Osteology

• Osteology: The study of the anatomy, physiology and related diseases of bone is referred to as osteology.

Bone

• Bone: A specialized type of connective tissue that consists of living cells held in place by a rigid intercellular matrix of collagen fibers embedded with calcium salts.

Matrix of Bone• Inorganic mineral salts provide bone’s hardness

– hydroxyapatite (calcium phosphate) & calcium carbonate

• Organic collagen fibers provide bone’s flexibility– their tensile strength resists being stretched or torn– remove minerals with acid & rubbery

structure results• Mineralization (calcification) is hardening of tissue

when mineral crystals deposit around collagen fibers• Bone is not completely solid since it has small

spaces for vessels and red bone marrow– spongy bone has many such spaces– compact bone has very few

Exercise, Hormones, and Nutrition

• Normal bone growth and maintenance depend on nutritional and hormonal factors– Vitamin C is required for collagen synthesis, and

stimulation of osteoblast differentiation

– Vitamin A stimulates osteoblast activity

– Vitamins K and B12 help synthesize bone proteins

– Growth hormone and thyroxine stimulate bone growth

– Estrogens and androgens stimulate osteoblasts

– Calcitonin and parathyroid hormone regulate calcium and phosphate levels

Factors Affecting Bone Growth• Nutrition

– adequate levels of minerals and vitamins• calcium and phosphorus for bone growth• vitamin C for collagen formation• vitamins K and B12 for protein synthesis

• Sufficient levels of specific hormones– during childhood need insulin like growth factor

• promotes cell division at epiphyseal plate• need hGH (growth), thyroid (T3 &T4) and insulin

– sex steroids at puberty• growth spurt and closure of the epiphyseal growth

plate• estrogens promote female changes -- wider pelvis

Exercise, Hormones, and Nutrition

Hormonal Abnormalities

• Oversecretion of HGH during childhood produces giantism ( in adults=acromegally)

• Undersecretion of HGH or thyroid hormone during childhood produces short stature

(dwarfism) • Both men or women that lack estrogen

receptors on cells grow taller than normal– estrogen responsible for closure of growth plate

Exercise, Hormones, and Nutrition

FIGURE 6–14 Examples of Abnormal Bone Development.

Calcium Homeostasis & Bone Tissue

• Skeleton is reservoir of Calcium & Phosphate• Calcium ions involved with many body

systems– nerve & muscle cell function– blood clotting– enzyme function in many biochemical

reactions

• Small changes in blood levels of Ca+2 can be deadly (plasma level maintained 9-11mg/100mL)

– cardiac arrest if too high– respiratory arrest if too low

Calcium Homeostasis

• Calcium Regulation

– Calcium ions in body fluids

• Must be closely regulated

– Homeostasis is maintained

• By calcitonin and parathyroid hormone

• Which control storage, absorption, and excretion

Calcium Homeostasis

• Calcitonin and parathyroid hormone control and

affect

– Bones

• Where calcium is stored

– Digestive tract

• Where calcium is absorbed

– Kidneys

• Where calcium is excreted

Calcium Homeostasis• Parathyroid Hormone (PTH)

– Produced by parathyroid glands in neck– Increases calcium ion levels by

• Stimulating osteoclasts

• Increasing intestinal absorption of calcium

• Decreasing calcium excretion at kidneys

• Calcitonin– Secreted by C cells (parafollicular cells) in

thyroid– Decreases calcium ion levels by

• Inhibiting osteoclast activity

• Increasing calcium excretion at kidneys

Hormonal Influences

• Parathyroid hormone (PTH) is secreted if Ca+2 levels falls

– PTH gene is turned on & more PTH is secreted from gland

– osteoclast activity increased, kidney retains Ca+2 and produces calcitriol

• Calcitonin hormone is secreted from parafollicular cells in thyroid if Ca+2 blood levels get too high

– inhibits osteoclast activity– increases bone formation

by osteoblasts

Calcium Homeostasis

Figure 6–15 A Chemical Analysis of Bone.

Calcium Homeostasis

Figure 6–16a Factors That Alter the Concentration of Calcium Ions in Body Fluids.

Calcium Homeostasis

Figure 6–16b Factors That Alter the Concentration of Calcium Ions in Body Fluids.

Exercise & Bone Tissue• The pull on bone by skeletal muscle and

gravity is mechanical stress .• Stress increases deposition of mineral

salts & production of collagen (calcitonin prevents bone loss)

• Lack of mechanical stress results in bone loss – reduced activity while in a cast– astronauts in weightlessness– bedridden person

• Weight-bearing exercises build bone mass (walking or weight-lifting)

Osteopenia

• Bones become thinner and weaker with

age

– Osteopenia begins between ages 30 and 40

– Women lose 8% of bone mass per decade,

men 3%

Osteopenia• The epiphyses, vertebrae, and jaws are most

affected:– Resulting in fragile limbs– Reduction in height– Tooth loss

• Osteoporosis– Severe bone loss – Affects normal function– Over age 45, occurs in

• 29% of women• 18% of men

Osteopenia

Figure 6–19 The Effects of Osteoporosis on Spongy Bone.

Aging

• Hormones and Bone Loss

– Estrogens and androgens help maintain bone mass

– Bone loss in women accelerates after menopause

• Cancer and Bone Loss

– Cancerous tissues release osteoclast-activating

factor

• That stimulates osteoclasts

• And produces severe osteoporosis

Osteoporosis• Decreased bone mass resulting in porous bones • Those at risk

– white, thin menopausal, smoking, drinking female with family history

– athletes who are not menstruating due to decreased body fat & decreased estrogen levels

– eating disorders whose intake of calcium is too low

• Prevention or decrease in severity– adequate diet, weight-bearing exercise– behavior when young may be most important factor

Osteoporosis• Osteoporosis is a disorder characterized by a decrease in total

bone material which is experienced primarily by females. It is theorized that osteoporosis is caused primarily by an estrogen deficiency. Estrogen is a parathyroid antagonist. When insufficient estrogen is produced by the female, the parathyroid hormone that is present can significantly de-mineralize the skeletal system. Osteoporosis begins at about the age of 18 years, where lifestyle factors (smoking, poor diet and sedentary lifestyle) play the most significant roles. At age 35 years, the amount of estrogen produced by most females begins to decrease and bone demineralization accelerates. After menopause, osteoporosis progresses rapidly because of the absence of estrogen. Osteoporosis is visible on an x-ray only after at least 30% of the bone mass has been lost. Patients, however, only experience symptoms after at least 50% of the total bone mass has been lost. It is necessary for individuals at risk to undergo early diagnostic imaging tests (single/dual photon absorptiometry) in order to detect osteoporosis in its earliest stages. The most effective therapy for osteoporosis is prevention. Individuals should attempt to maintain a healthy skeletal system in their youth. Causes of osteoporosis include: genetic factors, estrogen deficiencies, poor diet (high phosphate/low calcium), smoking, and environmental factors.

Lateral View of Osteoporotic Thoracic Spine

Normal Bone VS Osteoporotic Bone (Cod Fish Vertebra)

Hyperkyphosis

Disorders of Bone Ossification

• Rickets• calcium salts are not deposited properly• bones of growing children are soft• bowed legs, skull, rib cage, and pelvic

deformities result

• Osteomalacia• new adult bone produced during remodeling fails

to ossify• hip fractures are common

Functions of Bone

• 1) Support• 2) Protection• 3) Locomotion• 4) Mineral homeostasis• 5) Hematopoiesis• 6) Triglyceride storage

Anatomy of a Long Bone• Diaphysis: The long cylindrical portion (shaft/bone) of a long

bone.

• Epiphysis: The proximal and distal ends of a long bone.

• Metaphysis: In a mature/adult bone, the metaphysis represents the region of the bone where the diaphysis joins to the epiphysis. In a growing bone, the metaphysis contains the epiphyseal (growth) plate. The epiphyseal plate is a layer of hyaline cartilage existing within the metaphysis of a long bone that allows the diaphysis of the bone to grow in length, but not width.

• Articular Cartilage: Articular cartilage is a thin layer of hyaline cartilage that covers the proximal and distal epiphyses where the bone forms articulations/joints. Articular cartilage reduces friction in moveable joints, and assists in shock absorption

Typical Long Bone

Articular Cartilage

• Articular Cartilage: Articular cartilage is a thin layer of hyaline cartilage that covers the proximal and distal epiphyses where the bone forms articulations/joints. Articular cartilage reduces friction in moveable joints, and assists in shock absorption

Periosteum

• Periosteum: The periosteum is a tough sheath of dense irregularly arranged connective tissue that covers the surface of bone except where articular cartilage exists. The periosteum. The periosteum contains cells which are involved in bone formation and allows the bone to grow in diameter/thickness. The periosteum also helps to nourish the bone, assist in fracture repair, protects the bone and acts as an attachment site for tendons and ligaments.

Periosteum and Endosteum

Medullary Cavity

• Medullary Cavity: The space within the diaphysis of a long bone that contains the red (infant) or yellow (adult) bone marrow.

Endosteum

• Endosteum: The membrane that contains bone forming cells that lines the internal surface of the medullary cavity and external surface of the boney trabeculae.

Spongy Bone and the Endosteum

Histology of Bone

• Bone is a typical connective tissue. It contains a small number of cells existing in a large amount of intercellar matrix. The matrix of bone is approximately 25% water, 25% protein fibers, and 50% crystallized mineral salts. There are four types of cells that can be found in bone:

• a) osteogenic cells• b) osteoblasts• c) osteocytes• d) osteoclasts.

Osteogenic Cells

• Osteogenic Cells: Osteogenic cells are undifferentiated stem cells that are found in the inner surface of the periosteum, the endosteum and in the canals that transmit blood vessels within the bone. These cells are the only bone cells that are capable of reproduction and ultimately differentiate into osteoblasts.

Bone Cells

Osteoblasts

• Osteoblasts: Osteoblasts synthesize and secrete collagen fibers as well as other organic compounds that are needed to build bone. They are also involved in initiating the calcification of these organic components of bone.

Osteocytes

• Osteocytes: Osteocytes represent the principle type of bone cell in bone tissue. Osteocytes are mature cells that arise from osteoblasts that have been trapped in the mineral intercellular matrix of bone. Osteocytes essentially maintain bone tissue.

Osteoclasts

• Osteoclasts: Osteoclasts are large cells which result from the fusion of as many as 50 monocytes. Osteoclasts exist primarily within the endosteum of bone. These cells contain a ruffled border that faces the bone, from which powerful lysosomal enzymes and acids are released that break bone down.

Types of Bone

• Bone essentially occurs as either:

• a) compact bone or • b) spongy bone.

Compact VS Spongy Bone

Haversian System

• Compact bone is dense and smooth in appearance. It forms the external layer of all of the bones of the body and makes up the principle portion of the diaphysis of the long bones. Compact bone contains few spaces between its mineralized components and is arranged in units called Haversian systems/osteons. Compact bone provides bone with protection, support and the ability to resist weight bearing stresses.

Three Dimensional Structure of the Haversian System/Osteon

Micrograph of the Osteon

Histology of Bone

The Haversian System• The Haversian system is the basic unit of compact

bone. Blood vessels, lymphatic vessels and nerves penetrate through the compact layer of bone through small openings known as Volkmann’s/perforating canals. These blood vessels will connect with the blood vessels of the periosteum, medullary cavity, and the central canal of the Haversian system. The central canals of the Haversian system and the blood vessels which are contained within them, run in a longitudinal direction through the compact bone. Surrounding these canals/blood vessels, are concentric rings composed of the mineralized intercellular matrix of bone. Contained within these rings, are small spaces known as lacunae which contain the osteocytes. Extending from each osteocyte are cytoplasmic projections referred to as canaliculae. The canaliculae of the osteocytes from each successive ring contact each other and allow the osteocytes to pass/exchange material between themselves and the blood vessels within the Haversian canal. The exchange of materials via the canaliculae of the osteocytes allows the passage of substances such as nutrients, hormones, dissolved gases, and wastes through the calcified intercellular matrix of bone.

Histology of Spongy Bone

• The histological architecture of spongy bone is different than that of compact bone. Spongy bone does not contain true Haversian systems. Instead, spongy bone consists of a lattice work of thin boney trabeculae. The strength of a bone is actually determined by the density and arrangement of the components making up the spongy bone. The trabeculae making up the bones of an individual are arranged in such a way as to allow the bone to withstand the maximum amount of stress that they would encounter in their particular lifestyle. If the lifestyle of an individual changes, the boney trabeculae will be broken down and remodeled in a new architectural arrangement that will allow the bon to withstand the maximum amount of stress that will be encountered in these new activities. This structural relationship between compact and spongy bone allows the bones to be both light and strong. The spaces contained between the boney trabeculae contain bone marrow. The osteoblasts, osteocytes and osteoclasts of the spongy bone exchange substances directly with the blood vessels in the bone marrow.

Bone Remodeling

• Bone, especially spongy bone, remodels itself throughout life in order allow the skeletal system to adapt to changing anatomical and physiological stresses.

• Woolfes Law: The more physical stress that is put on a bone, the denser and stronger the bone becomes.

Aneurysmal Bone Cyst

Aneurysmal Bone Cyst of the Fibula

Aneurysmal Bone Cyst of the Spine (Vertebra)

Types of Fractures

Comminuted and Compression Fractures

Spiral and Epiphyseal Fractures

Depressed and Greenstick Fractures

Stages of Healing In a Bone Fracture

• Hematoma Formation• Fibrocartilage Callus Formation• Bony Callus Formation• Bone Remodeling

Hematoma Formation

• Hematoma formation– Torn blood vessels

hemorrhage– A mass of clotted

blood (hematoma) forms at the fracture site

– Site becomes swollen, painful, and inflamed

Fibrocartilage Callus Formation• Fibrocartilaginous

callus forms• Granulation tissue

(soft callus) forms a few days after the fracture

• Capillaries grow into the tissue and phagocytic cells begin cleaning debris

Bony Callus Formation

• Bony callus formation– New bone trabeculae

appear in the fibrocartilaginous callus

– Fibrocartilaginous callus converts into a bony (hard) callus

– Bone callus begins 3-4 weeks after injury, and continues until firm union is formed 2-3 months later

Bone Remodeling

• Bone remodeling– Excess material on

the bone shaft exterior and in the medullary canal is removed

– Compact bone is laid down to reconstruct shaft walls

Long Bones

Short Bones

Flat Bones

Irregular Bones