Chapter 45: Musculoskeletal System (All Parts) Flashcards
(103 cards)
1
Q
What are the three types of muscle?
A
Skeletal, smooth, and cardiac
2
Q
What is the movement of an animal from place to place?
A
Locomotion
3
Q
What is a structure that serves one or more functions related to support, protection, and locomotion?
A
Skeleton
4
Q
What are the three types of skeletons found in animals?
A
Exoskeletons and endoskeletons, and a third type, called a hydroskeleton
5
Q
What is an external skeleton made primarily of chitin that surrounds and protects most of the body surface of animals such as insects?
A
Exoskeleton
Exoskeletons provide support for the body, protection from the environment and predators, and protection for internal organs.
6
Q
What is the process when exoskeletons are shed, regrown, and strengthened?
A
Ecdysis, or molting
Becomes more vulnerable during this time to predation and the environment.
7
Q
What is an internal skeleton covered by soft tissue; present in echinoderms and vertebrates?
A
Endoskeleton
Unlike exoskeletons, however, endoskeletons are internal structures and do not protect the body surface. Some endoskeletons do, however, protect internal organs such as those in the thorax of vertebrates.
Either cartilage, or bone, or both.
8
Q
What is a relatively hard component of the vertebrate skeleton; a living, dynamic tissue composed of organic materials and minerals?
A
Bone
9
Q
What are the cells that form bone, and what are the cells that break it down?
A
Osteoblasts and osteocytes form bone.
Osteoclasts break it down.
10
Q
What protein largely consists of the organic matter secreted from osteoblasts and osteocytes which has a unique helical structure that gives bone its strength and flexibility?
A
Collagen
11
Q
What mineral part of the bone is composed of a crystalline mixture that provide it with its rigidity?
A
Ca2+ and PO4 2- (Cacium phosphate) and other ions.
12
Q
What do the ways that bones connect allow for?
A
Support, protection of internal structures, and movement.
13
Q
How is the vertebrate skeleton considered in two parts and what do they consist of?
A
The axial and appendicular skeletons
The axial skeleton is composed of the bones that form the main longitudinal axis of an animal’s body, including the skull, vertebrae, sternum, and ribs.
The appendicular skeleton consists of the limb bones and the bones that connect them tothe axial skeleton.
14
Q
What is a juncture where two or more bones of a vertebrate endoskeleton come together?
A
Joint
15
Q
What are the three different types of joints and how do they function?
A
Pivot, hinge, and ball-and-socket.
They are fused joints, too, like those in the skull and cranium.
16
Q
Where are blood cells and platelets formed?
A
Within the soft, fatty interior (called the marrow) of certain bones including the ilia, the vertebrae, and the ends of the femurs.
17
Q
How is homestasis of calciuma and calcium phosphate levels in blood achieved?
A
Large part through exchanges of these ions between bone and blood.
For example, if dietary intake of Ca2+ is low, Ca2+ is removed from bone and added to the blood, so that all of the vital cellular activities that depend on Ca2+, such as neuron signaling and muscle contraction, can continue to function normally.
If dietary Ca2+ is restored to normal, any available excess Ca2+ is redeposited in bone.
18
Q
What is Ca2+ cycling under the control of?
A
Hormones like the parathyroid hormone produced by the parathyroid glands.
About 99% of all the Ca2+ in a typical vertebrate’s body exists in bone. This represents a huge reservoir of Ca2+ for the blood.
19
Q
[Start 45.2 Skeletal Muscle Structure and the Mechanism of Force Generation]
How are muscle types classified?
A
Their structure, function, and control mechanisms.
20
Q
What is a type of muscle tissue, found only in hearts, in which physical and electrical connections between individual cells enable many of the cells to contract simultaneously?
A
Cardiac muscle
21
Q
What is a type of muscle tissue that surrounds and forms part of the lining of hollow organs and tubes in vertebrate bodies; it is not under conscious control?
A
Smooth muscle
Surrounds and forms part of the lining ofhollow organs and tubes, including those of the digestive tract, urinarybladder, uterus, blood vessels, and airways.
Contraction of the smooth muscle in such organs may propel the contents forward or churn them up, as when the stomach contracts after a meal.
In other cases, smooth muscle regulates the flow of substances by changing the tube diameter, as in the widening or narrowing of blood vessels that occurs when different parts of the body require more or less nutrients and oxygen.
22
Q
T/F Smooth muscle contraction is not under voluntary control. Instead, it is controlled by the autonomic nervous system, hormones, and local chemical signals.
A
True
23
Q
What is a type of muscle tissue that is attached by tendons to bones in vertebrates and to the exoskeleton of invertebrates?
A
Skeletal muscle
24
Q
What type of potentials are generated in vertebrate skeletal muscle and what type of potentials are generated in invertabrate skeletal muscles?
A
Action potentials
Graded potentials
The action potentials of vertebrate skeletal muscle cells result in an increased concentration of Ca
2+ in the cytosol, which triggers force generation.
25
What are individual cells within a muscle?
Muscle fibers
26
What do you call muscle fibers that are bound together in bundles by a succession of connective tissue layers?
Fascicles
27
How are must skeletal muscles linked to bones?
Bundles of collagen fibers known are tendons.
The transmission of force from contracting muscle to bone can be likened to a number of people pulling on a rope attached to a heavy object. Each person corresponds to a single muscle fiber, the rope corresponds to the tendons, and the bone is the heavy object.
28
What is a muscle that bends a limb at a joint?
What is a muscle that straightens a limb at a joint?
What are two or more muscles that produce oppositely directed movements at a joint?
Flexors (Hamstrings)
Extensors (Quadriceps)
Antagonists (Hamstrings and quadriceps)
29
What do skeletal muscle fibers arise from?
Several cells that fuse to form a single mature cell with multiple nuclei.
30
What are rodlike collection of myofilaments within a muscle fiber (cell); and contains thick and thin filaments?
Myofibril
Myofibrils extend from one end of the fiber to the other and are linked to the tendons at the ends of the fiber.
31
What are arranged in a repeating pattern running the length of a myofibril?
The thick and thin filaments.
32
What is one complete unit of the repeating pattern of thick and thin filaments within a myofibril?
```
A sacomere ((from the Greek
sarco, meaning muscle, and mer, meaning part)
```
33
What is a section of the repeating pattern in a myofibril composed almost entirely of the motor protein myosin?
A thick filament.
Myosin is a motor protein found abundantly in muscle cells and also in other cell types.
34
T/F Myosin is a motor protein that does not hydrolyze ATP as a source of energy.
False, it does hydrolyze ATP.
35
What is a section of the repeating pattern in a myofibril that contains the cytoskeletal protein actin, as well as two other proteins—troponin and tropomyosin—that play important roles in regulating contraction?
Thin filaments
Actin is a cytoskeletal protein, found in the thin filaments of myofibrils.
36
Review: From the smallest to the largest. How is a myofibril designed in structure?
Small filaments known as thin and thick filaments are arranged in repeating patterns known as sarcomeres.
These sarcomeres are separated by z lines. Myofibrils are bundles of repeated sarcomeres in a cord and when multiple myofibrils are bundled, they make a muscle fiber and extend from one end of a fiber to the the other end which is attached to a tendon.
37
What are the components of a sarcomere? (5)
A band
Z line
I band
H zone
M line
38
Which component of a sacromere is formed by the thick filaments located in the middle of each sarcomere, where their orderly parallel arrangement produces a wide, dark band? A portion of the thin fi laments overlaps the thickfi laments in this band.
A band
39
Which component of a sacromere is a network of proteins to which thin filaments are attached?
Two successions of these lines define the boundaries of one sarcomere.
Z lines
40
Which component of a sacromere lies between the A bands of two adjacent sarcomeres which are on either side of a Z line?
I band
Each I band contains those portions of the thin filaments that do not overlap the thick filaments, and each I band is bisected by a Z line.
41
Which component of a sacromere is a narrow region in the center of the A band?
H zone
It corresponds to the space between the two sets of thin filaments in each sarcomere.
42
Which component of a sacromere is in the center of the H zone and is composed ofproteins that link the central regions of adjacent thick filaments?
M lines
43
What is a region of myosin molecules that extends from the surface of each thick filament toward a thin filament in skeletal muscle?
Cross-bridges
44
What does the term muscle contraction refer to since muscles can generate force, or contract, without producing movement?
Activation of cross-bridges within muscle fibers, which initiates the generation of force.
45
How is the structure of the thin filaments designed?
Its a helical structure made up of two intertwined actin molecules which as closely associated together with tropomyosin and troponin and have important functions in regulating contraction
46
How are myosin proteins' three-domain structure composed in thick filaments?
Two intertwined tails, two hinges, and two heads.
The hinges are flexible regions that connect the heads to the tails. Each filament is made up of many myosin proteins associated in a parallel array, with the hinges and heads extending out to the sides, forming cross-bridges that can bind to actin.
47
What are the two heads on each thick filament used to bind to?
One for actin binding and the other ATP.
48
What provides the energy for the cross-bridge to move via a bending motion at the hinge?
The hydrolysis of ATP by myosin.
49
What is the process by which a muscle fiber shortens during muscle contraction?
Sliding filament mechanism
In this mechanism, the sarcomeres shorten, but neither the thick nor the thin filaments change in length. Instead, the thick filaments remain stationary while the thin filaments slide, pulling on the Z lines and shortening the sarcomere.
The sliding filament movement is propelled by the myosin cross-bridges. During shortening, each cross-bridge attaches to an actin molecule in a thin filament and moves in a motion somewhat like your fist bending at your wrist.
Because of the opposing orientation of the thick filaments, the movement of a cross-bridge forces the thin filaments toward the center of the sarcomere (the M line in the H zone), thereby narrowing the H zone and shortening the sarcomere
50
What does the ability of a muscle fiber to generate force and movement depend on?
The amount of interaction between actin and myosin.
51
What is during muscle contraction, the sequence of events that occurs between the time when a cross-bridge binds to a thin filament and when it is set to repeat the process?
Cross-bridge cycle
52
When does cross-bridge cycling occur?
When the Ca2+ concentration exceeds a critical threshold in the cytosol.
This usually occurs when neural input results in the release of Ca2+ from intracellular storage sites.
In other words, the contraction of skeletal muscle fibers is under nervous control.
53
What are the four steps of the cross-bridge cycle?
1. Cross-bridge binding
2. Power stroke (moving)
3. Detaching
4. Resetting
54
When the cross-bridge cycle begins, the myosin cross-bridges are in an energized state because of what?
It is produced by the hydrolysis of their bound ATP to ADP and inorganic phosphate (Pi).
55
How long do the ADP and Pi remain bound to the cross bridge?
Until step 2, when they begin to move.
56
What is the sequence of storage and release of energy by myosin analogous to?
The operation of a mousetrap.
Energy is first stored in the trap by cocking the spring (ATP hydrolysis) and is then released by the springing of the trap (head binds to actin and moves in power stroke).
57
Facts of the Cross-bridge Cycle
1. Binding - When Ca2+ concentration is high, energized cross-brdige can bind to actin. (ADP and Pi are already bound to the cross-bridge.)
2. Power Stroke - Release of Pi causes cross-bridge to move toward the H zone of the sarcomere. This power stroke moves the actin filament toward the H zone. ADP is then released.
3. Detaching - ATP binds to myosin, causing the cross-bridge to detach from the actin filament.
4. Hydrolysis of ATP to ADP + Pi provides energy, which causes the cross-bridge to move away from the H zone. ADP and Pi remain bound to the re-energized cross-bridge. Cycle can begin again.
N/A
Book definition and explanation.
Step 1: Ca2+ concentration increases, triggering the cross-bridge to bind to actin.
When the Ca2+ concentration in the cytosol increases, an energized myosin cross-bridge, along with its associated ADP and Pi, binds to an actin molecule on a thin filament.
Step 2: Release of Pi fuels the power stroke. The cross-bridge and thin filaments move.
The binding of an energized myosin cross-bridge to actin in step 1 triggers the release of Pi. This release causes a conformational change in the hinge of the myosin molecule. The change in conformation causes the cross-bridge to rotate toward the M line in the H zone at the center of the sarcomere, as myosin returns to its lower energy conformation. This step is known as the power stroke, which moves the actin filament. At this time, ADP is released from the cross-bridge.
Step 3: ATP binds to myosin, causing the cross-bridge to detach.
During the power stroke, myosin is bound very firmly to actin. After the power stroke is completed, this linkage must be broken to allow the cross-bridge to be reenergized and repeat the cycle.
The binding of a new molecule of ATP to the myosin cross-bridge alters myosin’s conformation and breaks the link between actin and myosin. ATP is not hydrolyzed in this step. Instead, ATP functions at this stage as an allosteric modulator of the myosin head, weakening the binding of myosin to actin and leading to their dissociation.
Step 4: ATP hydrolysis re-energizes and resets the cross-bridge.
After actin and myosin dissociate, the ATP bound to myosin is hydrolyzed by the ATPase activity of myosin. This hydrolysis re-energizes myosin, causing it to reset to the position that allows actin binding.
If Ca2+ is still available at this time, the cross-bridge can reattach to a new actin molecule in the thin filament, and the cross-bridge cycle will repeat, causing the muscle fiber to shorten further.
58
The regulation of muscle contraction by Ca2+ is mediated by what?
Tropomyosin and Troponin
59
What is a rod-shaped protein that plays an important role in regulating muscle contraction?
Tropomyosin
Tropomyosin proteins are arranged end to end along the thin filament.
60
How is tropomyosin arranged on the actin molecule in the absence of Ca2+?
They partially cover the myosin-binding site on each actin molecule thereby preventing cross-bridges from making contact with actin.
61
What is a small globular-shaped protein that plays an important role in regulating muscle contraction through its ability to bind Ca2+?
Tropoin
62
In the relaxed muscle fiber, how is each tropomyosin molecule held in the blocking position preventing myosin from attaching to actin?
Tropoin, which binds to tropomyosin and actin
1. Ca2+ binds to tropoin, causing tropomyosin to move away from the myosin-binding sites.
2. Myosin-binding sites are exposed.
3. Energized cross-bridge binds to actin and generates force.
63
What does the propagation of action potentials do which triggers contraction of muscle fibers?
Increases the concentration of cytosolic Ca2+
64
What is the sequence of events by which an action potential in the plasma membrane of a muscle fiber leads to cross-bridge activity?
Excitation-contraction coupling
The electrical activity in the plasma membrane does not act directly on the contractile proteins but instead acts as astimulus to increase cytosolic Ca2+
concentration.
The increased Ca2+ concentration continues to activate the contractile apparatus long after electrical activity in the membrane has ceased.
65
What is a specialized form of endoplasmic reticulum in a muscle fiber that is the source of the increase in cytosolic calcium involved in muscle contraction?
Sarcoplasmic reticulum. Acts as a Ca2+ reservoir.
The sarcoplasmic reticulum, which is a specialized form of the endoplasmic reticulum, is composed of interconnected sleevelike compartments and sacs around each myofibril.
66
What are invaginations of the plasma membrane of skeletal muscle fibers that open to the extracellular fluid and conduct action potentials from the outer surface of the fibers to the myofibrils?
Transverse tubules (T-tubules)
A contraction continues until Ca2+ is removed from troponin and the cytosol. This is achieved by ATP-driven Ca2+ transporters in the sarcoplasmic reticulum that decrease the Ca2+ concentration in the cytosol back to its resting concentration.
67
What is the contact point between an axon terminal of a motor neuron and a skeletal or cardiac muscle fiber?
Neuromuscular junction
Near the surface of the muscle fiber, the axon divides into several short processes, or terminals, containing synaptic vesicles filled with the neurotransmitter acetylcholine (ACh).
The region of the muscle fiber plasma membrane that lies directly under an axon terminal is called the
motor end plate; it is folded into what are known as junctional folds, where the ACh receptors are located.
These folds increase the total surface area available for the membrane to respond to ACh. The extracellular space between the axon terminal and the motor end plate is called the synaptic cleft.
68
What is an enzyme located on membranes of postsynaptic cells that respond to the neurotransmitter acetylcholine, such as in muscle fibers in a neuromuscular junction; breaks down excess acetylcholine released into the synaptic cleft?
This prevents overstimulation of a muscle fiber.
Acetylcholinesterase
69
[Start 45.3 Types of skeletal muscle fibers and their functions]
What do all types of myosin, with slightly different characteristics, share?
The ability to hydrolyze ATP and bind actin.
70
Since different skeletal muscle fibers contain forms of myosin that differ in the maximal rates at which they can hydrolyze ATP, what does this then determine?
Determines the maximal rates of cross-bridge cycling and muscle shortening.
71
What is a skeletal muscle fiber containing myosin with low ATPase activity?
Slow fibers
72
What is a skeletal muscle fiber containing myosin with higher ATPase activity?
Fast fibers
Although the rate of cross-bridge cycling is about four times faster in fast fibers than in slow fibers, the maximal force produced by both types of cross-bridges is approximately the same.
73
What is the second means of classifying skeletal muscle fibers?
Based on the type of metabolic pathways available for synthesizing ATP.
74
What is a skeletal muscle fiber that contains numerous mitochondria and has a high capacity for oxidative phosphorylation?
Oxidative fiber
Most of the ATP production by such fibers depends on blood flow delivering oxygen and nutrients to the muscle. Not surprisingly, therefore, these fibers are surrounded by many small blood vessels.
75
What do oxidative fibers contain large amounts of which is an oxygen-binding protein that INCREASES the availability of oxygen in the fiber by providing an intracellular reservoir of the gas?
Myoglobin
The large amounts of myoglobin present in oxidative fibers give these fibers a dark-red color. For this reason, oxidative fibers are often referred to as red muscle fibers. The benefit of red muscle fibers is they can maintain sustained action over a long period of time without fatigue.
76
What is a skeletal muscle fiber that has relatively few mitochondria but possesses both a high concentration of glycolytic enzymes and a large store of glycogen?
Glycolytic fiber
Corresponding to their limited use of oxygen, these fibers are surrounded by relatively few blood vessels and contain little myoglobin. The lack of myoglobin is responsible for the pale color of glycolytic fibers and their designation as white muscle fibers.
77
What are the three major types of skeletal muscle fibers?
Slow-oxidative fibers, fast-oxidative fibers, and fast-glycolytic fibers.
78
What is a skeletal muscle fiber that has a low rate of myosin ATPase activity but has the ability to make large amounts of ATP; used for prolonged, regular movement?
Slow-oxidative fibers
Slow-oxidative fibers have low rates of myosin ATPase activity but have the ability to make large amounts of ATP.
These fibers are useful for prolonged, regular types of movement, such as steady flight over a period of time, long-distance swimming, or the maintenance of posture.
These muscles, for example, are what give the red color to the dark meat of ducks, which use the muscles for flight. Long-distance runners have a high proportion of these fibers in their leg muscles. These types of activities require muscles that do not fatigue easily.
79
What is a skeletal muscle fiber that has high myosin ATPase activity and can make large amounts of ATP; used for long-term actions?
Fast-oxidative fibers
Fast-oxidative fibers have high myosin ATPase activity and can make large amounts of ATP. Like slow-oxidative fibers, these fibers do not fatigue quickly and can be used for long-term actions.
They are also particularly suited for rapid actions, such as the rapid trilling sounds made by the throat muscles in songbirds or the shaking of a rattlesnake’s tail that produces a clicking sound.
80
What is a skeletal muscle fiber that has high myosin ATPase activity but cannot make as much ATP as an oxidative fiber because its source of ATP is glycolysis; best suited for rapid, intense actions?
Fast-glycolytic fibers
Fast-glycolytic fibers have high myosin ATPase activity but cannot make as much ATP as oxidative fibers, because their source of ATP is glycolysis.
These fibers are best suited for rapid, intense actions, such as a cheetah’s short sprint at maximum speed. Sloths, by contrast, have few or no fast-glycolytic fibers in their leg muscles, which is not surprising given a sloth’s very sedentary lifestyle.
Fast-glycolytic fibers fatigue more rapidly than fast-oxidative fibers. The breast meat of chickens, for example, appears white because, unlike ducks, chickens do not fly except for very short distances and therefore do not require oxidative pectoral muscles.
The fast-glycolytic muscles of chickens, however, are ideal for short flights in the air that help them quickly escape predators. When they land, chickens use slow-oxidative fibers in their leg muscles to run long distances as they continue to elude a predator.
81
T/F Muscle groups within an animal’s body have different proportions of each type of fiber interspersed with one another; many activities require the action of all three types of fibers at once.
True
82
What is hypertrophy of muscle fibers and what does it accomplish?
Increase in size of muscle fibers which happens with resistance exercise.
Because the number of fibers in a muscle does not normally change significantly throughout adult
life, the increases in muscle size that occur with resistance exercise result primarily from increases in the size of each fiber.
These fibers undergo an increase in diameter due to the increased synthesis of actin and myosin filaments, which form more myofibrils.
83
What changes are made to muscle fibers with relatively low intensity but long duration activity like running?
Exercise of relatively low intensity but long duration—popularly called aerobic exercise, including running and swimming—increases the number of mitochondria in the fibers that are required in this type of activity.
In addition, the number of blood vessels around these fibers increases to supply the greater energy demands of active muscle. All of these changes increase endurance.
By contrast, short-duration, high-intensity exercise, such as weightlifting, primarily affects fast-glycolytic fibers, which are used during strong contractions.
In addition, glycolytic activity is enhanced by increased synthesis of glycolytic enzymes. The results of such high-intensity exercise are the increased strength and bulging muscles of a conditioned weight lifter. Such muscles, although very powerful, have little capacity for endurance and therefore fatigue rapidly.
84
What is a reduction in the size of a structure, such as a muscle?
Atrophy
85
[Start 45.4 Animal Locomotion]
Although the precise mechanism may differ among animals, locomotion with few exceptions (such as the rhythmic beating of cilia in ctenophores) results from what?
Muscular contractions that exert force on oneof the types of skeletons discussed at the beginning of this chapter.
86
What have most swimming animals, including fi shes,amphibians, reptiles, diving birds, and marine mammals, have evolved to make swimming more efficient?
Evolved streamlined bodies that reduce drag.
87
What is an advantage of water for a water organism?
An energetic advantage to swimming is that fishes and other swimmers do not need to provide as much lift to overcome gravity. Because the density of water is similar to that of an animal’s body, water provides buoyancy, which helps support the animal’s weight.
88
What is the most costly means of locomotion?
Locomotion on land is, on average, the most energetically costly means of locomotion.
Whereas gravity is not an important factor for locomotion in swimming animals, terrestrial animals must overcome gravity each time they take a step.
89
What are the four different lineages that flying is hypothesized to evolve from?
Pterosaurs, insects, birds, and mammals (bats)
Flying provides numerous advantages: Animals can escape land-based predators, scan their surroundings over great distances, and inhabit environments such as high cliffs that may be inaccessible to non flying animals.
90
T/F The mechanics of flying is more costly than swimming but less costly than running on land.
True
As with swimming, resistance to movement in flight is decreased by streamlined bodies.
In flying vertebrates, lift and thrust are provided by pectoral and other muscles that move the wings. The pectoral muscles are so powerful and massive that they constitute as much as 15–20% of a bird’s total bodymass and up to 30% in hummingbirds, which use their wings not only to fly but also to hover.
The requirement for large, strong pectoral muscles is one reason why the body mass of flying vertebrates is limited.
91
[Start 45.5 Impact on Public Health]
What can affect bon structure and function in humans?
This may involve defects in either the mineral or organic components of bone.
Disease
In addition, many diseases or disorders directly affect the contraction of skeletal muscle. Some of them are temporary and not serious, such as muscle cramps, whereas others are chronic and severe, such as the disease muscular dystrophy.
Also, some muscle diseases result from defects that originate in parts of the nervous system that control contraction of the muscle fibers rather than from defects that originate in the fibers themselves. One example is amyotrophic lateral sclerosis, a degenerative disease in which the destruction of motor neurons leads to skeletal muscle atrophy that may result in death from respiratory failure.
92
What are the two major abnormalities that can occur in bone?
Bone diseases are fairly common, particularly among individuals older than 50.
1. The first isimproper mineral deposition in bone, usually due to inadequate dietary calcium intake or inadequate absorption of Ca2+ from the small intestine.
Without adequate minerals, bone becomes soft and easily deformed, as occurs in the weight-bearing bones of the legs of children with rickets (or osteomalacia, as it is called in adults)
2. A second major abnormality is a more common disease called osteoporosis, in which both the mineral and organic portions of bone are decreased. This disease, which affects four times as many women as men, occurs when the normal balance between bone formation and bone breakdown is disrupted.
93
What is a condition in children characterized by bone deformations due to inadequate mineral intake or malabsorption in the small intestine?
Rickets
94
What is a bone deformation in adults due to inadequate mineral intake or absorption from the small intestine?
Osteomalacia
95
Why is inadequate dietary calcium intake or inadequate absorption of Ca2+ from the small intestine treated with vitamin D?
This vitamin is the most important factor in promoting absorption of ingested Ca2+ from the small intestine.
96
What is one cause of osteoporosis?
Diuse of muscles.
In ways that are not completely clear, the force produced by active skeletal muscle contractions helps maintain bone mass. When muscles are not or cannot be used—due to paralysis or long-term immobilizing illnesses—bone mass declines.
97
Other than the disuse of muscles, what is another promotor of osteoporosis? Hence, why woman 4 times more than men are affected by this.
Hormonal imbalances.
Some hormones—for example, estrogen—stimulate bone formation.
When estrogen concentrations decline after menopause (the time when a woman’s reproductive cycles cease), bone density may decline, increasing the risk of bone fractures.
Men can get osteoporosis, too, but since they typically have more bone mass to start, and do not have a pronounced drop in sex hormone concentrations like women, the onset of the disease is usually later and less severe than in women.
98
What is another hormone that can act to demineralize bone, releasing Ca2+ into the extracellular fluid as a part of the way in which the body normally maintains Ca2+ homeostasis in the blood?
This hormone would have to be present in excess in order to cause enough demineralization of bone to result in osteoporosis.
Parathyroid hormone.
This may happen in rare cases when the glandsthat make these hormones malfunction and overproduce the hormones as such in hyperthyroidism.
Osteoporosis can be minimized with adequate calcium and vitamin Dintake and weight-bearing exercise programs. And even supplements of estrogen in postmenopausal women.
This therapy is controversial due tothe potential adverse effects of estrogen on cardiovascular health and possible increased risk of developing breast cancer.
99
Facts
Osteoporosis is the most prevalent bone disease in the U.S., affecting up to 15–30 millionin dividuals. It results in annual national expenditures of approximately $15–20 billion in hospital and other medical costs.
N/A
100
What is a group of diseases associated with progressive degeneration of skeletal and cardiac muscle fibers?
Muscular dystrophy is associated with the progressive degeneration of skeletal and cardiac muscle fibers, weakening the muscles and leading ultimately to death from heart failure and other causes.
The signs and symptoms become evident at about 2–6 years of age, and most affected individuals do not survive beyond the age of 30.
Affects 1 of every 3,500 American males; it is much less common in females.
101
What is the most common form of muscular dystrophy, and is an X-linked recessive disorder resulting from a defective gene on the X chromosome?
Duchenne muscular dystrophy
Because females have two X chromosomes, and males only one (plus one Y), a heterozygote female with one abnormal and one normal allele will not generally develop Duchenne muscular dystrophy. If she passes the abnormal allele to a son, however, he will have the disease.
102
What protein does the affected gene of Duchenne muscular dystrophy encode that becomes absent and is a large protein that links cytoskeletal proteins to the plasma membrane and is thought to maintain structural integrity of the plasma membrane in muscle fibers?
Dystrophin
In the absence of dystrophin, the plasma membrane of muscle fibers is disrupted, causing extracellular fluid to enter the cell. Eventually, the cell ruptures and dies.
103
What is one focus of interest in attempts to develop a treatment for muscular dystrophy, which is one of a large number of proteins that control muscle growth in mammals?
Myostatin
Myostatin functions to prevent overgrowth of skeletal muscle by inhibiting maturation of stem cells into new muscle fibers and by preventing excessive growth of mature fibers.
Researchers have identified animals with mutations in the gene that encodes myostatin. The mutations resultin the production of an inactive protein, and such animals show astonishing muscle development
