Bones, Skeletal, & Tissue System

What is the name for the science concerned with the study of bone?

Osteology

What are the functions of the skeletal system?

Two types: Biological and Mechanical

Mechanical

• Protects internal organs

• Facilitates movement

• Supports the body (weight bearing)

Biological

• Stores and releases fat

• Produces blood cells

• Stores and releases minerals

How many bones are humans born with? How many do we have at adulthood?

• 300-350 at birth

• 206 at adulthood

Describe: The mineral storage of bones

• The inorganic matrix of bone is composed of calcium and phosphorus, these give bones rigidity and account for 2/3 of the weight of bone

• 95% of calcium and 90% of phosphorus in the body are in our bones and teeth

• Magnesium and sodium salts are also stored in bones

Describe ways in which the skeleton protects our body/organs

• Skull/vertebral column house the central nervous system (brain/spinal chord)

• The thoracic cage (ribs) protects the heart, lungs, great vessels, liver, and spleen

• The pelvic cavity supports and protects pelvic organs

What are the two types of bone tissue?

• Compact bone (cortical): dense, smooth, and homogenous

• Spongy bone (cancellous/trabecular): open, sponge-like space, with small pieces of bone. (Surrounded by compact bone)

What are the 5 types of bone?

• Long

• Short

• Flat

• Irregular

• Sesamoid

Describe: Long Bones

• Longer than they are wide

• Used for mechanical strength

Ex) femur, tibia, fibula, humerus, ulna, radius

Describe: Short Bones

• Cube shaped

• Used for multi-directional motion

Ex) carpal bones of the hand/wrist, tarsal bones of the feet/ankle

Describe: Flat Bones

• Thin and flat (large surfaces for muscle attachment)

• Used for mechanical protection of soft tissues beneath

Ex) Cranial bones, sternum, ribs, scapulae

Describe: Irregular Bones

• Complicated shapes that cannot be classified as long, short, or flat

• Provide mechanical support for the body structures

Ex) Vertebrae, hyoid bone, sphenoid bone, facial bones

Describe: Sesamoid Bones

• Most sesamoid bones are unnamed

• Protects from additional friction and use, can form in palms and soles

Ex) Only one type is present in all normal human skeletons so it has a name: the patella (kneecap!)

Define: Closed Reduction

When a broken bone is manipulated and set into its natural
position without surgery

Define: Open Reduction

Requires surgery to expose the fracture and reset the bone.

The breaking of which bone can release fat globules into the bloodstream and result in respiratory distress and death?

A fractured diaphysis of the femur

What are the 8 types of bone fractures?

• Closed

• Open

• Transverse

• Spiral

• Comminuted

• Impacted

• Greenstick

• Oblique

Describe: Transverse fractures

Occurs straight across the long axis of the bone

Describe: Oblique fractures

Occurs at an angle that is not 90 degrees

Describe: Spiral fractures

Bone segments are pulled apart as a result of a twisting motion

Describe: Comminuted fractures

Several breaks result in many small pieces between two large bone segments

Describe: Impacted fractures

One fragment is driven into the other, usually as a result of compression

Describe: Greenstick fractures

A partial fracture in which only one side of the bone is broken

Describe: Open fractures

A fracture in which at least one end of the broken bone tears through the skin, carries a very high risk of infection

Describe: Closed fractures

A fracture in which the skin remains intact

What are the 4 stages of bone repair?

• Hematoma formation and inflammation

• Granulation formation (also called fibrocartilaginous callus formation)

• Callus formation (or bony callus formation)

• Remodeling

Describe: Hematoma formation + Inflammation

• Activation of coagulation cascade

• Changes of local environment

• Inflammatory cells and molecules are released

  • Clear necrotic tissues and recruit osteoprogenitor cells

Describe: Granulation (fibrocartilaginous callus formation)

• Active proliferation of osteoprogenitor cells

• Angiogenesis

• Extracellular matrix production

Describe: Bony callus formation

• Soft and hard differentiation of MSCs (mesenchymal stem cells) according to the mechanical environment

• Initial stabilization of fracture, then replaced by calcified tissue

Describe: Bone remodeling

• Long process (can take YEARS)

• Resorption of remaining cartilage

• Restoration of the Haversian system

• No scar formed

Define: The Haversian system

The Haversian system, also known as the osteon, is a fundamental structural unit of compact bone. It consists of concentric layers of bone tissue called lamellae, surrounding a central canal called the Haversian canal. Which contains blood vessels, nerves, and connective tissue. The lamellae are composed of collagen fibers and mineralized matrix, providing strength and support to the bone.

Why are calcium ions (Ca2+) needed in the body?

• for bone mineralization

• for tooth health

• regulation of the heart rate and strength of contraction

• blood coagulation

• contraction of smooth and skeletal muscle cells

• regulation of nerve impulse conduction

What is the normal amount of calcium in the blood?

The normal level of calcium in the blood is about 10 mg/dL.

How are calcium levels maintained? (homeostasis)

When Ca2+ levels are low: Osteoclasts dissolve and break down old or damaged bone cells and release Ca2+ to be reabsorbed by the kidneys to increase Ca2+ in blood.

When Ca2+ levels are high: The thyroid releases calcitonin, which inhibits osteoclast activity.

What are osteoBLASTS (not osteoCLASTS)?

Osteoblasts are cells that form bone tissue.

What are the three ways bones are classified?

• Shape

• Location

• Dynamic structure

Define: Axial skeleton

• 80 bones

• Protect internal organs

• Include: skull, vertebral column, and thoracic cage

Describe the bone structure of the skull

• Cranium is the entire skull

• Brain case is the rear and top of the cranium

• Facial bones are the front of the skull

Describe the vertebral column

• Called: spine, spinal column, or backbone

• Flexible hollow structure containing spinal cord

• Comprised of 33 vertebrae

• Occipital bone to tip of coccyx

Describe the regions of the vertebral column

• C1-C7: Cervical

• T1-T12: Thoracic

• L1-L5: Lumbar

• S1-S5: Sacrum (fused)

• Co1-Co4: Coccyx (fused)

Describe the thoracic cage

• Also called the rib cage

• 12 pairs of ribs (24 total)

  • First 7 pairs of ribs are attached to the sternum directly by cartilage (called true ribs)

  • 8-10th pairs are attached to the 7th rib by cartilage (false ribs)

  • The 11th and 12th are not attached to the sternum (spine only) called floating ribs.

What is the function of the spine?

• Protects the spinal cord from any mechanical injury by enclosing the cerebrospinal fluid (CSF), spinal cord, and nerve roots

• Protects internal organs like the heart and lungs

• Serves as the attachment point for several muscles, tendons, ligaments, and bones

Describe: the embryonic development of the human skull

3rd week of embryonic development

• Notochord develops along the length of the embryo

• Notochord tissues enlarge and form neural tube which will form the brain and spinal cord

4th week of embryonic development

• Mesoderm tissue located on either side of the notochord thickens and separates into block-like tissue structures called somite

• Somite enlarge and split into several parts, the middle is called a sclerotome

Sclerotomes consist of embryonic tissue called mesenchyme, which will give rise to fibrous connective tissues, cartilage, and bones.

Define: Appendicular skeleton

• 126 bones total

  • 64 bones in upper appendicular

  • 62 bones in lower appendicular

• Includes pectoral girdle (arm attachment), arms, pelvic girdle (leg attachment), and legs

Compare and contrast the axial and appendicular skeletons