Bio Chapter 6 Bone Tissue

The 6 Steps of Endochondral Ossification

1. Development of the Cartilage Model 2. Growth of the Cartilage Model 3. Development of the Primary Ossification Center 4. Development of the Medullary Cavity 5. Development of Secondary Ossification Center 6. Formation of Articular cartilage & Epiphyseal Plate

The 4 Steps of Intramembranous ossification

1. Development of the ossification Center 2. Calcification 3. Formation of Trabeculae 4. Development of Periosteum

7 Parts of Long Bones

1. Diaphysis 2. Epiphyses 3. Metaphyses 4. Articular Cartilage 5. Periosteum 6. Medullary Cavity 7. Endosteum

Medullary Cavity

A hollow, cylindrical, space within the diaphysis that contains yellow bone marrow and numerous blood vessels in adult long bones

Periosteum

A tough connective tissue sheath (and its blood supply) that surrounds the bone surface wherever its not covered by articular cartilage Has an inner osteogenic layer and an outer fibrous layer Helps bone grow in width, repair fractures, nourish the bone, and provide attachment points

Nutrient Foramen and Nutrient Artery

A whole in the bone that this passes through Divides once in bone and goes to the distal and proximal ends of the bone Supplies the inner diaphysis of compact bone and red bone marrow of spongy bone

Spongy Bone Tissue

Always located inside the bone Doe not contain osteons Consists of trabeculae Makes up interior of most short, flat, sesamoid, and irregular bones Makes up the core of the epiphyses in long bones

Perforating Fibers

Attaches the periosteum to the underlying bone Thick bundles of collagen fibers that extend from the periosteum into the bone ECM

Intramembranous ossification

Bone forms directly within mesenchyme Flat bones are formed this way

Endochondral Ossification

Bone forms within hyaline cartilage that develops from mesenchyme Most bones formed this way

Osteoblasts

Bone-building cells Synthesize and secrete collagen fibers and other ECM components Initiate calcification They become trapped in their secretions and the become osteocytes

Red Bone Marrow

Connective tissue found in certain bones It produces; RBC's, WBC's, and platelets It consists of; developing blood cells, fibroblasts, adipocytes, and macrophages All within a network of reticular fibers

Yellow Bone Marrow

Consists mainly of adipose cells They store triglycerides Which are a potential chemical energy reserve

Compact Bone Tissue

Contains few spaces, therefore is the strongest form of bone Found beneath the periosteum of all bones Makes up the bulk of the diaphyses Is composed of osteons and a central canal

Osteons

Cylindrical vascular tunnels The structural units of compact bone tissue Consists of concentric lamellae arranged around a central canal

Circumferential Lamellae

Developed during initial bone formation Arranged around the entire outer and inner circumference of the shaft of a long bone

Perichondrium

Develops around the cartilage model

Epiphyseal Artery

Enters the epiphyses, supplies the red bone marrow and bone tissues in those areas

Metaphyseal Artery

Enters the metaphysis, supplies red bone marrow and bone tissue of those areas

Appositional (Exogenous) Growth

Growth at the outer surface Happens in endochondral ossification ECM deposites on the surface of the growing bone

Interstitial (Endogenous) Growth

Growth from within Occurs in endochondral ossification Grows cartilage model in length

Osteoclasts

Huge cells derived from the fusion of as many as 50 monocytes (WBC) Concentrated in the endosteum The side facing the bones surface has its plasma membrane deeply folded into a ruffled border, which has powerful lysosomal enzymes and acids which digest the protein and minerals of the ECM

Calcification

Hydroxyapatite combines with other mineral salts in bone to crystallize in ECM and hardens tissue

Trabeculae

Lamellae arranged in an irregular patter of thin columns The small spaces between them hold red and yellow bone marrow Contains blood vessels to nourish the osteocytes

Osteocytes

Mature bone cells The main bone cell Maintain daily metabolism

Calcitrol

PTH stimulates the formation of this The active form of vitamin D Which increases the absorption of dietary calcium in the GI tract Increasing the blood levels of calcium

Ossification

Process of bone formation Occurs in 4 situations: 1. Initial formation in an embryo/fetus 2. Growth during infancy until adult size is reached 3. Remodling throughout life 4. Repair of fractures throughout life

Canaliculi

Radiate in all directions from the lacunae Filled with ECF Inside are slender processes of osteocytes Connect lacunae with each other and with the central canal Form interconnected canals through out the bone Help to transport nutrients and watses to and from osteocytes

Parathyroid Hormone (PTH)

Regulates calcium exchange Will increase blood levels of calcium by telling the osteoclasts to increase bone resorption and for the kidneys to retain calcium

Concentric Lamellae

Resembles growth rings of a tree circular plates of mineralized ECM of increasing diameter Surrounds a small network of blood vessels and nerves located in the central canal

Rickets (children)/Osteomalacia (adults)

Result from inadequate calcification of the extracellular bone matrix, usually caused by a vitamin D deficiency bones become "soft" or rubbery and are easily deformed

Periosteal Arteries

Small arteries accompanied by nerves that enter the diaphysis through perforating canals Supply the periosteum an outer part of compact bone

Lacunae

Small spaces between concentric lamellae Contains osteocytes

Bony (hard) Callus

The Fibrocartilaginous (soft) Callus is converted to spongy bone Lasts about 3-4 months

Bone Deposition

The addition of minerals and collagen fibers by osteoblasts

Resorption

The breakdown of the ECM of bone Done by the osteoclasts

Epiphysis

The proximal and distal ends of long bones

Metaphysis

The region between the diaphysis and the epiphysis

Diaphysis

The shaft/body of a long bone Long, cylindrical, main portion

Ossification Center

The site of mesenchyme cells clustering to begin to form bone They differentiate into osteoprogenitor cells

Articular Cartilage (long bones)

Thin layer of hyaline cartilage covering the epiphysis where the bone forms an articulation with another bone Reduces friction and absorbs shock in moveable joints Lacks perichondrium and blood vessels (therefore repair is limited)

Calcitonin (CT)

Thyroid glands secrete this This decreases blood levels of calcium by inhibiting activity of osteoclasts, speeds blood calcium uptake by bones, and accelerates calcium deposition into bones

Osteoprogenitor Cells

Unspecialized bone stem cells Derived from mesenchyme Only bone cell that undergoes cell division With the resulting cell being osteoblasts Found along inner portion of periosteum in, endosteum, and the canals within bone that contain blood vessels

Epiphyseal Line

What is formed when the epiphyseal plate is completely replaced by bone in a fully grown bone Located in the metaphysis region of long bones

Epiphyseal (growth) Plate

a layer of hyaline cartilage that allows the diaphysis of the bone to grow in length located in the metaphysis area of the bone in growing bones

Fibrocartilaginous (soft) Callus

a mass of repair tissue consisting of collagen fibers and cartilage that bridges the broken ends of the bone Takes about 3 weeks

Stress Facture

a series of microscopic fissures in bone that forms without any evidence of injury to other tissues

Fracture Hematoma

blood clot that forms at the fracture site Forms 6-8 hours after injury

Osteoporesis

bone resorption outpaces bone deposition. In large part this is due to depletion of calcium from the body—more calcium is lost in urine, feces, and sweat than is absorbed from the diet.

Cartilage Model

the hyaline cartilage that takes the shape of the future bone during endochondral ossification

Bone Resorption

removal of minerals and collagen fibers from bone by osteoclasts

Hydroxyapatite

the combination of calcium phosphate and calcium hydroxide Forms crystals of this

Endosteum

thin membrane that lines the medullary cavity, contains a single layer of bone-forming cells and a small amount of connective tissue