September 20, 2011
Lecture 4 – Connective Tissue Part 2
You won’t see reticular fibers in slides because they do not stain
Elastin is organized by microfibers called fibrillin. Elastic fibers have resiliency, which
means they stretch and recoil compared to collagen fibers. Proportion of these two fibers
will determine the characteristics of the tissue.
The space in between fibers and cells is the ground substance.
Hydrostatic pressure is pressure due to water. If it is being pressed by some force, the
pressure will be higher. Wherever there is water, there is hydrostatic pressure. There is a
gradient of hydrostatic pressure: higher in the plasma (because the heart is pushing on it),
lower in tissue fluid (so there is movement) and even lower in the lymph.
Edema is the condition where there is excess tissue fluid. There are numerous factors that
can cause edema (throwing off the balance). One example would be a decrease in plasma
protein, where the osmotic pressure is lower and there is less removal of tissue fluid (ex.
starvation but bloated appearance). Excess production of tissue fluid (because of
hypertension; hydrostatic gradient is higher than normal), reduced venous clearance
(increasing hydrostatic pressure will lead to reduced venous clearance because usually,
hydrostatic pressure is low in this area. Ex. in pregnancy where there is pressure) and
reduced lymphatic clearance are other ways to cause edema (if lymphatic vessels are
blocked, these cancer cells can leave by gaining access to lymph vessels and they will go
to the lymph nodes, proliferate and getting larger and larger. The tissue removal is no
longer working because it is obstructed).
Ground substance is tissue fluid plus organic components. Organic components can be
subdivided into proteoglycans or adhesive glycoproteins.
Proteoglycans look like a bottle brush. There is a core and there are bristles sticking out
in all directions. The bristles are made up of carbohydrates called glycosaminoglycans
(GAGs) which are unbranched polysaccharides. Since they are straight, they have a lot of
negative charge. They repel each other and tend to take up as much room as possible.
Because they are so negatively charged, water is attracted to it and they are slippery
because they repel each other.
These GAGs are linked to a core protein; the entire thing is called proteoglycans and
consists mainly of sugar. Proteoglycans are a family and they differ from each other and
can be thicker, more viscous, etc.
Hyaluronic acid is another GAG and is different from the bristles. It is specifically found
in cartilage. In cartilage, proteoglycans (brush) links with hyaluronic acid. Forming
agreccan. Sticking on the side of the hyaluronic acid are the proteoglycans (brush),
forming a bigger structure. This molecule sticks in all directions and will take up a lot of
space. Cartilage is very rubbery, because of the presence of these agreccan molecules. Proteoglycans are important for the gel-like consistency of matrix, the turgidity of the
tissue (saturated with fluid) and the ability of connective tissue to resist compression. It is
responsible for controlling the diffusion of molecules through the core substance. It can
also limit the diffusion of pathogens.
Adhesive glycoproteins are different (laminin, fibronectin). Adhesiv