Fundamentals of Tissues and Membranes in Anatomy & Physiology

Study Guide - Smart Notes

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Tissues and Their Classifications

Definition of Tissue

A tissue is a group of similar cells that work together to perform a specific function within the body. Tissues are the building blocks of organs and organ systems.

Four Kinds of Human Tissue

Epithelial tissue: Covers body surfaces, lines cavities, and forms glands.
Connective tissue: Supports, binds, and protects organs.
Muscle tissue: Responsible for movement.
Nervous tissue: Conducts electrical impulses and processes information.

Epithelial Tissue

Characteristics of Epithelial Tissue

Cellularity: Composed almost entirely of tightly packed cells.
Polarity: Has an apical (top) surface and a basal (bottom) surface.
Attachment: Basal surface attached to a basement membrane.
Avascularity: Lacks blood vessels; nutrients diffuse from underlying tissues.
Regeneration: High rate of cell division and repair.

Basement Membrane

The basement membrane is a thin, fibrous layer of collagen fibers and glycoproteins that anchors epithelial tissue to underlying connective tissue, provides structural support, and resists stretching and tearing.

Classifications of Epithelium by Layering and Cell Type

Simple epithelium: Single layer of cells.
Stratified epithelium: Multiple layers of cells.
Pseudostratified epithelium: Appears layered but all cells touch the basement membrane.
Transitional epithelium: Multiple layers with cells that can change shape.

Types of Epithelial Cells and Their Appearance/Location

Simple squamous: Single layer of flat cells; found in alveoli (lungs), lining of blood vessels.
Simple cuboidal: Single layer of cube-shaped cells; found in kidney tubules, glands.
Simple columnar: Single layer of tall, skinny cells; found in digestive tract lining.
Stratified squamous: Multiple layers; found in skin (keratinized), mouth, esophagus (non-keratinized).
Stratified cuboidal: Multiple layers of cube-shaped cells; found in sweat gland ducts.
Stratified columnar: Multiple layers of column-shaped cells; rare, found in male urethra.
Pseudostratified columnar: Appears layered, but all cells touch basement membrane; found in respiratory tract.
Transitional: Multiple layers, cells change shape; found in urinary bladder.

Glands and Secretion Types

Definition of Gland

A gland is an organ or group of cells that synthesizes substances for release, such as hormones or enzymes.

Types of Glands

Exocrine glands: Secrete products into ducts (e.g., sweat, salivary glands).
Endocrine glands: Secrete hormones directly into the bloodstream.
Acini: Cluster of secretory cells in a gland.
Adenoma: A benign tumor arising from glandular epithelium.

Types of Secretion

Merocrine secretion: Products released by exocytosis; most common (e.g., sweat glands).
Holocrine secretion: Products accumulate in cell, then cell ruptures (e.g., sebaceous glands).
Apocrine secretion: Products accumulate at cell apex, then pinched off (e.g., mammary glands).

Membranes

Mucous Membrane

A mucous membrane lines body cavities that open to the exterior, secreting mucus for protection and lubrication.

Serous Membrane

A serous membrane is a double-layered membrane that lines closed body cavities and covers organs, secreting serous fluid to reduce friction (e.g., pleura, pericardium).

Connective Tissue (CT)

Characteristics of Connective Tissue

Found throughout the body; most abundant tissue type.
Functions: supports, protects, insulates, transports.
Arises from mesenchyme (embryonic tissue).
Varying degrees of vascularity.

Components of CT Extracellular Matrix (ECM)

Mesenchyme: Embryonic connective tissue; gives rise to all other CT types.
Ground substance: Unstructured material filling space between cells; contains fibers.
Fibronectin & Laminin: Adhesion proteins; help cells attach to matrix.
Types of fibers: Collagen (strong), reticular (supportive), elastic (stretchy).

Types of CT Cells

Fibroblasts: Produce fibers and ground substance.
Chondroblasts/chondrocytes: Cartilage cells.
Osteoblasts/osteocytes: Bone cells.
Adipocytes: Fat cells.
Blood cells: RBCs, WBCs, platelets.

Types of Connective Tissue

Loose CT: Areolar, adipose, reticular.
Dense CT: Dense regular, dense irregular, elastic.
Cartilage: Hyaline, elastic, fibrocartilage.
Bone: Compact and spongy bone.
Blood: Atypical CT; fluid matrix (plasma).

Connective Tissue Table

Type	Main Cells	Fibers	Function	Location
Areolar (Loose)	Fibroblasts	Collagen, elastic, reticular	Support, bind, hold fluids	Under epithelia
Adipose (Loose)	Adipocytes	Few	Energy storage, insulation	Subcutaneous tissue
Reticular (Loose)	Reticular cells	Reticular	Support for lymphoid organs	Lymph nodes, spleen
Dense Regular	Fibroblasts	Collagen (parallel)	Strength in one direction	Tendons, ligaments
Dense Irregular	Fibroblasts	Collagen (random)	Strength in multiple directions	Dermis of skin
Elastic	Fibroblasts	Elastic	Stretch and recoil	Walls of arteries
Hyaline Cartilage	Chondrocytes	Collagen	Support, compressibility	Trachea, nose, ribs
Elastic Cartilage	Chondrocytes	Elastic	Flexibility	Ear, epiglottis
Fibrocartilage	Chondrocytes	Thick collagen	Strength, shock absorption	Intervertebral discs
Bone	Osteocytes	Collagen, inorganic matrix	Support, protection	Skeletal system
Blood	RBCs, WBCs, platelets	None	Transport	Blood vessels

Muscle Tissue

Characteristics and Functions

Composed of elongated cells (muscle fibers) that contract to produce movement.
Functions: movement, posture, heat production.

Types of Muscle Tissue

Skeletal muscle: Voluntary, striated, attached to bones.
Cardiac muscle: Involuntary, striated, found in heart.
Smooth muscle: Involuntary, non-striated, found in walls of hollow organs.

Nervous Tissue

Description

Composed of neurons and neuroglia.
Functions: transmit electrical impulses, process information, coordinate responses.

Tissue Repair

Definitions and Processes

Edema: Swelling due to fluid buildup in ECM during inflammation.
Regeneration: Replacement of damaged tissue by the same tissue type.
Adhesion: Scar tissue connects adjacent organs, limiting movement.
Keloid: Excessive scar tissue formation; large masses of scar after injury.

Key Formulas and Equations

General formula for tissue repair rate:

Summary Table: Tissue Types and Functions

Tissue Type	Main Function	Example Location
Epithelial	Protection, absorption, secretion	Skin, lining of GI tract
Connective	Support, binding, transport	Tendons, blood, bone
Muscle	Movement	Skeletal muscles, heart, intestines
Nervous	Communication, control	Brain, spinal cord, nerves

Additional info: Some details on tissue repair and ECM components were expanded for academic completeness.