A&P 1 - Bones Objectives - McClelland

Functions of the skeletal system:

- protection

- mineral storage & acid-base balance - stores calcium, phosphorus, & magnesium

- blood cell formation (hematopoiesis) - occurs in red bone marrow

- fat storage - yellow marrow stores triglycerides

- movement - bones act as levers for muscles

- support - provides body framework & posture

How are bones classified by shape?

- long bones

- short bones

- flat bones

- irregular bones

- sesamoid bones

Long bones

- longer than wide

- ex. femur & humerus

Short bones

- shorter than long --> cube-shaped

- ex. carpals & tarsals

Flat bones

- thin, broad

- ex. skull bones & sternum

Irregular bones

- complex shapes

- ex. vertebrae

Sesamoid bones

- develop in tendons

- ex. patella

Gross Structure of long bones

- diaphysis: shaft

- epiphyses: ends of the bone

- articular cartilage: covers joint surfaces

- periosteum: outer CT tissue covering

- spongy bone: inner porous layer

- medullary cavity: contains yellow marrow

Red bone marrow

- produces blood cells

- active hematopoiesis

- found in spongy bone

Yellow bone marrow

- stores fat (triglycerides)

- energy reserve

- found in medullary cavity of long bones

Inorganic components of the ECM of bone tissue

- mineral salts (mainly calcium phosphate)

- provide hardness & resistance to compression

Organic components of the ECM of bone tissue

- collagen fibers & ground substance

- provide flexibility & tensile strength

Function of Osteoblasts

build new bone (bone formation)

Function of Osteocytes

mature cells that maintain bone matrix

Function of Osteoclasts

break down bone (resorption)

Microscopic structure of compact bone

consists of repeating units called osteons

Components of the osteon

- central canal: blood vessels & nerves

- concentric lamellae: rings of matrix

- lacunae: spaces housing osteocytes

- canaliculi: tiny channels connecting cells

Microscopic structure of spongy bone

- made of trabeculae (lattice of bone plates)

- contains marrow-filled spaces

- lacks osteons

- lightweight but strong

Primary bone

- first to be formed

- disorganized collagen fibers

- temporary

Secondary bone

- mature bone

- organized layers

- much stronger

Process of intramembranous ossification

bone forms directly from CT membranes:

1. mesenchymal cells become osteoblasts

2. osteoid is secreted

3. mineralization occurs

4. trabeculae form

5. compact bone develops

- forms flat bones of skull & clavicle

Process of endochondral ossification

bone develops from a cartilage model:

1. hyaline cartilage model forms

2. bone collar develops

3. primary ossification center forms in diaphysis

4. medullary cavity forms

5. secondary ossification centers develop in epiphyses

- forms most bones of the body

How do long bones grow in length?

- occurs at the epiphyseal (growth plate)

- cartilage cells proliferate --> enlarge --> calcify --> replaced by bone

- growth stops when plates close (epiphyseal line forms)

Longitudinal bone growth

increases at growth plates

Appositional bone growth

thickness increase by adding bone to outer surface

Hormones involved in bone growth

- growth hormone

- thyroid hormons

- sex hormones (estrogen, testosterone)

- parathyroid hormone

- calcitonin

- vitamin D

Process of bone resportion

osteoclasts break down bone

Process of bone deposition

osteoblasts form new bone

The physical, hormonal, & dietary factors that influence bone remodeling

physical:

- weight-bearing strengthens bone

hormonal regulation

dietary factors:

- calcium, vitamin D, & protein

Role of calcitonin, parathyroid hormone, & vitamin D in bone remodeling & calcium ion homeostasis

calcitonin:

--> lowers blood calcium

--> inhibits osteoclasts

parathyroid hormone:

--> raises blood calcium

--> stimulates osteoclast activity

vitamin D:

--> increases calcium absorption from intestines

--> supports mineralization

General process of bone repair:

1. hematoma formation: blood clot forms

2. soft callus formation: fibrocartilage bridges fracture

3. hard callus formation: bone replaces cartilage

4. bone reshaped to original form