organ into unequal right and left sides.
  • Frontal Plane (Coronal Plane): A vertical plane dividing the body or organ into anterior (front) and posterior (back) portions.
  • Transverse Plane (Cross-Sectional / Horizontal Plane): A horizontal plane dividing the body or organ into superior (upper) and inferior (lower) portions.
  • Oblique Plane: Passes through the body or organ at an angle between a transverse plane and a sagittal or frontal plane.

• Anatomical Sections:
  • Cuts of the body or organs made along specific planes.
  • Includes transverse section, frontal section, and midsagittal section.

Abdominopelvic Regions and Quadrants

• Clinical Purpose: Used to describe precise locations of organs or the source of abdominal and pelvic pain.

• Nine Abdominopelvic Regions:

  • Epigastric Region: Upper central region.
  • Umbilical Region: Central region surrounding navel.
  • Hypogastric (Pubic) Region: Lower central region.
  • Right Hypochondriac Region: Upper right region.
  • Left Hypochondriac Region: Upper left region.
  • Right Lumbar Region: Middle right region.
  • Left Lumbar Region: Middle left region.
  • Right Inguinal Region: Lower right region.
  • Left Inguinal Region: Lower left region.

• Four Abdominopelvic Quadrants:
  • Right Upper Quadrant (RUQ): Right lobe of liver, gallbladder, right kidney, portions of stomach, small and large intestine.
  • Left Upper Quadrant (LUQ): Left lobe of liver, stomach, pancreas, left kidney, spleen, portions of large intestine.
  • Right Lower Quadrant (RLQ): Cecum, appendix, portions of small intestine, reproductive organs (right ovary in female and right spermatic cord in male), right ureter.
  • Left Lower Quadrant (LLQ): Most of small intestine, portions of large intestine, left ureter, reproductive organs (left ovary in female and left spermatic cord in male).

Medical Imaging Technologies

• Medical Imaging Defined: A specialized branch of anatomy and physiology essential for the diagnosis of many disorders.
• Function: Medical imaging techniques allow physicians to peer inside the body to provide clues to abnormal anatomy and deviations from normal physiology in order to help diagnose disease.
• Radiography: A division of medical imaging that includes the use of X-rays.
• Imaging Examples:
  • Computed Tomography (CT Scan): Cross-sectional imaging technique for internal structures.
  • Radiograph (Chest X-Ray): Standard projection technique using ionizing radiation.
  • Magnetic Resonance Imaging (MRI): Imaging modality utilizing magnetic fields and radio waves.
  • Echocardiogram: Ultrasound imaging technique used to observe cardiac chambers and structures.