Transcript lab 2: the simple epithelial tissue

Attention:
**Early unicellular forms evolved into multicellular forms.
**Such need to multicellularity is based on:
The limited cellular diffusion and transport of nutrients
and metabolites.
The result was a maximum limit on cell size followed by many cells working
in coorporation with each other, which in due course, led to specialization of
labor and to specialization of cells.
Although cells are the ultimate building blocks of the body, these cells are
organized into a higher levels of complexity in the formation of tissues.
Levels Of Organization:
Cells----- Tissues----- Organs----- Organ Systems---Organism
The four basic tissue
types.
•Epithelial tissue
•connective tissue (support cells, immune cells,
blood cells),
.muscle tissue (contractile cells), and
• nervous tissue.
Organs represent various combinations of these four basic
tissue types, which thus comprise the entire body. Each
tissue type retains its fundamental character wherever it
occurs.
For example, the stomach:
Epithelial tissue
The boundary between you and
your environment is marked by a
continuous surface, or epithelium,
of contiguous cells.
Several features characterize epithelial
tissue and distinguish it from connective
tissue, muscle tissue, and nervous tissue
• Epithelial tissues are arranged in sheets or layers
covering the surfaces or lining the cavities of the body.
• Epithelial cells are attached to one another. Special
devices (intercellular junctions, tonofilaments) provide for
structural integrity of the epithelium.
• Their cells lack protoplasmic processes except for
microvilli.
• Intercellular substance is little and intercellular spaces
are small.
•
•
•
•
Epithelial tissue lacks a vascular supply
Derived from all three of the embryonic germ layers.
Skin and body opinings ------- ectoderm
Lining of G.T., respiratoty system,and the glands of the
G.T.--------- endoderm
• Lining od kidney blood vessels --------mesoderm.
• Epithelial cells are polarized.
• Epithelial cells are separated from the
underlying tissue by a basement membrane
The basement membrane
• is a thin sheet of collagen and glycoproteins
produced:
• in part by the epithelial cells themselves and
• in part by underlying connective tissue cells
(specifically, fibroblasts).
• The basement membrane serves to regulate
cell behavior and can limit the spread of
some neoplasms.
By Electron microscopy, basement
membrane is composed of:
• Amorphous Basal lamina (50 t0 100 nm thick): is a
product of epithelial . It is separated from the basal cell
membrane by a lucent region of 50 nm
• A Reticular lamina containing reicular and
collagenous fibers.
• The basal lamina is seen no only in epithelial
tissues but also in smooth, skeletal and cardiac
muscle, in addition to fat cells.
Staining of the basement membrane
• Stains deep black in silver preparations
because of the reticular fibers
• Stains red in PAS preparations because of
the polysaccharides.
In H&E preparations:
• It may appear thick such as in trachea,
because of the fixed reticular lamina.
• It is very thin beneath transitional epithelium
and cannot be observed by light microscope.
• Basement membranes are at best
inconspicuous in glomeruli of the kidney.
basement membrane, kidney
(PAS)
lumen
Brush border
The nucleus of
the cell
Basement
membrane
Basal side of the
cells
lumen
Apical side of
the cells
Classification of the epithelium
I- According to the structure (number of
layers of cells rest on the basement
membrane):
• Simple epithelium: one layer of cells
• Pseudostratified epithelium: one layer
of cells
• Stratified epithelium: two or more
layers of cells
According the shape of cells on
the top:
• Simple epithelium:
1. Simple Squamous Epithelium
2. Simple Cuboidal Epithelium
3. Simple Columnar Epithelium
• Stratified epithelium:
1.
2.
3.
4.
Stratified Squamous Epithelium
Stratified cuboidal Epithelium
Stratified columnar Epithelium
Transitional Epithelium
Simple epithelium
1.Simple Squamous Epithelium
2.Simple Cuboidal Epithelium
3.Simple Columnar Epithelium
1- Simple squamous epithelium
• Squamous: from squama, scale
• consists of a single, very thin layer of
flattened (squamous) cells.
• Cells are large with clear or granular
cytoplasm and round, oval or eccentric
nuclei.
• In cross section, the cytoplasm is barely
visible
Simple squamous epithelium, cheek
cells, top veiw. These cells are large, but quite thin, and
have a prominent, protruding nucleus. A good analogy
to their shape is the sunny-side-up fried egg.
Simple squamous epithelium is
found in barriers where diffusion or filtration is
the basic requirement.
1- makes up the
lung alveoli.
The cells are
very thin, side
view.
Squamous
epithelium
2- at sites where very little activity is
occuring, such as Bowman's capsule in
the kidney.
• Simple
squamous
epithelium
Lateral view.
Lateral view, simple squamous
epithelium, kidney (H&E)
Nucleus of the
squamous cell
Simple
epithelium
Squamous
cell
Endothelium:
*is a simple squamous tissue lines all blood and
lymphatic vessels.
**Endothelial cells may be phagocytic and can form
stellate –shaped connective tissue fiberoblasts by cell
division
Cross section in blood vessel,
lateral view of endothelium.
The cells are very thin
simple squamous
Endothelium, (H&E)
endothelium
Lumen of the vessel
Endothelial cells
Endothelial cell
2- Simple cuboidal epithelium
• consists of boxy (cuboidal) cells on the
surface.
• The cells are smaller and more regular than
those of squamous epithelium.
• In vertical section, the cells are square and
contain a rounded nucleus
• Locations: lining thyroid follicles, kidney
tubules, salivary ducts, pancreatic ducts.
Thyroid follicle
Cuboidal Epithelium, Thyroid
Thyroid is an endocrine gland in which simple cuboidal
epithelium surrounds masses of storage protein.
Simple cuboidal and squamous
epithelia in kidney (H&E), T.S.
Simple Cuboidal epithelium:
1- Cuboidal epithelial cells with eosinophilic (i.e., pink) cytoplasm
belong to the ascending limb of the loop of Henle.
• 2- Cuboidal epithelial
cells with relatively
unstained (i.e, pale)
cytoplasm belong to
collecting ducts,
which are larger than
the tubules of the
loop of Henle. (t.s in
medulla)
collecting
ducts
collecting
ducts
ascending limb of the
loop of Henle.
Simple cuboidal epithelium lines
the proximal and distal convoluted tubules in
the kidney, t.s. in cortex.
Comparison of Duct and Blood Vessels:
Simple Cuboidal epithelium is commonly encountered in glandular
ducts. Small ducts typically have a simple cuboidal
epithelium. Larger ducts may have a stratified cuboidal epithelium.
3- Simple columnar epithelium
• In surface veiw, it appears like cuboidal;
• in sections, the cells are taller than board and are
rectangular, with the long axis perependicular to the
free surface
• The nucleus is oval and located close to the base ,
unless the cells are very compressed.
• The free or apical portion may have a plasma
membrane covered with mucous, cilia or microvilli.
• lines the digestive tract and the female reproductive
tract (as well as numerous other surfaces).
Types of Simple columnar epithelium
1. Without goblet cells: in gall bladder,
stomach,
2. With goblet cells : intestine and
respiratory tracts.
simple columnar epithelium without
goblet cells. This picture is from a gall
bladder. The red arrow is pointing to red
blood cells (erythrocytes).
Simple columnar epithelium (without
goblet cells) that form the surface of the
stomach mucosa.
fundic stomach (H&E)
Gastric pit
Mucous neck cells
Branched gland
Surface mucous cells
Lamina propria
Lamina
propria
Praital cells
Lamina
propria
Lamina
propria
The simple columnar epithelium with
goblet cells
The villi of the small intestine are lined by a single layer of columnar
cells (A). Note these cells are not as wide as they are tall with the darkly
stained nuclei (B) located at the base of the cells.
The cell membranes (C) are very thin but easily identified.
Goblet cell
columnar cells
Simple columnar epithelium
The epithelial tissue layer of the small intestine contains absorptive
cells, which take in nutrients, and goblet cells, which secrete
mucus. The epithelial surface forms many small projections, called villi,
one of which occupies most of this image.
Simple columnar with goblet cells,
of villus, Small Intestine
3-Simple columnar epithelium
with cilia
• In which the free border is supplied with
cilia e.g.
Fallopian tube, vasa efferentia, ependyma,
Ependymal cells:
line the ventricles of the brain and the central canal
of the spinal cord are lined with
The cells are often cilated
and form a simple
cuboidal or low columnar
epithelium.
The lack of tight junctions
between ependymal cells
allows a free exchange
between cerebrospinal
fluid and nervous tissue.