Compact bone; Many parallel Haversian canals contain: small blood vessels. very small nerve. Interconnected by Volkmann s canals.

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1 Special characteristics of COMPACT BONE (dense bone) Thick; well vascularized Osteocytes and lamellae Concentric rings around blood vessels Most bones: outer compact bone inner spongy bone Marrow cavity within yellow marrow 1 Special characteristics of COMPACT BONE (dense bone) Compact bone; Many parallel Haversian canals contain: small blood vessels very small nerve. Interconnected by Volkmann s canals. 2

2 Special characteristics of COMPACT BONE (dense bone) 3 Special characteristics of COMPACT BONE (dense bone) Haversian canal + osteocytes + lamellae= Haversian system (AKA, osteon). Osteocyte cell-extensions perpendicular to Haversian canal Join other cell-extensions Efficient diffusion Interstitial bone tissue between ostea. 4

3 Special characteristics of SPONGY BONE (cancellous bone) Spongy bone; other type Thin bone slivers, trabeculae Criss-cross in the marrow cavity. Avascular; thin enough for diffusion Diffusion with marrow, via the osteocyte extensions. Trabecula; matrix lamellae and osteocytes NO concentric cylindrical patterns. 5 Process of conversion of spongy bone to compact bone Temporary spongy bone during development. Trabeculae branch, thicken; enclose smaller spaces. Trabeculae thicken; new osteoblasts layers New lamella,. Enclosed marrow becomes Haversian canal Lined by osteoblasts and concentric lamellae 6

4 Fundamental patterns of formation of spongy bone tissue Intramembranous ossification (ossification: formation of bone) Spongy bone from mesenchyme. Uncommon; anterio-dorsal skull. Name misleading, does not occur within membrane Better; intramesenchymal ossification. 7 Fundamental patterns of formation of bone tissue Endochondral ossification (bone formation within cartilage) More common Rest of the bones. During embryonic development; hyaline cartilage model Precursor to bone. 8

5 Fundamental patterns of formation of bone tissue Cartilage invaded by blood vessels; carries in cells and materials Destroys cartilage; replaced by spongy bone Primary ossification center; vascular invasion at mid-diaphysis Short bones; one center Longer bones; two secondary centers; at the epiphyses. 9 Fundamental patterns of formation of bone tissue Special epiphyseal plate zones responsible for long elongation: Zone of reserve cartilage: chondrocytes ; reserve cells for the next zone Zone of proliferation: chondrocytes undergo mitosis, forms lines of chondrocytes separated by cartilage matrix. 10

6 Fundamental patterns of formation of bone tissue Zone of hypertrophy chondrocytes enlarge. Increase in thickness, bone elongation. Hypertrophy; enlargement of a tissue or an organ due cell enlargement over-feeding Cell grows Alternative mechanism; hyperplasia: Enlargement due to cell division Each cells same size 11 Fundamental patterns of formation of bone tissue Zone of calcified matrix: hydroxyapatite replaces cartilage Enlarged chondrocytes destroyed Osteoblasts cover slivers of calcified cartilage matrix; Deposit bone matrix Complete conversion of some of the calcified cartilage to bone. 12

7 Fundamental patterns of formation of bone tissue Ring of compact bone forms over spongy bone at diaphysis; thickens and lengthens. Secondary ossification centers; spongy bone remains, compact bone at outer (periosteal) surface. Hyaline cartilage epiphysis remains as articular cartilage. 13 RETICULAR CONNECTIVE TISSUE (lymphoid tissue) Reticular CT; matrix reticular fibers; collagen fibers limited; reticular fibers not visible. Cells fill volume; reticular cells, macrophages, and T- and B-lymphocytes. 14

8 RETICULAR CONNECTIVE TISSUE (lymphoid tissue) Lymphocytes B-lymphocytes active form, the plasmocyte Produce and release immunoglobulins (antibodies) Cells do not adhere Abundant reticular fibers present Cells; small cytoplasmic volume, neither eosinophilic nor basophilic 15 RETICULAR CONNECTIVE TISSUE (lymphoid tissue) Specific forms of lymphoid tissue: dense and loose lymphoid tissue. Dense lymphoid tissue More common Densely-packed; most of tissue volume Only nuclei visible Dense collection of nuclei Nuclei are spherical, moderately basophilic and darkly-stained 16

9 RETICULAR CONNECTIVE TISSUE (lymphoid tissue) Loose lymphoid tissue In some parts of lymphoid organ s (lymph nodes) Cells are more scattered Do not occupy a majority of the volume. RETICULAR CONNECTIVE TISSUE (lymphoid tissue) Identification of reticular cells: nuclei are usually relatively large, relatively lightstaining. Other cell types need special staining. Tissue functions part of the immune system for body defense against foreign infectious organisms, viruses, an malignant cells.