UNIT 12 - THE SKELETAL SYSTEM

What is Bone?

solid matrix which comprises:

• 35-45% water and organic matter (including collagen)

• 55-65% crystallized minerals (mainly CaPO4 & CaCO3)

• compact and spongy types

What are the functions of Bone in the Skeletal System?

1. forms the units which make up the skeleton

2. support; forms frame which supports body + muscle attachment

3. movement; muscle contraction results in movement

4. protection; some parts of skeleton protect internal organs

5. blood cell production; bone marrow in certain bones produce RBC and WBC

6. storage; store fats + acts as mineral reserve (e.g. Ca and PO4)

What are Long Bones?

greater length than width

(e.g. femur, radius)

What are Short Bones?

approx. equal in length & width

(e.g. carpal, tarsal bones)

What are Flat Bones?

flat & thin

• greater area for muscle attachment

• protection

(e.g. scapula, cranial bones, ribes)

What are Irregular Bones?

complex bones

(e.g. vertebrae, some facial bones)

What are Sesamoid Bones?

bones within ligaments or tendons

• only common e.g. is patella

• includes bones that develop in tendon via stress to protect from wear and tear

What is the function of Cartilage in the Skeletal System?

1. forms embryonic skeleton

2. covers ends of many bones; provides protection

3. provides cushioning in many joints

4. joins some  bones + allows for limited flexibility

5. gives support & flexibiity to various structures (e.g. nose, ears)

How is Cartilage composed?

• no blood vessels or nerves

• composed of chondrocytes

• occur singly or in groups in spaces called lacunae

• matrix contains translucent proteins

What are Osteogenic Cells?

stands for bone growth

• undifferentiated cells

• can divide to replace themselves + become osteoblasts

What are Osteoblasts?

cells involved in formation of bone matrix

• produce collagen fibres + lay down CaCO3 & CaPO4 crystals

• cannot divide

What are Osteocytes?

cells involved in bone maintenance & repair

• develops from osteoblasts

• found in lacuna

• mature; no longer secretes matrix

• binds to others via canaliculi

What are Osteoclasts?

huge cells involved in resportion (breaking down) of bone matrix

• secretes acids + protein digesting enzymes to dissolve bone matrix and released stored minerals

• doesn’t grow from osteogenic cells

What are the External Parts of the Bone?

• proximal epiphysis (head)

• metaphysis (neck)

• diahysis (shaft)

• distal epiphysis

What are the Internal Parts of the Bone?

• articular cartilage

• spongy bone

• epiphysial line

• Compact bone

• medullary cavity

• endosteum

• periosteum

What is Articular Cartilage in the Bone?

covers & protects ends of bones

What is Spongy Bone?

contains red bone marrow + area of RBC and WBC production

What is the Epiphysial Line?

region where bone grows in length

• contains cartilage

• present at both ends

What is the Medullary Cavity?

cavity in shaft of bone

• contains blood vessels

• fat storage area (yellow bone marrow)

What is the Endosteum?

thin membrane that lines medullary cavity

• contains cells involved in bone formation and maintenance

What is the Periosteum?

tough membrane that covers the outer surface of the bone + protects bone

• contains bone formation + maintenance cells

• contains blood vessels to aid in bone nourishment

What is the general structure of a Compact Bone?

organized and strong

• forms hard layer of bone in shaft of long bones + external layer of all bones

• contains yellow bone marrow for storage of triglycerides

What is the internal structure of Compact Bone?

• osteons; concentric lamellae rings of calcified matrix that surround blood vessel

• osteocytes; found between lacunae

  • communicate through canaliculi filled w/ ECF that connect one cell to another

What is Spongy Bone?

lattic like structure of thin plates of bone oriented along lines of stress (trabeculae)

• less organized

• spaces btwn trabeculae are filled with RBW

• found on ends of long bones + inside flat bones

What is Intramembranous Ossification?

bone formed directly on / within fibrous membranes

• simpler; used to form skull flat bones, parts of mandible, and parts of clavicle

What is Endochondral Ossification?

cartilage model is formed prior to bone formation

• more complex + is used for a majority of bones

• lasts from childhood to adolesence

• Bones Can’t Pop During Exercise

What is the First Step of Intramembranous Ossification?

the development of the ossification centre

• begins with mesenchymal cells (stem cells that turn into chondrocytes or osteocytes)

• clusters of osteoblasts secrete matrix (osteoid)

What is the Second Step of Intramembranous Ossification?

calcification

• osteoblasts differentiate into osteocytes

• lacuna (spaces) and canaliculi (communication) formation 

• calcium and phosphorus deposit in matrix (these bind to proteins for harder matrix)

What is the Third Step of Intramembranous Ossification?

formation of trabeculae (spongy bone)

• accumulated osteid is laid bwteeen embryonic blood vessels

• osteoblasts secrete matrix around blood vessels

What is the Fourth Step of Intramembranous Ossification?

development of the periosteum

• periosteum is the outer layer of compact bone outside of the spongy bone

• spongy bone is sandwiched between compact bone layers

What is the First Step of Endochondral Ossification?

bone collar forms around the diaphysis of the hyaline cartilage model

• layed down by osteoblasts

• mesenchyme → osteoblasts

What is the Second Step of Endochrondral Ossification?

cart8ilage calcifies in the center of the diaphysis and develops cavities

• cells die

What is the Third Step of Endochondral Ossification?

periosteal bud invades the internal cavities + forms spongy bone

• periosteal bud is large blood vessel

What is the Fourth Step of Endochondral Ossification?

• the diaphysis elongates

• medullary cvity forms

• secondary ossification centers appear in the epiphyses

What is the Fifth Step of Endochondral Ossification?

• epiphyses ossify

• hyaline cartilage remains in epiphyseal plates + articular cartilages when ossification is complete

What is the Epiphyseal Plate?

point where bone continues to grow

• becomes epiphyseal line when growing completes

What is the Zone of Resting Cartilage in the Epiphyseal Plate?

1st layer

• no bone growth

• functions to anchor cartilage to bone

What is the Zone of Proliferating Cartilage in the Epiphyseal Plate?

second layer

• cartilage cells divide and secretee extracellular matrix

• leads to new cartilage formation

What is the Zone of Hypertrophic Cartilage in the Epiphyseal Plate?

third layer

• contains enlarged + mature cartilage cells

What is the Zone of Calcified Cartilage in the Epiphyseal Plate?

fourth layer

• has dead + calcified cartilage cells

• osteoclasts dissolve cartilage

• osteoblasts lay down new bone to replace cartilage

What occurs in the Periosteum when bone grows in Width?

• periosteum cells differentiate into osteoblasts

• osteoblasts lay down new compact bone around perosteal blood vessels

• osteoblasts differentiate into osteocytes

What occurs in the Endosteum when bone grows in Width?

• osteocalsts erode endosteum

• calcium is released into blood stream

• medullary cavity enlarges without dramatically increasing bone weight

What is a Closed / Simple Fracture?

clean break + bone does not protrude through skin

What is an Open / Compound Fracture?

clean break + bone protrudes through skin

What is a Comminuted Fracture?

bone is crushed or splintered at the break

• fragments lie in btwn

What is a Greenstick Fracture?

one side is broken while other side is bent

• good example is in radius and ulna

How is the Skeleton divided?

• axial skeleton: 80 bones

• appendicular skeleton: 126 bones

What consists of the Axial Skeleton?

• skull

• hyoid bone

• vertabrae

• ribs

• sternum

• ear ossicles

How does the Axial Skeleton function?

• protects the brain, spinal cord, heart, and lungs

• serves as the attachment site for muscles that move the head, neck, and back

• stabalizes parts of the appendicular skeleton (ex. sternum)

What are all the bones in the Skull?

• parietal (posterior)

• frontal (anterior)

• occipital

• temporal (temple area)

• maxilla (upper jaw)

• mandible (lower jaw)

What is the Hyoid Bone?

u shaped structure located in the anterior neck

• tongue base above

• attached to larynx below

• attached to pharynx posteriorly

What is the Thorax?

• cage of bones

• ribs attach to vertberal column at the back

• ribs attach to sternum in the front via hyaline cartilage

How are the Ribs oriented in the Thorax?

• ribs 1-7: true ribs

• ribs 8-10: false ribs; attach tgt by cartilage

• ribs 11-12: floating; are not sternum attached

What consists of the Vertberal Column?

• cervical vertabrae (c1-c7)

• thoracic vertabrae (t1-t12)

• lumbar vertabrae (lower back, l1-l5)

• sacrum (pelvis attachment)

• coccyx (4 fused bones)

What are the Functions of the Vertabral Column?

• strong + flexible (curves to disperse pressure)

• protects spinal cord

• supports skull

• provides for attachment of ribs and muscles

What consists of the Appendicular Skeleton?

• pectoral (shoulder) girdle

• upper limb

• pelvic (hip) girdle

• lower limb

What are the Functions of the Appendicular Skeleton?

• facilitates human body movement

• provides leg and arm shape

• maintains mineral homeostasis in the body

What consists of the Upper Limb?

superior to inferior:

• clavicle

• scapula

• humerus

• radius (lateral)

• ulna (medial)

• carpals (wrist)

• metacarpals (palm)

• phalanges (fingers)

What consists of the Lower Limb?

superior to inferior:

• hip bone

• sacrum

• femur

• patella

• tibia (medial)

• fibula (lateral)

• tarsals (ankle)

• calcaneus (enlarged tarsel aka heel)

• metatarsals (flat part of foot)

• phalanges (toes)

What consists of a Typical Vertabrae?

• centrum (body)

• vertebral foramen (opening that contains spinal cord)

• transverse process (both sides)

• spinum process

What is the Atlas (C1)?

ring shaped bone with no centrum

• supports the head

• reduced spinous processes (it would get caught in skull)

• two large superior surfaces which articulate with skull condyles (allows nodding movement)

• lower surface articulates with axis

What is the Axis (C2)?

• peg shaped centrum aka dens that projects upwards

• atlas swivels on axis and around dens (side to side movement)

• reduced transverse processes

• longer spinous process than atlas

What are the components of the Pectoral Girdle?

• clavicle

• scapula

gives shoulder range of motion

What are the components of the Pelvic Girdle?

• ilium (superior)

• pubis (inferior + posterior)

• ischium (superior + anterior)

• sacrum

• coccyx

• pubic arch

How can we classify a Female Pelvis?

• broader, lighter, smoother

• larger + more circular opening (for birth)

• basin-shaped pelvis

• pubic arch is greater than 90 degrees

• less anterior curvature in sacrum and coccyx

• broader sciatic notch

How can we classify a Male Pelvis?

• heavier, more narrow

• smaller + pear shaped opening

• funnel-shaped pelvis

• pubic arch is smaller than 90 degrees

• more anterior curvature in sacrum and coccyx

• narrower sciatic notch

How can we distinguish a Baby Skull from an Adult Skull?

• baby: length of skull is ¼ of body length

  • less ossification

  • fontanels in baby skull

  • more cartilage than bone

• adult: length of skull is 1/8 of body length

  • fontanels have fused together

What is the difference between a Baby Vertabrae and an Adult one?

• babies have 1 single curvature

• adults have four different curvatures