Histology: The Study of Tissues

Tissues A tissue is a group of similar cells specialized for a particular function Classified according to their structure & function Four Primary Tissue Types Epithelial – covering Connective – support Muscular – movement Nervous - control

Epithelial Tissue - Epithelium Lining, covering, & glandular tissue of the body. Forms glands, outer layer of skin, & lines body cavities Contains many cells, close together with no blood vessels. Can easily regenerate Rely on diffusion from capillaries for food & oxygen Functions Protection, absorption, filtration, & secretion

Classification of Epithelium Classified according to cell shape & arrangement 3 cell shapes Squamous: flattened Cuboidal: cube-shaped Columnar: column shaped 2 Arrangements Simple epithelium: one layer of cells Stratified epithelium: more than one cell layer

Classification of Epithelium Simple Squamous Single layer of flattened cells Diffusion & filtration Lines the lungs, kidneys, heart & blood vessels Simple Cuboidal Single layer of cube-shaped cells Secretion & absorption Covers ovaries, kidneys, & eyes Simple Columnar Single layer of elongated cells Absorption & secretion of mucus Lines the entire digestive tract

Simple Squamous

Simple Cuboidal

Simple Columnar

Classification of Epithelium Stratified Squamous Protective tissue – outer portion of the skin Lines the mouth & esophagus Stratified Cuboidal Adult sweat glands, portions of the pharynx, & epiglottis Stratified Columnar Protects & secretes Male urethra & large excretory ducts

Stratified Squamous

Stratified Cuboidal

Stratified Columnar

Connective Tissue Most abundant tissue in the body Fewer cells with a rich blood supply except for tendons, ligaments, & cartilage Produces an extracellular matrix (ECM) Non-living substance found outside of cells Allows connective tissue to bear weight, stretch, & tolerate abrasion Can be soft (fat) or hard (bone) Functions Protects, supports, and binds together organs

Types of Connective Tissue Bone Bone cells surrounded by very hard ECM Protects & supports body organs Cartilage Less hard & more flexible then bone Embryonic skeleton, ends of bones, nose, attaches ribs to breast bone, external ear, between vertebrae, etc. Provides for movement & support Dense Connective Tissue Forms tendons & ligaments Close packing of fibers

Types of Connective Tissue Loose Connective Tissue Softer with more cells & fewer fibers Various types Adipose tissue – fat storage + body insulation Areolar tissue – cushions & protects body organs Reticular connective tissue – interlacing reticular fibers Found in the liver, spleen, & lymph nodes Blood – Vascular Tissue Blood cells & blood plasma Transport vehicle for the cardiovascular system

Bone

Muscle Tissue Highly specialized to contract (shorten) to produce movement Three types Skeletal muscle Striated – banded Voluntary movement Smooth muscle No striations Involuntary movements Breathing, digestion, birth, reflexes, etc. Cardiac muscle Found only in the heart – striated Involuntary control – pumps the heart

Nervous Tissue Neurons – nerve cells Unique structure: 3 parts Receive & conduct impulses from one part of the body to another Unique structure: 3 parts Dendrites – receive message Cell body – interprets message Axon – conducts the message There are 100 billion neurons in the brain alone

Nervous Tissue Supporting cells (neuroglia) insulate, protect, & supports the neurons

Tissue Inflammation & Repair An attempt to restore homeostasis Damage causes inflammatory response Redness, pain, heat, swelling Chemicals in the body initiate inflammatory responses & isolate infected area Pus is often produced – can form an abscess Damaged tissue is then replaced by healthy cells Tissue repair is completed after harmful substances are removed/neutralized Vit. A,B,C,D,E,&K help tissue repair Needs adequate blood circulation – process slows with aging