Chapter 6 - Osseous Tissue

Endochondral Ossification

A superficial layer of bone, or bone collar, forms early in endochondral ossification. After that, the developing bone increases in diameter through appositional growth at the outer surface. In this process, cells of the inner layer of the periosteum differentiate into osteoblasts and deposit superficial layers of bone matrix. Eventually, these osteoblasts become surrounded by matrix and differentiate into osteocytes. Over much of the surface, appositional growth adds a series of layers that form circumferential lamellae. In time, the deepest circumferential lamellae are recycled and replaced by osteons typical of compact bone. However, blood vessels and collagen fibers of the periosteum can sometimes become enclosed within the matrix produced by osteoblasts. Osteons may then form around the smaller vessels. While bone matrix is being added to the outer surface of the growing bone, osteoclasts are removing bone matrix at the inner surface, but at a slower rate. As a result, the medullary cavity gradually enlarges as the bone gets larger in diameter.

Osteoprogenitor Cells

Also known as Osteogenic Cells. They are squamous stem cells that divide to produce daughter cells that differentiate into osteoblasts. These cells maintain populations of osteoblasts and are important in the repair of a fracture (a break or a crack in a bone). are found in the inner, cellular layer of the periosteum. They are also found in an inner layer, or endosteum, that lines medullary cavities and passageways for blood vessels penetrating the matrix of compact bone.

Trabeculae

An open network of ___________, Formed in the matrix of a spongy bone. Has no blood vessels. The space between __________ is filled with Red Bone Marrow.

Bone Classification

Are classified by: Shape, Internal tissue organization, and Bone Markings (surface features; marks)

Circumferential Lamellae

Are found at the outer and inner surfaces of the bone, where they are covered by the periosteum and endosteum. These lamellae are produced during the growth of the bone, as we will describe in a later section.

Homeostasis in Bones

Bone building (by osteoblasts) and bone recycling (by osteoclasts) must balance. More breakdown than building causes bones to become weaker. While Exercise, particularly weight-bearing exercise, causes osteoblasts to build bone.

Bone Cells

Bone contains four types of cells: Osteocytes, Osteoblasts, Osteoprogenitor Cells, and Osteoclasts

Osteogenesis

Bone formation

Dense Matrix

Characteristic of bone tissue. Contains: deposits of calcium salts and Osteocytes (bone cells) within lacunae organized around blood vessels.

Periosteum

Characteristic of bone tissue. Covers outer surfaces of bones and consists of outer fibrous and inner cellular layers.

Canaliculi

Characteristic of bone tissue. Form pathways for blood vessels and exchange nutrients and wastes

Appositional Growth

Compact bone thickens and strengthens long bone with layers of circumferential lamellae

Lamellae

Concentric layers; the concentric layers of bone within an osteon.

The Structure of Compact Bone

Contains, Osteon, Central canal, Perforating canal, Concentric lamellae, Circumferential Lamellae, and Interstital lamellae.

Bone (Osseous) Tissue

Dense, supportive connective tissue, contains specialized cells, produces solid matric of calcium salt deposits, around collagen fibers

The Structure of Spongy Bone

Does not contain osteons, but does contain Trabeculae, red bone marrow, and Yellow bone marrow in some.

Bone Markings

Elevations or projections form where tendons and ligaments attach, and where adjacent bones articulate (that is, at joints). Depressions, grooves, and tunnels in bone are sites where blood vessels or nerves lie alongside or penetrate the bone.

Periosteum

Except within joint cavities, the superficial layer of compact bone that covers all bones is wrapped by a _____________, a membrane with a fibrous outer layer and a cellular inner layer. The ___________ (1) isolates the bone from surrounding tissues, (2) provides a route for the blood vessels and nerves, and (3) takes part in bone growth and repair.

Red Bone Marrow

Has red blood vessels, forms red blood cells, and supplies nutrients to osteocytes

Irregular Bones

Have complex shapes. Examples: Spinal vertebrae, pelvic bones

Bone Development

Human bones grow until about age 25.

Yellow Bone Marrow

In some spongy bones. It is yellow because it stores fat as an energy reserve.

Metaphysis

In the long bone where the diaphysis and epiphysis meet.

Skeletal System

Includes: Bones of the skeleton, Cartilages, ligaments, and connective tissues.

Long Bones

Long and thin. Found in arms, legs, hands, feet, fingers, and toes

Skeletal System - Leverage (force of motion)

Many bones function as levers that can change the magnitude and direction of the forces generated by skeletal muscles. The movements produced range from the precise motion of a fingertip to changes in the position of the entire body.

Calcium Phosphate

Mineral that makes up two-thirds of the Bone Matrix.

Skeletal System - Storage of Minerals and Lipids

Minerals are inorganic ions that contribute to the osmotic concentration of body fluids, as you will learn in Chapter 25 . Minerals also take part in various physiological processes, and several are important as enzyme cofactors. Calcium is the most abundant mineral in the human body. The calcium salts of bone are a valuable mineral reserve that maintains normal concentrations of calcium and phosphate ions in body fluids. In addition, the bones of the skeleton store energy as lipids in areas filled with yellow bone marrow.

Bone Matrix

Minerals: two-thirds is calcium phosphate, reacts with calcium hydroxide to form Crystals of hydroxyapatite(which incorporates other calcium salts and ions) Bone Matrix Proteins: one-third of bone matrix is protein fibers(collagen). Bone cells make up only 2% of bone mass.

Perforating Canals

Other passageways extend perpendicular to the surface. Blood vessels in these canals supply blood to osteons deeper in the bone and to tissues of the medullary cavity.

Skeletal System - Blood Cell Production

Red blood cells, white blood cells, and other blood elements are produced in red bone marrow, which fills the internal cavities of many bones. We will describe blood cell formation when we examine the cardiovascular and lymphatic systems

Skeletal System - Protection

Skeletal structures surround many soft tissues and organs. The ribs protect the heart and lungs, the skull encloses the brain, the vertebrae shield the spinal cord, and the pelvis cradles digestive and reproductive organs.

Sesamoid Bones

Small and flat. Develop inside tendons near joints of knees, hands and feet.

Short Bones

Small and thick. Examples: ankle and wrist bones

Structure of a Long Bone

Structure includes: Diaphysis, Epiphysis, and Metaphysis

5 Primary Functions of the Skeletal System

Support, Storage of Minerals (calcium) and Lipids (yellow marrow), Blood Cell Production (red marrow), Protection, Leverage (force of motion)

Six Bone Shapes

Sutural Irregular Short Flat Long Sesamoid

Osteon

The basic functional unit of mature compact bone. Inside this functional unit, the osteocytes are arranged in concentric layers around a vascular central canal, or Haversian canal.

Osteolysis

The breakdown of the mineral matrix of bone.

Osteogenesis

The formation of bone; ossification

Concentric Lamellae

The lamellae of each osteon form a series of nested cylinders around the central canal. In transverse section, these _____________ lamellae create a targetlike pattern, with the central canal as the bull's-eye. Collagen fibers within each lamella form a spiral pattern that adds strength and resiliency.

Structure of a Flat Bone

The parietal bone of the skull. Resembles a sandwich of spongy bone. Between two layers of compact bone. Within the cranium, the layer of spongy bone between the compact bone is called the diploe

Calcification

The process of depositing calcium salts. Occurs during bone ossification and in other tissues.

Ossification

The process of replacing other tissues with bone

Diaphysis

The shaft of the long bone with a heavy wall of compact bone, or dense bone, Is a central space called medullary (marrow) cavity

Skeletal System - Support

The skeletal system provides structural support for the entire body. Individual bones or groups of bones provide a framework for the attachment of soft tissues and organs.

Epiphysis

The wide part at each end of the long bone, articulation with other bones, mostly spongy (cancellous) bone. Covered with compact bone (cortex)

Flat Bones

Thin with parallel surfaces. Found in the skull, sternum, ribs, and scapulae

Central canal

This canal contains one or more blood vessels (normally a capillary and a venule, a very small vein) that carry blood to and from the osteon. These type of canals generally run parallel to the surface of the bone.

Major Function of Osteocytes

To maintain protein and mineral content of matrix and to help repair damaged bone

Endosteum

an incomplete cellular layer, lines the medullary cavity. This layer is active during bone growth, repair, and remodeling. It covers the trabeculae of spongy bone and lines the inner surfaces of the central canals of compact bone. The endosteum consists of a simple flattened layer of osteogenic cells that covers the bone matrix, generally without any intervening connective tissue fibers.

Osteoclasts

are cells that absorb and remove bone matrix. They are large cells with 50 or more nuclei. They are not related to osteogenic cells or their descendants. Instead, they are derived from the same stem cells that produce monocytes and macrophages, which are cells involved in the body's defense mechanisms. Acids and protein-digesting enzymes secreted by osteoclasts dissolve the matrix and release the stored minerals. This erosion process is called osteolysis or resorption. It is important in the regulation of calcium and phosphate concentrations in body fluids.

Hydroxyapatite Crystals

are formed in the Bone Matrix when calcium phosphate reacts with calcium hydroxide. This incorporates other calcium salts and ions

Osteocytes

are mature bone cells that make up most of the cell population. Each osteocyte occupies a lacuna, a pocket sandwiched between layers of matrix. The layers are called lamellae. cannot divide, and a lacuna never contains more than one osteocyte. Narrow passageways called canaliculi penetrate the lamellae, radiating through the matrix and connecting lacunae with one another and with sources of nutrients, supplied by blood vessels in the central canal.

Intramembranous Ossification

begins when osteoblasts differentiate within a mesenchymal or fibrous connective tissue. This type of ossification is also called dermal ossification because it normally takes place in the deeper layers of the dermis. The bones that result are called dermal bones. Examples of dermal bones are the flat bones of the skull, the mandible (lower jaw), and the clavicles (collarbones).

Interstitial lamellae

fill in the spaces between the osteons in compact bone. These lamellae are remnants of osteons whose matrix components have been almost completely recycled by osteoclasts.

Osteoid

matrix produced by osteoblasts, but not yet calcified to form bone

Sutural Bones

or Wormian bones, are small, flat, irregularly shaped bones between the flat bones of the skull. There are individual variations in the number, shape, and position of the sutural bones.

Osteoblasts

produce new bone matrix in a process called ossification, or osteogenesis. make and release the proteins and other organic components of the matrix. Before calcium salts are deposited, this organic matrix is called osteoid. also help increase local concentrations of calcium phosphate above its solubility limit, triggering the deposition of calcium salts in the organic matrix. This process converts osteoid to bone. Become osteocyte cells when they have become completely surrounded by bone matrix.