Skeletal System

Author: Chris Kaboo

July 23rd, 2021

Fundamentals of Anatomy & Physiology

Eleventh Edition

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Skeletal System

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Chapter 6

Bones and Bone Structure

Lecture Presentation by

Deborah A. Hutchinson

Seattle University

Learning Outcomes

6-1 Describe the major functions of the skeletal system.

6-2 Classify bones according to shape and structure, giving examples of each type, and explain the functional significance of each of the major types of bone markings.

6-3 Identify the cell types in bone, and list their major functions.

6-4 Compare the structures and functions of compact bone and spongy bone.

6-5 Compare the mechanisms of endochondral ossification and intramembranous ossification.

Learning Outcomes

6-6 Describe the remodeling and homeostatic mechanisms of the skeletal system.

6-7 Discuss the effects of exercise, nutrition, and hormones on bone development and on the skeletal system.

6-8 Explain the role of calcium as it relates to the skeletal system.

6-9 Describe the types of fractures, and explain how fractures heal.

6-10 Summarize the effects of the aging process on the skeletal system.

6-1 Functions of Skeletal System

Skeletal system includes

Bones of the skeleton

Cartilages, ligaments, and other connective tissues

6-1 Functions of Skeletal System

Primary functions of the skeletal system

Support

Storage of minerals and lipids

Blood cell production

Protection

Leverage

6-2 Classification of Bones

Bones are classified by their

Shape

Structure

6-2 Classification of Bones

Bone shapes

Sutural

Irregular

Short

Flat

Long

Sesamoid

Figure 6–1 A Classification of Bones by Shape.

Sutural Bones

Sutural bone

Sutural bones, or

Wormian bones, are

small, flat, oddly

shaped bones found

between the flat bones

of the skull. They range

in size from a grain of

sand to a quarter. Their

borders are like pieces

of a jigsaw puzzle.

Posterior view

Flat Bones

Flat bones have thin, parallel surfaces. Flat

bones form the roof of the skull, the sternum

(breastbone), the ribs, and the scapulae

(shoulder blades). They provide protection for

underlying soft tissues and offer an extensive

surface area for the attachment

of skeletal muscles.

Parietal bone

Sectional

view

Irregular Bones

Irregular bones have

complex shapes with

short, flat, notched, or

ridged surfaces. The

vertebrae that form the

spinal column, the bones

of the pelvis, and several

bones in the skull are

examples of irregular bones.

Long Bones

Long bones are relatively

long and slender. They are

located in the arm and

forearm, thigh and leg,

palms, soles, fingers, and

toes. The femur, the long

bone of the thigh, is the

largest and heaviest bone in

the body.

Vertebra

Humerus

Short Bones

Short bones are

boxlike in

appearance.

Examples of short

bones include the

carpal bones (wrists)

and tarsal bones

(ankles).

Sesamoid Bones

Carpal

bones

Patella

Sesamoid bones are

usually small, round, and

flat. They are found near

joints of the knees, hands,

and feet. Few people have

sesamoid bones at every

possible location, but

everyone has sesamoid

patellae (pa-TEL-ē;

singular, patella, a small

shallow dish), or kneecaps.

Sutures

6-2 Classification of Bones

Sutural bones (Wormian bones)

Small, flat, irregularly shaped bones

Between flat bones of the skull

Number varies among individuals

Irregular bones

Have complex shapes

Examples: spinal vertebrae, pelvic bones

Figure 6–1a A Classification of Bones by Shape.

Sutural Bones

Sutural bone

Sutural bones, or

Wormian bones, are

small, flat, oddly shaped

bones found between

the flat bones of the

skull. They range in size

from a grain of sand to a

quarter. Their borders

are like pieces of a

jigsaw puzzle.

Sutures

Posterior view

Figure 6–1b A Classification of Bones by Shape.

Irregular Bones

Irregular bones have

complex shapes with

short, flat, notched, or

ridged surfaces. The

vertebrae that form the

spinal column, the bones

of the pelvis, and several

bones in the skull are

examples of irregular bones.

Vertebra

6-2 Classification of Bones

Short bones

Boxy

Examples: carpal bones and tarsal bones

Flat bones

Thin with parallel surfaces

Examples: bones of skull roof, sternum, ribs, and scapulae

Figure 6–1c A Classification of Bones by Shape.

Short Bones

Short bones are

boxlike in

appearance.

Examples of short

bones include the

carpal bones

(wrists) and tarsal

bones (ankles).

Carpal

bones

Figure 6–1d A Classification of Bones by Shape.

Flat Bones

Flat bones have thin, parallel surfaces. Flat bones

form the roof of the skull, the sternum (breastbone),

the ribs, and the scapulae (shoulder blades). They

provide protection for underlying soft tissues and

offer an extensive surface area for the attachment

of skeletal muscles.

Parietal bone

Sectional

view

6-2 Classification of Bones

Long bones

Long and slender

Found in arms, legs, palms, soles, fingers, toes

Sesamoid bones

Usually small, round, and flat

Develop within tendons near joints of knees, hands, and feet

Location and number vary between individuals

Example: patellae

Figure 6–1e A Classification of Bones by Shape.

Long bones are relatively

long and slender. They are

located in the arm and

forearm, thigh and leg,

palms, soles, fingers, and

toes. The femur, the long

bone of the thigh, is the

largest and heaviest bone in the body.

Humerus

Long Bones

Figure 6–1f A Classification of Bones by Shape.

Sesamoid Bones

Patella

Sesamoid bones are

usually small, round, and

flat. They are found near

joints of the knees, hands,

and feet. Few people have

sesamoid bones at every

possible location, but

everyone has sesamoid

patellae (pa-TEL-ē;

singular, patella, a small

shallow dish), or kneecaps.

6-2 Classification of Bones

Bone markings (surface features)

Projections

Where muscles, tendons, and ligaments attach

At articulations with other bones

Openings and depressions

For passage of blood vessels and nerves

Figure 6–2 An Introduction to Bone Markings (Part 1 of 2).

Openings

Sinus:

Chamber within

a bone, normally

filled with air

Projections

Process:

Projection or

bump

Ramus:

Part of a bone

that forms an

angle with the

rest of the

structure

Skull, anterior view

Foramen:

Rounded

passageway for

blood vessels

and/or nerves

Fissure:

Deep furrow,

cleft, or slit

Meatus:

Passage or

channel,

especially the

opening of a canal

Canal:

Duct or channel

Skull, lateral view

Figure 6–2 An Introduction to Bone Markings (Part 2 of 2).

Projections where

muscles, tendons, or

ligaments attach

Trochanter:

Crest:

Spine:

Head

Line:

Tubercle:

Pelvis

Neck

Prominent

ridge

Pointed

process

Low ridge

Small,

rounded

projection

Femur

Projections for forming joints

Head:

Expanded articular

end of an epiphysis,

often separated from

the shaft by a

narrower neck (see

Figure 6–3a)

Narrow connection

between the

epiphysis and

diaphysis (see

Figure 6–3a)

Neck:

Depressions

Sulcus:

Narrow

groove

Fossa:

Shallow

depression

Humerus

Tuberosity:

Rough

projection

Facet:

Small, flat

articular surface

Condyle:

Smooth, rounded

articular process

Condyle

Trochlea:

Smooth, grooved

articular process

shaped like a pulley

Large, rough

projection

6-2 Classification of Bones

Structure of a long bone

Diaphysis (shaft)

Wall of compact bone

Central space called medullary cavity (marrow cavity)

Epiphysis (wide part at each end)

Mostly spongy bone (trabecular bone)

Metaphysis

Where diaphysis and epiphysis meet

Figure 6–3a Bone Structure.

Epiphysis

Spongy

bone

Metaphysis

Compact

bone

Medullary

cavity

Diaphysis

(shaft)

Metaphysis

Epiphysis

The structure of a representative

long bone (the femur) in longitudinal

section

6-2 Classification of Bones

Structure of flat bones

For example, parietal bones of the skull

Consist of spongy bone between two layers of compact bone (cortex)

Within the cranium, the layer of spongy bone is called the diploë

Figure 6–3b Bone Structure.

Cortex

(compact bone)

Diploë

(spongy bone)

The structure of a flat bone (the parietal bone)

6-3 Bone Tissue

Bone tissue

Dense, supportive connective tissue

Contains specialized cells

Solid extracellular matrix with collagen fibers

6-3 Bone Tissue

Characteristics of bone

Dense matrix due to deposits of calcium salts

Osteocytes (bone cells) within lacunae organized around blood vessels

Canaliculi

Narrow passageways that allow for exchange of nutrients, wastes, and gases

Periosteum

Covers outer surfaces of bones (except at joints)

Consists of outer fibrous and inner cellular layers

6-3 Bone Tissue

Bone matrix

Calcium phosphate, Ca3(PO4)2 makes up almost two-thirds of bone mass

Interacts with calcium hydroxide, Ca(OH)2, to form crystals of hydroxyapatite, Ca10(PO4)6(OH)2

Incorporates other calcium salts such as calcium carbonate (CaCO3) and ions (e.g., magnesium)

A bone lacking a calcified matrix looks normal, but is very flexible

Figure 6–4 Bone Lacking a Calcified Matrix.

6-3 Bone Tissue

Bone matrix

Matrix proteins

About one-third of bone mass is collagen fibers

6-3 Bone Tissue

Bone cells

Make up only 2 percent of bone mass

Four types

Osteogenic cells

Osteoblasts

Osteocytes

Osteoclasts

Figure 6–5 Types of Bone Cells.

Types of Bone Cells

Endosteum

Osteogenic

cell

Medullary

cavity

Osteogenic cell: Stem

cell whose divisions

produce osteoblasts

Osteoblast: Immature

bone cell that secretes

organic components of

matrix

Medullary

cavity

Ruffled

border

Osteoclast

Matrix

Osteoblast

Osteoid

Matrix

Osteocyte

Canaliculi

Osteocyte: Mature bone

cell that maintains the bone

matrix

Osteoclast: Multinucleate

cell that secretes acids and

enzymes to dissolve bone

matrix

6-3 Bone Tissue

Osteogenic cells (osteoprogenitor cells)

Mesenchymal cells that divide to produce osteoblasts

Located in inner cellular layer of periosteum and in endosteum

Assist in fracture repair

Figure 6–5a Types of Bone Cells.

Endosteum

Osteogenic

cell

Medullary

cavity

Osteogenic cell: Stem

cell whose divisions

produce osteoblasts

6-3 Bone Tissue

Osteoblasts

Immature cells that produce new bone matrix during osteogenesis (ossification)

Osteoid—matrix produced by osteoblasts that has not yet become calcified

Osteoblasts surrounded by bone matrix become osteocytes

Figure 6–5b Types of Bone Cells.

Osteoblast

Osteoid

Matrix

Osteoblast: Immature

bone cell that secretes

organic components of

matrix

6-3 Bone Tissue

Osteocytes

Mature bone cells that do not divide

Live in lacunae between layers of matrix

Have cytoplasmic extensions that pass through canaliculi

Two major functions

Maintain protein and mineral content of matrix

Help repair damaged bone

Figure 6–5c Types of Bone Cells.

Matrix

Osteocyte

Canaliculi

Osteocyte: Mature bone

cell that maintains the

bone matrix

6-3 Bone Tissue

Osteoclasts

Absorb and remove bone matrix

Large, multinucleate cells

Secrete acids and protein-digesting enzymes

Dissolve bone matrix and release stored minerals

This osteolysis is important in homeostasis

Derived from the same stem cells that produce monocytes and macrophages

Figure 6–5d Types of Bone Cells.

Medullary

cavity

Ruffled

border

Osteoclast

Matrix

Osteoclast: Multinucleate

cell that secretes acids and

enzymes to dissolve bone

matrix

6-4 Compact Bone and Spongy Bone

Osteon—functional unit of compact bone

Central canal contains blood vessel(s)

Perforating canals

Perpendicular to surface of bone

Carry blood vessels into deep bone and marrow

Lamellae—layers of bone matrix

Concentric lamellae surround central canal

Interstitial lamellae fill spaces between osteons

Circumferential lamellae are at outer and inner bone surfaces

Figure 6–6 Osteons of Compact Bone.

Osteon

Lacunae

Central canal

Lamellae

Osteons

SEM × 182

Figure 6–7a The Structure of Compact Bone.

Venule

Capillary

Periosteum

Concentric

lamellae

Interstitial

lamellae

Circumferential

lamellae

Osteons

Perforating fibers

Endosteum

Central

canal

Concentric

lamellae

Trabeculae of

spongy bone

(see Figure 6–8)

The organization of osteons

and lamellae in compact bone

Perforating

canal

Central

canal

Arteriole

Vein

Artery

Figure 6–7b The Structure of Compact Bone.

Collagen

fiber

orientation

The orientation of collagen

fibers in adjacent lamellae

of an osteon

6-4 Compact Bone and Spongy Bone

Spongy bone lacks osteons

Matrix forms an open network of trabeculae

Lacks capillaries and venules

Red bone marrow fills spaces between trabeculae

Forms blood cells

Contains blood vessels that supply nutrients to osteocytes by diffusion

Yellow bone marrow

Found in other sites of spongy bone

Stores fat

Figure 6–8 The Structure of Spongy Bone.

Trabeculae of

spongy bone

Canaliculi

opening

on surface

Lamellae

Endosteum

6-4 Compact Bone and Spongy Bone

Weight-bearing bones

Trabeculae in epiphysis of femur transfer forces from pelvis to compact bone of femoral shaft

Medial side of shaft compresses

Causing tension on the lateral side

Figure 6–9 The Distribution of Forces on a Long Bone.

Body weight (applied force)

Tension on lateral

side of shaft

Compression on

medial side of shaft

The femur, or thigh bone, has a diaphysis (shaft) with walls of compact bone and epiphyses filled with spongy bone. The body weight is transferred to the femur at the hip joint. Because the hip joint is off center relative to the axis of the shaft, the body weight is distributed along the bone in a way that compresses the medial (inner) portion of the shaft and stretches the lateral (outer) portion.

6-4 Compact Bone and Spongy Bone

Periosteum—membrane that covers outside of bones

Except within joint cavities

Outer, fibrous layer and inner, cellular layer

Fibers are interwoven with those of tendons

Perforating fibers—fibers that become incorporated into bone tissue

Increase strength of attachments

6-4 Compact Bone and Spongy Bone

Functions of periosteum

Isolates bone from surrounding tissues

Provides a route for blood vessels and nerves

Participates in bone growth and repair

Figure 6–10a The Periosteum and Endosteum.

Circumferential

lamellae

Periosteum

Fibrous layer

Cellular layer

Canaliculi

Osteocyte

in lacuna

Perforating

fibers

The periosteum contains outer (fibrous) and

inner (cellular) layers. Collagen fibers of the

periosteum are continuous with those of the

bone, adjacent joint capsules, and attached

tendons and ligaments.

6-4 Compact Bone and Spongy Bone

Endosteum—incomplete cellular layer that lines medullary cavity

Active during bone growth, repair, and remodeling

Covers trabeculae of spongy bone

Lines central canals of compact bone

Consists of flattened layer of osteogenic cells

Figure 6–10b The Periosteum and Endosteum.

Endosteum

Osteoclast

Bone matrix

Osteocyte

Osteogenic

cell

Osteoid

Osteoblast

The endosteum is an incomplete

cellular layer containing osteoblasts,

osteogenic cells, and osteoclasts.

6-5 Bone Formation and Growth

Bone development

Ossification (osteogenesis)—bone formation

Calcification—deposition of calcium salts

Occurs during ossification

Two forms of ossification

Endochondral ossification

Intramembranous ossification

Some human bones grow until about age 25

6-5 Bone Formation and Growth

Endochondral ossification

How most bones form

Primary ossification center develops inside hyaline cartilage

Cartilage is gradually replaced by bone

Seven main steps

SmartArt Video: Endochondral Ossification

Figure 6–11 Endochondral Ossification (Part 1 of 7).

As the cartilage

enlarges, chondro-

cytes near the center

of the shaft increase

greatly in size. The

matrix is reduced to

a series of small

struts that soon

begin to calcify. The

enlarged chondro-

cytes then die and

disintegrate, leaving

cavities within the

cartilage.

Enlarging

chondrocytes within

calcifying matrix

Hyaline

cartilage

Disintegrating

chondrocytes

of the cartilage

model

Figure 6–11 Endochondral Ossification (Part 2 of 7).

Blood vessels grow

around the edges of

the cartilage, and the

cells of the perichon-

drium convert to

osteoblasts. The

shaft of the cartilage

then becomes

ensheathed in a

superficial layer of

bone.

Perichondrium

Epiphysis

Bone collar

Blood

vessel

Diaphysis

Periosteum

formed from

perichondrium

Figure 6–11 Endochondral Ossification (Part 3 of 7).

Blood vessels penetrate the

cartilage and invade the

central region. Fibroblasts

migrating with the blood

vessels differentiate into

osteoblasts and begin

producing spongy bone at a

primary ossification center.

Bone formation then

spreads along the shaft

toward both ends of the

former cartilage model.

Medullary

cavity

Primary

ossification

center

Superficial

bone

Spongy

bone

Figure 6–11 Endochondral Ossification (Part 4 of 7).

Remodeling occurs as

growth continues,

creating a medullary

cavity. The osseous

tissue of the shaft

becomes thicker, and the

cartilage near each

epiphysis is replaced by

shafts of bone. Further

growth involves increases

in length and diameter.

Medullary

cavity

Metaphysis

Figure 6–11 Endochondral Ossification (Part 5 of 7).

Capillaries and osteoblasts

migrate into the epiphyses,

creating secondary

ossification centers.

Hyaline cartilage

Epiphysis

Metaphysis

Periosteum

Secondary

ossification

center

Compact

bone

Figure 6–11 Endochondral Ossification (Part 6 of 7).

The epiphyses eventually become filled

with spongy bone. The metaphysis, a

relatively narrow cartilaginous region

called the epiphyseal cartilage, or

epiphyseal plate, now separates the

epiphysis from the diaphysis. On the

shaft side of the metaphysis,

osteoblasts continuously invade the

cartilage and replace it with bone. New

cartilage is produced at the same rate on

the epiphyseal side.

Articular cartilage

Spongy

bone

Epiphyseal

cartilage

Diaphysis

Within the epiphyseal cartilage, the

chondrocytes are organized into zones.

Chondrocytes at the

epiphyseal side of the

cartilage continue to

divide and enlarge.

Chondrocytes degenerate

at the diaphyseal side.

Osteoblasts migrate

upward from the diaphysis

and cartilage is gradually

replaced by bone.

Figure 6–11 Endochondral Ossification (Part 7 of 7).

At puberty, the rate of epiphyseal cartilage

production slows and the rate of osteoblast

activity accelerates. As a result, the

epiphyseal cartilage gets narrower and

narrower, until it ultimately disappears.

This event is called epiphyseal closure.

The former location of the epiphyseal

cartilage becomes a distinct epiphyseal

line that remains after epiphyseal growth

has ended.

Articular cartilage

Epiphyseal line

Spongy

bone

Medullary

cavity

A thin cap of the original cartilage

model remains exposed to the joint

cavity as the articular cartilage.

This cartilage prevents damaging

the joint from bone-to-bone

contact.

Figure 6–11 Endochondral Ossification.

6-5 Bone Formation and Growth

Interstitial growth—growth in length

Secondary ossification centers develop

Epiphyseal closure—completion of epiphyseal growth

Width of epiphyseal cartilages reveals timing of endochondral ossification

Former location of epiphyseal cartilage is visible on x-rays as an epiphyseal line

Remains after epiphyseal closure

Figure 6–12a Bone Growth at Epiphyseal Cartilages.

An x-ray of growing epiphyseal cartilages (arrows)

Figure 6–12b Bone Growth at Epiphyseal Cartilages.

Epiphyseal lines in an adult (arrows)

6-5 Bone Formation and Growth

Appositional growth—growth in width

Thickens and strengthens long bones

Layers of circumferential lamellae are added at outer surface

Deepest layers become replaced by osteons

During this process, osteoclasts slowly remove bone matrix at inner surface of bone

Enlarging medullary cavity

6-5 Bone Formation and Growth

Intramembranous ossification

Also called dermal ossification

Because it occurs in the dermis

Produces dermal bones such as mandible (lower jaw) and clavicles (collarbones)

Five main steps

Figure 6–13 Intramembranous Ossification (Part 1 of 5).

Parietal bone

Frontal

bone

Occipital bone

Mesenchymal cells clus-

ter together, differentiate

into osteoblasts, and

start to secrete the

organic components of

the matrix. The resulting

osteoid then becomes

mineralized with calcium

salts forming bone

matrix.

Bone matrix

Osteoid

Mesenchymal cell

Ossification center

Blood vessel

Osteoblast

Mandible

Intramembranous ossification

starts about the eighth week of

embryonic development. This

type of ossification occurs in

the deeper layers of the dermis,

forming dermal bones.

Figure 6–13 Intramembranous Ossification (Part 2 of 5).

As ossification proceeds,

some osteoblasts are

trapped inside bony pockets

where they differentiate into

osteocytes. The developing

bone grows outward from the

ossification center in small

struts called spicules.

Spicules

Osteocyte

Figure 6–13 Intramembranous Ossification (Part 3 of 5).

Blood vessels begin to

branch within the region

and grow between the

spicules. The rate of bone

growth accelerates with

oxygen and a reliable

supply of nutrients. As

spicules interconnect,

they trap blood vessels

within the bone.

Blood vessel

trapped

within bone

matrix

Figure 6–13 Intramembranous Ossification (Part 4 of 5).

Continued deposition of bone

by osteoblasts located close

to blood vessels results in a

plate of spongy bone with

blood vessels weaving

throughout.

Figure 6–13 Intramembranous Ossification (Part 5 of 5).

Areas of spongy bone are

remodeled forming the

diploë and a thin covering

of compact bone.

Subsequent remodeling

around blood vessels

produces osteons typical

of compact bone.

Osteoblasts on the bone

surface along with

connective tissue around

the bone become the

periosteum.

Fibrous periosteum

Compact bone

Blood vessels

trapped within

bone matrix

Spongy bone

Compact bone

Cellular periosteum

6-5 Bone Formation and Growth

Blood supply to bones

Nutrient artery and vein

Most bones have one of each (some have more)

Pass through nutrient foramina in diaphysis

Metaphyseal vessels

Supply blood to epiphyseal cartilages

Where bone growth occurs

Periosteal vessels

Supply blood to superficial osteons

And to secondary ossification centers

Figure 6–14 The Blood Supply to a Mature Bone.

Vessels in Bone

Epiphyseal

artery and vein

Metaphyseal

artery and vein

Articular

cartilage

Branches of

nutrient artery

and vein

Nutrient artery

and vein

Periosteal

arteries and veins

Periosteum

Compact

bone

Medullary

cavity

Nutrient

foramen

Artery and vein in

perforating canal

Metaphyseal

artery and vein

Metaphysis

Epiphyseal

line

6-5 Bone Formation and Growth

Periosteum also contains

Network of lymphatic vessels

Sensory nerves

6-6 Bone Remodeling

Bone remodeling

Occurs throughout life

Functions in bone maintenance

By recycling and renewing bone matrix

Involves osteocytes, osteoblasts, and osteoclasts

Normally, activities are balanced

If removal is faster than replacement, bones weaken

If deposition predominates, bones strengthen

6-7 Exercise, Nutrition, and Hormones

Effects of exercise on bone

Mineral recycling allows bones to adapt to stress

Heavily stressed bones become thicker and stronger

Exercise, particularly weight-bearing exercise, stimulates osteoblasts

Bone degeneration

Bone degenerates quickly

Up to one-third of bone mass can be lost in a few weeks of inactivity

6-7 Exercise, Nutrition, and Hormones

Nutritional and hormonal effects on bone

Minerals

Calcium and phosphorus are required in the diet

Plus small amounts of magnesium, fluoride, iron, and manganese

Calcitriol and vitamin D3

Calcitriol is made in the kidneys

Essential for normal calcium and phosphate ion absorption in digestive tract

Synthesized from vitamin D3 (cholecalciferol)

6-7 Exercise, Nutrition, and Hormones

Nutritional and hormonal effects on bone

Vitamin C is required for collagen synthesis

And it stimulates osteoblast differentiation

Vitamin A stimulates osteoblast activity

Vitamins K and B12 are required for synthesis of bone proteins

6-7 Exercise, Nutrition, and Hormones

Nutritional and hormonal effects on bone

Growth hormone and thyroxine stimulate bone growth

Sex hormones

Estrogen and testosterone stimulate osteoblasts

Parathyroid hormone and calcitonin maintain calcium ion homeostasis

SmartArt Video: The Hormones Regulating Calcium Ion Metabolism

6-8 Calcium Homeostasis

The skeleton as a calcium reserve

Bones store 99 percent of the body’s calcium

In addition to other minerals

Calcium is the most abundant mineral in the body

Calcium ions are vital to many physiological processes

Figure 6–15 A Chemical Analysis of Bone.

Organic

compounds

(mostly collagen)

33%

Total inorganic

components

67%

Composition of Bone

Bone Contains

Calcium 39%

Potassium 0.2%

Sodium 0.7%

Magnesium 0.4%

Carbonate 9.7%

Phosphate 17%

99% of the body’s phosphate

80% of the body’s carbonate

50% of the body’s magnesium

35% of the body’s sodium

4% of the body’s potassium

99% of the body’s calcium

6-8 Calcium Homeostasis

Hormones and calcium ion balance

Calcium ion concentrations in body fluids must be closely regulated

Parathyroid hormone and calcitonin affect storage, absorption, and excretion of calcium ions in

Bones (storage)

Digestive tract (absorption)

Kidneys (excretion)

6-8 Calcium Homeostasis

Parathyroid hormone (PTH)

Produced by parathyroid glands in neck

Increases blood calcium ion levels by

Stimulating osteoclast activity (indirectly)

Increasing intestinal absorption of calcium by enhancing calcitriol secretion by kidneys

Decreasing calcium excretion by kidneys

6-8 Calcium Homeostasis

Calcitonin

Secreted by C cells in thyroid

Decreases blood calcium ion levels by

Inhibiting osteoclast activity

Increasing calcium excretion and reducing calcitriol secretion by kidneys

Decreasing intestinal absorption of calcium

Figure 6–16 Factors That Increase the Blood Calcium Ion Level.

Factors That Increase Blood Calcium Ion Level

These responses are triggered

when blood calcium ion level

decreases below 8.5 mg/dL.

Low Calcium Ion Level in Blood

(below 8.5 mg/dL)

Parathyroid Gland Response

Low calcium level causes the

parathyroid glands to secrete

parathyroid hormone (PTH).

PTH

Bone Response

Osteoclasts stimulated to

release stored calcium

ions from bone

Osteoclast

Bone

Intestinal Response

Intestinal

absorption

of calcium

increases

Kidney Response

Kidneys absorb

calcium ions

calcitriol

Factors That Decrease Blood Calcium Ion Level

Intestinal and kidney

responses are triggered when

blood calcium ion level rises

above 11 mg/dL.

High Calcium Ion Level in Blood

(above 11 mg/dL)

Thyroid Gland Response

C cells in the thyroid

gland secrete calcitonin.

Calcitonin

Bone Response

Osteoclast activity

decreases; osteoblast

activity unaffected

Osteoclast

Bone

Intestinal Response

Intestinal

absorption

of calcium

decreases

Kidney Response

Kidneys

excrete

calcium ions

less

calcitriol

Calcium released

Calcium absorbed

Calcium conserved

Calcium release slowed

Calcium absorbed slowly

Calcium excreted

Ca2+

level in

blood

increases

Decreased calcium

loss in urine

Ca2+

level in

blood

decreases

Increased calcium

loss in urine

Figure 6–16a Factors That Increase the Blood Calcium Ion Level.

Factors That Increase Blood Calcium Ion Level

These responses are triggered

when blood calcium ion level

decreases below 8.5 mg/dL.

Low Calcium Ion Level in Blood

(below 8.5 mg/dL)

Parathyroid Gland Response

Low calcium level causes the

parathyroid glands to secrete

parathyroid hormone (PTH).

PTH

Bone Response

Osteoclasts stimulated to

release stored calcium ions

from bone

Osteoclast

Bone

Intestinal Response

Intestinal

absorption

of calcium

increases

Kidney Response

Kidneys

absorb

calcium ions

calcitriol

Calcium released

Calcium absorbed

Calcium conserved

Ca2+

level in

blood

increases

Decreased calcium

loss in urine

Figure 6–16b Factors That Increase the Blood Calcium Ion Level.

Factors That Decrease Blood Calcium Ion Level

Intestinal and kidney

responses are triggered when

blood calcium ion level rises

above 11 mg/dL.

High Calcium Ion Level in Blood

(above 11 mg/dL)

Thyroid Gland Response

C cells in the thyroid

gland secrete calcitonin.

Calcitonin

Bone Response

Osteoclast activity

decreases; osteoblast

activity unaffected

Osteoclast

Bone

Intestinal Response

Intestinal

absorption

of calcium

decreases

Kidney Response

Kidneys

excrete

calcium ions

less

calcitriol

Calcium release slowed

Calcium absorbed slowly

Calcium excreted

Ca2+

level in

blood

decreases

Increased calcium

loss in urine

6-9 Fractures

Fractures

Cracks or breaks in bones due to physical stress

Open (compound) or closed (simple)

Major types of fractures

Transverse, displaced, compression, spiral, epiphyseal, comminuted, greenstick, Colles, Pott’s

Figure 6–17 Types of Fractures and Steps in Repair.

Epiphyseal

fracture

Transverse fracture

Greenstick fracture

Comminuted

fracture

Displaced fracture

Compression

fracture

Colles fracture

Spiral fracture

Pott’s fracture

Figure 6–17 Types of Fractures and Steps in Repair (Part 1 of 9).

Transverse fracture

Figure 6–17 Types of Fractures and Steps in Repair (Part 2 of 9).

Displaced fracture

Figure 6–17 Types of Fractures and Steps in Repair (Part 3 of 9).

Compression

fracture

Figure 6–17 Types of Fractures and Steps in Repair (Part 4 of 9).

Spiral fracture

Figure 6–17 Types of Fractures and Steps in Repair (Part 5 of 9).

Epiphyseal

fracture

Figure 6–17 Types of Fractures and Steps in Repair (Part 6 of 9).

Comminuted

fracture

Figure 6–17 Types of Fractures and Steps in Repair (Part 7 of 9).

Greenstick fracture

Figure 6–17 Types of Fractures and Steps in Repair (Part 8 of 9).

Colles fracture

100

Figure 6–17 Types of Fractures and Steps in Repair (Part 9 of 9).

Pott’s fracture

101

6-9 Fractures

Fractures are repaired in four steps

Fracture hematoma formation

Callus formation

Spongy bone formation

Compact bone formation

102

6-9 Fractures

Fracture hematoma formation

Production of a large blood clot

Establishes a fibrous network

Bone cells in the area die

Callus formation

Cells of endosteum and periosteum divide and migrate into fracture zone

Calluses stabilize the break

Internal callus develops in medullary cavity

External callus of cartilage and bone surrounds break

103

Figure 6–17 Types of Fractures and Steps in Repair (Part 1 of 4).

Fracture

hematoma

Dead bone

Bone fragments

Fracture hematoma

formation.

Fracture

hematoma

104

Figure 6–17 Types of Fractures and Steps in Repair (Part 2 of 4).

Spongy bone of

internal callus

Cartilage of

external callus

Spongy bone of

external callus

Periosteum

Callus formation.

105

6-9 Fractures

Spongy bone formation

Osteoblasts replace central cartilage of external callus with spongy bone

Compact bone formation

Repaired bone may be slightly thicker and stronger than normal

106

Figure 6–17 Types of Fractures and Steps in Repair (Part 3 of 4).

Internal callus

External callus

Spongy bone formation.

107

Figure 6–17 Types of Fractures and Steps in Repair (Part 4 of 4).

External

callus

Compact bone

formation.

108

6-10 Effects of Aging on Skeletal System

Bones become thinner and weaker with age

Osteopenia—inadequate ossification (reduction of bone mass)

Begins between ages 30 and 40

Women lose 8 percent of bone mass per decade

Men lose 3 percent

Epiphyses, vertebrae, and jaws are most affected

Results in fragile limbs, reduced height, and tooth loss

109

6-10 Effects of Aging on Skeletal System

Osteoporosis—severe loss of bone mass

Compromises normal function

Over age 45, occurs in

29 percent of women

18 percent of men

Hormones and bone loss

Sex hormones help maintain bone mass

In women, osteoporosis accelerates after menopause

110

Figure 6–18 The Effects of Osteoporosis on Spongy Bone.

Spongy bone in osteoporosis

SEM × 21

Normal spongy bone

SEM × 25

111

6-10 Effects of Aging on Skeletal System

Cancer and bone loss

Cancerous tissues release osteoclast-activating factor

Stimulates osteoclasts

Produces severe osteoporosis

112

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