Skeletal System

OverviewChapter 7

p. 192 – p. 204

What makes up bone?

Osteocytes (bone forming cells) and extracellular matrix Osteocytes are found in lacunae

(holes in the bony matrix) Extracellular matrix is made up of

collagen and inorganic salts (nonliving)

What tissues are associated with bone?

What tissues are associated with bone?

Cartilage Dense connective tissue Blood Nervous tissue

Types of Bones

Long bones Short bones Flat bones Irregular bones Sesamoid bones

Long Bones Epiphysis Articular Cartilage Diaphysis

Spongy bone Compact bone

Parts of the Long Bone Periosteum

Vascular, fibrous outer covering of bone

Endosteum Lines medullary cavity Contains bone forming cells

Medullary Cavity Hollow region of bone Continuous with the spongy bone Marrow, blood vessels found here Adults: yellow marrow

Spongy Bone Trabeculae: branching bony

plates Space between the bony

plates allows for cushion

Spongy bone is usually found at the ends of long bones

In adults: red marrow found here

Compact Bone

Made up of osteons Circular units with central blood vessels

and nerves Also called Haversian systems Resists compression Run parallel with the diaphysis Canaliculi connect osteocytes

Allow for the transport of nutrients and waste

Compact Bone

Made up of osteons Circular units with central blood vessels

and nerves Also called Haversian systems Resists compression Run parallel with the diaphysis Canaliculi connect osteocytes

Allow for the transport of nutrients and waste

Volkmann’s canals Also known as perforating canals Contain blood vessels and nerves Communicate with surface of the bone Run perpendicular to the diaphysis

Osteon

Volkmann’s Canals

Short Bones Make up hands and feet

Flat Bones Scapula (shoulder blade) Skull Ribs

Irregular Bones Vertebrae Facial bones

Sesamoid Bones

Not always a separate category

Round bones Patella

Bone Marrow

Bone Development

Osteogenesis: development of bone Intramembranous Bone (flat bones)

Unspecialized cells appear at site of new bone formation

Blood vessels move into these cells and allow cells to differentiate into osteoblasts Deposit bony matrix to form

spongy bone Spongy bone would fill in with

higher amounts of bony matrix to form compact bone

Bone Development

Endochondral Bones Develop from masses of hyaline

cartilage Hyaline cartilage lays down basic bone

layout Over time, bone forms over the cartilage

template Osteoblasts form and secrete bony

matrix Once bony matrix surrounds the

osteoblasts, they are called osteocytes Endochondral ossification

Bone Development

Primary ossification center Bone begins to replace hyaline

cartilage in the diaphysis Osteoblasts in periosteum deposit

compact bone Secondary ossification centers

Epiphyses Spongy bone

Epiphyseal plate – zone of cartilage between diaphysis and epiphysis

Bone Development

Growth at the Epiphyseal Plate 4 layers

Resting cartilage No growth Closest to the epiphysis

Proliferating cartilage Young cells, mitosis

Zone of hypertrophic cartilage Older cells

Zone of calcified cartilage Dead cells and extracellular

matrix

Growth at the Epiphyseal Plate

http://www.gla.ac.uk/ibls/US/fab/tutorial/generic/bone5.html

Osteoclasts

Invade areas of calcified cartilage Break down extracellular matrix Osteoblasts then move in

Deposit bony matrix in place of calcified cartilage

Ossification Timetable (p. 200)Age Occurrence3rd month of prenatal development

Ossification of long bones begins

4th month of prenatal development

Primary ossification centers are present in long bones

Birth to 5 years Secondary ossification centers present

F: 5-12 years; M: 5-14 years Ossification rapid through ossification centers

F: 15-18 years; M: 17-20 years Bones of upper limb/scapulae completely ossified

F: 16-20 years; M: 18-23 years Lower limbs and hips completely ossified

F: 21-23 years; M: 23-25 years Sternum, clavicles, vertebrae completely ossified

F: by 23; M: by 25 Nearly all bones are completely ossified

Bones under the microscope

Osteoporosis

Stages of Human Bone Development

Infant

Less than one year old Approximately 300 bones (small bones

have not fused yet) Skull much larger than body

Bones are not fused Smaller pelvis

Toddler

1 – 2 years Begin teeth growth Ossification of bones

Youngster

Ages 3 – 9 Bones complete fusion Cervical vertebrae thicken Lower jaw thickens Skull becomes rounder, less elongated Increase in teeth number Ribs ascend Pelvis broadens

Youth

Ages 10 – 13 Angular jaw More teeth Longer neck Sacrum shorter Fibula separates farther from tibia

Adolescent / Young Adult

Ages 14 – 25 pelvis wider at the top Rib cage elongates Vertebrae thicken Growth plates close

Adult

26+ Mature bones Back curves Sharp ridges on neck Rough edges on bone

High amounts of deposits Hip angle increases (more triangular) Heel bone extends Vertebrae begin to shrink

Adult with Osteoporosis

Vertebrae shrink Pronounced curvature of

the back Bone becomes brittle,

breaks easily

Skull Development

Work with a partner to answer the following question:

How does the skull change from birth to adulthood? Why?

Summarize the changes in each stage of life.

Factors Effecting Bone Growth and Repair

Nutrition Exposure to sunlight Hormones Physical exercise

Work with a partner to research a factor effecting bone growth and it’s effect on development

Look up a bone growth disorder, too. (Brief!)

Fractures

Greenstick – incomplete, across bone (usually in developing bone)

Fissured – incomplete, longitudinal Comminuted – complete, shatters the bone Transverse – complete, right angle to bone

axis Oblique – at an angle other than a right

angle Spiral – caused by excessive twisting of the

bone Compound – bone breaks the skin

Fractures

Bone Repair

Hematoma forms (blood released from vessels within the bone)

Formation of spongy bone and fibrocartilage

Bony callus Osteocytes, osteoblasts and

osteoclasts

Functions of the Skeletal System

Support and Protection Movement

Origin and insertion of muscle Origin: immovable end of the muscle Insertion: movable end – during

contraction, insertion will move toward the origin

Functions of the Skeletal System

Blood production Hematopoiesis Bone marrow – long

bones, spongy bone, larger canals of compact bone

Red marrow: produces red blood cells, white blood cells and platelets

White marrow: fatty tissue

Functions of the Skeletal System

Inorganic salt storage Salts account for approximately 70%

of extracellular matrix of bone Mostly calcium phosphate –

hydroxyapatite Also: magnesium, sodium,

potassium, carbonate ions Will also absorb small amounts of

harmful metallic elements (lead, strontium)