Basics of tissue structure

1
Basics of tissue structure

• Cells are embedded within an extracellular matrix
• Adhesion molecules hold cells together and to
  surfaces

2
Cells and their environment

• Cells survive in their environments through
  physiological and biological adaptation
• The environment is important for full phenotypic
  expression of the cell
• In adapting, cell can also modify their
  environment

3
What do cells interact with?
Cell - extracellular matrix e.g. during
embyogenesis, matrix molecules are involved in
cell migration and cell function Cell -
cell e.g. lymphocytes interact with antigen
presenting cells Cell - growth factor
4
There is an extracellular structure that
surrounds the cell
fibroblasts in connective tissue
5
(No Transcript)
6
The ECM in animals helps give tissue its strength
Cell
ECM with Calcium deposits
7
In animals the ECM is composed of

• Structural fiber -gt Collagen and elastin
• Matrix -gt proteoglycans
• Adhesive -gt fibronectins laminin
• Receptors -gt integrin

8
Collagen fibers are an important structural
component of the ECM
Collagen fibers
fibroblast cells
9
Collagen is a series of twisted protein
fibers Collagen is a repetitive protein with
lots of glycine.
10
Collagen assembly
11
(No Transcript)
12
Elastin provides elasticity to the ECM structure

• a fiborous protein that crosslinks
• particularly prevalent in flexible tissue such as
  skin, lungs, and the intestine
• as one ages, elastin is lost from tissue
• (do the pinching experiment)

13
(No Transcript)
14
Proteoglycans make up the matrix
15
Proteoglycans provide cushion

• Up to 95 carbohydrate
• carbohydrates bind water (provides cushion)
• can bind up to 50x their weight in water
• crosslinked by hyaluronic acid
• composed of glycosaminoglycans (GAGs) which are
  O-linked to serine or threonine

16
Proteoglycans are composed of GAGs
GAGs are composed of disaccharide units
17
PG structure is complex
18
ECM Function

• Support for cells
• Pattern of ECM regulates
• cell division
• adhesion
• motility
• Development
• migration
• differentiation
• Growth factors
• Reservoir

19
ECM Function continued

• Dynamic reciprocity (Bissel et al.)
• Signal transduction
• ECM molecules cell surface receptors gene
  expression

20
ECM Adhesive molecules and their receptors
21
Surface adhesion molecules hold cells to the ECM
through proteoglycan linkages

• Adhesive glycoproteins mediate this
• Bind collagen and PG to each other and to cell
  surface
• Two most common adhesive molecules are laminin
  and fibronectin

22
Fibronectin binds cells to ECM
Fibronectin has multiple binding sites
23
Integrin also binds to fibronectin

• fibronectins are a family of glycoproteins
• composed of globular domains that bind heparin,
  receptors, collagen, specific proteoglycans
• RGD sequences on the fibronectin protein are
  bound by integrin
• Not the only thing required for specific binding

24
Fibronectin helps connect the inside of the cell
to the outside
25
Laminin binds cells to Basal lamina
26
Epithelial sheets are polarized and are linked to
each other and basal lamina by surface adhesion
molecules that bind laminin
Cell Junction
laminin
SAMs are located here
27
Fibronectin and Laminin bind to receptors like
the fibronectin receptor These receptors are
sometimes called SAMs
28
Migrating cells bind to ECM via focal adhesions
29
Stationary epithelial cells bind to ECM via
hemidesmosomes
Note differences in cytoskeleton
30
Holding cells together

• Cell adhesion molecules

31
Forming a sheet of cells

• Most cells in your body are involved in
  epithelial sheets
• Epithelial sheets can be simple or stratified

32
Cell Adhesion molecules bind cells to cells

• Components glycoproteins and glycolipids are
  involved
• Cellular adhesion molecules or CAMs
• cadherin

33
(No Transcript)
34
(No Transcript)
35
Cell adhesion molecules come in many
varieties Homophilic heterophilic
36
Adhesive Junctions

• Adherens junctions
• Found in heart muscle, thin tissue that line body
  cavities and cover organs
• Desmosome junctions
• Button like adhesions
• Provide strength
• Found in many tissues but especially skin, uterus
  and heart muscle

37
Tight junctions
38
Gap Junctions allow cytoplasmic exchange
39
How do cells form tissue?Lets look at an example
40
Cells form layers each layer is held together by
cell adhesions, ECM, or both
lets look at one tissue close up
41
Another tissue Skin
42
Skin
43
Tissue Development regulated by a complex set of
events in which cells interact with each other,
with general and specific growth factors, and
with the ECM

• Both chemical and ECM gradients exist which
  signal the cell to move along tracks of
  molecules into a defined tissue area
• High concentrations of the attractant or other
  signals serve to localize and control the cell

44
Progenitor or Differentiated cell
Substrate/Scaffold
45
Recap

• Be able to identify the different types of cell
  junctions and their function
• Be able to identify components of the ECM
• Be able to explain the function of the ECM