Skeletal System-Lecture Notes

Anatomy & Physiology 2004-2005Unit 4 – Skeletal System Lecture Notes

Unit 4 – Skeletal System (Ch. 6)Slides 1-4I. Bone Basics

A. Functions of the Skeletal System1. Support – weight bearing (bone), flexible (cartilage),

holds bones together (ligament)2. Protection – skull, vertebrae, rib cage3. Movement – tendons, muscles, joints, smooth cartilage,

ligaments4. Storage – minerals (calcium & phosphorus) and fat

(energy)5. Blood cell production – bone marrow forms blood cells and

platelets

Slides 5-9B. Composition of the Skeletal System (Connective Tissue)

1. bones, cartilage, tendons, ligaments2. ECM: collagen (glue + producing), proteoglycans (protein

+ polysaccharide), other organic molecules, water, mineralsa. Tendon/ligament ECM - collagen (tough)b. Cartilage (gristle) ECM – collagen + proteoglycans

(tough, smooth, & resilient)c. Bone ECM – collagen & minerals

(hydroxyapatite – CaPO4) for weight bearing strength; like rebar in concrete

Slides 10-11C. Types of Bone (based on shape)

1. Long bones – longer than wide, limb bones Slide 12

2. Short bones – length = width; wrist & ankle Slide 13

3. Flat bones – thin & flat; skull bones, ribs, scapulae, sternum 14

4. Irregular bones – shapes don’t fit in other categories; vertebrae, facial bones Slide 15

Slides 16-18Slide 19

D. Anatomical Terminology of Bones1. diaphysis (growing between) – central

shaft2. epiphysis (growing upon) – ends of

bone3. articular cartilage (joint) – covers

epiphyses

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4. epiphyseal plate (growth plate) – made of cartilage; between epiphysis and diaphysis; growing long bone

5. epiphyseal line – bone replaces cartilage when growth stops

6. medullary cavity – in diaphysis; filled with marrow (soft tissue)a. yellow marrow – mostly fat (higher in adults); in

diaphysisb. red marrow – produces blood cells (higher in youth);

in spongy/cancellous bone; in adult axis bones and proximal epiphyses of limbs

7. periosteum (around bone) – blood vessels, nerves; covers bones

8. endosteum (inside bone) – line medullary cavity (connective tissue)

Slides 20-22Slides 23-24

9. osteoblasts (bone forming cells) – in both periosteum and endosteum; bone formation, repair, and remodeling

Slides 25-26E. Bone Histology (study of bone tissue)

1. Compact Bone Slides 27-28a. Compose the diaphysis of long bones and thinner

surfaces of all other bones

Slide 29b. Osteon/haversian system – make up compact bone

i. Lamellae (plate) – thin sheets that make up bone, formed in concentric circles (like tree rings)

ii. Lacunae (hollow) – in between lamellae, hold osteocytes

iii. Osteocytes (bone cells) – inside lacunae between lamellae

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iv. Canaliculi (little canal) – provide communication between osteocytes via blood vessels

v. Haversian/central canal – hollow canal inside osteons housing blood vessels (nutrients, blood, waste removal), lymph, and nerve fibers Blood vessels also connected to the blood vessels in periosteum and endosteum

Slides 30-31Slides 25-26

2. Cancellous Bone (spongy)a. Epiphyses of long bones and interior of all bonesb. Trabeculae (beam) – thin bony spicules in sheets

arranged perpendicular to major force to bonei. Get same strength and less weight

as if were solid (“I” beam vs. solid beam)

ii. Spaces filled with marrow & blood vessels

iii. No blood vessels or Haversian canals in trabeculae Nutrients from blood vessels in marrow diffuse through canaliculi to osteocytes

iv. Spiculues of trabeculae composed of osteons

Slides 31-32Slide 33

F. Ossification (bone + to make) in fetus1. Synthesis of organic matrix (collagen +

proteoglycans = osteoid) and hydroxyapatite crystalsa. osteoblasts mineralized osteocytes (mature)b. all bone growth is a result of bone deposition a

preexisting surfacec. Constant remodeling

Slide 342. Bone cells:

a. Osteoblasts – bone builder; make boneb. Osteoclasts – bone dissolver, bone resorption;

multinucleatec. Osteocytes – bone maintainer; regulatory function

Slide 353. Two types of ossification:

a. Intramembranous ossification (between membranes)(Fig.6.5)i. Primarily in skull (frontals and parietals of

cranial vault) and some shoulder girdleii. For flat and irregular bone growth

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Slide 36iii. Ossification centers – osteoblasts retreat making

bone matrix by forming trabeculae (radiate out) fusion of ossification centers results in skull bones

Slide 37b. Endochondral ossification

Most common (basicranium, base of skull, rest of body’s bones)

Bone forms from cartilage model

Slide 38i. Perichondrium (around

cartilage) – surrounds cartilage model

Slide 39ii. Step #1: Chondrocytes (cartilage cells) – central

chondrocytes increase in number, hypertrophy ( in size), & die forming lacunae which are calcified. Blood vessels in perichondrium accumulate causing formation of osteoblasts in perichondrium.

Slide 40iii. Step #2: Osteoblasts form periosteum = bone collar.

Slide 41iv. Step #3: Primary ossification center – center of

diaphysis where bone first appears Blood vessels invade calcified cartilage Osteoblasts invade spaces left by dying chondrocytes forming trabeculae (cancellous)

Osteoclasts remove some calcified cartilage forming medullary cavity in center (fills with marrow)

Slide 42v. Step #4: Secondary ossification centers – appear in

epiphyses (same process as above)

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Slide 434. Bone Growth

a. Appositional growth – deposition of bone lamellae onto existing bone or connective tissue (adding width)i. Osteoclasts remove bone

endosteum while osteoblasts add bone to periosteum, increasing bone diameter

b. Adding length – occurs at epiphyseal plate

Chondrocytes increase in #, form lines, elongating bone

Chondrocytes mature, hypertrophy, & die

Cartilage matrix around chondrocytes calcifies.

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Fig. 6.7


Osteoclasts remove cartilage matrix, osteoblasts replace chondrocytes.

Osteoblasts form bone (deposit lamellae on surface of calcified cartilage) on diaphysis side of plate.

Slide 445. Bone Remodeling

a. Deposit new bone & remove bonei. osteoclasts remove existing bone, osteoblasts add

bone cancellous → compact (conversion)

ii. medullary cavity increases in size as bone diameter increases to avoid heavy bones

b. Occurs in all bonec. Functions:

i. Changes in bone shapeii. Adjustment to stress

iii. Bone repairSlide 45

iv. Blood calcium regulation & storage (removal & deposition via hormone control)

Slide 446. Bone Repair – when a bone is broken

Slide 46a. clot formation – from vessel damageb. callus formation – begins 2-3 days after injury.

Blood vessels and fibrous network of connective tissue invade clot between bone fragments, filling gap

c. callus ossification – complete after 4-6 weeks. Osteoblasts form cancellous bone (bone must be immobile).

d. bone remodeling – several months. Cancellous → compact + cancellous (can result in stronger bone).

Show x-rays

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Fig. 6.8


Slide 47G. Bone and Calcium Homeostasis

1. bone stores calcium; deposition and removal of Ca2+ to maintain appropriate blood calcium levelsa. needed for nervous & muscle system functionb. Ca2+ deposited during bone building (osteoblasts), if

blood [Ca2+]c. Ca2+ removed when bone broken down (osteoclasts via

enzymes), if blood [Ca2+]2. Parathyroid hormone (PTH) - ’s

blood [Ca2+] by ’g osteoclasts activity (break down bone)a. Also Ca resorption from

urine in kidneyb. Stimulates vitamin D

formation by kidneys – needed for intestinal Ca2+ absorption

c. PTH stimulated by blood [Ca2+]

d. Secreted from parathyroid gland (on kidneys)

3. Calcitonin - ’s blood [Ca2+] by ’g osteoclasts activity (stores Ca2+)a. Calcitonin stimulated by

blood [Ca2+]b. Secreted from thyroid gland

Slide 48H. Skeletal Disorders

1. Growth & Developmental a. Giantism – abnormally increased size, excessive

Endochondral growth @ epiphyseal platesb. Dwarfism – person is abnormally small, improper growth

@ epiphyseal platesc. Osteogenesis imperfecta (bone + production +

imperfect) – genetic disorders causing brittle bones with insufficient collagen; easily fractured, especially in fetus; poor healing/misalignment

d. Rickets (to twist) – bone growth retardation due to Ca, P, or vitamin D deficiency (sunlight or dietary); bones soft/weak, can twist and/or break

2. Bacterial infection a. Osteomyelitis – bone marrow inflammation, can be

caused by Stapholococcus (type of bacterium) through wounds or tuberculosis

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Fig. 6.9


3. Bone tumors 4. Decalcification

a. Osteomalacia (bone softness) – due to calcium depletion from bonesi. Pregnancy or “Adult Rickets” from vitamin D

deficiencyb. Osteoporosis (bone-pore-condition) – general reduction

in bone qualitySlide 49

I. Bone Fractures1. open/compound – skin perforated by bone2. closed/simple – skin not perforated3. complete – two bone fragments are separate4. incomplete – two bone fragments are not separated

a. greenstick – partly broken and partly bent5. comminuted - > 2 fragments6. impacted – 1 fragment pushed into cancellous portion of

another fragment7. linear – parallel to long axis of bone8. transverse – perpendicular to long axis9. oblique/spiral – at an angle other than perpendicular

Note: joint immobilization during mid-late bone healing results in 3x decrease in strength

o Muscles lose mass (atrophy)o Bone not subject to the stresses that helps it

form Solution = walking cast

Slide 50J. Bone Features – common terms

1. 206 bones in human body (varies between people & age)2. Major features:

a. body/shaft – main portionb. head – enlarged (often rounded) endc. neck – constricted end between head and body

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d. condyle (knuckle) – smooth rounded end of bone forming an articulation with another bone

e. facet – small, flattened articular surfacef. crest – prominent ridgeg. process – projectionh. tubercle/tuberosity – lump; often sites of muscle

attachment, can change in size with muscle usagei. trochanter – large tuberosity found only on the

proximal femurj. epicondyle – enlargement near or above a condyle

Slide 513. Openings or Depressions:

a. foramen/foramina (to pierce) – holes in bones for nerves or blood vessels

b. canal/meatus (passage) – tunnel through bonec. fissure – cleftd. sinus – cavitye. fossa – depression

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Skeletal System-Lecture Notes