skeletal ststem

Functions of the Skeletal System

• Supports the body
• Facilitates movement
• Protects internal organs
• Stores and releases minerals and fat
• Produces blood cells

Supporting the Body

• Bones and cartilage compose the scaffold that supports the rest of the body
• Without the skeletal system, the body would be a limp mass of organs, muscle, and skin

Facilitating Movement

• Bones facilitate movement by serving as points of attachment for muscles
• Bones act as levers and joints serve as fulcrums
• Unless a muscle spans a joint and contracts, a bone is not going to move

Protecting Internal Organs

• Bones protect internal organs from injury by covering or surrounding them
• Examples include the ribs protecting the lungs and heart, and the bones of the vertebral column protecting the spinal cord

Storing and Releasing Minerals and Fat

• Bone tissue performs several critical functions on a metabolic level
• Bone matrix acts as a reservoir for several minerals essential to the body, especially calcium and phosphorus
• These minerals can be released back into the bloodstream to maintain levels needed to support physiological processes
• Calcium ions are essential for muscle contractions and controlling the flow of other ions involved in the transmission of nerve impulses
• Bone also serves as a site for fat storage

Producing Blood Cells

• Bone is also the site for blood cell production
• The softer connective tissue that fills the interior of most bones is referred to as bone marrow
• There are two types of bone marrow: yellow marrow and red marrow
• Red marrow is where hematopoiesis—the production of blood cells—takes place
• Red blood cells, white blood cells, and platelets are all produced in the red marrow

Organs of the Skeletal System

• Bones
• Cartilage
• Joints
• Ligaments and tendons

Bones

• Bone, or osseous tissue, is a hard, dense connective tissue that forms most of the adult skeleton
• The skeletal system is the body system composed of bones and cartilage and performs several critical functions for the human body

Types of Bones

• Long bones
• Short bones
• Flat bones
• Irregular bones
• Sesamoid bones

Long Bones

• A long bone is one that is cylindrical in shape, being longer than it is wide
• Long bones function as levers; they move when muscles contract

Short Bones

• A short bone is one that is cube-like in shape, being approximately equal in length, width, and thickness
• Short bones provide stability and support as well as some limited motion

Flat Bones

• The term “flat bone” is somewhat of a misnomer because, although a flat bone is typically thin, it is also often curved
• Examples include the cranial bones, the scapulae, the sternum, and the ribs
• Flat bones serve as points of attachment for muscles and often protect internal organs

Irregular Bones

• An irregular bone is one that does not have any easily characterized shape and therefore does not fit any other classification
• Examples include the vertebrae that support the spinal cord and protect it from compressive forces
• Many facial bones, particularly the ones containing sinuses, are classified as irregular bones

Sesamoid Bones

• A sesamoid bone is a small, round bone that, as the name suggests, is shaped like a sesame seed
• These bones form in tendons where a great deal of pressure is generated in a joint
• Sesamoid bones protect tendons by helping them overcome compressive forces
• Sesamoid bones are typically found in tendons associated with the feet, hands, and knees

The Vertebrae

• Provides support for the weight of the head, neck, and the trunk
• Protects the spinal cord
• Maintains an upright body position
• Consists of 26 bones

Cartilage

• Cartilage is composed of specialized cells called chondrocytes that produce a large amount of collagenous extracellular matrix, abundant ground substance that is rich in proteoglycan and elastin fibers
• Cartilage does not contain blood vessels or nerves

Joints

• A joint, also called an articulation, is any place where adjacent bones or bone and cartilage come together to form a connection
• Joints are classified both structurally and functionally

Ligaments and Tendons

• A ligament is the fibrous connective tissue that connects bones to other bones
• A tendon connects muscle to bone
• They are all made of connective tissue
• Tendons and ligaments function is to support muscles and joints

The Axial Skeleton

• The axial skeleton forms the vertical, central axis of the body and includes all bones of the head, neck, chest, and back
• It serves to protect the brain, spinal cord, heart, and lungs
• It also serves as the attachment site for muscles that move the head, neck, and back, and for muscles that act across the shoulder and hip joints to move their corresponding limbs

The Appendicular Skeleton

• The appendicular skeleton includes all bones of the upper and lower limbs, plus the bones that attach each limb to the axial skeleton
• There are 126 bones in the appendicular skeleton of an adult

Factors Affecting Bone Growth and Maintenance

• Heredity
• Nutrition
• Hormones
• Exercise or stress

Heredity

• Genetic factors play a significant role in determining bone mass

Nutrition and Bone Tissue

• Calcium is a critical component of bone, especially in the form of calcium phosphate and calcium carbonate
• Vitamin D is essential for calcium absorption

Hormones

• The skeletal system is no exception, as multiple hormones modulate and support bone health
• Two hormones that affect the osteoclasts are parathyroid hormone (PTH) and calcitonin

Exercise and Bone Tissue

• Lack of mechanical stress causes bones to lose mineral salts and collagen fibers, and thus strength
• Mechanical stress stimulates the deposition of mineral salts and collagen fibers
• Resistance training is especially important to slow down the eventual bone loss due to aging and for preventing osteoporosis

Disorders of the Skeletal System

• Arthritis
• Bursitis
• Gout
• Osteomyelitis
• Osteoporosis
• Rickets
• Tumors
• Scurvy
• Fractures