Anatomy Skeletal System

What are the five main functions of the skeletal system?

1. Support

2. Protection

3. Movement

4. Storage of calcium and phosphate

5. Hematopoiesis (blood cell production)

What are the characteristics of compact bone?

• It is dense and looks uniform

What is compact bone made of?

• Osteons/Haversian systems

Osteocyte

• Mature bone cells

Osteoblasts

• Bone building cells

• Become osteocytes when surrounded by matrix (mature)

Lacunae

• Cavities in matrix that house osteocytes

Lamellae

• Concentric circle arrangement of lacunae around Haversian canal

Canaliculi

• Tiny canals that radiate out from Haversian canal to the lacunae that permits circulation to osteocytes

What are the characteristics of spongy bone?

• Have small needle-like trabeculae

• The open space is filled with red marrow

What is a short bone?

• Cube-shaped, mostly spongy

What bones are classified as short bones? (2)

• Carpals

• Tarsals

What is a flat bone?

• Thin, curved

• Layer of spongy bone between compact bones (sandwich)

What bones are classified as flat bones? (4)

• Skull

• Ribs

• Sternum

• Scapulae

What bones are classified as irregular bones? (2)

• Pelvis

• Vertebrae

What is a sesamoid bone?

• Small, and embedded in tendons

What bones are classified as sesamoid bones? (2)

• Patella

• Pisiform carpal bone

What is a long bone?

• Act as levers and are pulled by contracting muscles

• Bones that are longer than they are wide

What bones are classified as long bones? (3)

• Limbs

• Phalanges

• Metacarpals, metatarsals

What is the diaphysis?

• The bone shaft

What type of bone constructs the diaphysis?

• Compact bone

What is the medullary cavity?

• Found in diaphysis

• Storage for yellow marrow in adults (fat) and red marrow in infants up to age 7 (hematopoiesis)

What is the periosteum?

• A fibrous connective tissue membrane that covers diaphysis

What secures the periosteum to the bone?

• Sharpey’s fibers

What does the periosteum contain?

• Nerves and capillaries

What are the epiphyses?

• Bulbous ends of bone that consist of a thin layer of compact bone around spongy bone

What is the epiphyseal plate/growth plate?

• Site of long bone growth

What is the epiphyseal plate/growth place made of?

• A thin line of hyaline cartilage

What is articular cartilage?

• Hyaline cartilage that covers epiphyses

What is the function of articular cartilage?

• Decreases friction at the joints

What is the epiphyseal line?

• When the epiphyseal plate turns into after it ossifies during puberty

What makes up the axial skeleton? (4)

• Skull

• Vertebral column

• Ribs

• Sternum

Where is the body of vertebrae located?

• Ventrally

Where is the vertebral arch located on the vertebrae?

• Dorsal to the body

What is the vertebral foramen?

• Serves as a canal for the spinal cord

What is are transverse processes?

• Lateral projections from vertebral arch

What is a spinous process?

• Dorsal projection from vertebral arch

What are the superior and inferior articular processes?

• Sites where one vertebra joins to the next

What are the five regions that the vertebral column is divided into?

• Cervical

• Thoracic

• Lumbar

• Sacral

• Coccyx

What type of motion do the cervical vertebrae have?

• Wide range of motion

What is the first cervical vertebrae?

• C1, atlas

• Rotates on odontoid process of axis

Does the atlas have a body?

• No

What is the second cervical vertebrae?

• C2, axis

What “special” process does the axis have?

• Odontoid process

What are the characteristics of C3-C7 of cervical vertebrae?

• Short spinous process (except C7)

• Transverse foramina

What are the transverse foramina in cervical vertebrae?

• Small holes in transverse processes for vertebral artery

What range of motion do the thoracic vertebrae have?

• Limited range of motion, non-weight bearing

What type of body do the thoracic vertebrae have?

• Heart-shape body

What are the characteristics of thoracic vertebrae?

• Have facets for ribs on the lateral ends of transverse processes

• Have long spinous processes that hook inferiorly

What range of motion does lumbar vertebrae contain?

• Limited range of motion, but weight bearing

What type of body do the lumbar vertebrae have?

• Massive, block-like body

What type of spinous process does the lumbar vertebrae have?

• Hatchet shaped spinous process

What is the sacrum?

• 5 fused vertebrae on the inferior wall of pelvis

• Articulates with ilium to form sacroiliac joint (pelvis girdle joins axial skeleton)

What is the coccyx?

• Tailbone

• 3-5 fused vertebrae

What consists of the appendicular skeleton?

• Limbs and girdles

• (Limbs are primarily long bones, except carpals, tarsals, patella)

What is the shoulder girdle?

• Clavicle and scapula

Where does the scapular articulate with the clavicle?

• Acromion process

Where does the scapular articulate with the humerus?

• Glenoid cavity

Where does the clavicle articulate with sternum?

• Sternoclavicular joint, braces arm away from thorax

What range of motion does the shoulder girdle have?

• Free range of motion

What bones does the pelvic girdle contain?

• 2 fused hip bone

• Each hip bone contains fused ilium, ischium, and pubis

What is the ilium?

• Large, wing-like

What is the ischium?

• Posterior bones of pelvis

What is the pubis?

• Anterior bones of pelvis

What is the obturator foramen?

• Paired opening in hip bone formed by pubis and ischium

What is the acetabulum?

• Articulates with femurs to form hip bone

What is sacroiliac joint?

• Connects sacrum to pelvis

Male vs. female true pelvis

• Male: narrower true pelvis

• Female: larger, more circular true pelvis

Male vs. female pelvis

• Male: deeper

• Female: shallower, ilia flare more laterally

Male vs. female sacrum

• Male: longer, more curved sacrum

• Female: shorter, less curved sacrum

Male vs. female pubic arch

• Male: “v” shaped

• Female: “u” shaped

What are the 4 reasons for bone remodeling?

• Allows for growth

• Repairs microscopic cracks

• Meets changing mechanical needs (mechanical stress causes higher osteoblast activity)

• Maintains constant blood calcium levels

What is bone remodeling?

• A constant, life-long process of bone turnover

• Breaking down old bone and building new via osteoclasts and osteoblasts

What happens if blood calcium levels drop too low?

• Neurons will fire spontaneously and can cause sustained muscle contraction that results in suffocation

What is released when blood calcium is too low?

• Parathyroid hormone (PTH)

What happens when PTH is released?

• Activates osteoclasts

• Increases calcium absorption in kidneys

• Activates vitamin D to increase absorption of calcium from foods you eat

How do osteoclasts work?

1. “Park” on the bone

2. “Ruffle”

3. Stick to bone via adhesion molecules

4. Release acid proteases and HCl

What are acid proteases?

• Enzymes that break down protein in acidic environments

What 2 substances do osteoclasts release to break down 2 components of bone?

• Organic component: collagen that make bone flexible

  • Digested away by acid proteases

• Inorganic component: hydroxyapatite crystals (calcium salts) that make bone hard

  • Dissolved by HCl

What is released when blood calcium levels are too high?

• Calcitonin, the antagonist hormone to PTH

What does calcitonin do?

• Increases osteoblast activity

• Plays a bigger role in kids than adults

What is vitamin D (cholecalciferol)?

• Made from cholesterol by skin when exposed to UV light

• Can be consumed in our diet

• Inactive in this form

How do you activate vitamin D?

1. In liver is hydroxylated to 25,hydroxyvitamin D (still not active)

2. In kidney is hydroxylated again to 1,25,dihydroxyvitamin D (now the activity form)

• (PTH turns on hydroxylated enzyme in kidney)

What three things does vitamin D do?

1. Increases enzyme in the intestines that break down calcium into free Ca2+ for absorption

2. Increase calbindin in intestinal cells that bind Ca2+

3. Increases an ATPase that pumps Ca2+ out of the intestinal cell into the blood

How does PTH activate osteoclasts?

1. Osteoblasts have a PTH receptor that binds PTH

2. Binding of PTH causes osteoblast to…

• Secrete M-CSF

• Express RANK ligand on its surface

3. The pre-osteoclasts express RANK, the receptor for RANKL and the binding occurs

4. The pre-osteoclasts also express a receptor for M-CSF and binding occurs

5. Bind of RANKL and M-CSF stimulate the pre-osteoclast to become a mature and active osteoclast

What are the two ways bones can be classified?

• Functional classification (what kind of movement it allows)

• Structural classification (what tissue types hold the joint together)

What are the three types of functional classification?

• Synarthroses: immovable

• Amphiarthroses: allow a little movement

• Diarthroses: freely moveable

What are the three types of structural classifications?

• Fibrous

• Cartilaginous

• Synovial

What are the characteristics of fibrous joints?

• Mostly synarthroses

• Bones joined by fibrous tissue

What is an example of fibrous joint?

• Sutures of skull

What are the characteristics of cartilagenous joints?

• Mostly amphiarthroses

• Bones joined by cartilage

What are examples of cartilagenous joints?

• Pubic symphysis

• Intervertebral joints

• Between ribs and sternum

What are the characteristics of synovial joints?

• Mostly diarthroses

• Bones ends are connected by a joint cavity containing synovial fluid