September 23, 2011
Lecture 5 – Connective Tissue Part 3
Lymphocytes are programmed to specific antigens with specific receptors. When exposed
to antigens, they will bind to their respective receptors on lymphocytes.
Lymphocytes convert to plasma cells, producing antibodies. Antibodies will bind to
receptors on the lymphocytes. These receptors are reserved specifically for antibodies.
This process is called “arming of the mast cell” where there is now specificity to
Second exposure will lead to degranulation which leads to the clinical effects for
instance, allergic reactions.
Mast cell release causes:
Histamine causes vasodilation which causes increase of blood flow and increased
vascular permeability (accumulation of tissue fluid known as edema). This leads to
redness and swelling.
NCF attracts neutrophils; ECF attracts eosinophils which help to fight the inflammatory
Fat cells have a signet ring shape. There is a thin rim of cytoplasm and the nucleus is
squished off to one side because the cytoplasm contains a large droplet of stored lipid and
forms a globule that the nucleus is squished over to the side.
Lipid is extracted in the slides but the basic shape is still the same.
Adipose tissue is tissue that is dominated by adipocytes.
Macrophages are derived from monocytes. Monocytes move into tissue spaces and
mature into macrophages. It can proliferate locally and are phagocytic cells. They
participate in the immune response, presenting pieces of the antigen on its surface if
engulfed, sending signals to the immune system.
Macrophages are small and inconspicuous when unaffected. When they are active, they
become very large.
In loose connective tissue, they are called macrophages. In the liver, they are called
Kupffer cells. Microglial cells in the CNS, Langerhans cells of the skin and osteoclast of
White blood cells (leukocytes) are carried in circulation, but function largely in the
connective tissue. In cases of infection, WBC count increases wherever they are needed.
Neutrophils stain neither with acid dye (pink) or basic dye (blue) and it is in between.
Connective Tissue Proper:
o Loose CT has fewer fibers and more ground substance. This includes areolar CT,
reticular CT, adipose tissue (there are also adipocytes in areolar CT but they don’t
dominate). o Dense CT is where fibers dominate with fewer ground substances. There is dense
regular CT (strong and tensile, being bundled together to make it even stronger)
and dense irregular CT (fibers running in different directions, creating a network
[sheet that resists tensile forces in all directions]) depending on organization.
Elastic tissue is where elastic fibers dominate.
Supporting Connective Tissue:
o Cartilage – hyaline cartilage (the most common where collagen type II
dominates), elastic cartilage (where elastic fibers dominate), and fibrocartilage (a
medium between hyaline cartilage and dense regular CT because it is stronger
Areolar CT is the least specialized. It’s got all the fiber and cell types and it can do a lot
of jobs. It’s mostly ground substance by volume. There are adipocytes, macrophages,
fibrocytes, elastic fibers, collagen fibers, mast cells, etc. Ex. superficial fascia is the part
that loosely binds your skin to your muscle, blood vessels, nerves, and joints. It can be
pushed and pulled but there is a limit. It attaches different parts together but there is still
Reticular CT is dominated by delicate reticular fibers. CT in the livers, kidneys, spleen,
lymph nodes, smooth muscles and bone marrow. It provides support for these structures.
Forms the stroma (scaffolding).
Adipose CT is dominated by adipocytes and is found with areolar CT. Distribution varies
with age, sex, and activity levels. Women adipose CT accumulates more in the hips and
men accumulates more in the abdomen. It is particularly abundant deep to the skin,
behind the eyes (there is a lot of fat behind the eyes) and around the kidneys. There is
only a rim of cell being seen and the nucleus will be squished. In between the cells, there
are capillaries, erythrocytes, etc.
Dense Regular CT is mostly collagen type I fibers arranged parallel. The nuclei are
found between fibrocytes. This is found where in tendons (tendons are cord-like),
aponeuroses (another type of attachment for muscle, like tendons but this is flat like a
sheet of paper. Ex. abdominal muscles) and ligaments (attaches bone to bone, reinforcing
a joint and preventing movement in particular directions). In a light microscope, some are
wavy, some are straight.
Dense Irregular CT are mostly type I collagen fibers but are arranged in a meshwork
sheet. Within the skin, there is a layer of dense irregular CT (reticular layers of the
dermis). Periosteum, perichondrium, organ capsules, joint capsules, submucosa of GI
tract are all locations with dense irregular CT.
Elastic Tissue has a high concentration of elastic fibers which provides resiliency,
meaning it bounces back after being stretched. Found in structures