Histology Week 2 Flashcards
What are the fiber types in connective tissue?
Connective tissue fibers:
- collagen
- reticular
- elastic
What are the different cell types in connective tissue?
Resident Cells: Relatively stable, permanent residents of connective tissue. These cells remain in the connective tissue and include:
Fibroblasts and myofibroblasts (primary cells involved in collagen and ground substance secretion).
Macrophages (arise from migrating monocytes).
Adipose cells.
Mast cells (arise from stem cells in the bone marrow). Mesenchymal cells.
Transient Cells Wandering cells that have migrated into the connective tissue from the blood in response to specific stimuli (usually during inflammation). This population is not normally found in connective tissue and is composed of cells involved in the immune response: Lymphocytes Plasma cells Neutrophils Eosinophils Basophils Monocytes
Connective tissue cells can be put in two categories:
Structural: fibroblast, chondrocytes, osteoblasts, tendon, adipocytes
Migratory: (blood stream) produce bone marrow, part of the blood stream
Describe fibroblasts
Fibroblasts: large, flat, branching cells which appear spindle-shaped in a side view. In mature tissue they are quiescent. After injury, they begin to form new fibers. Under the electron microscope, the activated fibroblast shows the extensive rough ER needed for the synthesis of collagen and elastin fibgers. Proteoglycans, a chief component of the ground substances of connective tissues are also synthesized by these cells. Fibroblasts have large, oval and faint staining nuclei with one or two conspicuous nucleoli.
Describe Macrophage (histiocyte)
next in abundance to the fibroblasts in loose connective tissue, these cells are initially non-motile. During inflammation, they become very actively amoeboid and phagocytic (“angry macrophages”). They readily engulf blood cells, bacteria, dead cells and debris digesting this material with powerful enzymes. The nucleus of this cell type is often indented and dark staining. Nucleoli are not conspicuous. These cells are an important component of the reticuloendothelial system (RES) located in the spleen, liver, lymph nodes and other organs.
Describe Adipose cells
These cells are commonly seen in loose connective tissue (areolar). They are often found arranged around small blood vessels. Initially they resemble fibroblasts but with numerous vacuoles of fat droplets. In adult cells, the droplets coalesce bloating the fat cells with a huge fat vacuole.
Describe Leukocytes
are white blood cells which wander into the connective tissues surrounding blood vessels. Eosinophiles are very common throughout the respiratory and digestive tracts, as well as in active mammary tissue. Neutrophiles are found at sites of inflammation. Plasma cells, derived from B lymphocytes, are common in areas of chronic inflammation.
Describe Mast cells
Mast cells - are large cells (20 to 30 um) filled with deeply basophilic granules which often obscure the nucleus. They are usually adjacent to blood vessels. Like the blood
Describe Melanocytes
are pigment cells found in the connective tissues of the skin and choroid coat of the eye. The melanin produced by these cells is known to absorb ultra violet light.
List the major classes of extracellular molecules that comprise the ground substance of connective tissue and relate how the molecular structures support the functions of these molecules.
Ground substance is a viscous, clear substance that occupies the space between the cells and fibers within connective tissue. Ground substance contains three main types of macromolecules:
- Proteogylcans
- Glycoproteins
- Fibrous proteins
The fibrous proteins and glycoproteins are embedded in a proteoglycan gel, where they form an extensive ECM that serves both structural and adhesive functions.
What is the core molecule of a proteoglycan aggregate? Describe its function:
hylauronic acid
These macromolecules consist of a core protein that is covalently attached to approximately 100 glycosaminoglycan (GAG) molecules and a linker protein, which binds hyaluronic acid (HA) and strengthens its interaction with the proteoglycan molecule. Proteoglycans are very large, highly negatively charged macromolecules that attract water into the ground substance, giving it a gel-like consistency. This highly hydrated gel is able to resist compressive forces while allowing diffusion of O2 and nutrients between the blood and tissue cells.
Describe how the combination of cells, fibers and ground substance combine to produce the different varieties of connective tissue.
Ground substance may be highly modified in the special forms of connective tissue:
- blood: lacks stabilizing macromolecules, free-flowing ground substance plasma.
- skeletal tissue: mineralized by deposition of calcium salts = bone = rigid ground substance
- cartilage: more solid than in ordinary connective tissue but still retains more resiliency than bone.
Distinguish between nucleated and non-nucleated blood cells and describe how morphology and cell structures support the cell function.
Red blood cells are non-nucleated:
WBC = leukocytes: nucleated
Only the red blood cells, like trolley cars, are confined to the highways (i.e., blood vessels). All other cell types in blood, and most plasma constituents as well, can circulate rather freely from blood to connective tissue and back again. Thus, most of the mobile cellular components of ordinary connective tissue are interchangeable with those in blood.
Distinguish between granulocytes and agranulocytes and what the functions are for each cell type
Granulocytes (innate immune system) are a category of white blood cells characterized by the presence of granules in their cytoplasm.[1] They are also called polymorphonuclear leukocytes (PMN, PML, or PMNL) because of the varying shapes of the nucleus, which is usually lobed into three segments. This distinguishes them from the mononuclear agranulocytes.
- Basophil granulocytes: the circulating equivalent of tissue mast cells. Prevent blood from clotting too quickly. Contain vasodilator histamine.
- Eosinophil granulocytes: involved in responses to allergy and parasites.
- Neutrophil granulocytes: phagocytic cells travel in blood until called out into peripheral tissues. An inflammatory response (triggered in part by mast cells) summons neutrophils to the affected area. Neutrophils have the ability to approach, engulf, and kill most bacteria. bone marrow derived
Mast cells: bone marrow derived
Mnemonic: “BEN”
Agranulocytes, (adaptive immune system) also known as mononuclear leukocytes, are white blood cells with a one-lobednucleus. They are characterised by the absence of granules in their cytoplasm, which distinguishes them from granulocytes.
- Lymphocytes: ability to recognize and bind to foreign substances
- Monocytes: circulating precursors of macrophages.
- Macrophage: remove and digest the by-products of both bacterial warfare and normal growth and degeneration. Enter connective tissue from the blood as monocyte, also recycles iron, involved phagocytosis
Introduce the role that blood cells play in the host defense
Connective tissue forms the principal battleground for invasions: Bacteria do not easily proliferate within epithelia –cell membranes block entry into cells, and there is little extracellular food for bacteria within epithelia. On the other hand, connective tissue offers a potential paradise. The abundant extracellular material provides all the necessary nutrients as well as an ideal warm, humid, oxygenated environment. Without vigorous immunological defenses within the connective tissue, any small break in the epithelium would convert the body into an excellent bacterial culture.
Inflammation is a specific function of connective tissue.
