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Histology of Connective Tissue &
the Anatomy of Bone
Section 4-1: Page 112
Tissue = groups of cells that are similar in structure and function
o Two or more tissue types combine to form an organ
o Typically, all four tissue types are found in each organ
The Four Basic Types of Tissues and Their Functions
1. Nervous - control
 Note: Each tissue type has many subclasses or
2. Muscle - movement
varieties and therefore each has many functions in
3. Connective - support
addition to those listed
4. Epithelial - covering
Sections 4-4/4-5: Pages 124-134
Connective Tissue
Connective tissue is the most abundant and
widely distributed of the tissue types. Skin
(the deeper layers) is composed mainly of
connective tissue, while the brain has very
little connective tissue.
Examples of Connective Tissue
1. Blood
2. Bone
3. Cartilage
4. Connective tissue proper – includes fat and fibrous ligaments and tendons
Functions of Connective Tissue
o Protection – cartilage, fat, bone
o Insulation - fat
o Transportation - blood
o Support - bone
Common Characteristics of Connective Tissue
1. Common Origin – arise from a certain embryonic tissue
2. Varying Degrees of Vascularity – tendons and ligaments have poor blood supply and
cartilage is avascular, while other types of connective tissue (such as adipose) is highly
vascular. Those tissues that have a poor blood supply heal more slowly when injured.
3. Extracellular Matrix – connective tissue is composed largely of nonliving extracellular
matrix secreted by the connective tissue cells that allows the tissue to provide support and
withstand great tension. In comparison to muscle tissue that is very cellular, connective
tissue is not highly composed of cells.
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Connective Tissue Pertaining to the Skeletal System
1. Bone (Osseous Tissue)
a. Composed of bone cells sitting in cavities called lacunae and
surrounded by layers of very hard matrix that contains
calcium salts
b. Basic Characteristics – protection, support, synthesis of blood
cells
c. Bone becomes rigid because of deposits of calcium salts. In
addition, unlike cartilage, bone has a lot of blood vessels
within
2. Blood (Vascular Tissue)
a. Carries nutrients, wastes, respiratory gases and many
other substances throughout the body. Although
blood does not connect things as the other connective
tissues do, blood originates from the same embryonic
tissue as other connective tissues do!
3. Connective Tissue Proper
a. Adipose – (fat tissue) is very vascularized, indicating its high metabolic rate (Humans
body fat % is commonly 18-50%)
i. White Fat- stores nutrients in adults
ii. Brown Fat – consumes nutrient stores in order to produce heat or warm the body
(occurs in babies because babies lack the ability to shiver and produce heat!!)
b. Elastic and fibrous connective tissues of tendons (connects muscle to bone) and
ligaments (connects bones to bones)
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4. Skeletal cartilage– stands up to compression and tension, is avascular, and lacks nerve fibers. It
is also up to 80% water! The skeleton of a fetus is composed of hyaline cartilage, but by the
time the baby is born most of the cartilage has been replaced by bone.
During the aging process calcium salts may be deposited in cartilage making it appear and feel
tough like bone. However, these are two truly distinguishable tissues and cartilage cannot
become bone.
i. Hyaline Cartilage – the most abundant of the cartilages, which provides support with
flexibility and resistance.
Hyaline cartilage is found:
1. Covering the ends of most bones at movable joints
2. Connecting ribs to the sternum
3. Forming the skeleton of the larynx (voicebox) and
reinforcing passageways of the respiratory system
4. Supporting the external nose
ii. Elastic Cartilage – similar to hyaline cartilage but contains more elastic fibers and is
able to withstand repeated bending.
These cartilages are only found in two areas
1. External ear
2. Forming the epiglottis (the flap that bends to cover
the opening of the larynx when we swallow).
iii. Fibrocartilage – a highly compressible cartilage
This Cartilage is found:
1. In padlike cartilages of the knee
2. In discs between the vertebrae of the spine
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Chapter 6: Osseous Tissue and Bone Structure
The skeletal system includes bones, joints, cartilage, and ligaments.
CLASSIFICATION OF BONES
There are 206 named bones of the human body. They are classified into two
skeletons.
1. Axial Skeleton – forms the longitudinal axis of the body and includes the
bones of the skull, vertebral column, and rib cage. These are the bones that
are most involved in protecting, supporting, and carrying other body parts.
2. Appendicular Skeleton – consists of the bones of the upper and lower
limbs and the shoulder and pelvic girdle. These bones assist in locomotion
and help us manipulate the environment.
Source:
http://www.heumann.org/body
.of.knowledge/a1/axial.skeleto
n.html September 9, 2008
BONE FUNCTION
1. Support – the bones support the body and cradle the organs
2. Protection – skull cases the brain, vertebrae protect the spinal
cord, and the ribs protect the vital organs of the thorax
3. Leverage – the skeletal muscles contract using the bones as
levers to create locomotion
4. Mineral and Lipid Storage – Fat is stored in the internal
cavities of bones. Bones are also a reservoir for minerals
(most importantly calcium and phosphate). These stores of
minerals are released into the bloodstream depending on the
needs of the body. The storage and release of the minerals is
regulated by hormones.
5. Blood Cell Formation (hematopoiesis) – the bulk of red
blood cell formation occurs within the marrow cavities of
certain bones
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BONE STRUCTURE & HEMATOPOIESIS (he – ma – to – po – e – sis)
Bones are living organs. They contain nervous tissue in their nerves, cartilage tissue and other
connective tissue in their cavities, and muscle and epithelial tissue in their blood vessels.
Compact Bone – the outer portion of the bone that appears smooth and solid to the naked eye
Spongy Bone – the internal portion of the bone that appears honeycomb in shape (within the
hollow areas of living bone is yellow or red bone marrow)
Within the bones of adults, there is a central cavity within long bones
that contains fat (yellow marrow). The cavity is called the yellow
bone marrow cavity or the medullary cavity. Short, irregular and
flat bones do not contain a medullary cavity.
The medullary cavities of adults contained red marrow as infants. The red marrow
(hematopoietic tissue) is the area where Red Blood Cells (RBCs) are formed. In adults, red
marrow is confined to the cavities of spongy bone within flat bones, irregular bones, and the ends
of long bones.
Source:
http://www.cmlalliance.com/images/
bone-marrow-blood-samplesillustration.jpg September 9, 2008
BONE CLASSIFICATION
1. Long Bones – all bones of the limbs except patella and the
bones of the wrist and ankle. These bones are longer than
they are wide and contain a shaft plus two ends. Mostly
composed of compact bone
2. Short Bones – roughly cube-shaped (bones of the wrist and
ankle). Mostly composed of spongy bone
3. Flat Bones – thin, flattened bones such as the sternum,
scapulae (shoulder bones) , ribs, and most skull bones.
Composed of 2 layers of compact bone sandwiching a layer
of spongy bone between them
4. Irregular Bones – have complicated shapes the fit none of
the preceding classes (vertebrae and pelvis)
5. Sutural Bones (Wormian Bones) – bones within in the
sutures of the skull
6. Sesamoid Bones - small, flat bones (patella); sesamoids
also form in at least 26 other locations (typically joints)
throughout the body. Vary person to person.
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GROSS ANATOMY OF LONG BONES including BONE MEMBRANES
Diaphysis – shaft of a long bone; composed of compact bone
The outer surface of diaphysis is protected by a
double-layered membrane called the periosteum.
The periosteum is anchored to the compact bone by
Sharpey’s fibers.
The periosteum is richly supplied with nerve fibers,
lymphatic vessels, and blood vessels. It also
contains osteoblasts (bone germinators) and
osteoclasts (bone breakers).
The inner surface of bone cavities and canals
contains a membrane called the endosteum. The
endosteum also contains both osteoclasts and
osteoblasts.
Source:
http://www.shoppingtrolley.
net/lesson1-bone-types.shtml
September 9, 2008
Epiphyses – the ends of the long bones; composed of a thin layer of compact bone surrounding an area
filled with spongy bone. The epiphyses are not covered by periosteum, instead
they are covered by articular cartilage (type of hyaline cartilage) that provides a
smooth joint surface
Metaphysis – narrow zone connecting diaphysis to epiphysis
Epiphyseal Plate – a flat plate of hyaline cartilage found in young growing
bones that causes the lengthwise growth of a long bone. As a person reaches
adulthood the bone stops growing and an epiphyseal line marks where the
epiphyseal plate has been replaced by bone.
Source:
http://www.shoppingtrolley.net/lesson1bone-types.shtml September 9, 2008
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MICROSCOPIC ANATOMY OF BONE
Compact Bone (the outer portion of the bone that appears smooth and solid to the naked eye) is not
actually solid, but under a microscopic view illustrates a vast network of nerves, blood vessels, and
lymphatic vessels.
65% of the mass of a bone is composed of mineral salts (mostly calcium phosphates)
The calcium crystals that are present give bone its most notable characteristic of hardness.
Healthy bone is half as strong as steel in resisting compression, and fully as strong as steel in resisting
tension.
Bone salts allow bones to last many years beyond the life of a vertebrate organism. Some have been
known to last centuries.
Osteocytes – mature bone cells found in tiny cavities within the matrix
Lacunae (lah-ku’ne) – tiny cavities found within the matrix that contain osteocytes
Lamellae (lah-mel’e) concentric circles of Lacunae that surround central canals called Haversian Canals
Haversian Canals, which carry blood vessels and nerves to all areas of the bone. Each complex
consisting of central canal and matrix rings is called a Haversian system or Osteon.
Canaliculi (Kan”ah-lik’u-li) are tiny canals branching from the Haversian canals to all lacunae bringing
nutrients to all bone cells.
Volkmann’s canals – canals that run into the bone at right angles to the shaft serving as the
communication pathway (nervous pathway) from the outside of the bone to its interior
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Source:
http://bioweb.wku.edu/courses/
Biol131/images/haversiansmall.
JPG September 9, 2008
Source:
http://www.mc.vanderbilt.edu/histolog
y/labmanual2002/labsection1/Cartilage
andBone03.htm September 9, 2008
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BONE DEVOLOPMENT
Osteogenesis and ossification – synonyms that mean bone growth or bone formation
Most of the skeleton of an embryo is composed of hyaline cartilage. By the time an infant is born most
of the cartilage is replaced by bone. The cartilage does not become bone, it is replaced by bone. During
this process the hyaline cartilage is completely covered with bone matrix by osteoblasts. The hyaline
cartilage is then digested away, opening up a medullary cavity within the newly formed bone.
Bones grow in size (length) until a person becomes an adult. Bones may increase in thickness
throughout an adult’s life, but most growth in adults occurs as repair of damaged bone.
There is a growth plate (Epiphyseal Plate) located at the end of long bones. Throughout infancy,
childhood, and adolescence, the growth plate allows the bones to grow.
Each week we recycle 5-7% of our bone mass.
Spongy bone is replaced every 3-4 years.
Compact bone is replaced every 10 years.
BONE REMODELING
Different areas of bone are replaced at different rates throughout your body.
In a healthy adult, the total bone mass remains constant
Bone deposition – accomplished by osteoblasts and occurs when bone is injured or when added bone
strength is needed.
In order for bone remodeling to occur, the following nutrients must be available in the diet:
Proteins, Vitamin C, Vitamin D, Vitamin A, Calcium, Phosphorus, Magnesium, Manganese
Bone Resorption – accomplished by osteoclasts (bone breakers) that use enzymes and acid to break
down bone material and dead osteocytes (mature bone cells).
When blood calcium levels drop below homeostatic levels, the parathyroid glands release parathyroid
hormone (PTH). PTH activates osteoclasts breaking down bone and releasing calcium ions into the
blood. When calcium levels in the blood become too high the calcium is stored in the matrix of bone
once again.
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RESPONSE OF BONE GROWTH TO MECHANICAL STRESS
Wolff’s Law - A bone grows or remodels in response to the forces or demands that it encounters.
For example, if a person continually applies stress to muscles that in turn pull on bones, the bones in that
area will increase in size. (Weightlifting not only increases muscles size, it also increases bone size). On
the other hand, lack of exercise leads to bone atrophy because they are no longer subjected to stress.
This law causes the following inconsistencies in bones:
1. Long bones bend slightly when used under heavy tension. The bending occurs in the middle
of the shaft, and the shaft becomes thicker at this point.
2. Curved bones are thicker where they are more likely to buckle (Head of femur to shaft)
3. Large, bony projections occur where heavy, active muscles attach (watch for this when
studying muscles)
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BONE DISORDERS
Osteomalacia – (soft bones) a number of disorders in adults in which the bones are inadequately
mineralized (deficiency of calcium or Vitamin D in the diet)
Rickets – (analogous to osteomalacia, but in children) having soft bones in children can be more
severe because children are still growing. This may result in bowed legs and more common
deformities of the pelvis, skull, and rib cage.
Osteoporosis – refers to a group of diseases in which bone resorption occurs quicker than bone
deposition (bone mass is reduced)
These diseases affect the entire skeletal system, but the spongy bone of the spine is most
vulnerable, which results in compression fractures of the vertebrae
The top portion of the femur is also susceptible, which results in a broken hip
Postmenopausal women (have low estrogen levels), people who do not exercise and stress their
bones to increase bone production, and those who have diet deficient in calcium, protein, and
Vitamin D have increased occurrence of osteoporosis. Also, smokers are more susceptible
because estrogen levels decrease with smoking as they do after menopause.
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BONE FRACTURES {also refer to Table 5.2 on Page 122}
During youth, bones break from trauma of sports, falls, car accidents, etc.
As a person ages, the bone becomes thinner and more brittle. Many elderly people think they are
“saving their strength” by not doing too much in a day. They are actually setting themselves up for
pathological fractures (spontaneous breaks without apparent injury)! This is the #1 reason to get your
grandparents pumping some iron!!
Types of Fractures
1. Nondisplaced Fractures – the ends of the broken bones retain their normal position
2. Displaced Fractures – the ends of the broken bone are no longer aligned
3. Complete Fracture – the bone is broken through
4. Incomplete Fracture – the bone is not broken through (hair line fracture of a bone)
5. Linear Fracture – the bone is broken parallel to the length of the bone
6. Transverse Fracture – the bone is broken perpendicular to the long axis of the bone
7. Open (Compound) Fracture – the broken bone penetrates the skin
8. Closed (Simple) Fracture – the broken bone does not penetrate the skin
9. Comminuted Fracture – bone breaks into many fragments (elderly)
10. Spiral Fracture – ragged break from excessive twisting of bone (sports)
11. Greenstick Fracture – bone breaks incompletely like green twig (children)
12. Compression Fracture – bone is crushed (spine)
13. Depressed Fracture – broken bone portion is pushed inward (skull)
14. Impacted Fracture – broken bone ends are forced together
15. Stress Fracture – incomplete fracture from repeated stress (hairline fracture of foot)
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The process of placing displaced broken bones back into place is called reduction.
There are two types.
1. Closed Reduction – the ends of the broken bone are coaxed back in place by the physician’s
hands
2. Open Reduction – the ends of the broken bones are surgically pinned or wired into place.
Once the broken bone has been reduced, it is then
immobilized by a cast.
Source:
http://www.fairview.org/healthlib
rary/content/sma_fracture_art.ht
m September 9, 2008
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HEALING TIME
Simple Fracture – 6 to 8 weeks (longer for larger weight bearing bones and for bones of elderly people
“poor circulation”)
Four Major Phases of Bone Repair
1. Hematoma Formation – due to the damage of the periosteum, bone, and sometimes the
surrounding tissue, blood vessels break and form a mass of clotted blood called a hematoma
2. Fibrocartilaginous callus formation – capillaries grow into the hematoma and phagocytes
(WBCs) clean away dead tissue. Bone begins to regenerate from surrounding osteoblasts. The
new bone hardens to form what is called a hard callus or fibrocartilage callus. This entire mass
of repair tissue creates splints between the broken ends of the bone.
3. Bony Callus Formation – the Fibrocartilaginous callus gradually becomes a bony callus of
spongy bone (occurs from 3-4 weeks after the injury until 2-3 months later)
4. Bone Remodeling – bony callus is removed and compact bone is laid down to reconstruct the
shaft walls
Source:
http://www.myhealth.gov.my/myhealth/eng/dewas
a_content.jsp?lang=dewasa&sub=0&bhs=eng&st
oryid=1144236626689 September 9, 2008