Introduction to Human Anatomy and Physiology

Origins of Medical Science

  • Early healers relied heavily on superstition and magic to explain health and illness.

  • Development progressed through the observation of injuries, the healing process of wounds, and the examination of dead bodies.

  • This evolution led to experimentation and the development of specialized terminology for anatomy and physiology.

  • The study of corpses and the practice of cadaver dissection eventually provided foundational knowledge of the human body structure.

  • Historical Illustration: The 1543 Vesalius Illustration is a classic example of early anatomical study.

Anatomy and Physiology

  • Anatomy: The study of the structure or morphology of the human body and its various parts.

    • Etymology: Derived from the Greek word for "a cutting up."

  • Physiology: The study of the functions of the human body and its parts.

    • Etymology: Derived from the Greek word for "relationship to nature."

  • Key Principle: The structure of organs and parts of the human body determines their specific function.

Levels of Organization

All materials (living and non-living) are composed of chemicals consisting of atoms. The hierarchy of complexity is organized as follows:

  • Subatomic Particles: Protons, neutrons, and electrons that constitute atoms.

  • Atom: Tiny particles representing the basic unit of a chemical (e.g., hydrogen, carbon).

  • Molecule: Particles composed of two or more atoms joined together (e.g., water, glucose).

  • Macromolecule: Large particles consisting of many joined molecules (e.g., DNADNA, protein).

  • Organelle: A functional part of a cell (e.g., mitochondrion, lysosome).

  • Cell: The basic unit of structure and function in the body (e.g., muscle, nerve, or blood cell).

  • Tissue: A layer or mass of cells that perform a specific function (e.g., adipose tissue).

  • Organ: A group of different tissues that work together to perform a function (e.g., heart, kidney, stomach).

  • Organ System: A group of organs that share a common function (e.g., digestive system).

  • Organism: The highest level of organization, composed of interacting organ systems (e.g., human).

Clinical Applications of Medical Imaging

Noninvasive procedures allow for the visualization of internal structures without surgery:

  • Ultrasound: Employs high-frequency sound waves to provide images of soft internal structures; commonly used to produce sonograms of a fetus in the uterus.

  • Magnetic Resonance (MR) Scan: Uses a magnetic field to change the alignment and spin of specific atoms; provides high-resolution images of internal structures, such as the brain.

Core Themes of Anatomy and Physiology

Key Concepts:

  • The Cell: All living things are composed of cells.

  • Internal Environment: The environment found within the body.

  • Homeostasis: The maintenance of a relatively constant internal environment.

  • Interdependency of Cells: Living cells depend on one another for survival.

  • Structure and Function: These two aspects are fundamentally interrelated.

Mechanisms and Processes:

  • Gradients and Permeability: Substances move from high to low areas (down pressure and concentration gradients) across permeable membranes.

  • Cellular Differentiation: The specialization of cells through specific gene expression.

  • Cell Membrane Mechanisms: Determine which substances enter the cell and how the cell responds to signals.

  • Cell-to-Cell Communication: Facilitated through membrane receptors.

  • Feedback Loops: Homeostatic mechanisms used to maintain stability.

  • Balance: Involves the replacement of lost substances and the elimination of excesses.

  • Energy Processes: Provide the necessary energy to keep cells active.

Characteristics of Life

Living organisms exhibit the following traits:

  • Growth: Increase in the number and size of cells, resulting in a larger body size.

  • Reproduction: The production of new cells and new organisms.

  • Responsiveness: The ability to react to changes occurring inside or outside the body.

  • Movement: Change in body position or location; also includes the motion of internal organs.

  • Metabolism: The sum of all chemical reactions within a living system, encompassing energy production and nutrient cycling.

  • Respiration: The process of making energy; most organisms take in oxygen (O2O_2) and release carbon dioxide (CO2CO_2).

  • Digestion: Breaking down food into usable nutrients for absorption into the bloodstream.

  • Circulation: The movement of chemicals and cells through body fluids.

  • Excretion: The removal of metabolic waste products.

Environmental Requirements of Organisms

Life depends on five critical environmental factors:

  • Water: The most abundant substance in the body; provides the environment for metabolic processes (intracellular and extracellular fluids); necessary for transport and temperature regulation.

  • Food: Supplies the nutrients needed for energy.

  • Oxygen (O2O_2): Essential for releasing energy from food.

  • Heat: A form of energy that helps maintain body temperature and controls the rate of metabolic reactions.

  • Pressure: The application of force. Atmospheric pressure is vital for breathing, while hydrostatic (blood) pressure keeps blood flowing through the body.

Fluids and Chemicals:

  • Intracellular Fluid: Fluid located within the cells.

  • Extracellular Fluid: Comprised of interstitial fluid (outside cells) and blood plasma.

Homeostasis and Feedback Mechanisms

Homeostasis is the maintenance of a stable internal environment via self-regulating homeostatic mechanisms.

Components of a Homeostatic Mechanism:

  • Receptor: Detects a stimulus and provides information about changes in the internal environment.

  • Control Center: The decision-maker that evaluates the information and maintains the "set point."

  • Effector: A muscle or gland that responds to the control center to cause the necessary change.

Negative Feedback:

  • The most common homeostatic mechanism.

  • Effectors return conditions toward the normal range, and the deviation from the set point decreases.

  • Termed "negative" because the response moves the variable in the opposite direction of the deviation.

  • Function: Prevents sudden, severe changes in the body.

  • Examples: Regulation of body temperature (37 ∘C37\,^{\circ}C or 98.6 ∘F98.6\,^{\circ}F), blood pressure, and glucose levels.

Positive Feedback:

  • An uncommon mechanism where the deviation from the set point is intensified rather than reversed.

  • The activity of the effector is initially increased.

  • Conditions are short-lived and produce unstable states that eventually lead back to homeostasis.

  • Examples: Blood clotting and uterine contractions during childbirth.

Organization of the Human Body

Main Portions:

  • Axial Portion: Includes the head, neck, and trunk.

  • Appendicular Portion: Includes the upper and lower limbs.

Major Axial Body Cavities:

  • Cranial Cavity: Houses the brain.

  • Vertebral Canal (Spinal Cavity): Contains the spinal cord.

  • Thoracic Cavity: Houses lungs and thoracic viscera.

  • Abdominopelvic Cavity: Contains the abdominal and pelvic viscera.

Cavity Subdivisions and Separations:

  • Diaphragm: The muscle separating the thoracic and abdominopelvic cavities.

  • Mediastinum: The region between the lungs containing the heart, esophagus, trachea, and thymus gland.

  • Abdominal Cavity: Extends from the diaphragm to the top of the pelvis; contains the stomach, liver, spleen, kidneys, and most of the small and large intestines.

  • Pelvic Cavity: Enclosed by pelvic bones; contains the end of the large intestine, urinary bladder, and internal reproductive organs.

Small Cavities of the Head:

  • Oral cavity.

  • Nasal cavity (includes frontal and sphenoidal sinuses).

  • Orbital cavities (eyes).

  • Middle ear cavities.

Thoracic and Abdominopelvic Membranes

These cavities are lined by double-layered serous membranes that secrete slippery serous fluid to reduce friction.

  • Visceral Layer: The inner layer covering an organ.

  • Parietal Layer: The outer layer lining the wall of the cavity.

Specific Serous Membranes:

  • Pleura: Lines the thorax and covers the lungs (Visceral and Parietal Pleura).

  • Pericardium: Surrounds the heart (Visceral and Parietal Pericardium).

  • Peritoneum: Lines the abdominopelvic cavity and covers its organs (Visceral and Parietal Peritoneum).

Detailed Overview of Organ Systems

  • Integumentary System:

    • Organs: Skin, hair, nails, sweat glands, sebaceous glands.

    • Functions: Protection, temperature regulation, sensory reception, Vitamin D production.

  • Skeletal System:

    • Organs: Bones, ligaments, cartilages.

    • Functions: Framework, protection of soft tissues, muscle attachment, blood cell production, storage of inorganic salts.

  • Muscular System:

    • Organs: Muscles.

    • Functions: Movement, posture maintenance, body heat production.

  • Nervous System:

    • Organs: Brain, spinal cord, nerves, sense organs.

    • Functions: Detection of changes, interpretation of sensory info, stimulation of muscles/glands via neurotransmitters; rapid effects.

  • Endocrine System:

    • Organs: Glands (pituitary, thyroid, parathyroid, adrenal, pancreas, ovaries, testes, pineal, thymus).

    • Functions: Control of metabolic activities via hormones; slow, long-lasting effects.

  • Cardiovascular System:

    • Organs: Heart, arteries, capillaries, veins.

    • Functions: Transport of gases, nutrients, hormones, and wastes.

  • Lymphatic System:

    • Organs: Lymphatic vessels, lymph nodes, thymus, spleen.

    • Functions: Return tissue fluid to blood, transport fats from digestive system, immunity.

  • Digestive System:

    • Organs: Mouth, tongue, teeth, salivary glands, pharynx, esophagus, stomach, liver, gallbladder, pancreas, intestines.

    • Functions: Food breakdown, nutrient absorption, waste excretion.

  • Respiratory System:

    • Organs: Nasal cavity, pharynx, larynx, trachea, bronchi, lungs.

    • Functions: Air movement, gas exchange between air and blood (O2O_2 and CO2CO_2).

  • Urinary System:

    • Organs: Kidneys, ureters, urinary bladder, urethra.

    • Functions: Blood waste removal, water/electrolyte balance, urine production and excretion.

  • Reproductive System:

    • Organs: Male (testes, scrotum, etc.); Female (ovaries, uterus, etc.).

    • Functions: Produce/maintain sex cells (sperm/eggs), hormone production, fetal development, and childbirth.

Lifespan Changes

As the body ages, changes occur from the cellular to the systemic level:

  • Loss of hair pigment (gray/white hair).

  • Skin wrinkles due to decreased subcutaneous fat and stiffness from decreased collagen and elastin.

  • Tissue atrophy and shrinking of organs.

  • Increased body fat percentage.

  • Stiffness in joints.

  • Rise in blood pressure (potential hypertension).

  • Rise in blood glucose (potential Type 2 diabetes mellitus).

  • Decreased metabolic rate and lower production of proteins/enzymes.

  • Diminished cell division as chromosome tips are lost.

  • Potential development of dementia or Alzheimer disease.

Anatomical Positioning and Relative Terms

Anatomical Position: Standing erect, facing forward, upper limbs at sides, palms facing forward. All relative terms assume this position.

Terms of Relative Position:

  • Superior: Above.

  • Inferior: Below.

  • Anterior (Ventral): Toward the front.

  • Posterior (Dorsal): Toward the back.

  • Medial: Toward the midline.

  • Lateral: Away from the midline.

  • Bilateral: Paired structures, one on each side.

  • Ipsilateral: On the same side.

  • Contralateral: On opposite sides.

  • Proximal: Closer to the point of attachment to the trunk.

  • Distal: Farther from the point of attachment to the trunk.

  • Superficial: Close to the surface.

  • Deep: More internal.

Body Planes and Sections

  • Sagittal section: A longitudinal cut dividing the body into left and right.

    • Mid-sagittal (Median): Equal left and right portions.

    • Parasagittal: Unequal portions lateral to the midline.

  • Transverse (Horizontal) section: Divides the body into superior and inferior portions.

  • Coronal (Frontal) section: A longitudinal cut dividing the body into anterior and posterior portions.

Sections of Cylindrical Organs:

  • Cross section: A cut across the structure.

  • Oblique section: An angular cut.

  • Longitudinal section: A lengthwise cut.

Abdominal Regions and Quadrants

9 Abdominal Regions:

  • Epigastric region (upper middle).

  • Umbilical region (center).

  • Pubic region (lower middle).

  • Right/Left hypochondriac regions (upper sides).

  • Right/Left lateral (lumbar) regions (middle sides).

  • Right/Left inguinal (iliac) regions (lower sides).

4 Abdominal Quadrants:

  • Right Upper Quadrant (RUQ).

  • Left Upper Quadrant (LUQ).

  • Right Lower Quadrant (RLQ).

  • Left Lower Quadrant (LLQ).

Anatomical Region Terminology

  • Anterior View: Cephalic (head), Frontal (forehead), Orbital (eye), Otic (ear), Nasal (nose), Oral (mouth), Buccal (cheek), Mental (chin), Cervical (neck), Sternal, Acromial (shoulder point), Axillary (armpit), Pectoral (chest), Mammary (breast), Brachial (arm), Antecubital (front of elbow), Antebrachial (forearm), Abdominal, Umbilical (navel), Coxal (hip), Carpal (wrist), Palmar (palm), Digital (finger/toe), Inguinal (groin), Genital, Femoral (thigh), Patellar (knee front), Crural (leg), Tarsal (ankle), Pedal (foot).

  • Posterior View: Occipital (back of head), Vertebral (spinal column), Dorsal (back), Lumbar (lower back), Sacral (between hips), Gluteal (buttocks), Perineal (between anus and genitalia), Popliteal (back of knee), Sural (calf), Calcaneal (heel), Plantar (sole).