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Chapter 4:

The Tissue Level of Organization
Introduction
Cell types arrange in various combinations to form tissues, which are structures with
discrete structural and functional properties
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4-1
The 4 tissue types are epithelia, connective, muscle, and neural
The human body contains trillions of cells, but only about 200 types of cells
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Maintaining the integrity of epithelia:
Intercellular connections
Attachment to the basement membrane
• two layers keeps the cell firmly connected to their support surface
Epithelial maintenance and repair
• epithelia are replaced by division of germative cells (stem cells)

*Epithelial cells exhibit modifications that adapt them for secretions

Cell adhesion molecules (CAMs) transmembrane proteins
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3 most common types of cell junctions are:
1 tight junctions, 2 gap junctions, and 3 desmosomes
AT
Gap junctions) 2 cells are held together by 2 interlocking transmembrane proteins called
connexons
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CAMs and proteoglycans link the opposing plasma
membranes
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There are 2 types of Desmosomes:
Spot desmosomes small discs connected to bands of intermediate filaments, that stabilize the
shape of the cell
Hemidesmosomes resemble half of a spot desmosome
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They are exposed to everything
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They are located near the basement membrane, in a
relatively protected location
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Squamose Epithelium
Mesothelium) the name given to special simple squamose epithelia that does not communicate
with the outside world
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Transitional Epithelia
Transitional epithelium) an unusual stratified epithelium
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(located in the urinary system)
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(Specialized types of Epithelium):
Glandular Epithelia
Many epithelia contain glands that are specialized for secretion
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Others, known as exocrine glands
(release their secretions into passageways called ducts that open onto an epithelial surface
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Endocrine glands are
often called ductless glands because their secretions are not released into ducts
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Chapter 4:

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Exocrine Glands
Produce Exocrine secretions
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:
Modes of secretion
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Mucin is a merocrine secretion that mixes with
water to form mucus
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The apical portion of
the secretory cell of the gland pinches off and enters the lumen
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(example sebaceous glands)

Types of secretions
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Serous glands
• watery secretions that contain enzymes
• Example; parotid salivary gland
Mucus glands
• secret mucins that hydrate and become mucus
• Example; sublingual salivary glands, small intestine mucous glands
Mixed exocrine glands
• both serous and mucus
• Example; submandibular glands

4-4
Connective tissue provides a protective structural framework for
other tissue types
In essence, connective tissue connects the epithelium to the rest of the body
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Connective tissues occur throughout the body but they are never exposed to the outside environment,
they are highly vascular, and contain sensory receptors
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We classify connective tissue by their physical properties and the 3 general categories are:
Connective tissue proper) loose connective tissue (adipose) and dense connective
tissue (tendons)
Fluid connective tissue) 2 types blood and lymph
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Supporting connective tissue) 2 types cartilage and bone (the matrix of bones is

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Chapter 4:

Connective Tissue Proper Cell Populations
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Fibroblasts
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most abundant cell type; in all connective tissue proper
secrete proteins and hyaluronan (cellular cement)

Fibrocytes
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2nd most abundant cell type; in all connective tissue proper
maintain the fibers of connective tissue proper
Adipocytes (fat cells)
• each cell stores a single, large fat droplet

Mesenchymal cells
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stem cells that respond to infection or injury
differentiate into fibroblasts, macrophages, or other connective tissue cells

Macrophages
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large immune cells that that eat pathogens and damaged cells

Mast cells
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stimulate inflammation after injury or infection (histamine and heparin)

Lymphocytes
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specialized immune cells in lymphatic (lymphoid) system
Microphages (neutrophils and eosinophils)
• phagocytic blood cells
• respond to signals from macrophages and mast cells

Melanocytes
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synthesize and store the brown pigment melanin

Connective tissues
3types of fibers occur in connective tissues collagen, reticular, and elastic fibers
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Stronger than steel (tendons consist
almost entirely of collagen fibers) (tendons connect 1 bone to another bone)

Reticular fibers: tough yet flexible
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After stretching they return to their original length
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Ground substance fills the spaces between cells and surrounds connective tissue fibers
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GIVES RISE TO ALL OTHER
CONNECTIVE TISSUES
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Loose Connective Tissues
Are the ''packing materials'' of the body
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Includes areolar tissue, adipose tissue, and
reticular tissue
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It is the common site
for injections due to high blood supply
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It provides padding, absorbs
shocks, acts as an insulator to slow heat loss, and serves as packing filler around structures
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Reticular tissue: organs such as the spleen and liver contain this tissue
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Dense Connective Tissue
Often called collagenous tissues because collagen fibers are the dominant type of fiber in them
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Tendons- are cords of dense regular connective tissue that attach skeletal muscles to bones
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Aponeurosis- is a tendinous sheet that attaches a broad, flat muscle to another muscle or to
several bones of the skeleton
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Giving skin its strength
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Elastic tissue- is a dense regular connective tissue they help stabilize the position of the
vertebrae in the spinal column
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In blood the watery
matrix is called plasma
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There are 3 types of formed elements: red blood cells, white blood cells, and platelets
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*Capillaries- the smallest blood vessels and were exchange of waste and nutrients take place
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*Lymph forms as interstitial fluid enters lymphatic vessels
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Cartilage
The matrix of cartilage is a firm gel that contains polysaccharides derivatives called
chondroitin sulfates) that form complexes with proteins in the ground substance, producing
proteoglycans
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Are the only cells in the cartilage matrix
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Antiangiogenesis) the chemical inhibitor that discourages the formation of blood vessels going
in cartilage
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Appositional growth) adds new layers of cartilage to the surface
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Types of Cartilage
The body contains 3 major types of cartilage: 1 hyaline, 2 elastic, and 3 fibrocartilage
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Elastic cartilage) extremely resilient and flexible because it contains numerous elastic fibers
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(intervertebral discs)

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Chapter 4:

Cartilage function
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3 types
Gel-type ground substance
For shock absorption and protection

Bone
Bone or Osseous are remarkably strong and resistant to shattering
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Periosteum) a covering composed of fibrous layers
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Bone function
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Calcified (made rigid by calcium salts, minerals)
For weight support

4-6
Tissue membranes are physical barriers of 4 types: mucus,
serous, cutaneous, and synovial
Mucus membranes
also known as mucosae) line passageways and chambers that communicate with the exterior
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Lamina propria) what the areola tissue component of a mucus membrane is called
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These membranes consist of mesothelium supported by areolar tissue
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The function of any serous membrane is to lubricate to minimize friction between surfaces that
it covers
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Chapter 4:

The Cutaneous membrane
Cutaneous membrane) is the skin that covers the surface of your body (skin)
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Synovial membranes
Synovial fluid is produced by the synovial membrane which lines the joint cavity
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Fasciae) are connective tissue layers and wrapping that surround and support organs
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Separates the skin
from the underlying tissues and organs
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Superficial

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4-8
The 3 types of muscle tissue are skeletal, cardiac, and smooth
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Muscle Tissue
• Specialized for contraction
• Produces all body movement
• 3 types of muscle tissue
• Classification
• Striated (muscle cells with a banded appearance)
• Nonstriated (not banded; smooth)
• Muscle cells can be controlled voluntarily (consciously)
• Muscle cells can be controlled involuntarily (automatically)

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Chapter 4:

Skeletal Muscle Tissue (Striated voluntary muscle)
Contains very large muscle cells
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Muscle fibers) individual muscle cells are relatively long and slender
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Skeletal muscles are incapable of dividing
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Cardiac Muscle Tissue (Striated involuntary muscle)
Is found in the heart
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Intercalated discs) specialized region where cells of the heart are connected
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Smooth Muscle Tissue Nonstriated involuntary muscle)
Is found in the walls of blood vessels, around hollow organs such as the urinary bladder, and in
layers around the respiratory, cardiovascular, digestive, and reproductive tract
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4-9
Neural tissue responds to stimuli and propagates electrical
impulses throughout the body
Neural tissue) also known as nervous tissue
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It contains 2 basic types of cells
Neurons) a cell in neural tissue that is specialized for intercellular communication through 1
changes in membrane potential and 2 synaptic connections
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Typically, they have a large cell body
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Neuroglia) cells of the CNS and PNS that support and protect neurons; also called glial cells
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Regeneration) is the repair process that restores normal function after inflammation has subsided
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It begins
several hours after the injury
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4-11
With advancing age, tissue repair declines and cancer rates
increase
Aging has 2 important effects on tissues
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Aging and Tissue Structure
Epithelial get thinner and connective tissues become more fragile
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It has been estimated that 70-80% of cancer cases
result from chemical exposer, environmental factors, or some combonation of the 2, and 40% is caused
by smoking
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Chapter 4:

Related Clinical Terms
autopsy) an examination of a dead body to discover the cause of death or the extent of disease
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Cachexia) weakness and wasting of the body due to severe chronic illness
carcinoma) a cancer arising in the epithelial tissue of the skin or of the lining of the internal organs
immunotherapy) the prevention or treatment of disease with substances that stimulate the immune response
lesion) a region in an organ or tissue that has suffered damage from injury or disease; a wound, ulcer, abscess, or tumor,
for example

metaplasia) a reversible structural change that alters the character of a tissue
pathologist) a physician who specializes in the study of disease processes and body fluids
remission) abatement, ending, or lessening in severity of the signs and symptoms of a disease
sarcoma) a malignant tumor of connective or other nonepithelial tissue
tissue engineering) tissue is either grown in or outside of a body to be transplanted into a patient or used for testing
tissue rejection) occurs when a recipient's immune system attacks a transplanted organ or tissue
tumor grading) a system used to classify cancer cells in terms of how abnormal they look under a microscope and how
quickly the tumor is likely to grow and spread

tumor staging) defining at what point the patient is in in the development of the malignant disease when the diagnosis is
made

xenotransplant) the process of grafting or transplanting organs or tissues between members of different species

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