M04 - Skeletal System Part 1

Skeletal System is composed of:

Skeletal System is composed of:

1. bone tissue

2. cartilage

3. dense connective tissue

4. blood

5. nervous tissue

The skeletal system is __________ and _________

Alive; multifunctional

1. support and protect softer tissues

2. movement

3. blood cell formation

4. mineral storage

Skeletal system is divided into?

Axial and Appendicular divisions

The adult skeleton has how many number of bones?

206

extra bones include: sutural (wormian) in sutures between major skull bones, small sesamoid bones in tendons (reduce friction), a vertebra

The axial skeleton includes

1. skull - cranium and facial bones

2. middle ear bones - move sound to receptors in inner ear

3. hyoid bone - supports tongue and is muscle attachment site

4. vertebral column - forms central axis of skeleton

5. thoracic cage - ribs and sternum, protects organs

TOTAL OF 80 BONES

The appendicular skeleton includes

1. pectoral girdle - scapula and clavicle, upper limb movement

2. upper limbs - humerus, radius, ulna, hand

3. pelvic girdle - hip bones, lower limb movement, forms pelvis

4. lower limbs - femur, tibia, fibula, patella, foot

TOTAL OF 126 BONES

Bones of the skeletal system vary greatly in these ways

Size and Shape

Bones are similar in these features

Structure, development, function

Long Bones

1. long and narrow

2. have expanded ends

short bones

1. cube-like, length = width

2. include sesamoid (round) bones, which are embedded in tendons

Flat Bones

plate-like with broad surfaces

Irregular Bones

1. variety of shapes

2. most are connected to several other bones

Parts of a Long Bone

1. epiphysis - expanded end

2. diaphysis - bone shaft

3. metaphysis - between diaphysis and epiphysis, widening part

4. articular cartilage - covers epiphysis

5. periosteum - encloses bone, dense connective tissue

6. compact (cortical) bone - wall of diaphysis

7. spongy (cancellous) bone - makes up epiphysis

8. trabeculae - branching bony plates, make up spongy bone

9. medullary cavity - hollow chamber in diaphysis, contains marrow

10. endosteum - lines spaces, cavity

11. bone marrow - red or yellow marrow, lines medullary cavity, spongy bone spaces

Osteocytes

mature bone cells

Lacunae

chambers occupied by osteocytes

Canaliculi

tiny passageways through which the cell processes of osteocytes exchange nutrients and wastes

Extracellular Matrix of bone contains

1. Collagen fibers - gives bone resilience

2. Inorganic salts - makes bone hard

Compact Bone

1. consists of cylindrical units = osteons

2. osteons and layers of matrix (lamellae) cluster around central canal in each osteon

3. strong and solid

4. weight-bearing

5. resists compression

Spongy Bone

1. consists of branching plates called trabeculae

2. somewhat flexible

3. has spaces between trabeculae that reduce the bone’s weight

Major Functions of Bones

1. provide shape to body - head, face, thorax, limbs

2. support body structures - bones of lower limbs, pelvis, vertebral column

3. protect body structures - skull bones protect brain, ears, eyes

4. aid body movements

5. contain tissue that produces blood cells

6. store inorganic salts

Hematopoiesis

blood cell formation

occurs in red bone marrow, includes production of RBC, WBC, platelets

yellow marrow stores fat

red marrow remains in adult skull, ribs, sternum, clavicles, vertebrae, hip bones

Most abundant sale is crystals of

hydroxyapatite (calcium phosphate)'

other salts include: magnesium ions, sodium ions, potassium ions, carbonate ions

Osteoporosis

condition that results from loss of bone mineralization

blood calcium level is regulated by parathyroid hormone and calcitonin

Bones form when bone tissue replaces existing connective tissue in one of two ways:

Intramembranous bones and endochondral bones

Blood calcium level is regulated by?

Parathyroid hormone and calcitonin

Intramembranous Ossification

• flat skull bones, clavicles, sternum, and some facial bones

• bones form between sheets of primitive connective tissue

Endochondral Ossification

• long bones and most of skeleton

• bones form from hyaline cartilage models

Osteogenesis Imperfecta

hereditary collagen defect, in which forming bones are brittle, and fetus may have many bone fractures

Process of Intramembranous Ossification

1. mesenchymal cells in primitive tissue differentiate into osteoblasts

2. osteoblasts: bone-forming cells that deposit bone matrix around themselves

3. when osteoblasts are completely surrounded by matrix, they are now osteocytes in lacunae

4. mesenchyme on outside forms periosteum

Process of Endochondral Ossification

1. begin as hyaline cartilage models

2. chondrocytes (cartilage cells) enlarge, lacunae grow

3. matrix breaks down, chondrocytes die

4. osteoblasts invade the area, deposit bone matrix

5. osteoblasts form spongy and then compact bone

6. once encased by matrix, osteoblasts are now osteocytes

Development of Endochondral Long Bones

Primary Ossification Center: area in center of diaphysis, where bone tissue first replaces cartilage

Secondary Ossification Center: area of the epiphyses, where spongy bone forms later in development

Epiphyseal Plate

band of cartilage that persists between the ossification centers

Growth at the Epiphyseal Plate

Zone of resting cartilage: layer closest to end of epiphysis, resting cells; anchor epiphyseal plate to epiphysis

Zone of proliferating cartilage: rows of young cells, undergoing mitosis

Zone of hypertrophic cartilage: rows of older cells left behind when new cells appear; thicken epiphyseal plate, lengthening the bone, matrix calcifies, cartilage cells die

Osteoclasts

break down calcified matrix

Osteoblasts

invade, replacing cartilage with bone tissue

Bone can thicken by depositing compact bone on outside under ______

periosteum

Bone Remodeling

occurs throughout life

Bone Resorption

removal of bone by osteoclasts

Bone Deposition

formation of bone by osteoblasts

Vitamin D

calcium absorption, deficiency causes rickets, osteomalacia

Vitamin A

osteoblast and osteoclast activity, deficiency retards bone development

Vitamin C

collagen synthesis, deficiency results in slender, fragile bones

Growth Hormone

stimulates cartilage cell division, insufficiency in a child can result in pituitary dwarfism, excess causes gigantism in child and acromegaly in adult

Thyroid Hormone

causes replacement of cartilage with bone in epiphyseal plate, osteoblast activity

Parathyroid Hormone (PTH)

stimulates osteoclasts, bone breakdown

Sex Hormones

promote bone formation, stimulate ossification of epiphyseal plates

Physical Stress

stimulates bone growth

Condyle

rounded process that usually articulates with another bone

Crest

narrow, ridge-like projection

Epicondyle

projection situated above a condyle

Facet

small, nearly flat surface

Fissure

cleft or groove

Fontanel

soft spot in the skill where membranes cover the space between bones

Foramen

opening through a bone that usually serves as a passageway for blood vessels, nerves, or ligaments

Fossa

relatively deep pit or depression

Fovea

tiny pit or depression

Head

enlargement on the end of a bone

Linea

narrow ridge

Meatus

tube-like passageway within a bone

Process

prominent projection on a bone

Ramus

branch or similar extension

Sinus

cavity within a bone

Spine

thorn-like projection

Sulcus

furrow or groove

Suture

interlocking line of union between bones

Trochanter

relatively large process

Tubercle

knob-like process

Tuberosity

knob-like process usually larger than a tubercle

The skull contains how many bones

22

Cranium = 8 bones to enclose and protect the brain

Facial Skeleton = 14 to form the shape of the face

Paranasal Sinuses

air filled cavities found in some cranial and facial bones

reduce weight of skull and increase intensity of voice

Vertebral Column

forms vertical axis of skeleton

consists of many vertebrae separated by cartilaginous intervertebral discs, connected by ligaments

supports head and trunk, permits several types of movements

protects spinal cord in vertebral canal

33 separate bones in infant, 26 in adult

4 Curvatures of Vertebral Column

Cervical (2ndary)

Thoracic (Primary)

Lumbar (2ndary)

Sacral (Primary)

Vertebral Column Consists of

7 cervical

12 thoracic

5 lumbar

5 fused sacral

4 fused coccygeal

Vertebral Body

drum-shaped, anterior portion

Vertebral Pedicles

stalks that project from body, form sides of vertebral foramen

Vertebral Laminae

plates that arise from pedicles, fuse to become spinous process

Spinous Process

posterior projection

Transverse Processes

lateral projections

Vertebral Formane

opening for spinal cord

Superior and Inferior Articular Processes

project upward and downward, to articulate with adjacent vertebrae

Facets

cartilage-covered articulating surfaces of articular processes

7 Cervical Vertebrae

found in neck region, smallest vertebrae

Transverse Foramina

openings for arteries leading to brain; only found on cervical vertebrae

Bifid spinous processes on C2 to C6

Atlas

C1, supports head, articulates with occipital condyles

Axis

C2, atlas pivots around the dens of axis

12 Thoracic Vertebrae

found in chest region, larger than cervical vertebrae, articulate with ribs, long/pointed spinous process/slopes downward

5 Lumbar Vertebrae

found in small of back, large bodies, weight-bearing, thick/short spinous processes/almost horizontal

Sacrum

• triangular structure at base of vertebral column

• typically 5 fused vertebrae

• median sacral crest: fused spinous processes of vertebrae

• posterior sacral foramina: openings for blood vessels and nerves

• forms sacroiliac joints, which transmit body weight to legs

• forms posterior wall of pelvic cavity

• sacral promontory: projection at upper margin

• sacral canal: formed by vertebral foramina

• sacral hiatus: opening at inferior tip of sacrum

Coccyx

• tailbone

• usually 4 fused vertebrae

• fuse between ages 25 and 30

Thoracic Cage

• includes ribs, thoracic vertebrae, sternum, and costal cartilages that attach the ribs to the sternum

• supports pectoral girdle and upper limbs

• protects thoracic and upper abdominal viscera

• role in breathing

Ribs

• 12 pairs of ribs

• true ribs = vertebrosternal, 7 pairs, connect directly to the sternum

• false ribs = 5 pairs

  • vertebrochondral ribs = upper 3 pairs, costal cartilages connect to cartilage 7

  • floating ribs = vertebral, lower 2 pairs, no connection to sternum

Structure of Rib

shaft: main portion, long and slender

head: posterior end, articulates with vertebrae

tubercle: articulates with vertebrae

costal cartilage: hyaline cartilage; connects rib to sternum

Sternum

• along midline of anterior thoracic cag

• 3 parts:

  • manubrium: upper part

  • body: middle and largest part

  • xiphoid process: lower part

• articulates with costal cartilages of ribs, and clavicles