Chapter 1: The Human Body – An Orientation

Objectives

• Define anatomy and physiology, and describe their subdivisions.

• Use word roots to aid in understanding anatomical terminology.

• Identify the levels of structural organization in the human body and explain their interrelationships.

• List the organ systems of the body and briefly state their functions.

• Use metric units to quantify the dimensions of cells, tissues, and organs.

• Define the anatomical position.

• Use anatomical terminology to describe body directions, regions, and planes.

• Describe the basic structures that humans share with other vertebrates.

• Locate the major body cavities and their subdivisions.

• Name the four quadrants of the abdomen and identify the visceral organs located within each quadrant.

An Overview of Anatomy

Definition and Branches

• Anatomy: The study of structure.

• Physiology: The study of body function.

• Gross (Macroscopic) Anatomy: Study of structures visible to the naked eye.

• Regional Anatomy: Study of all structures in a particular region.

• Systemic Anatomy: Study of body systems.

• Surface Anatomy: Study of internal structures as they relate to the overlying skin.

• Microscopic Anatomy: Study of structures too small to be seen with the naked eye (includes cytology and histology).

• Developmental Anatomy: Study of structural changes throughout the lifespan.

• Embryology: Study of developmental changes before birth.

• Pathological Anatomy: Study of structural changes caused by disease.

• Radiographic Anatomy: Study of internal structures using imaging techniques.

• Functional Morphology: Study of functional properties of body structures.

The Hierarchy of Structural Organization

Levels of Organization

• Chemical Level: Atoms combine to form molecules.

• Cellular Level: Cells and their functional subunits.

• Tissue Level: Groups of similar cells performing a common function.

• Organ Level: Discrete structures made up of more than one tissue.

• Organ System Level: Organs working together for a common purpose.

• Organismal Level: The result of all simpler levels working in unison.

Overview of Organ Systems

Integumentary System

• Forms the external body covering.

• Protects deeper tissues from injury.

• Synthesizes vitamin D.

• Site of cutaneous receptors (pain, pressure, etc.), sweat, and oil glands.

Skeletal System

• Protects and supports body organs.

• Provides a framework for muscles.

• Blood cells formed within bones.

• Stores minerals.

Muscular System

• Allows manipulation of the environment, locomotion, and facial expression.

• Maintains posture.

• Produces heat.

Nervous System

• Fast-acting control system.

• Activates muscles and glands.

Endocrine System

• Glands secrete hormones that regulate growth, reproduction, and nutrient use.

Cardiovascular System

• Blood vessels transport blood, carrying oxygen, carbon dioxide, nutrients, and wastes.

• Heart pumps blood through blood vessels.

Lymphatic System/Immunity

• Picks up fluid leaked from blood vessels and returns it to blood.

• Disposes of debris in the lymphatic system.

• Houses white blood cells (lymphocytes).

• Mounts attack against foreign substances in the body.

Respiratory System

• Keeps blood supplied with oxygen.

• Removes carbon dioxide.

• Gas exchange occurs through walls of air sacs in the lungs.

Digestive System

• Breaks down food into absorbable units.

• Indigestible foodstuffs eliminated as feces.

Urinary System

• Eliminates nitrogenous wastes.

• Regulates water, electrolyte, and acid-base balance of the blood.

Male and Female Reproductive Systems

• Overall function is to produce offspring.

• Testes produce sperm and male sex hormones; ducts and glands aid in delivery of sperm.

• Ovaries produce eggs and female sex hormones; structures serve as sites for fertilization and development of the fetus.

• Mammary glands produce milk.

Measurement & Terminology

• The metric system is used in anatomy (meter, centimeter, micrometer, kilogram, gram).

• Terminology is based on ancient Greek or Latin, providing standard nomenclature worldwide.

Gross Anatomy—An Introduction

Anatomical Position

• Standard reference point for describing body parts and positions.

• Body erect, feet slightly apart, eyes forward, palms facing anteriorly with thumbs pointed away from the body.

• Directional terms always refer to the body in this position.

• Right and left refer to the body being viewed, not those of the observer.

Regional Terms

• Axial region: Head, neck, and trunk.

• Appendicular region: Limbs (arms and legs).

Directional Terms

• Directional terms are paired with opposites:

  • Superior / Inferior

  • Anterior (Ventral) / Posterior (Dorsal)

  • Medial / Lateral

  • Proximal / Distal

  • Superficial / Deep

Body Planes and Sections

• Body plane: Flat surface along which the body or structure may be cut for anatomical study.

• Section: Cut made along a body plane.

• Sagittal plane: Divides the body into right and left parts.

• Median (midsagittal) plane: Lies exactly in the midline.

• Frontal (coronal) plane: Divides the body into anterior and posterior parts.

• Transverse (horizontal) plane: Divides the body into superior and inferior parts.

Anatomical Variability

• Most anatomical structures match textbook descriptions, but variations exist (e.g., nerve or blood vessel location, presence/absence of small muscles).

• Extreme variations are rare and often incompatible with life.

Body Cavities

• Body cavities are closed spaces that protect organs and allow for organ movement and growth.

• Dorsal body cavity: Protects the nervous system; includes cranial and vertebral cavities.

• Ventral body cavity: Houses internal organs (viscera); includes thoracic and abdominopelvic cavities.

• Thoracic cavity: Contains lungs (pleural cavities) and heart (pericardial cavity within the mediastinum).

• Abdominopelvic cavity: Subdivided into abdominal cavity (liver, stomach, kidneys, etc.) and pelvic cavity (bladder, reproductive organs, rectum).

• The diaphragm separates the thoracic and abdominopelvic cavities.

Body Cavities and Membranes

• Serous cavities: Slit-like spaces lined by a thin, double-layered serous membrane.

• Parietal serosa: Lines the outer wall of the cavity.

• Visceral serosa: Covers the organs within the cavity.

• Serous fluid: Produced by both layers, reduces friction between moving organs.

Abdominal Quadrants

• The abdomen is divided into four quadrants for clinical reference:

  • Right Upper Quadrant (RUQ)

  • Left Upper Quadrant (LUQ)

  • Right Lower Quadrant (RLQ)

  • Left Lower Quadrant (LLQ)

• Each quadrant contains specific visceral organs (e.g., liver in RUQ, stomach in LUQ).

Table: Orientation and Directional Terms

Example: Application of Anatomical Terms

• The heart is medial to the lungs.

• The fingers are distal to the elbow.

• The skin is superficial to the skeletal muscles.

Additional info: Some details, such as the specific contents of abdominal quadrants and the full list of directional terms, have been expanded for academic completeness.