A & P Chapter 7

Skeletal System

Bones

Organs of the skeletal system, composed of many tissues. Alive and multifunctional.

Bones are composed of

Bone tissue
Cartilage
Dense connective tissue
Blood
Nervous tissue

Bone functions

Provide shape to body.
Support and protect softer tissues.
Provide points of attachment for muscles, aiding in movement.
House blood-producing cells.
Store inorganic salts.
Store triglycerides.

Bones vary greatly in

size and shape.

Bones are similar in

Structure, development, and function.

Bone Classification by Shape

Long, short, flat, or irregular.

Long bones

Long and narrow, have expanded ends.

Short bones

Cube-like. Length = width.
Includes sesamoid (round) bones.

Flat Bones

Plate-like with broad surfaces.

Irregular Bones

Variety of shapes, usually connected to several other bones.

Sesamoid bones

Round, type of short bone. Embedded in tendons.

Epiphysis

Expanded end of a long bone.

Diaphysis

Bone shaft of long bone.

Metaphysis

Between diaphysis and epiphysis of long bone, widening part.

Articular cartilage

covers the epiphysis

Periosteum

Encloses the bone; dense connective tissue. Enables bone growth in diameter. Assists in fracture repair. Inflammation causes shin splints.

Compact (cortical) bone

Makes up wall of diaphysis. External portion of all bones. Haversian system.

Haversian system

Osteons. Closely packed unit of structure of the compact bone. Regular pattern of bone formation around blood vessels.

Spongy (cancellous) bone

Irregular lattice work of thin plates of bone. Makes up epiphyses of long bones. Found in in short, flat, and irregular bones. Filled with red bone marrow.

Trabeculae

branching bony plates, make up spongy bone

Medullary cavity

Hollow chamber in diaphysis; contains yellow bone marrow.

Endosteum

Thin membrane that lines the medullary cavity. Contains bone-forming cells. 

Bone marrow

Red or yellow, lines medullary cavity, spongy bone spaces.

Red bone marrow

Responsible for blood cell production. Red blood cells, white blood cells, platelets.

Yellow bone marrow

Contains adipose cells that store triglycerides. Potential chemical energy reserve.

Osteogenic Cells

Stem cells that undergo cell division to become osteoblasts.

Osteoblasts

Bone-building cells that become osteocytes. Trapped in own secretions by surrounding extracellular matrix.

osteocytes

mature bone cells

lacunae

The chambers that osteocytes occupy

canaliculi

Tiny passageways where osteocytes exchange nutrients and wastes via cell processes

extracellular matrix of bone

consists of collagen fibers (resilience) and inorganic salts (hardness)

Compact Bone Traits

Consists of cylindrical units called osteons. Strong and solid. Weight-bearing. Resists compression.

Spongy Bone Traits

Consists of branching plates called trabeculae. Somewhat flexible. Has spaces between trabeculae that reduce the bone’s weight.

Compact Bone Composition

Consists of osteons. Osteocytes in lacunae. Osteons cemented together by bone matrix. Lamellae. Perforating canals join adjacent central canals.

Lamellae

layers of matrix around central canal.

Two types of bone development

intramembranous and endochondral bones.

Intramembranous Ossification

Flat skull bones, clavicles, sternum and some facial bones are forming between sheets of primitive connective tissue.

Endochondral Ossification

Long bones and most of skeleton are forming from hyaline cartilage models.

Intramembranous Bone Traits

Originate within sheet-like layers of connective tissue. Broad, flat bones.

Intramembranous Ossification Process

Replacing embryonic connective tissue to form bone.
Mesenchymal cells in primitive tissue differentiate into osteoblasts- bone-forming cells that deposit bone matrix around themselves. When osteoblasts are completely surrounded by matrix, they are now osteocytes in lacunae. Mesenchyme on outside forms periosteum.

Endochondral Ossification Process

Replacing hyaline cartilage to form bone.

Begin as hyaline cartilage models. Chondrocytes (cartilage cells) enlarge, lacunae grow. Matrix breaks down, chondrocytes die. Osteoblasts invade area, deposit bone matrix. Osteoblasts form spongy and then compact bone. Once encased by matrix, osteoblasts are now osteocytes.

Epiphyseal Plate

The part of a long bone where new growth takes place.

Epiphyseal Plate Layers

Zone of resting cartilage.
Zone of proliferating cartilage.
Zone of hypertrophic cartilage.
Zone of calcified cartilage.

Zone of resting cartilage

First layer of the epiphyseal plate, closest to end of epiphysis. Resting cells; anchor epiphyseal plate to epiphysis.

Zone of proliferating cartilage

Second layer of the epiphyseal plate. Rows of young cells, undergoing mitosis.

Zone of hypertrophic cartilage

Third layer of the epiphyseal plate. Rows of older cells left behind when new cells appear. Thicken epiphyseal plate, lengthening the bone. Matrix calcifies, cartilage cells (chondrocytes die).

Zone of calcified cartilage

Fourth layer of the epiphyseal plate. Thin layer of dead cartilage cells and calcified matrix.

Osteoclasts

Cells that break down calcified matrix.

bone can no longer grow in length

when ossification centers meet, and epiphyseal plate ossifies.

Bone can thicken by

depositing compact bone on outside, under periosteum.

Bone can continue to grow in length as long as

cartilage cells of epiphyseal plate remain active.

Ossification- Third month of prenatal development

Ossification in long bones begins.

Ossification- Fourth month of prenatal development

Most primary ossification centers have appeared in the diaphyses of long bones

Ossification- Birth to 5 years

Secondary ossification centers appear in the epiphyses of long bones.

Ossification- 5 to 12/14 years

12 female, 14 male. Ossification rapidly spreads from the ossification centers.

Ossification- 15-18/17-20 years

Bones of the upper limbs and scapulae completely ossified.

Ossification- 16-21/18-23 years

Bones of the lower limbs and hip bones completely ossified.

Ossification- 21-23/23-25 years

Bones of the sternum, clavicles, and vertebrae completely ossified.

Ossification- 23/25 years

Nearly all bones completely ossified.

Bone remodeling

Occurs throughout life. Opposing processes of deposition and resorption occur on surfaces of endosteum and periosteum. 10% to 20% of skeleton is replaced each year.

Bone Resorption

Removal of bone, action of osteoclasts.

Bone Deposition

Formation of bone, action of osteoblasts.

Vitamin D

Calcium absorption; deficiency causes rickets, osteomalacia.

Vitamin A

Osteoblast & osteoclast activity; deficiency retards bone development.

Vitamin C

Collagen synthesis; deficiency results in slender, fragile bones.

Growth Hormone

stimulates cartilage cell division. Insufficiency in a child can result in pituitary dwarfism. Excess causes gigantism in child, acromegaly in adult.

Thyroid Hormone

causes replacement of cartilage with bone in epiphyseal plate, osteoblast activity.

Parathyroid Hormone (PTH)

stimulates osteoclasts, bone breakdown.

Sex Hormones

estrogen, testosterone. Promote bone formation; stimulate
ossification of epiphyseal plates.

Physical Stress

stimulates bone growth

Classification of fractures

Simple (closed) or compound (open)- partial or complete.

Types of Fractures

greenstick, fissured, comminuted, transverse, oblique, spiral

greenstick fracture

Incomplete. The break occurs on the convex surface of the bend in the bone.

fissured fracture

Incomplete longitudinal break.

comminuted fracture

Complete; fragments the bone.

transverse fracture

Complete; the break occurs at a right angle to the axis of the bone.

oblique fracture

Complete; occurs at an angle other than a right angle to the axis of the bone.

spiral fracture

Complete; caused by excessive twisting of a bone.

Steps in Fracture Repair

Hematoma
Cartilaginous callus
Bony callus
Remodeling

Hematoma

First step of fracture repair. Large blood clot.

Cartilaginous callus

Second step of fracture repair. Phagocytes remove debris, fibrocartilage invades.

Bony callus

Third step of fracture repair. Osteoblasts invade, hard callus fills space.

Remodeling

Fourth step of fracture repair. Osteoclasts remove excess bony tissue, restores close to original shape. Old bone tissue is also replaced with new bone tissue throughout life.

Hematopoiesis

Blood cell formation. Occurs in red bone marrow. Red blood cells, white blood cells, and platelets.

About 70% of bone matrix

consists of inorganic mineral salts.

Most abundant bone salt is

hydroxyapatite (calcium phosphate).

Other bone salts include

Magnesium, Sodium, Potassium, Carbonate.

Osteoporosis

a condition that results from loss of bone mineralization.

blood calcium level is regulated by

Parathyroid hormone and Calcitonin.

calcium is vital in

nerve impulse conduction and muscle contraction

Fragility Fracture

Fracture that occurs after a fall from less than standing height; a sign of low bone density.

Age density reduces with age because

Osteoclasts remove more bone tissue than osteoblasts deposit.

Number of bones in the adult skeleton

About 206. Some people have extra bones, while others lack certain bones.

skull

Composed of 22 bones typically. Bones are interlocked along sutures, except the lower jaw (mandible).

Major Sutures of the Cranium

Coronal.
Sagittal.
Squamous.
Lambdoid.

Fontanels

Soft spots. Fibrous membranes connect cranial bones, where intramembranous ossification is incomplete in infants.

Vertebral Column

Forms vertical axis of skeleton. 33 separate bones in infant, 26 in adult.

4 Curvatures of Vertebral Column

Cervical curvature (secondary).
Thoracic curvature (primary).
Lumbar curvature (secondary).
Sacral curvature (primary).

Parts of vertebrae

Body.
Pedicles.
Laminae.
Spinous process.
Transverse processes.
Vertebral foramen.
Facets.
Superior and inferior articular processes.

Herniated or Ruptured (protruding) disc

break in the outer portion of an intervertebral disc; compresses spinal nerves, causing numbness, pain, loss of muscle function.