Histology 4 Connective Tissue 2

Cells of connective tissue

•Fibroblasts •Macrophages •Plasma cells •Mast cells •Fat cells (adipocytes) •White blood cells (leukocytes)

Macrophages

•Immigrant phagocytic cells in the C.T. •Originate in the bone marrow

Mast cells

•Originate from bone marrow stem cells •Storage granules containing histamine, heparin, other chemical mediators •Although best known for their role in allergy and anaphylaxis, __cells play an important protective role in wound healing and defense against pathogens Stimulated release leads to immediate allergic reactions (anaphylactic shock) next to small blood vessels They also contain neutral proteases and signaling molecules

Fibroblast Microscopy

Fibroblasts are very large cell! cannot miss them on tissue cell. migratory, move to where they are needed. relocate. help the body in wound healing. scars are built from connective tissue, which fibroblasts are primarily responsible for. Bundles of collagen fibers. EM: look and see heterochromatin in repressed state. very large cytoplasm, see prominent ER and golgi. see cross sections. very easy to distinguish connective tissue near fibroblast.

histamine

a substance that causes vasodilation and increased permeability of capillaries.

Mononuclear phagocyte system

•Macrophages are found in many organs •Derived from stem cells of the bone marrow •Among the most independent cells in the body - mobile •Intense phagocytic activity •Characteristic irregular surface morphology •Generally long-lived cells

Fibroblasts

•The most common cells in C.T. •These cells produce the ECM of C.T. •Collagen is the major component of ECM

Multiocular (brown adipose tissue)

Brown, or multilocular, fat cells are smaller in size, and contain several fat droplets rather than one very large one. As a result, the nucleus is not pushed to the periphery. They also contain more mitochondria. Brown fat is found in newborns. Brown fat generates heat. The mitochondria in brown fat cells are uncoupled, which allows them to burn metabolic stores without generating ATP, thereby producing heat.

Adipocytes

Fat cells, or adipocytes, are very large and contain major lipid inclusions. In mature adipocytes of white, (unilocular) fat, the nucleus and cytoplasm are pushed to the periphery and appear as a thin rim surrounding the lipid droplet(s). The fat is usually dissolved during histological processing, leaving a large, empty vacuole. The loss of lipid leads to a "chicken wire" appearance. However, the fat can be stained by special procedures (Sudan black, Sudan red (right panel), or osmic acid). The precursors of adipocytes resemble fibroblasts and are derived from mesenchymal cells.

Macrophages description

_ are the next most common class of differentiated connective tissue cells, found in all loose connective tissues. These cells function in the body's defense mechanisms. Free, wandering _ are highly phagocytic, amoeboid cells derived from precursor cells of the bone marrow. _ are best identified when actively phagocytic, because ingested particles can then be viewed in the cytoplasm. _ingest foreign materials, such as dead cells (i.e., neutrophils), tissue debris, including connective tissue fibers, bacteria, surgical sutures, etc. Some of the phagocytosed material is digested by lysosomes, and some is stored indefinitely in the cytoplasm. _ increase in number in areas of inflammation.

Fibroblast description

__Cells are resident C.T. cells, and are the most common cells of differentiated connective tissue. They produce the fibers and ground substance of the extracellular matrix. __Cells are similar in appearance to mesenchymal cells. They may be large and somewhat flattened, with branching cytoplasmic processes. It is often difficult to identify the boundary of ___ with only their nuclei being visible. Electron microscopy reveals extensive rER, numerous free ribosomes, and a prominent Golgi complex.

heparin

anticoagulant

Leukocytes

circulate in the blood, but function in C.T! Blood leukocytes (white blood cells) are normal components of some connective tissues. Although leukocytes are transported by the blood, they leave blood vessels to perform their functions outside the blood in the surrounding connective tissue.

Plasma cell microscopy hint

ghost golgis translucent spaces that don't stain

Plasma cells

immigrant cells that produce antibodies Plasma cells produce circulating antibodies that then diffuse through the blood plasma, lymph, and other body fluids. In areas of chronic inflammation, the number of plasma cells increases.

mast cells

large, oval cells with coarse granules, containing these substances densely packed in the cytoplasm.