Connective Tissue Flashcards
What is the function of fibroblasts?
These cells make most of the extracellular matrix (ground substance, fibers, glycoproteins). They are also responsible for making collagen.
What cells are transient in connective tissue?
Cells of the mononuclear phagocytic system. They come from bone marrow precursors, are phagocytic (with lots of lysosomes) and have surface receptors for immnoglobulins and compliment (opsonin). Most of these are macrophages, which differentiate from monocytes in the blood. Mast cells are important in anaphylactic shock and allergic response. They bind to certain imunoglobulins that are involved in allergies (IgE) and will discharge granules when activated. They contain metachromatic granules containing vasoactive and immunoreactive properties (including SRS-A & heparin). Plasma cells differentiate from B lymphocytes and make antibodies.
Where is collagen synthesized?
Collagen synthesis is initiated intracellularly in fibroblasts and completed extracellularly.
What are the steps in synthesis of collagen?
Synthesis begins in rER of fibroblasts, with protein transferred to Golgi exocytotic vesicles (Lys residues get hydroxylated to help in h-bonding). Alpha chains are assembled into triple helix, which is packaged and secreted into fibroblast cove (outside cell). The ends are cleaved to make the propeptides, tropocollagen. The enzyme lysyl oxidase is used to assemble into fibrils (needs vitamin C)
What is collagen type I and where is it found?
This is the most abundant type of collagen. It is found in connective tissue, tendons and bone. It has a distinctive banding pattern and long fibers.
What is collagen type II and where is it found?
Collagen type II is found in cartilage (hyaline and elastic).
What is collagen type III and where is it found?
Collagen type III is found in reticular fibers. It is PAS+ and argyrophillic (like silver stains). It usually provides in internal structure of organs.
What is collagen type IV and where is it found?
Collagen type IV is important in the basement membrane. It forms a lacy network without definite fibers.
What is the structure of elastic fibers?
These are fibers comprised of the proteins elastin and fibrillin. Elastin is made up of demosine and isosemosine (unique amino acid sequences that is similar to a thin collagen fiber without hydroxylysine).
What is ground substance, and what makes it up?
Ground substance is the material between fibers and cells of a connective tissue. It is made of hydrated gel and is essential for transport of nutrients within the tissue. A major constituent is proteoglycans having a protein core with glycosaminoglycans attached (looks like a test tube brush). These are highly hydrophilic.
What is the difference between loose and dense connective tissue?
Loose CT has lots of cells and ground substance and not a lot of fibers. Dense connective tissue has few cells and ground substance with lots of fibers.
What are the two types of dense connective tissue?
Dense connective tissue can be regular or irregular (loose connective tissue is always irregular).
Which organelle is more prevalent in multilocular (brown) fat than unilocular (white) fat?
Mitochondria are much more prevalent in brown fat. The oxidative chain in brown fat cells is uncoupled from the process of producing chemical energy in brown fat cells and, therefore, produces heat.
