Histology

4 Types of Tissues

Human Body

Tissues

Epithelial

Connective

Muscle

Neural

What are Epithelial Tissues?Structure• Cover internal and external surfaces• Close together• Avascular• Easily regenerated• Life span: 1-2 days

• Basement membrane: attaches epithelia to underlying connective tissue• Made of protein fibers

Functions• Protection• Permeability• Secretion• Exocrine glands

Epithelial SurfacesApical Surface• Microvilli• Increase surface area• Absorption and

secretion• Cilia• Beat to move materials

across the surface

Basolateral Surface• Attached to underlying

cells or tissues• Sides of the cell

Basolateral Surface

Apical Surface

Squamous Epithelium• Simple Squamous• Shape: thin, flat cells; 1 layer• Function: diffusion; filtration• Found: forms capillary walls;

lines air sacs in lungs

• Stratified Squamous• Shape: thin, flat cells;

multiple layers• Function: protection• Found: skin surface; lines

tongue, mouth, esophagus, & anus

Cuboidal Epithelium• Simple Cuboidal• Shape: box-shaped; 1 layer• Function: secretion;

absorption• Found: covering the surface

of ovaries; lining kidney tubules, salivary ducts, & pancreatic ducts

• Stratified Cuboidal • Shape: box-shaped; multiple

layers• Function: strengthen lumen

walls• Found: ducts of large sweat

glands, salivary glands, & pancreas

Columnar Epithelium• Simple Columnar• Shape: tall, rectangular; 1

layer• Function: absorption,

secretion, & protection• Found: lines stomach,

intestinal tract, excretion ducts, gall bladder

• Pseudostratified Columnar• Shape: single layer, irregularly

shaped (looks like multiple layers)• Function: protection,

secretion• Found: lining respiratory

passageways & auditory tubes

Transitional Epithelium

• Transitional• Shape: Numerous layers

of rounded cells• Function: withstands

stretching• Found: lines urinary

bladder and portions of ureters & urethra

4 Types of Tissues

Human Body

Tissues

Epithelial

Connective

Muscle

Neural

What are Connective Tissues?Structure• Highly vascular• 3 Components:

1. Cells2. Protein Fibers3. Ground Substance

Functions (lots of variation!)• Support & Protect – framework• Transport materials – fluid with dissolved materials• Energy reserve – fat in adipose tissue• Defense – responds to pathogens by releasing

antibodies• Protection of organs

3 Types of Connective Tissues1. Connective Tissue Proper• Syrupy ground substance• Ex: Loose (areolar, adipose) & Dense (ligaments, tendons)

2. Fluid Connective Tissue• Cells suspended in watery ground substance with dissolved

proteins• Ex: Blood & Lymph

3. Supporting Connective Tissue• Dense ground substance• Closely packed fibers• Ex: Cartilage (hyaline, elastic, fibrocartilage) & Bone

1. Connective Tissue Proper – Cell Types

• Fibroblasts• Produce and maintain connective tissue

fibers & ground substance• Permanent• Local maintenance & repair

• Macrophages• Defense: Engulf pathogens & damaged

cells• Release chemicals to stimulate immune

response• Fixed or migrating (reinforcement)

• Adipocytes• Fat cells• Permanent• Nuclei & organelles pushed to the side

1. Connective Tissue Proper – Fiber Types

• Collagen• Long, straight, unbranched• Flexible

• Elastic• Protein – elastin• Wavy, branched, stretchy

1. Connective Tissue Proper – Loose Connective Tissue

• Areolar Tissue• Contains all cells and fibers of

connective tissue proper• Separates skin from muscles• Provides padding• Allows movement• Extensive blood supply

• Adipose Tissue• Adipose (fat) cells• Behind eyes, kidneys, heart,

abdomen, buttocks, & breasts

1. Connective Tissue Proper – Dense Connective Tissue

• Mostly collagen• Regular – collagen fibers

are parallel• Tendons – connect

skeletal muscle to bone• Ligaments – connect

bone to bone, contain elastin

2. Fluid Connective Tissue

• Blood• Plasma – watery matrix

with dissolved proteins• Red Blood Cells• White Blood Cells• Platelets

• Lymph• Interstitial fluid (water &

solutes) enters lymphatic vessels

3. Supporting ConnectiveTissue - Cartilage

• Cartilage – gel with embedded fibers• Chondrocytes – cells found in lacunae• Difficult to repair – no blood vessels• 3 Types:

1. Hyaline – closely packed fibers, tough but flexible• Connects ribs to sternum, supports trachea of respiratory tract,

covers bone surfaces in joints

2. Elastic – elastic fibers, very flexible• External flap of outer ear, epiglottis, auditory tube

3. Fibrocartilage – little ground substance, collagen fibers, durable & tough• Between vertebrae, between pubic bones, around or within some

joints

Hyaline Cartilage

Elastic Cartilage

Fibrocartilage

3. Supporting ConnectiveTissue - Bone

• Osseous Tissue – bone• Matrix – hard calcium & flexible collagen• Little ground substance

• Osteocytes found in lacunae• Lacunae surrounded by blood vessels• Canaliculi extend from central canal

4 Types of Tissues

Human Body

Tissues

Epithelial

Connective

Muscle

Neural

What are Muscle Tissues?• Specialized for contraction• 3 Types:

1. Skeletal Muscle – striated, voluntary muscle• Large multinucleated cells (long &

slender)• Striations (series of bands)

2. Cardiac Muscle – striated, involuntary muscle• Smaller striated cells, one nucleus• Interconnected by intercalated discs• only found in the heart

3. Smooth Muscle – nonstriated, involuntary muscle• Small, slender cells with one nucleus• walls of blood vessels, hollow tube-

like organs

4 Types of Tissues

Human Body

Tissues

Epithelial

Connective

Muscle

Neural

What are Neural Tissues?• Specialized for conducting electrical impulses• Neurons – communicate through electrical events• Long cell with 3 main parts

1. Cell body with nucleus2. Dendrites – branching projections that receive info3. Axon – long projections (with synaptic terminals) that relay

signals to other cells• Limited ability to repair

4 Types of Tissues

Human Body

Tissues

Epithelial

Connective

Muscle

Neural

Tissue Injury & Repair

• Inflammation• In response to pathogens, impact, abrasion,

extreme temperatures, or chemical irritation• Mast cells release chemicals (i.e. histamine)

that dilate blood vessels to induce swelling, redness, heat, & pain

• Regeneration• Fibroblasts produce dense collagen fibers

called fibrous tissue (aka scar tissue)