Skeletal system

Healthy bones

properly functioning cells and adequate quantities and qualities of ECM for effective functioning

Healthy bone is composed of

osseous tissue, dense regular and irregular CT, and bone marrow

why is bone an organ?

Multiple tissues make it up

functions of the skeletal system

• protects internal organs

• mineral storage and pH balance

• blood cell formation

• fat storage

• movement with muscles

• support

How does the skeleton provide protection?

It’s hard substance enables it to be a strong shell for underlying organs like the brain, heart, lungs, and sensory organs

What do the skull, sternum, ribs, and pelvis d

Protect underlying organs

Minerals stored by bone

calcium, phosphorus, and magnesium

Magnesium is found in

blood as electrolytes, acids, and bases

What balance does the skeletal system maintain?

pH, electrolyte, and chloride balance

Bones generate movement at

joints

what are bones the attachment site for?

skeletal muscles

What kind of blood cells does the skeletal system make?

ALL blood cells

Bone supports

the weight of the body by giving it structural framework

The 5 general shapes of bone

flat, short, irregular, sesamoid, and long

how many bones are there?

206

long bone

longer than wide, has an epiphysis and diaphysis

long bone examples

humerus, femur, hands, feet, fingers, and toes

short bones

equal length and width, cube shaped

examples of short bones

carpals and tarsals

flat bones

thin and broad, flat/curved

flat bones examples

bones of the skull, ribs, sternum, and pelvic bones

irregular bones

don’t fit any other classes

examples of irregular bones

vertebrae, sacrum, coccyx, temporal, sphenoid, ethmoid, zygomatic, maxilla, mandible, and hyoid

sesamoid bones

small, relatively flat, oval shaped bones in tendons and ligaments

What do tendons and ligaments provide for sesamoid bones?

Mechanical advantage, extra leverage, and reduction of wear and tear

sesamoid bones example

patella

Components of long bones

diaphysis, epiphyses, medullary cavity, and epiphyseal plates and lines

Periosteum

white outer coating of long bones, dense irregular CT with blood vessels and nerves

perforating fibers

collagen that connects and secures the periosteum to the bone matrix

diaphysis

shaft, deep center of the bone that contains yellow bone marrow

epiphysis

• enlarged, rounded ends covered with articular cartilage (hyaline)

• houses red bone marrow

medullary cavity

sounded by diaphysis, houses bone marrow

compact bone

dense outer layer that resists stress, compression, and twisting forces to provide strength

spongy bone

• inner framework at the ends of long bones

• resists forces from many directions

• honeycomb-like cavity for bone marrow

endosteum

• thin, inner-most lining of all bones

• lacks a fibrous center

Components of short, flat, irregular, and sesamoid bones

• two layers of compact bone that surrounds spongy bone

• perforating fibers attached to periosteum

• blood vessels and nerves

Nerve and blood supply in bones

lots of blood vessels and nerve/sensory fibers

Blood supply for short, flat, irregular, and sesamoid bones comes from

blood vessels in the periosteum

Blood supply in long bones comes from

• mainly the nutrient artery (via nutrient foramen)

• periosteum for compact bone

Red bone marrow

• aids in hematopoiesis with hematopoietic cells

• reticular fibers

• decreases with age

• in epiphysis

hematopoietic cells

stem cells that increase the activity of blood cells to trigger blood production

Bone marrow transplant

Red bone marrow is injected into someone to make blood

In children, red bone marrow is found in

most places, some is replaced with yellow marrow at age 5

Adults have lots of

yellow bone marrow

ECM of bone

bone matrix that is not found in other tissue

Bone cells

responsible for bone’s dynamic nature, older bones are broken down for materials to build new bone

What bone cells for responsible for bone’s dynamic nature?

Osteoblasts, osteocytes, and osteoclasts

Inorganic Matrix

• calcium and phosphorus (makes hydroxyapatite crystals)

• also has potassium, magnesium, bicarbonate, and sodium

Without the inorganic matrix bone cannot

resist compression, it would be bendy and flexible

hydroxyapatite crystals

made of calcium and phosphorus, makes bone one of the hardest substances on the planet

Organic matrix

• collagen (protein fibers) and osteocalcin

• proteoglycans, glycosaminoglycans, glycoproteins

The organic matrix is referred to as

osteoid

without the organic matrix bone would

be brittle and shatter easily

collagen in the organic matrix

forms cross links to resist twisting and pulling, enhances hardness for strength

osteocalcin

helps to organize the organic matrix by binding to calcium and hydroxyapatite

osteoblasts

• builds bone into osteocytes/becomes osteocytes

• lays down bone matrix

• derived from osteogenic cells

osteoblasts are cuboidal or columnar cells found in the

inner periosteum and endosteum

Osteocytes

• surrounded and trapped by bone matrix in lacuna

• no longer metabolically actively other than to secrete chemicals needed to maintain the ECM

• recruits osteoblasts for bone reinforcement when tension is applied

what happened when osteoblasts become trapped in lacunae?

They no longer actively synthesize bone matrix and become osteocytes

Osteogenic cells

• flattened cells that differentiate into osteoblasts when stimulated by chemical signals

• stem cells for bone

Osteoclasts

• large, multi-nucleated

• derived from bone marrow

• recycles materials

• jellyfish looking

Bone resorption

• osteoclasts secrete H+ ions and enzymes from ruffled border

• H+ creates acid and dissolves the inorganic matrix (calcium and phosphate)

• enzymes break down the organic matrix

In bone resorption, portions of calcium and phosphate are

put back into bone or transferred to the blood stream

The Haversian System is used to

withstand stress

lamella

• rings of the osteon made up of collagen fibers

• enhances strength and resists twisting, bending, and stress in multiple/opposite directions

To withstand stress and damage compact bone must be

made up of a tightly packed unit called an osteon/haversian system

Osteons have multiple

lamella

Central canal

• endosteum lined center of the osteon

• Contains blood vessels and nerves that supply blood to the osteon

lacunae

cavities between lamellae filled with ECF and osteocytes

canaliculi

• small canals (cytoplasmic extensions) that connect lacunae and allow oxygen and nutrients from blood to reach osteocytes (lacunae communication and resource sharing)

• take nutrients from the central canal

osteons are not

• permanent structures since they are constantly being rebuilt or broken down depending on the body’s needs

• osteons are tightly packed with lamella between them to reflect this

Interstitial lamellae

remnants of reabsorbed or old osteons between individual circular osteons

Circumferential lamella

• Outer/inner rings of lamellae inside the periosteum

• at the boundary (superficial to) of spongy bone

• add strengths and tension resistance to bone

Perforating (volkmans) canals

• connects central canals of neighboring osteons

• originate from periosteum’s blood vessels and travel at right angles ro merge with blood vessels of the central canal

The structure of spongy bone uses a network of struts (trabeculae) to…

reinforce compact bone by resisting forces from many directions and forming a protective framework for bone marrow

Is spongy bone densely or loosely packed? Why?

It is loosely packed because it’s usually not weight bearing

Trabeculae

• struts or ribs of bone covered with endosteum

• made of concentric lamella with osteocytes

How do trabeculae communicate?

Through canaliculi

Trabeculae lack

an osteon arrangement and blood supply from central/perforating canals

Where do trabeculae get blood supply from?

Blood vessels in bone marrow