The Tissue Level of Organization

• Group of similar cells

– common function
• Histology
– study of tissues
• Pathologist
– looks for tissue changes
that indicate disease

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 Epithelium
Epithelial tissue is found throughout the
body where it covers internal and
external surfaces. It also forms most of
the glands. It consists of a single layer of
cells or multiple layers of epithelial cells
between free surfaces and basement
membrane.
 Function of epithelia

• The major function of epithelia includes

1. Protecting underlying structure
Examples includes the outer layer of the
skin ad epithelium of the oral cavity

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Acting as a barriers
Epithelium prevents the movement of many
substance through the epithelial layer.
Example: the epithelium of the skin acts a
barrier to water and reduces water loss from
the body. The epithelium of the skin prevents
entry of toxic molecules and microorganism

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Permitting the passage of substance
Epithelium allows the movement of substance
through the epithelial layer.
Example: oxygen and carbon dioxide are
exchanged between air and blood diffusion
through the epithelium in the lungs

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Secreting substances
• Sweat gland, mucous gland and the enzyme
secreting portion of the pancreas

• Absorbing substance
• Carriers of molecules
• Epithelial cells of intestine that absorb
digested food molecules and vitamins.

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 4 Basic Tissues (1)
• Epithelial Tissue
– covers surfaces because cells are in contact
– lines hollow organs, cavities and ducts
– forms glands when cells sink under the surface
• Connective Tissue
– material found between cells
– supports and binds structures together
– stores energy as fat
– provides immunity to disease

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 4 Basic Tissues (2)

• Muscle Tissue
– cells shorten in length producing movement
• Nerve Tissue
– cells that conduct electrical signals
– detects changes inside and outside the body
– responds with nerve impulses

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Epithelial Tissue -- General Features
• Closely packed cells forming continuous sheets
• Cells sit on basement membrane
• Apical (upper) free surface
• Avascular---without blood vessels
– nutrients diffuse in from underlying connective
tissue
• Rapid cell division
• Covering / lining versus glandular types

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Basement Membrane
• holds cells to connective
tissue

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 Types of Epithelium

• Covering and lining epithelium

– epidermis of skin
– lining of blood vessels and ducts
– lining respiratory, reproductive, urinary & GI
tract
• Glandular epithelium
– secreting portion of glands
– thyroid, adrenal, and sweat glands

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 Classification of Epithelium
• Classified by arrangement of cells into layers
– simple = one cell layer thick
– stratified = many cell layers thick
– pseudostratified = single layer of cells where all cells
don’t reach apical surface
• nuclei at found at different levels so it looks multilayered
• Classified by shape of surface cells
– squamous =flat
– cuboidal = cube-shaped
– columnar = tall column
– transitional = shape varies with tissue stretching
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 Simple Squamous Epithelium

• Single layer of flat cells

– lines blood vessels (endothelium), body cavities
(mesothelium)
– very thin --- controls diffusion, osmosis and filtration
– nuclei centrally located
• Cells in direct contact with each other
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 Examples of Simple Squamous

• Surface view of • Section of intestinal

lining of peritoneal showing serosa
cavity

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 Simple Cuboidal Epithelium

• Single layer of cube-shaped cells viewed from the side

• Nuclei round and centrally located
• Lines tubes of kidney
• Absorption or secretion
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 Example of Simple Cuboidal

• Sectional view of kidney tubules

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 Simple Columnar

• Single layer rectangular cells

• Unicellular glands =goblet cells secrete mucus
– lubricate GI, respiratory, reproductive and urinary systems
• Microvilli = fingerlike cytoplasmic projections
– for absorption in GI tract (stomach to anus)
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Ex. Simple Columnar

• Section from small intestine

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 Stratified Squamous Epithelium

• Several cell layers thick

• Surface cells flat
• Keratinized = surface cells
dead and filled with keratin
– skin (epidermis)
• Nonkeratinized = no
keratin in moist living cells
at surface
– mouth, vagina

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Example of Stratified Squamous

• Section of vagina
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Papanicolaou Smear (Pap smear)

• Collect sloughed off cells of uterus and

vaginal walls
• Detect cellular changes (precancerous
cells)
• Annually for women over 18 or if sexually
active

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 Transitional Epithelium

• Multilayered
• Surface cells varying in shape
from round to flat if stretched
• Lines hollow organs that
expand from within (urinary
bladder) 4-22
Pseudostratified Columnar
• Single cell layer
• All cells attach to
basement membrane
but not all reach free
surface
• Nuclei at varying
depths
• Respiratory system,
male urethra &
epididymis

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 Connective Tissue

Functions
1. Enclosing and separating
Sheet of connective tissue form capsules
around organs such as liver and kidneys
Example: connective tissue that separates
muscles
2. Connecting tissue to one another
Tendons are strong cables or bands of
connective tissue that attach muscles to bone
and ligaments are connective tissue bands
that hold bones together

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Supporting and moving
Bones of the skeletal system provide
rigid support for the body and semi rigid
carti;age support such as nose ears and
surfaces joints.

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Storing
Adipose tissue (fat) stores high energy
molecules and bone marrow minerals
such as calcium and phosphate

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Cushioning and Insulating
Adipose cushion and protect tissue
through it surrounding and provides
an insulating layer beneath the skin
the help conserve heat.

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Transporting
Blood transport substance throughout the
body such as gases, nutrients, enzymes

Protecting
Cell of the immune system and blood provide
protection against toxins and tissue injury as
well as microorganism.

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 Connective Tissues
• Cells rarely touch due to extracellular matrix
• Matrix(fibers & ground substance secreted by cells)
• Consistency varies from liquid, gel to solid
• Does not occur on free surface
• Good nerve & blood supply except cartilage & tendons

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 Cell Types
• Blast type cells = retain ability to divide & produce
matrix (fibroblasts, chondroblasts, & osteoblasts)

• Cyte type cells = mature cell that can not divide or

produce matrix (chondrocytes & osteocytes)

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Connective Tissue Ground Substance
• Supports the cells and fibers
• Helps determine the consistency of the matrix
– fluid, gel or solid

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 Types of Connective Tissue Fibers
• Collagen (25% of protein in your body)
– tough, resistant to pull, yet pliable
– formed from the protein collagen
• Elastin (lungs, blood vessels, ear cartilage)
– smaller diameter fibers formed from protein elastin
surrounded by glycoprotein (fibrillin)
– can stretch up to 150% of relaxed length and return to
original shape
• Reticular (spleen and lymph nodes)
– thin, branched fibers that form framework of organs
– formed from protein collagen
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Mature Connective Tissue

• Loose connective tissue

• Dense connective tissue
• Cartilage
• Bone
• Blood
• Lymph

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 Loose Connective Tissues

• Loosely woven fibers throughout tissues

• Types of loose connective tissue
– areolar connective tissue
– adipose tissue
– reticular tissue

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Areolar Connective Tissue

• Black = elastic fibers,

• Pink = collagen fibers
• Nuclei are mostly fibroblasts
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 Adipose Tissue

• Peripheral nuclei due to large fat storage droplet

• Deeper layer of skin, organ padding, yellow marrow
• Reduces heat loss, energy storage, protection

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 Reticular Connective Tissue

• Network of fibers & cells that produce framework of organ

• Holds organ together (liver, spleen, lymph nodes, bone
marrow)
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 Dense Connective Tissue

• More fibers present but fewer cells

• Types of dense connective tissue
– dense regular connective tissue
– dense irregular connective tissue

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 Dense Regular Connective Tissue

• Collagen fibers in parallel bundles with fibroblasts between

bundles of collagen fibers
• White, tough and pliable when unstained (forms tendons)
• Also known as white fibrous connective tissue
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 Dense Irregular Connective Tissue

• Collagen fibers are irregularly arranged (interwoven)

• Tissue can resist tension from any direction
• Very tough tissue -- white of eyeball, dermis of skin 4-41
 Cartilage

• Network of fibers in rubbery ground substance

• Resilient and can endure more stress than
loose or dense connective tissue
• Types of cartilage
– hyaline cartilage
– fibrocartilage
– elastic cartilage

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 Hyaline Cartilage

• Bluish-shiny white rubbery substance

• Chondrocytes sit in spaces called lacunae
• No blood vessels or nerves so repair is very slow
• Reduces friction at joints as articular cartilage
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 Fibrocartilage

• Many more collagen fibers causes rigidity & stiffness

• Strongest type of cartilage (intervertebral discs)

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 Elastic Cartilage

• Elastic fibers help maintain shape after deformations

• Ear, nose, vocal cartilages
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 Growth & Repair of Cartilage

• Grows and repairs slowly because is avascular

• Interstitial growth
– chondrocytes divide and form new matrix
– occurs in childhood and adolescence
• Appositional growth
– chondroblasts secrete matrix onto surface
– produces increase in width

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 Bone (Osseous) Tissue
• Spongy bone
– sponge-like with spaces and trabeculae
– trabeculae = struts of bone surrounded by red bone
marrow
– no osteons (cellular organization)
• Compact bone
– solid, dense bone
– basic unit of structure is osteon (haversian system)
• Protects, provides for movement, stores
minerals, site of blood cell formation
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 Compact Bone

• Osteon = lamellae (rings) of mineralized matrix

– calcium & phosphate---give it its hardness
– interwoven collagen fibers provide strength
• Osteocytes in spaces (lacunae) in between lamellae
• Canaliculi (tiny canals) connect cell to cell
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 Blood

• Connective tissue with a liquid matrix = the plasma

• Cell types = red blood cells (erythrocytes), white blood
cells (leukocytes) and cell fragments called platelets
• Provide clotting, immune functions, carry O2 and CO2
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 Muscle

• Cells that shorten

• Provide us with motion, posture and heat
• Types of muscle
– skeletal muscle
– cardiac muscle
– smooth muscle

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 Skeletal Muscle

• Cells are long cylinders with many peripheral nuclei

• Visible light and dark banding (looks striated)
• Voluntary or conscious control
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 Cardiac Muscle

• Cells are branched cylinders with one central nuclei

• Involuntary and striated
• Attached to and communicate with each other by
intercalated discs and desmosomes 4-52
 Smooth Muscle

• Spindle shaped cells with a single central nuclei

• Walls of hollow organs (blood vessels, GI tract, bladder)
• Involuntary and nonstriated
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 Nerve Tissue

• Cell types -- nerve cells and neuroglial (supporting) cells

• Nerve cell structure
– nucleus & long cell processes conduct nerve signals
• dendrite --- signal travels towards the cell body
• axon ---- signal travels away from cell body 4-54
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