HISTOLOGY OF BONE TISSUE

 Histology of Bone Tissue  Bone Function and Structure  Bone Growth & Development  Joints  The Axial Skeleton  The Pectoral Girdle  The Upper Limbs  The Pelvic Girdle  The Lower Limbs

Copyright 2009, John Wiley & Sons, Inc.  Abundant extracellular matrix surrounding widely separated cells  Matrix  25% water  25% collagen fibers  50% crystallized mineral salts: calcium phosphate combines with salt, calcium hydroxide to form crystals of hydroxyapatite then crystals combine with calcium carbonate and ions of magnesium, fluoride, potassium and sulfate.  Most abundant mineral salt = calcium phosphate

 Remember: Bones = Connective Tissue (okay…it is a composite of connective tissues)  Bone tissue consists of four specialized cell types  Osteogenic cells  Undergo cell division; the resulting cells develop into osteoblasts  Osteoblasts  Bone-building cells  Synthesize extracellular matrix of bone tissue  Osteocytes  Mature bone cells  Exchange nutrients and wastes with the blood  Osteoclasts  Release enzymes that break down mineral components of bone matrix (resorption)  Regulate blood calcium level Copyright 2009, John Wiley & Sons, Inc.

 A process called calcification is initiated by bone- building cells called osteoblasts.  Bone:  organic material (mostly collagen, a spongy protein),  Bone’s flexibility from collagen fibers  within an inorganic matrix = hydroxyapatite (mostly calcium and potassium).  Mineral salts are deposited and crystallize in the framework formed by the collagen fibers of the extracellular matrix

Copyright 2009, John Wiley & Sons, Inc.

 Bone may be categorized as:  Compact  Spongy

Copyright 2009, John Wiley & Sons, Inc.  Compact Bone  Resists stresses caused by weight & movement  Components of compact bone – arranged into repeating structural units called osteons or Haversian systems

 Osteon  Central (Haversian) canals run longitudinally through bone  Around central canals are concentric lamellae  Rings of calcified matrix (like rings of tree trunk)  Between lamellae are small spaces = lacunae (which contain osteocytes) Copyright 2009, John Wiley & Sons, Inc.

 Osteon (cont.)  Radiating in all directions from lacunae are tiny canaliculi (filled with extracellular fluid)  Canaliculi connect lacunae, forming system of interconnected canals  Routes for nutrients and oxygen to reach osteocytes  Organization of osteons changes in response to physical demands placed on skeleton Copyright 2009, John Wiley & Sons, Inc.

Compact Bone

 Bone  Dense, hard mineral matrix  Replaced every 9 months.

Histology of Compact Bone Compact bone is also called dense bone. Compact bone is composed of closely packed osteons. An osteon is also called a Haversian system. An osteon is the cylindrical structure with bone. Histology of Red Marrow Red marrow contains active hematopoietic tissue. Histology slide of bone marrow. Histology slide courtesy of CDC/Dr. Gordon D. McLaren

 Spongy Bone  Lacks osteons  Lamellae are arranged in open-lattices of thin columns called trabeculae  Spaces between trabeculae make bones lighter  Trabeculae of spongy bone support & protect the red bone marrow  Hemopoiesis (blood cell production) occurs in spongy bone Copyright 2009, John Wiley & Sons, Inc.

 Spongy Bone  Within each trabecula are lacunae that contain osteocytes  Osteocytes are nourished from blood circulating through trabeculae  Trabeculae of spongy bone - oriented along lines of stress  helps bones resist stresses without breaking  Interior bone tissue = primarily spongy bone Copyright 2009, John Wiley & Sons, Inc.

Spongy Bone

 Histology of Bone Tissue  Bone Function and Structure  Bone Growth & Development  Joints  The Axial Skeleton  The Pectoral Girdle  The Upper Limbs  The Pelvic Girdle  The Lower Limbs