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Four Types of Tissues

Tissues are collections of cells and cell

products that perform specific, limited

functions

Types of tissue

Epithelial tissue

Covers exposed surfaces

Lines internal passageways

Forms glands

Four Types of Tissues

Types of Tissue (cont’d)

Connective tissue

Fills internal spaces

Supports other tissues

Transports materials

Stores energy

Muscle tissue

Specialized for contraction

Skeletal muscle, heart muscle, and walls of hollow organs

Neural tissue

Carries electrical signals from one part of the body to another

Epithelial Tissues

Epithelia

Layers of cells covering internal or external

surfaces

Glands

Structures that produce secretions

Epithelial Tissues

Characteristics of Epithelia

Cellularity (cell junctions)

Polarity (apical and basal surfaces)

Attachment (basal lamina)

Avascularity

Regeneration

Epithelial Tissues

Figure 4–1 The Polarity of Epithelial Cells.

Epithelial Tissues

Functions of Epithelial Tissue

Provide physical protection

Control permeability

Provide sensation

Produce specialized secretions (glandular

epithelium)

Epithelial Tissues

Specializations of Epithelial Cells

Move fluids over the epithelium (protection)

Move fluids through the epithelium (permeability)

Produce secretions (protection and messengers)

Free Surface and Attached Surface

Polarity

Apical surfaces:

– microvilli increase absorption or secretion

– cilia (ciliated epithelium) move fluid

Basolateral surfaces

Epithelial Tissues

Figure 4–2 Intercellular Connections

Epithelial Tissues

Intercellular Connections

Cell junctions

Form bonds with other cells or extracellular material:

– occluding (tight) junctions

– gap junctions

– macula adherens (desmosomes)

Intercellular Connections

Epithelial Tissues

Attachment to the Basal Lamina

Clear layer (Lamina lucida)

Thin layer

Secreted by epithelia

Barrier to proteins

Dense layer (Lamina densa)

Thick fibers

Produced by connective tissue

Strength and filtration

Epithelial Tissues

Epithelial Maintenance and Repair

Epithelia are replaced by division of

germinative cells (stem cells)

Near basal lamina

Classification of Epithelia

Singular epithelium; plural epithelia

Classes of Epithelia

Based on shape

Squamous epithelia: thin and flat

Cuboidal epithelia: square shaped

Columnar epithelia: tall, slender rectangles

Based on layers

Simple epithelium: single layer of cells

Stratified epithelium: several layers of cells

Squamous Epithelia

Simple squamous epithelium

Absorption and diffusion

Mesothelium

Lines body cavities

Endothelium

Lines heart and blood vessels

Figure 4–3 Squamous Epithelia.

Squamous Epithelia

Stratified squamous epithelium

Protects against attacks

Keratin protein adds strength and water resistance

Figure 4–3 Squamous Epithelia.

Cuboidal Epithelia

Simple cuboidal epithelium

Secretion and absorption

Figure 4–4 Cuboidal Epithelia.

Cuboidal Epithelia

Stratified cuboidal epithelia

Sweat ducts and mammary ducts

Transitional Epithelium

Tolerates repeated cycles of stretching and recoiling

and returns to its previous shape without damage

Appearance changes as stretching occurs

Situated in regions of the urinary system (e.g. urinary

bladder)

Columnar Epithelia

Simple columnar epithelium

Absorption and secretion

Figure 4–5 Columnar Epithelia.

Columnar Epithelia

Pseudostratified columnar epithelium

Cilia movement

Columnar Epithelia

Stratified columnar epithelium

Protection

Glandular Epithelia

Endocrine glands

Release hormones:

– into interstitial fluid

– no ducts

Exocrine glands

Produce secretions:

– onto epithelial surfaces

– through ducts

Mechanisms of Glandular Secretion

Modes of Secretion in Glandular Epithelia

Merocrine secretion

Is produced in Golgi apparatus

Is released by vesicles (exocytosis)

For example, sweat glands

Figure 4–6 Modes of Glandular Secretion.

Apocrine secretion

Is produced in Golgi apparatus

Is released by shedding cytoplasm

For example, mammary gland

Holocrine secretion

Is released by cells bursting, killing gland cells

Gland cells replaced by stem cells

For example, sebaceous gland

Glandular Epithelia

Types of secretions

Serous glands:

– watery secretions

Mucous glands:

– secrete mucins

Mixed exocrine glands:

– both serous and mucous

Glandular Epithelia

Gland structure

Unicellular glands

– Mucous (goblet) cells are the only unicellular

exocrine glands:

» scattered among epithelia

» for example, in intestinal lining

Glandular Epithelia

Gland structure

Multicellular glands:

– structure of the duct:

» simple (undivided)

» compound (divided)

– shape of secretory portion of the gland:

» tubular (tube shaped)

» alveolar or acinar (blind pockets)

– relationship between ducts and glandular areas:

» branched (several secretory areas sharing one duct)

Figure 4–7 A Structural Classification of Exocrine Glands.

Tissue Injuries and Repair

Tissues respond to injuries to maintain

homeostasis

Cells restore homeostasis with two processes

Inflammation

Regeneration

Inflammation = inflammatory response

The tissue’s first response to injury

Signs and symptoms of the inflammatory

response include

Swelling

Redness

Inflammatory Response

Can be triggered by

Trauma (physical injury)

Infection (the presence of harmful pathogens)

The Process of Inflammation

Damaged cells release chemical signals into the

surrounding interstitial fluid

Lysosomes release enzymes that destroy the injured cell

And attack surrounding tissues. Tissue destruction is called

necrosis

As cells break down

Necrotic tissues and cellular debris (pus) accumulate

in the wound

Injury stimulates mast cells to release

Histamine, Heparin, Prostaglandins

The Process of Inflammation

Dilation of blood vessels

Increases blood circulation in the area

Causes warmth and redness

Brings more nutrients and oxygen to the area

Removes wastes

Plasma diffuses into the area

Causing swelling and pain

Phagocytic white blood cells

Clean up the area

Regeneration

When the injury or infection is cleaned up

Healing (regeneration) begins

The Process of Regeneration

Fibrocytes move into necrotic area

Lay down collagen fibers

To bind the area together (scar tissue)

New cells migrate into area

Or are produced by mesenchymal stem cells

Not all tissues can regenerate

Epithelia and connective tissues regenerate well

Cardiac cells and neurons do not regenerate (or regenerate

poorly)

Aging and Tissue

Aging and Tissue Structure

Speed and efficiency of tissue repair

decreases with age, due to

Slower rate of energy consumption (metabolism)

Hormonal alterations

Reduced physical activity

Aging and Tissue

Effects of Aging

Chemical and structural tissue changes

Thinning epithelia and connective tissues

Increased bruising and bone brittleness

Joint pain and broken bones

Cardiovascular disease

Mental deterioration

Aging and Tissue

Aging and Cancer Incidence

Cancer rates increase with age

1 in 4 people in the United States develops cancer

Cancer is the #2 cause of death in the United

States

Environmental chemicals and cigarette smoke

cause cancer

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