Anatomy & Physiology: Body Cavities, Planes, Cells, and Tissues

Body Cavities and Anatomical Divisions

Thoracic and Abdominal Cavities

The human body contains several major cavities that house vital organs and provide protection and compartmentalization for physiological functions.

• Thoracic Cavity: The upper portion of the ventral cavity, enclosed by the rib cage. Contains the heart and lungs.

• Abdominal Cavity: The lower, larger portion of the ventral cavity. Contains digestive organs (stomach, intestines, liver, pancreas), and kidneys.

• Pelvic Cavity: Contains reproductive organs and the rectum.

Directional Terms help describe the location of structures:

• Superior: Toward the top of the body

• Inferior: Below or lower than another part

• 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 origin of the body part

• Distal: Farther from the origin

Anatomical Planes and Sections

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

• Transverse (Cross): Divides the body into superior (upper) and inferior (lower) sections.

• Sagittal: Divides the body into right and left sections.

• Midsagittal: Divides the body into equal right and left halves.

• Parasagittal: Divides the body into unequal right and left sections.

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

Body Orientation Terms:

• Bilateral: On both sides of the body (e.g., kidneys)

• Unilateral: On one side only

• Ipsilateral: On the same side of the body as another structure

• Contralateral: On the opposite side of the body

Cell Structure and Function

Cellular Components

Cells are the basic structural and functional units of life. Each cell contains specialized organelles that perform distinct functions.

• Plasma Membrane: Phospholipid bilayer that separates the cell's interior from the external environment.

• Nucleus: Contains genetic material (DNA) and controls cell activities.

• Ribosomes: Produce proteins; found free in cytoplasm or attached to rough endoplasmic reticulum.

• Endoplasmic Reticulum (ER):

  • Rough ER: Studded with ribosomes; synthesizes proteins for secretion or membrane insertion.

  • Smooth ER: Lacks ribosomes; synthesizes lipids and detoxifies chemicals.

• Golgi Apparatus: Modifies, packages, and distributes proteins and lipids.

• Mitochondria: Powerhouse of the cell; converts food into ATP (energy).

• Lysosomes: Contain digestive enzymes to break down waste.

• Cytoskeleton: Provides structural support and facilitates movement.

Central Dogma of Molecular Biology: Flow of genetic information from DNA to RNA to protein through transcription and translation.

• Transcription: Synthesis of mRNA from a DNA template.

• Translation: Synthesis of protein from mRNA at the ribosome.

Cell Membrane and Transport

Membrane Structure and Function

The plasma membrane is a selectively permeable barrier composed of a phospholipid bilayer with embedded proteins, cholesterol, and carbohydrates.

• Phospholipids: Form the basic structure; hydrophilic heads face outward, hydrophobic tails inward.

• Cholesterol: Stabilizes membrane fluidity.

• Proteins: Serve as channels, receptors, enzymes, or anchors.

• Carbohydrates: Involved in cell recognition and adhesion.

Transport Mechanisms:

• Passive Transport: Movement of substances down their concentration gradient (e.g., diffusion, osmosis, facilitated diffusion).

• Active Transport: Movement of substances against their concentration gradient, requiring energy (e.g., sodium-potassium pump).

Tissues: Types and Functions

Primary Tissue Types

The human body is composed of four main tissue types, each with specialized functions.

• Epithelial Tissue: Covers and lines organs and body surfaces; functions in protection, absorption, secretion, and sensation.

• Connective Tissue: Supports and binds other tissues; includes bone, blood, and adipose tissue.

• Muscle Tissue: Contracts to produce movement; includes skeletal, cardiac, and smooth muscle.

• Nervous Tissue: Transmits and receives electrical impulses; includes neurons and glial cells.

Epithelial Tissue: Structure and Classification

Epithelial tissue is classified by the number of layers and the shape of the cells.

• Simple Epithelium: Single layer of cells; allows for absorption, secretion, and filtration.

• Stratified Epithelium: Multiple layers; provides protection.

• Cell Shapes:

  • Squamous: Flat, scale-like cells; suited for diffusion and filtration.

  • Cuboidal: Cube-shaped; specialized for secretion and absorption.

  • Columnar: Tall, column-like; suited for absorption and secretion.

Specialized Structures:

• Microvilli: Increase surface area for absorption (e.g., small intestine).

• Cilia: Move substances across the cell surface (e.g., respiratory tract).

Glandular Epithelium

Glands are specialized epithelial cells that produce and secrete substances.

• Exocrine Glands: Secrete products onto body surfaces or into body cavities (e.g., sweat, salivary glands).

• Endocrine Glands: Secrete hormones directly into the bloodstream (e.g., thyroid, pituitary glands).

Cell Junctions

Cell junctions are specialized connections between adjacent cells that maintain tissue integrity and communication.

• Tight Junctions: Seal adjacent cells to prevent passage of molecules between them.

• Desmosomes: Provide mechanical strength by anchoring cells together.

• Gap Junctions: Allow direct communication and passage of ions and small molecules between cells.

Connective Tissue: Structure and Function

Connective tissue is characterized by cells embedded in an extracellular matrix composed of fibers and ground substance.

• Fibroblasts: Most common cell type; produce fibers and ground substance.

• Collagen Fibers: Provide strength and flexibility.

• Elastic Fibers: Allow stretch and recoil.

• Reticular Fibers: Form supportive networks in soft tissues.

Types of Connective Tissue:

• Loose Connective Tissue: Fills spaces between organs; provides cushioning.

• Dense Connective Tissue: Forms tendons and ligaments; provides strong attachment.

• Specialized Connective Tissue: Includes bone, cartilage, blood, and adipose tissue.

Muscle and Nervous Tissue

Muscle tissue is responsible for movement, while nervous tissue is specialized for communication.

• Skeletal Muscle: Voluntary movement; attached to bones.

• Cardiac Muscle: Involuntary; found only in the heart.

• Smooth Muscle: Involuntary; found in walls of hollow organs.

• Neurons: Transmit electrical signals.

• Glial Cells: Support and protect neurons.

Embryonic Tissue Layers

Germ Layers and Their Derivatives

During embryonic development, three primary germ layers form and give rise to all tissues and organs.

• Ectoderm: Forms the nervous system, epidermis, hair, nails, and tooth enamel.

• Mesoderm: Forms muscle, bone, connective tissue, blood, and the cardiovascular system.

• Endoderm: Forms the lining of the digestive and respiratory tracts, liver, and pancreas.

Summary Table: Tissue Types and Functions

Tissue Type	Main Function	Location
Epithelial	Protection, absorption, secretion, sensation	Body surfaces, lining of organs
Connective	Support, binding, storage, transport	Bone, blood, fat, cartilage
Muscle	Movement	Skeletal muscles, heart, walls of hollow organs
Nervous	Communication, control	Brain, spinal cord, nerves

Key Terms and Definitions

• Homeostasis: The maintenance of a stable internal environment.

• Histology: The study of tissues.

• Organ: A structure composed of two or more tissue types that performs a specific function.

• Organ System: A group of organs that work together to perform a major function.

Additional info:

• Some content was inferred and expanded for clarity and completeness based on standard Anatomy & Physiology curriculum.