Anatomy - Bone Tissue

What are the Six Tissues that make up a bone?

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bone (osseous) tissue
cartilage tissue
dense connective tissue
epithelium
adipose tissue
nervous tissue

Six Main Functions of the Skeletal System

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Support
Protection
Assistance in Movement
Mineral Storage and Release
Blood Cell Production
Triglyceride storage

Support

The skeleton serves as the structural framework for the body by supporting soft tissues and providing attachment points for the tendons of most skeletal muscles

Protection

The skeleton protects the most important internal organs from injury. For example, cranial bones protect the brain, vertebrae (backbones) protect the spinal cord, and the rib case protects the heart and lungs

Assistance in Movement

Most skeletal muscles attach to bones; when they contract, they pull on bone to produce movement

Mineral storage and release

Bone tissue stores several minerals, especially calcium and phosphorus, which contribute to the strength of bone. Bone tissue stores about 99% of total body calcium. On demand, bone releases minerals into the blood to maintain critical mineral balances and to distribute the minerals to other parts of the body.

Blood Cell Production

Within certain bones, a connective tissue called red bone marrow produces red blood cells, white blood cells, and platelets, a process called hemopoiesis. Red bone marrow consists of developing blood cells, adipocytes, fibroblasts, and microphages within a network of reticular fibers. It is present in developing bones of the fetus and in some adult bones, such as the hip bones (pelvic bones), ribs, sternum (breastbone), vertebrae (backbones), skull, and ends of the humerus (arm bone) and femur (thigh bone). In a newborn, all bone marrow is red and is involved in hemopoiesis. With increasing age, much of the bone marrow changes from red to yellow.

Triglyceride Storage

Yellow bone marrow consists mainly of adipose cells, which store triglycerides. The stored triglycerides are a potential chemical energy reserve.

Types of Bones

Long
Short
Flat
Irregular
Sesamoid

Long Bones

have greater length than width and consist of a shaft and a variable number of extremities (ends). They are slightly curved for strength. Long bones consist mostly of compact bone tissue, which is dense and has smaller spaces but they also contain considerable amounts of spongy bone tissue, which has larger spaces. Long bones include the humerus (arm bone), ulna and radius (forearm bones), femur (thigh bone), tibia and fibular (leg bones), phalanges (finger and toe bones).

Short Bones

are somewhat cube-shaped and nearly equal in length and width. They consist of spongy bone except at the surface, where there is a thin layer of compact bone. Examples of short bones are the carpal (wrist) bones and tarsal (ankle) bones

Flat bones

generally thin and composed of two nearly parallel plates of compact bone enclosing a layer of spongy bone. Flat bones afford considerable protection and provide extensive areas for muscle attachment. Flat bones include cranial (skull) bones, which protect the brain; the sternum (breastbone) and ribs which protect organs in the thorax; and the scapulae (shoulder blades).

Irregular Bones

have complex shapes and connot be grouped into any of the three categories just described. The yalso vary in amount of spongy and compact bone present. Such bones include the vertebrae (backbones), certain facial bones, and aforementioned calcaneus (heel bone)

Sesamoid Bones

develop in certain tendons where is considerable friction, compression, and physical stress. They are not always completely ossified and measure only a few millimeters in diameter except for the two patellae (kneecaps). Sesamoid bones vary in number from person to person

Sutural (Wormian) Bones

are small bones located within the sutures (joints) of certain cranial bones. The number of sutural bones varies greatly from person to person.

Anatomy of a Bone

diaphysis
epiphysis
metaphysis
articular cartilage
periosteum
medullary cavity
endosteum

Diaphysis

is the bone's shaft, or body - the long, cylindrical, main portion of the bone

Epiphysis

are the proximal and distal ends of the bone

Metaphysis

are the regions between teh diaphysis and the epiphyses. In a growing bone, each metaphysis contains an epiphyseal plate - a layer of hyaline cartilage that allows the diaphysis of the bone to grow in length

Articular Cartilage

a thing layer of hyoline cartilage covering the part of the epiphysis where the bone forms an articulation joint with another bone. Articular cartilage reduces friction and absorbs shock at freely movable joints. Because articular cartilage lacks a perichondrium and lacks blood vessels, repair of damage is limited.

Periosteum

is a tough sheath that surrounds the bone surface wherever it is not covered by a layer of articular cartilage. It is composed of an outer fibrous layer of dense irregular connective tissue and in inner osteogenic layer that consists of cells. The periosteum protects the bone, assists in fracture repair, helps nourish tissue and serves as an attachmetn point for ligaments and tendons.

Medullary Cavity

is a hollow, cylindrical space in the diaphysis that contains fatty yellow bone marrow and numerous blood vessels in adults.

Endosteum

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

Bone Surface Markings

DEPRESSIONS AND OPENINGS:
Fissure
Foramen
Fossa
Sulcus
Meatus
PROCESSES:
Condyle
Facet
Head
Crest
Epicondyle
Line
Spinous process
Trochanter
Tubercle
Tuberosity

Depression and Opening
Fissure

Narrow slit between adjacen parts of bones through which blood vessels or nerves pass
Example: Superior orbital fissure of the sphenoid bone

Depression and Opening
Foramen

Opening through which blood vessels, nerves, or ligaments pass
Example: Optic foramen of the sphenoid bone

Depression and Opening
Fossa

Shallow depression
Example: Coronoid fossa of the humerus

Depression and Opening
Sulcus

Furrow along a bone surface taht accommodates a blood vessel, nerve or tendon.
Example: Intertubercular sulcus of the humerus

Depression and Opening
Meatus

Tubelike opening
Example: External and internal auditory meatus of the temporal bone

Processes that form joints
Condyle

Large, round protuberance at the end of a bone
Example: Lateral condyle of the femur

Processes that form attachment points for connective tissue
Epicondyle

Projection above a condyle
Example: Medial epicondyle of the femur

Process that form joints
Facet

Smooth flat articular surface
Example: Superior articular facet of a vertebra

Process that form joints
Head

Rounded articular projection supported on the neck (constricted portion) of a bone
Example: head of the femur

Processes that form attachment points for connective tissue
Crest

Prominent ridge or elongated projection
Example: Iliac crest of the hip bone

Processes that form attachment points for connective tissues
Line

Long, narrow ridge or border (less prominent than a crest)
Example: Linea aspera of the femur

Processes that form attachment points for connective tissues
Spinous process

Sharp, slender projection
Example: Spinous process of a vertebra.

Processes that form attachment points for connective tissue
Trochanter

Very large projection
Example: Great trochanter of the femur

Processes that form attachment points for connective tissue
Tubercle

Small, rounded projection
Example: Great tubercle of the humerus

Tuberosity

Large, rounded usually roughened projection
Example: Ischial tuberosity of the hip bone

Four types of cells present in bone tissue

Osteogenic cells
Osteoblasts
Osteocytes
Osteoclasts

Osteogenic Cells

are unspecialized stem cells derived from mesenchyme, the tissue from which almost all connective tissues are formed. They are the only bone cells to undergo cell division. They are found along the inner portion of the periosteum, in the endosteum and in the canals within bone that contain blood vessels

Osteoblasts

are bone building cells. They synthesize and secrete collagen fibers and other organic components needed to build the extracellular matrix of bone tissue, and they iniate calcification.

Osteocytes

mature bone cells, are the main cells in bone tissue and maintain its daily metabolism, such as the exchange of nutrients and wastes with the blood. Like osteoblasts, osteocytes do not undergo cell division.

Osteoclasts

are huge cells derived from the fusion of as many as 50 monocytes (a type of white blood cell) and are concentrated at the endosteum. Here the cell releases powerful lysosomal enzymes and acids that digest the protein and mineral components of the underlying extracellular matrix of the bone. This is termed resorption.

Compact Bone Tissue

the type of bone tissue observed at the surfact of a bone, but it also can extend deeper into the bone tissue and makes up the bulk of the diaphysis of long bones. The surface layers of the compact bone form as thing concentric layers of bone called circumferential lamellae. in the deeper compact bone, the osteon, or haversian system is the basic structural unit. Resembling the growth rings of a tree, the osteon is a series of concentric lamellae.

Central Canal

a hollow where a network of blood vessels, lymphatics and nerves are located

Lacunae

spaces between the concentric lamellae which contain osteocytes

Canalculi

tiny channels filled with extracellular matrix

Spongy Bone Tissue

This tissue does not contain osteons. It is always located in the interior of a bone, protected by a covering of compact bone. It consists of lamellae that are arranged in an irregular lattice of thin columns of bone called trabeculae. Microscopic spaces between the trabeculae are filled with red bone marrow in some bones which produce blood cells and yellow bone marrow (adipose tissue) in other bones.

Bone Formation

Occurs in four principal situations (1) the initial formation of bones in an embryo and fetus (2) the growth of bones during infancy, childhood, and adolescence until their adult sizes are reached (3) the remodeling of bone (replacement of old bone by new bone tissue throughout life) and (4) the repair of fractures (breaks in bones) throughout life.

Two Methods of Bone Formation

Intramembranous Ossification
Endochondrial Osssification

Intramembranous Ossification

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

Endochondrial 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 the secondary ossification centers
6. Formation of articular cartilage and epiphyseal plate

Bone Growth in Thickness

As new bone tissue is deposited on the outer surface of bone by osteoblasts, the bone tissue lining the medullary cavity is destroyed by osteoclasts in the endosteum.

Bone Growth in Thickness #1

Ridges in periosteum create groove for periosteal blood vessel

Bone Growth in Thickness #2

Periosteal ridges fuse forming and endosteum-lined tunnel

Bone Growth in Thickness #3

Osteoblasts in endosteum build new concentric lamellae inward toward center of tunnel, forming a new osteon.

Bone Growth in Thickness #4

Bone grows outward as osteoblasts in periosteum build new circumferential lamellae. Osteon formation repeats as new periosteal ridges fold over blood vessels.

Remodeling of Bone

the ongoing replacement of old bone tissue by new bone tissue. It involves bone resorption, the removal of minerals and collagen fibers from bone by osteoclasts, and bone deposition, the addition of minerals and collagen fibers to bone by osteoblasts.

Osteoporosis

literally a condition of porous bones; in large part due to depletion of calcium from the body - more calcium is lost in urine, feces, and sweat than is absorbed from teh diet.

Types of Bone Fractures

Open Fracture
Comminuted Fracture
Greenstick Fracture
Impacted Fracture
Pott's Fracture
Colles' Fracture

Steps Involved in Repair of Bone Fracture

1. Formation of Fracture Hematoma
2. Fibrocartilaginous Callus Formation
3. Bony Callus Formation
4. Bone Remodeling

Factors Affecting Bone Growth

1. Minerals
2. Vitamins
3. Hormones

Exercise and Bone Tissue

unstressed bones diminishes because of the loss of bone minerals and decreased numbers of collagen fibers. Weight bearing activities such as walking or moderate weight lifting, help build and retain bone mass.