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A doctor oberves a teenager who noticed that one of his legs is about two inches longer than the other. He also sees that the patient had broken one of his legs when he was 8 years old, but the patient's notes don't indicate which leg. What conclusion is the doctor likely to come to?
The epiphyseal plate is the site of longitudinal growth in bones. The patient likely broke the leg along the plate, which caused it to grow less than the other leg.
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A fetal rat's femoral cartilage is injected with a marker prior to endochondral ossification. The marker becomes deactivated as the cartilage is converted to bone. In which part of the femur would we expect to see a high concentration of the marker once the rat reaches adulthood?
The first important concept to understand for this question is the process of endochondral ossification. In this process, cartilage is converted into bone during the early life of an organism. Since the question specifies that the rat has reached adulthood, it must refer to the parts of the final bone product that remain as cartilage once endochondral ossification is complete.
Spongy bone and compact bone in the diaphysis have already ossified, and the medullary cavity contains bone marrow and adipose. To find cartilage in any of these regions would indicate a developmental abnormality.
The ends of bones that are in contact with other bones are protected from frictional damage by articular cartilage. Articular cartilage is essential to maintaining healthy joint function. Deterioration of this cartilage results in arthritis, or inflammation in the joints.
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Which of the following is true relating cartilage to the skeletal system?
Cartilage is a flexible, avascular connective tissue. It is less flexible than muscle, but softer and more flexible than bone. These properties make it an ideal candidate for joints, providing a medium between the muscles and bones that enact forces on the joint. Cartilage is found on the epiphyses of long bones and between certain bones, such as vertebrae, to cushion the motion of the joints.
Due to its avascular nature, cartilage does not easily regenerate. It is formed by chondroblasts (cartilage cells) in a chondrin matrix. In endochondral ossification, cartilage can be used as a precursor to bone, but will never be formed as a result of bone breakdown. Finally, there are three types of cartilage: elastic cartilage, hyaline cartilage, and fibrous cartilage.
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An adolescent girl is suffering from reduced longitudinal bone growth in her humerus. Which of the following bone regions should be examined closely in order to determine the cause of the growth deficiency?
Longitudinal bone growth occurs at the epiphyseal plate through the process of endochondral ossification. Cartilage cells undergo rapid mitosis in this region forming the structure that is later replaced by bone tissue.
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In childbirth, the child’s skull is flexible due to fontanelles, or soft regions that are composed of connective tissue. Through what process does the connective tissue of the infant’s skull become bone?
Intramembranous ossification is the process in which bones are formed within dermal tissue. This process is responsible for forming the flat bones of the skull, as well as the clavicle. Other bones of the body are formed by the process of endochondral ossification, in which cartilage is replaced by bone tissue.
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What type of bone cell is responsible for resorbing bone tissue?
Osteoclasts are bone cells that are responsible for resorbing—or breaking down—bone tissue. Osteoblasts, on the other hand, deposit bone tissue.
Cartilage is not a type of bone cell at all; it is a type of connective tissue consisting of chondrocytes suspended in an avascular matrix. Lacunae are small cavities within the bone matrix that house osteocytes; osteocytes are mature bone cells.
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How do bones maintain a functional weight as they grow?
Osteoclasts dissolve bony matrix and repatriate calcium as the bone grows. This expands the meduallary cavity and maintains a manageable mass for the bones, while allowing the body to recycle valuable calcium deposits.
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Where are osteocytes located?
Osteoytes, the long-lived star-shaped cells found in established bones, are primarily found within Haversian systems—the target-shaped tubes of bone matrix. They are encased in a bubble of interstitial fluid known as a lacuna.
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The diaphysis is able to grow in length because of thin layers of cartilage cells located in which of the following regions?
Thin layers of cartilage cells in the epiphyseal plate enable the diaphysis (bone shaft) to grow in length. The epiphyseal line forms when growth stops and ossification occurs, permanently fusing the diaphysis and epiphysis.
The periosteum is a tough connective tissue sheath that covers the outer surface of bones. The medullary cavity is a hollow cylinder inside the diaphysis. The medullary cavity contains bone marrow, which contains blood cells in different stages of development. The Haversian canals perforate bony structure and contain blood vessels, lymph vessels, and nerves.
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An individual with long cancer is advised to undergo radiation therapy. The radiation therapy destroys all of his bone marrow. Which of the following will be deficient in this individual?
The primary function of red bone marrow is to make red blood cells in the process known as erythropoiesis. If all bone marrow is destroyed, then an individual will lose the ability to make red blood cells.
Myogenesis is performed by muscle fibers and satellite cells. Osteogenesis is performed by osteoblasts. Neurogenesis primarily occurs during early development and is performed by neural stem cells.
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Hematopoietic stem cells are the cells that are targeted in bone marrow transplants. These stem cells are found in the red marrow of the bone. Which part of a long bone would be targeted in order to extract hematopoietic stem cells for a transplant?
Red bone marrow is filled with hematopoietic stem cells. Red bone marrow is found in the heads, or epiphyses, of long bones. Yellow marrow fills the medullary cavity and consists mostly of fats. The diaphysis contains the medullary cavity and therefore contains no red marrow. The periosteum has no marrow in it at all.
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Hypoxia would result in which of the following?
Since red bone marrow is a site of red blood cell and platelet production, hypoxia (low oxygen) would result in an increase in red marrow and therefore RBC concentration. Yellow bone marrow (typcially adipocyte-filled) can be converted into red bone marrow under conditions of low oxygen or blood loss.
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What is the main function of red bone marrow?
Red bone marrow is primarily located in flat bones (such as the sternum and pelvis) and in the epiphyses of long bones. It is responsible for producing red blood cells, a process known as erythropoiesis. At birth, all bones of the human skeleton carry out erythropoesis, but many bones stop this function as the newborn ages.
It is important to note that yellow bone marrow is found in the medullary cavity within the diaphyses of long bones and assists in fat storage.
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Duchenne Muscular Dystrophy is an X-linked recessive genetic disorder, resulting in the loss of the dystrophin protein. In healthy muscle, dystrophin localizes to the sarcolemma and helps anchor the muscle fiber to the basal lamina. The loss of this protein results in progressive muscle weakness, and eventually death.
In the muscle fibers, the effects of the disease can be exacerbated by auto-immune interference. Weakness of the sarcolemma leads to damage and tears in the membrane. The body’s immune system recognizes the damage and attempts to repair it. However, since the damage exists as a chronic condition, leukocytes begin to present the damaged protein fragments as antigens, stimulating a targeted attack on the damaged parts of the muscle fiber. The attack causes inflammation, fibrosis, and necrosis, further weakening the muscle.
Studies have shown that despite the severe pathology of the muscle fibers, the innervation of the muscle is unaffected.
When a healthy muscle fiber is activated, Ca2+ ions will __________.
The troponin-tropomyosin complex wraps around actin when the muscle fiber is inactive, blocking all myosin-binding sites. When Ca2+ is released it binds to troponin, inducing a change in tropomyosin, which shifts its position to expose the myosin-binding sites on the actin filament.
Calcium does not bind any of the other listed answer choices.
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Duchenne Muscular Dystrophy is an X-linked recessive genetic disorder, resulting in the loss of the dystrophin protein. In healthy muscle, dystrophin localizes to the sarcolemma and helps anchor the muscle fiber to the basal lamina. The loss of this protein results in progressive muscle weakness, and eventually death.
In the muscle fibers, the effects of the disease can be exacerbated by auto-immune interference. Weakness of the sarcolemma leads to damage and tears in the membrane. The body’s immune system recognizes the damage and attempts to repair it. However, since the damage exists as a chronic condition, leukocytes begin to present the damaged protein fragments as antigens, stimulating a targeted attack on the damaged parts of the muscle fiber. The attack causes inflammation, fibrosis, and necrosis, further weakening the muscle.
Studies have shown that despite the severe pathology of the muscle fibers, the innervation of the muscle is unaffected.
ATP is required for muscle contraction. Identify which of the following are true
I. ATP binding causes myosin to release actin
II. Actin carries an inactive ADP when myosin binds
III. The myosin head movement to contract the muscle converts ATP to ADP
This question requires us to know the ATP binding cycle associated with muscle contraction. I is true; binding of ATP causes myosin to release actin. When there is no ATP present, the myosin remains bound and the muscle becomes stiff (rigor mortis). II is false; actin does not bind ATP. III is also false; ATP is converted to ADP when the myosin head goes from the contracted position to the relaxed position, not the other way around.
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The area where the motor neuron intersects the muscle is known as the __________.
The neuromuscular junction is where the nerve fibers directly connect to the muscle to deliver signals from the brain to the muscle tissue. "Cross bridge" refers to the linkage of actin and myosin filaments. The other answers sound similar, but are incorrect.
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Muscle contraction is mainly powered by which chemical?
ATP (adenosine triphosphate) is the primary chemical that provides the power for muscle contraction. ADP (adenosine diphosphate) is the resulting chemical when ATP is expended. ATP is required for the cross-bridge cycle. Acetylcholine is a neurotransmitter used in muscle contraction, but does not provide a power source. Lactic acid results from anaerobic production of ATP.
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A sarcoplasmic reticulum is found within a muscle cell. The sarcoplasmic reticulum is a modified version of the endoplasmic reticulum.
What is the modified characteristic of a sarcoplasmic reticulum?
The sarcoplasmic reticulum contains a large amount of Ca2+ ions. This calcium is released from the sarcoplasmic reticulum when an electrical signal is sent to the cell. This release of calcium allows for contraction.
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A muscle will not have all of its fibers contract at once. Instead, the muscle is divided into multiple bundles of muscle fibers, with a neuron innervating all of the fibers in a given bundle. Each collection of fibers controlled by a single neuron is referred to as a motor unit.
Which of the following statements is false when discussing motor units?
Smaller motor units are activated first during muscular contraction. If more force is needed, larger motor units will be recruited in order to provide the necessary force.
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A toxin prevents calcium from being actively pumped back into the sarcoplasmic reticulum. What would you expect to be a consequence of this toxin's presence in the body?
Before a contraction, calcium is released from the sarcoplasmic reticulum and attaches to troponin. Troponin will then remove tropomyosin from the active site on actin where myosin is able to attach.
If calcium is never pumped back into the sarcoplasmic reticulum, the active site on actin will stay exposed, which allows myosin to attach at all times.
Note that calcium is also responsible for initiating acetylcholine release from the neuron at the neuromuscular junction; however, this process involves extracellular calcium ions and is not linked to the sarcoplasmic reticulum.
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