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Chapter 6: The Skeletal System (6.1 - Skeletal System Functions (support…
Chapter 6: The Skeletal System
6.1 - Skeletal System Functions
support
provide framework for tissues
storage
mineral reserve; yellow marrow
blood cell production
red, white, and other blood elements produced; red marrow
protection
protects vital organs from damage
leverage
range of motion
6.2 - Bone Shape and Structure
Macroscopic Features
Long Bones
diaphysis (central shaft), surrounds marrow cavity, epiphyses at each end covered by articular cartilages
Short Bones
Flat Bones
Irregular Bones
Compact Bone
relatively solid
Spongy (Cancellous) Bone
network of bony rods separated by spaces
Periosteum
outer surface of bone; fibers of tendons/ligaments intermingle w/ this; isolates bone; route for circulatory/nerve supplies; bone growth/repair
Endosteum
lines marrow cavity/inner surfaces; active during bone growth and repair/remodeling
Microscopic Features
Osteocytes
bone cells
Lacunae
small pockets found in lamellae
Lamellae
narrow sheets of calcified matrix
Canaliculi
small channels through matrix; interconnect lacunae
Cells in Bone
Osteocytes
mature bone cells; recycle calcium salts; help repair
Osteoclasts
giant cells w/ 50 or more nuclei; osteolysis process regulates calcium and phosphate concentrations
Osteoblasts
produce new bone; osteogenesis process; promotes deposition of calcium salts
6.3 - Ossification and Appositional Growth
ossification - process of replacing other tissues with bone
intramembranous ossification
- bone develops within sheets/membranes of connective tissue
osteoblasts differentiate within embryonic or fetal fibrous connective tissue
occurs deep in the dermis
first occurs in ossification center
ex. skull bones
endochondral ossification
- bones replaces existing cartilage
formed through hyaline cartilage
ex. limbs
Steps:
1
- chondrocytes within cartilage enlarge and matrix calcifies;
2
- inner cells of perichondrium form into osteoblasts to make bone;
3
- blood vessels invade cartilage and spongy bone forms;
4
- osteoclasts break down spongy bone and marrow cavity formed;
5
- epiphyses centers calcify
Bone Growth/Body Proportions
differences in sex hormones account for variations in body size and proportions between men and women
Bone Growth Requirements
reliable source of minerals (Vitamin D3)
Vitamin A and C
minerals absorbed from mother's bloodstream during pregnancy
hormones (growth, thyroid, sex, and those involved in calcium metabolism)
6.4 - Bone Growth and Development
Role of Remodeling
heavily stressed bones become thicker and stronger; develop more pronounced surface ridges
bones not subjected to ordinary stress become weak and brittle
Calcium Reserve
parathyroid hormone and calcitriol work together to elevate calcium levels in body fluids
calcitonin from thyroid gland reduces calcium levels
Repair of Fractures
Step 1
- fracture hematoma (blood clot) forms and closes off the injured blood cells
Step 2
- cells of periosteum and endosteum undergo mitosis; daughter cells go to fracture zone to form external callus and internal callus (localized thickenings; hyaline cartilage is made
Step 3
- osteoblasts replace central cartilage w/ spongy bone; calluses produce spongy bone at fracture site
Step 4
- spongy bone remodeling will continue for about 4 months to a year; only living compact bone will remain; bone thicker than normal at the fracture site
6.5 - Osteopenia
inadequate ossification
happens as we age; bone mass reduction begins around age 30-40
6.6 - Surface Markings and Skeletal Divisions
Skeletal Divisions
axial skeleton
skull (22)
auditory ossicles (6)
hyoid bone
thoracic cage
sternum
vertebral column
appendicular skeleton
limbs of pectoral and pelvic gurdles