Skeletal System1
Honors Anatomy
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Bone
• a combination of CT, epithelial & nervous
tissues
• 18% of weight of human body
• Skeletal System includes bones & cartilage
• Part 1: Bone
• Part 2: Axial Skeleton
• Part 3: Appendicular Skeleton
• Part 4: Joints
FUNCTIONS
1. SUPPORT
• skeleton serves as
structural
framework by
supporting soft
tissues & providing
attachments for
tendons of muscle
2. PROTECTION
• Protects most
important soft tissue
organs from injury
FUNCTIONS
3. MOVEMENT
• Skeletal muscles
attach to bones,
when the muscle
contract the bones
move
4. MINERAL
HOMEOSTASIS
• Bone stores calcium,
phosphorus which
both help make bone
strong
• If body needs these
minerals bone
releases them
Parts of a long bone
1. Diaphysis:
shaft or body; the long
cylindrical portion of
the bone
2. Epiphysis:
distal & proximal
ends of bone
Parts of a long bone
3. Metaphysis:
• region between
diaphysis &
epiphysis
• in growing bone
includes
metaphyseal plate
(hyaline cart. that
allows bone to
lengthen
4. Articular Cartilage:
• layer of hyaline
cartilage covering
part of epiphysis
where bone forms a
joint with
articulating bone
metaphysis
Structure of Long Bones
7. ENDOSTEUM
• thin membrane that
lines marrow cavity
• contains 1 layer of
bone-forming cells
and CT
Histology of bone
• bone consists of widely separated cells
surrounded by large amts extracellular
matrix
• *bone is hard due to crystallized
inorganic mineral salts
• *bone is flexible due to collagen
Types of Bone Cells
1. OSTEOGENIC CELLS
• Stem cells from mesenchyme (origin of all
CT)
• only bone cells to divide
Types of Bone Cells
2. OSTEOBLASTS
• bone-building cells
• synthesize & secrete collagen fibers
• initiate calcification
Types of Bone Cells
3. OSTEOCYTES
• mature bone cells
• main cells in bone
• maintain exchange of nutrients & wastes
with blood
Types of Bone Cells
4. OSTEOCLASTS
• huge cells that form by merging of many
(50)monocytes
• in endosteum
• ruffled border faces bone surface: releases
lysosomal enzymes & acids that digest
underlying bone (bone resorption): part of
normal maintenance, growth, development, &
repair of bone
Types of bone (2)
1. Compact bone
– few open spaces
– outer bone layer of all bones
2. Spongy bone
– inside bones
COMPACT BONE
• strongest form of bone
• beneath periosteum of all bone
• functions:
– protection & support
– resists stresses produced by weight &
movement
Parts of Compact Bone
• OSTEON:
– aka Haversian Systems
– repeating units thru out compact bone
– each one has central canal with
concentrically arranged lamellae
(rings), lacunae (filled with 1
osteocyte)
– aligned in same direction along lines of
stress
– space between osteon filled with
interstial lamellae
Compact bone
Spongy Bone
• absence of osteons
• made of lamellae arranged in irregular
columns called trabeculae
• makes up most of inside of short, flat, or
irregular bones & epiphysis of long bones
• lighter than compact bone
• Function:
– support & protect red bone marrow
Spongy bone
Bone growth
1.
•
1.
•
•
longer:
@ epiphyseal plate
wider:
called appositional growth
periosteal osteoblasts on outer
surface of bone
• osteoclast remove compact bone inner
border
Bone growth: longer
Bone growth: wider
Bone Remodeling
• Most bones are formed b/4 birth but each one
continually renews itself for rest of life
• ~5% of bone being remodeled @ any given
time
• bone remodeling is the ongoing replacement
of old bone tissue by new bone tissue
1. Bone Resorption
2. Bone Deposition
Bone Resorption
• removal of minerals & collagen fibers from
bone by osteoclasts
• results in destruction of bone extracellular
matrix
Bone Deposition
• addition minerals & collagen fibers to bone by
osteoblasts
Factors Affecting Bone Growth
& Remodeling
1. Minerals
– Ca, P, F, Mg, Fe, Mn
2. Vitamins
– C needed to make collagen fibers & for
osteoblast  osteocyte
– E & B12 needed for protein synthesis
3. Hormones
– IGF’s in childhood (insulin-like growth
factors)
– estrogens & androgens important in puberty
Fracture & Repair of Bone
• Fracture: any break in a bone
• Fractures named by:
– severity
– shape or position of fracture line
– person who 1st described it
Fracture Repair
Calcium Homeostasis
• Bone is body’s main reservoir for calcium
(stores 99% of total body Ca)
• Normal blood level Ca 9 -11 mg/100mL
• Calcium important for:
– Muscle contraction
– Nerve impulses
– Blood clotting
– Many enzymes require Ca as cofactor)
Control of Calcium
• 2 hormones control Ca in/out bone:
1. Calcitonin
– Decreases blood Ca levels by putting
more Ca into bone
2. Parathyroid Hormone (PTH)
– Increases blood Ca levels by taking Ca
out of bone (increasing osteoclast
resorption)
Homeostatic Imbalances in Bone
1. Osteoporosis
– condition of porous bones (resorption >
deposition)
– causes: deficient Ca in diet
– USA: > 1 million fractures (hip, wrist,
vertebrae) & afflicts 30 million
Americans
– decreased stature, hunched back, bone
pain
Homeostatic Imbalances in Bone
1. Osteoporosis
– condition of porous bones (resorption >
deposition)
– causes: deficient Ca in diet
– USA: > 1 million fractures (hip, wrist,
vertebrae) & afflicts 30 million
Americans
– decreased stature, hunched back, bone
pain