BIO 141 Chapter 4: The Tissue Level of Organization - Study Notes

Tissue Level of Organization

Introduction to Tissues and Histology

Tissues are groups of cells that are similar in structure and function, forming the basic building blocks of organs. Histology is the study of tissues, essential for understanding how organs function and how diseases affect them.

• Tissue: Group of cells with similar structure and function.

• Histology: Study of tissues.

• Four main types: epithelial, connective, muscle, nervous.

Types of Tissues

Epithelial Tissue

Epithelial tissue covers body surfaces, lines internal cavities, and forms glands. It is specialized for protection, absorption, filtration, and secretion.

• Structure: Forms sheets; covering and lining epithelium, glandular epithelium.

• Functions: Protection, absorption, filtration, secretion.

• Polarity: Has an apical (top) and basal (bottom) surface.

• Specializations: Cilia (move fluids), microvilli (increase absorption/secretion).

• Regeneration: Rapidly replaces lost cells.

Support and Properties of Epithelial Tissue

Epithelial tissue is supported by connective tissue, rests on a basement membrane, and is avascular (lacks blood vessels). It relies on diffusion for nutrients and oxygen.

• Basement membrane: Lamina that anchors epithelium to connective tissue.

• Cell junctions: Tight, gap, desmosomes, hemidesmosomes.

• Avascular: No direct blood supply.

• Regeneration: High capacity for renewal.

Intercellular Connections

Cell junctions are specialized structures that connect epithelial cells and regulate communication and permeability.

• Gap junctions: Allow rapid communication via channel proteins (connexons).

• Tight junctions: Seal cells together, control fluid/solute movement.

• Desmosomes: Tie cells together, provide mechanical strength.

• Hemidesmosomes: Attach cells to the basal lamina.

Classification of Epithelial Tissue

Epithelial tissues are classified by the number of cell layers and the shape of the cells.

• Cell layers: Simple (one layer), stratified (multiple layers).

• Cell shapes: Squamous (flat), cuboidal (cube-shaped), columnar (tall).

Simple Epithelium

Simple epithelium is a single layer of cells, specialized for absorption, secretion, and filtration.

• Simple squamous: Filtration, rapid diffusion; found in capillaries, air sacs, kidneys.

• Simple cuboidal: Secretion and absorption; lines ducts, kidney tubules, ovary surface.

• Simple columnar: Absorption and secretion; lines digestive tract, often with microvilli or cilia.

Stratified Epithelium

Stratified epithelium consists of two or more layers, providing protection against abrasion and friction.

• Stratified squamous: Withstands abuse; found in esophagus, mouth, skin.

• Stratified cuboidal: Usually two layers; found in ducts of large glands.

• Stratified columnar: Thick, waterproof; found in pharynx, male urethra, lining ducts.

Transitional Epithelium

Transitional epithelium can change shape from cuboidal to squamous, allowing it to stretch. It lines hollow urinary organs such as the bladder, ureter, and urethra.

• Function: Stretches when filled with urine.

• Location: Urinary bladder, ureters, urethra.

Glandular Epithelium

Glandular epithelium forms glands that produce and secrete products. Glands are classified as endocrine (secrete hormones into blood) or exocrine (secrete products into ducts).

• Exocrine glands: Sweat, mucous, oil, saliva.

• Endocrine glands: Hormones, estrogen.

• Modes of secretion: Merocrine (exocytosis), apocrine (shedding cytoplasm), holocrine (cell bursts).

Connective Tissue

Overview and Functions

Connective tissue is the most abundant and widely distributed tissue in the body. It supports, binds, protects, insulates, and transports substances.

• Main classes: Connective tissue proper, cartilage, bone, blood, fat.

• Functions: Binding/support, protection/insulation, transport.

Classification and Structure

Connective tissues vary in blood supply and have an extracellular matrix composed of ground substance and fibers.

• Blood supply: Avascular (cartilage), poorly vascular (tendons/ligaments).

• Extracellular matrix: Ground substance (water, proteins, polysaccharides), fibers (collagen, elastic, reticular).

Connective Tissue Proper Cells and Fibers

Connective tissue proper contains various cell types and fibers, each with specific functions.

• Cells: Fibroblasts, fibrocytes, macrophages, adipocytes, mesenchymal, melanocytes, mast cells, lymphocytes.

• Fibers: Collagen (strength), reticular (network), elastic (stretch).

Loose Connective Tissue

Loose connective tissue is the universal packing material, providing cushioning, nutrient storage, and internal framework.

• Subclasses: Areolar, adipose, reticular.

• Structure: Softer, fewer fibers, gel-like matrix.

• Functions: Cushion/protect organs, store nutrients, internal framework, fight infection.

• Locations: Under skin, lymph nodes, hips, behind eyeballs.

Dense Connective Tissue

Dense connective tissue is found in tendons, ligaments, and organ capsules, providing strength and elasticity.

• Subclasses: Dense regular, dense irregular, elastic.

• Structure: Mainly collagen fibers.

• Functions: Resist tension, provide elasticity.

• Locations: Tendons, ligaments, skin, around organs.

Cartilage

Cartilage is a supporting connective tissue, flexible and avascular, found in joints, ear, nose, and intervertebral discs.

• Subclasses: Hyaline, elastic, fibrocartilage.

• Structure: Flexible, no nerves or blood.

• Functions: Support, compression.

• Locations: Larynx, joints, tip of nose, ear, discs, rib-breastbone, knee.

Bone (Osseous Tissue)

Bone tissue is hard and calcified, providing structural support, protection, and blood cell formation.

• Subclasses: Compact, spongy.

• Structure: Hard matrix, blood vessels.

• Functions: Support, protect, store calcium, blood cell formation.

• Locations: Bones.

Blood

Blood is a fluid connective tissue, transporting nutrients, wastes, gases, and hormones throughout the body.

• Subclasses: Blood cells, plasma.

• Structure: Fluid, no fibers.

• Functions: Transport vehicle.

• Cells: White blood cells, red blood cells, platelets.

• Locations: Blood vessels.

Membranes and Fascia

Membranes

Membranes are physical barriers that cover portions of the body, composed of epithelium and connective tissue.

• Mucous: External connections.

• Serous: Line cavities not open to outside.

• Cutaneous: Skin.

• Synovial: Lubricate ends of bones.

Fascia

Fascia is the internal framework of the body, supporting organs and tissues.

Muscle Tissue

Types and Functions

Muscle tissue is responsible for movement and includes three types: skeletal, cardiac, and smooth muscle.

• Skeletal muscle: Voluntary movement.

• Cardiac muscle: Heart contraction.

• Smooth muscle: Involuntary movement in organs.

Nervous Tissue

Structure and Function

Nervous tissue regulates and controls body functions, consisting of neurons and supporting cells.

• Structure: Neuron = dendrite + cell body + axon.

• Location: Brain, spinal cord, nerves.

Tissue Repair

Wound Healing

Tissue repair occurs through regeneration (replacement by same cells) or fibrosis (scar tissue formation). The process depends on tissue type and injury severity.

• Regeneration: Replace destroyed tissue with same kind of cells.

• Fibrosis: Form scar tissue (dense fibrous connective tissue).

Steps to Tissue Repair

1. Inflammation: Capillaries become permeable, WBCs and clotting proteins enter, clot forms and dries as a scab.

2. Granulation tissue formation: New capillaries, collagen fibers, epithelial cells multiply.

3. Surface epithelium regenerates: Epithelium thickens, fibrous tissue matures into scar tissue.

Regenerative Capacity of Different Tissues

Different tissues have varying abilities to regenerate, affecting healing outcomes.