A&P Chapter 7

Osseous Tissue

Osteology

Study of bones

Bones are made of 7 things

1. Osseous tissue

2. blood

3. bone marrow

4. cartilage

5. adipose

6. nervous tissue

7. 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)

1. Support

2. Protection

3. Movement

4. Electrolyte balance

5. Blood formation

2 major types of osseous tissue

Compact bone and spongey bone

4 types of bones

1. Long bone

2. Flat bone

3. Irregular bone

4. short bone

Characteristics of long bone

1. Longer than they are wide

2. Produced by endochondral ossification

3. Allows movement

4. Has compact and spongey

Examples of flat bone

cranial bones, sternum, scapula, and ribs

Characteristics of short bone

1. About the same in length and width

2. Often slide against one another to produce gliding movement

3. Examples include wrists and ankle bones

Examples of irregular bones

vertebrae and ossicles of the ear

Gross anatomy of long bones

1. Articular cartilage

2. Diaphysis

3. Epiphysis

4. Periosteum

5. 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

1. spongey bone covered by compact bone

2. has periosteum and endosteum

3. no diaphysis or epiphysis

Gross anatomy of short bones

1. about equal in length and width

2. spongey bone covered by compact bone

3. has periosteum and endosteum

4. no diaphysis and epiphysis

Gross anatomy of irregular bones

1. spongey bone covered by compact bone

2. has periosteum and endosteum

3. no diaphysis or epiphysis

Microscopic anatomy of compact bone (6)

1. Osteon

2. Lamella

3. Lacuna

4. Central Canal

5. Perforating Canal

6. Canaliculi

Osteon

fundamental unit; also known as Haversion System

Lamella

Bone matrix ring around osteon

2 types of lamella

1. 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)

1. Consists of spicules and trabeculae

2. appears sponge-like but is still hardened lamella containing osteocytes

3. 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

1. Red bone marrow

2. Yellow bone marrow

What is red bone marrow?

Site of hematopoiesis (blood cell formation;

1. also known as myeloid tissue

2. dominates all marrow cavities in CHILDREN

3. in adults, it’s found in the skull, vertebrae, ribs, etc

What is yellow bone marrow?

fat storage

1. In adults, it’s found in medullary cavity of long bone diaphysis

2. 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

1. makes up 35% of bone tissue mass

2. called osteoid

3. Provides flexibility and tensile strength

4. secreted by osteoblasts

Inorganic material of bone matrix characteristics

1. makes up about 65% of bone tissue mass

2. provides rigidness and compression resistance

3. 85% is hydroxyapatite

4. 10% is calcium carbonate

5. 5% is magnesium, sodium, potassium, fluoride, sulfates, carbonates, and hydroxide ions

3 major processes of bone development

1. Bone formation: embryos through early childhood

2. Bone growth: embryos through early adulthood

3. 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

1. Bones in one limb are thicker than those in the less-used limb

2. Curved bones are thickest where they are most likely to break

3. Trabeculae form along lines of compression

4. 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

1. Osteoblasts create organic osteoid as a template for osseous tissue

2. Mineral crystalize on the osteoid

3. Osteoblasts must also “neutralize” inhibitors that prevent mineralization

Mineral resportion

due to osteoclasts

1. Osteoclasts detect falling levels of Calcium in the tissue fluid

2. Secrete lysozymes

3. Secrete hydrochloric acids

4. 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

1. Calcitriol

2. Calcitonin

3. 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

1. Nondisplaced vs displaced

2. complete vs incomplete

3. 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

1. osteoid is produced but adequate calcium is not mineralized

2. 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

1. Bone resorption is significantly greater than bone deposition

2. 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