Chapter 4 -1
Histology
Tissues and Membranes
Common Course Objectives
•
Identify tissues and their specific
characteristics
•
Define membrane structure, and its
importance for cell integrity, function and
identity
Tissues
• Groups of similar cells in close association with each
other that work and perform similar functions.
• Four basic types we will learn in detail:
• Epithelial
• Connective
• Nervous
• Muscle
Four basic types we will learn
Epithelial Tissue
• Consists of cells arranged in continuous sheets of
either single or multiple layers supported by a
connective tissue underlayment (basement
membrane).
• They are closely packed and held together by
specialized cell junctions (tight junctions, gap
junctions, desmosomes).
• There is an intercellular space between adjacent cells.
• Contain 3 surfaces: Apical (superficial), lateral
(intercellular space), and basal (deep).
Intercellular connections
• Tight junctions formed by fusion of lipid layers
between cells prevent substances from entering
between cells.
• Gap junctions consist of interlocking
membrane proteins that allow ions and small
molecules to pass from one cell to another.
• Desmosomes formed by a thin layer of
intercellular cement reinforced by protein
filaments resulting in strong junctions holding
adjacent cells together.
Intercellular connections
Epithelial Tissue
• Cell surface orientation
- Apical surface is in the lumen
-Basal infrastructure of cell (foundation)
Epithelial Tissue
• Is avascular and receives nutrients from a
connective tissue layer below via diffusion.
• It is innervated and highly sensitive to touch,
pain and pressure.
• May be divided into 2 types: Covering and lining
epithelium (e.g. skin, vessels, body cavities,
etc.) and Glandular epithelium (secreting
portion of glands – (e.g. thyroid, sweat,
adrenal).
• It is capable of regenerating itself as it is worn
off or abraded away.
Classification of Epithelia
• Classified by layers:
– Simple vs. Stratified
• Classified by cell shape:
– Squamous
– Cuboidal
– Columnar
Types of
Epithelia
Simple Cells vs. Stratified Cells
Simple
Single lining layer
Stratified
Cell layers stacked up.
Simple cells vs. Stratified cells
• Simple is a single layer of cells (i.e. the cells
are not stacked on top of each other).
– Function in diffusion, osmosis, filtration,
secretion and absorption.
• Stratified is composed 2 to 20+ layers. Only
the deepest layers rest on a basement
membrane.
– Found in locations where there is considerable
wear and tear.
Simple epithelial cells
• Squamous = arranged like floor tiles and are
thin and flat.
• Cuboidal = shaped like cubes or hexagons.
• Columnar = much taller than wide and protect
underlying tissues.
• Transitional = may be any of the 3 above and
exhibits variable cell shapes.
Simple Squamous Epithelium
Single layer of flat cells.
-Lines internal surface of
internal body cavities,
blood vessels, heart,
renal tubules & alveoli
of lungs.
Allows for easy diffusion,
filtration or secretion.
Simple Cuboidal Epithelium
Single layer of cuboidal
shaped cells.
-Found in gland ducts,
kidney tubules, and
thyroid follicles.
-Act in secretion and
absorption.
Simple Columnar Epithelium
Single layer of tall,
column-shaped cells
with oblong nuclei.
May be ciliated or
non-ciliated.
-Non-ciliated found in
stomach, small and
large intestine and gall
bladder.
-Ciliated found in uterine
(fallopian) tubes.
Ciliated Simple Columnar Epithelium
Ciliated found in uterine
(fallopian) tubes and
large bronchioles.
Why would cilia be
found here??
Stratified vs. Pseudostratified
• Stratified consists of 2 or more layers of cells
that protect underlying tissues. Found in
locations where there is considerable wear
and tear (skin, mouth, intestines, etc.).
• Pseudostratified contains only a single layer of
epithelial cells, but appears to have multiple
layers because the cell nuclei lie at different
levels and not all cells reach the apical
surface.
Stratified vs. Pseudostratified
Stratified
Pseudostratified
Stratified Squamous Epithelium
Consists of 2 different
types: Keratinized and
Non-keratinized.
Bottom layer is either
cuboidal or columnar cells
that are active in cell
division.
-Keratinized is found in
the epidermis of the skin.
-Non-keratinized is in
mouth, pharynx, anus,
esophagus, and vagina.
Stratified Squamous Epithelium
Keratinized is found
in epidermis of skin.
Stratified columnar epithelium
• Basal cells tend to be
more cuboidal and the
apical surface cells
are columnar in
shape.
• Found in ducts of
larger glands as in the
submucosa of the
esophagus.
Pseudostratified columnar epithelium
A single row of cells.
Most cells look columnar
while others cells may
look cuboidal shape.
Note that all cells are
attached to basal lamina.
-Ciliated epithelium is
found in nasal cavity,
trachea and bronchi.
-Non-ciliated is in ducts of
male reproductive tract
Transitional epithelial cells
• Cells change shape, from cuboidal to flat and back.
• Occurs in organs that stretch to a larger size and then
collapse to a smaller size.
• Present only in the urinary system. Lines ureters,
urinary bladder, urethra and renal pelvis.
• In relaxed state, it looks like cuboidal cells at basal
surface, columnar in middle and large dome shaped at
surface. When stretched dome shaped cells flatten
out.
Transitional epithelium
Glandular epithelium
• Functions in secretion and is performed by
glandular cells that lie deep to the lining
epithelial cells. Keep the membranes moist.
• May consist of a single cell or a group of cells
that secrete substances into ducts or onto a
surface (exocrine) or directly into the blood
(endocrine).
Shapes of Exocrine Glands
Glandular secretions
• Merocrine – vesicles synthesized by ribosomes
are secreted in small portions. Most exocrine
glands are of this type in the body.
– (Ex. salivary, gastric and pancreatic glands).
• Apocrine – accumulate their secretion at the
surface and then pinch off from the rest of the
cell. - (Ex. Sweat glands in armpit and groin).
• Holocrine – whole cell is released as a
secretion and is then replaced by mitosis.
– (Ex. Sebaceous glands of skin).
Exocrine secretions
Connective Tissues
• Are all derived from Mesenchymal cells of
embryo.
• Four types in body:
-Fibrous connective tissue (2 Types; 6
kinds)
-Cartilage (3 kinds)
-Bone (2 kinds)
-Blood [liquid connective tissue composed of
plasma, and formed elements (cells)].
Fibrous Connective Tissue
Two broad categories: Loose and Dense
Loose
1. Areolar connective tissue
2. Adipose connective tissue
3. Reticular connective tissue
Dense
1. Dense regular connective tissue
2. Dense irregular connective tissue
3. Elastic connective tissue
Fibrous connective tissue functions to support and
protect the body and its organs as well as bind
tissues and organs together.
Areolar (loose) CT matrix
• Characterized by:
1. Protein fibers: collagen; reticular; elastic
2. Ground substance/ interstitial fluid
3. Defensive cells: macrophages, mast cells,
plasma cells, neutrophils, lymphocytes and
eosinophils
4. Fat cells: store triglycerides as nutrients
Areolar connective tissue is found under epithelia
as in the lamina propria and around organs and
capillaries.
Areolar Connective Tissue
Areolar Connective Tissue
Protein fibers in connective tissue
• Collagen fibers- occur in parallel bundles,
strongest (stronger than steel) and most
abundant. Withstand tremendous pulling forces.
• Reticular fibers- short bundles of specialized
collagen fibers. Important in support of vessels
and tissues.
• Elastic fibers- smaller in diameter, branching
and form networks. Consist of protein elastin
and fibrillin. Highly stretchable (150%) but
strong and return to original length.
Areolar Connective Tissue
Ground substance
• Binds, supports and provides medium for transport
and exchange between cells.
• Consists of water, proteoglycans, hyaluronic acids,
glycosaminoglycans (GAGs), fibronectin and other
substances that hold the cells together.
• Interstitial fluid - liquid faction that bathes tissues and
contains all of the preceding substances and cells.
Connective tissue cells
• Fibroblasts- large flat branching cells secrete
fibers and ground substance in the matrix
• Macrophages- derived from monocytes, large
irregular shape. Phagocytic action.
• Plasma cells- derived from B lymphocytes,
secrete antibodies= immune response
• Mast cells- produce histamine
• Adipocytes- store triglycerides
• White blood cells- neutrophils, eosinophils, and
lymphocytes for fighting infection