Tissues Introduction
Epithelial Tissue Classification
Glands
Cell Specialization
Multicellularity requires a division of
labor
 Cells look and function differently
(specialize) in different parts of the
body (ex. bone cell vs. nerve cell)
 Cells specialize into types of tissues,
then form organs.

Histology
Study of tissues (groups of cells that are
similar in structure and function)
4 Tissue Types
1. Connective Tissue
Support
 Connect layers of tissue to each other
 Bone, ligaments, fat

(we will study these in great detail in class later…)
2. Nervous Tissue



Control
Brain, nerves,
spinal cord
Highly specialized
cells that
generate and
conduct nerve
impulses
3. Muscular Tissue
Movement
 Highly vascular
 Contracts with cytoskeletal
microfilament (actin) that works with
motor protein called myosin
 2 categories:

 Striated
muscle tissue (voluntary or indirect
voluntary control)
 Smooth muscle tissue (involuntary)
3. Muscular Tissue

Striated Muscle

Ex. Skeletal
 Attached
to skeletal bones
 Long, cylindrical multi-nucleited cells (as in
background)
 Visible striations
 Voluntary control

Ex. Cardiac
 Also
striated, but uni-nucleated
 Branching cells fit tightly with special junctions
called intercalated discs
3. Muscular Tissue
Smooth muscle
 No striations
 Spindle shaped
 One central nucleus
 Involuntary muscle

 Ex.
digestive system
4. Epithelial Tissue
Interface tissue that forms boundaries
between environments and lines surfaces
“epithe-” means “laid on”




Coverings and Protection (ex. skin, serous membranes)
Excretion & Secretion (ex. glands)
Filtration (ex. kidneys)
Absorption (ex. digestive system)
Identifying Characteristics of
Epithelial Tisues
1. Tight fitting
sheets
Regardless of cell shape
or number of layers
Identifying Characteristics
2. Apical-Basal Polarity
 Apical Surface = top
surface that borders an
“open” space called
LUMEN
 Basal Surface = bottom
surface that borders
underlying supportive
connective tissue
LUMEN
Connective Tissue
Identifying Characteristics
Apical Surface
 Often w/ microvilli
(brush border)


LUMEN
Increases SA in areas
that need to absorb or
secrete
Some with cilia
(longer) to move
substances along
lumen
Connective Tissue
Identifying Characteristics
Basal Surface

Has adhesive sheet of LUMEN
glycoproteins secreted by
epithelial cells called the
basal lamina

Connective Tissue beneath
secretes collagen, creating
the Reticular Lamina.

Basal Lamina + Reticular
Lamina = Basement
Membrane (defines the
epithelial boundary)
LUMEN
Connective Tissue
Identifying Characteristics
3. Avascular (a = without)
 Lacks blood vessels
 Nourished by
connective tissue
But Innervated
 w/ nerve fibers
4. Regeneration and repair
quickly
Classification of
Epithelial Tissue:
Cell Shape
Cross-section



Squamous – flat, like a fried
egg, or scale-like
Cuboidal – cubes, large
spherical central nuclei
Columnar – columns, long
oval nuclei, usually near
basal surface
Classification of Epithelial Tissue
Cell Layers





Simple (one layer)
Thin: limited, no protection 

Sparse cytoplasm
Found where rapid diffusion
is a priority (ex. kidneys, lungs) 

Stratified (many layers)
Thick
Protective role, subject to
wear and tear
Regenerate from basal
surface to replace apical
surface cells that rub off
or die
Cells differ in shape at
apical and basal surface.
(named for apical
surface)
Pseudo-stratified
false



Shapes vary in height
Nuclei at different levels – appear
stratified, but aren’t.
All cells reach basement membrane; only
a few reach the surface
Simple Squamous Epithelium
One layer
Flat
Function and Location

Areas of high diffusion rates:
 gasses (ex lungs)
 nutrients and waste exchange
vessels and surrounding cells)
(blood
 filtrates (kidneys)

Makes lubricating fluid in lining of body
cavities (ex. serous membranes)
Simple Squamous Epithelium
(Top View) – cells fit like tiled floor
Simple Squamous Epithelium
(side view/cross section)
– cells look like fried egg
LUMEN
Figure 4.2
Kidney
LUMEN
Nucleus of squamous cell
Simple Cuboidal Epithelium
One layer
Cubed
Function and Location
Secretion and Absorption
 Covers walls of SMALL ducts, glands,
kidney tubules, ovaries

Cuboidal Cell
Spherical,
large nuclei
LUMEN
Apical surface
Basement
membrane
Basal surface
Spherical, large nuclei
LUMEN
Apical surface
Simple Columnar Epithelium
One layer


columns
Function and Location
 Absorption & Secretion (ex. digestive tract)
 When in open to body cavities – called mucous
membranes
Special Features


Often w/ microvilli on apical surface (brush border)
Goblet cells, single cell glands, produce
protective mucus.
Basal surface
Apical surface
LUMEN
Pseudostratified Epithelium

Function




Absorption
Secretion of mucus by goblet cells
Cilia (larger than microvilli) sweep mucus
Location

Respiratory Linings & Reproductive tract
LUMEN
LUMEN
Basement Membrane
Cilia
Multilevel nuclei
Stratified Squamous Epithelium
Multi-layer (thick!)

Structure


Cells often cuboidal or columnar below apical
squamous layer
Function and Location



Flat (only cells on apical surface)
Protection
Keratin (protein) is accumulated in older cells
near the surface – waterproofs and toughens skin
Location

Skin (keratinized), mouth & throat
keratin
Squamous
Cuboidal
Columnar
Basement Membrane
Dense-Irregular Connective Tissue
Transitional
Epithelium

Structure




Function


Multi-layer
Basal surface cells are cuboidal or columnar
Apical surface cells vary: changes shape to
accommodate for change in volume due to
stretching
Allows stretching
Location

Urinary bladder, ureters & urethra
Figure 4.10
Glands



Cells that secrete or export a product.
Secretion = protein, lipids, hormones, steroids,
acids
Endocrine glands (internally secreting)




No duct, release secretion into blood vessels
Often hormones
Thyroid, adrenal and pituitary glands
Exocrine glands (externally secreting)


Contain ducts, empty onto epithelial surface
Sweat, Oil glands, Salivary glands, Mammary glands.
Shapes of Exocrine glands
Branching of ducts
 Simple – single, unbranched duct
 Compound – branched duct.
Shape of glands:
 Tubular – tube - like
 Alveolar – flasks or sacs
 Tubuloalveolar – has both tubes and sacs in
gland
Merocrine
Modes of Secretion
Holocrine
Merocrine


Released by exocytosis
Gland is not altered (Ex: Sweat glands and salivary glands)
Holocrine


Gland ruptures and releases secretion and
dead cells as well.
Sebaceous (ex. oil glands on the face)