Bones and Skeletal Tissues

Major Function of Bones

• Support – form the framework that supports the body and cradles soft organs.

• Protection – provide a protective case for the brain, spinal cord, and vital organs.

• Movement – provide levers for muscles.• Mineral storage – reservoir for minerals

especially calcium and phosphorus – that can be released into the blood if the body needs

them.• Blood cell formation – hematopoiesis occurs

within the marrow cavities of bones

Minor Functions of Bones

• Acid/Base Balance: Absorbs or releases alkaline mineral salts if blood pH changes drastically.

• Detoxification: Helps remove heavy metals and foreign elements from the blood to protect other vitals organs. – It will try to release them slowly to prevent

excessive stress on the kidneys who must excrete them.

Bone: Cell Types• Bone is considered connective tissue that contains several

types of cells make it capable of adapting and changing according to stresses placed on it. – Osteoblast (build): Produced by osteogenic cells if there is

an increase in stress or fracture to the bone. • They lay down building blocks of bone matrix (collagen

and glycoaminoglycans) ( GAGs). This plays an important role in mineralization of bone.

– Osteocyte: As the osteoblast deposit matrix they become trapped in lacunae. They stop producing matrix and assume a role in maintaining calcium and phosphate balance between bone and blood.

Bone: Cell Types

– Osteoclast: (Break) break down bone matrix by secreting acids and enzymes . Components of the matrix mainly Calcium and Phosphorus are released in the blood.

– Osteoid – unmineralized bone matrix composed of proteoglycans, glycoproteins, and collagen

Bone Membranes

• Periosteum – double-layered protective membrane– Outer fibrous layer is dense regular connective

tissue– Inner osteogenic layer is composed of

osteoblasts and osteoclasts– Richly supplied with nerve fibers, blood, and

lymphatic vessels, which enter the bone via nutrient foramina

• Endosteum – delicate membrane covering internal surfaces of bone

Microscopic Structure of Bone: Compact Bone

Figure 6.6a, b

Gross Anatomy of Compact Bone

• Compact bone – dense and heavy bone designed for compressive

forces • Haversian system, or osteon – the structural unit of

compact bone– Lamella – weight-bearing, column-like matrix tubes

composed mainly of collagen– Haversian, or central canal – central channel

containing blood vessels and nerves– Volkmann’s canals – channels lying at right angles

to the central canal, connecting blood and nerve supply of the periosteum to that of the Haversian canal

– Canaliculi – hairlike canals that connect lacunae to each other and the central canal

Microscopic View of Compact Bone

Histology of Compact Bone

Structure of Spongy Bone

Spongy bone

Trabeculae: Light weight porous bone that’s arrangement is aligned to the stresses placed on them.

part of the bone that weakens and fractures with osteoporosis.

Red bone marrow is found within the trabeculae cavities

Structure of Long Bones

Structure of Long Bone

Red Marrow• In infants

– Found in the medullary cavity and all areas of spongy bone

• In adults– Found in the diploë

of flat bones, and the head of the femur and humerus

The Skeleton

• The human adult skeleton has 206 bones. – Axial skeleton – bones

of the skull, vertebral column, and rib cage

– Appendicular skeleton – bones of the upper and lower limbs, shoulder, and hip

Shapes of Bones

Response to Mechanical Stress

• Trabeculae form along lines of stress

• Large, bony projections occur where heavy, active muscles attach

Remodeling of Bone

• Mechanical and gravitational forces acting on the skeleton influence bone remodeling. – Less stimulation on bone increases osteoclasts

activity resulting in the resorption of bone matrix which:

• Demineralization of bone • releases the calcium and phosphate into the blood

• Increasing stress levels stimulate of osteoblasts resulting in the deposition of bone matrix which:– removes calcium and phosphate from the blood– increases bone density

• Hormonal mechanism maintains calcium homeostasis in the blood

Hormonal Mechanism

• Rising blood Ca2+ levels trigger the thyroid to release calcitonin

• Calcitonin stimulates calcium salt deposit in bone

• Falling blood Ca2+ levels signal the parathyroid glands to release PTH

• PTH signals osteoclasts to degrade bone matrix and release Ca2+ into the blood

Hormonal Mechanism

Response to Mechanical Stress

• Wolff’s law – a bone grows or remodels in response to the forces or demands placed upon it.

• Observations supporting Wolff’s law include– Who will have a higher bone density.

• A 32 year old astronaut how has been in space for 6 months.

• A 55 year old active female• An 18 year old female who has been paralyzed from the

waist down for 6 months.

Osteoporosis

• In premenopausal women the hormone Estrogen has a protective effect on the bone by increasing osteoblastic activity and limiting osteoclastic activity.

• When levels of estrogen drop( menopause) there is a shift is towards osteoclastic. This weakening of the bone leads to a condition called Osteoporosis.

• It is critical to consume most of your dietary calcium between the years of 14-24.

• This is when you deposit most of the calcium that will protect your bone for the rest of your life.

Osteoporosis

The spongy bone in the thoracic spine is very susceptible to osteoporosis.

Female Athlete Triad

• Disordered eating:– Energy output is greater than energy input.

• Loss of menstrual period (Amenorrhea) – Females who loose to much weight or have a body fat

percentage less than 12% often experience hormonal irregularities secondary to inhibition of hypothalamic function.

• Osteoporosis – The hypothalamus is needed to produce estrogen

which has important for bone health.– The lack of this hormone leads to the premature

weakening of bones.• Stress fractures in the young is a red flag !

Table 6.2.1

Table 6.2.2

Common Types of Fractures

Table 6.2.3

Joints and Their Classification

• Arthrology = study of the joints

• Kinesiology = study of musculoskeletal movement

• Classified by freedom of movement– diarthrosis (freely movable)– amphiarthrosis (slightly movable)– synarthrosis (little or no movement)

• Classified how adjacent bones are joined – fibrous, cartilaginous, bony or synovial

• Immovable fibrous joints– bind skull bones together– Considered a

synarthrosis

Fibrous Joint -- Sutures

• Two bones bound by ligament only– interosseus

membrane

• Most movable of fibrous joints– Amphiarthrosis

• Interosseus membranes unite radius to ulna and tibia to fibula

Fibrous Joint -- Syndesmosis

Cartilaginous Joint -- Symphysis

• 2 bones joined by fibrocartilage– pubic symphysis

and intervertebral discs

• Only slight amount of movement is possible– Amphiarthrosis

General Anatomy of Synovial Joint

• Articular capsule encloses joint cavity– continuous with periosteum– lined by synovial membrane

• Synovial fluid = slippery fluid; feeds cartilages• Articular cartilage = hyaline cartilage covering the joint

surfaces• Articular discs and menisci

– jaw, wrist, sternoclavicular and knee joints– absorbs shock, guides bone movements and distributes forces

• Tendon attaches muscle to bone• Ligament attaches bone to bone

Synovial Joint

• Joint in which two bones are separated by a space called a joint cavity• Most are freely movable

– diarthrosis

Tendon Sheaths and Bursae

• Bursa = saclike extension of joint capsule – between nearby structures so slide more easily past each other

• Tendon sheaths = cylinders of connective tissue lined with synovial membrane and wrapped around a tendon

Types of Synovial Joints

Arthritis• Arthritis ( Arthro= Joint) itis =inflammation

• Osteoarthritis results from years of joint wear– articular cartilage softens and degenerates– accompanied by crackling sounds called crepitus– bone spurs develop on exposed bone tissue

causing pain

What Joint is this? Which has Arthritis?

Osteoarthritis

Total Hip Replacement.

Arthritis and Artificial Joints

• Rheumatoid arthritis is autoimmune attack on joint– antibodies attack synovial membrane,

enzymes in synovial fluid degrade the cartilage, bones ossify

– remissions occur, steroids and aspirin control inflammation

• Arthroplasty is replacement of diseased joint with artificial device called prosthesis

Rheumatoid Arthritis