Skeletal System

Chapter 6

Objectives

1. Identify the different structures and fuctions of the Skeletal system.

2. Label a long bone and internal structures of bone.

3. Explain bone development and growth.4. Apply knowledge of homeostatic

mechanisms to explain the regulation of blood calcium levels.

Introduction

• Bones are very active tissues• Each bone is made up of several types of

tissues and is an organ

Skeletal System Components

• Bone• ________________-

connect bones to muscle

• ________________-connect bones to bones

Functions

• ___________________ attachment

• Protection• Contain ___________-

producing cells• Storage of inorganic salts• Passageway for

___________ & blood vessels

Types of Bone Tissue

• _____________________ bone: homogeneous

• _________________ bone: small needle-like pieces of bone; many open spaces

Classification of Bones

Long Bones • Characteristics: Typically

_________________ than they are ______________, have a shaft with heads at both ends

• Structure: contain mostly ____________________ bone

• Examples: – Humerus, Femur, Ulna, Radius,

Clavicle, Phalanges

Short Bones

• Characteristics: Generally _________________-shaped

• Structure: contain mostly ___________________ bone

• Examples: – ______________ bones– Foot bones

Flat Bones • Characteristics:

_____________, flattened, and usually __________________

• Structure: two thin layers of _________________ bone surrounding a layer of _______________ bone

• Example:– Scapula – Sternum

Irregular Bones

• Characteristics: ___________________ shape, do not fit into other bone classification categories

• Example:– ____________________– vertebra

Bone Classification

• Sesmoid

Long Bone Anatomy

Bone Structure• Bones differ in size and shape, yet are similar in

several ways• Parts of a long bone– _________________________ – expanded ends of

bones that form _________________ with adjacent bones

– _______________________ cartilage (hyaline cartilage) – covers the epiphysis

– _________________________ – the shaft of the bone– _______________________________ – a tough layer of

vascular connective tissue that covers the bone and is continuous with ligaments and tendons

Parts of a long bone• A bone’s shape makes possible its function• Bony ________________________ or grooves

indicate places of attachment for muscles• ____________________ bone makes up the wall of

the ______________________• The ______________________ are filled with

__________________ bone to reduce the weight of the skeleton

• The diaphysis contains a hollow medullary cavity that is filled with _______________________

Microscopic Structure

• Compact (Cortical) Bone: __________________ and layers of ECM are concentrically clustered around a ________________________ Canal (Osteon). – Haversian Canals contain

_______________ vessels and nerve fibers which nourish the bone cells.

Microscopic structure

• ________________________ – bone cells that are located within ______________________ that lie in concentric circles around osteonic canals

• Intercellular material consists of _______________________ and inorganic _________________

• In compact bone, osteocytes and intercellular material are organized into ___________________ that are cemented together.

Microscopic structure

• __________________________________ contain blood vessels and nerve fibers and extend longitudinally through bone.

• Osteonic canals are interconnected by transverse perforation canals.

• Unlike __________________ bone, the osteocytes and intercellular material in ____________________ bone are not arranged around osteonic canals.

Microscopic structure

Microscopic Structure

Bone Growth and Development

• Osteoclasts – break down cartilage and bone• Osteoblasts – bone-building cells• Osteocytes – bone cells

Bone Development

• Intramembranous Bones:– Originate between

sheetlike layers of connective tissue.

• Endochondral Bones:– Begin as masses of

cartilage that bone tissue replaces.

Bone Development

• Intramembranous Ossification:1. Connective tissue appears at the sites of future bones. 2. Connective tissue cells differentiate into osteoblasts.3. Osteoblasts deposit bony material around themselves and form spongy bone.4. Membranous tissue cells give rise to the periosteum.5. Osteoblasts inside the periosteum form compact bone.

Intramembranous Bones

Bone Development• Endochondral Ossification (Condensed Version):

1. Cartilage breaks down in the center of the diaphysis. (primary ossification center)

2. Periosteum forms around the developing dipahysis from connective tissue.3. Blood vessels and osteoblasts from periosteum invade the cartilage and

form spongy bone.4. Epiphysis remain cartilaginous and later secondary ossification centers

appear and form spongy bone.5. Epiphyseal plate undergoes mitosis and produces new cells which enlarge ,

while calcium salts accumulate in the extracellular matrix, they calcify, and the cartilage cells die.

6. Osteoclasts secrete acid that dissolves part of the calcified matrix and osteoblasts deposit new bone tissue in place of the calcified cartilage.

7. Bone continues to grow at the epiphyseal plate until adulthood.

Endochondral Ossification

Objectives

• To explain the different functions of bone in detail.

• To apply your knowledge of homeostasis and negative feedback loops to explain hormonal regulation of bone calcium resorption and deposition.

Bone Functions

• Support and Protection– Bones give shape to the head, thorax, and limbs– The pelvis and lower limbs provide support for the

body– Bones of the skull protect the brain, ears and eyes

• Movement– Muscles attach to bones– Push and pull bones for movement

Bone Functions• Blood cell Formation– Two kinds of marrow occupy the medullary cavities of

bone• Red marrow – formation of red blood cells, white blood cells

and platelets• Yellow marrow – stores fat

• Storage of Inorganic Salts– Bone stores inorganic mineral salts in the form of

calcium phosphate– Calcium in bone is a reservoir for body calcium• When blood levels of calcium are low, osteoclasts release

calcium from bone.• Calcium is stored in bone under the influence of calcitonin

when blood levels of calcium are high.

Hematopoiesis

• Hematopoeiesis=Red blood cell formation• RBC’s form in the liver, spleen, and bone marrow– Red Marrow:

• Found in infants as well as in spongy bone of skull, ribs, sternum, clavicles, vertebrae, and hip bones of adults

• Produces red blood cells (erythrocytes), white blood cells (leukocytes), and platelets.

– Yellow Marrow:• In adults• Stores fat• *doesn’t produce RBC’s

Inorganic Salt Storage

• ECM of bone is rich in calcium• Calcium is required for muscle contraction,

nerve impulse conduction, blood clotting, and other physiological processes.

• Our bodies must maintain a sufficient blood-calcium level using a homeostatic mechanism.

Calcium Regulation

Low calcium levels

• Causes Parathyroid Hormone (PTH) to be released– PTH causes stored calcium in bone to be released– PTH causes calcium reabsorption in the kidney

(not excreted in urine)– PTH causes the synthesis of Vit. D. which increases

Ca+ absorption in the small intestines.

High calcium levels

• Causes the release of calcitonin from the thyroid gland– Calcitonin Inhibits Ca2+ absorption by the

intestines– Inhibits osteoclast activity in bones– Inhibits renal tubular cell reabsorption of Ca2+

allowing it to be excreted in the urine

Hypo vs. Hypercalcemia

• Hypocalcemia: can cause muscle stiffness and seizures

• Hypercalcemia: too much calcium, causes kidney stones or even kidney failure, could cause heart problems

Bone Fractures

• Definition: 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• Treatment: reduction and immobilization

Common types of Fractures

Repair of Bone fractures

• Steps in repair of bone fractures 1. Hematoma: blood-filled swelling is formed2. Fibrocartilage callus: break is connected by

fibrocartilage3. Bony Callus: fibrocartilage replaced by

spongy bone4. Bone remodeling: permanent healing

Repair of Bone fractures

Hematoma

Externalcallus

Bonycallus ofspongybone

Healedfracture

Newbloodvessels

Internalcallus(fibroustissue andcartilage)

Spongybonetrabecula

Hematomaformation

Fibrocartilagecallus formation

Bony callusformation

Bone remodeling

Curve of the Spine

• The spine has a normal curvature• Primary curvatures: curvatures of the thoracic

and sacral regions– Present from birth

• Secondary curvatures: spinal curvatures of the cervical and lumbar regions– Develop after birth

Skeletal changes throughout life

• Osteoporosis– Bone-thinning disease afflicting • 50% of women over age 65• 20% of men over age 70

– Disease makes bones fragile and bones can easily fracture

– Vertebral collapse results in kyphosis (also known as dowager’s hump)

– Estrogen aids in health and normal density of a female skeleton

Skeletal changes throughout life

Skeletal changes throughout life

Objectives

• To Identify the major bones of the skull. • To label the major features of the bones of the

skull.

Skeletal Organization

• Axial Skeleton– Consists of the skull, hyoid bone, vertebral column

and thorax (ribs and sternum)• Appendicular Skeleton– Consists of the pectoral girdle (scapula and

clavicle), upper limbs, pelvic girdle (coxal bones) and lower limbs

Skeletal Organization

The Skull!!

• Structure: made up of two sets of bones– Cranium– Facial bones

• Bones are joined by sutures

Human Skull, Lateral View

Human Skull, Superior View

Human Skull, Inferior View

Human Skull, Anterior View

Paranasal Sinuses

• Structure: hollow portions of bones surrounding the nasal cavity

• Functions:– Lighten the skull– Amplify voice

Paranasal Sinuses

The Vertebral Column

• Structure: 24 single vertebral bones separated by intervertebral discs– Cervical vertebrae: 7 in neck– Thoracic vertebrae: 12 in chest region– Lumbar vertebrae: 5 in lower back– Sacrum and coccyx: 9 fused vertebrae in gluteal

region

The Vertebral Column

Superior view of vertebrae

Atlas and Axis

• Structure: most superior vertebrae– Atlas: C1– Axis: C2

• Function: form joint connecting skull and spine; allow for movement of head

Regional characteristics of vertebrae

Regional characteristics of vertebrae

Regional characteristics of vertebrae

Regional characteristics of vertebrae

Sacrum and coccyx

The Bony Thorax

• Structure: made of three parts1. Sternum2. Ribs• True ribs (pairs 1-7)• False ribs (pairs 8-12)• Floating ribs (pairs 11-12)

3. Thoracic vertebrae • Function: forms a cage to protect major

organs

The Bony Thorax

Male and Female Pelvis

• Differences in male and female pelvis aid in childbirth– Female inlet is larger and more cicular– Female pelvis as a whole is shallower and the bones

are lighter and thinner– Female ilia flare more laterally– Female sacrum is shorter and less curved– Female ischial spines are shorter and further apart– Female pubic arch is more founded because the angle

of the pubic arch is greater

Joints

• The functional junctions (articulations) between bones

• Enable a wide variety of body movements• Can be classified according to the degree of

movement possible:– Immovable– Slightly movable– Freely movable

Joints

• Can also be classified according to the type of tissue that binds them together:– Fibrous– Cartilaginous– Synovial

Fibrous Joints• Held together by dense

connective tissue• Immovable or only

slightly moveable– Examples:• Sutures of the skull

(immovable)• Joint between the

distal tibia and fibula (slightly movable)

Cartilaginous Joints

• Hyaline cartilage or discs of fibrocartilage unite the bones in cartilaginous joints– Example: intervertebral

disks

Synovial Joints • Makes up most joints of the skeletal• More complex than fibrous or cartilaginous

joints• Articular ends of bone in a synovial joint are

covered with hyaline cartilage• Articulating surfaces within the joint are

lubricated with synovial fluid• Are classified (and named) based on the

shapes of their parts and the movements they permit

Ball and Socket Joint• Consists of a bone with

a globular or egg-shaped head articulating with the cup shaped cavity of another bone

• Permits a very wide range of motion

• Examples:– Hip and Shoulder Joints

Condyloid Joint

• Consists of an ovoid condyle fitting into an elliptical cavity

• Permits a wide variety of motions

• Example:– Joint between a

metacarpal and a phalange

Gliding Joints

• Occur where articulating surfaces are nearly flat or slightly curved

• Permits a “back and forth” motion

• Example:– Joints of the wrist and

ankle

Hinge Joint

• Occurs where a convex surface fits into a concave surface

• Movement is in one plane only

• Example:– Elbow and phalange

joints

Pivot Joint

• Occurs where a cylindrical surface rotates within a ring of bone and fibrous tissue

• Example:– Joint between the

proximal ends of the radius and ulna

Saddle Joint

• Forms where articulating surfaces have both concave and convex areas

• Permits a wide range of movements

• Example:– The metacarpal of the

thumb

Inflammatory Disorders of the Joints

• Bursitis: inflammation of bursa (synovial membrane); water on the knee

Inflammatory Disorders of the Joints

• Sprain– Ligaments or tendons reinforcing joint are

damaged by excessive stretching or are torn away from bone

– Slow to heal because of poor blood supply• Dislocation– When a bone is forced out of normal position in

the joint cavity

Inflammatory Disorders of the Joints

• Arthritis– Most widespread, crippling disease in the U.S.– 1 in 7 Americans suffer with it– Initial symptoms: Pain, stiffness, and swelling of

the joint– Acute and Chronic forms of Arthritis

Inflammatory Disorders of the Joints

• Acute Arthritis– Result from bacterial invasion– Treated with antibiotic– Synovial membrane thickens and fluid production

decreases, leading to increased friction and pain

Inflammatory Disorders of the Joints

• Chronic Arthritis – Osteoarthritis

• Most common form• Degenerative condition, usually affects the aged• Wear and tear affects• Can cause bone spurs which restrict joint movement

– Rheumatoid arthritis• Occurs between 40-50 years of, but can occur at any age• Affects more women than men• Many joints affected at the same time and usually in symmetrical manner

(left elbow then right elbow)• Marked by remission (goes away) and flare ups (comes back)• Autoimmune disease – body attacks its own tissues

– Gouty arthritis