Osseous Tissue
Osteology
Study of bones
Bones are made of 7 things
Osseous tissue
blood
bone marrow
cartilage
adipose
nervous tissue
Fibrous CT
In bones the CT matrix is
hardened and mineralized
Ligaments
connects bone to bone
Tendons
connects muscle to bone
Functions of the skeleton (5)
Support
Protection
Movement
Electrolyte balance
Blood formation
2 major types of osseous tissue
Compact bone and spongey bone
4 types of bones
Long bone
Flat bone
Irregular bone
short bone
Characteristics of long bone
Longer than they are wide
Produced by endochondral ossification
Allows movement
Has compact and spongey
Examples of flat bone
cranial bones, sternum, scapula, and ribs
Characteristics of short bone
About the same in length and width
Often slide against one another to produce gliding movement
Examples include wrists and ankle bones
Examples of irregular bones
vertebrae and ossicles of the ear
Gross anatomy of long bones
Articular cartilage
Diaphysis
Epiphysis
Periosteum
Endosteum
What is articular cartilage?
Hyaline cartilage covering both ends; it reduces friction between bones
What is diaphysis?
shaft of long bones; made of compact bone covering spongey bone; contains medullary cavity (marrow cavity)
What is epithysis?
ends of long bones; made of compact bone and spongey bone; adults have epiphyseal line and children have epiphyseal plate
What is periosteum?
2 layer membrane; outer is fibrous layer and inner is osteogenic layer; provides attachment for tendons and ligaments
The periosteum has a rich supply of
nerve fibers and blood vessels that pass through diaphysis to medullary cavities via nutrient foramina
What is endosteum?
internal surface membrane; made of dense irregular CT; covers up trabeculae in spongey bone
Gross anatomy of flat bones
spongey bone covered by compact bone
has periosteum and endosteum
no diaphysis or epiphysis
Gross anatomy of short bones
about equal in length and width
spongey bone covered by compact bone
has periosteum and endosteum
no diaphysis and epiphysis
Gross anatomy of irregular bones
spongey bone covered by compact bone
has periosteum and endosteum
no diaphysis or epiphysis
Microscopic anatomy of compact bone (6)
Osteon
Lamella
Lacuna
Central Canal
Perforating Canal
Canaliculi
Osteon
fundamental unit; also known as Haversion System
Lamella
Bone matrix ring around osteon
2 types of lamella
Concentric lamallae- around osteon
Circumferential lamallae- perimeter of bone around diaphysis
Lacuna
Space containing the osteocyte
Central canal
contains blood vessel and nerves in compact bone; also called Haversion Canal
Perforating Canal
transverse canals in compact bone; they link central canals
Canaliculi
microscopic canals between lacunae
Microscopic anatomy of spongey bone (3)
Consists of spicules and trabeculae
appears sponge-like but is still hardened lamella containing osteocytes
Trabeculae are not randomly arranged but form along stress lines
What are stress lines
Tiny little fractures heal and resist stress that is put on the bone
What is bone marrow?
Soft tissue that occupies medullary cavities of long bones and spaces between trabeculae of spongy bone
2 types of bone marrow
Red bone marrow
Yellow bone marrow
What is red bone marrow?
Site of hematopoiesis (blood cell formation;
also known as myeloid tissue
dominates all marrow cavities in CHILDREN
in adults, it’s found in the skull, vertebrae, ribs, etc
What is yellow bone marrow?
fat storage
In adults, it’s found in medullary cavity of long bone diaphysis
Can convert to red marrow in case of chronic anemia
4 major bone cells
Osteogenic cells, osteoblasts, osteocytes, and osteoclasts
Osteogenic cells
give rise to most other bone cells; found in the osteogenic layer of the periosteum and endosteum; multiply continually
Osteoblasts
bone-forming cells; secrete protein mixture that hardens and becomes the bony matrix; non-mitotic; formed from osteogenic cells in response to mechanical stress
Osteocyte
mature bone cells; reside in spaces called lucanae which are connected by canaliculi; canaliculi allow osteocytes to connect and communicate via gap junction; function is to MAINTAIN bony matrix
Osteoclasts
bone dissolving cells; perform osteolysis; formed from fusion of stem cells
Matrix of osseous tissue contains
Organic and inorganic material
Organic material of bone matrix characteristics
makes up 35% of bone tissue mass
called osteoid
Provides flexibility and tensile strength
secreted by osteoblasts
Inorganic material of bone matrix characteristics
makes up about 65% of bone tissue mass
provides rigidness and compression resistance
85% is hydroxyapatite
10% is calcium carbonate
5% is magnesium, sodium, potassium, fluoride, sulfates, carbonates, and hydroxide ions
3 major processes of bone development
Bone formation: embryos through early childhood
Bone growth: embryos through early adulthood
Bone remodeling: lifelong
Bones form and grow via
Endochondral ossification and intramembranous ossification
Bones thicken via
appositional growth
Wolff’s Law
remodel in response to mechanical stress
Effects of Wolff’s Law
Bones in one limb are thicker than those in the less-used limb
Curved bones are thickest where they are most likely to break
Trabeculae form along lines of compression
Large bony projections occur at sites of strong, active muscle
Where do bone deposition and resorption occur?
At the surface of the periosteum and endosteum
Amount of resorption is equal to
the amount of deposition
As you age resorption
becomes greater than deposition
Mineral depostition
Osteoblasts create organic osteoid as a template for osseous tissue
Mineral crystalize on the osteoid
Osteoblasts must also “neutralize” inhibitors that prevent mineralization
Mineral resportion
due to osteoclasts
Osteoclasts detect falling levels of Calcium in the tissue fluid
Secrete lysozymes
Secrete hydrochloric acids
Liberates the minerals and ions back into blood stream
What maintains blood calcium levels?
Bone remodeling
Calcium is required for
muscle contractions and nervous system physiology
Normal blood calcium levels
9.2 - 10.4 mg/dL
Hypocalcemia
deficiency in blood calcium levels
Hypocalcemia leads to
excessive excitability of neurons and muscle tetany
Tetany
occurs when blood calcium levels reach less than 6 mg/dL
Rickets
chronic hypocalcemia in children
Hypercalcemia
too much blood calcium
Hypercalcemia leads to
decreases neuron excitability and muscle function
People with hypercalcemia experience
sluggish reflexes, depression of the nervous system, emotional disturbances, and cardiac arrest
Calcium homeostasis depends on
balance between dietary intake and urinary/fecal loss of calcium
Calcium is regulated by 3 horomones
Calcitriol
Calcitonin
Parathyroid horomone
Calcitriol
“try”ing to bring calcium up
Calcitonin
“ton”ing calcium levels down
Parathyroid horomone
Bring calcium up
Stress fractures
purely mechanical damage
Pathological fractures
imbalance in bone physiology
Fracture classification
Nondisplaced vs displaced
complete vs incomplete
compound vs simple
Fracture treatment
Reduction & Immobilization
Reduction
realign the broken bone
Closed reduction
external; bones aligned “by hand”; cast only
Open reduction
Bones secured with surgical pins and wires
Osteomalacia
osteoid is produced but adequate calcium is not mineralized
Pain in back and joints, muscle weakness, trouble walking, and spinal deformity
Rickets
only children; leads to bowed legs, deformities of pelvis, skull, and rib cage; Caused by insufficient calcium and vitamin D
Osteoporosis
Bone resorption is significantly greater than bone deposition
Bones become fragile
Explain what happens during appositional growth
osteoblasts beneath the periosteum lay new bone, osteoclasts on endosteum remove bone, and leads to increase in overall thickness of the bone while keeping the bone weight low