Physiology - Organization of the Body

Physiology

The study of how the body functions, focusing on the mechanisms that keep cells, tissues, organs, and organ systems working together to maintain homeostasis.

Pathophysiology

The study of how normal physiological processes become disrupted, explaining the mechanisms behind disease and how altered function leads to symptoms.

Body Hierarchy (Layers of Organization)

A structural progression showing how the body is built:
Cells → Tissues → Organs → Organ Systems → Organism.
Each level becomes more complex and specialized, with higher levels depending on the proper function of the levels below.

Cell

The basic structural and functional unit of life. All higher levels of organization depend on coordinated cell activity.

Cell Functions

Cells perform essential tasks that support life:

• Exchange materials with the environment (nutrients, gases, wastes)

• Obtain energy from nutrients

• Synthesize complex molecules (proteins, lipids, signaling molecules)

• Duplicate to support growth and repair

• Detect and respond to signals to coordinate with other cells

Muscle Tissue

Specialization: Mechanical contraction to produce movement or force.
Types & Examples:

• Skeletal muscle — voluntary control; moves bones

• Cardiac muscle — involuntary; pumps blood

• Smooth muscle — involuntary; lines organs and vessels, controls diameter and movement

Neural Tissue

Made of: Neurons + supporting glial cells.
Specialization: Initiates and conducts electrical signals, allowing rapid communication and control of other cells (e.g., muscle, glands).

Epithelial Tissue

Also called: Epithelium.
Specialization: Absorption, secretion, and protection; forms barriers and interfaces.
Types:

• Simple epithelium — one layer; optimized for absorption/secretion

• Stratified epithelium — multiple layers; protection from stress
  Arranged by: Cell shape (squamous, cuboidal, columnar) and number of layers.

Connective Tissue

Specialization: Connects, supports, and anchors body structures; forms the extracellular matrix (ECM).
Types:

• Loose connective tissue — flexible support (e.g., adipose)

• Dense connective tissue — strong, fibrous support (e.g., tendons, ligaments)
  Examples: Blood, adipose tissue, cartilage, bone.

Organ

A structure made of two or more tissue types working together to perform a specific function (e.g., the heart contains muscle, connective, neural, and epithelial tissues).

Organ System

A group of organs coordinated to carry out major physiological functions (e.g., cardiovascular system, digestive system). Organ systems interact to maintain whole‑body homeostasis.