MCAT Biology Missed Questions and Concept Checks

Respiratory failure refers to inadequate ventilation to provide oxygen to the tissues. How would the pH change in respiratory failure?

In respiratory failure, ventilation slows, and less carbon dioxide is blown off. As this occurs, the buffer equation shifts to the right, and more hydrogen ions are generated. This results in a lower pH of the blood.

2. Starting with the site of impulse initiation, what are the structures in the conduction system of the heart?

Sinoatrial (SA) node, atrioventricular (AV) node, bundle of His (AV bundle) and its branches, Purkinje fibers

1. What are the components of plasma?

Plasma is an aqueous mixture of nutrients, salts, respiratory gases, hormones, and blood proteins (clotting proteins, immunoglobulin, and so on).

2. List the vessels in the renal vascular pathway, starting from the renal artery and ending at the renal vein.

Renal artery, afferent arterioles, glomerulus, efferent arterioles, vasa recta, renal vein.

Which of the following is both an endocrine and exocrine gland? A. Liver B. Parathyroid Glands C. Adrenal Glands D. Thyroid Gland

A Endocrine glands are ductless glands whose hormones end up in the blood stream. Exocrine glands secrete products into ducts. The liver secretes bile into a duct that eventually travels to the duodenum to emulsify fats. It also carries out the ductless secretion of hormones, chief among them insulin-like growth factor, into the bloodstream.

Which of the following accurately describes thyroid hormone? A. Binds to receptors on the inside of the cell B. Binds to receptors on the outside of the cell C. Derived from cholesterol D. Released from the anterior pituitary

A In general, steroid hormones readily diffuse across the cell membrane and peptide/amine hormones are hydrophilic and bind to cell receptors on the surface. Thyroid hormone is derived from the amino acid tyrosine. Thyroid hormone is an exception. Even though it is derived from the amino acid tyrosine, it is lipid soluble and diffuses across the cell membrane and will bind to receptors inside the cell. Thyroid hormone acts like a steroid.

The nephron reabsorbs glucose through a sodium / glucose transporter. What sort of transporter is it? Choose 1 answer: (Choice A) A Symporter (Choice B) B Antiporter (Choice C) C Sodium pump (Choice D) D Protein channel

A Nephrons take advantage of the sodium concentration gradient to transport glucose. Hint #22 / 3 Sodium concentrations are higher outside the cell. Hint #33 / 3 The sodium / glucose transporter is a symporter which couples the transport of the two molecules to move glucose against its concentration gradient.

Bronchodilators are a class of drug often used in the treatment of asthma and COPD, which act on β-adrenergic receptors of the airways to induce smooth muscle relaxation. The anatomic distribution of these receptors is closely correlated to the function of each structural component of the lungs. What structural component(s) of the airway would be most affected by the use of a bronchodilator, and in what functional zone(s) are they found? A. Lobar bronchi, which are found in the conducting zone B. Lobar bronchi and alveoli would be affected equally, and they are both found in the respiratory zone C. Lobar bronchi and alveoli would be affected equally, and they are found in the conducting and respiratory zones respectively D. Alveoli, which are found in the respiratory zone

A The conducting zone is simply a series of tubes through which gases travel, while the respiratory zone directly participates in gas exchange. The respiratory zone is made up of only the alveoli and the respiratory bronchioles/ alveolar ducts. The walls of the airways contain smooth muscle, which is the site of action of bronchodilators. The alveoli are made of only a single layer of cells, and their walls do not contain smooth muscle. Bronchodilators do not directly affect the alveoli. The lobar bronchi would be most affected by the use of a bronchodilator, and they are found in the conducting zone.

Which term describes the cell membrane potential of a neuron at rest? Choose 1 answer: Choose 1 answer: (Choice A) A Polarized (Choice B) B Hyperpolarized (Choice C) C Repolarized D Depolarized

A neuron at rest (or resting potential) has a stable separation of charges across the membrane. Hint #22 / 3 At resting potential, there are more positive charges on the layer directly outside of the membrane, and more negative charges on the inside of the membrane. Hint #33 / 3 This separation of charges refers to polarization. The membrane potential of a neuron at rest is slightly negative, thus it is polarized.

13. Which cell type is a phagocyte that attacks bacterial pathogens in the bloodstream? A. Neutrophils B. Eosinophils C. Basophils D. Dendritic cells

A. The only phagocytes that attack bacteria on this list are neutrophils and dendritic cells. Dendritic cells can sample and present any type of material, and reside in the skin. Neutrophils, on the other hand, are present in the bloodstream and can attack bacteria present there or in tissues. Eosinophils and basophils are involved in the formation of allergies; eosinophils also defend against parasites.

Biosynthesis of steroids begins with: A. Binding of pyrophosphate to a terpene B. Generation of a sterol C. Methylation of a sesquiterpene D. Binding of two terpene groups

A. This question really just requires recall of the steps of steroid biosynthesis. Remember that the pathway starts with a terpene, not a sesquiterpene. Generation of sterols occurs further along the steroid-synthesis pathway. The biosynthesis of steroids begins with adding a pyrophosphate to a terpene.

A researcher who needs to separate proteins according to size should use which method? A SDS-PAGE B PAGE only C Isoelectric focusing D ELISA

Answer choice A is correct. The treatment of proteins with SDS, a detergent, equalizes the charge to mass ratio, removing the factor of charge from their electrophoretic mobility. Under that condition, they separate according to size. Choice B is PAGE alone. Under these circumstances, the proteins' electrophoretic mobility is partly determined by charge. Isoelectric focusing, Choice C, separates proteins based on their isoelectric point, so this choice should be eliminated. Choice D can be eliminated as the ELISA method relies on immunological techniques to identify the presence of a particular protein. All four laboratory techniques are commonly addressed in biochemistry and to a lesser degree in biology and organic chemistry. Ironically, when originally released, the Altius MCAT-2015 practice materials were criticized by many students for covering these techniques, SDS-PAGE and ELISA being absent from every other MCAT prep resource. We stood firm and told our students that they must know these topics. Many months later, when the AAMC released their first scored full-length practice exam and the AAMC Section Banks, our foresight was proven to be accurate. These topics are tested multiple times on recently-released AAMC materials. In the AAMC Section Bank alone you can find them on Passage 7, as well as stand-alones #52, #69, and #70. This is only one of dozens of cases in which our experience team of PhD authors PREDICTED an AAMC trend only to see that prediction realized on future materials. Rather than get defensive when you miss a challenging question, decide to trust us. Master the question types we present and you won't face unnecessary surprises or frustrations come test day.

Ftt is an obligate intracellular bacterium. An antibody response can still be effective against Ftt because antibodies: A enhance the rate of phagocytosis of Ftt. B bind to Ftt plasma B-cells, stimulating antibody production. C bind to Ftt and prevent it from entering the cell. D cross the Ftt cell membrane and prevent translation of Ftt proteins.

Answer choice C is correct. The primary function of antibodies is to activate complement, enhance phagocytosis, and neutralize infectious agents by preventing binding to the receptor on the target cell. Although answer choice A is correct in that antibodies can enhance the phagocytosis of bacteria into the cell, this would not be effective given that Ftt are already obligate intracellular bacteria. Ftt is a prokaryotic cell, therefore it does not have its own immune system, or plasma B-cells that produce antibodies—making choice B incorrect. The best answer is that the antibodies will neutralize the infection by preventing F. tularensis from interacting with its cellular receptor and thereby preventing its entry into the host cell. Answer choice D is incorrect because antibodies are not widely known to cross the cell membrane and have no known function in preventing translation. This is even less likely for a bacterium with a cell wall.

What is the most probable impact of a point mutation that substitutes the terminal guanine of a 5' exon with an alternate nucleotide? A The mRNA will be prematurely terminated. B The protein will be nonfunctional due to an amino acid change. C The intron will not be spliced from the mRNA transcript. D There will be no effect, because this is a silent mutation.

Answer choice C is the correct answer. A guanine at the 5' position is required for RNA splicing. If a different nucleotide were present, the process would not function and the intron would not be removed. This makes choice C the best answer. This will not create a stop codon, making choice A incorrect. Answer B may be tempting because failure of the splicing mechanism may well result in a non-functional protein. However, given both answers, B and C, answer C is a more complete and accurate description that emphasizes the primary importance of guanine in the splicing mechanism. This is particularly important given that the importance of a guanine substitution was specifically referenced in the stem. Examinees should expect AAMC questions to feature distractors that may be true, or could be true, but are not as complete, or as correct, as the best answer. Answer D must be incorrect because, as already described, failure of exon splicing will have multiple deleterious effects.

An individual suffering from a paralyzing fear of clowns visits a therapist. The therapist gradually exposes the patient to an image of a clown, then a movie featuring clowns, and finally to an in-person encounter with a clown. Which perspective is most consistent with this therapeutic approach? A Psychoanalytic B Humanistic C Social-cognitive D Behaviorist

Answer choice D is the correct answer. The process described is known as systematic desensitization, a process which relies on principles of associative learning. This approach would be most consistent with the behaviorist perspective. Answer A can be eliminated because the psychoanalytic perspective espoused by Freud focused on the role that the unconscious mind played on conscious behavior. Nothing in the scenario described in the stem mentions or infers that the clown therapy was focused on the unconscious mind. Answer B is incorrect because the humanistic perspective espoused by Maslow and Rogers focuses on the potential for self-fulfillment that resides among all human beings. Self-fulfillment is unrelated to the story of gradual exposure to clowns. Answer C should be dismissed because the social-cognitive perspective espoused by Bandura focuses on modeling behavior observed in others (a.k.a., social learning). No modeling or social learning is described in the given scenario.

Which statement describes the membrane potential at the peak of an action potential? Choose 1 answer: Choose 1 answer: (Choice A) A The membrane potential is much more positive than the Na+ equilibrium potential. (Choice B) B The membrane potential is slightly less positive than the Na+ equilibrium potential. (Choice C) C The membrane potential is slightly more positive than the Na+ equilibrium potential. (Choice D) D The membrane potential is the same as the Na+ equilibrium potential.

At the peak of an action potential, there is more sodium inside of the membrane than outside. Hint #22 / 4 Resting potential is approximately -70mV. Hint #33 / 4 Action potentials peak around 40mV. Hint #44 / 4 Sodium equilibrium potentials are around 50mV. Thus, the membrane potential is slightly less positive than the sodium equilibrium potential at the peak of an action potential.

8. Idiopathic pulmonary fibrosis (IPF) is a disease in which scar tissue forms in the alveolar walls, making the lung tissue significantly stiffer. Which of the following findings would likely be detected through spirometry in a patient with IPF? I. Decreased total lung capacity II. Decreased inspiratory reserve volume III. Increased residual volume A. I only B. II only C. I and II only D. I, II, and III

B In a patient with IPF, the increased stiffness of the lungs would likely decrease the volume of air the individual could inhale, which would decrease both the total lung capacity and inspiratory reserve volume. However, spirometry cannot measure the total lung capacity accurately because it cannot determine the residual volume - the volume of air left in the lungs when an individual has maximally exhaled. Because the residual volume makes up a portion of the total lung capacity (total lung capacity = vital capacity + residual volume), a spirometer cannot be used to determine the total lung capacity. Therefore, while Statement I is a true statement about individuals with IPF, it cannot appear in the answer choice. Finally, increased stiffness of the lungs would be expected to decrease the residual volume, not increase it; further, residual volume, as described above, cannot be measured with a spirometer.

How do potassium ions travel as they move into the cell? Choose 1 answer: (Choice A) A Down the concentration gradient and down the membrane potential (Choice B) B Up the concentration gradient and down the membrane potential (Choice C) C Up the concentration gradient and up the membrane potential (Choice D) D Down the concentration gradient and up the membrane potential

B Potassium ions are cations. The inside of a cell is more negative than the outside of a cell. Hint #33 / 4 Extracellular potassium concentration is about 4mEq/L Hint #44 / 4 Potassium moves up its concentration gradient, but down the membrane potential when it enters a cell.

Selective serotonin reuptake inhibitors (SSRIs), used to treat depression, block a specific protein in the pre-synaptic neuron to keep the neurotransmitter in the synaptic cleft for a longer period of time. What sort of protein do they block? Choose 1 answer: (Choice A) A A neurotransmitter channel (Choice B) B A sodium-neurotransmitter symporter (Choice C) C A neurotransmitter ATP pump (Choice D) D A phagocytosis-inducing protein

B Primary active transport is very costly to the cell, and is used sparingly. Hint #22 / 3 Neurotransmitter are recycled through neurotransmitter reuptake, and so the cell must be specific about what it is uptaking. Hint #33 / 3 A sodium-neurotransmitter symporter couples the energy released by sodium moving down its gradient to also bring the neurotransmitter into the cell. These are the proteins blocked by many SSRIs.

At the instant following the second heart sound, which heart valves are open? Choose 1 answer: A Semilunar valves only B All valves are closed C Atrioventricular valves only D Both atrioventricular valves and semilunar valves

B The second heart sound indicates the beginning of diastole. Hint #22 / 6 The second heart sound, "Dup," is due to the closure of the semilunar valves. Hint #33 / 6 The heart is in systole between the first and second heart sounds. Hint #44 / 6 During systole, the heart pumps blood from the ventricles, and the atrioventricular valves are closed to prevent regurgitation into the atria. Hint #55 / 6 The closure of the semilunar valves is the start of a brief period of "isovolumetric relaxation." Hint #66 / 6 All valves are closed during the second heart sound.

2. Compare B- and T-cells: Cell Type Site of Development Site of Maturation Major Functions Specific or Nonspecific? Humoral or Cell-Mediated?

B-cell: Bone marrow Bone marrow (but are activate in spleen or lymph nodes) Produce antibodies Specific Humoral T-cell: Bone marrow Thymus Coordinate immune system and directly kill infected cells Specific Cell-mediated

5. A patient presents to the emergency room with a stab wound to the left side of the chest. On a chest x-ray, blood is noted to be collecting in the chest cavity, causing collapse of both lobes of the left lung. The blood is most likely located between: A. the parietal pleura and the chest wall B. the parietal pleura and the visceral pleura C. the visceral pleura and the lung D. the alveolar walls and the lung surface

B. The intrapleural space, bounded by the parietal and visceral pleurae, is a potential space. As such, it is normally collapsed and contains a small amount of fluid. However, introduction of fluid or air into the intrapleural space can fill the space, causing collapse of the lung. The other options listed are too firmly apposed to permit blood to collect in these spaces.

5. Iodine deficiency may result in: A. galactorrhea B. cretinism C. gigantism D. hyperthyroidism

B. Inflammation of the thyroid or iodine deficiency can cause hypothyroidism, in which the thyroid hormones are under secreted or not secreted at all. Hypothyroidism in newborn infants causes cretinism, which is characterized by poor neurological and physical development (including mental retardation, short stature, and coarse facial features). While iodine deficiency can result in a swelling of the thyroid gland (called a goiter), which can also be seen in causes of hyperthyroidism, iodine deficiency does not cause hyperthyroidism, eliminating D. Galactorrhea, A, is associated with prolactin; gigantism, C, is associated with growth hormone.

12. Starch is hydrolyzed into maltose by enzymes from the: I. salivary glands II. brush border. III. pancreas. A. I only B. I and III only C. II and III only D. I, II, and III

B. Starch is hydrolyzed to maltose by two enzymes: salivary amylase (secreted by the salivary glands) in the mouth and pancreatic amylase (secreted by the pancreas) in the duodenum. Brush-border disaccharides can further break down maltose, but do not break down starch.

2. Which of the following is the correct sequence of a cardiac impulse? A. SA node, AV node, Purkinje fibers, bundle of His, ventricles B. AV node, bundle of His, Purkinje fibers, ventricles, atria C. SA node, atria, AV node, bundle of His. Purkinje fibers, ventricles D. SA node, AV node, atria, bundle of His, Purkinje fibers, ventricles

C. An ordinary cardiac contraction originates in, and is regulated by, the sinoatrial (SA) node. The impulse travels through both atria, stimulating them to contract simultaneously. The impulse then arrives at the atrioventricular (AV) node, which momentarily slows conduction, allowing for completion of atrial contraction and ventricular filling. The impulse is then carried by the bundle of His and its branches through the Purkinje fibers in the walls of both ventricles, generating a strong contraction.

12. A patient presents to the emergency room with an asthma attack. The patient has been hyperventilating for the past hour and has a blood pH of 7.52. The patient is given treatment and does not appear to respond, but a subsequent blood pH reading is 7.41. Why might this normal blood pH NOT be a reassuring sign? A. The patient's kidneys may have compensated for the alkalemia. B. The normal blood pH reading is likely inaccurate. C. The patient may be descending into respiratory failure. D. The patient's blood should ideally become academic for some time to compensate for the alkalemia.

C. When a patient with an asthma attack does not respond to treatment and has been hyperventilating for over an hour, he or she may become fatigued and may not be able to maintain hyperventilation. In this case, the patient begins to decrease his or her breathing rate and is not receiving adequate oxygen. By extension, carbon dioxide is trapped in the blood, and the pH begins to drop. Even though this pH is normal now, this patient is crashing and may start demonstrating acidemia soon. While the kidneys should compensate for alkalemia, this is a slow process and would not normalize the blood pH within an hour; further, compensation by the kidneys would be a reassuring sign, eliminating A. There is no evidence to believe the measurement was inaccurate, eliminating B. Finally, after treatment, the patient should return to a normal blood pH with adequate ventilation and would not be expected to overcompensate by becoming acidemic, eliminating D.

Hormones secreted by the hypothalamus would be classified as: A. Endocrine B. Introcrine C. Paracrine D. Autocrine

C. Autocrine signaling occurs when an organ secretes a hormone that acts on that same organ, and similarly, intracrine signaling involves a cell secreting a hormone that acts within that same cell. Endocrine signaling involves the hormone traveling to a distant target. Paracrine signaling, in contrast, means that the hormone acts on a nearby, but different, organ. Remember that the hypothalamic hormones primarily act on the pituitary. Therefore this should be classified as paracrine signaling.

In a situation where the respiratory bronchioles become inflamed and narrowed, such as is seen in asthma, which aspect of respiration would be most mechanically impaired? A. Normal expiration B. Forced inhalation C. Forced expiration D. Normal inhalation

C. Contraction of the diaphragm produces a negative pressure within the intrathoracic cavity. The negative pressure gradient pulls air into the lungs, the lungs expand, and thus the radius of respiratory bronchioles increases during inspiration. During expiration, the elastic force of the lungs and chest wall induce a positive pressure on the air in the lungs, which forces air out. The airways within the thoracic cavity (such as the respiratory bronchioles) are also acted upon by this positive pressure, and this force causes their radius to decrease. If these airways are inflamed and smaller than usual, they would be much more prone to collapsing entirely. In fact, this is precisely what occurs during expiration in asthma; inflamed airways within the thoracic cavity collapse, interfering with expiration and trapping air within the lungs. A forced expiration generates additional force on the air within the lungs; this pressure is not only a greater magnitude than normal exhalation but also occurs much more rapidly. Therefore, an inflamed airway would collapse much sooner in this setting, and more air would be trapped. In a situation where the respiratory bronchioles become inflamed and narrowed, such as is seen in asthma, forced respiration would be most greatly impaired.

The partial pressures of carbon dioxide (pCO2) and oxygen(pO2) in the atmosphere at sea level are 0.3 mmHg and 160 mmHg respectively, but the partial pressures of these gases in blood leaving the lungs are 40 mmHg (pCO2) and 95 mmHg (pO2). What factor most likely accounts for this difference? A. CO2 is less soluble in the blood than O2. B. O2 penetrates more deeply into small airways than CO2. C. CO2 penetrates more deeply into small airways than O2. D. CO2 is more soluble in the blood than O2.

D The lungs do not mechanically discriminate between gasses. Both carbon dioxide and oxygen 'penetrate' throughout the entire lung. Henry's law states that the amount of gas that dissolves in a given liquid is directly proportional to the partial pressure of the gas in equilibrium with that liquid. If the only factor influencing dissolved gas concentrations is the partial pressure of the gas in the air in contact with the liquid, then we would assume that the ratio of oxygen to carbon dioxide would be equal both within and outside of the liquid. However, if a given gas were more soluble in a given liquid, a greater proportion of the gas could be dissolved within that liquid. CO2 is more soluble in the blood than O2

How would action potentials be affected in a myelinated axon if nodes are far apart? Choose 1 answer: Choose 1 answer: (Choice A) A Action potentials would not be affected (Choice B) B Action potentials might travel more slowly (Choice C) C Action potentials might stop (Choice D) D Action potentials might travel more quickly

In myelinated axons, action potentials only form in nodes. Hint #22 / 3 Nodes that are close together might cause action potentials to slow down. Hint #33 / 3 Nodes that are far apart might cause action potentials to stop.

Which adaptive immunity cell type is most effective at removing a cancerous cell from the body without the assistance of other immune cells? A Cytotoxic T Lymphocyte B Regulatory T Lymphocyte C Helper T Lymphocyte D Natural Killer Cell

The correct answer is A since the Cytotoxic T Lymphocytes are very specific for the cells that they kill and they are designed to kill virus-infected or cancerous cells. Regulatory (Answer B) and Helper (Answer C) T Lymphocytes are very specific, but they only aid in the removal of cancer cells by preventing wrongful activation (regulatory) or by activating B cells (helper). Further, the clue given in the stem, "without the assistance of other immune cells," negates the possibility of a helper cell such as the helper T Lymphocyte. Natural killer cells (Answer D) also kill cancerous cells, but they are innate immune cells and the stem specifies adaptive immune cells.

3. What arm of the nervous system is responsible for contraction of the detrusor muscle?

The parasympathetic nervous system causes contraction of the detrusor muscle.

4. Why does the right side of the heart contain less cardiac muscle than the left side?

The right side of the heart pumps blood into a lower-resistance circuit and must do so at lower pressures; therefore, it requires less muscle. The left side of the heart pumps blood into a higher-resistance circuit at higher pressures; therefore, it requires more muscle.

What is the mathematical relationship between vital capacity (VC), inspiratory reserve volume (IRV), expiratory reserve volume (ERV), and tidal volume (TV)?

Vital capacity is the sum of the inspiratory reserve volume, expiratory reserve volume, and tidal volume: VC = IRV + ERV + TV

5. For each segment of the nephron listed below, what are its major functions? Bowman's capsule Proximal convoluted tubule Descending limb of the loop of Henle Ascending limb of the loop of Henle Distal convoluted tubule Collecting duct

• Bowman's capsule: the site of filtration, through which water, ions, amino acids, vitamins, and glucose pass (essentially everything besides cells and proteins). • Proximal convoluted tubule: controls solute identity, reabsorbing vitamins, amino acids, and glucose, while secreting potassium and hydrogen ions, ammonia, and urea. • Descending limb of the loop of Henle: important for the reabsorption of water using the medullary concentration gradient. • Ascending limb of the loop of Henle: important for salt reabsorption and allowing dilution of urine in the diluting segment. • Distal convoluted tubule: also important for solute identity by reabsorbing salts, while secreting ammonia, urea, potassium and hydrogen ions. • Collecting duct: important for urine concentration; its variable permeability allows water to be reabsorbed based on the needs of the body.

1. What are the two circulatory vessels in a villus? What biomolecules are absorbed in each?

• Capillaries: Water-soluble nutrients, like monosaccharides, amino acids, small fatty acids, water-soluble vitamins, and water itself. Lacteals: Fat-soluble nutrients, like fats, cholesterol, and fat-soluble vitamins

1. List at least one pancreatic enzyme that digests each of the three major classes of biomolecules: Carbohydrates: Proteins: Fats:

• Carbohydrates: Pancreatic Amylase • Proteins: Trypsin, carboxypeptidases A and B, chymotrypsin • Fats: pancreatic lipase

2. What are the three main effects circulating antibodies can have on a pathogen?

• Circulating antibodies can mark a pathogen for destruction by phagocytic cells (opsonization) • cause agglutination of the pathogen in insoluble complexes that can be taken up by phagocytic cells, or • neutralize the pathogen by preventing its ability to invade tissues.

6. Which cell type(s) in blood contain nuclei? Which do not?

• Contain nuclei: Only leukocytes (including neutrophils, eosinophils, basophils, monocytes/macrophages, and lymphocytes) contain nuclei. • Do not contain nuclei: Erythrocytes and platelets do not.

2. An individual with B+ blood is in an automobile accident and requires a blood transfusion. What blood types could he receive? The same individual is so thankful that, after recovery, he decides to donate blood. To which blood types could he donate?

• Could receive from: A B+ person could receive blood from a B+, B-, O+, or O- person. • Could donate to: A B+ person can donate blood to a B+ or AB+ person.

4. What are the three processes by which solutes are exchanged between the filtrate and the blood? What happens in each process?

• Filtration: Movement of solutes from blood into filtrate at Bowman's capsule. • Secretion: The movement of solutes from blood into filtrate anywhere besides Bowman's capsule. • Reabsorption: Movement of solutes from filtrate into blood.

3. Which cells are considered granulocytes? Which are considered agranulocytes?

• Granulocytes: Basophils, neutrophils, eosinophils • Agranulocytes: B- and T-cells (lymphocytes) and monocytes (macrophages).

Which muscle(s) are involved in inhalation? Exhalation?

• Inhalation: Inhalation uses the diaphragm and external intercostal muscles; in labored breathing, muscles of the neck and back may also be involved. • Exhalation: Passive exhalation uses the recoil of these same muscles; active exhalation also uses the internal intercostal muscles and abdominal muscles.

1. What are the differences between innate and adaptive immunity?

• Innate immunity: Innate immunity consist of defenses that are always active against pathogens, but that are not capable of targeting specific invaders. • Adaptive immunity: It takes longer to mount a response with adaptive immunity, but the response targets a specific pathogen and maintains immunologic memory of the infection to mount a faster response during subsequent infections.

1. What is the difference between mechanical and chemical digestion?

• Mechanical digestion: Such as chewing, physically breaks food into smaller pieces. • Chemical digestion: Involves hydrolysis of bonds and breakdown of food into smaller biomolecules.

3. What effect does the parasympathetic nervous system have on the digestive system? What effect does the sympathetic nervous system have?

• Parasympathetic nervous system: Increases secretions from all the glands of the digestive system and promotes peristalsis. Sympathetic nervous system: Slows peristalsis

1. For each of the lymphocytes listed below, what are its main functions? Plasma cell Memory B-cell Helper T-cell Cytotoxic T-cell Suppressor (regulatory) T-cell Memory T-cell

• Plasma cell: form from B-cells exposed to antigen and produce antibodies. • Memory B-cell: also forms from B-cells exposed to antigen and lie in wait for a second exposure to a given antigen to be able to mount a rapid, robust response. • Helper T-cell: coordinate the immune system through lymphokines and respond to antigen bound to MHC-II. • Cytotoxic T-cell: directly kill virally infected cells and respond to antigen bound to MHC-I. • Suppressor (regulatory) T-cell: Quell the immune response after a pathogen has been cleared and promote self-tolerance. • Memory T-cell: Like memory B-cells, lie in wait until a second exposure to a pathogen to be able to mount a rapid, robust response.

4. What is meant by positive and negative selection?

• Positive selection: Positive selection occurs when T-cells in the thymus that can respond to antigen presented on MHC can survive (those that do not respond undergo apoptosis). • Negative selection: Negative selection occurs when T-cells that respond to self-antigens undergo apoptosis before leaving the thymus.

4. What can cause a right shift of the oxyhemoglobin dissociation curve? What can cause a left shift?

• Right shift: Increased [H+], decreased pH, increased temperature, increased CO2, or increased 2,3-BPG • Left shift: Increased pH, decreased [H+], decreased temperature, decreased CO2, decreased 2,3-BPG, or in fetal hemoglobin (in comparison to adult hemoglobin).

1. What two main enzymes are found in saliva? What do these enzymes do?

• Salivary amylase (ptyalin), which digests starch into smaller sugars (maltose and dextrin). • Lipase: digests fats

14. A drug is used that prevents the conversion of angiotensin I to angiotensin II. What is the likely effect of this drug? A. Increased sodium reabsorption B. Increased potassium reabsorption C. Increased blood pressure D. Increased blood pH

A. An excess of acetylcholine will lead to activation of all parasympathetic neurons, preganglionic sympathetic neurons, and the postganglionic sympathetic neurons that innervate sweat glands. Because the parasympathetic nervous system causes contractions of the bladder, one would expect increased urination. The increased activation of sweat glands would lead to increased sweating as well.

3. How do antibodies become specific for a given antigen?

B-cells originally mature in the bone marrow and have some specificity at that point; however, antibodies that can respond to a given antigen undergo hypermutation, or rapid mutation of their-antigen binding sites. Only those B-cells that have the highest affinity for the antigen survive and proliferate, increasing the specificity of the antigen over time.

2. In which of the following segments of the nephron is sodium NOT actively transported out of the nephron? A. Proximal convoluted tubule B. Thin portion of the ascending limb of the loop of Henle C. Distal convoluted tubule D. Thick portion of the ascending limb of the loop of Henle

B. Sodium is actively transported out of the nephron in the proximal and distal convoluted tubules, where the concentration of sodium outside of the nephron is higher than inside; thus, energy is required to transport the sodium molecules against their concentration gradient, eliminating A and C. In the inner medulla, however, sodium and other ions (such as chloride) diffuse passively down their concentration gradients from the thin ascending limb of the loop of Henle, making B the correct answer. The thick ascending limb of the loop of Henle is thick because its cells contain many mitochondria - which produce the ATP needed for active transport of sodium and chloride out of the filtrate, eliminating D.

Urine is formed in a three-step process: which of the following gives the correct order in which these steps take place in the nephron? Choose 1 answer: A Tubular reabsorption, tubular secretion, glomerular filtration B Tubular secretion, tubular reabsorption, glomerular filtration C Glomerular filtration, tubular secretion, tubular reabsorption D Glomerular filtration, tubular reabsorption, tubular secretion

Glomerular filtration represents the initial filtration of the blood by the nephron. Hint #22 / 4 Tubular reabsorption represents the reabsorption of small molecules from the tubular fluid back into the blood. Hint #33 / 4 Tubular secretion is the method by which many toxins are transferred from the blood into the tubular fluid; it occurs via active transport downstream of glomerular filtration. Hint #44 / 4 Urine is formed successively by glomerular filtration, tubular reabsorption, and tubular secretion.

1. What is the predominant cell type in the epidermis?

Keratinocytes are the primary cells of the epidermis.

5. Where do platelets come from?

Platelets are cellular fragments or shards that are given off by megakaryocytes in the bone marrow.

Absolute and relative refractory periods are important aspects of which of the following? Choose 1 answer: Choose 1 answer: A Graded potentials (Choice B) B Equilibrium potentials (Choice C) C Action potentials (Choice D) D Resting potentials

Resting potentials are not associated with refractory periods. Hint #22 / 3 Graded potentials are not associated with refractory periods. Hint #33 / 3 Refractory periods (both relative and absolute) are times when a membrane is resistant to starting another action potential.

What is the purpose of surfactant?

Surfactant reduces surface tension at the air-liquid interface in the alveoli. This prevents their collapse.

3. Where should you look on the oxyhemoglobin dissociation curve to determine the amount of oxygen that has been delivered to tissues?

The amount of oxygen delivery is a drop in the y-value (percent hemoglobin saturation) on an oxyhemoglobin dissociation curve. For example, if the blood is 100% saturated while in the lungs (at 100 mmHg O2) and only 80% saturated while in tissues (at 40 mmHg O2), then 20% of the oxygen has been released to tissues.

The resting potential for a particular neuron is measured to be -60 mV. Which of the following distributions of ions could not produce this measurement? Choose 1 answer: Choose 1 answer: (Choice A) A More cations than anions on both sides of the cell membrane (Choice B) B More anions than cations on the outside of the membrane, more cations than anions on the inside of the membrane C More cations than anions on the outside of the membrane, more anions than cations on the inside of the membrane (Choice D) D More anions than cations on both sides of the cell membrane

The resting potential for a neuron is measured by setting the net charge on the outside of the membrane as zero. Hint #22 / 3 Thus, the negative sign on a resting potential signifies a relative difference in charge, not an absolute difference. Hint #33 / 3 More anions than cations on the outside of the membrane with more cations than anions on the inside of the membrane is not consistent with a resting potential of -60 mV.

How are potassium ions typically moved out of a neuron when the membrane is at rest? Choose 1 answer: Choose 1 answer: (Choice A) A Electrical gradients move potassium ions out of the cell. (Choice B) B Concentration gradients move potassium ions out of the cell. (Choice C) C Potassium ions are stable and do not move when a membrane is at rest. (Choice D) D The sodium-potassium pump moves potassium ions out of the cell.

The sodium-potassium pump pulls potassium ions in and moves sodium ions out of the cell. Hint #22 / 3 Because potassium is positively charged and the inside of the cell is negatively charged, the electrical gradient tends to pull potassium in, not out. Hint #33 / 3 When a membrane is at rest, sodium ions are more concentrated outside of the neuron; potassium ions are more concentrated inside. Concentration gradients move potassium ions out of the cell.

6. What is the difference between active and passive immunity?

• Active immunity: Active immunity refers to the stimulation of the immune system to produce antibodies against a pathogen. • Passive immunity: Passive immunity refers to the transfer of antibodies to prevent infection, without stimulation of the plasma cells that produce these antibodies.

4. What are some mechanisms the body uses to cool itself? What are some mechanisms the body uses to retain heat?

• Cooling: Sweating, vasodilation Heating: Vasoconstriction, piloerection, and shivering

3. What are the layers of the dermis, from superficial to deep?

• Papillary layer Reticular layer

1. For each of the non-cellular nonspecific immune defenses listed below, provide a brief description of its immunologic function: Skin Defensins Lysozyme Mucus Stomach acid Normal gastrointestinal flora Complement

• Skin: Provides a physical barrier and secretes antimicrobial enzymes. • Defensins: examples of antimicrobial enzymes on the skin. • Lysozyme: antimicrobial and is present in tears and saliva. • Mucus: present on mucous membranes and traps incoming pathogens in the respiratory system, cilia propel the mucus upward so it can be swallowed or expelled. • Stomach acid: an antimicrobial mechanism in the digestive system. • Normal gastrointestinal flora: provides competition, making it hard for pathogenic bacteria to grow in the gut. • Complement: a set of proteins in the blood that can create holes in bacteria.

3. What are the three sections of the small intestine, in order? What are the three sections of the large intestine, in order?

• Small intestine: Duodenum, jejunum, ileum • Large intestine: Cecum, Colon, rectum

5. Exposure of which sub-endothelial compounds start the coagulation cascade? What protein helps stabilize the clot?

• Starts the cascade: The coagulation cascade can be started by exposure of collagen and tissue factor. • Stabilizes the clot: Fibrin

2. What are the layers of the epidermis, from superficial to deep?

• Stratum corneum • Stratum lucidum • Stratum granulosum • Stratum spinosum • Stratum basale

3. Where is bile synthesized? Where is bile stored? Where does bile carry out its digestive function?

• Synthesized: Liver • Stored: Gallbladder • Carries out function: Duodenum

In cardiac muscle tissue, what is the primary purpose of intercalated discs? Choose 1 answer: (Choice A) A Permitting the passage of ions between cells (Choice B) B Preventing separation of muscle cells during contraction (Choice C) C Generating electrical impulses in cells (Choice D) D Depolarization and repolarization of cells

A Cardiac muscle cells must be able to coordinate contraction. Hint #22 / 3 For contraction to be coordinated, an action potential must be able to rapidly spread from cell to cell. Hint #33 / 3 In cardiac muscle cells, intercalated discs permit the passage of ions between cells, allowing an action potential to spread very rapidly to produce a coordinated contraction.

What is the correct order of steps in a common G-Protein coupled receptor (GPCR) signal transduction? The answer does not include all steps. I. Formation of ligand-receptor complex II. Release of neurotransmitter into synapse III. Alpha subunit regulates target protein IV. Intracellular phosphorylation cascade V. G protein acquires GTP VI. Dissociation of G protein subunits VII. Cross-phosphorylation of G proteins VIII. Hormone binds to GPCR Choose 1 answer: Choose 1 answer: (Choice A) A I, V, VI, III, IV (Choice B) B I, V, III, IV, VI (Choice C) C II, I, V, VII, III, IV (Choice D) D VIII, I, V, VII, III, IV

A Be careful not to assume G protein-coupled receptors (GPCRs) serve any one specific function (such as neurotransmitter signaling or hormone signaling). GPCRs are widespread and diverse, serving a large variety of functions in different tissue types. Hint #22 / 6 There are three main stages of cell signaling: reception, transduction, and response. Hint #33 / 6 In the reception phase of a GPCR system, the ligand-receptor complex forms and a conformational change on the inside of the receptor allows G protein to exchange GDP for GTP. Hint #44 / 6 G proteins contain three subunits: alpha, beta, and gamma. Typically, when a GPCR receives a signal the alpha subunit dissociates from beta and gamma and regulates a target protein. Hint #55 / 6 Regulation of the target protein typically leads to an intracellular phosphorylation cascade. This would be the transduction stage. Hint #66 / 6 The correct order of steps in a GPCR system is I, V, VI, III, IV. (The response stage is not included in these steps.)

What path do bile salts take? Choose 1 answer: A Liver, gall bladder, duodenum, jejunum, ileum, liver B Liver, gall bladder, duodenum, jejunum, tissues C Gall bladder, stomach, duodenum, juejunum, ileum, tissues D Gall bladder, stomach, duodenum, tissues, liver

A Bile salts help fat be emulsified and absorbed. Bile salts are recycled by the body. Bile travels from the liver to the gall bladder through the common hepatic and cystic ducts, then to the duodenum through the cystic and common bile ducts, passes through the jejunum, and is absorbed through the ileum and returned to the liver to begin the process again.

Pulmonary edema occurs when fluid builds up in the interstitium between the pulmonary capillaries and the alveoli, and eventually enters the alveoli. How do you decrease the risk of pulmonary edema? Choose 1 answer: (Choice A) A Decrease hydrostatic pressure and increase osmotic pressure (Choice B) B Decrease hydrostatic pressure and decrease osmotic pressure C Increase hydrostatic pressure and decrease osmotic pressure (Choice D) D Increase hydrostatic pressure and increase osmotic pressure

A Hydrostatic pressure is the pressure a liquid exerts on its container, and reflects the volume of liquid in a space. Hint #22 / 3 Osmotic pressure is the pressure required to prevent movement across a semipermeable membrane, and reflects the protein content of the blood. Hint #33 / 3 To decrease the risk of pulmonary edema, hydrostatic pressure exerted by the fluid must decrease, and osmotic pressure exerted on the fluid must increase.

A cell is injected with ion X and placed into a solution. The following potentials are measured inside and outside the cell, yet there is no net flow of X ions. Why? (-70 mV inside the cell, 0 mV outside, much more X inside the cell than outside). Choose 1 answer: A X is a cation, so it remains in the cell B There is no permeability for X C X must be transported via facilitated diffusion, but there is no transport protein D X must be transported via active transport, and there is no ATP

A If X was injected into the cell, but some X could be found outside it, X must be able to cross the membrane. Hint #22 / 3 In order for a membrane potential to exist, the cell must be permeable, and there must be a concentration gradient. Hint #33 / 3 X must be a positively charged ion, a cation, so that the electrical gradient is enough to keep its concentration higher in the cell at an equilibrium state.

2. What are the four fat-soluble vitamins?

A, D, E, and K.

13. Premature infants with respiratory distress are often placed on ventilators. Often, the ventilators are set to provide positive end-expiratory pressure. Why might this setting be useful for a premature infant? A. Premature infants lack surfactant. B. Premature infants lack lysozyme. C. Premature infants cannot thermoregulate. D. Premature infants are unable to control pH.

A. This question requires a few different levels of thinking. The question stem states that premature infants often require ventilation using positive end-expiratory pressures. While you are not expected to know ventilator settings for the MCAT, you should be able to decode what this phrase means: at the end of expiration, the ventilator will provide a higher pressure than normal, which forces extra air in the alveoli. This pressure must be used to prevent alveolar collapse, which should remind you that surfactant serves the same purpose by reducing surface tension. Thus, it makes sense that if premature babies lack surfactant, providing extra air pressure at the end of expiration would be beneficial.

Damage to which gland of the oral cavity would lead to an increase in the concentration of triglycerides in the esophagus? Choose 1 answer: A Von Ebner's B Submandibular C Sublingual D Parotid

A. Triglycerides are composed of three fatty acids and a glycerol molecule, and are fat polymers. Fat is digested by lipase. Von Ebner's gland secretes lingual lipase, and damage to this gland could lead to decreased fat digestion and increased triglyceride concentration in the esophagus.

5. The accessory organs of digestion originate from which primary germ layer?

As outgrowths of the gut tube, the accessory organs of digestion rise from embryonic endoderm.

3. What does hematocrit measure? What are the units for hematocrit?

Hematocrit measures the percentage of a blood sample occupied by red blood cells. It is measured in percentage points.

4. How do bile and pancreatic lipase work together to digest fats?

Bile accomplishes mechanical digestion of fats, emulsifying them and increasing their surface area. Pancreatic lipase accomplishes chemical digestion of fats, breaking their ester bonds.

2. What are the main components of bile?

Bile is composed of bile salts (amphipathic molecules derived from cholesterol that emulsify fats), pigments (especially bilirubin from the breakdown of hemoglobin), and cholesterol.

1. List the structures in the excretory pathway, from where filtrate enters the nephron to the excretion of urine from the body.

Bowman's space, proximal convoluted tubule, descending of the loop of Henle, ascending limb of the loop of Henle, distal convoluted tubule, collecting duct, renal pelvis, ureter, bladder, urethra.

A hepatic lobule can be split into three zones radiating outward from each other. Which of the following statements about the three zones is true? See image Choose 1 answer: A Zone 1 is the most susceptible to ischemic injury (due to lack of oxygen) B Zone 2 is where most of gluconeogenesis takes place C Zone 1 is the most susceptible to infection D Zone 3 is the most highly oxygenated zone

C Hepatic lobules have a central vein surrounded by small portal triads. A portal triad consists of a bile duct, a portal vein, and a hepatic artery. Arteries carry oxygenated blood, making Zone 1 the most oxygenated, and the least susceptible to ischemic injury. The large amounts of oxygen also make Zone 1 the area that does most of the gluconeogenesis. Since Zone 1 is where blood first enters the liver lobule, it is carrying the "dirtiest" blood, and thus is the most susceptible to infection.

A researcher plans to determine the rate of diffusion of a substance across a plasma membrane by measuring how quickly it moves across a single layer of cells. Which type of cellular junction will best accommodate her experiment? Choose 1 answer: A Desmosomal adhesion B Intercalated discs C Tight junctions D Gap junctions

C The researcher wants to measure the rate of diffusion across a cell membrane. How can she be sure the substance is moving through the cell membrane? Hint #22 / 3 Some cellular junctions allow fluids and ions to pass between them, while others do not. Hint #33 / 3 Tight junctions do not permit the movement of ions through the space between cells. Thus any diffusion must have gone through the cells, across their plasma membranes, which is what the researcher hopes to determine.

What is the chemical equation for the bicarbonate buffer system?

CO2 (g) + H2O (l) <--> H2CO3 (aq) <--> H+ (aq) + HCO3- (aq)

2. What is the chemical equation for the bicarbonate buffer system? What enzyme catalyzed this reaction?

CO2 (g) + H2O (l) H2CO3 (aq) H+ (aq) + HCO3- The combining of carbon dioxide and water is catalyzed by carbonic anhydrase

2. For each of the cell types below, list the major secretions of the cell and the functions of these secretions. Mucous cell Chief cell Parietal cell G-cell

Cell Secretions Functions Mucous cell Mucus Protects lining of stomach, increases pH (bicarbonate) Chief cell Pepsinogen Digests proteins, once activated by H+ Parietal cell HCl, intrinsic factor HCl: decreases pH, kills microbes, denatures proteins, some chemical digestion; intrinsic factor: absorption of vitamin B12 G-cell Gastrin Increases HCl production, increases gastric motility.

Replacing the topoIb catalytic tyrosine with which amino acid best mimics wild-type topoIb, while eliminating catalysis? A Phenylalanine B Threonine C Tryptophan D Alanine

Choice A is the best answer. Recall that Tyrosine is a polar aromatic amino acid that contains a hydroxyl group attached to an aromatic ring. Phenylalanine and tryptophan are the only options that include a bulky ring structure similar to the tyrosine side chain, meaning neither threonine nor alanine provide adequate mass or hydrophobicity to mimic wild-type topoIb. Thus, neither B nor D can be the correct answer. Tryptophan, however, carries two rings, making the side-chain structure too large to properly mimic the tyrosine side-chain. Phenylalanine is nearly identical to tyrosine, but lacks the primary alcohol used in catalysis. These facts make Answer A better than Answer choice C.

The Hardy-Weinberg equation is shown. Assuming q represents the recessive allele in a hypothetical population, which variable can be determined using a population survey? p² + 2pq + q² = 1 A p B p^2 C 2pq Dq^2

Choice D is correct. Assume the dominant allele is A and the recessive allele is a. The sum of the frequency of each genotype in a population must equal one, therefore: AA homozygotes + Aa heterozygotes + aa homozygotes = 1. The stem states that q is the frequency of the recessive allele, so p must be the frequency of the dominant allele. Thus, the frequencies of gametes and progeny can be determined from a simple Punnet Square: p2 = the frequency of individuals of genotype AA, 2pq = the frequency of individuals of genotype Aa, and q2 = the frequency of individuals of genotype a (p2 + 2pq + q2 = 1). The value q2 then, is the frequency of homozygous recessive individuals in the population, which can be easily counted or observed because they will show the recessive phenotype; this is answer choice D. Choices B and C cannot be counted directly, as it is impossible to distinguish between homozygous dominant individuals and heterozygotes for a gene exhibiting simple dominance. Answer choice A, which is p, can be determined from p2, but through calculation, not from a population survey.

Antibiotics that harm prokaryotic cells, but not eukaryotic cells, most likely target which cellular organelle? A Nucleus B Endoplasmic reticulum C Plasma membrane D Cell wall

Choice D is the correct answer. Bacteria are prokaryotic cells and therefore they lack a nucleus and the other membrane-bound organelles found in eukaryotic cells. This rules out answer choices A and B. Bacteria do have peptidoglycan cell walls, and peptidoglycan is a biomolecule that is unique to the prokaryotic domain. Therefore, scientists have developed a number of antibiotics that interfere with peptidoglycan/bacterial cell wall synthesis. Answer choice C, the plasma membrane, would not be the best choice because all cells have a plasma membrane.

In terms of cell lineage, how are red blood cells, macrophages, and B cells each classified? Choose 1 answer: A B cells are of myeloid lineage, red blood cells and macrophages are of lymphoid lineage B Macrophages and B cells are of myeloid lineage, red blood cells are of lymphoid lineage C Red blood cells are of myeloid lineage, macrophages and B cells are of lymphoid lineage D Red blood cells and macrophages are of myeloid lineage, B cells are of lymphoid lineage

D Myeloid means a derivative of bone marrow progenitor cells while lymphoid cells are derived from lymph organs such as lymph nodes, the spleen, and the thymus. Hint #22 / 5 Lymph organs are associated with adaptive immunity. Hint #33 / 5 Macrophages are important cells in the innate immune system. B cells participate in the adaptive immune system. Hint #44 / 5 Most hematopoiesis occurs within the bone marrow. Hint #55 / 5 Red blood cells and macrophages are of myeloid lineage, B cells are of lymphoid lineage.

In terms of being open or closed, what is the state of the mitral and tricuspid valves (left and right atrioventricular valves, respectively) at the end of the first heart sound? A Mitral is closed, tricuspid is open B Both are open C Mitral is open, tricuspid is closed D Both are closed

D The first heart sound, "Lub," indicates that the heart has entered systole. Hint #22 / 5 Systole is typically defined as ventricular contraction. Hint #33 / 5 As the ventricles contract, the AV valves close to prevent regurgitation into the atria. Hint #44 / 5 The first heart sound indicates the closure of the mitral and tricuspid valves. Hint #55 / 5 Both are closed.

Septic shock is a serious condition resulting from the body's response to systemic bacterial infections, which may impair oxygen uptake and delivery. What physiological change may result from septic shock which would decrease the ability of hemoglobin in the alveolar capillaries to become fully saturated with oxygen? A. Decreased afferent capillary pO2. B. Decreased alveolar wall thickness. C. Increased blood pH. D. Increased capillary flow.

D Two 'broad' categories must be considered which may affect hemoglobin saturation: 1. Is there enough oxygen present to saturate the hemoglobin, and 2. physiological factors which affect Hb's oxygen affinity. An increase in temperature, pCO2, and 2,3-BPG concentration, or a decrease in pH will decrease O2 affinity. If the pO2 in the afferent capillary is low (the capillary coming TO the alveoli), concentration gradients will favor greater diffusion of oxygen into the vessel, thereby increasing the amount of oxygen available to bind. Factors affecting gas diffusion into the capillaries include wall thickness, wall surface area, partial pressure difference, and the ventilation-perfusion ratio. The longer blood 'hangs around' in the alveolar capillaries, the longer the hemoglobin has to recruit oxygen. If blood is flowing too quickly for ventilation to match it, the hemoglobin saturation will decrease. Septic shock may produce an increase in heart rate, and a profound decrease in blood pressure due to vasodilation. Increased capillary blood flow may decrease the ability of hemoglobin in the alveolar capillaries to become fully saturated with oxygen.

If the mouth and nose are closed at the peak of a complete inspiration, but before expiration, and the breath is held, what is the pressure of gases within the alveoli relative to the pressure of atmospheric air? A. Cannot be determined without more information. B. Alveolar pressure is equal to the pressure of atmospheric air. C. Alveolar pressure is greater than the pressure of atmospheric air. D. Alveolar pressure is less than the pressure of atmospheric air.

During inspiration, contraction of the diaphragm produces a negative pressure within the alveoli. Hint #22 / 6 During expiration, the diaphragm relaxes and the elastic recoil force of the alveoli and chest wall produce a positive force on the alveoli, and passively drive the outflow of air. Hint #33 / 6 At the peak of inspiration (or expiration) airflow stops momentarily, even as the mouth and airway remain open. The lack of flow indicates that the pressure of air in the alveoli is equal to that of atmospheric air. Hint #44 / 6 With the airway closed (mouth and nose), the lungs and chest wall become a closed system, and are therefore isolated and unable to equilibrate with the atmosphere. Hint #55 / 6 Though the air cannot escape, the elastic recoil force of the alveoli and the chest wall still exert a force on the air within the lungs. Hint #66 / 6 If the mouth and nose are closed at the peak of a complete inspiration, at the start of expiration, and the breath is held, alveolar pressure is greater than the pressure of atmospheric air.

5. If all autonomic input to the heart were cut, what would happen?

If all autonomic innervation to the heart were lost, the heart would continue beating at the intrinsic rate of the pacemaker (SA node). The individual would be unable to change his or her heart rate via the sympathetic or parasympathetic nervous system, but the heart would not stop beating.

What are some of the mechanisms used in the respiratory system to prevent infection?

Immune mechanisms in the respiratory system include vibrissae in the nares, lysozyme in the mucous membranes, the mucociliary escalator, macrophages in the lungs, mucosal IgA antibodies, and mast cells.

1. Starting from entering the heart from the venae cavae, what are the four chambers through which blood passes in the heart? Which valve prevents backflow into each chamber?

Heart Chamber Valve that Prevents Backflow Right atrium Tricuspid valve Right ventricle Pulmonary valve Left atrium Mitral (bicuspid) valve Left ventricle Aortic valve

4. Which types of leukocytes are involved in the specific immune response?

Lymphocytes are involved in specific immune defense.

5. Which cells account for the fact that the secondary response to a pathogen is much more rapid and robust than the primary response?

Memory B- and T-cells allow the immune system to carry out a much more rapid and robust secondary response.

List the structures in the respiratory pathway, from where air enters the nares to the alveoli.

Nares, nasal cavity, pharynx, larynx, trachea, bronchi, bronchioles, alveoli

1. In bacterial sepsis (overwhelming bloodstream infection), several capillary beds throughout the body open simultaneously. What effect would this have on the blood pressure? Besides the risk of infection, why might sepsis be dangerous for the heart?

Opening more capillary beds (which are in parallel) will decrease the overall resistance of the circuit. The cardiac output will therefore increase to maintain constant blood pressure. This is a risk to the heart because the increased demand on the heart can eventually tire it, leading to a heart attack or a precipitous drop in blood pressure.

2. Trace the path of food through the body, starting with ingestion and ending with excretion of feces:

Oral cavity (mouth), pharynx, esophagus, stomach, small intestine, large intestine, rectum, anus.

3. For each of the following substances, determine whether it is a digestive enzyme or hormone and briefly summarize its functions. Sucrase Secretin Dipeptidase Cholecystokinin Enteropeptidase

Substance Enzyme or Hormone? Functions Sucrase Enzyme Brush-border enzyme; breaks down sucrose into monosaccharides Secretin Hormone Increases pancreatic secretions, especially bicarbonate, reduces HCl secretion, decreases motility Dipeptidase Enzyme Brush-border enzyme; digests dipeptides into free amino acids Cholecystokinin Hormone Recruits secretions from gallbladder and pancreas; promotes satiety Enteropeptidase Enzyme Activates trypsinogen, which initiates an activation cascade

What sort of transporters would be required to move glucose from the blood to the lumen? see image Choose 1 answer: A Apical sodium/glucose antiporter and basolateral sodium/potassium pump and glucose channel B Apical sodium/glucose symporter and basolateral sodium/potassium pump and glucose channel C Apical glucose channel and basolateral sodium/potassium pump and sodium/glucose antiporter D Apical glucose channel and basolateral sodium/potassium pump and sodium/glucose symporter

The apical side faces the lumen, while the basolateral side of the cell is the one closer to the capillary system. Hint #22 / 4 There is effectively no glucose inside the cell. Hint #33 / 4 To bring glucose into the cell requires some amount of energy. Hint #44 / 4 To bring glucose from the blood to the cell, a basolateral glucose channel will allow glucose to move down its gradient. An apical sodium/glucose antiporter will move glucose against its gradient by using the energy of sodium following its gradient. A sodium/potassium pump maintains sodium concentration.

What coagulation factor is common to both the intrinsic and extrinsic pathway? Choose 1 answer: A X (Stuart-Prower factor) B IX (Antihemophilic factor B/ Christmas factor) C VIII (Antihemophilic factor A) D VII (Proconvertin/ stable factor)

The extrinsic pathway is initiated by tissue injury by the release of tissue factor. Hint #22 / 5 Tissue factor catalyzes the formation of factor VII, which catalyzes the formation of factor X. Hint #33 / 5 Be careful to remember that the coagulation factors are not numbered in sequential order, but rather for the order in which they were discovered. Hint #44 / 5 The intrinsic factor is the 'workhorse' of the coagulation cascade. The order of factor activation in the intrinsic pathway is: XII→ XI→ IX→ X. Hint #55 / 5 Factor X is common to both the intrinsic and extrinsic pathways.

4. List at least four functions of the liver:

The liver processes nutrients (through glycogenesis and glycogenolysis, storage and mobilization of fats, and gluconeogenesis), produces urea, detoxifies chemicals, activates or inactivates medications, produces bile, and synthesizes albumin and clotting factors.

In the developing fetus, prenatal hematopoiesis (the differentiation and development of immune cells) is not generally known to occur in which of the following organs? Choose 1 answer: (Choice A) A Appendix (Choice B) B Liver (Choice C) C Spleen (Choice D) D Lymph nodes

The liver, spleen, and lymph nodes all maintain a large population of immune cells that scan bodily fluids (blood, lymph) for the presence of immune-activating particles. Hint #22 / 3 The appendix is a vestigial organ; although it is in close proximity to gut-associated lymphoid tissues, it does not itself harbor significant populations of immune cells, and is not known as a site of hematopoiesis at any point in human development Hint #33 / 3 The appendix is not known to be a site of fetal hematopoiesis A

What layer of the heart would be most immediately susceptible to infections caused by bacteria circulating in the blood? Choose 1 answer: A Pericardium B Endocardium C Epicardium D Myocardium

The myocardium is the muscular portion of the heart, and is the "middle" layer. Hint #22 / 5 The pericardium is a double walled sac which encloses the heart, which provides structural support and lubrication. Hint #33 / 5 Where the pericardium contacts the heart wall (at the myocardium), it is called the epicardium. Hint #44 / 5 The endocardium lines the inside of the heart and is in direct contact with circulating blood. Hint #55 / 5 Infectious bacteria carried in the blood would come into close contact with the endocardium, which would be most susceptible to infection.

3. Compare arteries, capillaries, and veins: Vessel Carries Blood Which Direction? Relative Wall Thickness Smooth Muscle Present? Contains Valves?

Vessel Carries Blood Which Direction? Relative Wall Thickness Smooth Muscle Present? Contains Valves? Artery Away from heart Thick Yes, a lot No Capillary From arterioles to venules Very thin (one cell layer) No No Vein Toward heart Thin Yes, a little Yes

If blood levels of CO2 become too low, how does the brain alter the respiratory rate to maintain homeostasis?

When CO2 levels become too low, the brain can decrease the respiratory rate to raise CO2 levels.

4. Vibrio cholera causes a severe infection of the intestines, leading to massive volumes of water diarrhea - up to 20 liters per day. Given these symptoms, does cholera likely impact the small intestine or the large intestine?

While the large intestine's main function is to absorb water, the small intestine absorbs a much larger volume of water. Thus, massive volumes of watery diarrhea are more likely to arise from infections in the small intestine than the large intestine.