Skeletal System

Functions of the Bones

• Provide shape and structure

• Protect Internal Organs

• Enable Movement

• Produce Blood Cells

• Store Calcium and Phosphorus

Axial Skeleton

Supports the head, neck, back, and chest and thus forms the vertical axis of the body

Appendicular Skeleton

Made up of all bones of the upper and lower limbs

What is the skeletal system comprised of?

Bones, cartilages, joints, and ligaments

• accounts for 20% of body mass

Axial Skeleton - in depth

• Forms vertical central axis of the body

• Protects internal organs

• allows movement of head, neck. back, and respiratory muscles

• consists of 80 bones in total

  • Skull

  • Vertebral Column

  • Ribs

  • Sternum

Appendicular Skeleton - In depth

• Composed of

  • Bones found in the upper and lower limbs

    • Humerus, ulna, radius, carpal bones, bones of the hand

    • Femur, tibia, fibula, patella, tarsal bones, bones of the foot

  • Bones that attach the limbs to axial skeleton

    • pectoral girdle - clavicle and scapula

    • pelvic girdle - os coxae

Bone Tisse

• Very rigid, osseous tissue with a rough surface

• vascular

• osteocyte is mature bone cell

Cartilage Tissue

• slightly flexible, dense connective tissue with a smooth surface

• avascular

• chondrocyte is mature cartilage tissue

How many bones are in the body?

206

How many categories of bones are there and what are they classified by?

The 206 bones are divided into 5 categories based on their shape and function

Long Bones

Longer than they are wide, cylindrical

• function as levers to enable movement

• in arms: humerus, radius, ulna; and legs: femur, tibia, fibula; and appendages: metacarpals, metatarsals, and phalanges

Short Bones

Cube-like in shape

• Provide stability and support

• in carpals of the wrist and tarsals of the ankle

Flat Bones

thin, but often curved

• Provide point of attachment for muscles and protect internal organs

• Cranial bones, scapulae, sternum, and ribs

Irregular Bones

Irregular, complex shapes

• Vertebrae, facial bones

• Sutural bones (Wormian bones) are small, flat, irregular shaped bones between flat bones of the skull

Sesamoid Bones

small and round, like sesame seeds

• help protect tendons from compressional forces

• number and placement vary from person to person

• feets, hands, knees, patellae

Anatomy of a lone bone

Diaphysis, Epiphysis, and Metaphysis

Diaphysis

long tubular shaft that runs the length of the bone

• made primarily of compact bone

• site of medullary cavity which is filled with yellow marrow which stores fat

• membraneous lining of the endosteum is where bone growth, repair, and remodeling occur

• the periosteum forms the outer surface of bone and is composed of dense irregular tissue held on by Sharpeys fibers (collagen)

Epiphysis

Wider sections at each end of the bone

• made primarily of spongy bone, also called trabecular bone

• latticework spaces filled with red bone marrow which is responsible for hematopoiesis (formation of blood cells)

• covered by a thin layer of compact bone and articular cartilage

Metaphysis

Narrow zone that connects the diaphysis with the epiphysis

• Location of the epiphyseal plate (growth plate): thin layer of hyaline cartilage than allows for growth in long bones but eventually calcified into the epiphyseal line

Periosteum

forms the outer surface of bone

• composed of dense irregular tissue and held on by Sharpeys fibers (collagen)

Endosteum

lines the medullary cavity

• composed of connective tissue

• also lines the canals that pass through bone to supply it with blood and nerves

Nutrient artery

delivers oxygen and nutrients to the bone

Nutrient vein

delivers waste and carbon dioxide away from bone

metaphysis - blood supply

artery and vein carry blood to and from the areas of the metaphysis and epiphysis

Anatomy of flat bones

• Layer of spongey bone (dipole)

• Layer of compact bone on either side of dipole

• Lined on outside of both sides with periosteum

this composition provides extra protection to the internal organs they protect

articulations

help bones join securely

projections

where an area of the bone projects above the surface

holes (foramen)

an opening or groove in the bone that allows vessels and nerves to either enter and exit bone

Osteon

basic structural and functional unit of bone

How many bone cells are found within bone tissue?

4

Osteogenic (osteoprogenitor)

these cells are mesenchymal undifferentiated cells that develop into osteoblasts

Osteoblasts

immature bone cells that produce new bone matrix through osteogenesis (ossification). Before calcium salts are deposited, this mix is called osteoid

Osteocytes (mature bone cells)

form when osteoblasts get trapped within the calcified matrix (lacuna), changing their structure and function. Osteocytes rebuild and repair the matrix

Osteoclasts

develop from monocytes and macrophages and differ in appearance from other bone cells. Osteoclasts remove and recycle bone matrix (osteolysis)