Structure and Function of the Human Body

Levels of Structural Organization

The human body is organized into a hierarchy of structural levels, each building upon the previous one. Understanding these levels is fundamental to the study of anatomy and physiology.

• Chemical Level: Atoms and molecules essential for life (e.g., water, proteins).

• Cellular Level: Basic units of life, such as muscle cells or nerve cells.

• Tissue Level: Groups of similar cells performing a common function (e.g., epithelial tissue).

• Organ Level: Structures composed of two or more tissue types (e.g., heart, liver).

• System Level: Groups of organs working together (e.g., digestive system).

• Organism Level: The complete living being (the human body as a whole).

Example: Oxygen (chemical) is used by muscle cells (cellular), which form muscle tissue (tissue), making up the heart (organ), part of the cardiovascular system (system), within the human organism (organism).

Difference Between Anatomy and Physiology

• Anatomy: The study of body structure (e.g., the location of the heart).

• Physiology: The study of body function (e.g., how the heart pumps blood).

Example: Anatomy describes the chambers of the heart; physiology explains how the heart contracts to circulate blood.

Organ Systems and Primary Functions

The human body contains several organ systems, each with specific functions:

• Integumentary System: Protection, sensation, temperature regulation.

• Skeletal System: Support, movement, protection, blood cell production.

• Muscular System: Movement, posture, heat production.

• Nervous System: Control, coordination, response to stimuli.

• Endocrine System: Hormone production, regulation of body processes.

• Cardiovascular System: Transport of nutrients, gases, wastes.

• Respiratory System: Gas exchange (oxygen and carbon dioxide).

• Digestive System: Breakdown and absorption of nutrients.

• Urinary System: Removal of wastes, water balance.

• Reproductive System: Production of offspring.

Example: The endocrine system produces hormones such as insulin.

Types of Diseases

Diseases can be classified into several categories:

• Infectious: Caused by pathogens (e.g., bacteria, viruses).

• Genetic: Result from inherited mutations (e.g., cystic fibrosis).

• Autoimmune: Immune system attacks the body (e.g., lupus).

• Degenerative: Progressive loss of function (e.g., osteoarthritis).

• Metabolic: Disruption of normal metabolism (e.g., diabetes).

• Neoplastic: Abnormal cell growth (e.g., cancer).

Homeostasis

Homeostasis is the process by which the body maintains a stable internal environment despite external changes.

• Examples: Regulation of body temperature, blood glucose levels.

Example: Sweating to cool the body when overheated.

Anatomical Planes and Directions

Anatomical Planes

Anatomical planes are imaginary lines used to divide the body for study and reference.

• Sagittal Plane: Divides the body into right and left portions.

• Transverse Plane: Divides the body into superior (upper) and inferior (lower) parts.

• Coronal (Frontal) Plane: Divides the body into anterior (front) and posterior (back) sections.

Note: The coronal plane is also called the frontal plane.

Directional Terms

Directional terms describe the locations of structures relative to other structures or locations in the body.

• Anterior (Ventral): Toward the front of the body.

• Posterior (Dorsal): Toward the back of the body.

• Medial: Toward the midline of the body.

• Lateral: Away from the midline.

• Proximal: Closer to the point of attachment or origin.

• Distal: Farther from the point of attachment or origin.

• Superior: Above or higher.

• Inferior: Below or lower.

Example: The elbow is proximal to the wrist; the nose is medial to the ears.

Medical Terminology Basics

Word Parts

Medical terms are often constructed from word parts that provide clues to their meaning.

• Prefix: Added to the beginning of a word to modify its meaning (e.g., hyper-).

• Root: The main part of the word, indicating the primary meaning (e.g., cardi for heart).

• Suffix: Added to the end of a word to modify its meaning (e.g., -itis for inflammation).

• Combining Vowel: Usually "o", used to connect word parts for easier pronunciation (e.g., oste/o).

Example: Electrocardiogram = electro- (electricity) + cardi (heart) + -gram (record).

Constructed Terms vs Non-Constructed Terms

• Constructed Terms: Built from standard word parts (prefix, root, suffix) following word-building rules.

• Non-Constructed Terms: Do not follow standard construction; include eponyms, acronyms, abbreviations, and terms from other languages.

Examples: Parkinson disease (eponym), AIDS (acronym).

Common Prefixes, Suffixes, and Combining Forms (Chapters 1–5)

Prefixes

• hypo-: Below, deficient

• hyper-: Above, excessive

• ab-: Away from

• pre-: Before

• in-: In, into, or not (context-dependent)

Suffixes

• -itis: Inflammation

• -emia: Blood condition

• -logy: Study of

• -gram: Record or picture

• -plasty: Surgical repair

• -oxia: Oxygen

Combining Forms

• angi/o: Vessel

• myel/o: Spinal cord or bone marrow

• leuk/o: White

• pariet/o: Wall (of a cavity)

• oste/o: Bone

• arthr/o: Joint

• chondr/o: Cartilage

Example: Osteoarthritis = oste/o (bone) + arthr/o (joint) + -itis (inflammation).

Diagnostic Imaging

Common Imaging Types

Diagnostic imaging allows visualization of internal body structures for diagnosis and treatment.

• X-ray: Uses radiation to view bones and dense structures.

• CT (Computed Tomography): Cross-sectional images using X-rays; good for bones, organs, and soft tissues.

• MRI (Magnetic Resonance Imaging): Uses magnetic fields and radio waves; excellent for soft tissues.

• Ultrasound: Uses sound waves; commonly used for soft tissues and pregnancy monitoring.

• PET (Positron Emission Tomography): Traces radioactive substances (e.g., glucose) to assess metabolic activity.

Example: MRI is preferred for brain imaging; PET scans are used to detect cancer activity.

The Integumentary System

Main Functions

The integumentary system, primarily the skin, serves several vital functions:

• Protection: Acts as a barrier against injury, infection, and dehydration.

• Sensation: Contains sensory receptors for touch, pain, and temperature.

• Regulation: Helps regulate body temperature through sweating and blood flow.

Anatomy of the Skin

The skin consists of three main layers:

• Epidermis: Outermost layer; provides waterproof barrier and creates skin tone.

• Dermis: Middle layer; contains connective tissue, hair follicles, and sweat glands.

• Subcutaneous (Hypodermis): Deepest layer; made of fat and connective tissue for insulation and cushioning.

Example: The epidermis is the layer you see and touch; the dermis contains nerves and blood vessels.

Combining Forms Associated with the Integumentary System

• derm/o, dermat/o: Skin

• cutane/o: Skin

• melan/o: Black (refers to melanin pigment)

• kerat/o: Hard tissue (keratinized tissue)

• trich/o: Hair

• onych/o: Nail

Example: Dermatitis = dermat/o (skin) + -itis (inflammation); melanoma = melan/o (black) + -oma (tumor).