Connective tissue cells Flashcards
How is connective tissue formed
by three components: cells, fibers, and ground substance
Connective tissue
Is fibrous, less cellular, vascular, and its cells are randomly dispersed in the ground substance.
The connective tissue originates from the mesenchyme, an embryonic tissue made of mesenchymal cells.
Functions of Connective tissue
binding of organs, support, physical protection, immune protection, movement, storage, temperature regulation, transport, repair, or regeneration of damaged organs.
Classification of Connective Tissue
loose irregular, dense irregular, dense regular, embryonal (mesenchymal and mucous), reticular, elastic, and adipose (note, cartilage, bone, and blood are also considered CT, but they are described separately).
Connective Tissue Cells
include those that are formed locally and remain in the CT (mesenchymal, fibroblasts, pericytes, mast, adipocytes) and those that are formed elsewhere and remain in the CT transiently (macrophages, lymphocytes, plasma cells, neutrophils, eosinophils) or permanently (macrophages).
Mesenchymal
undifferentiated stem cells present throughout the body.
Fibroblasts
‘blast’ means metabolically active and ‘cyte’ means inactive; most prevalent CT cell type, synthesize fibers and ground substance, spindle-shaped with long tapering ends and thus cytoplasm is difficult to discern in tissue sections stained with H&E; associated with wound healing.
Macrophages
Originate in the bone marrow as monocytes, which circulate in the blood and then migrate to the CT, where they mature into functional macrophages.
They are mononuclear cells, are abundantly rich in lysosomes, have a huge phagocytic activity, can remove large particles and form a second line of defense in the body.
Their surface contains IgG and IgM receptors and thus they play an important role in body’s immune system.
Macrophages may fuse to form a giant cell, which is multinucleated and is capable of phagocytosing larger foreign bodies.
Macrophages may encircle the foreign body and form epithelioid cells (like epithelial cells), which ward off the foreign body (e.g., Mycobacterium tuberculosis).
Macrophages are distributed throughout the body and constitute the mononuclear phagocytic system, including monocytes in the blood, Kupffer cells in the liver, microglia cells in the nervous system, Langerhans cells in the skin, dendritic cells in the lymph node, osteoclasts in the bone, giant cells in the CT (note, all of them have their origin from blood monocyte).
Mast cells
found in groups near blood vessels, their granules are water-soluble and thus are difficult to see with H&E, but are metachromatic which means they change the color of metachromatic dyes (blue dyes to red or purple); granules contain histamine, heparin, eosinophil chemotactic factor, and leukotriene C. Outer surfaces of mast cells contain Ige receptors, which mediate hypersensitivity reactions (anaphylactic shock) as follows: the first exposure to foreign antigen (e.g., plant pollens, insect venoms, certain drugs) leads to the production of Ige antibodies, which bind to receptors on the surface of mast cells, which then become sensitized to the antigen. The second exposure to the same antigen triggers mast cells to de-granulate and release histamine and leukotriene C. Histamine increases the permeability of blood vessels and contraction of smooth muscle cells, especially in the lungs, which then can lead to dyspnea (difficulty in breathing; hopefully, you now understand why your doctor asks you if you are allergic to any medicine). Leukotriene C also induces contraction of smooth muscles, but at a slower rate.
Lymohocyte
Originate from lymphoid stem cells of the bone marrow; structurally two types: small and large, based upon the size of the nucleus and the amount of cytoplasm; functionally two types: B and T, based upon the surface receptors.
Both B and T lymphocytes increase in number in viral infection, surgical transplantation, and leukemia.
B cell
B cells originate and differentiate in the bone marrow (note differentiation occurs in the cloacal bursa in birds and that is the reason for their name).
B cells differentiate into plasma cells, which produce antibodies and thus B cells are called to mount a humoral immune response because antibodies circulate throughout the body; B cells only account for 5-15% of blood lymphocytes (most remain in the lymphoid organs).
T cell
T cells originate in the bone marrow but differentiate in the thymus; both cells circulate back and forth between the CT and blood.
T cells secrete cytokines, which attack foreign cells directly and thus T cells are called to mount a cell-mediated immune response; T cells account for 80-90% of blood circulating lymphocytes; subtypes of T lymphocytes: helper, suppressor, and killer.
null cells
Type of lymphocyte
Which lack surface receptors characteristics for T and B cells but may have cytotoxic activity against tumor cells.
B cell
