HISTOLOGY The study of tissues

Levels of organization in the biosphere

What is a tissue? Groups of cells with a common structure and function –Structure is suited to its function

General types of tissues Epithelial tissue Connective tissue Nervous tissue Muscle tissue

Epithelial tissue Covers outside of body and lines organs and cavities inside the body –Functions as a protective barrier Protects against injury Protects against invasion by bacteria, etc.

Epithelial Tissue Classified by number of cell layers and shape of cells Remember: form reflects function!

Epithelial Tissue By Layers: –Simple epithelium Single layer of cells –Stratified epithelium Multiple layers of cells –Pseudostratified epithelium Single layer of cells that appears to be multi- layered

Epithelial Tissue By shape: –Cuboidal –Columnar –squamous

Epithelial Tissue

Epithelial Tissue: Examples Simple cuboidal epithelium

Epithelial Tissue: Examples Simple columnar epithelium

Epithelial Tissue: Examples Simple squamous epithelium

Epithelial Tissue: Examples Stratified squamous epithelium

Epithelial Tissue: Examples Stratified squamous epithelium with layer of keratin

Epithelial Tissue: Examples Pseudostratified columnar epithelium

Connective Tissue Functions to bind and support other tissues –Few cells scattered in a matrix of various substances

Connective tissue fibers Collagenous Elastic reticular

Collagenous fibers Made of collagen Non-elastic

Elastic fibers Long threads made of elastin Rubbery

Reticular fibers Thin Branched Composed of collagen Form tightly woven fabric

Main types of connective tissue Loose connective tissue Adipose tissue Fibrous connective tissue Cartilage Bone blood

Loose connective tissue Most common Has all 3 fiber types (collagenous, elastic, reticular) Binds epithelia to underlying tissues, holds organs in place Fibroblasts and macrophages scattered in the mesh Also called “areolar” connective tissue

Loose connective tissue

Adipose tissue Specialized form of loose connective tissue Stores fat Act as insulation and fuel

Adipose tissue

Fibrous connective tissue Large numbers of collagen fibers –Arranged in parallel bundles –Strong –Found in tendons (join muscle to bone) and ligaments (join bone to bone)

Fibrous connective tissue

Cartilage Collagen fibers embedded in a rubbery matrix of chondroitin sulfate –Strong, yet flexible –In human ears, nose, rings of trachea Flexible support –Chondrocytes secrete chondroitin and collagen

Cartilage

Bone Mineralized connective tissue--hard Osteoblasts = bone-forming cells May be compact or spongy (cancellous) Repeating units are called osteons (Haversian systems)

Bone

Blood Matrix = plasma –Made of salt, water, dissolved proteins Types of cells: –Erythrocytes = RBC’s –Leukocytes = WBC’s –platelets

General types of tissues Epithelial Connective Nervous Muscle

Nervous Tissue Functional unit = neuron –Transmit nerve impulses Structure: –Cell body, dendrites, axons Dendrites transmit impulses from tips toward the neuron cell body Axons transmit impulses toward another neuron or a muscle cell

Neuron

Muscle Tissue Fibers are capable of contraction Made of proteins, actin and myosin 3 types –Skeletal –Cardiac –smooth

Skeletal Muscle tissue Attached to bones by tendons Responsible for voluntary movement Striated appearance

Cardiac Muscle In heart Striated, but cells are branched

Smooth Muscle Lacks striations Spindle-shaped Responsible for involuntary movements Lines digestive tract, bladder, arteries

Types of Muscle tissue