Four Types of Tissues - WCJC
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
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
Characteristics of Epithelia
Cellularity (cell junctions)
Polarity (apical and basal surfaces)
Attachment (basal lamina)
Avascularity
Regeneration
Functions of Epithelial Tissue
Provide physical protection
Control permeability
Provide sensation
Produce specialized secretions (glandular epithelium)
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
Maintaining the Integrity of Epithelia
Intercellular connections
Attachment to basal lamina
Epithelial maintenance and repair
Intercellular Connections
Support and communication
CAMs (cell adhesion molecules):
transmembrane proteins
Intercellular cement:
proteoglycans
Hyaluronan (hyaluronic acid):
glycosaminoglycans
Cell junctions
Form bonds with other cells or extracellular material:
occluding (tight) junctions
gap junctions
macula adherens (desmosomes)
[Insert Animation: Intercellular Connections]
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
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
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 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
Squamous Epithelia
Stratified squamous epithelium
Protects against attacks
Keratin protein adds strength and water resistance
Cuboidal Epithelia
Simple cuboidal epithelium
Secretion and absorption
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
Pseudostratified columnar epithelium
Cilia movement
Stratified columnar epithelium
Protection
Glandular Epithelia
Endocrine glands
Release hormones:
into interstitial fluid
no ducts
Exocrine glands
Produce secretions:
onto epithelial surfaces
through ducts
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
Glandular Epithelia
Types of secretions
Serous glands:
watery secretions
Mucous glands:
secrete mucins
Mixed exocrine glands:
both serous and mucous
Gland structure
Unicellular glands
Mucous (goblet) cells are the only unicellular exocrine glands:
scattered among epithelia
for example, in intestinal lining
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)
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
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
Classification of Connective Tissues
Connective tissue proper
Connect and protect
Fluid connective tissues
Transport
Supportive connective tissues
Structural strength
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
Fibroblasts
Fibrocytes
Macrophages
Adipocytes
Mesenchymal cells
Melanocytes
Mast cells
Lymphocytes
Microphages
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
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.
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
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 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
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
Elastic fibers
Contain elastin
Branched and wavy
Return to original length after stretching
For example, elastic ligaments of vertebrae
Ground Substance
Is clear, colorless, and viscous
Fills spaces between cells and slows pathogen movement
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
Loose Connective Tissues
The packing materials of the body
Three types in adults
Areolar
Adipose
Reticular
Areolar Tissue
Least specialized
Open framework
Viscous ground substance
Elastic fibers
Holds blood vessels and capillary beds
For example, under skin (subcutaneous layer)
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
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
Reticular Tissue
Provides support
Complex, three-dimensional network
Supportive fibers (stroma)
Support functional cells (parenchyma)
Reticular organs
Spleen, liver, lymph nodes, and bone marrow
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
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)
Elastic Tissue
Made of elastic fibers
For example, elastic ligaments of spinal vertebrae
Fluid Connective Tissues
Blood and lymph
Watery matrix of dissolved proteins
Carry specific cell types (formed elements)
Formed elements of blood
red blood cells (erythrocytes)
white blood cells (leukocytes)
platelets
Fluid Elements of Fluid Connective Tissues
Extracellular
Plasma
Interstitial fluid
Lymph
Lymph
Extracellular fluid
Collected from interstitial space
Monitored by immune system
Transported by lymphoid (lymphatic) system
Returned to venous system
Fluid Tissue Transport Systems
Cardiovascular system (blood)
Arteries
Capillaries
Veins
Lymphoid (lymphatic) system (lymph)
Lymphatic vessels
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
Cartilage Matrix
Proteoglycans derived from chondroitin sulfates
Ground substance proteins
Chondrocytes (cartilage cells) surrounded by lacunae (chambers)
Cartilage Structure
No blood vessels:
Chondrocytes produce antiangiogenesis factor
Perichondrium:
Outer, fibrous layer (for strength)
Inner, cellular layer (for growth and maintenance)
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
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
Membranes
Are physical barriers
That line or cover portions of the body
Consist of
An epithelium
Supported by connective tissues
Four Types of Membranes
Mucous membranes
Serous membranes
Cutaneous membrane
Synovial 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
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
Three Serous Membranes
Pleura:
Lines pleural cavities
Covers lungs
Peritoneum:
Lines peritoneal cavity
Covers abdominal organs
Pericardium:
Lines pericardial cavity
Covers heart
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
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
Superficial fascia
Deep fascia
Subserous fascia
Specialized for contraction
Produces all body movement
Three types of muscle tissue
Skeletal muscle
Large body muscles responsible for movement
Cardiac muscle
Found only in the heart
Smooth muscle
Found in walls of hollow, contracting organs (blood vessels; urinary bladder; respiratory, digestive, and reproductive tracts)
Classification of Muscle Cells
Striated (muscle cells with a banded appearance)
Nonstriated (not banded; smooth)
Muscle cells can have a single nucleus
Muscle cells can be multinucleate
Muscle cells can be controlled voluntarily (consciously)
Muscle cells can be controlled involuntarily (automatically)
Skeletal Muscle Cells
Are long and thin
Are usually called muscle fibers
Do not divide
New fibers are produced by stem cells (myosatellite cells)
Cardiac muscle cells
Are called cardiocytes
Form branching networks connected at intercalated discs
Are regulated by pacemaker cells
Smooth muscle cells
Are small and tapered
Can divide and regenerate
Also called nervous or nerve tissue
Specialized for conducting electrical impulses
Rapidly senses internal or external environment
Processes information and controls responses
Neural tissue is concentrated in the central nervous system
Brain
Spinal cord
Two Kinds of Neural Cells
Neurons
Nerve cells
Perform electrical communication
Neuroglia
Supporting cells
Repair and supply nutrients to neurons
Cell Parts of a Neuron
Cell body
Contains the nucleus and nucleolus
Dendrites
Short branches extending from the cell body
Receive incoming signals
Axon (nerve fiber)
Long, thin extension of the cell body
Carries outgoing electrical signals to their destination
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
Heat
Pain
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
Prostaglandins
Proteins
Potassium ions
As cells break down
Lysosomes release enzymes
That destroy the injured cell
And attack surrounding tissues
Tissue destruction is called necrosis
The Process of Inflammation
Necrotic tissues and cellular debris (pus) accumulate in the wound
Abscess:
pus trapped in an enclosed area
Injury stimulates mast cells to release
Histamine
Heparin
Prostaglandins
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
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 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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