Unit I: Framework

Bone Structure

Chapter 6

The Human Skeleton

Advantage Disadvantage

Weight

Structure

Number of Bones

Bone Shapes

Figure 6.1 1

Long Bones• long and slender

• serve as levers to produce movement Humerus

Humerous

Radius

Ulna

Metacarpals

Phalanges

Femur

Tibia

Fibula

Metatarsals

Bone Shapes

Figure 6.1 1

Flat Bones• thin, roughly parallel surfaces

• provide protection and surface area for the attachment of skeletal muscles.

Parietal bone

Cranial

Ribs

Sternum

Scapula

Pelvis

Bone Shapes

Figure 6.1 1

Short BonesCarpalbones

•small and boxy

• movement in multiple directions

Tarsals

Carpals

Bone Shapes

Figure 6.1 1

Sesamoid Bones• small, flat, sesame seed shaped

• develop inside tendons

• knees, hands, and feet

Patella

Bone Shapes

Figure 6.1 1

Sutural Bones• small, flat, irregularly shaped

• between the flat bones of the skull

Suturalbone

Sutures

Bone Shapes

Figure 6.1 1

Irregular Bones• complex shapes

Vertebra

Vertebrae

Facial bones

Bone Structure

• Osseous tissue (bone) is a connective tissue

• Hardened by calcification/mineralization

• Ossification

• Osteogenesis

• “Bone” can include many other types of tissues

• Bone is a composite for strength and flexibility

• Collagen – strong and flexible

• Minerals – rigid

Osteoporosis:• Loss of bone mass compromises normal function• ↓ osteoblast activity• Impacted by other systems: Endocrine, Integumentary, Digestive, Muscle

Diaphysis – shaft

Epiphysis – enlarged ends

Metaphysis – found between the diaphysis and epiphysis

Bone Structure

• Compact bone – strength

• Spongy bone - lightweight

• Medullary cavity –

•Red marrow –

•Yellow marrow –

Bone Structure

• Nutrient Foramen – allows nutrients and blood vessels passage

•Articular cartilage – hyaline cartilage covering the joint surface

• Periosteum – external sheath bone covering

• Epiphyseal plate/line – zone of growth

Bone Development

1. Intramembranous Ossification

2. Endochondral Ossification

Intramembranous Ossification

• Produces the flat bones of the skull and the clavicle

Connective Tissue

Site of future bone

Membrane-like layers of connective tissue form at sites of future bones.

Some of the connective tissue cells enlarge and differentiate into osteoblasts.

Osteoblasts on inside of periosteum form compact bone.

Cells of the membrane-like layer of connective tissue that remain outside the developing bone give rise to the periosteum.

Endochondral Ossification

• Most bones of the skeleton develop this way

• Bones develop from an existing model made of hyaline cartilage

Bone Remodeling

• Osteoprogenitor – stem cells divide to produce osteoblasts

• Osteoblasts – deposit new tissue, produces collagen fibers

• Osteoclasts – remove matrix

• Regulated by hormones: Parathyroid, Calcitonin, Calcitriol

Figure 6 Section 2

Composition of Bone Bone Contains …

99% of the body’s calcium

4% of the body’s potassium

35% of the body’s sodium

50% of the body’s magnesium

80% of the body’s carbonate

99% of the body’s phosphate

Calcium 39%

Potassium 0.2%

Sodium 0.7%

Magnesium 0.5%

Carbonate 9.8%

Phosphate 17%

67%Total inorganiccomponents

Organiccompounds

(mostly collagen)33%

Intestines absorb calciumand phosphate ions from the diet.

Rate of absorption ishormonally regulated.

Normal Ca2+

levels inplasma

Kidneys excrete calcium and phosphate ions in the urine.

Rate is hormonally regulated.

Bone

In the skeleton, osteoblasts and osteoclasts are working simultaneously.

Rate is hormonally regulated.

Homeostasis

• Disturbances can disrupt the functioning of the nervous and muscular systems in particular.

– Hypercalcemia

– Muscle weakness and sluggish reflexes

– Hypocalcemia

– Muscle spasms and tremors

Factors That Increase Blood Calcium Levels

Secrete parathyroid hormone (PTH).

(below 8.5 mg/dL)Low Calcium Ion Levels in Plasma

Parathyroid Gland Response

Osteoclast

Bone

•stimulates osteoclasts

•accelerates erosion of bone matrix

Enhances thecalcium-absorbingeffects of calcitriolon the intestines.

Increases renal production of calcitriol,which iscontinuously secreted at low levels.

PTH

more

calcitriol

Calcium released Calcium absorbed quickly Calcium conserved

Less calcium lostin urine

Ca2+

levels inplasma increase

Bone Response Intestinal Response Kidney Response

Figure 6.9 1

Figure 6.9 2

Factors That Decrease Blood Calcium Levels

Bone Response Intestinal Response Kidney Response

High Calcium Ion Levels in Plasma(above 11 mg/dL)

Thyroid Gland Response

C cells secrete calcitonin.

Calcitonin

• Inhibits osteoclasts

• osteoblasts continue todeposit calcium withinthe matrix of bones.

Bone

less

calcitriol

Decrease inthe rate ofcalcium ionabsorptionfrom theintestinalcontents.

Inhibitory effect: Suppresses calcium ion reabsorption.

Calcium storedCalcium absorbed slowly Calcium excreted

More calcium lostin urine

Ca2+

levels inplasma decrease