The Tissue Level of Organization
• Group of similar cells
– common embryonic
origin
– common function
– bound together by
intercellular substance
• Histology
– study of tissues
The Origin of Tissues
Morula
Blastula
Gastrula
4 Basic Tissues Types
•
•
•
•
Epithelial
Connective
Muscle
Nervous
Epithelial Tissue -- General Features
• Cover surfaces, line cavities and form glands
• FUNCTION – To create tissue that line, cover, protect,
secrete.
• Attached to underlying connective tissue by a basement
membrane.
• Cells are tightly packed together, to form tight network.
• Avascular---without blood vessels
– nutrients diffuse in from blood vessels in underlying
connective tissue
– What does this mean for especially thick epithelia like skin?
• Rapid cell division; responsive to environmental stresses.
• Named according to the shape and arrangement of cells.
Epithelial Tissues and Their
Basement Membrane
Simple Squamous Epithelium
• Single layer of flat cells.
– lines blood vessels, form capillary walls, form
alveoli.
– VERY THIN LAYER--.
What is the primary function of this tissue?
Examples of Simple Squamous
Epithelium
• Surface view of lining
of peritoneal
(abdominal) cavity
• Section of intestine
Simple Cuboidal Epithelium
• Single layer of cube-shaped cells viewed from the side.
• Cuboidal cells usually are found lining/forming gland
ducts.
Example of Simple Cuboidal
Epithelium
• Sectional view of kidney tubules.
Nonciliated Simple Columnar
• Unicellular glands =goblet cells secrete mucus
– lubricate GI, respiratory, reproductive and urinary systems.
• Microvilli = fingerlike cytoplasmic projections on the cell
membrane’s top surface. Microvilli are designed to increase
surface area to increase absorption.
Example Nonciliated Simple
Columnar Epithelium
• Section from small intestine
The term “brush border” is often used
to describe this tissue.
Ciliated Simple Columnar Epithelium
• Single layer of rectangular cells with cilia, cilia are
locomotive structures that consist of a 9 +2 arrangement
of microtubules that are covered with cell membrane.
• Mucus from goblet cells moved along by cilia.
• Why would we want the bronchi and bronchioli lined
with this type of tissue?
Example Ciliated Simple
Columnar Epithelium
• Section of fallopian tube.
• Why would we want this structure lined with cilliated
columnar cells?
Stratified Squamous Epithelium
• Several cell layers thick
• Surface cells flat
• Keratinized = surface cells
dead and filled with
Keratin protein
– Examples include the
skin (epidermis) and
mucous membranes
(non-keratinized)
What is the primary function of this type of epithelium?
Example of Stratified Squamous
• Section of vagina
Stratified Cuboidal Epithelium
• Multilayered
• Surface cells cuboidal
– rare (only found in
sweat gland ducts &
male urethra)
Stratified Columnar Epithelium
• Multilayered
• Surface cells columnar
• Rare (very large ducts & part of male urethra)
Transitional Epithelium
• Multilayered
• Surface cells varying in shape
from round to flat if stretched
• Lines hollow organs of the
urinary tract that expand from
within.
Pseudostratified Columnar
PSEUDO = FALSE
• Single cell layer
• All cells attach to
basement membrane but
not all reach free surface
• Nuclei at varying depths
Non-Ciliated version found in
part of male Urethra and in Vas
Deferens
Ciliated version found in
Trachea