•Histology : Study of tissues
•Tissues : Group of similar cells and the
substances surrounding them
•Four major tissue types:
• Epithelial tissue
• Connective tissue
• Muscle tissue
• Nervous tissue
• Covers body surfaces & lines many body cavities, eg lung,
kidney, heart
• Forms glands
• Epithelial tissues are made up
of closely packed cells with
very little extracellular matrix
• Has free or apical, lateral and basal surfaces
• Basal surface is attached to
basement membrane
• It helps attach epithelial cells to the underlying tissue
• Basement membrane is a mixture of
carbohydrates & proteins secreted
by the epithelial & connective tissue
• Avascular, Nutrient and waste exchange
occurs through diffusion
• Undergoes mitosis to replace
damage cells with new
epithelial cells eg. Skin cells
• Protecting underlying structures: e.g., outer layer of skin, protect
underlying tissue from mechanical injury & epithelium lining of oral
cavity protect from abrasion
• Acting as barriers: e.g., skin reduces water loss, reduces entry of
toxic chemicals and microorganisms
• Diffusion: Promotes diffusion of gases, liquids and nutrients
because of a thin lining, eg. walls of capillaries and lungs
• Secreting substances: In glands, epithelial tissue secrete specific
chemical substances such as enzymes, hormones and lubricating
fluids
• Absorbing substances: e.g., epithelial lining the small intestine
absorb nutrients
 Epithelium is classified according to no. of
cell layers & shape of the cells
 Three major types of epithelium
based on number of layers of cells:
– Simple- one layer of cells
– Stratified- more than one layer
– Pseudostratified- Special type of
simple epithelium. Tissue appears to
be stratified, but all cells contact
basement membrane
 There are three types of epithelium
based on shape of the epithelial cells:
– Squamous- Cells are flat or scale
like
– Cuboidal- cube-shaped
– Columnar- Cells are taller than
they are wide
• Simple epithelium can be subdivided according
to the shape and function of its cells:
•Simple Squamous Epithelium:
• single layer of flat cells rest on basement membrane
• Functions: diffusion, filtration, some protection against
friction, secretion, absorption
• Location: forms the lining of cavities such as the mouth, blood vessels,
heart, lungs & make up the skin outer layer
• Single layer of cube-shaped cells
• Location: Kidney tubules, glands & their ducts, lining of terminal
bronchioles of the lungs, ovary surface
• Functions:
– Secretion and absorption in the kidney
– Secretion in glands
– Movement of particles out of the bronchioles by ciliated cells
• single layer of tall, narrow cells. Some have cilia (bronchioles of
lungs, auditory tubes, uterine tubes, and uterus) or microvilli
(intestine)
• Functions:
– Movement of particles out of the bronchioles by ciliated cells
– Aids in the movement of oocytes through the uterine tubes by
ciliated cells
– Secretion by glands of the stomach and the intestine
– Absorption by cells of the intestine
• Location: glands & some ducts, bronchioles of
lungs, auditory tubes, uterus, uterine tubes,
stomach, intestines, gallbladder, bile ducts and
ventricles of the brain
• Stratified epithelium can be subdivided according to the
shape and function of its cells:
• Stratified Squamous Epithelium:
• multiple layers of cells that are cube shaped in the basal
layer and progressively flatten toward the surface
• can be keratinized (cells are dead)
• or non-keratinized (cells are moist)
• Location: Found in skin (keratinized), mouth, throat,
larynx, vagina, esophagus, anus, inferior urethra, and
cornea ( moist)
• Functions: protection against abrasion, water loss, and
infection
• Consists of multiple layers of cube-shaped cells
• Location: sweat gland ducts, ovarian follicular cells,
and salivary gland ducts.
• Functions: secretion, absorption and protection against
infections.
• Consists of multiple layers of tall thin cells on layers
of more cuboidal cells
• Found in mammary gland duct, larynx, portion of
male urethra.
• Function: protection and secretion.
• Are columnar shaped single layer, appear to consists of
more than one layer because nuclei are at various levels,
• Cells are ciliated
• Locations: lining of nasal cavity, nasal sinuses, auditory
tubes, pharynx, trachea, and bronchi of lungs.
• Functions:
– Move mucus (or fluid) that contains foreign particles over the free
surface and from passages
• Are stratified cells, cells change shape depending on
the stretching of the organ
• Stratified cuboidal – not streched
• Squamous - streched
• Location: lining of urinary bladder, ureter and superior
urethra
• Functions: accommodates fluctuations in the volume of
urine in an organ or tube
• Functions of epithelial tissues depends upon the
type and arrangement of organelles in cells, shape
of cells and the organization of cells
• Cell layers and Cell Shapes
• Simple Epithelium: single layer allows diffusion of gases
(lungs), filtration of blood (kidney), secretion (glands),
absorption (intestine)
• Stratified Epithelium: multiple layers for protection,
particularly against abrasion, eg. Skin, mouth, throat,
esophagus, anus and vagina
• Squamous Epithelium: Flat and thin shaped cells allows
diffusion or acts as filter, eg. Simple squamous epithelium
forms blood capillaries, air sacs of lungs, parts of kidney
tubules
• Cuboidal and columnar Epithelium: Cells that secrete or
absorb are usually cuboidal or columnar. Have greater
cytoplasmic volume. Eg. Trachea, bronchi of lungs,
salivary gland ducts
Functions of Free surfaces of epithelium
• Smooth: reduce friction eg. simple squamous
epithelium lining of blood vessel reduces friction
as blood flows through the vessels
• Microvilli: increase surface area for absorption or
secretion eg. Small intestine
• Cilia: move materials across the surface
• Folds: in transitional epithelium where organ must
be able to change shape. Urinary system.
• Structures present on lateral and
basal surfaces of cells which hold
the cells together
• Functions
– Bind cells together
– Form permeability barrier
– Provide mechanism for intercellular
communication
• Types
– Desmosomes
– Tight junctions
– Gap junctions
• Desmosomes: disk-shaped
structure
• Contain especially adhesive
glycoproteins that bind cells to
one another
– Eg. Striated squamous
epithelium of the skin
• Hemidesmosomes: half of a
desmosome; attach epithelial
cells to basement membrane.
• Tight Junctions: hold cells
together, form permeability barrier
– zonula adherens: found between
plasma membrane of adjacent
cells, acts as weak glue, hold
cells together. Simple epithelium
– zonula occludens: permeability
barrier
– Prevent the passage of materials
between cells
– e.g., stomach and urinary bladder,
chemicals cannot pass between
cells
• Gap Junctions: contains protein
channels that aid intercellular
communication
– Allows ions and small
molecules to pass through
– Coordinate function of cardiac
and smooth muscle
– Pass electric signals from cell
to cell
– Found in intercalated disks in
cardiac muscle cells
 Glands are secretory organs
 Composed of epithelium tissue with supporting
network of connective tissue
 Two types of glands formed by infolding of
epithelium:
– Endocrine: get separated from epithelium, no open
contact with exterior; no ducts; produce hormones
and are secreted directly into the blood and then
carried throughout the body
– Exocrine: Gland maintain open contact with
epithelium, duct is present and lined with epithelium
 Exocrine glands classified either by structure or by the
method of secretion
Classified by structure
– Unicellular: composed of a single cell
– eg. goblet cells of the respiratory system secrete
mucus
– Multicellular: Most of exocrine glands are
multicellular, composed of many cells
• Multicellular exocrine glands are
classified on the basis of the
structure of their ducts
• Types of ducts
– Simple: ducts with few
branches
– Compound: ducts with many
branches
• If ducts end in tubules
tubular. Duodenum
• sac-like structures: acini.
Pancreas
• If ducts end in simple hollow
sacs: alveoli. Lungs
• Merocrine
– Secretion leaves by either
active transport or
exocytosis.
– Sweat glands, pancreas
• Apocrine
– Fragments of the gland go
into the secretion. Apex of
cell pinches off.
– Mammary glands.
• Holocrine
– Whole cell becomes part
of secretion. Secretion
accumulates in cell, cell
ruptures and dies.
– Sebaceous (oil) glands,
shed entire skin cell
Consists of cells separated from each other
by extracellular matrix
Abundant, found in every organ
Many diverse structure
Performs variety of important functions
 Enclosing and separating: Sheets of connective tissues
form capsules around organs, such as Kidney, liver
 Separate tissues & organs from one another by
forming layers
eg. Muscles, arteries, veins, nerves
 Connect tissues to one another:
 Tendons (attach muscles to bone)
 Ligaments (hold bones together)
 Support & movement: Bones, cartilage, joints
 Storage: Adipose tissue (Fat), Bones (minerals)
 Cushion and insulate: Adipose tissue (Fat)
 Transport: Blood
 Protect: blood, bones
 Numerous cell types are found in connective tissue
 Adipose or fat cells (adipocytes): Common in some tissues
(dermis of skin); rare in some (cartilage)
 Mast cells: Found below membranes in loose connective
tissue, and along small blood vessels
 Release heparin, histamine, and proteolytic enzymes in
response to injury, play imp. role in inflammation
 White blood cells (leukocytes): Respond to injury or
infection
 Macrophages: Phagocytize foreign and injured cells,
provide protection against infection
– Fixed: do not move
– Wandering: move by amoeboid movement
Specialized cells of connective tissues
produce the extracellular matrix
– Blasts: create the matrix, eg. osteoblasts,
fibroblasts, chondroblasts
– Cytes: maintain the matrix, eg. Osteocytes,
fibrocytes, chondrocytes
– Clasts: break the matrix down for
remodeling, eg. Osteoclasts, fibroclasts,
chondroclasts
 Three major components of extracellular matrix of
connective tissue are:
– Protein fibers
– Ground substance
– Fluid
 Protein Fibers
 Three types of protein fibers:
– Collagen fibers: Most common protein in body; strong,
inelastic, eg. Tendons, ligaments, bones
– Reticular fibers: Fine collagen fibers,, not as strong as
collagen fibers, form branching networks and fill spaces between
tissues and organs, eg. liver, bone marrow, tissues and organs of
the lymphatic system
– Elastic fibers: Long, thin fibers contain rubber like protein,
elastin, which allow them to stretch & recoil like rubberband, eg.
Skin, lungs, blood vessel walls
 Ground substance: Composed of
– Hyaluronic acid:
polysaccharide. Good lubricant
– Proteoglycans: protein and
polysaccharide. Protein part
attaches to hyaluronic acid. Trap
large amounts of water
– Adhesive molecules: Found in
ground substance, hold
proteoglycan aggregates
together
– Eg. Chondronectin in cartilage,
osteonectin in bone,
fibronectin in fibrous connective
tissue
• Two major categories of connective tissue are:
• Embryonic connective tissue
• Adult connective tissue
• Embryonic Connective tissue
•Embryonic connective tissue is called mesenchyme
•Gel-like ground substance with fibers and star-shaped
mesenchymal cells
• Found in the embryo
• source of all adult connective tissue
• Consists of six types:
• Loose (areolar)
• Dense
– Dense regular
– Dense irregular
• Connective tissue with special properties
– Adipose
– Reticular
• Cartilage
• Bone
• Blood and hemopoietic tissue
• Loose packing material of most organs and tissues
• Attaches skin to underlying tissues
• Contains collagen, reticular, elastic fibers and variety of cells
• Cells include fibroblasts, mast cells, lymphocytes, adipose cells,
macrophages
 Has abundant collagen fibers
in matrix oriented in one
direction, resist stretching
– Tendons: Connect
muscles to bones;
– Ligaments: Connect
bones to bones
– Collagen fibers of
ligaments are less
compact, usually more
flattened than tendons &
form sheets or bands
• Consists of collagen & abundant elastin fibers
• eg. Ligaments in vocal folds; nuchal (back
of the neck) ligament
• Protein fibers arranged in a randomly oriented
network
• Forms innermost layer of the dermis of the skin,
capsules of kidney and spleen
• Bundles and sheets of collagenous and elastic
fibers oriented in multiple directions
• Found in walls of elastic arteries




Adipose tissue: Consists of adipocytes or fat cells
Made up of of loose collagen, reticular & some elastic fibers
Functions as insulator and energy storage
Exists in both yellow (white) & brown forms
 Yellow (white) adipose tissue: Most abundant type, has a wide
distribution. White at birth and yellows with age
 Because of accumulation of carotene pigment, can metabolize as a
source of vitamin A.
 Located in subcutaneous areas,
renal pelvis, mammary glands etc
 Brown adipose tissue:
Found only in specific
areas of body: axillae
(arm pits), neck and
near kidneys
 Brown color results
from:
 Cytochrome pigment in
mitochondria
 Prevalent in babies
• Forms the framework of lymphatic tissues such as spleen, lymph
nodes and bone marrow and liver
• Network of fine reticular fibers and reticular cells
• Spaces between reticular fibers contain other cells such as dendritic
cells (cells of immune system), macrophages, blood cells
• Composed of cartilage cells, chondrocytes located in
spaces called lacunae in matrix
• Next to bone, cartilage is the firmest structure in body
• Matrix contains protein fibers, ground substance and
fluid
• Protein fibers: Are collagen fibers or collagen & elastin
fibers
• Ground substance: Proteoglycans and hyaluronic acid
complexed together trap large amounts of water. And
allow tissue can spring back after being compressed.
• Avascular and no nerve supply. Heals slowly
• Types of cartilage
– Hyaline
– Fibrocartilage
– Elastic
• Has large amounts of collagen fibers and proteoglycans
• Very smooth surface in joints
• Locations:
– Found in areas for strong support and some flexibility:
eg. supports the tip of the nose, connects the ribs to the
sternum and supports most of respiratory system passages
– In embryo forms most of skeleton before bone is formed
• Has more collagen fibers than proteoglycans
• slightly compressible and very tough
• Locations: found in areas of body where a great deal of
pressure is applied to joints
– Knee, jaw, between vertebrae
• Has elastic fibers in addition to collagen fibers and
proteoglycans
• Has rigid but elastic properties
• Locations: external ears
• Bone: Is hard connective tissue composed of
living cells (osteocytes) and mineralized matrix
• Matrix: gives strength and rigidity; allows bone
to support and protect other tissues and organs
– Organic: collagen fibers
– Inorganic: hydroxyapatite (Ca plus PO4)
• Osteocytes (bone cells) located in lacunae in matrix
• Two types of bones:
– Cancellous or spongy bone
– Compact bone
• Cancellous or spongy
bone: Has spaces between
trabeculae (beams)
• Looks like a sponge. Found
inside bones.
• Compact bone: Found on
periphery of bones.
• more solid with no space
between many thin layers
or lamellae of bone
 Unusual connective tissue
 In blood matrix between the cells is liquid
 Abundant matrix : Plasma.
– Not stationary, move in/out of fluid matrix
– Matrix formed by other tissues, unlike other types of connective
tissue
• Formed elements: red cells, white cells, and platelets
• Forms blood cells
• Hemopoietic tissue is found in bone marrow
• Bone marrow: soft connective tissues in the cavities of
bones
• Types of bone marrow
– Red: hemopoietic tissue surrounded by a framework of
reticular fibers. Produces red and white blood cells
– Yellow: yellow adipose tissue, does not produce blood
cells
• As children grow, yellow marrow replaces much of red
marrow.
• Characteristics
– Contracts or shortens with force
– responsible for movement
– Moves entire body and pumps blood
• Three Types
– Skeletal
– Cardiac
– Smooth
– Skeletal: most attached to skeleton, and enables
body movement
– Striated and voluntary.
– cells are long, cylindrical cells with several nuclei
per cell
– Cardiac: muscle of the heart. Striated and
involuntary.
– shorter than skeletal muscle
–
–
–
–
–
Smooth: found in skin and eyes
Nonstriated and involuntary.
Functions
movement of food through digestive tract
emptying of urinary bladder
• Found in brain, spinal cord and nerves
• Neurons or nerve cells have the ability to
conduct electric signals called action
potentials
• Contains neurons and neuroglia
• NEURONS
• Conducting cells of nervous tissue
• Transport electric signals throughout the
body
– Three major parts
– cell body
– dendrites
– axons
• Cell body: contains nucleus
• site of general cell functions
• Axon: conducts impulses away from cell
body; usually only one per neuron
• Dendrite: receive impulses from other
neurons; can be many per neuron
• Support cells of the
brain, spinal cord and
nerves
• Nourish, protect, and
insulate neurons