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Histology
The Tissue Level of
Organization
Histology
The study of tissues and how tissues
are combined in various ways to
form organs & membranes of the
human body.
 The human body contains four
primary types of tissues:
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Epithelial
Connective
Muscle
Neural (nerve) tissue.
I. Epithelial Tissue
Made of cells with little space
between cells.
 The cells are so tightly packed
together that blood vessels can’t
penetrate between them and is
called avascular.

Epithelial Tissue

In certain areas of the body epithelial tissue may perform
the following functions:
 Control Permeability:
 Provide Sensitivity
 Provide Physical Protection:
 Produce Secretions:
Epithelial Tissue
Two Types Covering & Lining and
Glandular.
 Covering & Lining Epithelia is
classified based on the number of
cell layers and the cell shape.
 Glandular Epithelia is classified
based on if the tissue secretes its
product into a gland or not.
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Covering & Lining Epithelial
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Classification based on:

Number of cell layers.
• Simple- single layer.
• Stratified- many layers.
• Pseudostratified- appears to be many
layers but is actually a single layer.
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Cell Shape.
• Squamous- Flat.
• Cuboidal- Cube shaped.
• Columnar- Rectangular.
• Transitional- Cuboidal & Squamous.
Simple Squamous
Flat cells with central nucleus.
 Function: Permits the efficient
diffusion of materials.
 Location: Lining of body cavities,
lines the walls of blood & lymphatic
vessels, forms the walls of air sacs.

Simple Squamous
Simple Cuboidal
Single layer of cube-shaped cells
with central nucleus, often have cilia
and/or microvili.
 Function: Forms the walls of small
ducts and tubes that carry
secretions.
 Location: Kidneys, Liver, Glands.

Simple Cuboidal
Simple Columnar
Single layer of rectangle cells whose
nuclei lie near the base (basal) of
the cell.
 Function: Absorb and secrete;
mucus, enzymes, etc.
 Location: Uterus, Stomach,
Digestive Tract, Bronchi.

Simple Columnar
Stratified Squamous
Multiple layers, only top layer is
squamous the deeper layers are
cubiodal and or columnar.
 Function: Covers areas that must
resist wear & tear, protects openings
of the body from abrasions.
 Location: Esophagus, Mouth, Nose,
Vagina, etc.

Stratified Squamous
Stratified Cuboidal
Function: Protection.
 Location: Sweat Glands. Mammary
Glands, Salivary Glands.

Stratified Cuboidal
Stratified Columnar
Function: Protection & Secretion.
 Location: Male Urethra, some large
ducts, rare in the body.

Stratified Columnar
Pseudostratified
Columnar
Appears to be multilayered but is
not.
 Function: Often contains cilia which
creates currents to move mucus.
 Location: Lines parts of respiratory
tract, such as the trachea &
bronchi.
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Pseudostratified Columnar
Transitional
Multilayered cube-like cell shape.
 Function: Can stretch(elasticity) and
return to the original shape
(extensibility).
 Location: Lines Bladder, Urethra,
Ureters.
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Transitional
Glandular Epithelium
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Tightly packed cells that specialize in
manufacturing and secreting products.
Two categories:
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Exocrine: Releases products into ducts.
• sweat & oil glands, salivary, and mucus
glands.
Endocrine: Releases products into
extracellular space.
• pituitary gland, thyroid gland, and adrenal
gland.
II. Connective Tissue
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Is composed of scattered loosely packed
cells that are within a large amount of
nonliving intercellular material.
It is vascular
Its primary function is to hold other
tissues and organs in place.
Two categories of connective tissue
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Produces & Maintains-(matrix)
Protects From Infection (white blood cells)
Connective Tissue
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4 Types of connective tissue
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A. Connective tissue proper
B. Cartilage
C. Bone
D. Blood forming (spongy bone)
A. Connective Tissue
Proper
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Types of connective tissue proper:
Areolar, Adipose, Reticular, Dense
Connective.
1. Areolar Tissue:
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AKA: Loose Connective Tissue.
Contains fibroblast(producing cells) and
macrophages (protecting cells).
Function: Anchors and cushions organs,
vessels, nerves. Fights bacteria. Stores lipids.
Areolar Tissue
A. Connective Tissue
Proper
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2. Adipose Tissue:
Contains adipocytes (producing cells
which contain deposits of fat).
 Function: Provides reserve energy,
insulates & protects organs.
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Adipose Tissue
A. Connective Tissue
Proper
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3. Dense Connective Tissue
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Two Types:
• Dense Regular- Fibers are arranged in
parallel fashion. Attaches muscles to bones.
• Extremely resistant to stress.
• Location: tendons, ligaments.
• Dense Irregular- Fibers are arranged in an
interwoven meshwork. Forms an external
wrapping.
• Location: Wrapped around bone, cartilage, kidneys,
liver, spleen, and where the tendon connects to the
bone.
Dense Regular
Dense Irregular
A. Connective Tissue
Proper
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4.Reticular
Location: Lymphoid organs
 Function: Form a soft internal skeleton
to support other tissues.
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Reticular Tissue
B. Cartilage
Harder than connective tissue
proper.
 Contains chondrocytes (producing
cells).
 There are three types of cartilage:
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Hyaline, Elastic, Fibrocartilage.
B. Cartilage
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1. Hyaline CartilageBluish-white in color.
 Most abundant of all three.
 Function: Supports and reinforces,
with-stands compression.
 Location: Forms embryonic skeleton,
upper respiratory tract, costal cartilage,
moveable joints.
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Hyaline Cartilage
B. Cartilage
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2. Elastic Cartilage
Yellowish in color.
 Function: Maintains shape allows for
flexibility.
 Location: Ears, Nose, Epiglottis.
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Elastic Cartilage
B. Cartilage
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3. Fibrocartilage
Has an abundance of collagen.
 Is found in association with hyaline
cartilage.
 Function: Shock absorber.
 Location:intervertebral disc, pubis
symphysis, knee joint.
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Fibro Cartilage
C. Bone
Has dense intercellular material
composed of mineral salts and
collagenous fibers.
 Made up of osteocytes
 Also known as osseous tissue.
 Two Types of Bone
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Compact and Spongy.
C. Bone
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Compact Bone: Forms the bones of
the skeletal system.
Function: Provide structural support,
stores calcium.
 Location: All bones, the hard outside
layer of bone.
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Bone (compact)
C. Bone
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Spongy Bone: Found inside of
compact bone. Has blood forming
tissue called red marrow.
Function: to produce blood cells.
 Location: inside the bone of the skeletal
system.
 Blood: is a type of connective tissue
known as formed elements.
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• Also know as liquid tissue
• Has both solid (formed elements) and liquid
components.
Red Blood Cells
Spongy Bone
III. Muscle
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Tissue made of specialized cells that
contain protein filaments which allow the
cells to contract.
The protein fibers are arranged in parallel
bundles.
The Three types of muscle are:
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Skeletal, Smooth, and Cardiac.
A. Skeletal Muscle
Striated (has bands of stripes).
 Multi-nucleated
 Attaches to bone, is the primary
mover in the muscular system.
 Voluntary (you control).
 Function: Body movement.
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Skeletal Muscle
B. Smooth Muscle
Not striated, Single Nucleus.
 In the walls of blood vessels and
visceral organs.
 Involuntary (not consciously
controlled).
 Function: Movement of: food, blood
urine, child birth etc.
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Smooth Muscle
C. Cardiac Muscle
Striated, Single Nucleus
 Contains thick cell membranes
called intercalated disks.
 Found in the walls of the heart.
 AKA myocardium.
 Involuntary.
 Function: move blood in the
circulatory system.
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Cardiac Muscle
IV. Nervous Tissue
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Has well developed properties of
conductivity and excitability.
Transmits electrochemical signals.
Two Types of Nervous Tissue:
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Neurons-Basic functioning unit of nervous
tissue conducts electrochemical messages.
Neuroglia- Cells of the spinal cord and brain
that maintain and support neurons.
Nervous Tissue