Classification of Tissues: Study Guide for Anatomy & Physiology

Classification of Tissues

Introduction

Tissues are groups of cells similar in structure and function. In human anatomy and physiology, tissues are classified into four major types: epithelial, connective, muscle, and nervous. Each type contains various subtypes and specialized structures, which are essential for understanding the organization and function of the human body.

Epithelial Tissue

Overview

Epithelial tissue covers body surfaces, lines cavities, and forms glands. It is characterized by closely packed cells with minimal extracellular matrix and is classified based on cell shape and number of layers.

• Simple squamous epithelium: Single layer of flat cells; found in air sacs (alveoli) of lungs and lining of blood vessels.

• Simple cuboidal epithelium: Single layer of cube-shaped cells; found in kidney tubules and glandular ducts.

• Simple columnar epithelium: Single layer of tall, column-like cells; often contains goblet cells for mucus secretion; found in the digestive tract.

• Stratified squamous epithelium: Multiple layers; protects against abrasion; found in skin (keratinized) and lining of mouth/esophagus (non-keratinized).

• Pseudostratified columnar epithelium: Appears layered due to varying cell heights but is a single layer; often contains goblet cells; found in respiratory tract.

• Transitional epithelium: Multiple layers with cells that change shape; found in urinary bladder.

Key Structures:

• Lumen: The open space within a tubular structure.

• Basement membrane: Thin layer anchoring epithelium to underlying tissue.

• Goblet cells: Specialized for mucus secretion.

Example: The lining of the trachea contains pseudostratified columnar epithelium with goblet cells to trap particles.

Connective Tissue

Overview

Connective tissue supports, binds, and protects organs. It is characterized by cells scattered within an abundant extracellular matrix.

• Areolar (loose) connective tissue: Contains fibroblasts, macrophages, leukocytes, and mast cells; found under skin and around organs.

• Adipose tissue: Stores fat in vacuoles; insulates and cushions organs.

• Reticular connective tissue: Forms supportive framework in lymphoid organs.

• Dense regular connective tissue: Collagen fibers arranged in parallel; found in tendons and ligaments.

• Dense irregular connective tissue: Collagen fibers arranged randomly; found in dermis of skin.

• Elastic connective tissue: Contains abundant elastic fibers; allows stretching and recoil; found in arteries.

• Cartilage: Three types—hyaline, elastic, and fibrocartilage; provides support and flexibility.

• Bone: Rigid matrix with osteocytes; supports and protects body structures.

• Blood: Fluid matrix (plasma) with red and white blood cells and platelets; transports substances.

Key Cell Types:

• Fibroblasts: Produce fibers and ground substance.

• Adipocytes: Store fat.

• Chondrocytes: Found in cartilage.

• Osteocytes: Found in bone.

Example: Dense regular connective tissue forms tendons, connecting muscle to bone.

Connective Tissue Table

Type	Main Cells	Matrix/Fibers	Location
Areolar	Fibroblasts, macrophages	Collagen, elastic, reticular	Under skin, around organs
Adipose	Adipocytes	Minimal	Subcutaneous, around organs
Dense Regular	Fibroblasts	Parallel collagen fibers	Tendons, ligaments
Cartilage (Hyaline)	Chondrocytes	Collagen fibers	Trachea, larynx, joints
Bone	Osteocytes	Collagen, mineralized matrix	Skeletal system
Blood	RBCs, WBCs, platelets	Plasma	Blood vessels

Muscle Tissue

Overview

Muscle tissue is specialized for contraction and movement. There are three types: skeletal, cardiac, and smooth.

• Skeletal muscle: Voluntary, striated, multinucleated; attached to bones for movement.

• Cardiac muscle: Involuntary, striated, branched cells with one central nucleus; found in heart; contains intercalated discs for cell-to-cell communication.

• Smooth muscle: Involuntary, non-striated, spindle-shaped cells with one nucleus; found in walls of hollow organs.

Key Structures:

• Sarcolemma: Muscle cell membrane.

• Sarcoplasm: Cytoplasm of muscle cell.

• Striations: Alternating light and dark bands in skeletal and cardiac muscle.

Example: Skeletal muscle fibers contract to produce voluntary movements such as walking.

Nervous Tissue

Overview

Nervous tissue is specialized for communication via electrical and chemical signals. It consists of neurons and supporting neuroglial cells.

• Neurons: Main functional cells; transmit impulses; consist of cell body, axon, and dendrites.

• Neuroglia: Support, protect, and nourish neurons.

Key Structures:

• Axon: Transmits impulses away from cell body.

• Dendrites: Receive signals from other cells.

• Myelin sheath: Insulates axons to speed impulse transmission.

• Central canal: Found in spinal cord; contains cerebrospinal fluid.

Example: Neurons in the spinal cord transmit signals between the brain and body.

Blood and Blood Cells

Overview

Blood is a connective tissue with a liquid matrix (plasma) and formed elements (cells).

• Granulocytes: White blood cells with granules in cytoplasm.

  • Neutrophils: Most common; multilobed nucleus; phagocytize bacteria.

  • Eosinophils: Bilobed nucleus; pink granules; combat parasites.

  • Basophils: Least common; large purple-stained granules; release histamine.

• Agranulocytes: White blood cells without granules.

  • Lymphocytes: Large nucleus; immune response.

  • Monocytes: Largest WBC; kidney-shaped nucleus; become macrophages.

• Platelets: Cell fragments involved in clotting.

Example: Neutrophils are the first responders to infection, engulfing bacteria.

Artery, Vein, and Nerve (Cross Section)

Overview

Arteries, veins, and nerves often travel together in connective tissue. Recognizing their structure is important in histology.

Structure	Key Features
Artery	Thick muscular wall (mainly smooth muscle), small lumen, elastic fibers present, tunica media prominent
Vein	Thinner wall, large lumen, elastic fibers less prominent, tunica media thinner
Nerve	No lumen, cross-sections of axons with myelination, appears as bundles of frosty-like tissue

Example: In a cross-section of tissue, arteries appear round with thick walls, veins are collapsed with thin walls, and nerves are solid bundles.

Key Terms and Definitions

• Tissue: Group of similar cells performing a specific function.

• Epithelium: Tissue forming outer layer of body surfaces and lining cavities.

• Matrix: Extracellular material in connective tissue.

• Striation: Alternating light and dark bands in muscle tissue.

• Neuron: Nerve cell specialized for transmitting impulses.

Formulas and Equations

• Surface Area of a Cell: $A = 4\pi r^2$

• Volume of a Cell: $V = \frac{4}{3}\pi r^3$

Summary Table: Tissue Types and Functions

Tissue Type	Main Function	Location
Epithelium	Protection, absorption, secretion	Skin, lining of organs
Connective	Support, binding, transport	Bones, blood, fat, tendons
Muscle	Movement	Skeletal muscles, heart, walls of organs
Nervous	Communication, control	Brain, spinal cord, nerves

Additional info: Some details, such as the specific page numbers and figure references, are inferred to be from a standard Anatomy & Physiology textbook (e.g., Marieb). The study guide emphasizes the importance of recognizing tissue types, their subtypes, specialized structures, locations, and functions for laboratory and exam preparation.