Biol 2430 Anatomy and Physiology

Lect #2Muse9/14/11

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

Cell Junctions

• Contact points between the plasma membranes of tissue cells

– 5 most common types:

• Tight junctions

• Adherens junctions

• Desmosomes

• Hemidesmosomes

• Gap junctions

Stem and Progenitor Cells

Stem cell • can divide to form two new stem cells

• self-renewal• can divide to form a stem cell and a progenitor cell• totipotent – can give rise to every cell type• pluripotent – can give rise to a restricted number of cell types

Progenitor cell • committed cell• can divide to become any of a restricted number of cells • pluripotent

Stem and Progenitor Cells

Control of Cell Division• cell division capacities vary greatly among cell types

• skin and blood cells divide often and continually• neuron cells divide a specific number of times then cease

• chromosome tips (telomeres) that shorten with each mitosis provide a mitotic clock

• cells divide to provide a more favorable surface area to volume relationship• growth factors and hormones stimulate cell division

• hormones stimulate mitosis of smooth muscle cells in uterus• epidermal growth factor stimulates growth of new skin

Cancertumors are the consequence of a loss of cell cycle control

Traditional control of growth is lost: cells become independent of growth factors.

cells lose contact inhibition

in many cases cells become immortal

Telomeres cap the ends of chromosomes

Chromosomes tagged with anti-telomerase antibodies

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• Functions of Epithelial Tissue

– Provide physical protection

– Control permeability

– Provide sensation

– Produce specialized secretions (glandular

epithelium)

Epithelial Tissues

Figure 4–1 The Polarity of Epithelial Cells.

Epithelial Tissues• Maintaining the Integrity of Epithelia

– Intercellular connections

– Attachment to basal lamina

– Epithelial maintenance and repair

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 4–4 Cuboidal 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• 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• Glandular Epithelia

– Endocrine glands• Release hormones:

– into interstitial fluid

– no ducts

– Exocrine glands• Produce secretions:

– onto epithelial surfaces

– through ducts

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

• Fibroblasts

• Fibrocytes

• Macrophages

• Adipocytes

• Mesenchymal cells

• Melanocytes

• Mast cells

• Lymphocytes

• Microphages

Nine Cell Types of Connective Tissue Proper

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

– 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• 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

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

Connective Tissues

Figure 4–12 Formed Elements of the Blood.

Supportive Connective Tissues• Support soft tissues and body weight

– Cartilage

• Gel-type ground substance

• For shock absorption and protection

– Bone

• Calcified (made rigid by calcium salts, minerals)

• For weight support

Supportive Connective Tissues• Cartilage Matrix

– Proteoglycans derived from chondroitin sulfates

– Ground substance proteins

• Chondrocytes (cartilage cells) surrounded by

lacunae (chambers)

Supportive Connective Tissues

Figure 4–13 The Growth of Cartilage.

Supportive Connective Tissues• Types of Cartilage

– Hyaline cartilage• Stiff, flexible support• Reduces friction between bones• Found in synovial joints, rib tips, sternum, and trachea

– Elastic cartilage• Supportive but bends easily• Found in external ear and epiglottis

– Fibrous cartilage (fibrocartilage) • Limits movement• Prevents bone-to-bone contact• Pads knee joints• Found between pubic bones and intervertebral discs

Supportive Connective Tissues

Figure 4–14 The Types of Cartilage.

Supportive Connective Tissues

Figure 4–14 The Types of Cartilage.

Supportive Connective Tissues

Figure 4–14 The Types of Cartilage.

Supportive Connective Tissues• Bone or osseous tissue

– Strong (calcified: calcium salt deposits)– Resists shattering (flexible collagen fibers)

• Bone cells or osteocytes– Arranged around central canals within matrix– Small channels through matrix (canaliculi) access blood

supply

• Periosteum – Covers bone surfaces– Fibrous layer– Cellular layer

Supportive Connective Tissues

Figure 4–15 Bone.

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

Figure 4–16 Membranes.

Internal Framework of the Body

• Connective tissues

– Provide strength and stability

– Maintain positions of internal organs

– Provide routes for blood vessels, lymphatic vessels, and

nerves

• Fasciae

– Singular form is fascia

• The body’s framework of connective tissue

• Layers and wrappings that support or surround organs

Internal Framework of the Body

Figure 4–17 The Fasciae.

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)

Tissue Injuries and Repair• 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