Skeletal System

Inside look at the BONES

Image from: www.interactive-biology.com 

Parts of the Skeletal System

Bones (Skeletal

organ)

Joints

Cartilage

Ligaments

Tendons

Types of BonesBones are classified by their structure each vary

in proportions of compact and cancellous. Long Short Flat Irregular Sesamoid

Short, Flat, Irregular, Sesamoid Short

Cube or boxed shaped Examples: Carpals and Tarsals

Flat Broad and thin with flattened and curved surface Filled with marrow Example: Sternum

Irregular Misshaped bones found in groups Examples vertebral and facial bones

Sesamoid Found in locations where a tendon passes a joint Example: patella

Long BonesKnown for its length and

distinct structures Diaphysis

Main shaft of a long bone Hollow, cylindrical shape and thick

compact bone Function is to provide strong

support without cumbersome weight

Epiphyses Both ends of a long bone; made of

cancellous bone filled with marrow Function is to provide

attachments for muscles and give stability to joints

Long Bone (continued) Articular cartilage

Layer of hyaline cartilage that covers the articular surface of epiphyses

Function is to cushion jolts and blows

Periosteum Dense, white fibrous

membrane that covers bone Attaches tendons firmly to

bones Contains blood vessels essential for bone cell

survival and bone formation

Long Bone (continued) Medullary (or marrow) cavity

Tubelike, hollow space in the diaphysis

Filled with yellow marrow in adults

Endosteum: Thin, fibrous membrane that lines the

medullary cavity

Sharpey’s fibers Secure periosteum to underlying bone

Arteries Supply bone cells with nutrients

Distal

epiphysis

Proximal

epiphysis

diaphysis

yellow marrow

epiphyseal line

periosteum

compact bone

spongy bone

Endosteum

hyaline cartilage

Sharpey’s fibers

Anatomy of the Long Bone

Bone Tissues Most distinctive form of connective tissue Composition

Inorganic salts ( calcium, phosphate, magnesium and sodium)

Organic matrix (collagenous fibers, proteins and polysaccharides, glucosamine)

Two basic types Compact Bone Spongy Bone

Compact Bone Contains many cylinder-shaped

structural units called osteons, or haversian systems

Osteons surround haversian canals that run lengthwise through bone and are connected by transverse (Volkmann) canals

Living bone cells are located in osteon

Osteons permit delivery of nutrients and removal of waste products

Structures of Osteon Lamella- concentric calcified

matrix

Lacunae- spaces filled with tissue fluid between lamella

Canaliculi- ultra small canals that connect lacunae and harvesian canals

Harvesian canals- contain blood vessels and lymphatic vessels

Gray’s Anatomy of the Human Body from the classic 1918 publication

Cancellous (Spongy) Bone No osteons in

cancellous bone; it has trabeculae instead

Nutrients are delivered and waste products removed by diffusion through tiny canaliculi

Bony branches (trabeculae) are arranged along lines of stress to enhance the bone’s strength

Types of Bone Cells Osteocytes

Mature bone cells

Osteoblasts

Bone-forming cells

Osteoclasts

Bone-destroying cells

Break down bone matrix for remodeling and release of calcium

Bone remodeling is a process by both osteoblasts and osteoclasts

Blood supply

Bone cells are metabolically active and need a blood supply

Supplied from bone marrow

Bone marrow and blood vessels penetrates the bone and then, by way of transverse (Volkmann) canals, connects with vessels in the central canals of osteons

Bone Marrow Composition

Myoloid- soft connective tissue

Function Site of for production of

blood cells; hematopoises Location

Medullary cavities of long bones

Empty spaces of spongy bone

Types of Marrow Red marrow

Found in virtually all bones in an infant’s or child’s body Produces red blood cells

Yellow marrow As an individual ages, red marrow is replaced by yellow

marrow Marrow cells become saturated with fat and are no longer

active in blood cell production

Bones Function Support- form the framework that supports

the body and cradles soft organs.

Protection- provides a protective case for brain, spinal cord and vital organs

Movement- provides levers for muscles

Mineral Storage- reservoir for minerals especially calcium

Blood cell formation- hematopoiesis occurs in the within the marrow cavities of the bones

Calcium levels 98% calcium in the body is found in bones

Calcium levels change as a result of bone remodeling.

Homeostasis of calcium ion concentration affects several functions Bone formation, remodeling and repair Blood clotting Trasmission of nerve impulses Cardiac and skeletal muscle contractions

Mechanism of Calcium Homeostasis Parathyroid

hormone Primary regulator

of calcium homeostasis

Calcitonin Protein hormone

produced in the thyroid gland

Produced in response to high blood calcium levels

Bone Development Osteogenesis

development of bone small cartilage model to adult model

Endochondral ossification Bone formation

spreading essentially from the center to the ends

Replacement of hyaline cartilage

From cartilage to bone Cartilage cells (chondrocytes) begin to die, region

becomes known as the ossification center Primary- middle of diaphysis Secondary- epiphysis

Periosteum is forming around the outside of the cartilaginous model.

Periosteum produces osteoblast Osteoblasts build up on the periphery of the

spongy bone, they secrete their matrix and build compact bone all around the spongy bone.

This occurs simultaneously

The Growing Bone Epiphyseal plate

remain between diaphysis and both epiphysis.

Its is composed of 4 layers “Resting” cartilage cells- Zone of proliferation- cartilage

cells undergoing mitosis Zone of hypertrophy- older

cells undergoing degenerative changes

Zone of Calcification- dead cartilage cells undergoing calcification

Osteoclast widen the medullary cavity

Osteoblast build new bone around existing bone

Cartilage Characteristics

Avascular connective tissue Fibers of cartilage are embedded in a firm gel Has the flexibility of firm plastic No canal system or blood vessels

Functions Tough, rubberlike nature permits cartilage to

sustain great weight or serve as a shock absorber Strong yet pliable support structure Permits growth in length of long bones

Types of Cartilage Hyaline cartilage

Most common type Covers the articular surfaces of bones

Elastic cartilage Forms external ear, epiglottis, and eustachian

tubes Fibrocartilage

Occurs in pubic symphysis and intervertebral disks Strong and rigid

Bone Fractures Fracture—break in a bone

Types of bone fractures Closed (simple) fracture—break that does not

penetrate the skin Open (compound) fracture—broken bone

penetrates through the skin

Bone fractures are treated by reduction and immobilization

Common Types of Fractures

Table 5.2

Bone repair Healing

1. Fractures destroy blood vessels

2. Vascular damage initiates repair

3. Dead bone is removed by osteoclastic resorption

4. Fracture hematoma(blood clot cause duiring break) is

reabsorbed and callus ( Specialized repair tissue) is

deposited in bones