Chapter 5

1. Chapter 5 Bones

2. Functions of the bones Our skeletal system provides 5 main functions for our body…

3. 5 Main Functions of Bones: • Support: • “Reinforced Concrete of Body” • Forms internal framework that supports and anchors all soft organs • Examples: • Bones of legs act as pillars to support the body trunk when we stand • Rib cage supports the thoracic wall

4. 5 Main Functions of Bones: • Protection: • Bones protect soft body organs • Examples • Skull protects brain • Vertebrae protect spinal chord • Rib cage protects organs of thorax

5. 5 Main Functions of Bones: • Movement: • Skeletal muscles attached to bones by tendons use the bones as levers to move the body and its parts!

6. 5 Main Functions of Bones: • Storage: • Fat is stored in the internal cavities of bones • Bones itself serves as a storehouse for minerals…the most important being Calcium and Phosphorous (others are stored as well)

7. Calcium in the bones… • A small amount of calcium in its ion form (Ca2+) must be present in the blood at all times for • the nervous system to transmit messages • for muscles to contract • for blood to clot • Most of the body’s calcium is deposited in the bones as calcium salts; the bones are a convenient place to get more calcium ions for the blood as they are used up. • Problems occur if there is not enough OR too much calcium in the blood…hormones control the movement of calcium to and from the bones and blood according to the needs of the body.

8. 5 Main Functions of Bones: • Hematopoiesis: • AKA: Blood cell formation • Occurs within the marrow cavities of certain bones.

9. Classificationof Bones The adult skeleton is composed of 206 bones There are 2 basic types of bone tissue or “osseous” There are 4 shape groups as well

10. 2 Types of Osseous (bone tissue): • Compact Bone • Dense • Looks smooth and homogenous • Spongy Bone • Composed of small needlelike pieces of bone and lots of open space

11. 4 bone shape groups: • 1. Long bones • Longer than they are wide • Have a shaft with heads at both ends • Mostly compact bone • All the bones of the limbs, except the wrist and ankle bones are long bones • 2. Short bones • Generally cube-shaped • Contain mostly spongy bone • The bones of the wrist and ankle are short bones • Sesamoid bones (which form within tendons) are a special type of short bone. • The best known examples is the patella

12. 4 bone shape groups: • 3. Flat bones • Thin, flattened, and usually curved • Have 2 thin layers of compact bone sandwiching a layer of spongy bone between them • Most bones of the skull, ribs, and the sternum (breastbone) are flat bones • 4. Irregular bones • Bones that do not fit the preceding categories • The vertebrae, which make up the spinal column, and the hip bones fall into this group

13. Examples of each bone shape in the body…

14. Structure of a Long Bone Gross and Microscopic Anatomy

15. Gross Anatomy of Long Bone • Diaphysis or Shaft • Makes up most of the bone’s length and is composed of compact bone • Is covered by periosteum (a fibrous connective tissue membrane)

16. Gross Anatomy of Long Bone • Epiphyses • Ends of the long bone • Consists of a thin layer of compact bone enclosing an area filled spongy bone • Is covered by articular cartilage instead of periosteum. Articular cartilage is a smooth, slippery surface…friction at joint surfaces is decreased. • In adult bones, there is a thin line of bony tissue spanning the epiphysis that looks a bit different from the rest of the bone in that area called the epiphyseal line which is a remnant of the epiphyseal plate which is a flat plate of cartilage seen in a young, growing bone. Epiphyseal plates cause the lengthwise growth of a long bone. By the end of puberty, when hormones inhibit long bone growth, epiphyseal plates have been completely replaced by bone, leaving only the epiphyseal lines to mark their previous location!

17. Gross Anatomy of Long Bone • Medullary Cavity • In adults the cavity of the shaft is primarily a storage area for adipose (fat) tissue. • It is called the yellow marrow or medullary cavity. • However, in infants this area forms blood cells, and red marrow is found there. • In adult bones, red marrow is confined to the cavities of spongy bone of flat bones and the epiphyses of some long bones.

18. Gross Anatomy of Long Bone • Bone Markings • Bone surfaces are not smooth, but scarred with bumps, holes, and ridges. • These “bone markings” reveal where muscles, tendons, ligaments were attached and where blood vessels and nerves passed. See page 134. • 2 types of bone markings • Projections or processes-grow out from bone surface. • Depressions or cavities-indentations in the bone.

19. Microscopic Anatomy of Long Bone • To the naked eye, spongy bone looks open and spiky, whereas, compact bone looks very dense…. • However, when looking at compact bone through a microscope, one can see that it has a complex structure. It is riddles with passageways carrying nerves, blood vessels and the like, which provide the living bones cells with nutrients and a route for waste disposal.

20. Microscopic Anatomy of Long Bone • Osteocytes: mature bone cells found in tiny cavities within the matrix called lacunae. • The lacunae are arranged in concentric circles called lamellaearound central “Haversian” canals.

21. Microscopic Anatomy of Long Bone • Each complex consisting of central canal and matrix rings is called an osteon, or Haversian system. • Central canals run lengthwise through the bony matrix, carrying blood vessels and nerves to all areas of the bone. • Tiny canals, canaliculi, radiate outward from the central canals to all lacunae. The canaliculi form a transportation system that connects all the bone cells to the nutrient supply through the hard bone matrix…because of this bone cells are well nourished in spite of the hardness of the matrix, and bone injuries heal quickly and well.

22. Microscopic Anatomy of Long Bone • The communication pathway from the outside of the bone to its interior (and the central canals) is completed by perforating “Volkman’s” canals, which run into the compact bone at right angles to the shaft.

23. subdivisions of the Skeleton Axial and Appendicular

24. Subdivisions of the Skeleton • Axial: • The bones that form the longitudinal axis of the body. • Appendicular: • The bones of the limbs and girdles.

25. Spine (Vertebral Column) • Extends from the skull to the pelvis where it transmits the weight of the body to the lower limbs. • Formed from 26 irregular bones connected and reinforced by ligaments in such a way that a flexible, curved structure results. • Running through the central cavity of the vertebral column is the delicate spinal cord. • Before birth, the spine consists of 33 separate bones called vertebra, but 9 of these eventually fuse to form the 2 composite bones, the sacrum and the coccyx. • Of the 24 single bones, the 7 vertebrae of the neck are cervical vertebrae, the next 12 are the thoracic vertebrae, and the remaining 5 supporting the lower back are lumbar vertebrae. • The single vertebrae are separated by pads of flexible fibrocartilage-intervertebral discs-which cushion the vertebrae. • The disks and the S-shaped structure of the vertebral column work together to prevent shock to the head when we walk or run. They also make the body trunk flexible

26. In addition to bones, the skeletal system includes joints, cartilages, and ligaments. We are going to look closer at Joints…

27. Joints • AKA “articulations” • Give the body flexibility and allow movement to occur. • With one exception (the hyoid bone of the neck), every bone in the body forms a joint with at least one other bone! • Joints have 2 functions: • 1. They hold the bones together • 2. Give the rigid skeleton mobility

28. Joints are classified in 2 ways-functionally & structurally • Focuses on the amount of movement allowed by the joint • Synarthroses: immovable joints • Amphiarthroses: slightly movable joints • Diarthroses: freely movable joints • Based on whether fibrous tissue, cartilage, or a joint cavity separates the bony regions at the joint • Fibrous: bones united by fibrous tissue, Example- Skull sutures • Cartilaginous: bone ends are connected by cartilage, Example-pubic symphysis of pelvis and intervertebral joints of spinal column • Synovial: those in which the bone ends are separated by a joint cavity containing synovial fluid, account for ALL joints of the limbs, examples and more to follow…. Functional Classification Structural Classification

30. Types of synovial joints based on shapeRefer to page 166 as we discuss! • Plane joint: • articular surfaces are flat and only short slipping or gliding movements are allowed. • Hinge joint: • the cylindrical end of one bone fits into a trough-shaped surface on another bone…angular movement is allowed in just one plane (like a door hinge). • Pivot joint: • the rounded end of one bone fits into a sleeve or ring of bone…the rotating bone can turn only around its long axis. • Condyloid joint: • “knuckle-like”, the egg shaped articular surface of one bone fits into an oval concavity in another…these joints allow the moving bone to travel from side to side and back and forth but it cannot rotate around its long axis. • Saddle joint: • each articular surface has both convex and concave areas, like a saddle…these joints allow essentially the same movement as the condyloid joint. • Ball & Socket joint: • the spherical head of one bone fits into a round socket in another…these multiaxial joints allow movements in all axes, including rotation! They are the most freely moving joints.

31. Developmental Aspects of the skeleton • Read page 168 starting at “development aspects of the skeleton” through page 169 stopping before “prove it yourself”.

32. Fontanels • When a baby is born, its skeleton is still unfinished. In a newborn, the skull has fibrous regions that have yet to be converted to bone. • These fibrous membranes are called fontanels or you may have heard them called “soft spots”. The rhythm of the baby’s pulse can be felt in these areas. • The fontanels allows compression during the birthing process and give room for growth during the later part of pregnancy and infancy. • The fontanels are gradually converted to bone during the early part of infancy and can no longer be felt by 22-24 months after birth. • There are 4 fontanels: • Anterior-largest on top of head (one you may know of) • Posterior • Mastoid • Sphenoid

33. A few interesting, random parts of skeletal system • Mandible-lower jaw bone…is the largest and strongest bone of the face. • Hyoid bone-closely related to the mandible, but not really a part of the skull…is unique because it is the only bone of the body that does not articulate directly with any other bone…it is suspended in the mid-neck region, held in place by ligaments! • Phalanges-each hand contains 14 phalanges…there are three in each finger (proximal, middle, and distal) except in the thumb, which only has two (no middle).

34. Hands & Feet

35. Another interesting thought… Male and Female Skeletons are different…the pelvic girdle…Record the differences listed on page 159 in your text, then refer to your handout.

36. A few common Disorders of the Skeletal System: Scoliosis Fractures Arthritis Gout Osteoporosis

37. Abnormal Spine curvatures • Disorders of the spine may be congenital (present at birth) or result from disease, poor posture, or unequal muscle pull on the spine. There are 3 main types of abnormal spinal curvatures: • Scoliosis • Kyphosis • Lordosis

38. Fractures • For their relatively low mass, bones are amazingly strong. Despite their remarkable strength, bones are susceptible to fractures, or breaks, all through life. • A fracture is treated by reduction (which is the realignment of the broken bone ends.) • Closed reduction: bone ends are coaxed back into their normal position by the physician’s hands. • Open reduction: surgery is performed and the bone ends are secured together with pins or wires. • After the broken bone is reduced, it is immobilized by a cast or traction to allow the healing process to begin. The healing process is 6-8 weeks, but it is much longer for large bones and for the bones of elderly people (because of their poorer circulation).

39. Table in your book: pg. 137

40. Arthritis • Describes over 100 different inflammatory or degenerative diseases that damage the joints. • In all its forms, arthritis is the most widespread, crippling disease in the US… 1 out of 7 Americans suffer its ravages. • All forms of arthritis have the same initial symptoms: pain, stiffness, and swelling of the joint. Then, depending on the specific form, certain changes in the joint structure occur.

41. Chronic forms of arthritis include: • Osteoarthritis (OA) • Most common form, typically affects the aged, also called “wear & tear arthritis” • Over time, there is a softening, fraying, and eventual breakdown of the cartilage…as the disease progresses, the bone thickens and extra bone tissue, called “bone spurs” grows around the eroded cartilage and restricts joint movement • Usually slow and irreversible, but is rarely crippling…symptoms are typically controllable. • Rheumatoid arthritis (RA) • Onset usually occurs between the ages of 40-50, but may occur at any age. Affects 3 times as many women as men. • The course of RA is marked by remissions and flare-ups • Autoimmune disease-a disorder in which the body’s immune system attempts to destroy its own tissue. • Current therapy for RA involves many different kinds of drugs and exercise is recommended…replacement joints or bone removal is a last resort for severely crippled RA patients. • Gouty arthritis “gout” • A disease in which uric acid (a normal waste product of nucleic acid metabolism) accumulates in the blood and may be deposited as needle-shaped crystals in the soft tissues of joints which leads to an agonizingly painful attack that typically affects a single joint, often in the great toe! • Gout is most common in males and rarely appears before the age of thirty…it tends to run in families, so genetic factors are definitely implicated. • Untreated gout can be very destructive; the bone ends fuse and the joint becomes immobilized…fortunately, several drugs are successful in preventing gout attacks.

42. Osteoporosis • A bone thinning disease that afflicts half of women over 65 and some 20% of men over the age of 70. • Makes the bones so fragile that even a hug or a sneeze can cause bones to fracture. • The bones of the spine and the neck of the femur are particularly susceptible…vertebral collapse frequently results in a hunched over posture (kyphosis) also known as “dowager’s hump” • Estrogen helps to maintain the health and normal density of a woman’s skeleton, and the estrogen deficiency that occurs after menopause is strongly implicated as a cause of osteoporosis • Other factors may include diet poor in calcium and protein, lack of vitamin D, smoking, and insufficient weight-bearing exercise to stress bones.