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Tissues & Junctions
Lecture 34
Chapter 21 - Part 1
A)
TISSUES
What is tissue?
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Biological tissue is a collection of
similar cells
and the intercellular substances surrounding them.
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There are four basic kinds of tissue in the body:
1. epithelium
2. connective tissues
– including adipose tissue, blood, bone, and cartilage
3. muscle tissue
4. nerve tissue
With most multicellular organisms there are different types of cells,
which are organized in to discrete groupings called tissues
21_02_tissues.jpg
Plants
Plant cells produce a primary cell wall followed by a secondary
cell wall. The21_05_model_plantwall.jpg
cell wall - which is on the outside of the plasma
membrane - is made of cellulose - a polysaccharide
The cell wall will only allow the cell to grow in one direction,
which is dependant upon the orientation of the fibers that were
laid down during the production of the primary cell wall.
A) Here the plant
tissue may only
expand in a
vertical direction
21_06_cellulose.jpg
B) Here the plant
tissue may only
expand in a
horizontal
direction
The celulose
synthase
complex, that
is embedded in
the plasma
membrane,
oozes out
cellulose
microfibrils 21_07_Microtubules.jpg
Animals
Animals have just 4 classes of tissue - connective, epithelial,
nervous, and
muscular (the last three are basically similar).
21_08_Extracellu_matrix.jpg
Animal cells do not use cellulose. They instead have a protein
extracellular matrix of collagen, which has great tensile strength.
Collagen is made of many bundles of a simple polypeptide
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21_09_Collagen_fibrils.jpg
Mutations in the arrangement of these fibers may result in
21_11_elastic_skin.jpg
various abnormal
outcomes.
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Fibroblasts are the cells that secrete collagen and also the ones
that maintain 21_13_align_collagen.jpg
it.
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How are cells held together?
The interlinks between cells is made between collagen fibers and
the actin filaments of cells using transmembrane and adaptor
proteins known as integrins
21_14_Integrins_link.jpg
Fibronectin - is a linker
protein
Epithelial sheets and cell-cell junctions
21_17_epithelial_sheet.jpg
Most tissue cells have a polarized structure. They rest on the
21_18_sheet_polarized.jpg
basal lamina.
The basal lamina is just a layer of type IV collagen, plus other
molecules.
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Lung Tissue
The intestine is made of two main cell types.
The absorptive
cells take in nutrients and the goblet cells secrete
21_20_polarize_line_gut.jpg
mucus.
Animal cells are held together by a number of types of cellcell junctions.
21_21_cell_cell_junction.jpg
a) Tight Junctions - b) Adherens junction - c) desmosomes
d) gap juctions - e) hemidesmosomes
Tight junctions prevent the passage of solutes between cells.
They also allow the cell to maintain discrete types of plasma
membrane regions
21_22_Tight_junctions.jpg
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Tight junctions
consist of proteins,
for example,
claudins,
occludins and
junctional
adhesion
molecules that are
anchored in the
membranes of two
adjacent cells and
interact with each
other to hold the
cells together and
prevent other
molecules from
passing between
them.
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Adheren junctions and desmosome junctions are build on a
common theme - 21_23_Cadherin.jpg
they make use of transmembrane proteins that
belong to the cadherin family - these molecules from adjacent
cells link directly to each other.
actin or intermediate filament
Adheren junctions form large deposits as belts permitting
adjacent cells
to transmit mechanical forces
21_24_Adherens_junct.jpg
Vital part in development
21_25_tube_or_vesicle.jpg
Desmosomes
21_26_Desmosomes.jpg
Hemidesmosomes
21_27_Hemidesmosome.jpg
Gap junctions permit the free passage of small ions and small
water soluble molecules to pass. However, they can be closed on
demand. Plants have these too.
21_30_plasmodesmata.jpg
A little perspective…
The Inner Life of a Cell - Short Version
Annotated Version