Histology summary
Chapter 4 The tissue level of organization
Types of tissue
Epithelial tissue → Covers exposed surfaces, lines internal passageways and
chambers, and forms glands
Connective tissue → Fills internal spaces, provides structural support for other tissues,
transports materials within the body, and stores energy
Muscle tissue → Is specialized for contraction and includes the skeletal muscles of
the body, the muscle of the heart, and the muscular walls of hollow
organs
Nervous tissue → Carries information from one part of the body to another in the
form of electrical impulses
Epithelial tissue
Consist of epithelia and glands
→ epithelia: layers of cells that cover surfaces
→ glands: structures that produce fluids secretions
Functions of epithelial tissue:
- Provide physical protection
- Control permeability
- Provide sensation due to sensory nerve supply (neuroepithelium)
- Produce specialized secretions (gland cells)
o To provide physical protection or temperature regulation
o To act as chemical messengers
Important features
1. Polarity
o Presence of structural and functional differences between the exposed and
attached surfaces
2. Cellularity
o Cells are closely bound together by interconnections
3. Attachment
o Attached to a thin, noncellular basement membrane
4. Avascularity
o Lack of blood vessels
o Get nutrients by diffusion or absorption
5. Regeneration
o Damaged or lost cells are continuously replaced through stem cell division
o Much higher rate than in other tissues
,Maintaining the integrity of epithelium:
1. Intercellular connections
a. Gap junctions
i. Two cells are held together by two embedded interlocking trans-
membrane proteins (connexons)
ii. Let small molecules and ions pass
b. Tight junctions
i. Lipid portions of two plasma membranes are tightly bound together
by interlocking membrane proteins (adhesion belts)
ii. Prevent water and solutes from passing
c. Desmosomes
i. Link the opposing plasma membranes
ii. Spot desmosomes: stabilize the shape of the cell
iii. Hemidesmosomes: attaches a cell to extracellular filaments in the
basement membrane
2. Attachment to the basement membrane
a. Must be attached to other cells or they will die
b. Basal lamina: restricts the movement of proteins and large molecules
c. Reticular lamina: gives the basement membrane its strength and acts as filter
3. Epithelial maintenance and repair
a. Maintain its structure by the continual division of stem cells
, Classification of epithelia:
Simple squamous: reduces friction,
controls vessel permeability, performs
absorption and secretion (blood vessels,
lungs, kidney tubules)
Stratified squamous: provides physical
protection against abrasion, pathogens,
and chemical attack (mouth, skin,
esophagus)
Simple cuboidal: limited protection,
secretion, absorption (glands, kidney
tubules)
Stratified cuboidal: protection, secretion,
absorption (ducts)
Simple columnar: protection, secretion,
absorption (intestine, stomach)
Stratified columnar: protection
(mammary glands, urethra)
Pseudostratified ciliated columnar:
protection, secretion, move mucus with
cilia (trachea, nasal cavity)
Transitional: stretching without damage,
cells can change between squamous and
cuboidal shape (urinary bladder)
Glandular epithelia:
- Endocrine glands (no ducts) → produces hormones that enter the bloodstream for
distribution
- Exocrine glands (ducts) → produces secretions that are discharged onto an epithelial
surface
Chapter 4 The tissue level of organization
Types of tissue
Epithelial tissue → Covers exposed surfaces, lines internal passageways and
chambers, and forms glands
Connective tissue → Fills internal spaces, provides structural support for other tissues,
transports materials within the body, and stores energy
Muscle tissue → Is specialized for contraction and includes the skeletal muscles of
the body, the muscle of the heart, and the muscular walls of hollow
organs
Nervous tissue → Carries information from one part of the body to another in the
form of electrical impulses
Epithelial tissue
Consist of epithelia and glands
→ epithelia: layers of cells that cover surfaces
→ glands: structures that produce fluids secretions
Functions of epithelial tissue:
- Provide physical protection
- Control permeability
- Provide sensation due to sensory nerve supply (neuroepithelium)
- Produce specialized secretions (gland cells)
o To provide physical protection or temperature regulation
o To act as chemical messengers
Important features
1. Polarity
o Presence of structural and functional differences between the exposed and
attached surfaces
2. Cellularity
o Cells are closely bound together by interconnections
3. Attachment
o Attached to a thin, noncellular basement membrane
4. Avascularity
o Lack of blood vessels
o Get nutrients by diffusion or absorption
5. Regeneration
o Damaged or lost cells are continuously replaced through stem cell division
o Much higher rate than in other tissues
,Maintaining the integrity of epithelium:
1. Intercellular connections
a. Gap junctions
i. Two cells are held together by two embedded interlocking trans-
membrane proteins (connexons)
ii. Let small molecules and ions pass
b. Tight junctions
i. Lipid portions of two plasma membranes are tightly bound together
by interlocking membrane proteins (adhesion belts)
ii. Prevent water and solutes from passing
c. Desmosomes
i. Link the opposing plasma membranes
ii. Spot desmosomes: stabilize the shape of the cell
iii. Hemidesmosomes: attaches a cell to extracellular filaments in the
basement membrane
2. Attachment to the basement membrane
a. Must be attached to other cells or they will die
b. Basal lamina: restricts the movement of proteins and large molecules
c. Reticular lamina: gives the basement membrane its strength and acts as filter
3. Epithelial maintenance and repair
a. Maintain its structure by the continual division of stem cells
, Classification of epithelia:
Simple squamous: reduces friction,
controls vessel permeability, performs
absorption and secretion (blood vessels,
lungs, kidney tubules)
Stratified squamous: provides physical
protection against abrasion, pathogens,
and chemical attack (mouth, skin,
esophagus)
Simple cuboidal: limited protection,
secretion, absorption (glands, kidney
tubules)
Stratified cuboidal: protection, secretion,
absorption (ducts)
Simple columnar: protection, secretion,
absorption (intestine, stomach)
Stratified columnar: protection
(mammary glands, urethra)
Pseudostratified ciliated columnar:
protection, secretion, move mucus with
cilia (trachea, nasal cavity)
Transitional: stretching without damage,
cells can change between squamous and
cuboidal shape (urinary bladder)
Glandular epithelia:
- Endocrine glands (no ducts) → produces hormones that enter the bloodstream for
distribution
- Exocrine glands (ducts) → produces secretions that are discharged onto an epithelial
surface
