Essentials of Human Anatomy and Physiology: The Human Body Orientation Notes on Human Body Orientation

Anatomy, Physiology, and Pathology Definitions

• Anatomy: The study of the structure and shape of the body and its parts. This discipline utilizes observation to identify the sizes and relationships of various body components.
• Physiology: The study of how the body and its parts work or function.
  • Principle of Complementarity: Structure determines function. For example, the air sacs of the lungs possess extremely thin walls, a structural feature that enables the specific function of gas exchange and oxygen provision to the body.
• Pathology: The study and diagnosis of disease.
  • Clinical Pathology: Involves the examination of surgically removed organs, tissues (biopsy samples), bodily fluids, and, in some cases, the whole body (autopsy).

Levels of Structural Organization

The human body is organized into six hierarchical levels, ranging from the microscopic to the macroscopic:

• Chemical Level: Atoms combine to form molecules.
• Cellular Level: Cells are made up of molecules. An example provided is the smooth muscle cell.
• Tissue Level: Tissues consist of similar types of cells working together. An example is smooth muscle tissue.
• Organ Level: Organs are composed of different types of tissues. For instance, a blood vessel (organ) includes epithelial tissue, smooth muscle tissue, and connective tissue.
• Organ System Level: Organ systems consist of different organs that work together closely, such as the cardiovascular system comprised of the heart and blood vessels.
• Organismal Level: Human organisms are made up of many organ systems integrated to maintain life.

The 11 Organ Systems of the Human Body

1. Integumentary System

• Components: Skin, hair, and fingernails.
• Functions:
  • Forms the external body covering.
  • Waterproofs the body.
  • Acts as a physical barrier against invading pathogens and injury.
  • Produces vitamin D with the assistance of sunlight.
  • Excretes salts in perspiration.
  • Assists in regulating body temperature.
  • Location of cutaneous nerve receptors (pain, pressure, etc.) and sweat and oil glands.

2. Skeletal System

• Components: Bones, cartilages, ligaments, and joints.
• Functions:
  • Provides the body's structural framework.
  • Provides muscle attachment points for movement.
  • Protects vital organs.
  • Serves as the site of blood cell formation (hematopoiesis).
  • Stores minerals.

3. Muscular System

• Components: Skeletal muscles attached to the skeleton.
• Mechanism: Muscles contract (shorten) to move or stabilize bones and parts of the skeleton.
• Functions:
  • Produces movement of bones.
  • Supports and stabilizes body structures.
  • Generates heat as a byproduct of contraction.
  • Allows locomotion, facial expression, and manipulation of the environment.

4. Nervous System

• Components: Brain, spinal cord, nerves, and sensory receptors.
• Mechanism: Uses neurons and chemical messengers called neurotransmitters to send impulses for communication and coordination.
• Functions:
  • Acts as a fast-acting control system.
  • Responds to internal and external stimuli.
  • Sensory receptors detect changes.
  • Messages are sent to the Central Nervous System (CNS).
  • The CNS assesses information and activates effectors (muscles and glands).

5. Endocrine System

• Components: Glands that secrete hormones into the blood.
• Key Glands: Hypothalamus, pituitary gland, thyroid and parathyroids, adrenal glands, thymus, pancreas, pineal gland, and gonads (ovaries in females, testes in males).
• Functions:
  • Regulates and controls bodily functions alongside the Nervous System.
  • Governs growth, reproduction, and the use of nutrients (metabolism).

6. Cardiovascular System

• Components: Heart, blood, and blood vessels.
• Functions:
  • The heart pumps blood.
  • Vessels transport blood to tissues.
  • Blood carries oxygen ($O_2$), carbon dioxide ($CO_2$), nutrients, hormones, and metabolic waste products.

7. Lymphatic System

• Components: Lymph, lymphatic vessels, lymph nodes, and lymphoid organs (Spleen, thymus, and MALT tissue).
• Functions:
  • Picks up fluid leaked from blood vessels into extracellular spaces and returns it to the bloodstream.
  • Absorbs lipids and lipid-soluble vitamins from the digestive tract.
  • Houses white blood cells involved in immunity.
  • Disposes of debris in the lymphatic stream.

8. Respiratory System

• Components: Nasal passages, pharynx, larynx, trachea, bronchi, and lungs.
• Mechanism: Gas exchange occurs through the walls of air sacs called alveoli within the lungs.
• Functions:
  • Supplies the body with necessary oxygen ($O_2$) via absorption.
  • Removes carbon dioxide ($CO_2$) via excretion.

9. Digestive System

• Components: Oral cavity (mouth), esophagus, stomach, small and large intestines, rectum, and accessory organs.
• Functions:
  • Breaks down and digests food into absorbable nutrients.
  • Allows nutrient absorption into the blood for distribution to cells.
  • Eliminates indigestible materials as feces.

10. Urinary System

• Components: Kidneys, ureters, urinary bladder, and urethra.
• Functions:
  • Eliminates nitrogenous wastes.
  • Maintains acid-base balance of the blood.
  • Regulates water and electrolyte balance.
  • Helps regulate blood pressure.

11. Reproductive System

• General Purpose: Production of offspring.
• Male Reproductive System:
  • Components: Testes, scrotum, penis, accessory glands, and duct system.
  • Functions: Testes produce sperm and male sex hormones; the duct system delivers sperm.
• Female Reproductive System:
  • Components: Ovaries, uterine tubes, uterus, vagina, and mammary glands (in breasts).
  • Functions: Ovaries produce eggs and female sex hormones; other structures serve as sites for fertilization and fetal development. Mammary glands produce milk for newborns.

The Language of Anatomy

Anatomical Position

• Definition: A standard body position used to avoid confusion regardless of the actual position of the person.
• Criteria: Stand erect, feet parallel, arms hanging at the sides with palms facing forward and thumbs pointing away from the body.

Directional Terms (Paired Opposites)

• Superior (cranial/cephalic): Toward the head or upper part of a structure; above.
• Inferior (caudal): Away from the head or toward the lower part of a structure; below.
• Anterior (ventral): Toward the front of the body; in front of.
• Posterior (dorsal): Toward the backside of the body; behind.
• Medial: Toward the midline of the body; on the inner side of.
• Lateral: Away from the midline of the body; on the outer side of.
• Intermediate: Between a more medial and a more lateral structure.
• Proximal: Close to the origin of the body part or the point of attachment of a limb to the body trunk.
• Distal: Farther from the origin of a body part or the point of attachment of a limb to the body trunk.
• Superficial (external): Toward or at the body surface.
• Deep (internal): Away from the body surface; more internal.

Usage Notes:

• Caudal is synonymous with inferior only at the inferior end of the spine.
• In humans, anterior and ventral are synonymous, as are posterior and dorsal. In four-legged animals, ventral refers to the belly (inferior surface) and dorsal refers to the back (superior surface).

Regional Terms and The Antecubital Fossa

• Anterior Regional Terms: Cephalic (orbital, nasal, buccal, oral, mental), Cervical, Thoracic (sternal, axillary, pectoral), Abdominal (umbilical), Pelvic (inguinal), Pubic, Upper limb (acromial, deltoid, brachial, antecubital, antebrachial, carpal, manus/digital), Lower limb (coxal, femoral, patellar, crural, fibular, pedal/tarsal/digital).
• Posterior Regional Terms: Cephalic (occipital), Cervical, Back (scapular, vertebral, lumbar, sacral, gluteal), Upper limb (olecranal), Lower limb (popliteal, sural, fibular, calcaneal, plantar).
• Antecubital Fossa: A collection of veins located in the elbow pit (inner arm opposite the elbow). Phlebotomists use this site for the following three veins:
  • Median cubital vein
  • Cephalic vein
  • Basilic vein

Body Planes and Sections

1. Sagittal Section: Divides the body or organ into left and right parts.
   • Midsagittal: Divides into equal left and right parts.
   • Parasagittal: Divides into unequal left and right parts.
2. Frontal (Coronal) Section: Divides the body or organ into anterior and posterior parts.
3. Transverse (Horizontal) Section: Divides the body or organ into superior and inferior parts.

Body Cavities and Subdivisions

Dorsal Body Cavity

Located toward the back of the body; provides protection to the nervous system.

• Cranial Cavity: Houses the brain; protected by the skull.
• Spinal Cavity: Houses the spinal cord; protected by the vertebrae.

Ventral Body Cavity

Located toward the front of the body.

• Thoracic Cavity: Houses the heart and lungs.
• Abdominopelvic Cavity: Houses digestive, urinary, and reproductive organs.
• Separation: The Diaphragm separates the thoracic cavity from the abdominopelvic cavity.

Abdominopelvic Subdivisions

Four Quadrants:

• Right Upper Quadrant (RUQ)
• Left Upper Quadrant (LUQ)
• Right Lower Quadrant (RLQ)
• Left Lower Quadrant (LLQ)

Nine Regions (Anterior View):

• Epigastric Region: Middle upper region above the stomach.
• Right/Left Hypochondriac Regions: Flanking the epigastric region.
• Umbilical Region: Center-most region surrounding the navel.
• Right/Left Lumbar Regions: Flanking the umbilical region.
• Hypogastric (Pubic) Region: Middle lower region below the stomach.
• Right/Left Iliac (Inguinal) Regions: Flanking the hypogastric region.

Homeostasis

• Definition: Maintenance of relatively stable internal conditions; a state of equilibrium necessary for life and normal functioning.
• Control Systems: Predominantly the Nervous and Endocrine systems. A disturbance in homeostasis can result in disease or illness.

Elements of a Homeostatic Control System

1. Receptor: Senses and responds to changes in the environment (stimuli). Sends information to the control center via the afferent (sensory) pathway.
2. Control Center: Determines the set point (optimal values). It analyzes the incoming information, compares it to the set point, and determines the appropriate response.
3. Effector: Typically a muscle or gland. It receives a message from the control center via the efferent (motor) pathway and causes a response to occur.

Feedback Mechanisms

• Negative Feedback: Decreases or inhibits the original stimulus to return the variable toward the normal set point. Most homeostatic mechanisms function this way (e.g., body temperature regulation).
• Positive Feedback: Increases the original stimulus to push the variable further away from the set point. These are rare, fast-acting, and short-lived until a specific goal is reached (e.g., blood clotting, childbirth).

Metabolism

Metabolism refers to the sum of all chemical reactions in the body. It consists of two subdivisions:

• Catabolism: The breakdown of compounds to form energy.
• Anabolism: The buildup of molecules to form structures.
• ATP (Adenosine Triphosphate): The molecule of chemical energy formed during metabolism that allows for cellular function.