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Osseous Tissue and Skeletal Structure
Function: Support, storage of minerals and lipids, blood cell production, and protection.
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Classification of bones:
206 major bones in the adult body
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compact bone:
dense bone, relatively solid to endure the stress of impact (femur can withstand 10-15x body weight from end to end, only in one direction).
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osteon:
basic functional and structural unit of compact bone. Osteons are structural cylinders that run parallel to the bone’s axis.
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spongy bone:
(cancellous bone) open network of trabecular cross bracing for support, lighten bone, and provide framework and protect red bone marrow.
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trabecular:
loose tubular complex of lamella, canaliculi and osteocytes. Nutrients are via diffusion.
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periosteum: (Fig. 6-8a)
Fibrous outer layer with a cellular inner layer. Periosteum is the attachment site for tendons and ligaments.
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endosteum: (Fig. 6-8b)
incomplete cellular layer of osteoprogenitor cells, epithelial cells, osteoblasts, and osteoclasts that lines the bone surface closest to the marrow cavity. Endosteum is active during growth, remodeling, and bone repair.
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diaphysis:
tubular bone shaft
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epiphysis:
ends of the bone
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setocyte:
region that has a narrow zone of hyaline cartilage (epiphyseal cartiage, epiphyseal plate Fig. 6-11) that connects the epiphysis with the diaphysis. Post growth the epiphyseal plate or cartilage becomes the epiphyseal line.
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marrow cavity:
(medullary cavity) central space in the diaphysis.
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yellow bone marrow:
has fat cells that serve as an energy reserve. Most adult marrow is yellow marrow. Yellow bone marrow can convert to red bone marrow to help the body recover from an extreme blood loss.
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red bone marrow:
site for blood element formation (WBCs, RBCs, and platelets). Locations of red bone marrow in the adult are: sternum, ribs, skull, scapulae, pelvis, humerus, and femur.
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matrix:
Calcium salts, 3Ca3(PO4)2 + Ca(OH)2 = hydroxyapatite Ca10(PO4)6(OH)2 crystals, calcium carbonate, ions (Mg, Fl, Na), collagen fibers
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osteocytes:
mature bone cells that maintain matrix (lamella)
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lamella:
concentric layers of matrix
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lacunae: pocket where setocyte resides
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canaliculi:
narrow passageways that penetrate lamellae and connect the lacunae. Nutrients flow through the canaliculi and setocyte processes (cytoplasmic extensions) extend through the canaliculi.
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central canals:
hold blood vessels in the center of the osteon
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perforating canals:
carry blood vessels that transverse osteons
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osteon:
structural and functional unit of compact bone
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Cells of bone:
- Osteoblasts
- Osteoprogenitor cells
- Osteocytes
- Osteoclasts
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osteoblasts:
immature bone cells that secrete organic components of matrix. Osteoblasts mature to osteocytes.
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osteogenesis:
process of making new bone matrix
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osteoprogenitor cells:
bone stem cells that provide daughter cells that will differentiate into osteoblasts
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osteocytes:
mature bone cell that maintains the bone matrix
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osteoclasts:
giant multinucleated (50 or more) cells that secrete acids and enzymes to dissolve bone matrix to release minerals (Ca, PO4)in the blood stream. Osteoclasts are derived from monocytes.
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osteolysis:
erosion of bone, resorption, remodeling
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Ossification vs. Calcification –
Calcification is the deposit of calcium salts. Calcification occurs during ossification but calcification also occurs in other tissues as well. Ossification is the replacement of other tissues with bone tissue.
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Intramembranous Ossification (Fig. 6-12)
(dermal ossification) osteoblasts differentiate within mesenchymal or fibrous connective tissue. Intramembraneous ossification occurs in the deeper layers of the dermis. Examples of bones from intramembraneous ossification (dermal bones) are falt bones of the skull, mandible, and clavicle.
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Endochondral Ossification (Fig. 6-10)
is the most common form of bone formation. Hyaline cartilage becomes calcified and infiltrated with blood vessels. Fibroblasts that migrate into the calcified cartilage differentiate into osteoblasts and form cancellous bone. Bone remodeling occurs widening the bone marrow cavity. Capillaries and osteoblasts migrate into epiphysis making secondary ossification centers with cancellous bone in the center. As long as the rate of cartilage growth keeps up with the pace of osteoblast invasion the bone will continue to lengthen. At puberty the rise of sex hormones, growth hormone, and thyroid hormones accelerates bone growth so that it exceeds the rate of epiphyseal cartilage. The epiphyseal cartilage becomes ‘sealed’ and bone lengthening ceases.
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Appositional Bone Growth
bone grows in diameter on the outside while osteoclasts remodel and enlarge the marrow cavity within the inside.
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Remodeling
– organic and mineral components of bone matrix are continuously being recycled and renewed for normal bone maintenance and mineral balance
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Effects of Exercise on the Bone –
Bone will remodel and reform its shape to adapt to stresses of the body. For example a tendon pulls on a bone mark (ridge, bump) with an increase force. The bone mark will increase in thickness to adapt to the increase stress on that area of the bone. If a bone becomes inactive or decrease demands of stress, then the bone will degenerate and become thinner. Theory: calcium crystals produce an electrical field when they are stressed. Osteoblasts are attracted to these fields and produce bone. Electrical therapy is used to repair fractures.
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Mineral requirement
– Ca, PO4 salts, Mg, Fl, Mn
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Calcitriol:
synthesized and released by the kidneys to increase intestinal Ca and P absorption
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Vitamins C
(needed for collagen synthesis, stimulates osteoblasts differentiation),
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Vitamin A
(stimulates osteoblasts activity),
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Vitamines K and B12
(needed for protein synthesis),
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Vitamine D3
(to help make more calcitriol).
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Scurvy
is a vitamin C deficiency that causes loss of bone mass and loss of bone strength.
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Growth Hormone
– stimulates protein synthesis and cell growth throughout the body
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Thyroxine (T4)
increases cell metabolism and increases osteoblast activity
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Sex hormones:
estrogens and androgens stimulate osteoblast activity to exceed the rate of epiphyseal cartilage growth. Estrogen closes the epiphyseal plates faster (a reason why women are shorter than men)
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Abnormal Bone Growth
– due to abnormal growth hormone levels
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Gigantism:
overproduction of growth hormone before puberty
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Acromegaly: (Figs. 27a, 57, Application Manual)
overproduction of growth hormone after puberty, bone shapes change and cartilage tissues enlarge (broad face and enlarged mandible, abnormal growth of hands, feet, and clavicle)
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Marfan’s Sydrome: (Fig. 27b, p57 Application Manual, Fig. 6-14b Martini text)
excessive cartilage formation yields long body.
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Pituitary Dwarfism:
inadequate growth hormone level, decreased epiphyseal cartilages, short bone development.
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The Skeleton as a Calcium Reserve (Fig. 6-15)
- Calcium is the most abundant mineral stored (bones) in the body. Membranes of neurons, muscles, heart muscles are sensitive to extracellular calcium levels. Too much or too little calcium in the blood can cause cardiac arrhythmias. Therefore extracellular calcium levels must be maintained between 4.5-5.3 mEq/L. Three organs in the body tightly regulate extracellular Ca2+ levels.
- i. kidneys Ca2+ excretion
- ii. bones Ca2+ storage
- iii. intestines Ca2+ absorption
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Parathyroid Hormone (PTH):
produced by parathyroid gland, increase osteoclast numbers, increase absorption of Ca2+ by the intestines (with Calcitriol), stimulates the formation and secretion of calcitriol by the kidneys, decrease excretion Ca2+ by the kidneys. Goal of PTH is raise blood Ca2+ levels.
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Calcitriol:
produced by kidneys, works with PTH to increase Ca2+ absorption by the intestines.
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Calcitonin:
produced by thyroid gland, inhibit osteoclast activity, increase excretion Ca2+ by the kidneys. Goal of calcitonin is to lower blood Ca2+ levels.
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Fracture Repair (Fig. 6-17)
- fracture hematoma
- spongy bone works internally
- cartilage works externally
- bone repaired
- remodeling
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Pott fracture
Occurs at the ankleand affects both bones of the leg
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Comminuted fractures
Shatter the affected are into a multitude of bony fragments
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Transverse fractures
A break in a bone shaft across its long axis
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Spiral fractures
Produced by twisting stresses that spread along the length of the bone
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Displaced fractures
Produce new and abnormal bone arrangements; non displaced fractures retain normal alignment of the bone or fragments
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Colles fracture
A brak in the distal portion of the radius, is typically a result of reaching out to fall
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Greenstick fracture
Only one side of the shaft is broken, and the other side is bent This type of fracture generally occurs in children whose long bones have yet to fully ossify
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Epiphyseal fractures:
Tend to occure when the bone matrix is undergoing calsification and condrocytes are dying. A clean transverse fracture along this line generally heals well. Unless carefully treated, fractures between the epiphyseal cartialage can perminantly stop growth at this state
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Compression fractures
Occur in vertebre subjected to extreme stresses, such as thoseproduced by the forces that arise when you land on your seat in a fall.
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Osteopenia:
inadequate ossification, weaker, thinner bones, decreased osteoblast activity while osteoclast activity remains the same. As a result bones are prone to fractures, shrink in height, and lose teeth.
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Osteoporosis (Fig. 6-19)
loss of bone mass severe, bones break and fracture, become immobile, lose more bone mass
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osteoclast-activating factor:
released by some bone marrow or breast cancer cells, increase number and activity of osteoclasts
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Bone Markings (Surface features) (Table 6-1) also in lab text (Tab. 9-1).
Forensic scientists and archaeologists study anatomical features of bones to determine size, weight, sex, and appearance of individual based on the stress put on the bones and the adaptations the bones made. Surface markings are also for physiological functions such as muscle attachment, nerve passage ways, etc.
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Part II: The Axial Skeleton
Most of the bones in the axial skeleton are cover in the first laboratory practical. However some terms that pertain to the axial skeleton are listed below.
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Temporomandibular Joint (TMJ) Syndrome:
involuntary behavior such as grinding teeth induced by stress contributes to TMJ syndrome. Mandible is out of alignment by jaw muscle spasms, facial pain, can’t open mouth fully, Vicious cycle of muscle spasm, misalignment, pain, muscle spasm, etc.
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Lordosis: (Fig. 7-17b)
sway back, exaggeration of lumbar curvature (seen in beer gut people, last trimester of pregnancy)
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Kyphosis: (Fig. 7-17a)
hunch back, exaggerated thoracic curvature (seen in osteoporosis compression fractures of the vertebra)
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Spina bifida:
vertebral arch to close off spinal foramen is incomplete, meninges bulge out. Cases of spina bifida can range from mild (occurance in lumbar or sacral regions) to severe (area affected involve brain and spinal cord)
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Scoliosis: (Fig. 7-17c)
abnormal lateral curvature of the spine
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Fontanels: (Fig. 7-15 Martini text, Fig. 12.2 lab text)
membranous fibrous connections between the fetal and baby’s bone plates. About 5 years of age sutures develop. What are two purposes of fontanels?
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Craniostenosis:
The premature closure of one or more fontanels, which can lead to disorders of the brain and skull
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Hyoid Bone: (Fig. 7-12c)
horseshoe shape bone, supports the larynx, attachment site for larynx, pharynx, and tongue. Only bone in the body that does not articulate with any other bone in the body.
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Sinuses:
(paranasal sinuses, Fig. 7-14 in Martini text, Fig. 10.9 in lab text) cavities in skull that make the skull lighter without weakening the skull’s integrity. Sinuses have passageways that lead to the nasal cavity.
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Deviated (nasal) septum
The bony nasal septum is made between the vomer (inferior) and the perpendicular plate of the ethmoid septum (superior). A deviated nasal septum is bent usually at the junction between the bony and cartilaginous regions of the nasal septum. This bend causes sinus drainage problems that can lead to chronic cycles of infections and inflammation of the sinuses.
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Part III: The Appendicular Skeleton
Most of the bones in the appendicular skeleton are cover in the first laboratory practical. However some terms that pertain to the appendicular skeleton are listed below.
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Carpal Tunnel Syndrome:
Carpal tunnel syndrome is an example of cumulative trauma disorder or overuse syndrome where an inflammation of the tendon sheath of the palm flexor tendons occurs. This inflammation puts pressure on the nerve causing pain, numbness, and tingling. Carpal tunnel syndrome is due to repetitive motions of hand movements over an extended period of time. Treatment includes anti-inflammatory drugs, wrist support/ guard to immobilize and stabilize the region, and/or surgery.
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Why is the clavicle the most frequent bone to break in the human body? The clavicle bones are small and fragile; they are also in vulnerable areas of your skeleton.
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What are the differences between men’s pelvic girdles and women’s pelvic girdles? (Fig. 8-9, 8-10 in Martini text, Tab. 11.1 in lab text)
- 1. Pubic angle in women is greater than 90o; men have 90o or less pubic angle.
- 2. The ilia of women hips spread more laterally; men’s ilia tend to spread more superior to the sacrum.
- 3. Women have a larger pelvic outlet than men.
- 4. Women’s pelvic inlet is larger and rounder than men’s pelvic inlet. Also the man’s pelvic inlet is heart shaped.
- 5. Women have less curvature on the sacrum and coccyx, whereas a man’s sacrum and coccyx tucks tighter into the pelvis.
- 6. Women have a lower pelvis.
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______1.The long shaft of the bone is the _______, the _______ is the area at the end of the bone, and the two sections are connected at a narrow zone called the _______.
b. diaphysis, epiphysis, metaphysis
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______2. Greenstick fractures occur
d. when one side of the shaft is broken, and the other side is bent
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______3. The suture that separates the parietal bones from the frontal bone is the
a. coronal suture
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______4. The ___________is the part of the sternum that articulates with the clavicle.
c. manubrium
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______5. The hip bones are connected to each other in the anterior region of the pelvic girdle by a fibrocartilage joint called the
d. pubic symphysis
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______6. The socket where the head of the femur articulates with the hip bone is called
a. acetabulum
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______7. The fibrous connections between the cranial bones of the fetal skull are
b. fontanels
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______8. In anatomical position, the ulna lies
b. medial to the radius
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______9. The large medial bone of the leg is the
a. tibia
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______10. These mature bone cells maintain the matrix.
b. osteocytes
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11. Draw a figure of an osteon of compact bone. Label 5 features, structures, and/or cells.
See Figure 6-5a in text for osteon or Figure 9.3 in laboratory text
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12. Often pregnant women are given large daily doses of folic acid to prevent neural tube defects (NTD). a.What is the most common neural tube defect? b.How does the spinal cord develop abnormally in this particular NTD?
a.spina bifida, b. at the third week of development the vertebral arches of the embryo start to form. If the arches are incomplete (do not enclose the spinal cord), then the meninges bulge out causing mild to severe nervous development issues depending on the site of where spina bifida occurred. For example: the closer to the brain spina bifida occurs, the more severe the developmental defects.
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13. List the six hormones involved in the regulation of bone growth and how they affect the skeletal system.
See Table 6-2 in the text.
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