The Skeletal System

The Skeletal System Parts of the skeletal system Bones (skeleton) Cartilages Ligaments Articulations (joints)

Functions of Bones Support of the body Protection of soft organs (like the brain) Movement due to attached skeletal muscles Storage of minerals and some fat Blood cell formation (erythropoiesis)

Bones of the Human Body The skeleton has 206 bones Two basic types of bone tissue 1. Compact bone ● hardened bone 2. Spongy bone small needle-like pieces of bone many open spaces

Classification of Bones Long bones Found on the limbs Have a shaft (a long part) with knobby structures called heads at the ends The shaft is compact bone surrounding a hollow center, and the heads are filled spongy bone Examples: femur, humerus

Classification of Bones Short bones Found on the hand and foot Generally cube-shape bones that fit snuggly into one another Thin layer of compact bone filled with spongy bone Examples: carpals, tarsals

Classification of Bones on the Basis of Shape

Classification of Bones Flat bones Thin and usually curved Two thin layers of compact bone with a layer of spongy bone in between Examples: skull, ribs, sternum

Classification of Bones Irregular bones Odd shaped Do not fit into other bone classification categories Usually have a “hole” and have parts that project out Example: vertebrae and sacrum

Classification of Bones on the Basis of Shape

Gross Anatomy of a Long Bone Diaphysis AKA: Shaft Composed of compact bone surrounding a medullary cavity Epiphysis Ends of the bone Composed mostly of spongy bone epiphysis diaphysis epiphysis

Structures of a Long Bone Periosteum Tough membrane covering the outside of the diaphysis Present when bone is living Endosteum ● Membrane that lines the medullary cavity Arteries Supply bone cells with nutrients Figure 5.2c

Structures of a Long Bone Articular cartilage Covers the external surface of the epiphyses Made of hyaline cartilage Decreases friction at all joint surfaces

Structures of a Long Bone Medullary cavity Cavity in the shaft Contains yellow marrow (mostly fat) in adults Contains red marrow (for blood cell formation) in infants Epiphyseal plate Figure 5.2a

Changes in the Human Skeleton In embryos, the skeleton is primarily cartilage During development, much of this cartilage is replaced by bone In adults, cartilage remains in isolated areas The nose Parts of ribs At point of contact at the articulations

Bone Growth Epiphyseal plates on long bones allow for growth during childhood New cartilage is continuously formed just inside of the growth plate The cartilage causes bone to increase in length Eventually, bone replaces cartilage (ossification)

Long Bone Formation and Growth

Bone Growth Bones are lengthened until growth stops After that, bones can only grow in width Bones can change shape somewhat, usually due to disease

Bone Homeostasis Bone is constantly being broken down and rebuilt. This is known as bone remodeling Minerals from bone are removed when they are needed by the body. Minerals are deposited into bones when they are found floating in the bloodstream.

Osteoclasts break down and dissolve osseous tissue Osteoblasts produce new osseous tissue

Physiology of Bone Growth Osteocytes are bone cells that form when an osteoblast becomes embedded within the matrix that it secretes. These are found within an osteon, the functional unit of compact bone

Physiology of Bone Growth Lamellae are the thin layers of bone that surround lacunae Lacunae are the indentations or spaces within a bone where osteocytes are located

Physiology of Bone Growth Haversian canals are the tubes within the osteon that contain blood vessels. These tubes form the osteon, also called the Haversian System. Bone canaliculi are microscopic canals between the lacunae of compact bone. Filled with osteocytes and a fluid, filled with particles too large to be transported through the gap junctions

Physiology of Bone Growth Volkmann’s canals are microscopic spaces that connect the Haversian System (osteons).