Chapter 4: The Tissue
Level of Organization
There are 4 types of
tissues – We will only
study epithelial now.
Epithelial Tissue
 Covers exposed surfaces
– Example: The skin
 Lines internal passageways
– Example: The intestines
 Forms glands
– Example: Sweat glands
KEY CONCEPT
 Tissues are collections of cells and cell
products that perform specific, limited
functions
 4 tissue types form all the structures of the
human body:
– epithelial, connective, muscle, and neural
Epithelial Tissues
 Epithelia:
– layers of cells covering internal or external
surfaces
 Glands:
– structures that produce secretions
 What are the special structures and
functions
of epithelial tissues?
Characteristics of Epithelia
1.
2.
3.
4.
5.
Cellularity (cell junctions)
Polarity (apical and basal surfaces)
Attachment (basal lamina)
Avascularity
Regeneration
Functions of Epithelial Tissue
1. Provide physical protection
2. Control permeability
a. Move fluids over the epithelium (protection)
b. Move fluids through the epithelium (permeability)
3. Provide sensation
4. Produce specialized secretions (glandular
epithelium)
a. Produce secretions (protection and messengers)
Free Surface and
Attached Surface
 Polarity:
– apical and
basolateral
surfaces
Increasing Surface Area
 Microvilli increase absorption or secretion
 Cilia (ciliated epithelium) move fluids
Effective Barriers
 Physical integrity is maintained by:
– intercellular connections
– attachment to basal lamina
– maintenance and repair
Intercellular Connections
 Support and
communication
Large Connections
 CAMs (cell adhesion molecules):
– transmembrane proteins
 Intercellular cement:
Cell Junctions
 Form bonds with other cells or extracellular
material:
– tight junctions
– gap junctions
– desmosomes
Tight Junctions
 Between 2 cell
membranes
Gap Junctions
 Allow rapid
communications
Desmosomes
 CAMs, dense
areas, and
intercellular
cement
Attachment to Basal Lamina
 Hemidesmosomes
Repairing and
Replacing Epithelia
 Epithelia are replaced by division of
germinative cells (stem cells)
– Continuous
 Near basal lamina
Classes of Epithelia
 Based on shape and layers
Layers
 Simple epithelium:
– single layer of cells
 Stratified epithelium:
– several layers of cells
Cell Shape
 Squamous epithelia:
– Thin, flat, irregular shaped (fish scale)
 Cuboidal epithelia:
– square shaped (cube)
 Columnar epithelia:
– tall shaped (column)
Simple Squamous Epithelium
Stratified Squamous Epithelium
Cuboidal Epithelia
 Simple cuboidal epithelium: Example – Kidney tubules
– secretion and absorption
Cuboidal Epithelia
 Stratified cuboidal epithelia: Sweat gland ducts
– sweat and mammary ducts
Transitional Epithelium
 Urinary bladder
Columnar Epithelia
 Simple columnar epithelium: Intestinal Lining
– absorption and secretion
Columnar Epithelia
 Pseudostratified columnar epithelium: Trachea
– cilia movement
Columnar Epithelia
 Stratified columnar epithelium: Salivary Gland Duct
– protection
Glandular Epithelia
 Endocrine and
exocrine glands
Endocrine Glands
 Release hormones:
– into interstitial fluid
– no ducts
Exocrine Glands
 Produce secretions:
– onto epithelial surfaces
– through ducts
Modes of Secretion – Exocrine
Glands
 Merocrine secretion
Modes of Secretion
 Apocrine secretion
Modes of Secretion
 Holocrine secretion
Types of Secretions – Exocrine
Glands
 Serous glands:
– watery secretions
 Mucous glands:
– secrete mucins
 Mixed exocrine glands:
– both serous and mucous
Gland Structure – Exocrine Glands
 Exocrine glands can be classified as:
– unicellular glands
– multicellular glands
Unicellular Glands
 Goblet cells are the only unicellular exocrine
glands:
– scattered among epithelia
– e.g., in intestinal lining
Structure of Multicellular Exocrine
Glands
 Structural classes of exocrine glands
Structure of Multicellular Exocrine
Glands