Histology of Soft Connective Tissue
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Describe what is meant by connective tissue
Consists of cells embedded in an extracellular matrix. The matrix varies in composition depending on function
List the structures in and around connective tissue from outside to inside
Above connective tissue is epithelium and basal lamina. In the connective tissue is collagen fiber, macrophages, capillaries, mast cells, fibroblasts, glycoproteins
What makes up the majority of the extracellular matrix?
Proteoglycans
What are the functions of soft connective tissue? (5)
• Space filler and mechanical support • Attachment and protection • Highway for nutrients • Storage - fat and calcium • Site of immunological defence
What are the 5 types of soft connective tissue and describe each?
• Mesenchyme = embryonic • Loose (areolar) = mesentery, under dermis • Dense = tendon, dermis, capsules • Reticular = bone marrow, lymph nodes • Adipose = fat cells
What are the 3 major proteins in the extracellular matrix?
Collagen for strength, elastin for elasticity and adhesive proteins for attachment of proteins to cells
What does collagen form in the extracellular matrix?
It forms fibrils
What are type 1, 2 and 3 collagen for?
1 is for skin, bone, tendons, dentine. 2 is for cartilage and 3 is for blood vessels and skin
What protein cross links cells of the connective tissue to extracellular matrix?
Integrins
What are major extracellular matrix that integrins bind cells to called?
Fibronectin & Collagen, Tenascin and Laminin
What are GAG’s synthesised as?
Proteoglycans
What does the basal lamina (basement membrane) separate?
The connective tissue from the epithelial cell layer. It is a physical barrier maintaining cell integrity.
What is the structure of all GAG’s?
70-200 sugar polymers formed of a repeating disaccharide subunit.
Give 4 properties of GAG’s
• Sugar chains are too stiff to fold into compact structures • Strongly hydrophilic • Tend to adopt highly extended shaped occupying a large volume • Water sucked into the matrix by osmotically active ‘ion cloud’ due to all those negative charges
What is the job of GAG’s?
Water creates swelling pressure (turgor) and this enables extracellular matrix to withstand compressive forces.
What are the two types of connective tissue called?
• Indigenous (permanent residents) 2. Immigrant (immune system cells which come in and out depending on the state of the body)
What are 3 examples of indigenous cells?
1 = Fibroblasts to produce extracellular matrix 2 = Adipocytes which store fat and leptin secretion 3 = Mast cells for histamine secretion
What stem cells give rise to indigenous cells?
Mesenchymal cells