Tissues and Histology
Tissues and Histology
Tissues and Histology
Tissue
Is a group of specialized cell and extracellular substance surrounding them.
Histology
The microscopic study of tissue structure
Epithelial Tissue
Also known as epithelium
Covers and protects surfaces both inside and outside the body
Characteristics
Mostly composed of cells
Cover body surface area and forms glands that are derived
developmentally from body surface. These includes lining
of the digestive tract, urinary, reproductive, respiratory, the
heart and blood vessels and many body cavities
Distinct sell surfaces
Free or Apical surfaces – cells are exposed and not
attached to other cells
Lateral surface – where cells are attached to other
cells
Basal surface – attached to the basement
membrane which is a specialized type of
extracellular material secreted by epithelial and
connective tissue cell.
o The basement membrane helps attached
the epithelial cells to the underlying tissue.
Cell and matrix connections
Specialized cells contacts bind adjacent epithelial
cells together and to the extracellular matrix of the
basement membrane
Desmosomes which are mechanical links that bind
cells together and anchors to the basement
membrane
Tight junctions bind adjacent cell together and
form permeability barriers that prevent the
passage of materials between epithelial cells.
Gap junctions are small channels that allow small
molecules and ions to pass from one epithelial cells
to an adjacent one which act as communication
signals to coordinate the activities of the cells
Non vascular
Blood vessels in the underlying connective tissue
do not penetrate the basement membrane to
reach the epithelium
Nutrients reach the cells through diffusion
Capable of regeneration
Epithelial cells has the capability to replace
damaged cells with new epithelial cells through
undifferentiated stem cells.
Functions
o Protecting underlying structure
Outer layer of the skin and oral cavity
o Acting as barrier
Prevent substances from moving through it such as the skin
o Permitting the passage of substance
Allows the passage of other substances such as the air to
the blood by diffusion through the epithelium of the lungs
o Secreting substance
Secreting glands are composed of epithelial cells
o Absorbing substance
Cell membranes of certain epithelial tissues contains
certain proteins that regulate the absorption of substance
such as the epithelium of the digestive tract.
Classifications
o According to the number of cell layers and the shape of the
superficial cells
Simple epithelium – single layer extending from the basal
to the surface
Stratified epithelium – more than one layer with only the
basal layer attaches the basement membrane
Pseudostratified columnar – a specialized type of simple
epithelium consist of one layer that attaches to the
basement membrane however it appears to be stratified
even if not because other cells are tall that extend to the
free surface whereas others are not and are shorter.
o According to the idealized shapes of the epithelial cells
Squamous – cells are flat and scale like
Cuboidal – cells are cube shape
Columnar – cells are taller than they are wide
o Mixed classifications
Simple squamous epithelium
Single layer of thin flat cell layer
Allows substance to pass through this thin layers
but others substance do not
Lungs allows the exchange of O2 and CO2, in the
kidneys filter wastes from the blood
Prevents abrasions through secretions of slippery
fluid that lubricates the surface of the organs
Simple cuboidal
Single layer of cube-like cells that carry out active
transport, facilitated diffusion or secretion
May have cilia for the movement of the lucus in the
respiratory tract or microvilli that increase the
surface area for secretion and absorption
Simple columnar
Single layer of tall thin cells which allows them to
perform complex functions such as the columnar
epithelium of the small intestine that produce
mucus or digestive enzymes
Pseudostratified columnar epithelium
Secrets mucus which cover the free surface. Cilia in
the airways move the mucus and debris toward the
throat
Stratified squamous epithelium
Form a thick epithelium because it consists of
several layers of cell
The deepest cells are cuboidal or columnar and are
capable of dividing and forming new cells
As the newly formed cells are pushed to the surface
they become flat and thin and as they are flatten
the cytoplasm are replaced with protein called the
keratin and the cells die. They are called keratinized
squamous epithelium
They provide protection from abrasion and as
barriers
Stratified cuboidal epithelium
More than one layer of cuboidal epithelial cells
Found in sweat glands, ovarian follicular cells and
salivary glands
They functions for absorption, secretion and
absorption
Stratified columnar epithelium
More than one layer of columnar epithelial cells
Found in mammary ducts, the larynx and male
urethra
For secretion protection and absorption
Transitional epithelium
Special type of stratified epithelium that can be
greatly stretched that lines cavity that that can
expand greatly such as the urinary bladder
Connective tissue
It consist of cells separated from each other by abundant extracellular
matrix
Functions
o Enclosing and separating other tissue – form capsule around organs
and separate other tissue or organ.
o Connecting tissue to one another – tendons are strong cables or
bands of connective tissue that attached the muscle to bone and
ligaments are connective tissue bands that hold bones together
o Supporting and moving parts of the body – cartilage supports the
nose ears and surfaces of the joints
o Storing compounds – adipose tissue fat stores high energy
molecules and bone store minerals such as calcium and phosphate
o Cushioning and insulating – adipose tissue cushion and protects the
tissue
o Transporting – blood transports gases, nutrients, enzymes,
hormones and cells of the immune system throughout the body
o Protecting – cells of the immune system and blood provides
protection against toxin and tissue injury
Cells of connective tissue
o The specialized cells of the connective tissue produces the
extracellular matrix
o The name of the cell identifies the cell functions by means of their
suffixes
Blast – create the matrix
Osteoblast (bone), Chondroblast ( Cartilage),
fibroblast (Fibrous connective tissue)
Cytes – maintain it
Osteocytes (bone), Chondrocytes ( cartilage )
Clasts – break it down for remodeling
Osteoclast ( bone)
o Macrophages – are cells of the immune system that ingest foreign
substance
o Mast cells – cells that release chemicals such as histamine that
promote inflammation
o Extracellular matrix – is responsible for the functional
characteristics of the connective tissue and has three major
component
Protein fiber
Has three types – collagen, reticular and elastic
o Collagen fibers– resembles microscopic
ropes that are very flexible but resist
stretching
o Reticular fibers – are very fine short
collagen fibers that branched to form a
supporting network
o Elastic fiber- have the ability to return to
their original shape after being stretched or
compressed
Ground substance
Consist of nonfibrous molecules and is a shapeless
background against which a collagen fibers are
seen through the microscopic
Proteoglycans that consist of protein attached to a
many long polysaccharides that trap large
quantities of water which allows them to return
their original shape when compressed or deformed
Fluid
Classification
o 2 types
Embryonic connective tissue – by 8 weeks of development
most of embryonic connective tissue has become
specialized to form the types of connective tissue seen in
adults
Adult connective tissue
3 types
o Connective tissue proper
Loose- areolar, adipose, reticular
Dense – more fibers and less
ground substance
Dense regular collagenous
Dense regular elastic
o Supporting connective tissue
Cartilage – hyaline, fibrocartilage,
elastic
Bone – spongy, compact
o Fluid connective tissue
Blood- blood, hemopoietic tissue
Muscle tissue
Main function of the muscle tissue is to contract or shorten making the
movement possible
Three types
o Skeletal muscle
Attaches to the skeleton and enables the body to move
(voluntary movement or involuntary movement)
Skeletal muscle cells also called muscle fiber tend to be
long and cylindrical with several nuclei per cell. And may
extend the length of an entire muscle.
Muscle fibers are striated or banded because of the
arrangement of contractile protein within the cells
o Cardiac muscle
Is the heart muscle and is responsible for the pumping of
the blood.
It is under involuntary control
Muscle fibers are cylindrical but much shorter than skeletal
muscle fiber and is striated with single nuclei per cell
Branched and connected to one another by intercalated
disc which contain specialized gap junctions and are
important in coordinating the contractions of the cardiac
muscle cells
o Smooth muscle
Forms the wall of hollow organs except the heart and is
also may be found in the skin and eyes
Controlled involuntarily
Smooth muscle cells are tapered at each end with single
nucleus and is non striated
It is responsible for number of functions such as moving of
food through the digestive tract and emptying the urinary
bladder
Nervous tissue
Forms the brain, spinal cord and the nerves
Responsible for coordinating and controlling many body activities
Many of its functions depend on the ability to communicate with the other
cells through the generations of action potentials
Consist of neurons and supporting cells
Neurons or nerve cell is responsible for conducting action potentials
composed of three parts
o Cell body- contains the nucleus and is the site of general cell
functions
o Dendrites – are tree like structure or extensions of the cell body
that receive stimuli leading to electrical changes that either
increase or decrease action potential in the neuron’s axon
o Axon – are nerve cell process or extension
Glial cells – are the supporting cells of the nervus system
that nourish, protect and insulate the neurons
Tissue membranes
Is a thin sheet or layer of tissue that covers a structure or lines a cavity
Mostly consist of epithelium and the connective tissue on which the
epithelium rest
Four types
o 1 external – skin or cutaneous membrane
Cutaneous membrane – composed of stratified squamous
epithelium and dense connective tissue
o 3 internal – mucous, serous and synovial membranes
Mucous membrane
Line cavities that open to the outside of the body
Digestive, respiratory, reproductive tract
Consist of epithelial cells, basement membrane and
layer of loose connective tissue
May contain layer of smooth muscle cells and
multicellular mucous gland that secrete mucus
Serous membrane
Line cavities that do not open to th exterior of the
body
Pericardial pleural and peritoneal cavities
Consist of three component – layer of simpe
squamous epithelium, basement membrane and a
delicate layer of connective tissue and secrete a
fluid called serous fluid which lubricates the surface
of the membranes
Protect the organs from frictions help hold in place
and act as selective permeable barrier to prevent
large amount of fluid from accumulating within the
serous cavity
Synovial membranes
Lin ethe cavities of freely movable joints
They are made up of only connective tissue an d
consist of modified connective tissue cells
It is either continuous with the dense connective
tissue of the join capsule or separated from the
capsule by areolar or adipose tissue
It produce synovial fluid which makes the joint very
slippery reducing friction and allowing smooth
movement of the joint
Tissue damage and Inflammation
Inflammation
Occur when the tissue are damage either through infection or trauma
Five major symptoms
o Redness, heat, swelling, pain and loss of functions
Process of inflammation
o Following an injury chemical mediators (histamine and
prostaglandins) are released or activated in the injured tissue or
nearby blood vessels
o These results in dilation of blood vessels causing redness and heat
o It also causes the increase in the permeability of the blood vessels
allowing materials and blood cells to move out of the vessels and
into the tissue and deal directly with the injury. These results in
edema or swelling.
o Fibrins form the fibrous network that walls off the site of injury that
prevent further spread. Neutrophil fights infection by ingestion of
the microorganism. Mixture of dead neutrophils and other cells and
fluid can accumulate and form pus.
o Pain is produced when nerve endings are stimulated by direct
damage and by chemical mediators to produce pain sensations and
by direct pressure in the tissue caused by edema and pus
accumulation.
Tissue repair
Is the substitution of viable cells for dead cells
Can occur by regeneration or by fibrosis depending on the tissue involve
and the severity of the injury
o Regeneration- replacement of new cells that are the same type as
those that were destroyed and normal function is usually restored.
Is accomplished primarily by stem cells that are self
renewing undifferentiated cells that continue to divide
throughout life
With each division, there is a daughter stem cell and a
second cell that undergo differentiation that are the same
cell type with the dead cells
o Fibrosis – replacement by a new type of tissue that eventually
causes scar production and the loss of some tissue functions
Most predominant type of repair in some tissues such as
the brain heart and skeletal muscle due to relatively few
stem cells and mature neurons cardiac muscle and skeletal
muscle do not divide