The Skeletal System

Operating Principle For Skeletons: We require muscles for external and internal movement and this occurs through activation, contraction, and relaxation of muscle cells…BUT… All muscles require the presence of some medium or structural element against which the force of contraction may be applied!

Three Primary Types of Skeletons: Hydrostatic:  Muscles work against an internal body fluid and redistribute it within a confined space Exoskeleton:  rigid, external body parts (shell) that receive the applied force of muscle contraction Endoskeleton:  rigid, internal body parts (bones) that receive the applied force of contraction

Endoskeleton  BONES!!  Function in movement, protection, support, mineral storage, and formation of blood cells  Reservoirs for CALCIUM and phosphorus ions!  OSTEOCYTES = mature bone cells

Types of Bone Tissue COMPACT  Organized as many thin, cylindrical dense layers around canals for blood vessels and nerves.  Each array that forms around blood vessels/nerves is called a HAVERSIAN SYSTEM (osteon)  The canal opening in the middle is called the Haversian Canal

SPONGY  at the end of the bones and down the middle  Contains bone marrow  YELLOW  within most mature bone ; largely fat  RED  not as prevalent in mature bone ; major site of blood cell formation Types of Bone Tissue **If you experience severe blood loss, the yellow marrow will convert to red marrow to help your body produce more red blood cells!

Other bone related items… OSTEOBLASTS  Bone-forming cells Osteoclasts  secretes enzymes that digest bones Bone Resorption = important in regulating the amt of bone **Osteoblasts make bone, Osteoclasts break bone ** In childhood, formation exceeds resorption ; as we get older, resorption exceeds formation

Joints = areas of contact or near-contact between bones (each has a bridge of connective tissue) Ligaments = long straps of connective tissue that bridge the gaps at synovial joints (the most common and most movable type of joint in mammals)

Arthritis General term given to both joint inflammation and degenerative disorders Osteoarthritis = cartilage at the knees and other movable joints wears down as we age Rheumatoid Arthritis = synovial membranes become inflamed and thickened, cartilage degenerates, and bone deposits build up (usually triggered by bacterial or viral infection)