His To Bone

BONE HISTOLOGY

Ma. Minda Luz M. Manuguid M.D.

Osseous tissue  BONE is a specialized form of connective tissue composed of specialized cells (Osteocytes) enclosed within shallow depressions (lacunae) widely scattered in a tough organic matrix in which minerals have been precipitated.

characteristics  composition: 20-30% organic matter; 25% water; 40-50% inorganic matter  high tensile & compressive strength  relatively lightweight; has some elasticity  dynamic tissue – constantly undergoing resorption & renewal

functions  provide (with Cartilage) mechanical support & protection of other organs especially within the skull & thoracic cage  principal internal support of the body  rigid structures for attachment of tendons & muscles --- movement; locomotion  mobilizable storage depot for Calcium  marrow is hematopoietic

Bone components  parenchymal cells: OSTEOCYTES and  OSTEOPROGENITOR CELLS;  OSTEOBLASTS;  OSTEOCLASTS

 matrix/ extracellular fibers : OSSEIN  matrix/extracellular ground substance

 inorganic: (mineralized) HYDROXYAPATITE crystals  organic: OSTEOID: Glycosaminoglycans, Glycoproteins: KERATAN SULFATE; CHONDROITIN SULFATE; HYALURONIC ACID

Bone cells  OSTEOPROGENITOR CELLS  relatively undifferentiated  found on all free surfaces of Bone  active during normal bone growth  pale oval to elongated nucleus  acidophilic to faintly basophilic cytoplasm  active during normal bone growth & during adult reorganization  can transform into Osteoblasts

Bone cells OSTEOBLASTS

 bone-forming cells found on the advancing surfaces of growing bone  ovoid nucleus with prominent nucleolus  basophilic cytoplasm with extensive ER, many ribosomes, numerous elongated mitochondria, & well-developed Golgi (+) alkaline phosphatase  secrete bone matrix (osteoid)  converted to Osteocytes

Bone cells OSTEOCYTES  main parenchymal cells of mature bone  flattened, found inside lacunae  with numerous fine processes inside canaliculi radiating outward, communicating with other canaliculi & with Haversian or Volkmann’s canals  can still secrete osteoid but to a lesser degree than osteoblasts

Bone cells OSTEOCLASTS  phagocytic, bone-destroying cells  multinucleated, syncitial – formed by coalescence/fusion of several macrophage-type cells; may have up to 50 nuclei  associated with Howship’s lacunae  (+) acid phosphatase

Bone matrix Extracellular fibers

 type I collagen, 50-70 nm in diameter, in cross-linkages of 67 nm periodicity  called OSSEIN – bone collagen

Amorphous ground substance

 organic: OSTEOID: Keratan sulfate, Chondroitin sulfate, Hyaluronic acid  inorganic: HYDROXYAPATITE crystals (Ca PO4 OH ); Ca carbonate, Mg, F, Na, Citrate; may be extracted by a weak acid/chelating agent

Bone morphology Gross:

 Long bones – femur, humerus,  Flat bones – skull bones  Short bones – carpals, tarsals,  Irregular bones – patella, ossicles

BONE MORPHOLOGY: GROSS  Periosteum - outer covering  Sharpey’s fibers

 Epiphysis - ends  Epiphyseal Plate – hyaline cartilage - region of vertical growth of long bones

 Metaphysis - broad ‘neck’ area  Diaphysis – shaft  Marrow Cavity  Endosteum – inner covering

Parts of a Long bone  DIAPHYSIS – shaft – thick-walled hollow cylinder of compact bone with voluminous central medullary cavity  EPIPHYSIS – end – spongy bone covered by a thin peripheral cortex of compact bone; Epiphyseal plate- cartilage between epiphysis & diaphysis, only seen in growing bones  METAPHYSIS – columns of spongy bone which unite the epiphyseal plate to the diaphysis

Bone coverings  PERIOSTEUM / PERICRANIUM – outer dense irregular connective tissue; inner layer of osteoblasts Sharpey’s fibers- coarse bundles of collagenous fibers from the periosteum which turn inward to penetrate the outer circumferential lamellae, anchoring the periosteum to the underlying bone; especially numerous in skull bones  ENDOSTEUM / DURA MATER – thin cellular membrane lining the marrow cavity & the cavities between trabeculae of spongy bone

BONE MORPHOLOGY: MICROSCOPIC  Microscopic: Compact bone – Substantia compacta – apparently solid/continuous but contains microscopic spaces Cancellous/Spongy bone – Substantia spongiosa – 3dimensional lattice of branching bony spicules/trabeculae delimiting a labyrinthine system of intercommunicating spaces occupied by bone marrow.

BONE MORPHOLOGY

BONE HISTOLOGY  COMPACT BONE:  Haversian system/OSTEON  Lamellae – layers of osteocytes & bone matrix  Haversian canals – lie parallel to long axis of bone  Volkmann’s canals – oblique/ horizontal

BONE MORPHOLOGY: MICROSCOPIC

Bone histology Lamella:

 Haversian lamellae- concentrically arranged lamellae around a longitudinal vascular channel: 4 – 20 /osteon  interstitial/angular lamellaeirregular lamellae between osteons  inner circumferential lamellae – just beneath the endosteum  outer circumferential lamellae – just beneath the periosteum

Bone histology Lacunae - lenticular cavities housing bone cells Canaliculi - slender tubular passages radiating from lacunae & penetrating the interstitial substance to anastomose with other canaliculi & vascular spaces

Bone histology  CANCELLOUS BONE  Trabeculae  Bone marrow

Cancellous (spongy) bone

Bone marrow  Bone marrow- a mixture of adipose & hematopoietic cells  Platelet precursors:  megakaryoblasts

 RBC precursors:  Erythroblasts / normoblasts  Reticulocytes

 WBC precursors:  myeloblasts  Lymphoblasts  Monoblasts

Bone marrow  Platelet precursors:  Megakaryoblasts  Megakaryocytes

Osteogenesis  Bone is formed from periosteal osteoblasts or from pre-existing connective tissue, most commonly hyaline cartilage  Endochondral ossification  Intramembranous ossification - periosteal bone growth

 Hormonal requirements: parathormone, growth hormone,  Nutritional requirements:  Vitamins C, D & minerals, esp Ca  Protein

Endochondral ossification

Endochondral ossificaton

Calcium metabolism & bone remodeling Hormone control

Parathormone – secreted by the chief cells of the parathyroid gland, it promotes release of Calcium from bone, thus raising blood Ca levels Calcitonin – secreted by the parafollicular ‘C’ cells of the thyroid gland, it promotes incorporation of Calcium into bone, thus lowering blood Ca levels Other hormones: GH, Thyroxine, Estrogen

Bone remodeling Nutritional requirements: Proteins Vitamins: A, C, D Minerals: Ca, PO4

Bone disorders  Osteoporosis – poor mineralization of bone due to deficiency of Calcium  Osteomalacia / Rickets – “softening” or demineralization of bone due to a deficiency of vitamin D in adults / children (bone deformities may become permanent)  Osteoma – benign bone growth  Osteosarcoma – malignant neoplasm of bone

That’s all !