Muscular, Skeletal and respiratory systems : skin

A researcher is looking at a tissue sample under a microscope. The tissue is striated and branched. The cells are mononucleate and connected to each other via gap junctions. This tissue is most likely: A. cardiac muscle B. visceral smooth muscle. C. multiunit smooth muscle. D. skeletal muscle.

A. A researcher is looking at a tissue sample under a microscope. The tissue is striated and branched. The cells are mononucleate and connected to each other via gap junctions. This tissue is most likely cardiac muscle. Skeletal muscle is striated, but the cells are multinucleate (skeletal muscle is wrong). Cardiac muscle is striated and has a branched appearance. The cells are mononucleate and form a functional syncytium where each cell is connected to several others via gap junctions (cardiac muscle is correct). Neither multiunit smooth muscle (such as in the iris of the eye) nor visceral smooth muscle (such as in the wall of the gut) is striated and neither is branched, although the cells are mononucleate (multiunit smooth muscle and visceral smooth are wrong).

Which of the following statements best explains why chemical thermogenesis, or the metabolism of brown fat to generate heat, is far more common in newborns rather than adult humans? Question 8 Answer Choices A. Newborns have a decreased ability to shiver when placed in a cold environment B. The mature nervous system in newborns is able to effectively trigger vasoconstriction in the skin. C. The mature nervous system in newborns is able to effectively trigger vasodilation in the skin. D. Newborns have a greater thickness of subcutaneous fat than adults.

A. Chemical thermogenesis, or the metabolism of brown fat, is far more common in newborns because newborns have a decreased ability to shiver when placed in a cold environment. Adult humans have other mechanisms for generating heat, including shivering (involuntary contraction of skeletal muscles) and cutaneous vasoconstriction. On the other hand, human newborns have a decreased capacity for these adaptations, and are unable to relocate to a warmer region or find shelter on their own. In addition, their nervous systems are still immature and cannot effectively stimulate and maintain vasoconstriction of the blood vessels in the skin to retain heat. Note that dilation of these blood vessels would result in more heat loss as opposed to less, and achieve cooling rather than warming.

Connective tissue functions to bind and support other tissues. Which of the following is/are example(s) of connective tissue? I. Cartilage II. Muscle III. Bone A. I and III only B. I only C. II only D. I, II, and III

A. Connective tissue functions to bind and support other tissues. I and III only are examples of connective tissue. I. Cartilage II. Muscle III. Bone Cartilage and bone are both connective tissue, acting to connect and support, and are related in their lineage and activities (items I and III are true; "I only" and "II only" can be eliminated). Muscle is a distinct tissue in form, function, and derivation (item II is false; "I, II, and III" can be eliminated).

Which of the following characteristics are true concerning cardiac muscle? I. It is striated. II. It acts as a functional syncytium. III. It is under the control of the autonomic nervous system. A. I, II, and III B. II only C. I only D. II and III only

A. I, II, and III are true concerning cardiac muscle. I. It is striated. II. It acts as a functional syncytium. III. It is under the control of the autonomic nervous system. Cardiac muscle contains essentially the same organization of actin/myosin myofilaments found in skeletal muscle that give this tissue a striated appearance under the microscope (Item I is true). Although cardiac muscle is not a true syncytium, with more than one nucleus per cell, it is a functional syncytium since neighboring cells are linked by gap junctions that communicate action potentials directly from the cytoplasm of one cell to another (Item II is true). Stimulation by the sympathetic system increases the heart rate, while parasympathetic stimulation decreases the heart rate (Item III is true).

Which of the following is NOT true of the sarcoplasmic reticulum (SR)? A. It contains ligand-gated Ca2+ channels as well as Ca2+-ATPase transporters B. It functions in calcium sequestering, storage and release. C. It is a type of smooth endoplasmic reticulum. D. It functions in regulation of skeletal muscle contraction.

A. It is NOT true of the sarcoplasmic reticulum (SR) that it contains ligand-gated Ca2+ channels as well as Ca2+-ATPase transporters. The sarcoplasmic reticulum is a type of smooth endoplasmic reticulum ("it is a type of smooth endoplasmic reticulum" is true and can be eliminated). It functions in calcium sequestering, storage and release ("it functions in calcium sequestering, storage and release" is true and can be eliminated) and therefore also in skeletal muscle contraction ("it functions in regulation of skeletal muscle contraction" is true and can be eliminated). However it contains voltage-gated Ca2+ channels (and Ca2+-ATPase transporters), not ligand-gated channels ("it contains ligand-gated Ca2+ channels as well as Ca2+-ATPase transporters" is false and the correct answer choice).

Migratory animals that move annually to warmer climates must dissipate metabolic heat. This is often accomplished by: Question 5 Answer Choices A. dilating blood vessels in the skin. B. a high metabolic rate. C. shivering. D. increased contraction of muscles.

A. Migratory animals that move annually to warmer climates must dissipate metabolic heat. This is often accomplished by dilating blood vessels in the skin. A mechanism used to get rid of excess heat is to dilate arterioles leading to the skin (dilating blood vessels in the skin), putting more blood closer to the atmosphere where the heat can radiate away. Shivering, increased contraction of muscles, and a high metabolic rate all generate, not dissipate heat.

Patients with poorly controlled diabetes can develop diabetic ketoacidosis (DKA). DKA is a condition in which low insulin levels lead to the breakdown of fatty acids into ketones and ketoacids, which then accumulate in the blood and affect blood pH. In addition, low insulin results in elevated serum—and ultimately urine—glucose levels. Which of the following compensatory mechanisms would be expected in a patient with DKA? Question 9 Answer Choices A. Hyperventilation (increased respiratory rate) B. Hypoventilation (decreased respiratory rate) C. Hypertension (increased blood pressure) D. Bradycardia (decreased heart rate)

A. Of the listed compensatory mechanisms, the one that would be expected in a patient with diabetic ketoacidosis is hyperventilation. Ketoacidosis occurs because the ketones produced from breakdown of fatty acids are acidic, and lower serum pH. This prompts compensatory hyperventilation to blow off carbon dioxide and increase serum pH. Elevated urine glucose levels lead to increased urination, which causes volume depletion and is manifest by tachycardia (elevated heart rate) and hypotension (low blood pressure).

Patients suffering a penetrating trauma to the chest from a gunshot or knife wound often have subsequent difficulty breathing. Which of the following is the most likely explanation? Question 12 Answer Choices A. Equalization of pressures between the interpleural space and the outside air B. Excessive parasympathetic activity due to increased pain C. Interruption of blood flow to the alveolar capillaries D. Paralysis of the intercostal muscles due to trauma

A. Patients suffering a penetrating trauma to the chest from a gunshot or knife wound often have subsequent difficulty breathing. The most likely explanation for this is the equalization of pressures between the interpleural space and the outside air. Ventilation (breathing) depends on pressure changes generated as the lungs expand and contract. Since the lungs are incapable of expanding themselves, they rely on changes in the size of the chest cavity to accomplish this. Changes in the size of the chest cavity occur by contracting and relaxing the diaphragm and the intercostal muscles; since the lungs are stuck to the inside wall of the chest cavity they expand and contract right along with it. The primary force holding the lungs to the inner chest cavity wall is a negative pressure in the interpleural space. This is the (theoretical) space between the parietal pleura of the chest wall (inner wall) and the visceral pleura of the lung (lung outer surface), and the pressure here is approximately -4 mm Hg relative to the atmosphere. If this negative pressure is disrupted, such as in a penetrating chest wound, the force holding the lungs to the inner wall disappears, and the elasticity of the lungs causes them to shrivel up and pull away from the chest cavity wall. Again, lungs are incapable of expanding and contracting by themselves, so this would lead to extreme difficulty in breathing. The intercostal muscles are spread throughout the chest cavity in layers between the ribs; even if bullet or knife interrupted one of these nerves and paralyzed some of the muscles, the other intercostal muscles could continue to contract. While bleeding from the wound might cause slightly less blood flow to a localized region of the alveolar surface of the lung, the lungs are covered with capillaries and it would be hard for a single wound to disrupt flow enough to affect overall oxygenation, and in any case, this would not affect breathing per se. Finally, while excess parasympathetic activity might make exhaling difficult due to constriction of the bronchi, sympathetic activity is more likely to predominate in response to pain; sympathetic neurons dilate the smooth muscle surrounding the bronchi, improving air flow.

What accounts for the greater fatigue resistance found in Type IIA fast twitch muscle fibers compared to Type IIB fibers? A. Increased numbers of mitochondria B. Faster recycling of lactic acid back into pyruvate C. Higher levels of translation D. More effective histone packaging

A. The greater fatigue resistance found in Type IIA fast twitch muscle fibers is cause by increased numbers of mitochondria. The liver converts lactic acid back into pyruvate, not the muscles. Higher levels of translation would burn more energy, not produce it. Genomic packaging and storage, as referenced with the histones, does not relate to cellular energetics or endurance.

As the pH of the body decreases, how is ventilation rate impacted? Question 6 Answer Choices A. Increased to release CO2 B. Decreased to preserve CO2 C. Increased to move more O2 into the blood D. Decreased to limit the transfer of O2 into the blood

A. Increased to release CO2

An infant is born in the sixth month of gestation. Which of the following best describes her alveoli as compared to an infant born in the ninth month of gestation? Question 10 Answer Choices A. Higher amount of surfactant leading to an increase in surface tension B. Lower amount of surfactant leading to an increase in surface tension C. Higher amount of surfactant leading to a decrease in surface tension D. Lower amount of surfactant leading to a decrease in surface tension

B. An infant is born in the sixth month of gestation. Her alveoli have a lower amount of surfactant leading to an increase in surface tension, compared to an infant born in the ninth month of gestation. Surfactant is a substance consisting of phospholipids, proteins and ions. It is released by Type II alveolar cells, and its primary function is to reduce the surface tension of the alveoli in order to prevent their collapse and thus, to make breathing easier. Surfactant is not produced until about eight months of gestation, so in a premature infant (an infant born prior to the eighth month of gestation) there is an insufficient amount of surfactant for the child to breathe easily upon birth. A lack of surfactant would lead to an increase in surface tension. Note that this question is asking you about two factors (a two-by-two question): the amount of surfactant and the amount of surface tension. You can focus on one factor and eliminate two answer choices before considering the other factor.

Anemia is characterized by a reduced oxygen-carrying capacity of the blood, most commonly due to a decrease in hemoglobin production or a reduction in red blood cell count. Would an individual who was mildly anemic due to iron deficiency experience an increase in resting ventilation rate? Question 19 Answer Choices A. No, in the absence of hemoglobin more oxygen would dissolve in the plasma. B. No, anemia does not directly affect blood gas concentrations or blood pH. C. Yes, the lack of oxygen would cause blood pH to increase. D. Yes, the lack of oxygen would lead to an excess of carbon dioxide and a decrease in blood pH.

B. Anemia is characterized by a reduced oxygen-carrying capacity of the blood, most commonly due to a decrease in hemoglobin production or a reduction in red blood cell count. An individual with mild anemia due to iron deficiency would not experience an increase in ventilation rate because anemia does not directly affect blood gas concentrations or blood pH. Ventilation rate is controlled by chemoreceptors that respond to blood pH or to gases dissolved in the blood (CO2 and O2). Because iron is required for hemoglobin production, an individual suffering from iron-deficiency anemia will have a reduced amount of hemoglobin and thus a reduced ability to transport oxygen in the blood. However, this will not change the ability of oxygen to dissolve in the plasma (this is a chemical property of oxygen, "no, in the absence of hemoglobin more oxygen would dissolve in the plasma" is wrong), hence the chemoreceptors would not detect any difference in dissolved blood gases and would not change ventilation rate. Blood pH would not be significantly affected, and if anything, might experience a slight decrease due to an increased reliance on glycolysis ("yes, the lack of oxygen would cause blood pH to increase" is wrong), and there is no reason to assume that a lack of oxygen would increase blood CO2 levels ("yes, the lack of oxygen would lead to an excess of carbon dioxide and a decrease in blood pH" is wrong).

Which of the following do both skeletal and cardiac muscle cells undergo? I. Depolarization via fast voltage-gated sodium channels II. Depolarization plateau due to slow voltage-gated calcium channels III. Repolarization via voltage-gated potassium channels Question 3 Answer Choices A. III only B. I and III C. I only D. I, II, and III

B. Both skeletal and cardiac muscle cells undergo I and III. I. Depolarization via fast voltage-gated sodium channels II. Depolarization plateau due to slow voltage-gated calcium channels III. Repolarization via voltage-gated potassium channels Item I is true: fast voltage-gated sodium channels are responsible for depolarization in both skeletal muscle cells and cardiac muscle cells (III only can be eliminated). Item II is false: only cardiac muscle cells have a depolarization plateau (I, II, and III can be eliminated). Item III is true: voltage-gated potassium channels are responsible for repolarization in both cell types (I only can be eliminated).

Which of the following is the most accurate, from largest to smallest? Question 1 Answer Choices A. Fascicle, myofibril, myofiber, sarcomere B. Fascicle, myofiber, myofibril, sarcomere C. Myofiber, myofibril, sarcomere, fascicle D. Fascicle, myofiber, sarcomere, myofibril

B. Fascicle, myofiber, myofibril, sarcomere is the most accurate, from largest to smallest. A fascicle is a bundle of many skeletal muscle cells held together with connective tissue, and is the largest structure here ("myofiber, myofibril, sarcomere, fascicle" is wrong). A skeletal muscle cell is also called a myofiber ("fascicle, myofibril, myofiber, sarcomere" is wrong) and contains actin and myosin bundled into myofibrils. The functional unit of a myofibril is the sarcomere, which is a small section of the myofibril bound by two Z lines ("fascicle, myofiber, sarcomere, myofibril" is wrong).

Which of the following organ(s) is directly involved in the synthesis of substances important in bone remodeling? I. Thyroid II. Parathyroid III. Live A. II only B. I, II, and III C. II and III only D. I and II only

B. I, II, and III are directly involved in the synthesis of substances important in bone remodeling. I. Thyroid II. Parathyroid III. Liver Calcitonin (made in the thyroid), parathyroid hormone (made in the four parathyroid glands), and the biologically active form of Vitamin D (which requires hydroxylation reactions in both the liver and kidneys) coordinate bone remodeling by acting on osteoblasts and osteoclasts in the bone. These hormones also act on the intestines and kidneys to regulate levels of calcium and phosphate, the constituents of the inorganic component of bone (hydroxyapatite). All items are correct.

Third degree burns involve the epidermis and the entire thickness of the dermis. Which of the following tissue types is/are LEAST likely to be affected by a third-degree burn? I. Epithelial cells II. Adipose tissue III. Neuron Question 11 Answer Choices A. III only B. II only C. I, II, III D. I and III

B. I. Epithelial cells II. Adipose tissue III. Neuron The tissue type LEAST likely to be affected by a third-degree burn is adipose tissue. Third-degree burns involve the epidermis and the entire thickness of the dermis. The epidermis is the most superficial layer of skin, and consists of epithelial cells (Item I would be affected). Deep to the epidermis is the dermis, which is composed of multiple cell types embedded in a matrix of connective tissue. The dermis includes neurons as well as sebaceous and sweat glands (Item III would be affected). Deep to the dermis lies the hypodermis, a protective layer of adipose tissue which is involved in fourth degree burns but spared in less severe burns (Item II is least affected).

Which of the following statements regarding the microscopic structure of bone is correct? Question 7 Answer Choices A. Individual osteons are anatomically separated and are not connected. B. Individual osteocytes communicate with one another via gap junctions. C. Compact bone is vascular but aneural (does not contain nerves). D. Compact bone is innervated but is avascular (is not supplied by blood vessels).

B. Individual osteocytes communicate with one another via gap junctions is a correct statement regarding the microscopic structure of bone. Osteoblasts that become entrapped by bone are called osteocytes and maintain cytoplasmic attachments with one another via gap junctions. These cytoplasmic extensions traverse tiny channels (canaliculi), which course through the surrounding bone. Central (Haversian) canals contain lymph vessels, blood vessels, and nerves ["compact bone is innervated but is avascular (is not supplied by blood vessels)" and "compact bone is vascular but aneural (does not contain nerves)" are wrong]. Individual osteons are physically connected and are also connected via perforating (Volkmann's) canals, which carry vessels ("individual osteons are anatomically separated and are not connected" is wrong).

Which muscle fiber type would predominate in the calf muscles of a long-jumper? Question 5 Answer Choices A. Type II A B. Type II B C. Red fast twitch D. Red slow twitch

B. Long jumpers are intensely active for very short periods of time, thus the muscle fiber that would predominate in their calves would be Type II B, also known as white fast twitch fibers. These muscle fibers contract quickly and with great force, but are not fatigue resistant so can only be used for short term activity.

Which of the following blood vessels carries blood with the highest PCO2? Question 15 Answer Choices A. Pulmonary vein B. Pulmonary artery C. Renal artery D. Aorta

B. The blood vessel that carries blood with the highest PCO2 is the pulmonary artery. The pulmonary artery carries deoxygenated blood from the right ventricle to the lungs, so it carries the blood with the highest amount of carbon dioxide. The pulmonary vein carries oxygen-rich, CO2-poor blood from the lungs to the left atrium (pulmonary vein is wrong), the aorta carries this same oxygen-rich, CO2-poor blood to the body (aorta is wrong), and the renal artery carries oxygen-rich, CO2-poor blood to the kidneys (renal artery is wrong).

In which of the following locations would you LEAST expect to find red marrow? Question 9 Answer Choices A. Spongy bone of flat bones B. Diaphyses of long bones C. Epiphyses of long bones D. Spongy bone of long bones

B. The location in which you would least expect to find red marrow is the diaphyses of long bones. The diaphyses, or shafts, of long bones consist of a tube composed only of compact bone. The shafts are filled with yellow, or fatty marrow that is not hematopoietically active (i.e., involved in the synthesis of red blood cells). Red, or hematopoietic, marrow, is found within spongy bone in both flat and long bones; in long bones, it is found within the epiphyses, covered by an outer shell of compact bone.

Which of the following substances is LEAST involved in bone remodeling? A. calcitonin. B. thyroxine. Correct Answer (Blank) C. vitamin D. D. parathyroid hormone.

B. The substance that is LEAST involved in bone remodeling is thyroxine. Vitamin D, parathyroid hormone, and calcitonin are all involved in calcium metabolism and bone remodeling. Thyroxine has important general metabolic effects, and plays some role in bone remodeling, but is less involved than the other three hormones.

What hormone directly stimulates osteoblasts? Question 5 Answer Choices A. Calcitriol B. Calcitonin C. Parathyroid hormone D. Thyroid stimulating hormone

B. Calcitonin

How are long bones lengthened during the growth characteristic of childhood and adolescence? Question 4 Answer Choices A. Deposition of hydroxyapatite within the diaphysis B. Deposition of cartilage at the epiphyseal plate C. Deposition of cartilage within the diaphysis D. Deposition of collagen at the epiphyseal plate

B. Deposition of cartilage at the epiphyseal plate

A motor unit is the group of skeletal muscle cells innervated by a single motor neuron. The muscle cells of a motor unit: Question 22 Answer Choices A. have cell walls and do not share cytoplasmic contents and nuclei with each other. B. are mononucleate and share cytoplasmic contents with each other. C. are multinucleate and do not share cytoplasmic contents with each other D. lack cell walls and share cytoplasmic contents and nuclei with each other.

C. A motor unit is the group of skeletal muscle cells innervated by a single motor neuron. The muscle cells of a motor unit are multinucleate and do not share cytoplasmic contents with each other. Skeletal muscle cells are long cells formed by the fusion of many smaller cells with one another, thus they are multinucleate. They lack cell walls (as do all animal cells), but do have a plasma membrane. The plasma membranes of skeletal muscle cells, however, does not contain gap junctions (as do the plasma membranes of cardiac and smooth muscle cells) so they do not share cytoplasmic contents.

All of the following are true EXCEPT: A. tropomyosin inhibits binding of myosin to actin. B. tropomyosin winds around actin. C. calcium binds tropomyosin D. troponin regulates tropomyosin.

C. All of the listed responses are true EXCEPT calcium binds tropomyosin. Tropomyosin winds around actin ("tropomyosin winds around actin" is true and can be eliminated), blocking the myosin binding sites ("tropomyosin inhibits binding of myosin to actin" is true and can be eliminated). Troponin regulates tropomyosin ("troponin regulates tropomyosin" is true and can be eliminated) via binding to Ca2+ ("calcium binds tropomyosin" is false and the correct answer choice).

Aplastic anemia is a condition where bone marrow is significantly damaged and does not produce sufficient new cells to replenish blood cells (e.g., in radiation poisoning). Which of the following is true with regard to aplastic anemia? A. It primarily affects the yellow marrow in the spongy bone of flat bones. B. It primarily affects the red marrow in the shafts of long bones. C. It primarily affects the red marrow in the spongy bone of flat bones. Correct Answer (Blank) D. It primarily affects the yellow marrow in the shafts of long bones.

C. Aplastic anemia is a condition where bone marrow is significantly damaged and does not produce sufficient new cells to replenish blood cells (e.g., in radiation poisoning). Aplastic anemia primarily affects the red marrow in the spongy bone of flat bones. This is a two-by-two question, where two decisions need to be made to determine the correct answer. Hematopoiesis (blood cell formation) occurs in red marrow (choices with "yellow marrow" can be eliminated), which is found in the spongy bone within flat bones. Yellow marrow is inactive, filled with fat, and found in the shafts of long bones.

Which of the following are components of the epidermis? I. Blood vessels II. Epithelial cells III. Secretory gland Question 4 Answer Choices A. I and III B. I and II C. II only D. I, II, III

C. I. Blood vessels II. Epithelial cells III. Secretory gland The epidermis consists exclusively of layers of squamous epithelial cells (Item II is correct). The innermost layer is mitotically active while the outer layers consist of dead cells. Blood vessels and glands that secrete sweat, oil and in some cases, wax, are found in the dermis (Items II and III are not correct).

Which one of the following would be the most effective cooling mechanism when the environmental temperature is greater than the body's core temperature? Question 13 Answer Choices A. Uncoupling of oxidative phosphorylation and electron transport B. Dilation of arterioles that supply blood to the skin C. Increased production of sweat D. Constriction of arterioles that supply blood to the skin

C. Increased production of sweat would be the most effective cooling mechanism when the environmental temperature is greater than the body's core temperature. Even if the environmental temperature is greater than the body's core temperature, the evaporative cooling provided by sweat will cool the skin. Under these conditions, it is not possible to radiate heat away from the body, so dilating skin arterioles to bring more blood to the surface of the body will not be effective. Constriction of arterioles in the skin is a heat retention mechanism, not a heat reduction mechanism. Uncoupling oxidative phosphorylation and electron transport is a heat production mechanism in brown fat.

Which of the following structures connects the gastrocnemius muscle in the calf to the calcaneus, a bone in the ankle? A. Patellar ligament B. Gastrocnemius fascicle C. Achilles tendon D. Achilles ligament

C. Tendons connect muscles to bones. Hence, the Achilles tendon is the structure that connects the gastrocnemius muscle in the calf to the calcaneus, a bone within the ankle. Ligaments connect bones to other bones; there are many ligaments holding together bones in the ankle, for example. A fascicle is a bundle of myocytes that composes a muscle; it does not connect the muscle to other structures.

At which of the following times in the respiratory cycle is the intrapleural pressure most negative? Question 14 Answer Choices A. At the beginning of exhalation B. At the beginning of inhalation C. At the end of inhalation D. At the end of exhalation

C. The intrapleural pressure is most negative at the end of inhalation during the respiratory cycle. Negative intrapleural pressure is what drives air into the lungs during inhalation. When the chest cavity increases in size, the intrapleural pressure becomes more negative. The chest wall is moving outward due to muscle contraction, and lung tissue is elastic, thus resisting the outward pull. Hence, while inspiration is happening, the pressure is getting more and more negative; i.e., the expansion of the lungs doesn't quite keep up with the chest wall, and pressure reaches its most negative value when the chest cavity is the most expanded at the end of inhalation ("at the end of inhalation" is correct and "at the beginning of inhalation" is wrong). Exhalation involves increasing the intrapleural pressure to push air out ("at the beginning of exhalation" and "at the end of exhalation" are wrong).

The skin serves which of the following roles? I. Non-specific immunity II. Thermoregulation III. Protection against ultraviolet radiation Question 7 Answer Choices A. III only B. II and III only C. I, II, and II D. II only

C. The skin serves roles I, II, and III. I. Non-specific immunity II. Thermoregulation III. Protection against ultraviolet radiation Item I is true: The skin serves as a barrier against invading pathogens and also maintains a natural flora of bacteria that out-compete potential infectious microbes. Item II is true: The skin is also a site of thermoregulation: Sweating allows heat loss by evaporation, and blood vessels in the dermis allow heat loss by conduction. Item III is true: Melanin is a dark pigment produced by cells called melanocytes. This pigment offers protection against UV-induced damage to cells' nucleic acids.

Which of the following does NOT participate in gas exchange? Question 3 Answer Choices A. Alveolus B. Alveolar duct C. Terminal bronchiole D. Respiratory bronchiole

C. The terminal bronchioles do NOT participate in gas exchange. Terminal bronchioles belong to the conduction zone, which is the portion of the respiratory system designed only to move air into and out of the system. Gas exchange occurs in the respiratory zone, which consists of alveoli, alveolar ducts, and respiratory bronchioles.

Rank the following volumes in order of increasing size in a normal, healthy person. I. Total lung capacity II. Tidal volume III. Vital capacity IV. Inspiratory capacity Question 18 Answer Choices A. IV < II < I < III B. III < II < IV < I C. II < IV < III < I D. II < I < III < IV

C. The volumes, in order of increasing size in a normal, healthy person are: II < IV < III < I. I. Total lung capacity II. Tidal volume III. Vital capacity IV. Inspiratory capacity This question looks scary, but note that you don't really have to know the definitions of the all volumes and capacities. You should know that tidal volume is the smallest volume (choices without Item II as the smallest size can be eliminated), and you should know (or should surmise) that total lung capacity is the largest volume (choice "II < I < III < IV" can be eliminated). The tidal volume (TV) is the amount of air that moves in and out of the lungs with normal breathing. The inspiratory capacity (IC) is the maximum amount of air that can be inspired after a relaxed expiration. It is equal to the tidal volume plus the inspiratory reserve volume (IRV). Thus, IC = TV + IRV. The vital capacity (VC) is the maximum amount of air that can be forced out of the lungs after taking the deepest breath possible. It is equal to the inspiratory capacity plus the expiratory reserve volume (ERV). Thus, VC = IC + ERV. Finally, the total lung capacity is the total volume of the lungs. It is equal to the vital capacity plus the residual volume. Thus, TLC = VC + RV, and TV < IC < VC < TLC.

Which components of the sarcomere change in length during muscle contraction? Question 1 Answer Choices A. A band and Z lines B. Z lines and H zone C. H zone and I band D. I band and A band

C. H zone and I band

What part of the sliding filament model of contraction requires ATP hydrolysis? Question 2 Answer Choices A. Forming crossbridge between myosin and actin B. Pulling on actin by myosin C. Resetting of myosin head groups D. Releasing myosin head groups from actin

C. Resetting of myosin head groups

All of the following are mechanisms by which the skin functions in thermoregulation EXCEPT: Question 6 Answer Choices A. skin increases heat loss by evaporation through sweating. B. vasoconstriction of blood vessels in the skin reduces heat loss by conduction. C. skin acts as an insulator to maintain heat generated by metabolism. D. vasodilation of blood vessels in the skin reduces heat loss by conduction.

D. All of the listed responses are mechanisms by which the skin functions in thermoregulation EXCEPT vasodilation of blood vessels in the skin reduces heat loss by conduction. Skin, especially subcutaneous fat, acts as a great insulator. This is why very thin people may feel cold quickly ("skin acts as an insulator to maintain heat generated by metabolism" is a thermoregulatory function of the skin and can be eliminated). Vasoconstriction would decrease blood flow near the skin's surface and reduce heat loss by conduction ("vasoconstriction of blood vessels in the skin reduces heat loss by conduction" is a thermoregulatory function of the skin and can be eliminated), and vasodilation would INCREASE heat loss by conduction ("vasodilation of blood vessels in the skin reduces heat loss by conduction" is false and is the correct answer choice). Sweating increases heat loss by evaporation ("skin increases heat loss by evaporation through sweating" is a thermoregulatory function of the skin and can be eliminated). Note that focusing in on answer choices that are opposites (e.g., "vasoconstriction of blood vessels in the skin reduces heat loss by conduction" and "vasodilation of blood vessels in the skin reduces heat loss by conduction") is a great strategy for the MCAT, as one of the opposites is often the correct choice.

All of the following are true regarding the innervation of skin by the autonomic nervous system EXCEPT: Question 17 Answer Choices A. the sympathetic nervous system causes increased sweating. B. postganglionic sympathetic neurons that innervate sweat glands release acetylcholine. C. the skin does not receive parasympathetic innervation. D. the sympathetic nervous system causes dilation of blood vessels in the skin.

D. All of the listed responses are true regarding the innervation of skin by the autonomic nervous system EXCEPT the sympathetic nervous system causes dilation of blood vessels in the skin. The sympathetic nervous system mediates the "fight or flight" response and causes increased sweating (to accommodate increased heat production from muscle activity, "the sympathetic nervous system causes increased sweating" is true and can be eliminated) and constriction of blood vessels in the skin (so that blood is shunted to the skeletal muscles, which are working overtime, "the sympathetic nervous system causes dilation of blood vessels in the skin" is false and the correct answer choice). The skin only receives sympathetic innervation ("the skin does not receive parasympathetic innervations" is true and can be eliminated). Answer "postganglionic sympathetic neurons that innervate sweat glands release acetylcholine" is actually true (and can be eliminated): The innervation of sweat glands is one exception to the rule that postganglionic sympathetic neurons only secrete norepinephrine.

Chronic renal failure results in impaired calcitriol formation in the kidneys irrespective of circulating parathyroid levels. Replacing calcitriol would have all of the following effects EXCEPT: Question 4 Answer Choices A. reabsorption of Ca2+ by kidney cells. B. release of Ca2+ from the bones. C. increased absorption of Ca2+ in the intestines. D. increased excretion of Ca2+ by kidney cells.

D. Chronic renal failure results in impaired calcitriol formation in the kidneys irrespective of circulating parathyroid levels. Replacing calcitriol would have all of the following effects EXCEPT increased excretion of Ca2+ by kidney cells. The effects of calcitriol include a release of Ca2+ from the bones, reabsorption of Ca2+ by the kidney cells, and increased absorption of Ca2+ by the intestines. Note that the answer choices "increased excretion of Ca2+ by kidney cells" and "reabsorption of Ca2+ by kidney cells" are opposites; if the latter is an effect, then the former must NOT be an effect, and is the correct answer choice.

Which of these proteins binds calcium in smooth muscle cells? A. Myosin B. Troponin C. Actin D. Calmodulin

D. Of these proteins, calmodulin binds calcium in smooth muscle cells. Instead of using the troponin-tropomyosin complex to bind calcium and facilitate actin-myosin interaction (as seen in striated muscle), calcium ions bind to calmodulin. This in turn activates myosin light-chain kinase (MLCK) to phosphorylate the myosin and enable it to bind actin. Myosin and actin are found in all muscle types, though their arrangement differs in striated and smooth muscle.

Which of the following is the correct sequence for the movement of air through the respiratory system? Question 16 Answer Choices A. larynx --> pharynx --> alveoli --> bronchioles --> lungs B. larynx --> pharynx --> bronchioles --> alveoli C. pharynx --> larynx --> alveoli --> bronchioles --> lungs D. pharynx --> larynx --> bronchioles --> alveoli

D. Pharynx larynx bronchioles alveoli is the correct sequence for the movement of air through the respiratory system. the correct sequence is pharynx --> larynx --> bronchioles --> alveoli.

If the production of surfactant were reduced, which of the following effects would be most likely to occur? Question 1 Answer Choices A. Surface tension in the alveoli would decrease B. Surface tension in the bronchioles would decrease C. Surface tension in the bronchioles would increase D. Surface tension in the alveoli would increase

D. Surface tension in the alveoli would increase if the production of surfactant were reduced. Surfactant is produced in the alveoli so it primarily affects surface tension in that region. It may have some small effect on the respiratory bronchioles (which contain alveoli in their walls) due to the leakage of surfactant from these alveoli into the respiratory bronchiole tube. However, it would not have any effect on the terminal bronchioles, nor on any structure higher in the respiratory tree. Since the question asks for the most likely effect, and since it does not differentiate between the respiratory and the terminal bronchioles, "surface tension in the bronchioles would decrease" and "surface tension in the bronchioles would increase" can be eliminated. Normally, the presence of surfactant reduces surface tension in the alveoli, so if the production of surfactant were decreased, we would expect to see an increase in alveolar surface tension ("surface tension in the alveoli would increase" is correct and "surface tension in the alveoli would decrease" is wrong).

The controlled balance between bone formation and resorption is regulated by at least three hormones, parathyroid hormone, calcitonin, and calcitriol, which respond to changes in serum Ca2+ levels. Paget's disease is caused by a high rate of bone resorption, which exceeds the rate of bone formation regardless of serum Ca2+ levels. A potential treatment for Paget's disease could be: Question 6 Answer Choices A. drugs that mimic the effect of calcitriol. B. parathyroid hormone. C. anti-calcitonin antibodies. D. drugs that mimic the effect of calcitonin

D. The controlled balance between bone formation and resorption is regulated by at least three hormones, parathyroid hormone, calcitonin, and calcitriol, which respond to changes in serum Ca2+ levels. Paget's disease is caused by a high rate of bone resorption, which exceeds the rate of bone formation regardless of serum Ca2+ levels. A potential treatment for Paget's disease could be drugs that mimic the effect of calcitonin. Calcitonin is secreted in response to high serum calcium levels; it inhibits osteoclast-mediated bone breakdown and increases osteoblast-mediated bone formation. Since Paget's disease is characterized by a high rate of bone breakdown, drugs that can reverse these effects might be effective at treating the disorder. Parathyroid hormone and calcitriol increase bone reabsorption and decrease bone formation; these would enhance the effects of Paget's disease. Likewise, anti-calcitonin antibodies would reduce the effect of calcitonin.

The effects of aldosterone on sudoriferous (sweat) glands of the skin are analogous to this hormone's effects on nephrons within the kidney. Which of the following is correct regarding how aldosterone influences the salt content of sweat? Question 2 Answer Choices A. Aldosterone increases the secretion of sodium, making sweat more concentrated. B. Aldosterone decreases the secretion of sodium, making sweat more concentrated. C. Aldosterone increases the secretion of sodium, making sweat more dilute. D. Aldosterone decreases the secretion of sodium, making sweat more dilute.

D. The effects of aldosterone on sudoriferous (sweat) glands of the skin are analogous to this hormone's effects on nephrons within the kidney. Aldosterone decreases the secretion of sodium, making sweat more dilute is correct regarding how aldosterone influences the salt content of sweat. Aldosterone increases renal sodium reabsorption, returning more sodium to the blood. In the skin, this hormone also acts to conserve sodium by decreasing this ion's secretion (i.e., leaving more sodium in the blood, "aldosterone increases the secretion of sodium, making sweat more concentrated" and "aldosterone increases the secretion of sodium, making sweat more dilute" are wrong). Sweat with less sodium (salt) will be more dilute, not more concentrated ("aldosterone decreases the secretion of sodium, making sweat more dilute" is correct and "aldosterone decreases the secretion of sodium, making sweat more concentrated" is wrong).

The influx of calcium from the sarcoplasmic reticulum is necessary to cause the sarcomeres to contract. Which part of a sarcomere stays the same length throughout muscle contraction? A. The entire sarcomere stays the same length. B. H zone C. I band D. A band

D. The influx of calcium from the sarcoplasmic reticulum is necessary to cause the sarcomeres to contract. The A band stays the same length throughout muscle contraction. During muscle contraction, myosin and actin fibers slide overtop of one another and the sarcomeres contract (get shorter). The H zone is the region composed of only myosin thick filaments. During muscle contraction, it also shortens. The I band is the region composed of only actin thin filaments; it also shortens during contraction. The A band, or the entire length of the myosin filament, stays the same throughout contraction; the Z lines (ends of the sarcomere) are pulled up to the ends of the A band.

Which of these is the primary source of calcium ions in smooth muscle? A. Intracellular space B. T-tubules C. Sarcoplasmic reticulum (SR) D. Extracellular space

D. The primary source of calcium ions in smooth muscle is the extracellular space. The sarcoplasmic reticulum is poorly developed in smooth muscle cells. As a result, they rely primarily on extracellular calcium to mediate contraction via calcium binding to calmodulin. There is some calcium stored in the SR that can be released when a smooth myocyte is depolarized, however, this is a significantly smaller amount compared to what enters the cell via calcium channels. The intracellular space is always low in calcium. T-tubules do not store calcium; they are responsible for propagating surface depolarization into myocytes.

What is the primary source of nutrition for the cartilage of the knee joint? Question 2 Answer Choices A. Blood supply to the cartilage of the knee B. Lymphatic fluid C. Blood supply to the muscles that support the knee D. Synovial fluid

D. The primary source of nutrition for the cartilage of the knee joint is synovial fluid. Cartilage is avascular; it does not have a blood supply. This is true of all joints in the body; none of them have a dedicated blood supply. As a result, nutrients and reparative substances can only reach articular cartilage of any joint via the synovial fluid, the fluid that bathes the joint. The cartilage within a joint is also unable to take advantage of blood supply to the muscles supporting the joint. Lymphatic fluid helps to clear excess fluid from the soft tissues of the body and return it to the circulation; it does not help to nourish cartilage.

Which type of muscle fiber has the highest concentration of myoglobin? Question 3 Answer Choices A. Type IIB B. Type IIA C. Type III D. Type I

D. Type I