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Tissue Level of
Organization
Dr. Michael P. Gillespie
Tissue Types
• Four basic tissue types exist in the body.
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1. Epithelial tissue
2. Connective tissue
3. Muscle tissue
4. Nervous tissue
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Epithelial Tissue
• Epithelial tissue covers body surfaces and lines
hollow organs, body cavities, and ducts. It also
forms glands.
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Connective Tissue
• Connective tissue protects and supports the
body and its organs. Various types of
connective tissue bind organs together, store
energy reserves as fat, and help provide
immunity to disease-causing organisms.
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Muscle Tissue
• Muscle tissue generates the physical force
needed to make body structures move.
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Nervous Tissue
• Nervous tissue detects changes in a variety of
conditions inside and outside the body and
responds by generating nerve impulses and
help maintain homeostasis.
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Biopsy
• A biopsy (bio = life, -opsy = to view) is the
removal of a sample of living tissue for
microscopic examination.
• Used to diagnose disorders.
• Compared to normal tissue.
• Removed surgically or through needle and
syringe.
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Cell Junctions
• Cell junctions are contact points between the
plasma membranes of tissue cells.
• Functions
• Forming seals between cells.
• Anchoring cells to one another or to
extracellular material.
• Channels between cells in a tissue (passage of
ions and molecules).
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Major Types of Cell
Junctions
• Tight junctions
• Adherens junctions
• Desmosomes
• Hemidesmosomes
• Gap junctions
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Adherens Junctions
• Help epithelial cells resist separation.
• Located in epithelial cells.
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Desmosomes
• Attach cells to one another.
• Contribute to the stability of the cells and
tissue.
• Found in the epidermis and between cardiac
muscle cells.
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Hemidesmosomes
• Hemi – half. Hemidesmosomes lack links to
adjacent cells.
• Anchor cells to the basement membrane.
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Gap Junctions
• Form fluid filled channels that connect
adjacent cells.
• Ions and small molecules can diffuse from the
cytosol of one cell to the next.
• Enable nerve impulses to travel more rapidly
among cells.
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Epithelial Tissue
• Cells arranged in continuous sheets.
• Avascular – without blood vessels.
• Exchange of substances occurs by diffusion.
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Apical Surface
• Apical (free) surface – faces the body surface,
a body cavity, the lumen (interior space) of an
internal organ, or a tubular duct that receives
secretions from cells.
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Lateral Surfaces
• The lateral surfaces of an epithelial cell face
adjacent cells.
• The lateral surfaces may contain tight
junctions, adherens junctions, desmosomes,
and gap junctions.
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Basal Surface
• Opposite the apical surface.
• Anchored to the basement membrane.
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Basement Membrane
• Attaches to and supports the epithelial layer.
• Restricts the passage of larger molecules
between the epithelial layer and connective
tissue.
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Types of Epithelium
• Covering and lining epithelium
• Forms the outer covering of skin and some internal
organs.
• Forms the lining of blood vessels, ducts, body
cavities, and the interior of the respiratory,
digestive, urinary, and reproductive systems.
• Glandular epithelium
• Forms the secreting portion of glands (I.e. thyroid,
adrenal and sweat glands).
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Classification of
Epithelium
• Classified by the # of layers.
• Classified by the shapes of cells.
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Arrangement of Cells in
Layers
• Simple epithelium - single layer of cells
• Functions in secretion and absorption
• Stratified epithelium – 2 or more layers of cells
• Protects underlying tissues
• Pseudostratified epithelium – contains a single
layer of cells, but the nuclei lie at different
levels.
• Some cells are ciliated or secrete mucus.
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Cell Shapes
• Squamous cells
• Flat, thin cells that allow for rapid movement of
substances through them.
• Cuboidal cells
• As tall as they are wide. Function in secretion or
absorption. May have microvilli.
• Columnar cells
• Taller than they are wide. Specialized for secretion or
absorption.
• Transitional cells
• Change shape as organs stretch and collapse.
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Types of Simple
Epithelium
• Simple squamous epithelium
• Simple cuboidal epithelium
• Simple columnar epithelium
• Nonciliated
• Ciliated
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Types of Stratified
Epithelium
• Stratified squamous epithelium
• Keratinized
• Nonkeratinized
• Stratified cuboidal epithelium
• Stratified columnar epithelium
• Transitional epithelium
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Pseudostratified
Columnar Epithelium
• Nonciliated
• Ciliated
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Simple Squamous
Epithelium
• Single layer cells.
• Flat cells.
• Location
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Bowman’s capsule of kidneys
Air sacs of lungs
Lining of the heart
Lining of blood vessels
Lining of lymphatic vessels
Inner surface of the tympanic membrane
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Simple Cuboidal
Epithelium
• Single layer of cells.
• Cells have an equal height and width.
• Functions of secretion and absorption.
• Location
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Surface of ovary
Kidney tubules
Ducts of many glands
Secreting portions of some glands
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Simple Columnar
Epithelium
• Single layer of cells.
• Cells are taller than they are wide.
• Location
• Ciliated
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Upper respiratory tract
Uterine (Fallopian) tubes
Paranasal sinuses
Central canal of spinal cord
• Nonciliated
• GI tract from stomach to anus
• Ducts of many galnds
• Gallbladder
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Stratified Squamous
Epithelium
• 2 or more layers of cells
• Apical layers of cells are flat
• Deep layers vary in shape from cuboidal to
columnar
• Keratinized and nonkeratinized forms
• Location
• Keratinized lines the surface of the skin
• Nonkeratinized lines wet surfaces such as the
mouth, esophagus, epiglottis, vagina and tongue
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Stratified Cuboidal
Epithelium
• 2 or more layers of cells
• Equal in height and width
• Location
• Ducts of adult sweat glands and esophageal
glands
• Part of male urethra
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Stratified Columnar
Epithelium
• 2 or more layers of cells
• Taller than they are wide
• Basal layer contains shortened, irregularly shaped
cells
• Only the apical layer has columnar cells
• Location
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Part of urethra
Excretory ducts of some glands (I.e. esophageal)
Anal mucous membrane
Conjunctiva of the eye
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Transitional Epithelium
• 2 or more layers of cells
• Variable in appearance
• Present in the urinary system
• Un-stretched it looks similar to stratified cuboidal
epithelium
• Stretched it looks similar to stratified squamous
epithelium
• Location
• Urinary bladder
• Portions of the ureters and urethra
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Pseudostratified
Columnar Epithelium
• Single layer of cells – appears to be more than
one layer due to uneven nuclei
• Some cells do not extend to the surface
• The cells that extend to the surface either
secrete mucous (goblet cells) or bear cilia
• Location
• Airways of the upper respiratory tract
• Larger ducts of many glands
• Epididymis
Part of male urethra 42
Dr. Michael •
P. Gillespie
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Glandular Epithelium
• Function – secretion
• Gland – a single cell or group of cells that
secrete substances into ducts, onto a surface,
or into the blood.
• 2 types
• Endocrine
• Exocrine
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Endocrine Glands
• The secretions of endocrine glands enter the
interstitial fluid and then diffuse directly into
the bloodstream.
• These secretions do NOT flow through a duct.
• These secretions are called hormones.
• Examples
• Pituitary, thyroid, and adrenal glands
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Exocrine Glands
• Exocrine glands secrete their products into
ducts that empty onto the surface of a
covering and lining epithelium.
• Types of secretions
• Mucus, sweat, oil, earwax, sailva, digestive
enzymes
• Examples
• Sudoriferous (sweat) and salivary glands
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Structural Classification
of Glands
• Unicellular – single celled
• Multicellular – many celled – distinct organ
• Simple - unbranched
• Compound - branched
• Tubular – tubular secretory parts
• Acinar – rounded secretory portions
• Tubular Acinar
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Simple Glands
• Simple tubular
• Glands in Large Intestine
• Simple branched tubular
• Gastric glands
• Simple coiled tubular
• Sweat glands
• Simple acinar
• Glands of penile urethra
• Simple branched acinar
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Dr. Michael P. Gillespie
Compound Glands
• Compound tubular
• Bulbourethral (Cowper’s) glands
• Compound acinar
• Mammary glands
• Compound tubuloacinar
• Acinar glands of the pancreas
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Functional Classification
of Exocrine Glands
• Merocrine glands
• The secretion is synthesizes on ribosomes on the
RER
• Released from the cell in secretory vesicles
• Most glands of the body
• Apocrine glands
• Accumulate secretory products on the apical
surface, which then pinches off.
• Holocrine glands
• Accumulate a secretory product in their cytosol.
The cell matures and ruptures,
thus releasing its
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secretory product.
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Connective Tissue
Functions
• Binds together, supports, and strengthens
other body tissues
• Protects and insulates internal organs
• Compartmentalizes structures such as skeletal
muscles
• Major transport system within the body (blood
is a fluid CT)
• Major site of stored energy reserves (adipose
tissue)
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Features of Connective
Tissue
• 2 Basic element
• Cells
• Matrix
• Fills the wide spaces between the cells
• Determines the tissue’s qualities
• In cartilage it is pliable
• In bone it is hard and not pliable
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Features of CT
continued…
• Does not usually occur on body surfaces, with
the exception of areolar which lines joint
cavities.
• Usually highly vascular, with the exception of
cartilage (avascular) and tendons (scanty).
• Contains a nerve supply with the exception of
cartilage.
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Types of CT Cells
• Fibroblasts
• Macrophages
• Plasma cells
• Mast cells
• Adipocytes
• White blood cells
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Fibroblasts
• Fibro = fibers
• Secrete fibers and ground substance of the
matrix
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Macrophages
• Macro = large; -phages = eaters
• Develop from monocytes (type of WBC)
• Engulf bacteria and cellular debris by
phagocytosis
• Fixed macrophages – reside in a particular
tissue
• Wandering macrophages – roam tissues and
gather at sites of infection or inflammation
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Plasma Cells
• Develop from WBCs
• Secrete antibodies which attack foreign
substances in the body
• Part of the immune system
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Mast Cells
• Produce histamine which dilates small blood
vessels
• Part of the inflammatory response
• Reaction to injury or infection
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Adipocytes
• Adipose cells (fat cells)
• Store triglycerides (fats)
• Found below the skin and around organs such
as the heart and kidneys
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White Blood Cells
• Migrate to CT under certain conditions
• Neutrophils – respond to infection
• Eosinophils – respond to parasites and allergic
responses
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Connective Tissue Matrix
• Ground Substance
• Supports cells, binds them together, and provides a
medium for the exchange of substances
• Fibers
• Strengthen and support CTs
• Types
• Collagen fibers – strong but not stiff (flexible)
• Elastic fibers – smaller in diameter than collagen – stretch
and return to their original shape
• Reticular fibers – support to walls of blood vessels, form a
network around tissues, form basement membrane
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Marfan Syndrome
• An inherited disorder caused by a defective
fibrillin gene
• Abnormal development of elastic fibers.
• Predominant structures affected:
• Periosteum of the bones
• Ligament that suspends the lens of the eye
• Walls of large arteries
• Features:
• Tall with disproportionately long arms, legs, and
digits
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Classification of
Connective Tissue
• Embryonic CT – present in the embryo and
fetus
• Mesenchyme – all CT arises from this
• Mucous CT (Wharton’s jelly) – umbilical cord
• Mature CT – present in the newborn
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Loose CT
Dense CT
Cartilage
Bone Tissue
Blood Tissue
Lymph
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Embryonic Connective
Tissue
• Mesenchyme
• Mucous CT
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Loose Connective Tissue
• Areolar CT
• Adipose Tissue
• Reticular CT
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Dense Connective Tissue
• Dense regular CT
• Dense irregular CT
• Elastic CT
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Cartilage
• Hyaline cartilage
• Fibrocartilage
• Elastic cartilage
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Loose Connective Tissue
• The fibers are loosely intertwined and many
cells are present
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Areolar Connective
Tissue
• Widely distributed throughout the body
• Contains fibroblasts, macrophages, plasma
cells, mast cells, adipocytes, and WBCs
• Fiber types
• Collagen, elastic, and reticular
• Combined with adipose tissue it forms the
subcutaneous layer
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Adipose Connective
Tissue
• Loose CT
• Adipocytes (adipo = fat) – store triglycerides
• Good insulator
• Energy Reserve
• Supports and protects organs
• Cytoplasm and nucleus are pushed to the
periphery of the cell from large triglyceride
droplet
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Liposuction
• Lip = fat; suction lipectomy ectomy = to cut out
• Suctioning out small sections of adipose tissue
• Complications
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Fat emboli (clots)
Fluid depletion
Injury to internal structures
Severe postoperative pain
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Reticular Connective
Tissue
• Forms the stroma (supporting framework) of
the liver, spleen, and lymph nodes
• Binds together smooth muscle cells
• Reticular fibers in the spleen filter blood and
remove worn-out blood cells
• Reticular fibers in the lymph nodes filter lymph
and remove bacteria
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Dense Connective Tissue
• More numerous, thicker, denser fibers and
fewer cells than loose CT
• Dense Regular CT – tendons and most
ligaments
• Dense Irregular CT – heart valves,
perichondrium, periosteum
• Elastic CT – lung tissue, elastic arteries
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Cartilage
• Dense network of cartilage fibers and elastic
fibers
• Endures more stress than loose and dense CT
• Chondrocytes = mature cartilage cells
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Hyaline Cartilage
• Most abundant cartilage in the body
• Weakest of the 3 types of cartilage
• Flexible
• Located in joints – reduces friction and shock
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Fibrocartilage
• Strongest of the 3 types of cartilage
• Strength and rigidity
• Located in intervertebral discs
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Elastic Cartilage
• Provides strength and elasticity
• Maintains the shape of external structures
• Located in the ear
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Bone Tissue
• The basic unit of compact bone is an osteon or
Haversian system
• 4 parts of the osteon
• Lamellae = little plates – concentric rings of matrix –
consist of mineral salts
• Lacunae = little lakes – spaces btwn. Lamellae that
contain osteocytes
• Canaliculli = little canals – contain processes of
osteocytes – routes for nutrients and waste
products
• Central (Haversian) canal – contains blood vessels
and nerves
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Blood Tissue
• Connective Tissue with a liquid matrix called
blood plasma – pale yellow fluid (mostly
water) with dissolved substances: nutrients,
wastes, enzymes, plasma proteins, hormones,
gases, ions
• Suspended
• Red blood cells
• White blood cells
• Platelets
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Lymph
• Extracellular fluid that flows in lymphatic
vessels
• Contains lymphocytes (type of WBC) and
dietary lipids
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Elephantiasis
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Membranes
• Flat sheets of pliable tissue that cover or line a
part of the body
• Two types
• Epithelial
• Mucous membrane
• Serous membrane
• Cutaneous membrane of the skin
• Synovial
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Mucous Membranes
• Lines a body cavity that opens directly to the
exterior
• Line digestive, respiratory, reproductive tracts
and much of the urinary tract
• Goblet cells secrete mucous
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Serous Membranes
• Serous = watery
• Line body cavities that do NOT open directly to
the exterior
• Two layers
• Parietal (pariet = wall) – attached to the cavity wall
• Visceral (viscer = body organ) – attaches to the
organs inside the cavity
• Secretes serous fluid
• Pleura / pericardium / peritoneum
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Synovial Membranes
• Syn = together
• Line the cavities of freely moveable joints
• Secrete synovial fluid which lubricates and
nourishes the joint
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Muscle Tissue
• Consists of elongated cells called muscle fibers
• Produces body movements, maintains
posture, and generate heat
• Types
• Skeletal muscle tissue
• Cardiac muscle tissue
• Smooth muscle tissue
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Skeletal Muscle Tissue
• Attaches to bones of the skeleton
• Striated
• Voluntary
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Cardiac Muscle Tissue
• Forms the wall of the heart
• Striated
• Involuntary
• Fibers attach to one another via intercalated
discs (intercalat = to insert between)
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Smooth Muscle Tissue
• Located in the walls of hollow internal
structures
• Involuntary
• Lacks striations (smooth)
• Located in blood vessels, airways to lungs,
stomach, intestines, gallbladder, and urinary
bladder
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Nervous Tissue
• Two types of cells
• Neurons – nerve cells
• Neuroglia (glia = glue) – supporting structures
• Parts of Neurons
• Cell body
• Dendrites
• Axon
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