TYPES OF TISSUES WE’LL DISCUSS:
I.
EPITHELIUM: a sheet of cells that lines tubes in the body, and the surface
of the skin.
II.
CONNECTIVE TISSUE: deep to the epithelium; supplies oxygen and
nutrients to epithelium.
a. Fibrous (Proper) Connective Tissue
b. Special Connective Tissue (Cartilage, Bone, Blood, muscle, nervous
tissue)
i. MUSCLE TISSUE: makes up muscles. It is bound together by
areolar tissue (discussed in later lectures)
ii. NERVOUS TISSUE: makes up brain and nerves (discussed in
later lectures)
EPITHELIA (plural form of epithelium): A sheet of cells that lines tubes in the body,
and the surface of the skin.
Function of epithelia:
• The epithelial cells are the type of tissue that protects the underlying structures
Epithelium is the tissue that covers the outside of the body (the top layer of the skin),
and it also lines the tubes within the body.
• Digestive tract
• Respiratory tract
• Cardiovascular system
• Urinary tract
• Reproductive tract
• Sweat glands and other exocrine glands
The hollow space within each of these tubes is called a lumen. The lumens are always
lined by epithelial cells.
Epithelial cells
Lumen of sweat
gland
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All epithelia sit on top of connective tissue, and is connected to it by a BASEMENT
MEMBRANE (which is not a cell membrane), made of protein fibers that connect to
epithelium. The only function of the basement membrane is to attach the epithelium to
the connective tissue beneath it. Epithelia get oxygen and nutrients from the blood vessels
in the connective tissue beneath the basement membrane.
Epithelium is always BIPOLAR:
1. APICAL SIDE: touches the space (inside heart, stomach, etc).
2. BASAL SIDE: touches the basement membrane
Different types of epithelium
1. SIMPLE EPITHELIUM has one cell layer. There are different types based on the
shape of the cells.
a. SIMPLE SQUAMOUS (the thinnest) EPITHELIUM is one layer of flat cells
that allow diffusion of materials between the cells. This type of epithelium is in regions
where a lot of diffusion is needed from one compartment to another, such as the lungs
and a region in the kidney called the glomerulus.
b. SIMPLE CUBOIDAL EPITHELIUM is cube shaped and is also found in
areas where there is a lot of material going across from one compartment to another, but
it has plenty of room for organelles. This epithelium is found in the region of the kidney
called the convoluted tubules, and other places that need room for cell organelles.
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c. SIMPLE COLUMNAR EPITHELIUM is shaped like a column and is found
in areas where the cells are needed for secretion and absorption (intestines). When they
are differentiated into GOBLET CELLS, they produce mucus.
d. PSEUDO-STRATIFIED EPITHELIUM is a single layer of cells that appears
to be more than one layer thick, but it is not. The nucleus on one cell is at the top, and
the nucleus of the next cell is at the bottom.
Pseudostratified epithelium always has cilia on its apical surface. Each cilium is a hairlike structure that moves back and forth to move material in a certain direction. This type
of epithelium needs goblet cells nearby to produce the mucus that contains the material to
be swept. These cells will be found in the respiratory tract (the trachea), where the
mucous catches the debris you inhale and the cilia sweeps the material up to your throat
where you cough and swallow it. Its only functions are protection and mucous
production.
2. STRATIFIED EPITHELIUM has more than one cell layer. The type of epithelium
is named by the APICAL layer.
a. STRATIFIED SQUAMOUS EPITHELIUM: the type is named by the
apical cells. Stratified squamous epithelium is found in regions of the body where there
is a lot of abrasions or wear-and tear, and it is protective.
1) KERATINIZED STRATIFIED SQUAMOUS EPITHELIUM has
apical cells that contain a protein called keratin, which is waterproof. All of our dry skin
is this type, and it is especially thick in the palms and soles. It is very good at resisting
abrasions.
2) NON-KERATINIZED STRATIFIED SQUAMOUS EPITHELIUM
does not have the keratin, so it will be moist skin, like what is found lining the mouth
and esophagus.
b. STRATIFIED CUBOIDAL EPITHELIUM usually consists of two layers,
and there is almost no diffusion between them. They are found in sweat glands.
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3. STRATIFIED COLUMNAR EPITHELIUM usually has just two layers and this
type of epithelium inhibits diffusion of materials. It is relatively rare, providing protection
along portions of the pharynx, urethra, and anus
4. TRANSITIONAL EPITHELIUM can stretch and change shape. This type is what
lines the urinary bladder and it looks like this as it goes from empty to full.
CONNECTIVE TISSUES
Types of Connective Tissues
 FIBROUS (PROPER) Connective tissues
 SPECIAL CONNECTIVE TISSUE
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Functions of Connective Tissues
Defend the body from invasion by microorganisms
Provide protection for delicate organs
Establish a structural framework for the body
FIBROUS (PROPER) Connective tissues
1. ADIPOSE- main cell type is adipocyte (stores fat)
a. Functions:
i. Cushions organs
ii. Food Storage
iii. Insulation
2. RETICULAR: Found in lymph nodes
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3. LOOSE connective tissue (aka AREOLAR connective tissue)
This is the least specialized type of connective tissue.
The main cell type in loose and dense connective tissue is a FIBROBLAST (a type of
cell, not just a part of a cell). Fibroblasts are what make collagen.
Areolar is common in areas just deep to epithelium (upper dermis).
It does NOT have much collagen because it does not have many fibroblasts.
4. DENSE REGULAR connective tissue
Dense regular and irregular connective tissue has lots of COLLAGEN FIBERS
Dense regular has more collagen than irregular.
Dense regular fibers have a pattern, and run in same direction
Even more strong than irregular, but only in one direction
Found in ligaments, tendons.
Note: tendons are not muscle tissue; they are dense regular connective tissue.
NOTE: If you get injured, you’d
rather break a bone than tear a
ligament, why?
The number of fibroblasts is the
same, but the ligament has a lot
more collagen to be made by
each fibroblast. And the blood
supply to bone is much better
than a ligament.
5. DENSE IRREGULAR connective tissue
a. Has lots of COLLAGEN FIBERS
b. Fibers have irregular position; no pattern
c. Extremely strong in all directions
d. Found in areas of body where strength is needed
(joint capsules and deeper layer of dermis).
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SPECIAL CONNECTIVE TISSUE
1. Cartilages
a. Main cell type is CHONDROCYTE
b. Extracellular matrix is dense collagen; almost solid, very rigid
c. Avascular (no blood vessels. Torn cartilage won’t heal).
d. There are three types of cartilage:
i. HYALINE CARTILAGE (most joints)
ii. ELASTIC CARTILAGE (ear)
iii. FIBROCARTILAGE (intervertebral discs; resists compression
forces)
2. Bone
a. Extracellular matrix is solid, full of minerals (instead of fluid)
b. Minerals are: Calcium carbonate and Calcium phosphate (same as limestone)
c. Main cell type is OSTEOCYTE = “bone cell”
i. Compact bone (shaft of long bones)
ii. Spongy bone (ends of long bones)
3. Blood
a. Main cell type is ERYTHROCYTE
b. Extracellular matrix is the plasma (no collagen or elastin in blood)
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