Anatomy and Physiology IUnit 4: The Skeletal System

Physiology of the Skeletal System

Skeletal System

• Bones are made of several tissues

• Primarily made of collagen and hydroxyapatite - Ca10(PO4)6(OH)2

• About 206 bones in the human body

Functions of Skeletal System• SUPPORT: Hard framework that supports and anchors

the soft organs of the body.

• PROTECTION: Surrounds organs such as the brain and spinal cord.

• MOVEMENT: Allows for muscle attachment therefore the bones are used as levers.

• STORAGE: Minerals and lipids are stored within bone material.

• BLOOD CELL FORMATION: The bone marrow is responsible for blood cell production.

Parts of the Skeletal System

• Axial skeleton– Skull and bones that support it– Includes vertebra and ribs– 80 bones

• Appendicular skeleton– Limbs– 126 bones

Features of a Long Bone:

Epiphysis: Ends of the bone.

Diaphysis: The shaft of the bone which surrounds the medullary cavity.

Articular Cartilage: Cushions the ends of the bones and allows for smooth movement.

Epiphyseal Plate:Areas made of cartilage allowing for the growth of the bone.

Joints

• Where bone meets bone

• Ligament – holds bone to bone

• Types of joints:– Immovable - skull– Ball-and-socket - shoulder– Hinge - knee– Pivot – forearm– Gliding - vertebrae

Joints

• Cartilage covers ends of movable bones– Reduces friction

• Lubricated by fluid from capillaries

Cartilage

Bone Structure

• Periosteum – hard outer covering– Cells for growth and repair

• Compact bone – hard strong layer– Bone cells, blood vessels, protein with Ca and P

• Spongy bone – at ends of long bones– Has small open spaces to lighten weight

• Marrow cavity – hollow in middle of long bones

Bone Marrow

• Red marrow – produces blood cells and clotting factors– Found in humerus, femur, sternum, ribs,

vertebrae, pelvis– Produces RBC 2 million per second

• Yellow marrow – stores fat– Found in many bones

Bone Structure

Haversian System

• Structure of compact bone

• Rings of bone tissue with blood vessels and nerves in the center

Haversian System

Bone Development• Initial skeleton of cartilage in infants

• Replaced with bone by osteoblasts

• More than 300 bones at birth – fuse to 206

• Always growing and breaking down– Osteoblasts – form new bone cells– Osteoclasts – break bone cells down– Osteocytes – mature bone cells

Broken Bones

• Fracture is a break of the bone

• Simple or Complex fracture

• Regrowth of bone:– Spongy bone forms in first few days– Blood vessels regrow and spongy bone hardens – Full healing takes 1-2 months

Homeostatic Imbalances

Rickets•Disease of children due to a lack of vitamin D.•Calcium is not deposited in bones.•Bones become soft.•Bowing of the bones, and other deformities occur.

Homeostatic Imbalances

Osteomalacia

•“Rickets” of adults.•Due to a lack of vitamin D.•Calcium is not deposited in the bones.•Bones become brittle.

Homeostatic Imbalances

Osteoporosis•Bone reabsorption is greater than bone deposition.•Due to any of the following:

•Lack of estrogen in women.•Lack of exercise to stress the bones.•Inadequate intake of calcium and phosphorus.•Abnormalities of vitamin D metabolism.•Loss of muscle mass.

Age Related DysfunctionsArthritis:

Osteoarthritis- 90% of pop. By age 40chronic inflammation of articular cartilagecan be normal age-dependent change can also be pathology due to ?

Age-related changesdecrease blood supplytrauma

Osteoarthritis

Osteoporosis

Decline in Bone DensityBone Resorption > Bone Deposition

Increase Risk for Fracturecompression fractures of vertebraehip fractures

Role of calcium, vitamin D, estrogen, exerciseCalcitonin vs. Parathyroid Hormone

Osteoporosis