Lecture 2:
An Introduction to
Tissues
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Learning Objectives
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By the end of this lecture you should:
Be able to recognize the four primary tissue types.
Understand how to classify epithelial tissue
Understand the composition of connective tissue
Understand how to classify connective tissue
The Big Picture
Tissue
Epithelial tissue
Connective tissue
Muscle tissue
Nervous tissue
Primary Tissue Types
epithelial
muscle
connective
nervous
Epithelial Tissue
Characteristics
• Located on a surface. Either external or an
lining an organ’s lumen.
• Composed almost entirely of cells, tightly
packed together.
• Polarity – has distinct basal and apical surface
• Organized in sheets or layers
• Anchored to a thin basement membrane.
• Avascular – no blood vessels permeating
tissue
• Regeneration- contains stem cells for
continuous regeneration and replacement of
cells.
Epithelial Tissue
Functions
• Protects Surfaces – from dehydration,
abrasion, and/or chemical and pathogenic
damage.
• Controls permeability – regulates and/or
facilitates what molecules get through this
tissue layer.
• Provides sensation – Many sensory receptors
are specialized epithelial cells (e.g. smell,
receptors and visual receptors). Nerves them
connect to these receptors.
• Produce secretions. Many epithelial cells are
factories for making and pumping out
chemicals. Glands are epithelial tissue that has
grown to line a pocket.
Epithelial Tissue
apical surface (free surface
basal surface
There is connective
tissue down here.
Basement membrane
a fiber layer that
connects bottom of
epithelial tissue to
underlying connective
tissue.
Epithelial Tissue
Categories of Epithelial
Tissue
1) Simple squamous ET
2) Stratified squamous ET
3) Simple cuboidal ET
4) Stratified cuboidal ET
5) Simple columnar ET
6) Stratified columnar ET
7) Psuedostratified
columnar ciliated ET
8) Transitional ET
Rules for identifying the category of
epithelial tissue.
1) Find the free space (it is usually
whiter or is the inside of a tube)
2) Find the basement membrane (look
for the difference between tightly
packed epithelial tissue and
dispersed connective tissue)
3) Count the number of cell layers
between free space and basement
membrane.
4) Determine the shape of the apical
layer.
5) Name is layers+shape+epithelial T
Survey of Epithelial Tissue
Survey of Epithelial Tissue
Survey of Epithelial Tissue
Survey of Epithelial Tissue
Survey of Epithelial Tissue
Glands are epithelial tissue lining dead-end tubes. The cells secrete “stuff” into the tube which
leaks out. Salivary glands, sweat glands, the liver and pancreas, and many more.
Connective Tissue
Characteristics
• Has three basic components:
• specialized cells
• extracellular fibers
• ground substance (fluid)
• Do not occur on a free or exposed
surface
• Cells are usually widely scattered (not
touching)
• Much extracellular fluid called matrix
• Most have a rich blood supply
Connective Tissue
Function
• Structural framework for the body
• e.g. skeleton
• Protect delicate organs
• fibrous pericardium, skull
• Support, surround, and interconnect
other tissue types
• basement membranes
• muscle tendons
• Store energy
• long term (fat storage)
• short term (elastic tendons)
• Transport fluid and dissolved
materials from one region to another
• Defend the body from invasion by
microorganisms.
Connective Tissue
Connective Tiss. Proper
Fluid Connective Tiss.
loose
dense
blood
• Fewer
fibers,
• big cell
space
• Mostly
fibers
• Tightly
packed
In
cardiovascular
system
lymph
In
lymphatic
system
Supporting Conct. Tiss
cartilage
Solid,
rubbery
matrix
bone
Solid,
crystiline
matrix
Connective Tissue Proper
Composed of three things:
1) specialized cells, 2) extracellular fibers, 3) ground substance
Connective Tissue Proper
Composed of three things:
1) specialized cells, 2) extracellular fibers, 3) ground substance
Fixed Cells
Fibroblast – makes extracellular fibers
Fibrocyte – maintains extracellular fibers
Fixed macrophage – engulf damaged
cells, dead cells, and pathogens.
Adipocyte – stores lipids.
Melanocyte – makes and stores brown
pigment (melanin).
Mesenchymal cells – makes all previous
cells. Divides and differentiates to repair
damage.
Connective Tissue Proper
Composed of three things:
1) specialized cells, 2) extracellular fibers, 3) ground substance
Wandering Cells
Mast Cell – release histamine and
heparin to stimulate local inflammation
makes extracellular fibers
Free macrophage – engulf damaged cells,
dead cells, and pathogens. Called in as
reinforcements when needed
Other Immune cells- injury reinforcments
• Lymphocytes
• Plasmocytes
• Neutrophills
• Eosinophils
Connective Tissue Proper
Composed of three things:
1) specialized cells, 2) extracellular fibers, 3) ground substance
Extracellular fibers
Collagen fibers – most common,
• strongest
• long
• straight
• unbranched
Reticular fibers – similar to collagen
(same protein subunits) but but branch
to form 3D mesh. (not shown)
Elastic fibers- injury reinforcments
• Very stretchy (150% resting length)
• Made of elastin
• Often connect collagen fibers
Connective Tissue Proper Loose
Connective Tissue Proper Loose
Connective Tissue Proper Loose
Connective Tissue Proper Dense
Connective Tissue Proper Dense
Connective Tissue Proper Dense
Connective Tissue Fluid
Connective Tissue Support
cartilage
bone
Connective Tissue Support
Connective Tissue Support
Connective Tissue Support
Connective Tissue Support