TISSUES
A. Types of Tissue
1. A TISSUE is a group of similar cells, usually with a common embryonic origin, that function together to
carry out specialized activities.
2. HISTOLOGY is the science that deals with the study of tissues.
3. The major tissue types are EPITHELIAL, CONNECTIVE, MUSCULAR, and NERVOUS.
B. EPITHELIAL TISSUE
1. EPITHELIAL tissue covers body surfaces; lines body cavities, hollow organs, and ducts (tubes) and
forms glands.
2. The two types of epithelium are COVERING AND LINING EPITHELIUM and GLANDULAR EPITHELIUM.
Epithelial tissue contains very little extracellular material and is avascular.
C. General Feature of Epithelial Tissue
1. The numerous features of epithelial tissue are:

Epithelium consists of closely packed cells with little extracellular material.
 Epithelial cells have free (apical) surfaces, exposed to a body cavity, lining of an internal organ, or
exterior
of body.

Epithelial tissues are avascular.

Epithelial tissues have a nerve supply.

Epithelial tissues have a high capacity for renewal by cell division.
Epithelial tissues function in protection, secretion, absorption, excretion, sensory reception and
generation of gametes (sperms and oocytes).
D. Covering and Lining Epithelium
1. Epithelial tissue can be classified by SHAPE being squamous (flat), cuboidal (as tall as they are wide
or hexagons), columnar (taller than they are wide) or transitional (vary from flat to cudoidal).
2. Epithelium can also be classified by the ARRANGEMENT OF LAYERS, being simple (single-layered),
stratified (multi-layered), or pseudostratified (one layer of cells but appears to have several layers).
Certain cells can also contain cilia and/or secrete mucus.
3. SIMPLE SQUAMOUS EPITHELIUM functions in the diffusion, osmosis, filtration, absorption, and secretion
in serous membranes.
4. SIMPLE CUBOIDAL EPITHELIUM functions to secrete tears and saliva and absorb water in the kidney
tubules.
5. SIMPLE COLUMNAR EPITHELIUM may have modifications such as microvilli, which serve to increase the
surface area or goblet cells which secrete mucus. Its functions involve secretion and absorption.
6. STRATIFIED SQUAMOUS EPITHELIUM usually contains a protein called keratin and serves as a protective
barrier against microbes, heat, and chemicals.
7. STRATIFIED CUBOIDAL EPITHELIUM is rare but functions in protection, and limited secretion and
absorption.
8. STRATIFIED COLUMNAR EPITHELIUM functions in protection and secretion.
9. TRANSITIONAL EPITHELIUM allows for organ expansion and prevents organ rupture.
10. PSEUDOSTRATIFIED COLUMNAR EPITHELIUM is not a true stratified tissue. All cells are attached to the
basement membrane, but not all reach the surface. It provides for the movement of materials
11. A SUMMARY OF EPITHELIAL TISSUES:
TYPES OF TISSUE
LOCATION
FUNCTION
simple squamous
LINES HEART, LYMPHATIC VESSELS AND
ABDOMINAL CAVITY, AND SEROUS SECRETIONS
FILTRATION,
ABSORPTION,
DIFFUSION, OSMOSIS
SIMPLE CUBOIDAL
COVERS OVARIES, LINES KIDNEY TUBULES AND
PART OF THE EYE LENS, AND FORMS PART OF
THE RETINA
SECRETION AND
ABSORPTION
SIMPLE COLUMNAR
LINES GI TRACT FROM STOMACH, EXCRETORY
DUCTS OF GLANDS, AND GALL BLADDER
SECRETION AND
ABSORPTION
SIMPLE CILIATED
COLUMNAR
LINES UPPER RESPIRATORY TRACT, UTERINE
TUBES, AND UTERUS
MOVES MUCUS BY
CILIARY ACTION
STRATIFIED SQUAMOUS
LINES THE MOUTH, TONGUE, ESOPHAGUS,
VAGINA, AND OUTER LAYER OF THE SKIN
PROTECTION
STRATIFIED CUBOIDAL
COMPRISES DUCTS OF SWEAT GLANDS AND
MALE URETHRA
PROTECTION AND
LIMITED SECRETION
AND ABSORPTION
STRATIFIED COLUMNAR
LINES MALE URETHRA, PART OF THE
CONJUCTIVA OF THE EYE
PROTECTION AND
SECRETION
TRANSITIONAL
LINES URINARY BLADDER AND PARTS OF
URETER AND URETHRA
PREVENTS DISTENTION
PSEUDOSTRATIFIED
COLUMNAR
LINES LARGE EXCRETORY DUCTS, EPIDIDYMIS,
MALE URETHRA, AND EUSTACHIAN TUBES,
UPPER SPERM RESPIRATORY TRACT AND MALE
REPRODUCTIVE SYSTEM
SECRETION AND
MOVEMENT OF MUCUS
E. GLANDULAR EPITHELIUM
1. The function of glandular epithelium is SECRETION.
2. A gland consists of one cell or a group of highly specialized epithelial cells secreting substances into
ducts, onto a surface, or into the blood.
3. EXOCRINE GLANDS secrete products into ducts (tubes) that empty at the surface of covering and lining
epithelium or directly onto a free surface. Examples are sweat glands, salivary glands, and digestive
tract glands.
4. ENDOCRINE GLANDS are ductless, release their secretions called hormones, directly into the
bloodstream. Some examples are the pituitary and adrenal glands.
F. Connective Tissue
1. CONNECTIVE TISSUE is one of the most abundant tissue in the body and is highly vascular. It also
contains a varied number of cells with a large quantity of extracellular matrix.
2. The general functions of connective tissue are protection, support, binding, and storage.
G. General Features of Connective Tissue
1. The following are general features of connective tissue:

Consists of two basic elements: cells and matrix (ground substance and protein fibers).

Connective tissues do not generally occur on free surfaces.

Connective tissue has a nerve supply, except for cartilage, which does not.

Connective tissue is highly vascular, except for cartilage, which is avascular.

The matrix can be fluid, semi fluid, gelatinous, fibrous, or calcified.
H. Connective Tissue Cells
1. Various types of cells are found in connective tissue. These include:

Fibroblasts

Macrophages

Plasma Cells (B lymphocytes)

Mast Cells

Adipocytes
I. Connective Tissue Matrix
1. Each type of connective tissue has unique properties due to its matrix between the cells. The matrix
contains protein fibers embedded in the fluid, gel, or solid GROUND SUBSTANCE. The ground
substance also contains several other substances.
2. The matrix also contains FIBERS, which provide strength and support for the tissue. The major type of
fibers include:

COLLAGEN which is very strong and resistant to pulling forces. These fibers occur in bundles and
afford great strength. Collagen is the most abundant protein in the human body representing
about 25% of all protein.

ELASTIC FIBERS are usually smaller than collagen. They are comprised of the protein ELASTIN
which provides both strength and elasticity.

RETICULAR FIBERS are comprised of collagen and glycoprotein, and provide strength and support
in the walls of blood vessels. Reticular fibers also form the stroma (supporting framework) of
many soft organs.
J. Muscular Tissue
1. MUSCULAR TISSUE is a highly specialized tissue generates force, motion, the maintenance of posture,
and the production of heat.
2. SKELETAL MUSCLE is usually attached to bones of the skeleton.
3. CARDIAC MUSCLE forms the bulk of the wall of the heart.
4. SMOOTH MUSCLE is located in the walls of hollow internal structures, such as blood vessels, stomach,
and urinary bladder.
K. Nervous Tissue
1. NERVOUS TISSUE contains two principal cells types: NEURONS and NEUROGLIA.
2. NEURONS are sensitive to stimuli, conduct impulses other neurons, muscle fibers, and glands.
3. NEUROGLIA are the cellular support for nervous tissue, which do not generate or conduct nerve
impulses.
L. Epithelial Membranes
1. EPITHELIAL MEMBRANES are a combination of an epithelial layer and underlying connective tissue.
The types of epithelial membranes are MUCOUS, SEROUS, AND SYNOVIAL MEMBRANES (which do not
contain any epithelial cells).
L. Classification of Connective Tissues
1. CONNECTIVE TISSUE includes LOOSE and DENSE CONNECTIVE TISSUE, CARTILAGE, BONE, BLOOD AND
LYMPH.
2. A SUMMARY OF MATURE CONNECTIVE TISSUES:
TYPE
DESCRIPTION
LOCATION
FUNCTION
AREOLAR
fibers of collagen, elastic and
reticular; fibroblasts,
macrophages, plasma cells,
mast cells, and adipocytes in
a matrix
around organs, dermis of skin
and tissue with fibroblasts,
subcutaneous layer
Strength, elasticity, and
support
Adipose
adipocytes used for fat
storage
subcutaneous tissue around
heart and kidneys, marrow of
long bones, joints
Heat loss reduction,
support, protection,
and energy reserve
Dense regular collagen fibers with
and irregular
fibroblasts
tendons, ligaments
protection, heart, bone, liver,
testes and lymph nodes
Support and
attachment, provides
strength
Elastic
elastic fibers with few
fibroblasts
lungs, arteries, trachea,
bronchi, and true vocal cords
Stretching
Reticular
reticular fibers with cells
wrapped around
liver, spleen, lymph nodes
Forms stroma of
organs
Hyaline
cartilage
Bluish-white shiny ground
substance with chondrocytes
end of long bones, parts of
the larynx, bronchi and
embryonic skeleton
Movements at joints,
support and flexibility
Fibrocartilage
chondrocytes in bundles of
collagenous fibers
joints between hip bones,
intervertebral discs and knees
support and fusion
Elastic
cartilage
chondrocytes in a network of
elastic fibers
epiglottis, external ear and
auditory tubes
support and shape
3. Connective tissue may contain a variety of CELL TYPES such as fibroblasts, macrophages, plasma
cells, mast cells, and adipocytes.
4. BONE TISSUE is a specialized connective tissue comprised of bone-forming cells (osteocytes), and
can exist either as compact or spongy bone.
5. The OSTEON or HAVERSIAN SYSTEM is the basic unit of compact bone consisting of lamellae (matrix
system), lacunae (small spaces between the lamellae with osteocytes), canaliculi (minute canals
projecting from lacunae), and the Central (Haversian) canal (containing the principal blood vessel).
6. BLOOD TISSUE is a specialized liquid connective tissue of plasma and formed elements. The formed
elements are Red Blood Cells (RBCs), White Blood Cells (WBCs), and Platelets.
7. LYMPH is a fluid that flows in lymphatic vessels.