Transcript Document

Developmental Aspects of Tissue
• Primary germ layers: ectoderm, mesoderm, and
endoderm
• Three layers of cells formed early in embryonic
development
• Specialize to form the four primary tissues
• Nerve tissue arises from ectoderm
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Developmental Aspects of Tissue
• Muscle, connective tissue, endothelium, and
mesothelium arise from mesoderm
• Most mucosae arise from endoderm
• Epithelial tissues arise from all three germ layers
Figure 4.13
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Skeletal Cartilage
• Contains no blood vessels or nerves
• Surrounded by the perichondrium (dense irregular
CT) that resists outward expansion
• Three types – hyaline, elastic, and fibrocartilage
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
BONES and SKELETAL TISSUE
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Bones and Cartilages of the Human Body
Figure 6.1
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Function of Bones
• Support – form the framework that supports the body
and cradles soft organs
• Protection – provide a protective case for the brain,
spinal cord, and vital organs
• Movement – provide levers for muscles
• Mineral storage – reservoir for minerals, especially
calcium and phosphorus
• Blood cell formation – hematopoiesis occurs within
the marrow cavities of bones
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Reminder -Structure of Long Bone
Figure 6.3a, c
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
ReminderStructure of Short, Irregular, and Flat Bones
Figure 6.4
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Location of Hematopoietic Tissue (Red Marrow)
• In infants
• Found in the medullary cavity and all areas of
spongy bone
• In adults
• Found in the spongy bone of flat bones, and the
head of the femur and humerus
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Chemical Composition of Bone: Organic
• Osteoblasts – bone-forming cells
• Osteocytes – mature bone cells
• Osteoclasts – large cells that resorb or break down
bone matrix
• Osteoid – unmineralized bone matrix composed of
proteoglycans, glycoproteins, and collagen
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Chemical Composition of Bone: Inorganic
• Hydroxyapatites, or mineral salts
• Sixty-five percent of bone by mass
• Mainly calcium phosphates
• Responsible for bone hardness and its resistance to
compression
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Bone Development
• Osteogenesis and ossification – the process of bone
tissue formation, which leads to:
• The formation of the bony skeleton in embryos
• Bone growth until early adulthood
• Bone thickness, remodeling, and repair
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Formation of the Bony Skeleton
• Begins at week 8 of embryo development
• Intramembranous ossification – bone develops from
a fibrous membrane
• Endochondral ossification – bone forms by replacing
hyaline cartilage
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Postnatal Bone Growth
• Growth in length of long bones
• Cartilage on the side of the epiphyseal plate closest
to the epiphysis is relatively inactive
• Cartilage abutting the shaft of the bone organizes
into a pattern that allows fast, efficient growth
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Long Bone Growth and Remodeling
• Growth in length –
cartilage
continually grows
and is replaced by
bone as shown
• Remodeling – bone
is resorbed and
added by
appositional
growth as shown
Figure 6.10
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Hormonal Regulation of Bone Growth During
Youth
• During infancy and childhood, epiphyseal plate
activity is stimulated by growth hormone
• During puberty, by testosterone and estrogens
• Initially promote adolescent growth spurts
• Cause masculinization and feminization of specific
parts of the skeleton
• Later induce epiphyseal plate closure, ending
longitudinal bone growth
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Bone Remodeling
• Remodeling units – adjacent osteoblasts (deposit)
and osteoclasts (resorb) bone at periosteal and
endosteal surfaces
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Bone Deposition
• Occurs where bone is injured or added strength is
needed
• Requires a diet rich in protein, vitamins C, D, and A,
calcium, phosphorus, magnesium, and manganese
• Alkaline phosphatase is essential for mineralization
of bone
• Sites of new matrix deposition are revealed by:
• Osteoid seam – unmineralized band of bone matrix
• Calcification front – abrupt transition zone between
the osteoid seam and the older mineralized bone
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Bone Resorption
• Accomplished by osteoclasts
• Resorption bays – grooves formed by osteoclasts as
they break down bone matrix
• Resorption involves osteoclast secretion of:
• Lysosomal enzymes that digest organic matrix
• Acids that convert calcium salts into soluble forms
• Dissolved matrix is transcytosed across the
osteoclast’s cell where it is secreted into the
interstitial fluid and then into the blood
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Importance of Ionic Calcium in the Body
• Calcium is necessary for:
• Transmission of nerve impulses
• Muscle contraction
• Blood coagulation
• Secretion by glands and nerve cells
• Cell division
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Control of Remodeling
• Two control loops regulate bone remodeling
• Hormonal mechanism that maintains calcium
homeostasis in the blood
• Mechanical and gravitational forces acting to the
skeleton
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Hormonal Mechanism
• Rising blood
Ca2+ levels
trigger the
thyroid to release
calcitonin
• Calcitonin
stimulates
calcium salt
deposit in bone
Figure 6.11
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Hormonal Mechanism
• Falling blood
Ca2+ levels signal
the parathyroid
glands to release
PTH
• PTH signals
osteoclasts to
degrade bone
matrix and
release Ca2+ into
the blood
Figure 6.11
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Response to Mechanical Stress
• Wolff’s law – a bone
grows or remodels in
response to the forces
or demands placed
upon it
Figure 6.12
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Response to Mechanical Stress
• Observations
supporting Wolff’s
law include:
• Long bones are
thickest midway
along the shaft
(where bending
stress is greatest)
• Curved bones are
thickest where they
are most likely to
buckle
Figure 6.12
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Response to Mechanical Stress
• Large, bony
projections occur
where heavy, active
muscles attach
Figure 6.12
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Bone Fractures (Breaks)
• Bone fractures are classified by:
• The position of the bone ends after fracture
• Completeness of the break
• The orientation of the bone to the long axis
• Whether or not the bones ends penetrate the skin
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Types of Bone Fractures
•Learn table with
fracture types 6.2?
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Stages in the Healing of a Bone Fracture
• Hematoma
formation
• Torn blood vessels
hemorrhage
• A mass of clotted
blood (hematoma)
forms at the
fracture site
• Site becomes
swollen, painful,
and inflamed
Figure 6.13.1
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Stages in the Healing of a Bone Fracture
• Fibrocartilaginous
callus forms
• Granulation tissue (soft
callus) forms a few
days after the fracture
• Capillaries grow into
the tissue and
phagocytic cells begin
cleaning debris
Figure 6.13.2
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Stages in the Healing of a Bone Fracture
• Bony callus formation
• New bone trabeculae
appear in the
fibrocartilaginous callus
• Fibrocartilaginous callus
converts into a bony
(hard) callus
• Bone callus begins 3-4
weeks after injury, and
continues until firm
union is formed 2-3
months later
Figure 6.13.3
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Stages in the Healing of a Bone Fracture
• Bone remodeling
• Excess material
on the bone shaft
exterior and in
the medullary
canal is removed
• Compact bone is
laid down to
reconstruct shaft
walls
Figure 6.13.4
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Homeostatic Imbalances
• Osteomalacia
• Bones are inadequately mineralized causing
softened, weakened bones
• Main symptom is pain when weight is put on the
affected bone
• Caused by insufficient calcium in the diet, or by
vitamin D deficiency
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Homeostatic Imbalances
• Rickets
• Bones of children are inadequately mineralized
causing softened, weakened bones
• Bowed legs and deformities of the pelvis, skull, and
rib cage are common
• Caused by insufficient calcium in the diet, or by
vitamin D deficiency
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Homeostatic Imbalances
• Osteoporosis
• Group of diseases in which bone reabsorption
outpaces bone deposit
• Spongy bone of the spine is most vulnerable
• Occurs most often in postmenopausal women
• Treatment
• Calcium and vitamin D supplements
• Increased weight bearing exercise
• Hormone (estrogen) replacement therapy (HRT)
• Prevented or delayed by sufficient calcium intake
and weight-bearing exercise
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Paget’s Disease
• Characterized by excessive bone formation and
breakdown
• Pagetic bone with an excessively high ratio of woven
to compact bone is formed
• Pagetic bone, along with reduced mineralization,
causes spotty weakening of bone
• Osteoclast activity wanes, but osteoblast activity
continues to work
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Developmental Aspects of Bones
• Mesoderm gives rise to embryonic mesenchymal
cells, which produce membranes and cartilages that
form the embryonic skeleton
• The embryonic skeleton ossifies in a predictable
timetable that allows fetal age to be easily
determined from sonograms
• At birth, most long bones are well ossified (except
for their epiphyses)
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Developmental Aspects of Bones
• By age 25, nearly all bones are completely ossified
• In old age, bone resorption predominates
• A single gene that codes for vitamin D docking
determines both the tendency to accumulate bone
mass early in life, and the risk for osteoporosis later
in life
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Joints (Articulations)
• Weakest parts of the skeleton
• Articulation – site where two or more bones meet
• Functions
• Give the skeleton mobility
• Hold the skeleton together
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Classification of Joints: Structural
• Structural classification focuses on the material
binding bones together and whether or not a joint
cavity is present
• The three structural classifications are:
• Fibrous
• Cartilaginous
• Synovial
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Classification of Joints: Functional
• Functional classification is based on the amount of
movement allowed by the joint
• The three functional class of joints are:
• Synarthroses – immovable
• Amphiarthroses – slightly movable
• Diarthroses – freely movable
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Example - Synovial Joints: Major Ligaments and
Tendons (Anterior View)
Figure 8.11c
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Inflammatory and Degenerative Conditions
• Bursitis
• An inflammation of a bursa, usually caused by a
blow or friction
• Symptoms are pain and swelling
• Treated with anti-inflammatory drugs; excessive
fluid may be aspirated
• Tendonitis
• Inflammation of tendon sheaths typically caused by
overuse
• Symptoms and treatment are similar to bursitis
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Arthritis
• More than 100 different types of inflammatory or
degenerative diseases that damage the joints
• Most widespread crippling disease in the U.S.
• Symptoms – pain, stiffness, and swelling of a joint
• Acute forms are caused by bacteria and are treated
with antibiotics
• Chronic forms include osteoarthritis, rheumatoid
arthritis, and gouty arthritis
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Osteoarthritis (OA)
• Most common chronic arthritis; often called “wearand-tear” arthritis
• Affects women more than men
• 85% of all Americans develop OA
• More prevalent in the aged, and is probably related to
the normal aging process
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Osteoarthritis: Treatments
• OA is slow and irreversible
• Treatments include:
• Mild pain relievers, along with moderate activity
• Magnetic therapy
• Glucosamine sulfate decreases pain and
inflammation
• SAM-e (s-adenosylmethionine) builds up cartilage
matrix and regenerates tissue
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Rheumatoid Arthritis (RA)
• Chronic, inflammatory, autoimmune disease of
unknown cause, with an insidious onset
• Usually arises between the ages of 40 to 50, but may
occur at any age
• Signs and symptoms include joint tenderness, anemia,
osteoporosis, muscle atrophy, and cardiovascular
problems
• The course of RA is marked with exacerbations and
remissions
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Rheumatoid Arthritis: Course
• RA begins with synovitis of the affected joint
• Inflammatory blood cells migrate to the joint, causing
swelling
• Inflamed synovial membrane thickens into a pannus
• Pannus erodes cartilage, scar tissue forms, articulating
bone ends connect
• The end result, ankylosis, produces bent, deformed
fingers
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Rheumatoid Arthritis: Treatment
• Conservative therapy – aspirin, long-term use of
antibiotics, and physical therapy
• Progressive treatment – anti-inflammatory drugs or
immunosuppressants
• The drug Embrel, a biological response modifier,
removes cells that promote inflammation
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Gouty Arthritis
• Deposition of uric acid crystals in joints and soft
tissues, followed by an inflammation response
• Typically, gouty arthritis affects the joint at the base
of the great toe
• In untreated gouty arthritis, the bone ends fuse and
immobilize the joint
• Treatment – colchicine, nonsteroidal antiinflammatory drugs, and glucocorticoids
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Developmental Aspects of Joints
• By embryonic week 8, synovial joints resemble adult
joints
• Few problems occur until late middle age
• Advancing years take their toll on joints including:
• Ligaments and tendons shorten and weaken
• Intervertebral discs become more likely to herniate
• OA is inevitable, and all people of 70 have some
degree of OA
• Prudent exercise (especially swimming) that coaxes
joints through their full range of motion is key to
postponing joint problems
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Sprains
• The ligaments (bone to bone) reinforcing a joint are
stretched or torn
• Partially torn ligaments slowly repair themselves
• Completely torn ligaments require prompt surgical
repair
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Cartilage Injuries
• The snap and pop of overstressed cartilage
• Common aerobics injury
• Repaired with arthroscopic surgery
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Dislocations
• Occur when bones are forced out of alignment
• Usually accompanied by sprains, inflammation, and
joint immobilization
• Caused by serious falls and are common sports
injuries
• Subluxation – partial dislocation of a joint
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings