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135 Ch 4 Tissues Bbd Essay

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carbon
atom

DNA 
molecule

organelle

cell

tissue

biosphere
ecosystem
organ

organ 
system
community

population

organism

Chapter 4:  The Tissue Level of 
Organization
 A tissue is a group of similar cells organized for a specific  function
 Understanding tissues is key to understanding organs, and the  function of organ systems
 Histology is the scientific field that studies tissues  The study of tissues is a critical tool that pathologists use to try  to understand disease

Tissue:  The Living Fabric
Cells in multicellular organisms (i.e. 
humans) do not operate independently 
or in isolation.
Instead, cells are highly specialized to 
perform specific functions.
This cell specialization allows the body 
to function in very sophisticated ways.

Tissues are Classified into Four Basic 
Types

 Epithelial tissues cover external and internal surfaces of the  body; epithelial tissues also form secretory glands
 Connective tissues protect and support other tissues and  various organs
 Muscle tissues create the forces that allow movement, and  also generate body heat
 Nervous tissues collect and analyze information about the  body, and signal muscles and glands to take appropriate  actions

Epithelial Tissue
(epithelium)
 Found in different areas
1. Body coverings & linings
2. Glandular tissue

 Functions
1.
2.
3.
4.

Protection
Absorption
Filtration
Secretion

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

Slide 3.42

Areas where epithelium is found …
1. Covering & lining epithelium
– Found on free surfaces of body such as outer 
layer of skin, dipping into and lining the open 
cavities of the digestive and respiratory systems, 
lines blood vessels and heart, and covers walls 
and organs of closed ventral cavity
– Nearly all substances received or given off by the  body must pass thru the epithelium  

2. Glandular epithelium
– Fashions (forms) the glands of the body

1.

4 functions of the epithelium
protection—skin (protects mechanical/ chemical/ 

bacterial)
2. Absorption—digestive tract
3. Filtration—kidneys (also do protection and 
absorption)
4. Secretion—specialty of glands

excretion, sensory reception  (other functions, but not  primary functions)

Epithelium Characteristics
1. Cellularity—
• Composed almost entirely of cells
• Epithelial cells fit closely together (in 
contrast, muscle & connective tissue 
cells are often widely separated)

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings: adapted by K. Roy

Slide 3.43

Epithelium Characteristics cont.
2.  Specialized contacts—form continuous sheet 
bound to adjacent cells by lateral contacts 
(including tight junctions, desmosomes, & 
gap junctions which eliminates the 
extracellular space b/w tissue layers)

Tight junctions—when adjacent plasma membranes fuse  together like a zipper

Desmosomes—anchoring junctions that prevent cells 
subjected to mechanical stress from being pulled apart

Gap junctions—allow communication b/w cells

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings: adapted by K. Roy

Slide 3.43

Epithelium Characteristics cont.
3. Polarity—

always has one free (apical) surface

portion of epithelium exposed to the body exterior 
or the cavity of an internal organ

some exposed surfaces are smooth & slick, others 
exhibit modifications such as microvilli or cilia

microvilli—fingerlike extensions of the plasma 
membrane;  increase surface area & are common in 
tissues that absorb & secrete substances (intestine &  kidney)

cilia—hairlike projections commonly found in lining  of trachea (& other internal tracts); propel substances  along the epithelial surface

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings: adapted by K. roy

Slide 3.43

Epithelium Characteristics cont.
4. Avascularity (have no blood supply)
• well supplied with nerve fibers, but has 
no blood vessels
• all cells receive nutrients by diffusion 
from underlying connective tissue

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings: adapted by K. roy

Slide 3.43

Epithelium Characteristics cont.
5. Basement membrane—epithelials rest on thin 
supporting basal lamina which separates it 
from connective tissue

Basal lamina (epithelial)—nonliving, adhesive 
material formed by glycoproteins

Reticular lamina (connective)—extracellular 
material made up of fine collagenous or reticular 
fibers

*these 2 lamina form the basement membrane
*this membrane reinforces epithelial tissues, helping it  to resist stretching and tearing forces
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings: adapted by K. roy

Slide 3.43

Epithelium Characteristics cont.
6. Regeneration

High capacity to regenerate

As long as the cells receive adequate nutrition, they  can replace lost cells rapidly by cell division

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings: adapted by K. roy

Slide 3.43

Classification of Epithelium
 The types of epithelia are identified by 
 shape of cells
 arrangement of cells (number of cell 
layers present)

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

Slide 3.44a

Classification of Epithelium
 Cell arrangement   (# of cell 
layers)
 2 major types of epithelium
1. Simple – one layer; typically 
found where absorption & 
filtration occur
2. Stratified – more than one 
layer stacked on top of the 
other; typically found...

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Keywords

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