The Tissue Level of Organization

Tissue –Definition – an aggregation of cells in which each cooperates with all others in the performance of a given function –Examples of general functions Movement Movement Protection Protection Support Support Production of chemicals Production of chemicals

Principal Tissue Types –Epithelial –Connective –Muscular –Nervous

Epithelial Tissue –Functions Coverings and linings Coverings and linings Forms glands Forms glands –Characteristics Closely packed cells Closely packed cells Continuous sheets Continuous sheets Basement membrane Basement membrane –Classification based on cell shape and layers Simple Simple Stratified Stratified

Epithelia and Basement Membranes

Epithelia of Coverings & Linings –Simple squamous –Stratified squamous –Simple cuboidal –Transitional –Simple columnar –Pseudostratified columnar

Simple Squamous Epithelium –1 layer, flat cells Thin sheet Thin sheet –Highly adapted to diffusion, osmosis, & filtration

Stratified Squamous Epithelium –2 or more layers Surface layer is flat Surface layer is flat Deep layers are cuboidal or columnar Deep layers are cuboidal or columnar Basal cells undergo mitosis Basal cells undergo mitosis –Function - protection

Squamous Epithelia

Simple Cuboidal Epithelium 1 layer, cube-shaped cells Lines glands and their ducts Cells function in secretion and absorption

Transitional Epithelium –Similar to stratified squamous epithelium Surface layer is large, rounded cells Surface layer is large, rounded cells –Can be stretched –Lines hollow structures that expand –Function – prevents rupture of organ

Cuboidal and Transitional Epithelia

Simple Columnar Epithelium –1 layer, column-shaped cells –Functions Protection Protection Absorption Absorption Secretion Secretion –Goblet cells

Pseudostratified Epithelium –Appear stratified but all cells connect to the basal lamina

Columnar Epithelia

Glandular Epithelium –Gland – 1 or more cells –Function – secretion –Types Exocrine – to surface or ducts Exocrine – to surface or ducts Endocrine – to blood Endocrine – to blood

Connective Tissue –Most abundant tissue –Functions are varied –Characteristics Specialized cells, widely scattered Specialized cells, widely scattered Rich blood supply Rich blood supply Much extracellular matrix Much extracellular matrix –Non-living substance found outside the cells –Extracellular fibers

Cell Types Found in Connective Tissue –Fibroblasts Secrete the molecules that form the matrix Secrete the molecules that form the matrix –Fibrocytes

Connective Tissue Fibers –Collagen fibers Most common type Most common type White White Strong, ropelike Strong, ropelike Form ligaments, tendons Form ligaments, tendons –Elastic fibers Yellow Yellow Thin Thin Stretch Stretch –Contain elastin

Types of Connective Tissue –Loose (Areolar) Connective Tissue –Adipose Tissue –Dense Connective Tissue –Cartilage –Bone –Blood

Loose Connective Tissue Fibers not abundant, do not prevent stretching Fibers not abundant, do not prevent stretching Examples of locations Examples of locations –Between skin and muscles –Around digestive tract –Around blood vessels

Adipose Tissue Similar to loose connective tissue Similar to loose connective tissue Most of the volume is adipocytes Most of the volume is adipocytes Provides padding, slows heat loss, food reserve Provides padding, slows heat loss, food reserve Locations Locations –Wherever there is loose connective tissue

Dense Connective Tissue Lots of collagen fibers Lots of collagen fibers Examples Examples –Tendons –Ligaments Some has elastic fibers Some has elastic fibers

Cartilage –Dense network of collagenous fibers & elastic fibers in a gel-like substance –Cells – chondrocytes in lacunae chondroblasts chondroblasts –Perichondrium – surrounds surface of cartilage

Hyaline Cartilage Most common Most common Provides flexibility and support Provides flexibility and support Locations Locations –Ends of bones –Trachea –Larynx –Embryonic skeleton

Fibrocartilage –Visible collagenous fibers with scattered chondrocytes –Provides strength and rigidity –Locations Intervertebral discs Intervertebral discs Symphysis pubis Symphysis pubis

Fibrocartilage Visible collagenous fibers with scattered chondrocytes Visible collagenous fibers with scattered chondrocytes Provides strength and rigidity Provides strength and rigidity Locations Locations –Intervertebral discs –Symphysis pubis

Bone Solid matrix Solid matrix Cells – Cells – –Osteocytes in lacunae –Osteoblasts –Osteoclasts Periosteum surrounds surface of bone Periosteum surrounds surface of bone

Blood Functions Functions –Transport medium –Regulation –Protection Composition Composition –Plasma – fluid –Formed elements – cells & cell fragments Red blood cell Red blood cell White blood cell White blood cell

A Red Blood Cell

SEM of RBCs

Muscular Tissue –Specialized cells –Function - contraction –3 types Skeletal muscle Skeletal muscle Cardiac muscle Cardiac muscle Smooth muscle Smooth muscle

Skeletal Muscle Tissue Connected to bones Connected to bones Striated Striated Multinucleated Multinucleated Voluntary Voluntary

Cardiac Muscle Tissue Found in the heart Found in the heart Striations Striations Intercalated discs Intercalated discs Involuntary Involuntary

Smooth Muscle Tissue Found in walls of Found in walls of internal organs internal organs Nonstriated Nonstriated Involuntary Involuntary

Nervous Tissue Specialized cells Specialized cells Function – conduction of electrical impulses Function – conduction of electrical impulses Cells Cells –Neurons –Neuroglia