The Skeletal System

Copy this chart on the top 1/3 of your paper and write as many things as you can about the following terms Skeleton Bones Skeletal System

THE SKELETAL SYSTEM - NOTES Skeletal System Parts: bones, cartilage, tendons, ligaments Functions: maintain body shape - support protects organs provides levers for movement mineral and fat storage blood cell formation

Skeletal System connective tissues: living cells in a matrix LIVING CELLS MATRIX bone cells calcium, phosphorus, collagen cartilage cells collagen and ground tissue tendons & ligaments parallel collagen fibers

Skeletal Cartilages Hyaline Cartilage – most abundant Frosted glass Support with flexibility and resilience Fine collagen fibers in matrix Articular, costal, respiratory, nasal

Skeletal Cartilage Elastic – resembles hyaline but has elastic fibers. External ear and epiglottis. Fibrocartilage – highly compressible with great strength. Seen in areas with pressure and stretch – pad like cartilages. Menisci in knee, discs between vertebrae.

Parts of the skeleton Axial Skeleton Appendicular Skeleton skull, spine, rib cage Appendicular Skeleton upper and lower limbs and girdles (shoulders and hips)

Bone Classification by Shape LONG BONE EX: humerus

SHORT BONE EX: trapezoid (bone in wrist)

FLAT BONE EX: sternum

IRREGULAR BONE EX: vertebra

SESAMOID BONE patella (knee cap)

Anatomical Features of Long Bones DIAPHYSIS shaft EPIPHYSIS end of the bone EPIPHYSEAL PLATE (or EPIPHYSEAL LINE) site of bone growth – bones grow from their ends epiphyseal plate epiphysis diaphysis

MEDULLARY CAVITY location: in diaphysis filled with yellow marrow (adipose tissue)

PERIOSTEUM outer covering of bone – tough connective tissue (dense irregular) contains blood vessels & nerves Inner layer – osteogenic cells

Anatomical Features of COMPACT BONE location: diaphysis solid matrix & tightly packed cells made up of OSTEONS or HAVERSIAN SYSTEMS

Microscopic Anatomy of Bone Figure 5.3a

Microscopic Anatomy of Bone Figure 5.3b–c

OSTEOCYTES bone cells – supplied by Haversian Canals with blood CANALICULI tiny canals that connect osteocytes together thin rings of bone that serve to anchor bone cells LAMELLAE

Anatomical Features of SPONGY BONE bone is not really “spongy” or soft, it only “looks” spongy Location: epiphysis made of TRABECULAE interconnecting rods of bone

spaces in trabeculae filled w/red marrow no Haversian Canals lighter than compact bone

Cell Types Osteogenic cells – mitotically active cells in periosteum Osteoblasts – bone-forming cells that secrete bone matrix. Osteocytes – mature bone cells that occupy spaces (lacunae) Osteoclasts – giant cells – job is bone resorption

BONE MARROW cells produced from within bones red marrow produces blood cells yellow marrow adipose tissue – stores fat (energy)

Bone Markings Projections, depressions, and openings on the bones. Sites of muscle, ligament and tendon attachment.

Formation of the Human Skeleton In embryos, the skeleton is primarily hyaline cartilage During development, much of this cartilage is replaced by bone Cartilage remains in isolated areas Bridge of the nose Parts of ribs Joints

Developmental Aspects of the Skeletal System At birth, the skull bones are incomplete Bones are joined by fibrous membranes called fontanelles Fontanelles are completely replaced with bone within two years after birth

Ossification Centers in a 12-week-old Fetus Figure 5.32

Figure 6.17 Fetal primary ossification centers at 12 weeks. Parietal bone Frontal bone of skull Occipital bone Mandible Clavicle Scapula Radius Ulna Humerus Femur Tibia Ribs Vertebra Ilium © 2013 Pearson Education, Inc.

Skeletal Changes Throughout Life Fetus Long bones are formed of hyaline cartilage Flat bones begin as fibrous membranes Flat and long bone models are converted to bone Birth Fontanels remain until around age 2

Skeletal Changes Throughout Life Adolescence Epiphyseal plates become ossified and long bone growth ends Size of cranium in relationship to body 2 years old—skull is larger in proportion to the body compared to that of an adult 8 or 9 years old—skull is near adult size and proportion Between ages 6 and 11, the face grows out from the skull

Skeletal Changes Throughout Life Figure 5.33a

The Fetal Skull The fetal skull is large compared to the infant’s total body length Fontanels—fibrous membranes connecting the cranial bones Allow the brain to grow Convert to bone within 24 months after birth

The Fetal Skull Figure 5.13a

The Fetal Skull Figure 5.13b

Skeletal Changes Throughout Life Curvatures of the spine Primary curvatures are present at birth and are convex posteriorly Secondary curvatures are associated with a child’s later development and are convex anteriorly Abnormal spinal curvatures (scoliosis and lordosis) are often congenital

The Vertebral Column Figure 5.15

Bone Growth (Ossification) Epiphyseal plates allow for lengthwise growth of long bones during childhood New cartilage is continuously formed Older cartilage becomes ossified Cartilage is broken down Enclosed cartilage is digested away, opening up a medullary cavity Bone replaces cartilage through the action of osteoblasts

Bone Growth (Ossification) Bones are remodeled and lengthened until growth stops Bones are remodeled in response to two factors Blood calcium levels Pull of gravity and muscles on the skeleton Bones grow in width (called appositional growth)

Long Bone Formation and Growth Bone starting to replace cartilage Epiphyseal plate cartilage Articular cartilage Spongy bone In a child In a fetus In an embryo New bone forming Growth in bone width Growth in bone length Blood vessels Hyaline cartilage New center of bone growth Medullary cavity Bone collar Hyaline cartilage model (a) Figure 5.4a

Long Bone Formation and Growth Bone starting to replace cartilage In an embryo Bone collar Hyaline cartilage model (a) Figure 5.4a, step 1

Long Bone Formation and Growth Bone starting to replace cartilage In a fetus In an embryo Growth in bone length Blood vessels Hyaline cartilage New center of bone growth Medullary cavity Bone collar Hyaline cartilage model (a) Figure 5.4a, step 2

Long Bone Formation and Growth Bone starting to replace cartilage Epiphyseal plate cartilage Articular cartilage Spongy bone In a child In a fetus In an embryo New bone forming Growth in bone width Growth in bone length Blood vessels Hyaline cartilage New center of bone growth Medullary cavity Bone collar Hyaline cartilage model (a) Figure 5.4a, step 3

Cartilage cells undergo mitosis. Figure 6.10 Growth in length of a long bone occurs at the epiphyseal plate. Resting zone 1 Proliferation zone Cartilage cells undergo mitosis. 2 Hypertrophic zone Older cartilage cells enlarge. 3 Calcification zone Matrix calcifies; cartilage cells die; matrix begins deteriorating; blood vessels invade cavity. Calcified cartilage spicule Osteoblast depositing bone matrix Osseous tissue (bone) covering cartilage spicules 4 Ossification zone New bone forms. © 2013 Pearson Education, Inc.

Long Bone Formation and Growth Figure 5.4b