Skeletal System Chapter 6 (7 & 8 from lab)

206 total named bones in the human body
FUNCTIONS:
1. Contribute to body shape and form
2. Support
3. Protection
4. Movement
5. Mineral storage
6. Hematopoiesis
CLASSIFICATION of BONES
Broken down into two groups
- appendicular
-
axial
Types of bones:
Long Bones:
Short Bones:
Sesamoid:
Flat Bones:
Sutural:
Irregular Bones:
STRUCTURE OF BONE: a typical long bone
Diaphysis:
-Medullary Cavity:
Epiphysis:
-Articular cartilage:
-Epiphyseal plate: (epiphyseal line)
Metaphysis:
Membranes
Endosteum:
Periosteum:
TWO TYPES OF BONE COMPOSITION:
A. COMPACT BONE:
-looks solid but contains few spaces
Haversian system “osteons”
lamellae
haversian canal
Volkmann’s Canals (perforating)
lacunae
-contains an
-all lacunae are interconnected
canaliculi
B. SPONGY (CANCELLOUS) BONE:
-doesn't have Haversian System
Trabeculae
-consists of many spaces filled with
-yellow marrow
-red marrow
COMPOSITION OF BONE:
Organic Framework:
Inorganic Salts:
-tiny crystals that imbed around collagen fibers in the extracellular matrix
Salts allow the bone to
Combination of fibers/salts makes bone
DEVELOPMENT OF BONE: ossification or osteogenesis
1. INTRAMEMBRANOUS OSSIFICATION – from mesenchyme or fibrous tissue
2. ENDOCHONDRAL OSSIFICATION – replaces hyaline cartilage
INTRAMEMBRANOUS:
occurs in the
-typically results in formation of
Major steps
1. ossification center - - grouping of mesenchymal cells which
differentiate into osteoblasts
2. osteoid (bone matrix) is secreted and surrounds osteoblasts 
develop into osteocytes
-deposition and hardening of salts is called
3. osteoid is laid down around penetrating blood vessels which form a
random network
4. periosteum is form which develops an underlying bone collar
(compact) surrounding spongy bone containing red marrow
-
the surface layer of periosteum now has less active osteoblasts lining its
inner layer
ENDOCHONDRAL OSSIFICATION:
During endochondral ossification, Perichondrium becomes vascularized and is converted
to periosteum
PRIMARY OSSIFICATION CENTER:
1. Osteoblasts in the periosteum secrete osteoid around cartilaginous
diaphysis to form
2. Cartilage in the center of diaphysis hypertrophy and signal surrounding
cartilage matrix to calcify
3. the periosteal bud invades the internal cavities and spongy bone forms
a. periosteal bud
4. The diaphysis elongates and a medullary cavity forms; blood vessels enter
the epiphyses
5. The epiphyses ossify through secondary ossification centers
SECONDARY OSSIFICATION CENTER:
INCREASE IN BONE LENGTH:
Epiphyseal plate:
Epiphyseal plate's cartilage cells reproduce to keep the thickness constant
- cartilage forms tall column of cells, dividing quickly at the top to push the
plate away from the diaphysis
-
the rate of cartilage growth on the epiphyseal side is equal to replacement
of bony tissue on diaphysis side
Plates become thinner and thinner as adolescence hits 18 to 21 yrs of age
Growth of bones controlled by hGH and Thyroid hormones
INCREASES IN DIAMETER:
Osteoblasts vs. Osteoclasts
REMODELING OF BONE: replacement of old with new
BONE DEPOSIT
Nutrients needed:
Osteoblasts:
BONE RESORPTION
Osteoclasts:
FACTORS WHICH AFFECT BONE REMODELING
Why?
1. Stress: Bone grows in response to prolonged heavy load
2 types of stressors bone normally experiences
A. gravitational forces:
B. functional forces:
-regular exercise can alter the form of the skeleton
2. Hormones : negative feedback mechanisms
A. PTH (parathormone)
B. Calcitonin
Conditions of Clinical Significance:
A. Fractures:
1. simple:
2. compound:
3. comminuted:
4. depressed:
5. impacted:
healing process:
1. bleeding occurs: hematoma
2. formation of a fibrocartilaginous callus
-fibroblasts
3. formation of a bony callus
-initially the area is comprised of chondrocytes: osteoblasts
-prolonged immobilization of a broken bone may be
detrimental to the healing process
4. Bone remodeling
B. Paget’s Disease
-excessive bone breakdown and formation
C. Osteoporosis:
-decreased rate of bone formation
3 factors to decrease risk of osteoporosis:
1.
2.
3.
D. Rickets and Osteomalacia
-demineralization & softening of bone
Read section 6-6 pg 201-202 and Classification of fractures pg 203