Chapter 4

Tissues

Muse 2430 lecture #21/14/13

The Cell Cycle

Stem and Progenitor Cells

What is a Tissue?

A tissue is a group of cells Common embryonic origin Function together to carry out specialized

activities

Hard (bone), semisolid (fat), or liquid (blood) Histology is the science that deals with the

study of tissues. Pathologist specialized in laboratory studies

of cells and tissue for diagnoses

Development of Tissues

Tissues of the body develop from three primary germ layers:

Ectoderm, Endoderm, and Mesoderm Epithelial tissues develop from all three

germ layers All connective tissue and most muscle

tissues drive from mesoderm Nervous tissue develops from ectoderm

A little embryology

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

Maintaining the Integrity of Epithelia

Intercellular connections

Attachment to basal lamina

Epithelial maintenance and repair

Epithelial Tissues

Intercellular Connections

Support and communication

CAMs (cell adhesion molecules):

– transmembrane proteins

Intercellular cement:

– proteoglycans

Hyaluronan (hyaluronic acid):

– glycosaminoglycans

Cell Junctions

Contact points between the plasma membranes of tissue cells 5 most common types:

Tight junctions Adherens junctions Desmosomes Hemidesmosomes Gap junctions

Epithelial Tissues

Cell Junctions Occluding (Tight) junctions—between two plasma

membranes Adhesion belt attaches to terminal web

Prevents passage of water and solutes

Isolates wastes in the lumen

Gap junctions—allow rapid communication Held together by channel proteins (junctional proteins,

connexons)

Allow ions to pass

Coordinate contractions in heart muscle

Epithelial Tissues

Cell Junctions Macula adherens (Desmosomes)

CAMs, dense areas, and intercellular cement

Spot desmosomes– tie cells together

– allow bending and twisting

Hemidesmosomes– attach cells to the basal lamina

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

Figure 4–2 Intercellular Connections

Epithelial Tissues

Figure 4–2 Intercellular Connections

Epithelial Tissues

Figure 4–2 Intercellular Connections

Epithelial Tissues

Figure 4–2 Intercellular Connections

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

Classification of Epithelia

Classification of Epithelia

Classification of Epithelia

Squamous Epithelia

Simple squamous epithelium

Absorption and diffusion

Mesothelium

Lines body cavities

Endothelium

Lines heart and blood vessels

Classification of Epithelia

Figure 4–3 Squamous Epithelia.

Classification of Epithelia

Squamous Epithelia

Stratified squamous epithelium

Protects against attacks

Keratin protein adds strength and water resistance

Classification of Epithelia

Figure 4–3 Squamous Epithelia.

Classification of Epithelia

Cuboidal Epithelia

Simple cuboidal epithelium

Secretion and absorption

Stratified cuboidal epithelia

Sweat ducts and mammary ducts

Classification of Epithelia

Figure 4–4 Cuboidal Epithelia.

Classification of Epithelia

Figure 4–4 Cuboidal Epithelia.

Classification of Epithelia

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)

Classification of Epithelia

Figure 4–4 Cuboidal Epithelia.

Classification of Epithelia

Columnar Epithelia

Simple columnar epithelium

Absorption and secretion

Pseudostratified columnar epithelium

Cilia movement

Stratified columnar epithelium

Protection

Classification of Epithelia

Figure 4–5 Columnar Epithelia.

Classification of Epithelia

Figure 4–5 Columnar Epithelia.

Classification of Epithelia

Figure 4–5 Columnar Epithelia.

Classification of Epithelia

Modes of Secretion in Glandular Epithelia Merocrine secretion

Is produced in Golgi apparatus Is released by vesicles (exocytosis) For example, sweat glands

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

Classification of Epithelia

Figure 4–6 Modes of Glandular Secretion.

Classification of Epithelia

Figure 4–6 Modes of Glandular Secretion.

Classification of Epithelia

Figure 4–6 Modes of Glandular Secretion.

Classification of Epithelia

Figure 4–6 Modes of Glandular Secretion.

Classification of Epithelia

Glandular Epithelia

Types of secretions

Serous glands:

– watery secretions

Mucous glands:

– secrete mucins

Mixed exocrine glands:

– both serous and mucous

Classification of Epithelia

Glandular Epithelia

Gland structure

Unicellular glands

– Mucous (goblet) cells are the only unicellular

exocrine glands:

» scattered among epithelia

» for example, in intestinal lining

Classification of Epithelia

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)

Classification of Epithelia

Figure 4–7 A Structural Classification of Exocrine Glands.

Connective Tissues

Connect epithelium to the rest of the body

(basal lamina)

Provide structure (bone)

Store energy (fat)

Transport materials (blood)

Have no contact with environment

Connective Tissues

Characteristics of Connective Tissues Specialized cells

Solid extracellular protein fibers

Fluid extracellular ground substance

The extracellular components of connective tissues (fibers and ground substance) make up the matrix

Majority of tissue volume

Determines specialized function

Connective Tissues

Classification of Connective Tissues

Connective tissue proper

Connect and protect

Fluid connective tissues

Transport

Supportive connective tissues

Structural strength

Connective Tissues

Categories of Connective Tissue Proper

Loose connective tissue

More ground substance, less fibers

For example, fat (adipose tissue)

Dense connective tissue

More fibers, less ground substance

For example, tendons

Connective Tissues

Fibroblasts Fibrocytes Macrophages Adipocytes Mesenchymal cells

Melanocytes Mast cells Lymphocytes Microphages

Nine Cell Types of Connective Tissue Proper

Connective Tissues

Connective Tissue Proper Cells Fibroblasts

The most abundant cell type:

– found in all connective tissue proper

– secrete proteins and hyaluronan (cellular cement)

Fibrocytes The second most abundant cell type:

– found in all connective tissue proper

– maintain the fibers of connective tissue proper

Connective Tissues

Connective Tissue Proper Cells Macrophages

Large, amoeba-like cells of the immune system:– eat pathogens and damaged cells

– fixed macrophages stay in tissue

– free macrophages migrate

Adipocytes Fat cells:

– each cell stores a single, large fat droplet

Mesenchymal Cells Stem cells that respond to injury or infection:

– differentiate into fibroblasts, macrophages, etc.

Connective Tissues

Connective Tissue Proper Cells

Melanocytes

Synthesize and store the brown pigment melanin

Mast Cells

Stimulate inflammation after injury or infection:

– release histamine and heparin

Basophils are leukocytes (white blood cells) that

also contain histamine and heparin

Connective Tissues

Connective Tissue Proper Cells

Lymphocytes

Specialized immune cells in lymphoid (lymphatic) system:

– For example, lymphocytes may develop into plasma cells

(plasmocytes) that produce antibodies

Microphages

Phagocytic blood cells:

– respond to signals from macrophages and mast cells

– For example, neutrophils and eosinophils

Connective Tissues

Connective Tissue Fibers

Collagen fibers

Most common fibers in connective tissue proper

Long, straight, and unbranched

Strong and flexible

Resist force in one direction

For example, tendons and ligaments

Connective Tissues

Connective Tissue Fibers

Reticular fibers

Network of interwoven fibers (stroma)

Strong and flexible

Resist force in many directions

Stabilize functional cells (parenchyma) and

structures

For example, sheaths around organs

Connective Tissues

Connective Tissue Fibers

Elastic fibers

Contain elastin

Branched and wavy

Return to original length after stretching

For example, elastic ligaments of vertebrae

Connective Tissues

Ground Substance

Is clear, colorless, and viscous

Fills spaces between cells and slows

pathogen movement

Connective Tissues

Figure 4–8 The Cells and Fibers of Connective Tissue Proper.

Connective Tissues

Figure 4–8 The Cells and Fibers of Connective Tissue Proper.

Connective Tissues

Embryonic Connective Tissues

Are not found in adults

Mesenchyme (embryonic stem cells)

The first connective tissue in embryos

Mucous connective tissue

Loose embryonic connective tissue

Connective Tissues

Figure 4–9 Connective Tissues in Embryos.

Connective Tissues

[INSERT FIG. 4.9b]

Figure 4–9 Connective Tissues in Embryos.

Connective Tissues

Loose Connective Tissues

The packing materials of the body

Three types in adults

Areolar

Adipose

Reticular

Connective Tissues

Areolar Tissue

Least specialized

Open framework

Viscous ground substance

Elastic fibers

Holds blood vessels and capillary beds

For example, under skin (subcutaneous layer)

Connective Tissues

Adipose Tissue Contains many adipocytes (fat cells) Types of adipose tissue

White fat:– most common – stores fat– absorbs shocks– slows heat loss (insulation)

Brown fat: – more vascularized – adipocytes have many mitochondria– when stimulated by nervous system, fat break down

accelerates, releasing energy – absorbs energy from surrounding tissues

Connective Tissues

Adipose Tissue

Adipose cells Adipocytes in adults do not divide:

– expand to store fat

– shrink as fats are released

Mesenchymal cells divide and differentiate:

– to produce more fat cells

– when more storage is needed

Connective Tissues

Reticular Tissue

Provides support

Complex, three-dimensional network

Supportive fibers (stroma)

Support functional cells (parenchyma)

Reticular organs

Spleen, liver, lymph nodes, and bone marrow

Connective Tissues

Figure 4–10 Adipose and Reticular Tissues.

Connective Tissues

Figure 4–10 Adipose and Reticular Tissues.

Connective Tissues

Dense Connective Tissues

Connective tissues proper, tightly packed with

high numbers of collagen or elastic fibers

Dense regular connective tissue

Dense irregular connective tissue

Elastic tissue

Connective Tissues

Dense Regular Connective Tissue

Tightly packed, parallel collagen fibers

Tendons attach muscles to bones

Ligaments connect bone to bone and stabilize

organs

Aponeuroses attach in sheets to large, flat

muscles

Connective Tissues

Figure 4–11 Dense Connective Tissues.

Connective Tissues

Dense Irregular Connective Tissue

Interwoven networks of collagen fibers

Layered in skin

Around cartilages (perichondrium)

Around bones (periosteum)

Form capsules around some organs (e.g., liver,

kidneys)

Connective Tissues

Figure 4–11 Dense Connective Tissues.

Connective Tissues

Elastic Tissue

Made of elastic fibers

For example, elastic ligaments of spinal vertebrae

Connective Tissues

Figure 4–11 Dense Connective Tissues.

Membranes

Membranes

Are physical barriers

That line or cover portions of the body

Consist of

An epithelium

Supported by connective tissues

Membranes

Four Types of Membranes

Mucous membranes

Serous membranes

Cutaneous membrane

Synovial membranes

Membranes

Mucous membranes (mucosae)

Line passageways that have external connections

In digestive, respiratory, urinary, and reproductive

tracts

Epithelial surfaces must be moist

To reduce friction

To facilitate absorption and excretion

Lamina propria

Is areolar tissue

Membranes

Serous Membranes

Line cavities not open to the outside

Are thin but strong

Have fluid transudate to reduce friction

Have a parietal portion covering the cavity

Have a visceral portion (serosa) covering the

organs

Membranes

Three Serous Membranes Pleura:

Lines pleural cavities Covers lungs

Peritoneum: Lines peritoneal cavity Covers abdominal organs

Pericardium: Lines pericardial cavity Covers heart

Membranes

Figure 4–16 Membranes.

Membranes

Cutaneous membrane

Is skin, surface of the body

Thick, waterproof, and dry

Synovial membranes

Line moving, articulating joint cavities

Produce synovial fluid (lubricant)

Protect the ends of bones

Lack a true epithelium

Membranes

Figure 4–16 Membranes.

Neural Tissue

Figure 4–19 Neural Tissue.

Tissue Injuries and Repair

Tissues respond to injuries to maintain

homeostasis

Cells restore homeostasis with two processes

Inflammation

Regeneration

Tissue Injuries and Repair

Inflammation = inflammatory response The tissue’s first response to injury

Signs and symptoms of the inflammatory

response include Swelling

Redness

Heat

Pain

Tissue Injuries and Repair

Inflammatory Response

Can be triggered by

Trauma (physical injury)

Infection (the presence of harmful pathogens)