chapter 6- bones. what do bones do for you other than make up 18% of your weight? 1. support-...
TRANSCRIPT
Chapter 6- Bones
What do bones do for you other than make up 18% of your weight?
• 1. Support- muscles• 2. Protection- organs• 3. Movement- with muscles• 4. Mineral storage- calcium (99% of body's),
phosphorus, • 45% of bone weight• 5. Hemopoiesis- Blood cell production, in the Red
bone marrow• 6. Fat storage- Yellow bone marrow
Figure 6-1 A Classification of Bones by Shape
Sutures
Suturalbone
Vertebra
Carpalbones
Parietal bone External table
Internaltable
Diploë(spongy
bone)
Humerus
Patella
Sutural Bones Flat Bones
Long Bones
Sesamoid Bones
Irregular Bones
Short Bones
Structure of Bone(pg 173)
• 1. Diaphysis- shaft• 2. Epiphyses- ends• 3. Metaphyses- b/w 1 & 2, includes the
epiphyseal plate (cartilage)- cartilage replaced by bone when
done growing = epiphyseal line• 4. Articular cartilage- reduces friction• 5. Periosteum-covering for protection &
nourishment• 6. Medullary cavity/ Marrow cavity-
yellow marrow• 7. Endosteum- lines the marrow cavity
6-3 Bone (Osseous) Tissue
• Matrix composed of:– Minerals:
• Hydroxyapatite (Calcium)• Function: Hard, brittle and can withstand
compression
– Protein Fibers:• Collagen• Function: Tensile strength, tolerates
twisting/bending
Bone Cells
Maintain matrix, help repair damage bone
Secrete new matrix (osteoid), become osteocytes
Produce osteoblasts, repair fractures
Remove/recycle matrix by dissolving with acids/enzymes (osteolysis)
Resorption- breakdown of bone *every 7 years you make a new skeleton
Bone Tissue
• 1. Compact- 80% of bone, few spaces– Haversian canals (bld vessels), Lamellae (layers),
Lacunae(pockets with osteocytes)
* All bone tissue has a rich supply of blood
2. Spongy- 20% of bone, found in the epiphyses
• No osteons
• Matrix = trabeculae
(lattice structures), appears to have holes
stores red marrow– Open network of fibers w/
no blood vessels
6-4 Compact Bone and Spongy Bone
• Periosteum:– Outer membrane
covering compact bone
– fibrous and cellular layer
– Functions:
– Isolates bone
– Route for blood vessels/nerves
– Bone growth/repair
6-4 Compact Bone and Spongy Bone
• Endosteum– incomplete cellular
layer lining the medullary cavity
– Contains osteoblasts, osteoprogenitor cells and osteoclasts
– Functions:– Covers trabeculae – Lines central canals– bone growth and repair
6-5 Bone Formation and Growth
• Ossification
• The process of replacing other tissues with bone
• Includes calcification: deposition of Ca salts
• Two Main forms of ossification:
• Endochondral Ossification and Intramembranous
Ossification
Endochondral Ossification
• Ossifies bones that originated as hyaline
cartilage
• Step 1:
• Chondrocytes increase in size
• Matrix begins to calcify
• Enlarged chondrocytes die
Endochondral Ossification
• Step 2:
• BVs grow into perichondrium
• Cells of perichondrium
convert to osteoblasts and
produce thin layer of
superficial bone
Endochondral Ossification
• Step 3:
• BVs penetrate cartilage
• Fibroblasts migrate and
differentiate into osteoblasts
• Form primary ossification
center, cartilage replaced with
spongy bone
Endochondral Ossification
• Step 4:
• Remodeling occurs
• Osseous tissue becomes thicker
• Cartilage near epiphysis
replaced by bone
• Osteoclasts erode spongy bone
and form medullary cavity
• Step 5:
• Capillaries and osteoblasts
migrate into epiphyses
• Secondary ossification
centers form
Endochondral Ossification
Endochondral Ossification• Step 6:
• Epiphyses fill with spongy bone
• Articular cartilage remains
• Metaphysis: epiphyseal cartilage
separates epiphysis from
diaphysis
• Epiphyseal cartilage lost after
puberty complete females 23, males 25when complete-no epiphyseal disks
Figure 6-11a Bone Growth at an Epiphyseal Cartilage
An x-ray of growing epiphysealcartilages (arrows) Epiphyseal lines in an
adult (arrows)
Intramembranous (Dermal) Ossification
Bone Formation Video
6-6 Bone Remodeling• The adult skeleton:
• Maintains itself
• Replaces mineral reserves
• Recycles and renews bone matrix
6-7 Exercise, Hormones, and Nutrition
• Exercise
– Mineral recycling allows bones to adapt to stress
– Heavily stressed bones become thicker and
stronger
• Bone Degeneration
– Bone degenerates quickly
– Up to one third of bone mass can be lost in a few
weeks of inactivity
6-7 Exercise, Hormones, and Nutrition• Nutrition
– Diet must include calcium and phosphate salts,
plus small amounts of magnesium, fluoride, iron,
and manganese
– Calcitriol
• Vitamin C required for collagen synthesis and stimulation of osteoblast differentiation
• Vitamin A stimulates osteoblast activity
• Vitamins K and B12 help synthesize bone proteins
6-7 Exercise, Hormones, and Nutrition
• Hormones
– Growth hormone and thyroxine stimulate
bone growth
– Estrogens and androgens stimulate
osteoblasts
– Calcitonin and parathyroid hormone regulate
calcium levels
Figure 6-16b Factors That Alter the Concentration of Calcium Ions in Body Fluids
Bone Response Intestinal Response Kidney Response
Thyroid Gland Response
Factors That Decrease Blood Calcium Levels
These responses aretriggered when plasmacalcium ion concentrationsrise above 11 mg/dL.
HIgh Calcium Ion Levels in Plasma(above 11 mg/dL)
Parafollicular cells (C cells) in thethryoid gland secrete calcitonin.
Osteoclasts inhibited whileosteoblasts continue to lockcalcium ions in bone matrix
Bone
Rate of intestinalabsorptiondecreases
Kidneys allowcalcium loss
Calcitonin
less
calcitriol
Calcium stored
Calcium absorbed slowly Calcium excreted
Increased calciumloss in urine↓Ca2+
levels inbloodstream
Figure 6-16a Factors That Alter the Concentration of Calcium Ions in Body Fluids
Bone Response Intestinal Response Kidney Response
Parathyroid Gland Response
Factors That Increase Blood Calcium Levels
These responses aretriggered when plasmacalcium ion concentrationsfall below 8.5 mg/dL.
Low Calcium Ion Levels in Plasma(below 8.5 mg/dL)
Low calcium plasma levels causethe parathyroid glands to secreteparathyroid hormone (PTH).
Osteoclasts stimulated torelease stored calcium ionsfrom bone
Osteoclast
Bone
Rate ofintestinalabsorptionincreases
Kidneys retaincalcium ions
PTH
more
calcitriol
Calcium released Calcium absorbed quickly Calcium conserved
Decreased calciumloss in urine↑Ca2+
levels inbloodstream
Cracks/breaks in bones
Caused by physical
stress
Repaired in four steps
Figure 6-17 Types of Fractures and Steps in Repair
Immediately after the fracture, extensivebleeding occurs. Over aperiod of several hours, alarge blood clot, or fracturehematoma, develops.
An internal callus forms as a network of spongy boneunites the inner edges, and anexternal callus of cartilage and bonestabilizes the outer edges.
PeriosteumSpongy bone ofexternal callus
Fracturehematoma
Bonefragments
Deadbone
REPAIR OF A FRACTURE
Figure 6-17 Types of Fractures and Steps in Repair
The cartilage of the external callus has been replaced bybone, and struts of spongy bone nowunited the broken ends. Fragments ofdead bone and the areas of boneclosest to the break have beenremoved and replaced.
A swelling initially marks the location ofthe fracture. Over time, thisregion will be remodeled,and little evidence of the fracture will remain.
Externalcallus
Externalcallus
Internalcallus
Fractures• 1. Open/Compound- through the skin• 2. Closed/ Simple- not through the skin• 3. Comminuted- smaller fragments• 4. Greenstick- only children, 1 side broken, 1 side
bends• 5. Impacted- bone through bone• Stress fracture- microscopic , repeated stress
• can withstand 24,000 lbs/sq in, 4x greater than steel
Transverse- break along shaft Spiral- from twistingDisplaced- produces abnormal bone alignment
6-10 Effects of Aging on the Skeletal System
• Bones become thinner and weaker with age
• Osteopenia begins between 30 - 40
• Inadequate ossification/osteoblast activity declines = loss of bone mass
• Women lose 8% of bone mass/decade, men 3%
• The epiphyses, vertebrae, jaws most affected
• Result = fragile limbs, reduction in height, tooth loss
SEM 25Normal spongy bone
Spongy bone in osteoporosis SEM 21
• Osteoporosis
• Severe bone loss
• Affects normal
function/increases possibility of
fracture
Causes:• inadequate intake of calcium and
vitamin D• lack of weight-bearing exercise• lack of certain hormones, particularly
estrogen in women (menopausal women are at higher risk)
• Cigarette smoking• eating disorders such as anorexia
nervosa or bulimia
Abnormal Development of Bone
Pituitary dwarfism =inadequate production of growth hormone resulting in short bones
Gigantism= overproduction of HGHRobert Wadlow (Alton) 8ft, 11in
Marfan’s syndrome =excess cartilage at epiphyseal plates