Functions of Bones

1. Functions of Bones • Support – form the internal framework that support and anchor our organs and let us stand upright • Protection – Keeps organs from being damaged (like the skull protects the brain) • Movement – Act as leverage points for muscles • Storage – fat and other minerals are stored in bones • Blood Cell Formation– occurs in bone marrow

2. There are 206 bones in the adult skeleton. As a result, we need to classify them into smaller categories.

3. Broad Classification of Bones • Compact Bone – dense, looks smooth and homogenous • Spongy Bone – composed of small needlelike pieces of bone and lots of open spaces

4. More Classification Terms • Long Bones – typically longer than they are wide. Usually have a shaft with two heads on each side and are mostly compact bone. • Short Bones – Generally cubed shape and contain mostly spongy bone • Flat Bones – thin, flattened, and usually curved. Two layers of compact bone sandwich a layer of spongy • Irregular Bones – odd shaped that don’t fit into the other categories.

5. Other Helpful Terms to Understanding Bones – Projections for muscle and ligament attachment • Process – any bony prominence (projection) • Tuberosity – large rounded projection • Crest – narrow ridge of bone • Line – narrow ridge of bone that is less prominent than a crest • Trochanter – Very large, blunt, irregularly shaped process • Tubercle – Small, rounded projection or process • Epicondyle – A raised area on or above a condyle • Spine – Sharp, slender, often pointed projection

6. Other Helpful Terms to Understanding Bones – Projections that help form joints • Head – Bony expansion carried on a narrow neck • Facet – smooth, nearly flat articular surface • Articular - of or relating to a joint • Condyle – rounded articular projection • Ramus – armlike bar of bone

7. Other Helpful Terms to Understanding Bones – Depression or Openings for blood vessels and nerves • Meatus – Canal-like passageway • Sinus – cavity within a bone, filled with air and lined with mucous membrane • Fossa – Shallow, basinlike depression in a bone • Groove – Furrow • Fissure– Narrow, slitlike opening • Foramen – Round or oval opening through a bone • Hint – projections start with T, depressions start with F (except for facet)

8. Gross Anatomy of a Long Bone • Diaphysis – the shaft. Makes up length of bone and is made up of compact bone. • Periosteum – bone cover. A fibrous connective tissue membrane that covers and protect the bone. • Endosteum – covering found in the middle of the bone around the medullary cavity. • Perfotaring or Sharpey’s Fibers – connect periosteum to the underlying bone. • Epiphyses – ends of bones. Compact bone on the outside, spongy inside. • Articular Cartilage – covers ends of bone. It is hyaline cartilage, which makes a smooth, slippery surface

9. Epiphyseal Line – remnants of the epiphyseal plate • Epiphyseal plate – site of cartilage where new bone growth occurs in young bones. After maturation, it turns to bone. • Medullary or Yellow Marrow Cavity – located in the center of the shaft, it is a site of adipose storage • Red Marrow – during infancy, blood cells are made in the center of the shaft. Later in life, this is namely preformed in spongy bone of flat bones.

10. Microscopic Anatomy • Osteocytes – mature bone cells • Lacunae – the matrix the bone cells are in • Lamellae – a concentric circle pattern that the lacunae make • Haversian or central canal – center of circle • Haversian or osteon system – this is a complex consisting of the central canal and matrix rings around it • Canaliculi – tiny canals that radiate outward from the central canal (transport system) • Perforating or Volkmann’s canal – pathway from the outside of the bone to its interior

11. How do bones form? • Ossification – bone formation • Most bones start as hyalinecartilage • The cartilage model gets covered in bone forming cells call osteoblasts • Enclosed cartilage is digested away, leaving the medullary cavity.

12. How do bones grow? • To grow longer, the answer is the epiphyseal plate. • New cartilage is formed on the side of the plate furthest from the medullary cavity. • At the same time, old cartilage near the medullary cavity is broken down and replaced by a bony matrix • To grow wider, osteoblasts in the periosteum add bone tissue as osteoclast in the endosteum remove bone from the inner wall

13. Bone Remodeling • Bone is remodeled (changed) all the time in response to: • Calcium levels • When calcium in the blood drops, parathyroid glands are stimulated releasing parathyroid hormone. This activates osteoclasts (bone destroying cells). These break down cells and release calcium back into the blood stream • If calcium is too high, calcium is deposited in the bone matrix as hard calcium salts • Pull of gravity and muscles • The body will thicken or thin areas depending on the stresses from different pulls. More pull = more bone to strengthen area