anatomy lecture 2
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Why are bones considered an organ?
It contains two tissues; Connective tissue and nervous tissue.
Name 6 functions of bones.
- 1- support
- 2- protects organs
- 3- movement
- 4- mineral and energy storage
- 5- cell formation (red bone marrow forms red and white blood cells)
- 6- Energy metabolism- blood-sugar regulation
Describe in detail the gross
anatomy of a long bone. Describe the gross anatomy of flat, short and irregular
Long bone- compact bone outer layer with a spongy bone inner layer filled with red or yellow bone marrow, diaphysis
Short, irregular, and flat- periosteum covered compact bone and endosteum covered spongy bone. no diaphysis (shaft forming a long axis as in long bones) no marrow cavity,
Draw and label an osteon.
Describe its histological features.
- Osteons are long cylindrical tubes aligned parallel to the bone. it has a central canal with a nerve, artery and vein. It is filled with lamallae, inside that there are osteocyes in lacunae, and canaliculi.
Describe differences between
compact bone tissue and spongy bone tissue.
conpact bone has the osteons looks solid
spongy bone has trabecula holes containing several layers of lamellae and osteocytes
Describe the chemical composition of bone and distinguish between its organic and inorganic components.
A_ Organic component: cells fibers and ground substances . 35% of bone tissue mass. The presence of large amount of collagen fibers gives bones flexibility.
- B_ Inorganic component: mineral salts of Calcium phosphate (hydroxyapatites) makes 65% of bone mass. The crystals are tightly packed and give bone hardness and
- the ability to resist compression.
What is the intramembranous ossification? List and describe the 4 phases of this process.
- A_ Intramembranous ossification:
- all bones of the skull (except few at the base) and the clavicle are formed with this process. Bone is formed within a mesenchymal membrane starting at the
- 8th gestational week. This process can be broken down into 4 stages:
- 1_ Within the mesenchyme membrane, selected cells cluster in the middle of the membrane and differentiate into osteoblasts, forming an ossification
- 2_ Osteoblasts start secreting osteoid (bone-like) matrix that is rapidly
- mineralized. Osteoblast are “trapped” in calcified matrix and survive into the lacunae, becoming osteocytes.
- 3_The ossification center is highly vascularized, and osteoblasts lay
- osteoid following the blood vessels. Osteoid is mineralized forming new osseous tissue. This type of bone is called woven bone. Mesenchyme at the periphery of
- the expanding ossification center condenses and becomes periosteum.
4_ Compact bone is deposited on the outermost surface of the bone, while trabeculae are deposited in the middle portion of the newly formed bone.
What is the endochondral
ossification? List and describe the 5 phases of this process.
- Endochondral ossification: all bones with the exception of those following the intramembranous ossification, are formed this way. Endochondral ossification begins during the late second gestational month, and proceeds until the second decade of postnatal life. In this osteogenic process, bones are modeled in hyaline cartilage that is after
- replaced by osseus tissue. In order to understand the first stages of this process remember that cartilage tissue is not vascularized and that nutrients reach chondroblast by diffusion. Endochondral ossification can be broken down into 5 stages (description refers to a long bone):
1_ The endochondral bone is first modeled by a hyaline cartilage structure. Around the 8th gestational week, the perichondrion is invaded by blood vessels that brings osteoblasts. The perichondrion becomes a periosteum as osteoblasts secrete osteoid that is quickly mineralized. This way osteoblasts deposit a collar of bone tissue along the diaphysis.
2_ The presence of a collar bone prevents the nutrients to diffuse into the diaphysis. Chondroblasts and chondrocytes will die, and the matrix, as a consequence, will calcify and deteriorate leaving a cavity in the middle of the diaphysis (cavitation of diaphysis).
- 3_ The newly formed cavity in the diaphysis is invaded by a periosteal bud (vessels, artery and vein) that brings nutrients, osteoblasts, osteoclasts. Osteoclasts remove the calcified cartilage, and osteoblasts start secreting osteoid that
- mineralizes. This way spongy bone is deposited in the middle of the diaphysis. This osseous tissue is called the primary ossification center and it is located in the diaphysis.
- 4_ Secondary ossification centers are formed in the epiphysis. Cartilage in the center of the epiphysis calcifies and deteriorates. Vessels invade this area and bring osteoblasts (that remove the calcified cartilage)
- and osteoblasts (that deposit osteoid). This way new bone tissue is formed. These are the secondary ossification centers.
5_ Ossification of the epiphysis continue until the entire structure is substituted by osseous tissue. Hyaline cartilage is still present at the level of the articular cartilage and of the epiphyseal plates. Epiphyseal plates are structures that will ensure the lengthening of the long bone until the second decade of life.
Short bones arise from a single ossification center. Irregular bones develop from several ossification centers. Short long bones have only 1 secondary ossification center.
What is “bone remodeling”? What are the cells responsible of this process? What are the hormones that regulates this process? What is an other factor regulating bone remodeling?
Bone remodeling is regulated by hormones and by mechanical and gravitational forces applied to the skeleton.
Hormonal regulation of bone remodeling: rising levels of Ca++ stimulates thyroid to secrete calcitonin. Calcitonin stimulates Ca++ deposition in osseus tissue by inhibiting osteoclasts. Decreasing levels of Ca++stimulates parathyroid glands to release the parathyroid hormone (PTH). PTH stimulates osteoclasts to degrade bone matrix in order to release Ca++ into the blood.
Mechanical regulation of bone remodeling: Many evidences support the statement that a bone grows or remodels in response to the forces or demands placed upon it. For example bones are thicker where mechanical stresses are greatest, trabeculae arrange a long lines of stress, the attachment of tendons and ligaments (points of great mechanical stress) leave markings on bones). In practical terms this means that a healthy diet and physical exercise guaranties strong healthy bones.
What is a compound fracture? And a simple fracture?
Bone fractures are classified as simple (where bone does not break the skin) and compound (when broken bones protrude from skin).
Name the six more common types of fracture.
- 1_ comminuted: Bone breaks into three or more fragments 2_ compression: bone is crushed
- 3_ spiral: bone break because of excessive twisting forces 4_ epiphyseal: bone breaks at the level of the epiphyseal plate
- 5_ depressed: broken bone is pressed inward
- 6_ greenstick: bone is broken incompletely
Describe the 4 phases of bone repair.
- 1_ Hematoma formation: blood vessels of the periosteum are broken and blood clot is formed around bone fracture.
- 2_ Fibrocartilage callus formation: new vessels grow into the hematoma and within days new fibrocartilage and hyaline cartilage is deposited (cartilaginous callus)
- 3_ Within a week fibrocartilage is substituted by trabeculae of osseus tissue (bony callus).
- 4_ Over a period of months, the bony callus is remodeled according to mechanical stress applied to the bone.
What is osteoporosis and how is it treated?
Osteoporosis: low bone mass and deterioration of bone structure. Osteoporotic bones are porous and light. Compact bone is thinner and spongy bone has fewer trabeculae. Bones with this structure are broken easily. Fractures (especially of the head of the femur and of the vertebrae) are common symptoms of osteoporosis. This disease is most common in postmenopausal Caucasian women. Estrogen levels are decreased after menopause reducing bone mass. Treatment includes a dietary supplement of Ca++ and Vitamin D, exercise, estrogen replacement or other drugs that slow down osteoclasts activity.
Define a joint.
• Rigid elements of the skeleton meet at joints or articulations. Body movement occur at joints (where two bones connect).
Describe the three classes of joints based on the functional classification
- 1_synarthroses- immovable
- 2_amphiarthroses- slightly moveable
- 3_ diarthroses-freely mov
Describe the three classes of joints based on the structural classification. For each class name each sublclass.
- 1_fibrous- dense ct lots of collagen fibers. Sutures, syndesmoses, gomphoses
- 2_cartilaginous- cartilage. Synchondroses, symphyses, 3_synovial- cavitys.
Describe the six basic features of synovial joints You can use a drawing but practice to describe the structural organization of a synovial joint in full sentences. Ex; long bones
- 1) Articular cartilage; the ends of opposing bones have a layer of hyaline cartilage that absorb compressive forces to prevent damage.
- 2) Joint cavity; a small space that holds synovial fluid
- 3) Articular capsule; joint cavity is surrounded by two layers, one being the fibrous capsule that is dense irregular ct and gives strength to the joint to keep from pulling apart. The inner layer is the synovial membrane composed of loose ct and produces synovial fluid.
- 4) Synovial fluid; egg white, filtrated from blood, arising from capillaries in the synovial membrane. Lubricates joint cavity, nourishes cells in the cartilage.
- 5) Reinforcing ligaments; joint cavities are reinforced by band-like ligaments which gives strength. They can be extracapsular or intracapsular.
- 6) Nerves and vessels; nerve fibers innervate the articular capsule. Some detect pain.
What factors influence the stability of a joint?
The stability of a joint is provided by the fibrous capsule dense irregular ct that prevents the bones from puling apart. The reinforcing ligaments play a large role as well by giving support and strength to the joint in or outside of the capsule.
Compare and contrast the structure, function and locations of bursae and tendon sheaths.
- *they both contain synovial fluid, associated with synovial joints, lubricate to reduce friction.
- Bursae- is a flattened fibrous sac lined by synovial membrane located where ligaments, muscles, skin, tendons or bones overlie and rub together.
- Tendon sheaths are much longer and wrap around tendons like hot dog buns. Located only in tendons subject to friction.
What are articular discs and where are they found?
- – Occur in the temporomandibular joint and at the knee joint – Occur in joints whose articulating bones have somewhat different shapes
- made of haylin cartilage
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