Chapter 5: The Skeletal System

Anatomy & Physiology Kasprowicz

Parts of the Skeletal System

·Bones (make up the skeleton)

· Joints (articulations)

·Cartilages

·Ligaments (dense, regular connective tissue connecting bone to bone)

Divisions of the Skeleton

Axial Skeleton• bones that form the longitudinal axis• skull, vertebrae, rib cage

Appendicular Skeleton• bones of the limbs (appendages) & girdles• arms, legs, pelvis

Functions of the Skeleton

1) Support for the body our internal framework

2) Protection of soft organs ex. skull brain rib cage lungs & heart vertebrae spinal cord

Functions of the Skeleton

3) Movement skeletal muscles use the bones as levers to

move the body & its parts

4) Storage Bone tissue stores minerals, such as calcium

and phosphorus Fat is stored in yellow marrow

Functions of the Skeleton

5) Blood Cell Formation Hematopoiesis occurs in red marrow

The adult skeleton is composed of 206 bones!

Classification of Bones

Bones can be classified based on their SHAPE or HISTOLOGICAL ORGANIZATION (STRUCTURE)

Classification of Bones: Shape

1) Long bones Typically long & slender Shaft with heads at both ends Mostly compact bone

Examples: arms, legs, fingers, toes

Classification of Bones: Shape

2) Short bones Typically box- or cube-shaped Mostly spongy bone

Examples: wrists & ankles

Classification of Bones: Shape

3) Flat bones thin, flattened usually curved thin layers of compact bone surrounding

spongy bone

ribs

Classification of Bones: Shape

4) Irregular bones Do not fit in other categories

Examples: VertebraeHip bones

Types of Bone (Osseous) Tissue

Compact Bone• dense, smooth &

homogenous

Spongy Bone• open network of struts

& plates

All bones contain both types of bone tissue. Their relationship & proportions vary depending on bone shape.

Gross Anatomy of a Long Bone

1) diaphysis a) tubular shaft b) compact bone

2) epiphysis a) ends of the bone b) mostly spongy bone

Gross Anatomy of a Long Bone

Structures of a Long Bone

1) periosteum a) outside covering of the diaphysis b) fibrous connective tissue membrane

2) Sharpey’s fibers connect periosteum to the underlying bone

Structures of a Long Bone

3) Arteries supply the osteocytes w/ nutrients & oxygen

4) Articular Cartilage a) covers the epiphyses b) made of hyaline cartilage c) decreases friction at the joints

Structures of a Long Bone

5) Medullary Cavity a) Cavity of the shaft b) bone marrow consists of loose connective tissue - yellow marrow (fat storage) in adults - Contains red marrow (for blood cell formation) in infants c) endosteum layer of cells lining the cavity

Bone Histology

• Osseous tissue (bone) is a type of connective tissue

• Four Characteristics of Bone 1) bone matrix is very dense & contains calcium salts 2) contains bone cells (osteocytes) in pockets called lacunae

Bone Histology

Four Characteristics of Bone cont… 3) Canaliculi allow for gas exchange and diffusion of nutrients and waste products 4) except at joints, bones are covered by the a periosteum

Let’s take a look at each characteristic…

Bone Histology: Matrix

1) 2/3 of bone matrix is calcium phosphate, Ca3(PO4)2

• w/ calcium hydroxide, forms crystals of hydroxyapatite, which incorporate other calcium salts & minerals into the matrix

2) 1/3 of bone matrix is collagen fibers

Only 2% of bone mass comes from cells

Bone Histology: Cells

1) There are 4 types of bone cells osteocytes are the most common2) Osteocytes sit in a pocket-like structure

called a lacuna (lacunae, plural)3) Lacunae are arranged in concentric rings,

or layers of matrix, called lamellae (lamella, singular)

Bone Histology: Canaliculi

Canaliculi (tiny canals)1) Radiate from the central canal (blood vessels)

to lacunae

2) Form a transport system between osteocytes and between the central canal & osteocytes

Bone Histology

Bone Histology: Periosteum

1) Covers all bones, except parts enclosed in joint capsules

2) It is made up of an:–outer, fibrous layer – inner, cellular layer

Bone Histology: Periosteum

3) Functions of periosteum a) Isolate bone from surrounding tissues

b) Provide a route for circulatory and nervous supply

c) Participate in bone growth and repair

Periosteum

Compact Bone

1) Osteon (Haversian System) osteon – the basic unit of compact bone

2) Organization of an Osteon a) Osteocytes are arranged in concentric lamellae around a central (Haversian) canal containing blood vessels

Compact Bone

2) Organization of an Osteon cont… b) Central (Haversian) canal

opening in the center of an osteon containing blood vessels and nerves

c) Perforating (Volkman’s) canal perpendicular to the central canal also containing blood vessels and nerves

Compact Bone

Compact Bone

osteon

Spongy Bone 1) Does not have osteons2) A “honeycomb” matrix forms an open network of trabeculae3) Trabeculae have no blood vessels

Spongy Bone

Spongy Bone: Yellow Marrow In some bones, spongy bone holds yellow bone marrow which is used to store fat

Spongy Bone: Red Marrow The space between trabeculae is filled with red bone marrow. Red marrow forms red blood cells and supplies nutrients to osteocytes.

Bone Markings · Surface features of bones that show… 1) Sites of attachment for muscles, tendons, and ligaments 2) Passages for nerves and blood vessels

Categories of bone markings· projections or processes – grow out from the bone

surface

· depressions or cavities – indentations

Bone Markings

Bone Markings

BONE FORMATION, GROWTH & REMODELING

The structure of bone is specialized for flexibility and tensile strength.

Bone Formation

· In embryos, the skeleton is primarily hyaline cartilage

· During fetal development, much of this cartilage is replaced by bone

· By the end of the toddler years, cartilage remains only in isolated areas:

- bridge of the nose

- parts of ribs

- articular cartilage (in the joints)

- epiphyseal plates

Bone Formation

•The process of “bone formation” is called ossification.

1) Unless it is a flat bone, a hyaline cartilage model is covered with bone matrix by osteoblasts. osteoblasts - immature, bone-forming cells

Over time, the “cartilage bone” is enclosed in a layer of real bone (kind of like an arm in a cast).

Bone Formation

2. The enclosed layer of hyaline cartilage is digested away by osteoclasts.

osteoclasts - bone destroying cells; break down bone matrix for remodeling and release of calcium The breakdown of the cartilage “model” leaves a medullary cavity in the bone.

Bone Formation

Bones must grow in both length and width.

Bone Growth

Epiphyseal plates allow for growth in the length of long bone during childhood & adolescence

Bone Growth

Bone Growth

Appositional growth increases thewidth of the bone.

1) Osteoblasts in the periosteum add bone tissue to the surface

At the same time…

2) Osteoclasts in the endosteum remove bone matrix from the inner surface.

In order for bones to retain normal proportions and strength as the body changes in size and strength, bones must constantly

remodel.

Bone Remodeling

1) Bones become thicker and form larger projections to increase strength for bulky muscles. When you lift its not just the muscles that have to respond!

Bone Remodeling

2) When bones are not subject to normal stress/exercise, they atrophy (shrink, shrivel).

Bone degenerates quickly! Up to 1/3 of bone mass can be lost in a few weeks of inactivity!

Bone Remodeling

Bone building (by osteocytes) and bone recycling (by osteoclasts) must balance

http://www.dnatube.com/video/8584/Learning-about-Bone-Modeling-and-Remodeling

Hormonal Control of Bone Growth &

Remodeling

Hormonal Control

1) Calcitriol - is made in the kidneys; synthesis requires vitamin D3 (cholecalciferol)

- helps absorb calcium and phosphorus from digestive tract

Hormonal Control

2) Parathyroid Hormone (PTH) - operates on a negative feedback loop

- activates bone resorption (osteoclast activity) & increases calcium levels in the blood

Hormonal Control

3) Other Hormones - growth hormone and thyroxine stimulate bone growth - estrogens and androgens stimulate osteoblasts - calcitonin (w/ PTH and calcitriol) regulate calcium and phosphate levels

The Effect of Nutrition on Bones

Nutrition & Bone

1) Minerals A dietary source of calcium and phosphate salts, plus small amounts of Mg, F, Fe and Mn

Nutrition & Bone

2) Vitamins - vitamin C needed (collagen synthesis & osteoblast differentiation) - vitamin A stimulates osteoblast activity- Vitamin K and B12 ( protein synthesis in bone)

Nutrition & Bone

Questions: 1. A pregnant woman is not getting enough calcium in her diet. How will her body respond? (hormone released, response)

2. Sally has a history of osteoporosis in her family. She includes many calcium-rich foods in her diet and takes a vitamin D supplement. How will her body respond? (hormone released, response)

Bone Fractures

Bone Fractures

Types of bone fractures1) Closed (simple) fracture –

break that does not penetrate the skin

2) Open (compound) fracture –

broken bone penetrates through the skin

· Bone fractures are treated by reduction (realignment of the bone) and immobilization

Bone Fractures

Bone Fractures

Bone Fractures

Bone Fracture Repair

Step 1: Bleeding• produces a clot (fracture hematoma)• establishes a fibrous network• bone cells in the area die

Bone Fracture Repair

Step 2: Callus Formation• Cells of the endosteum and periosteum divide and migrate into fracture zone

• fibrocartilage“Calluses” stabilize the break

Bone Fracture Repair

Step 3: Bone Formation• Osteoblasts and osteoclasts migrate to the area and multiply. • Osteoclasts deteriorate the fibrocartilage callus as osteoblasts replace it w/new bone tissue. This is now called a bony callus.

Bone Fracture Repair

Step 4: Bone Remodeling• Osteoblasts and osteocytes remodel the fracture for up to a year, reducing the bone calluses

Bone Fracture Repair