Tecido Ósseo

	Veterinary Histology UFF Department of Morphology - Biomedic Institute LaBEc - Laboratory of Cellular and Extracellular Biomorphology
	Veterinary Histology Atlas
			Versão em Português

Introduction

Osseous Tissue
General Characteristics • Rigid Tissue • Composed of Cells and Osseous Matrix
Functions • Main Component of the Skeleton • Support • Locomotion • Protection • Lodges and Protects the Bone Marrow(Hematopoiesis) • Stocks Calcium
Study Methods
	• By Decalcification
	• By Abrasion
Classification Macroscopic • Compact Bone • Spongy Bone • Diploe -Two layers of Compact Bone with a Spongy bone in-between. -Present in Flat Skull Bones
Microscopic • Woven or Immature Bone -Present Collagen Fibers with no defined organization -Smaller amount of Minerals -Greater amount of osteocytes when compared to the Matrix • Lamellar or Mature Bone -Found in Adults -Possess Collagen Fibers organized in concentric lamella around the Haversian
Haversian System or Osteons: Long Cylinders formed by 4 to 20 concentric lamellas.
Haversian Canal • Placed in the middle of the Haversian System • Lined by the Endosteum • Contain Vessels and Nerves
Volkmann's canal • Transverse or Oblique Canals • Communicate Haversian Canals with the Medullary Cavity and with the Outer Surface • Don’t have Concentric Lamellas
Cell Types Osteogenic or Osteoprogenitors • Stem-cells derived from the mesenchyme • Proliferate and Form a group of cells that differentiate into osteoblasts
	Osteoblasts • Cubical cells with few projections • Characteristics of a Secreting cell (well developed R.E.R. and G.A.) • Basophilia • Synthesize the Organic Osseous Matrix • Osteoid: Recently-deposited Organic Matrix, not yet calcified • Height of Osteoblasts varies according to its activity
	Osteocytes • Osteoblasts imprisoned inside the Matrix • Fusiform Cell • Present Cytoplasmic Projections that propitiate a cell/cell communication and nutrition • Acidophil(not as much protein synthesis) • Responsible for the Maintenance of the Osseous Matrix
	Osteoclasts • Giant Mobile Cells containing 6-50 nuclei • Derived from Monocytes(fusion) • Responsible for the osseous re-absorption and remodeling • Howship’s Lacuna: Contact sites for osteoclasts with the Osseous Matrix, forming depressions • Activity Regulated by Hormones -Parathormone: Increase the levels of Calcium in the bloodstream, activating the osteoclasts -Calcitonin: Reduce the levels of Calcium in the bloodstream, inhibiting the osteoclasts
Osseous Matrix Organic Part (50%) • Fibers of Collagen Type I(95%) • Ground Substance(5%) Inorganic or Mineral Part (50%) • Calcium phosphate under the form hydroxyapatite crystals • Bicarbonate, Magnesium, Potassium, Sodium and Citrate in small quantities
Periosteum and Endosteum Connective membrane that lines the internal and external sufaces of the bone. Functions: Nutrition, Innervation and Osteogenesis Periosteum • Fibrous Connective Tissue -Outer Fibrous Layer -Inner Cambium or Osteogenetic Layer (Presents Progenitor Cells) • Sharpey Fibers (Fibers of Collagen Type I that comes from the osseous matrix and insert themselves in the Periosteum) Endosteum • Similar to the Periosteum, however thinner and does not posess two layers
Ossification Intramembranous • Occurs inside the Connective Membranes • Form most os the Flat Bones • Formed by a group of mesenchymal cells in differentiation(osseous blastema) • Present Osteoid
Endochondral • Begins with a Cartilage Model • Forms most of the Short and Long Bones I – Cartilage suffers modifications(Hypertrophy of Chondrocytes) II – Chondrocytes dye and leave the cavities separated by septa of Cartilage Matrix III- Calcification of Cartilage Matrix right after death of chondrocytes IV – Cavities of Calcified Cartilage are invaded by capilaries and mesenchymal cells V – Mesenchymal Cells differentiate into Osteoblasts VI – Osteoblasts produce and deposit Osseous Matrix over the rest of the Calcified Cartilage
Layers of Endochondral Ossification(Epiphyseal Cartilage)
	• Zone of Resting Cartilage (Chondrocytes are scattered)
	• Zone of Cartilage Proliferation (Formation of Axial Isogenous Groups)
	• Zone of Cartilage Hypertrophy
	• Zone of Cartilage Calcification
	• Zone of Ossification