Physiology

Question 1

42 y/o woman complains of burning pain in upper middle region of her abdomen. Pain usually occurs about 2 hours after a meal and frequently awakens her at night. Antacids can usually relieve the pain within a few minutes. Xray reveals a typical duodenal ulcer identified as a discrete crater in the proximal portion of the duodenal bulb. Because the woman does not have a history of chronic use of aspirin or other nonsteroidal antiinflammatory drugs (NSAIDs), the bacterium Helicobacter pylori is assumed to be the ajor factor in the etiology of the ulcer. Which of the following is likely to be normal in this woman?

Answer 1

Fasting serum gastrin

The fasting serum gastrin is normal in patients with duodenal ulcer (DU), however, the gastrin response to a meal is increased. The increase in serum gastrin following a meal occurs, in part because acid suppresses gastrin release less effectively in DU patients compared with controls. DU patients have an increase in parietal cell mass which may be caused by the trophic growth promoting effects of gastrin. Patients with DU have increased basal acid output that totally disappears following eradication of H pylori infection.

However, the increase in maximal acid output which occurs in response to IV gastrin, can remain follwoing eradication of H pylori infection and is likely to result form the increased parietal cell mass. The secretion of pepsin is usually doubled in DU patients.

Question 2

Photographs taken of middle aged man over a period of 2 decades demonstrates gradual coarsening of facial features and progressive protrusion of the brows. Patient reports wear larger shoes that he did as a young man. which of the following pair of hormones normally regulates the hormone responsible for these changes?

Answer 2

Somatostatin and GHRH

The disease is acromegaly, which is typically produced by a growth hormone secreting pituitary adenoma. Growth hormone synthesis is predominately regulated by hypothalamic GHRH (growth hormone releasing hormone), and its pulsatile secretion is predominately regulated by hypothalamic somatostatin.

Acromegaly is a disorder that results from excess growth hormone (GH) after the growth plates have closed.[3] The initial symptom is typically enlargement of the hands and feet.[3] There may also be an enlargement of the forehead, jaw, and nose.[3] Other symptoms may include joint pain, thicker skin, deepening of the voice, headaches, and problems with vision.[3] Complications of the disease may include type 2 diabetes, sleep apnea, and high blood pressure.[3]

Acromegaly is usually caused by the pituitary gland producing excess growth hormone.[3] In more than 95% of cases the excess production is due to a benign tumor, known as a pituitary adenoma.[3] The condition is not inherited from a person’s parents.[3] Acromegaly is rarely due to a tumor in another part of the body.[3] Diagnosis is by measuring growth hormone after a person has drunk a glucose solution, or by measuring insulin-like growth factor I in the blood.[3] After diagnosis, medical imaging of the pituitary is carried out to determine if an adenoma is present.[3] If excess growth hormone is produced during childhood, the result is the condition gigantism rather than acromegaly.[3]

Question 3

Given these data below what is the net filtration pressure at the glomerulus?

Glomerular hydrostatic pressure = 44 mm / Hg

Bowmans capsule hydrostatic pressure = 9 mm / Hg

Osmotic presure of plasma = 28 mm / Hg

Osmotic pressure of tubular fluid = 0

Answer 3

7 mm / Hg

there is more than one way to tihink about this quesiton. one way is to determine which of each of the descriptions corresponds to Pc, Pp, (pi)c, (Pi)i and then to use the starling equation for net filtration pressure: (Pc - Pi) - (Pic - Pii). Perhaps faster and more intuitive is to just envision that the filtration pressure will be the difference betwen the forces pushing fluid out and the forces pulling fluid back into the glomerulus. The Pushing forces are the hydrostatic pressure of the glomerulus (44 mm / Hg) and the osmotic pressure of the tubular fluid 0. So the total pressure forcing fluid from the glomerulus into the tubular fluid is 44 mm / Hg. The forces pulling the fluid back are the hydrostatic pressure of the bowmans capsule 9 mm / Hg and the osmotic pressure of the plasma 28 mm / Hg. The total pressure pushing the fluid back into the glomerulus is 9 + 28 = 37 mm / Hg. The difference between the forces favoring filtration and those opposing it is therefore 44 - 37 = 7 mm Hg.

Question 4

50 y/o woman undergoes surgery to remove a large abdominal tumor. Histologic findings show that the mass contains a large number of blood vessels. Several metastases were found 2 months after surgery. A decrease in which of the following is the most likely cause for the development of metastases after the removal of th large tumor?

Answer 4

Endostatin

Tumors produce both angiogenic and anti-angiogenic factors (also called antiostatic factors). Angiogenic factors stimulate the growth of blood vessels (angiogenesis), whereas angiostatic factors inhibit blood vessel growth (anti-angiogenesis). Angiogenic factors such as VEGF and bFGF have relatively long half-lives in the blood compared with angiostatic factors such as endostatin or angiostatin. Large tumors often produce sufficient amounts of angiostatic factors to suppress the growth of blood vessels in small, undetectable tumors present elsewhere in the body. This suppression of angiogenesis in the smaller tumors also suppresses the overall growth of the tumors, because the small tumors cannot grow without an adequate blood supply, ie.e. tumor growth is angiogenesis-dependent.

When the large tumor is removed, the blood levels of angiostatic factor (endostatin) decrease, allowing angiogenesis to occur in the smaller tumors. The smaller tumors grow rapidly as a consequence of this angiogenesis and can be detected within a few weeks. Endostatin is a fragment of collagen XVIII, which inhibits angiogenesis an shrinks tumors. It shows promising behavior as an anticancer agent in early, preclinical trials.

The astute student may wonder how angiogenesis can occur in large tumors in the presence of angiostatic factors. The answer is that angiogenesis occurs when the levels (or activities) of angiogenic factors become greater compared with the levels of angiostatic factors, i.e. both angiogenic and angiostatic factors may be present in a tumor, but angiogenesis occurs when the influence of angiogenic factors predominates. The student may also ask how a large tumor can suppress angiogenesis in small tumors when both angiostatic and angiogenic factors are released from the large tumor. The answer is that angiostatic factors have long half-lives in the blood compared with that of angiogenic factors, as discussed above. Thus, the smaller tumors see higher levels of angiostaic factors compared with angiogenic factors.

Endostatin

Endostatin is a naturally occurring, 20-kDa C-terminal fragment derived from type XVIII collagen. It is reported to serve as an anti-angiogenic agent, similar to angiostatin and thrombospondin.

Question 5

48 y/o presents to emerg with chest pain that radiates to his jaw and left shoulder. Angina pectoris is suspected, and he is sent for an angiogram. Test reveals atherosclerotic coronary artery that is 50% occluded. The maximal blood flow through this artery is reduced by?

Answer 5

1/16

According to the equation

R = 8nl/(pi)r^4

where R is resistance, n is viscosity of blood, l is the length of the blood vessel and r^4 is the radius of the blood vessel wall to the fourth power, the resistance is inversely proportional to the fourth power of the radius. In other words, if the radius is reduced by one half the resistance is multiplied by 16. In addition, blood flow can be expressed as the following:

Q = DeltaP/R

where Q is blood flow, Delta p is the pressure gradient at both ends of the vessel, and R is the resistance. Blood flow is inversely proportional to resistance. So when the resistance is increassed by 16 fold, blood flow must decrease by 16 fold.

Question 6

24 y/o paraplegic after he severs his spinal cor at T1. Chronic constipation is a problem, but he wants to be independent. Physician advises him to distend the rectum digitally on a regular schedule to initiate the defecation reflex. Rectal distention causes which of the folloiwng in this patient?

Answer 6

Increased peristaltic waves

Defecation is initiated by defecation reflexes. An intrinsic reflex mediated entirely by the local enteric nervous system is stimulated when feces enters the rectum. Distention of the rectum initiates afferent signals that spread through the myenteric plexus to initiate peristaltic contractions in the descending colon, sigmoid, and rectum and force the feces toward the anus.

Question 7

14 y/o boy has a craniotomy performed under general endotracheal anestheia for removal of a craniopharyngioma. The anesthetic agent used is halothane, and when he awake he is extubated and sent to the floor. Five percent dextrose in one-third normal saline was dripping in his intravenous line at a rate of 125 ml/h. Four hours later, the nurses report that he cannot be roused from a deep sleep. point out his urinary output in 4 hours was 1050, 1100, 980, and 1250ml, respectively. Laboratory findsings show:

Sodium 156 mEq/L

Osmolarity 312 mOsm/L

pH 7.55

pCO2 28 mm Hg

Bicarbonate 24 mEq/L

what explains these findings?

Answer 7

surgical trauma to the posterior pituitary

The clinical and laboratory picture is that of diabetes insipidus. His surgical procedure took place in the vicinity of the pituitary gland (where craniopharyngiomas are typically located), thus, the most likely scenario is that of inadvertent damage to the posterior pituitary or the stalk.

Question 8

26 y/o woman stranded no food. what substances can be converted to glucose to supply the needs of the brain during this period. Starvation

Answer 8

Amino acids.

during starvation the diet is inadequate to provide sufficient glucose to maintain the brain, yet the brain requires glucose as energy source. Glucose used in the brain during starvation is synthesized rom amino acids, primarily derived from muscle protein. This use of amino acids in starvation leads to profound muscle wasting.

Question 9

54 y/o man complains of palpitations and light-headedness. Exam ramarkable for a heart rate of greater than 200 min and a blood pressure of 75/40 mm Hg. Which of the following adjustments have probably occurred in the cardiac cycle.?

Answer 9

Systolic time has decreased but diastolic time has decreased more.

Under normal conditions, one third of the cardiac cycle is spent in the systole and two thirds spent in diastole. As heart rate increases dramatically, the time spent in diastole falls precipitously but the time spent in systole falls to a lesser extent. A large increase in heart rate must produce a decrease in both diastole and systole. The major change with increased heart rate is in diastole not systole. Heart rate cannot increase if diastolic time increases. An increase in heart rate must be accompanied by a decrease in diastolic time.

Question 10

25 y/o visits friend living in mountain at 5000 meters. 5 days he increase ventilation rate and a decrease in arterial PCO2 what physiologic changes is also expected?

Answer 10

Increased renal excretion of HCO3-

Compensation for high altitude includes an increase in the renal excretion of bicarbonate. The diminished barometric pressure found at high altitude causes arterial hypoxia. which is sensed by peripheral chemoreceptors. The ventilation rate increases, thereby causing a respiratory alkalosis. The kidney then compensates by increasing the excretion of HCO3-.

High altitude leads to respiratory alkalosis. Renal compensation is a metabolic acidosis characterized by decreased H+ excretion and increased HCO3- excretion. Respiratory acidosis is reanally compensated with a metabolic alkalosis that would incrude increases in H+ excretion.

Question 11

As part of an experimental study a volunteer agrees to have 10g mannitol injected intravenously. After sufficient time for equilibration, blood is drawn, and the concentration of mannitol in the plasma is found to be 65mg/100ml. Urinalysis reveals that 10% of the mannitol had been excreted into the urine during this time period. What is the approximate extracellular fluid volume of this volunteer.

Answer 11

14L

Volume = amount/concentration

The amount of mannitol in the volunteer is equal to the amount injected minus the amount excreted:

10g - 1g = 9g = 9000mg. Therefore.

Volume = 9000/65mg/100ml = 13.8L

Question 12

A neuro physiologist is studying the functional properties of various receptor subtypes, using whole-cell voltage clamp recordings made from coronal brain slices. At a holding potential of -70mV, bath application of receptor agonists for four different receptor types consistently elicited either excitatory postsynaptic currents or inhibitory postsynaptic currents. During the study of one receptor, however, agonist application failed to elicit a postsynaptic response at -70mV but did elicit a reliable response at a holding potential of 0mV. This receptor is most likely which of the following?

Answer 12

N-Methyl-D-aspartate (NMDA)

The NMDA receptor, a type of glutamate receptor is unique in that it is both voltage and ligand-gated. In other words, it requires both an agonist and neuronal depolarization to be activated. The NMDA receptor is an ion channel that allows the passage of Na+ and Ca2+ when open. At resting membrane potential, the channel is plugged by a Mg2+ ion. Depolarization (and agonist activation) causes the Mg2+ ion to dislodge, allowing the receptor to be functional.

GABA receptor is a ligand-gated chloride channel.

Kainate receptor a type of glutamate receptor the nicotinic acetylcholine receptor and the 5-HT3 receptor are ligand-gated Na+ channels.

Question 13

Researcher experiment on anesthetized animal to study cardiovascular and neural responses to stimuli. measures blood pressure and monitor the electrocardiogram. Isolates the afferent nerves from carotid sinus and aortic arch and implants microelectrodes to record nerve activity. Take baseline measurements, massages teh right carotid artery for 60 seconds. Which of the following data sets coresponds best to his experimental findings during the carotid massage?

Answer 13

This is actually a straightforward question. The fastest way to approach it is to predict the physiologic responses that would occur as a result of a carotid massage and identify the appropriate graph, rather than spending the time to read all of the graphs.

During a carotid massage, the carotid sinus baroreceptors sense the distortion of the vessel wall. This leads to an increase in afferent traffic (firing rate) in the glossopharyngeal nerve. A signal indicating high blood pressure travels to the nucleus of the solitary tract (NTS) in the medulla, and the baroreceptor reflex occurs. The animal is tricked into thinking it has high blood pressure, so it decreases sympathetic outlfow and increases parasympathetic outflow, leading to decreases in blood pressure and heart rate. Meanwhile, the aortic arch baroreceptors, which are innervated by the vagus nerve, correctly sense that the blood pressure has decreased. This decreases afferent traffic along the vagus nerve to the brainstem.

If you simply knew that a crotid massage leads to a decrease in blood pressure and heart rate, you could immediately narrow choices. Knowledge of baroreceptor physiology allows you to distinguish between A and B.

Question 14

In clinical trials, an experimental drug is found to cause impotence in a large percentage of male patients. Inhibition of which of the following could be responsible for this side effect?

Answer 14

Nitric oxide synthase (NOS)

Penile erection is mediated by the parasympathetic nervous system. The neurons involved are termed nonadrenergic, noncholinergic (NANC) autonomic neurons, and they may release nitric oxide (NO). NO binds to the iron in the heme molecule of guanylate cyclase, activating it to form cGMP. This results in a decrease in intracellular calcium and subsequent smooth muscle relaxation and vasodilation in the corpus cavernosa, producing erection. Nitric oxide synthase (NOS) is the enzyme required for the formation of NO from circulating arginine, and androgens are necessary to maintain normal amounts of this enzyme. Inhibition of this enzyme could result in impotence (although most currently used drugs that have impotence as a side effect do not affect NOS).

Question 15

Healthy 22 y/o female medical student has an exercise stress test at local health club. Which of the following is most likely to decrease in her skeletal muscles during exercise?

Answer 15

Arteriolar resistance

The increase in muscle blood flow that occurs during exercise is caused by dilation of the arterioles (i.e. decreased arteriolar resistance). In normal skeletal muscles, the blood flow can increase as much as 20 fold during strenuous exercise. Most of this increase in blood flow can be attributed to the dilatory actions of metabolic factors (e.g. adenosine, alctic acid, carbon dioxide) produced by exercising muscles.

A decrease in vascular conductance occurs when the vasculatur is constricted. Resistance and conductance are inversely related, so that a decrease in arteriolar resistance is associated with an increase in arteriolar conductance.

Question 16

Young man go to gym ln way home. Runs on treadill for 30min, lifts weights for 20min, and does pushups and situps for 10min. Which of the following is quantitatively the most important method for transporting the CO2 in the blood that is produced by his muscles?

Answer 16

As bicarbonate in serum

Red blood cells (and many other blood cells) contain the enzyme carbonic anhydrase, which catalyzes the intracellular conversion of CO2 to bicarbonate and H+ ion. Most of the bicarbonate in the red cell is exchanged across the plasmalemma for chloride ion. This means that although the bulk of the production of bicarbonate occurs in the red cell, the bulk of the actual transport occurs in serum. Carbonic anhydrase is not present in serum. Bicarbonate can also be produced in serum by nonenzymatic means, but the process is slow.

Question 17

Answer 17

17 answer is C.

The various points on the volume-pressure diagram correspond to specific events of the cardiac cycle as follows. A the mitral valve opens and the period of filling begins.

B this is the period of filling

C this marks the beginning of ventricular systole. The mitral valve closes, and S1 can be heard. The end-diastolic pressure (5mm Hg) and end-diastolic volume (125ml) can be determined on the Y-axis and x-axis from this point.

D This is the period of isovolumetric contraction. Left ventricular pressure increases rapidly, but left ventricular volume remains constant. All heart valves are closed.

E the aortic valve opens, which marks the beginning of the period of ejection. The pressure at this point is equal to the aortic diastolic blood pressure, which is about 80mm Hg on the diagram.

F This is the period of ejection. The pressure at the apex of the curve is the peak systolic pressure of the left ventricle.

G This marks the beginning of diastole. The aortic valve closes, and S2 can be heard. The end-systolic volume (50ml) can be read from x-axis at this point.

H This is the period of isovolumetric relaxation. Left ventricular pressure is falling rapidly, but left ventricular volume remains constant. All heart valves are closed.

Question 18

43 y/o history of ulcer disease associated with diarrhea and strong family history of duodenal ulcer disease suspected of having Zollinger-Ellison syndrom (gastrinoma). Secretin (1 U/kg) is given as a rapid intravenous injection to test for gastrinoma. Which results would support the existence of gastrinoma following secretin administration?

Answer 18

Increased serum gastrin

Gastrinomas are gastrin-secreting tumors usually present in the pancrease. Patients with gastrinoma have high serum gastrin levels, which lead to hypersecretion of gastric acid and consequent duodenal and jejunal ulcers. Injection of secretin is the most specific and easiest test for gastrinoma.

Secretin inhibits antral release of gastrin, but it stimulates release of gastrin from gastrin tumors (gastrinoma) in almost all patients. A doubling of serum gastrin 5 to 10 minutes after admin of secreting (1U/kg), coupled with acid hypersecretion and increased basal serum gastrin, strongly indicates the presence of gastrinoma. Secretin can inhibit gastric emptying, inhibit gastric secretion and stimulate pancreatic HCO3- secretion, but these effects are not diagnostic for gastrinoma.

Question 19

Students studying clearance of inulin by the kidneys on a computer simulated patient. Professor programs the computer so patients ratio of urinary concentration to plasma concentration of inulin (U/P) inulin) decreases. Which of the following is true if the glomerular filtration rate remains constant?

Answer 19

Urine flow rate has increased.

Inulin is freely filtered, but is neither reabsorbed nor secreted. Since all inulin filtered in the glomerulus will appear in the urine, the amount of water in the urine will determine the concentration of the inulin. Therefore, (U/P) inulin will decrease if the urine flow rate increases.

Question 20

Blood is drawn from a 14 y/o boy with a bacterial meningitis for a complete blood count. The leukocyte count is elevated. Which of the following is released by the predominant type of white blood cell present?

Answer 20

Lysozyme

This question requires you to know that bacterial infections are associated with an elevated enutrophil count. These leukocytes have 3 to 5 nuclear lobes and are filled with granules that contain bactericidal products, including lysozyme. Note that neutrophils normally constitute 54 to 62% of leukocytes, so if you were unsure of the percentages occuring in response to bacterial infections, C still would have been a good guess. Had the infection been viral there would have been an increase in lymphocytes instead.

Question 21

21 y/o man competing in weight lifting competition. Lifts weight ove rhead, arms give way and he drops weight. Which of the following receptors is responsible for this sudden muscle relaxation.

Answer 21

Golgi tendon organ

Normally, stretching of muscle results in a reflex contraction: the harder the stretch, the stronger the contraction. At a certain point, when the tension becomes too great, the contracting muscle suddenly relaxes. the reflex that underlies this sudden muscle relaxation is called the golgi tendon organ (GTO) reflex, also known as the inverse stretch reflex or autogenic inhibition. The GTO is an extensive arborization of nerve endings (encapsulated by a connective tissue sheath and located near the muscle attachment). That is connected in series with the extrafusal skeletal muscle fibers. As a result, GTO’s respond to muscle tension rather than muscle length. Increased tension leads to stimulation of Ib afferents, which inhibit the homonymous muscle via spinal interneurons.

The Golgi tendon reflex[1] (also called inverse stretch reflex, autogenic inhibition,[2] tendon reflex[3]) is an inhibitory effect on the muscle resulting from the muscle tension stimulating Golgi tendon organs (GTO) of the muscle, and hence it is self-induced. The reflex arc is a negative feedback mechanism preventing too much tension on the muscle and tendon. When the tension is extreme, the inhibition can be so great it overcomes the excitatory effects on the muscle’s alpha motoneurons causing the muscle to suddenly relax.[1] This reflex is also called the inverse myotatic reflex,[4] because it is the inverse of the stretch reflex.

Question 22

16 y/o type 1 diabetic is noncompliant with insulin therapy and develops hyperglycemia after eating candy. Release of which intestinal hormones would most likely be stimulated?

Answer 22

GASRTRIC INHIBITORY PEPTIDE (GIP)

Gastric inhibitoriy peptide (GIP) is produced in the duodenal and jejunal mucosa by K cells. and is released in reponse to intraluminal glucose and fatty acids. GIP is sometimes called (glucose-dependent insulinotropic) peptide because it stimulates pancreatic insulin secretion in the presence of hyperglycemia. Note that although GIP release would be stimulated, the hormone would not have a pronounced effect in this type 1 diabetic, whose pancreatic islet cells do not produce adequate amounts of insulin.

Question 23

69 y/o alcoholic has had severe progressively increasing epigastric pain for the past 24 hours. He has been nauseous, and he vomited three times. Laboratory studies show hypocalcemia and metabolic hypochloremic alkalosis. The primary metabolic effect of the principal hormone secreted by the alpha cells of his organ is?

Answer 23

Stimulation of glycogenolysis

Glucagon is released from the alpha cells of the pancrease in response to hypglycemia and sitmulates glycogenolysis to increase serum glucose.

Question 24

Researcher studying the substance para-aminohippuric acid (PAH) and its interaction with the kidneys. She injects a volunteer with the substance. She finds that which of the following can be determined by calculating the clearance of PAH

Answer 24

Effective renal plasma flow (ERPF)

At less than saturating concentrations, PAH is completely secreted into the proximal tubule and excreted into the urine. Therefore, the volume of plasma cleared of PAH is approximately equal to the volume of plasma flowing through the peritubular capillaries, also called the effective renal plasma flow, or ERPF.

ERPF = Upah x V / Ppah

At very high concentrations, the clearance of PAH would be less than ERPF and approaches GFR.

Question 25

57 y/o woman with 30yr history of alcoholism and liver disease visits her physician complaining of abdominal swelling and shortness of breath. The physician determines that she has severe ascites. Which of the following factors contributes to the accumulation of fluid in the abdominal cavity?

Answer 25

Increased hydrostatic pressure in splanchnic capillary beds. Ascites often occurs in patients with cirrhosis and other forms of severe liver disease and is usually noticed by the patient because of abdominal swelling. Shortness of breath may occur because the diaphragm is elevated when the accumulation of fluid becomes more pronounced. A number of factors contribute to accumulation of fluid in the abdominal cavity. Portal hypertension plays an important role in the production of ascites by raising capillary hydrostatic pressure within the splanchnic bed.

Question 26

33 y/o man complains that his chest hurts when he eats, especially when he eats meat. Xray film shows dilated esopagus, and achalasia is suspected. Esophageal manometry is used to confirm the diagnosis. Swallowing induced relaxation is reduced at which anatomic location in this man?

Answer 26

Lower esophageal sphincter Achalasia is a disorder of esophageal motility that affects the lower esophageal sphincter (LES) and lower two thirds of the esophageal body. The LES remains tonically contracted and and does not relax as food moves down the esophagus. Relaxation is via the release of vasoactive intestinal peptide (VIP) from nerve endings. Therefore, food cannot move easily from the esophagus into the stomach. The distal esophagus often becomes greatly dilated. Patients with achalasia most commonly complain of dysphagia (difficulty swallowing), chest pain, and regurgitation. Relaxation of the upper esophageal sphincter occurs normally in patients with achalasia.

Question 27

substance filtered, but not secreted or reabsorbed (substance X) is infused into a volunteer until a steady state plasma level of 0.1mg/ml is achieved. The subject then empties his bladder and waits 1 hour, at which time he urinates again. The volume of urine in the second specimen is 60ml, and the concentration of substance X is 10mg/ml. What is the glomerular filtration rate (GFR) in this individual.

Answer 27

100ml/min Because substance X is filtered, but not secreted or reabsorbed (like inulin) the clearance of substance X can be used to approximate GFR. GFR = (U)x x V / (P)x GFR = (10mg/ml) x (60ml/hr) / 0.1mg/ml GFR = (10 mg/ml) x (1ml/min) / 0.1 m/ml = 100ml/min Note you need to convert 60ml/hour to 1ml/min to get the correct answer in the correct units. Checking to make sure the units are correct will help make sure you are using the formula properly.

Question 28

40 y/o with sleep apnea participates in a sleep study. During evaluation, normal sawtooth waves are observed on his EEG tracing. This pattern is associated with which period of sleep?

Answer 28

REM A sawtooth waves appearing in bursts are associated with REM sleep. Stage 1 is associated with 4-7Hz theta waves. Stage 2 is associatd with 12-14 Hz sleep spindles and k complexes. Stage 3 is associated with less than 4 Hz, high amplitude delta waves. STage 4 is characterized by an EEG composed of about 50% delta waves. Note that beta waves (15-18 Hz) ocur during periods of more intense mental activity while awake. Alpha waves (8-12 Hz) occur during awake, relaxed states. REM is the stage of sleep that most resembles the awake state on the EEG.

Question 29

48 y/o female presents with progressive difficulty typing over the past month. Notes that her hands begin to feel numb and weak after typing for long periods of time. On testing, which of the following deficits would be predicted?

Answer 29

Difficulty in flexing digits two and three at the metacarpophalangeal joints. This is a classic presentation of carpal tunnel syndrome, which typically affects women betweent he ages of 40 and 60. Who chronically perform repetitive tasks that involve movement of the structures that pass through the carpal tunnel. One important structure that passes though the carpal tunnel is the median nerve. Patients often note tingling, loss of sensation, or diminished sensation of the digits. There is also often a loss of coordination and strength in the thumb, because the median nerve also sends fibers to the abductor pollicis brevis, flexor pollicis brevis, and the opponens pollicis. A final function of the median nerve distal to the carpal tunel is control of the first and second lumbricals, which function to flex digits two and three at the metacarpophalangeal joints and extend interphalangeal joints of the same digits.

Question 30

70 y/o woman undergoes a gastrectomy for Zollinger-Ellison syndrome. Her physician informs her that she will need to take intramuscular vitamin B12 shots for the rest of her life. Absence of which of the following cell types is responsible for this vitamin replacement requirment.

Answer 30

Parietal cells Parietal cells of the stomach produce intrinsic factor, a glycoprotein that binds with vitamin B12 in the lumen of the stomach and facilitates its absorption in the terminal ileum. Patients without a stomach and those with pernicious anemia (autoimmune destruction of parietal cells) require B12 replacement therapy. Recall that B12 deficiency will lead to megaloblastic anemia and the USMLE favorite picture of a blood smear with hypersegmented neutrophils. Note that parietal cells also synthesize and secrete HCl.

Question 31

32 y/o man visits the physician for a periodic health maintenance examination. He has no complaints at thsi time. He is 170 cm 5'7" tall and weights 75kg (165lb). Physical examination is unremarkable. In this patient, the volumes of total body water, intracellular fluid,a nd extracellular fluid are, respectively?

Answer 31

45L, 30L, 15L Total body water (TBW) in liters equals approximately 60% of body weight in KG and therefore equals 45L in a 75kg person. Intracellular volume = 2/3 of TBW and is therefore 30L in this case. Extracellular volume = 1/3 of TBW and is therefore 15L.

Question 32

A 35 y/o sexually active woman visits her gynecologist complaining of mild right sided lower abdominal pain but no other symptoms. There are no peritoneal signs. Her surgical history is significant for an appendectomy at age 10. Her last period occured 14 days ago. Which of the following endometrial changes corresponds to this stage of the patients menstrual cycle?

Answer 32

Growth of the spiral arteries This patient appears to be experiencing mittelschmerz, abdominal pain occuring at the time of ovulation that can mimic acute appendicitis (which is ruled out cause of patients surgical history) If this information did not clue you into the stage of the menstrual cycle, you are told explicitly that the patients last menstrual period was 14 days ago. Therefore, she is at the conclusion of the proliferative (estrogenic) phase. This stage begins during the latter period of enstrual flow and cotinues through the 13-14th day of a stypical 28 day cycle. it is characterized by regrowth of the endometrium. The epithelial cells of the glandular structures remaining after menstruation migrate and proliferate to cover the new mucosal surface. Also, the spiral arteries grow into the regenerating endometrium (this process continues through the secretory stage as well). Significant edema develops by the end of the proliferative stage and continues to develop during the secretory phase.

Question 33

71 y/o woman undergoes elective sigmoid resection for recurrent diverticulitis. On the second postoperative day, it is noted that her urinary output is averaging ony 35 to 45ml/h. She is receiving 5% dextrose in half normal saline at a rate of 100ml/h. The intravenous rate of infusion is increased to 125ml/h. Two days later, her urinary output becomes 15 to 25 ml/h. A sample of urine shows a urinary sodium concentration of 85 mEq/L. Laboratory studies show the systemic arterial values as folows: pH 7.25 pCo2 30mm Hg Bicarbonate 15mEq/L Potassium 5.8 mEq/L BUN 85mg/dL Creatinine 5.1 mg/dL what is the most likely diagnosis?

Answer 33

Acute renal failure A scenario of postoperative oliguria raises the possibility of two potential diagnoses, fluid volume deficit and acute renal failure. The urinary sodium concentration provies a good indication of which of the two is present. If good kidneys are saving fluid because of a vloume deficit, the amount of sodium in the urine is very small, with a concentration typicallky less than 20 mEq/L. When the sodium in the urine exceeds a concentration of 40 mEq/L in the same general scenario, renal failure is the answer.

Question 34

47 y/o immigrant from Africa has significant edema of the left lower extremity. A polymerase chain reaction assay for DNA of Wucheria Bancrofti is positive. Which sequence of the numbered statements below corectly describes the pathway of the flow from the affected system on the affected side of the body? So, order these in sequence: 1) Junction of left internal jugular and let subclavian 2) Lymph capillaries 3) Thin lymph vessels 4) Thoracic duct

Answer 34

2-3-4-1 On the left side of the body, the lymphatic fluid flows from the lymphatic capillaries, to the thin lymphatic vessels, and then to the thoracic duct, which empties into the junction of the left internal jugular and left subclavian veins. On the right side, lymphatic fluid flows from the lymphatic capillaries to the thin lymphatic vessels, to the right thoracic duct, which empties into the junction of the right internal jugular and the right subclavian vein.

Question 35

The following data were collected from a normal patient before and after an intervention. Assume that plasma osmolarity and glomerular filtration rate remain constant. Numbers are Before and After: Urine osmolarity (mOsm/L) 900 250 Urine flow rate (mL/min) 0.65 2.3 Fractional clearance of sodium 1% 1% Osmolar clearance (mL/min) 2.0 2.0 The intervention that would best account for the observed changes is?

Answer 35

Administration of lithium Lithium inhibits the action of antidiuretic hormone (ADH; vasopressin) on the V2 receptors in the collecting duct that regulate the permeability to water. Therefore, lithium administration will decrease water permeability in the collecting duct, which will increase urine flow rate and decrease urine osmolarity. Because ADH has minimal effects on sodium reabsorption in humans, the fractional clearance of sodium and the osmolar clearance are unaffected. (Osmolar clearance refers to the clearance of all particles, including sodium and anions, from the plasma per minute)

Question 36

An unlabeled container of blood product is left in a laboratory. The technician must determine whether the sample is serum or plasma. An elevated level of which of the following substances would identify the specimen as plasma.

Answer 36

Fibrinogen This is a really simple definition question: What is the difference between serum and plasma? Essentially, serum is derived rom plasma by the extraction of fibrinogen and coagulation factors II, V, and VIII. This can be achieved by allowing whole blood to clot, then removing the clot.

Question 37

A Swan-Ganz catheter inserted into a patient with acute respiratory distress syndrome (ARDS) records a pulmonary artery wedge pressure of 6 mm Hg. The same pressure would be expected in which of the following structures?

Answer 37

Left Atrium Pressure in the left atrium can be approximated by wedging an arterial catheter into a small branch of the pulmonary artery. Remember that the pulmonary vascular tree abuts the left atrium anatomically. The pulmonary artery carries deoxygenated blood from the right ventricle into the pulmonary circulation, where it is oxygenated and then returned to the left atrium via the pulmonary veins.

Question 38

A patient hyperventilating and doubles his alveolar ventilation. If his initial alveolar PAco2 was 40 mm Hg, and is CO2 production remains unchanged what will his alveolar Pco2 be on hyperventilation?

Answer 38

20 mm Hg Requires use of alveolar ventilation equation PAco2 = Vco2/Va where PAco2 is the partial pressure of alveolar CO2, Vco2 is CO2 production and VA is alveolar ventilation, If Vco2 remains constant and alveolar ventilation doubles, PAco2 must decrease to half its original value. Therefore, PAco2 equals 20mm Hg after hyperventilation. Memorizing this formula is not necessary if you think about this intuitively, if CO2 production remains constant and alveolar ventilation doubles, the partial pressure of alveola CO2 must decxrease to half of its original value and would therefore equal 20 mm Hg after hyperventilation.

Question 39

Answer 39

E The maximum expiratory flow volume (MEFV) curve is created when the patient inhales as much air as possible and then expires with maximal efort until no more air can be expired. The amount of air that remains in the lungs after maximal expiration is the residual volume, and is depicted by point E. Note that the absolute value of the residual volume cannot be determined from MEFV curve alone. Additional studies such as helium dilution are needed to determine the absolute value. Choice A is the lung volume at the total lung capacity, however, absolute lung volumes cannot be determined from MEFV curve without additional methods. The other points correspond to the following. Choice B the patient has just begun to exhale with a maximal effort at this point. Choice C the patient is exhaling with maximal effort and the rate of air flow has reached its maximal value of nearly 400L/minute at this high lung volume. The descending portion of the curve choice D represents the maximu expiratory flow at each lung volume along the curve. This portion of the curve is sometimes referred to as the effort-independent portion of the curve because the patient cannot increase expiratory flow rate further by expending greater effort.

Question 40

42 y/o obese woman experiences episodic abdominal pain. She notes that the pain increases after the ingestion of a fatty meal. The action of which of the following hormones is responsible for the postprandial intensification of her symptoms?

Answer 40

Cholecystokinin (CCK) This woman has a risk profile (female, fat, forties) and symptomatology consistent with gallstones (cholelithiasis). As would be expected, contraction of the gallbladder following a fatty meal often exacerbates the pain caused by gallstones. Cholecystokinin (CCK) is the hormone responsible for stimulation of gallbladder contraction, the release of CCK is stimulated by dietary fat, it is produced in I cells fo the duodenum and jejunum. In additon to gallbladder conraction, CCK also stimulates pancreatic enzyme secretion and decreases the rate of gastric emptying. Gastrin is produced by the G cells of the antrum and duodenum. Gastrin stimulates the secretion of HCl from the parietal cells and pepsinogen from the chief cells of the stomach. Gastrin is stimulated by gastric distention, digestive products. e.g. amino acids. and vagal discharge.

Question 41

Answer 41

B The answer is B because. Renal blood flow = (renal artery pressure - renal vein pressure) / renal vascular resistance (RVR). Therefore if RVR is decreased to half its original value, with no pressure changes, renal blood flow must double (not increase 50%). Increased blood flow to the kidney and pressure in the glomerular capillaries increase renal oxygen use by increasing glomerular filtration rate, which increases the filtered load of sodium and other solutes. Since active sodium reabsorption is load-dependent, increased tubular fluid sodium increases all active sodium reabsorption, which requires more ATP hydrolysis and synthesis (and hence more oxygen use) Renal artery oxygen concentration does not change, since it is dependent on normal lung function, not oxygen extraction by the kidney.

Question 42

61 y/o woman develops purple striae on her abdomen and a rounded facial appearance. She has smoked two packs of cigs a day for the past 40 years. Chest xray shows a 4cm centrally located lung mass. This mass is most likely producing a hormone that promotes the production of cortisol by stimulating which of the following reactions?

Answer 42

Cholesterol to pregnenolone All of the choices listed are reactions that occur in the synthetic pathway from cholesterol to cortisol. ACTH stimulates the first reaction in the pathway: cholesterol to pregnenolone. This reaction is catalyzed by the enzyme cholesterol desmolase.

Question 43

69 y/o presents with unilateral hearing loss. A lesion in which of the following structures could be responsible for this loss

Answer 43

Organ of Corti The sequence of the auditory pathway is as follows: Organ of Corti - spiral ganglion in the cochlea - vestibulocochlear nerve (CN VIII) - cochlear nuclei (dorsal and ventral) - superior olivary nuclei - lateral lemniscus - inferior colliculus - medial geniculate nucleus of the thalamus (MGN) - primary auditory cortex (Heschl's gyrus). Each ear projects to both sides of the brainstem and cortex via multiple commissures, including the trapezoid body (which contains fibers crossing contralateral to the superior olivary nucleus), the commissure of the inferior colliculus (connecting the right and left inferior or colliculi), and another ocmmissure that connects the right and left nuclei of the lateral lemniscus. Therefore, a lesion of any structure up until the superior olivary nuclei will produce an ipsilateral deafness. the only structure listed that is proximal to the superior olivary nuclei is the organ of corti.

Question 44

Young boy presents with failure ot thrive. Biochemical analysis of a duodenal aspirate after a meal reveals a deficiency of enteropeptidase (enterokinase). The levels of which of the following digestive enzymes would be affected.

Answer 44

Trypsin Enteropeptidase, formerly called enterokinase, activates trypsinogen by limited proteolytic digestion to give trypsin. Trypsin is itself capable of activating trypsinogen, which produces a positive feedback effect. Trypsin also activates chymotrypsinogen (and several other proteolytic enzymes), so deficiency of enteropeptidase results in a severe deficiency of enzymes that digest protein.

Question 45

says failing heart

Answer 45

correct answer is B Diagram P shows a normal heart with an end-diastolic volume (EDV) of 125ml and an end-systolic volume (ESV) of 50ml. Stroke volume (SV) can be calculated as EDV - ESV = 75ml. and ejection fraction can be calculated as SV/EDV = 0.6. The untreated failing heart (Diagram R) has an EDV of 188ml, an ESV of 156 an SV of 32ml and an ejection fraction of only 0.17. Note also that the peak systolic pressure of the failing heart (95 mm Hg) is lower than that of the control heart (100mm Hg). Treatment with digitalis (Diagram Q) has increased the contractility of the myocardium. This increase in contractility has increased stroke volume to 45mm Hg and ejection fraction to 0.26. Note also on diagram Q that the peak systolic pressure has returned to a normal value of 100mm Hg. and is better maintained throughout systole.

Question 46

45 y/o man blood pressure reading of 160/100mm Hg on three separate visits. He refuses to take antihypertensive medication but is willing ot modify his lifestyle in an effort to lower his blood pressure. He quits smoking, joins a health club, and greatly reduces salt from his diet. Which of the following areas of the adrenal gland would be expected to increase in activity because of his diet.

Answer 46

Zona glomerulosa of the adrenal cortex This question requires you to equate salt restriction with an increased synthesis of aldosterone (aldosterone promotes sodium reabsorption) and then to remember that aldosterone is produced in the zona glomerulosa of the adrenal cortex. The zona glomerulosa is the outermost layer of the adrenal cortex.

Question 47

A med student is studying the fluid exchange in skeletal muscle capillaries in a laboratory animal. He determines that fluid is being forced out of a capillary with a net filtration pressure of 8 mm Hg and he obtains the following lab values: capillary hydrostatic pressure 24mm Hg capillary colloid osmotic pressure 17mm Hg interstitial hydrostatic pressure 7mm Hg What is the interstitial osmotic pressure?

Answer 47

8 mm Hg To calculate the direction and driving force for fluid ovement, use the starling equation net filtration pressure = (Pc - Pi) - (pic - pii). the net pressure in this case is positive because fluid is being forced out of the capillary. Pc = capillary hydrostatic pressure = 18 pic = capillary colloid osmotic pressure = 25 pii = interstitial osmotic pressure = 9. Substituting these values into the equation and solving for Pi we get. 8 mm Hg = (24-7) - (17 - pii) mm Hg pii = 8mm Hg

Question 48

37 y/o trying to get pregnant for past 16months. just as she is about to schedule an appointment with a fertility specialist she gets a premonition that she is pregnant, despite a negative home pregnancy test 7 days earlier. By the time of implantation in the uterine endometrium, the typical fertilized ovum has divided into how many cells?

Answer 48

Greater than 50 by the time of implantation, approximately 7 days after ovulation, the fertilized ovum has developed to the blastocyst stage. At this stage, the blastocyst typically contains 100 or more cells, which have differentiated into an inner cell mass (designed to become the embryo) and trophoblast (which surrounds both the outer edge o the inner cell mass and a large fluid-filled cavity). The blastocyst is able to burrow into the endometrium in less than 24 hours after touching the endometrial surface. During the next several days a primative placenta begins to develop that penetrates the maternal capillary bed and begins circulating maternal blood by about day 11.

Question 49

24 y/o woman suffers from epistaxis, gingival bleeding, and menorrhagia. Her mother and grandmother have similar symptoms, and her brother has incisional bleeding after surgery and dental extractions. All have similar lab findings including a prolonged bleeding time and reduced levels of factor VIII antigen, normal platelet aggregation, and reduced ristocetin cofactor activity. This family has a disorder characterized by a deficient or defective protein. In normal patients, which of the following binds to the affected protein at the platelet membrane.

Answer 49

Glycoprotein GPIb Glycoprotein GPIb on the platelet membrane binds von Willebrand factor, a plasma protein that circulates in a complex with factor VIII.

Question 50

25 y/o woman auto accident. Major artery severed in her leg caused an estimated 600ml blood to be lost. Blood pressure is 90/60 mm Hg. Which of the following would be expected to increase in response to hemorrhage.

Answer 50

Sympathetic nerve activity The decrease in blood pressure caused by hemmorrhage activates the baroreceptor reflex, which tends to increase sympathetic nerve activity and decrease parasympathetic (vagal) nerve activity. The increase in sympathetic nerve activity constricts arterioles in skeletal muscle and elsewhere in the body. The fact that the patient has lost 600ml blood and yet her blood pressure has decreased only slightly from a normal value. may be attributed to the following compensatory responses: baroreceptor reflex, chemoreceptor reflex, epinephrine and norepinephrine released rom the adrenal medulla, formation of angiotensin II,, formation of vasopressin, and the capillary fluid shift mechanism.

Question 51

In a controlled experiment, radiolabeled ATP is injected into an isolated muscle. The muscle is stimulated and allowed to contract for 10 seconds. An autoradiogram from a biopsy of the muscle will show radiolabeled ATP bound to?

Answer 51

Myosin During the contraction cycle, ATP binds to myosin cross-bridge heads, causing the dissociation of myosin from actin. Actin forms cross-bridges with myosin but does not bind to ATP. The sarcoplasmic reticulum is involved in storing and releasing Ca2+ for muscle contraction. Tropomyosin is a thin filament that runs alongside actin. In the abscence of calcium, tropomyosin lies in the groove of the actin filament and blocks actins myosin-binding sites. Troponin C is the calcium-binding subunit of the troponin complex. When troponin C binds calcium, a conformation change causes tropomyosin to shift, thereby exposing the myosin-binding sites on actin.

Question 52

Medical student decides to conduct a neurochemical experiment to measure extracellular neurotransmitter levels in the brain following electrical stimulation of the raphe nuclei. Which of the following neurotransmitter levels would be expected to rise?

Answer 52

Serotonin Serotonin is the primary neurotransmitter of the raphe nuclei. Ascending serotonin projections from the dorsal and median raphe nuclei distribute diffusely throughout the brain. Other raphe muclei provide descending serotonin projections to the spinal cord and brainstem.

Question 53

60 y/o with heart disease is brought to the emergency department. Cardiovascular evaluation reveals a resting O2 consumption of 200 ml/mi, a systemic arterial O2 content of 0.20ml O2/ml of blood, and a mixed venous O2 content of 0.15ml O2/ml of blood. What is his cardiac output? In liters

Answer 53

4L a min Cardiac output can be measued by way of O2 consumption using the Fick principle: Cardiac output = O2 consumption / O2 arterial - O2 venous In this case oxygen consumption was 200 and arterial was .20 of blood and O2 venous was .15 of blood. Cardiac output = 200 ml/min / .20ml o2/ml blood - 0.15ml O2/ml blood which equals 4000ml/min and in liters 4 L/min.

Question 54

A normal volunteer consents to an IV infusion of p-aminohippuric acid (PAH). After a short time, the plasma PAH is 0.02 mg/ml, the concentration of PAH in urine is 13 mg/ml, and the urine flow is 1.0 ml/min. What is the effective renal plasma flow (ERPF)? in ml a min

Answer 54

650 ml/min Approximately 90% of a small dose of PAH is cleared by the kidney in a single pass. If it were 100%, then the amount of PAH in urine (concentration times urine flow rate) divided by the amount of PAH in plasma would exactly equal the renal plasma flow. Because the extraction ratio (arterial-venous PAH concentration divided by arterial concentration is 0.9 (90%) instead of 100%, physiologists speak of the quantity UpahV/Ppah as the efective renal plasma flow, or ERPF, So, in this patient, we have (13 mg/ml x 1.0 ml/min) / 0.02 mg/ml = 650 ml/min

Question 55

Answer 55

Answer is D Following moderate exercise, the cardiac function curve is represented by curve 6, and the venous return curve is represented by curve 3 in the diagram. Note romt he point where curves 6 and 3 intersect that (a) drawing a horizontal liine to the y-axis gives a value of CO of about 18 L/min, (b) drawing a vertical line to the x-axis gives a RAP of about 2mm Hg and \*(c) the point where curve 3 (the venous return curve) intersects the x-axis is the MSFP, which is about +12 mm Hg. The increased level of the cardiac function curve results almost entirely form sympathetic stimulation of the heart, which increases heart rate and myocardial contractility. Note on the diagram that, without the increased level of the cardiac function curve, the maximal level of cardiac output would be about 15L/min (intersection of curves 3 and 5). Note also that the resting venous return curve (curve 2) would limit the maximal cardiac output to about 6L/min, even with enhanced performance of the heart, depicted by curve 6. The mean systemic fillling pressure (MSFP) is the pressure that exists in all parts of the circulation when the heart has been stopped and the blood volume has become redistributed in the system until all pressures are at equilibrium. The MSFP is thus a measure of the tightness with which the circulatory system is filled with blood. The greater the system is filled (i.e. whe MSFP increases), the easier it is for blood to flow into the heart, which tends to increase venous return. However, venous return also depends on the right atrial pressure because the pressure gradient for venous return is equal to MSFP - RAP. MSFP is increased during exercise because of venular constriction resulting from (a) sympathetic stimulation of veins and other capacitance vessels, and (b) compression of veins and other capacitance vessels by tensing the muscles in the abdomen. The venous return curve (curve 3) is also rotated upward (increased slope) because the resistance to venous return has decreased because the vessels in the exercising muscles have dilated greatly.

Question 56

Administration of an experimental drug that acts on peripheral nervous system (PNS) myelin is shown to increase the space-constant (icrease insulating effect of myelin) of an axon in a peripheral nerve. Action potentials travelling down the axon would be predicted to be?

Answer 56

FAster the space constant of an axon reflects the amount of passive or electrotonic spread of curent within the axon. The larger the space constant, the further th current can spread, allowing action potentials to propagate faster. This is why myelin increases the conduction velocity of action potentials down an axon. Conversely, demyelination decreases the space constant and slows action ptoential conduction.

Question 57

A patient undergoes a total gastrectomy because of a proximally located gastric cancer. After the surgery, which of the following digestive enzymes will be produced in reduced amounts?

Answer 57

Pepsin Pepsin is secreted (in an inactive or zymogen form as pepsinogen) by the chief cells of the stomach. Pepsinogen is activated by contact with stoach acid. Although protein digestion usually begins with the actions of hydrochloric acid and pepsin, pancreatic enzymes complete the job as the food passes into the small intestine. Gastrectomy is the removal of part or all of the stomach. There are three main types of gastrectomy: A partial gastrectomy is the removal of a part of the stomach. The lower half is usually removed. A full gastrectomy is the removal of the entire stomach.

Question 58

23 y/o woman gives blood to be a volunteer for bone marrow donation. She is found to be a match for a 7 y/o boy with leukemia. Her bone marow is harvested and examined for abnormalities. When the pathologist checks her marrow, what myeloid to erythroid ratio is she looking for to indicate that this young woman has a normal cell composition?

Answer 58

3:1 The ratio of cells in bone marrow developing along myeloid lines is 3:1. An alternative way to remember the normal marrow composition is that it typically contains about 60% granulocytes and their precursors, 20% erythroid precursors, 10% unidentified or disintegrating cells. These numbers are worth remembering, because shifts away from notmal values may be a subtle clue to marrow abnormalities. In hematopoiesis, myeloid or myelogenous cells are blood cells that arise from a progenitor cell for granulocytes, monocytes, erythrocytes, or platelets (the common myeloid progenitor, that is, CMP or CFU-GEMM), or in a narrower sense also often used, specifically from the lineage of the myeloblast

Question 59

Answer 59

D Lungs The graph indicates that blood flow decreases with hypoxia. Only the lungs exhibit vasoconstriction in resoponse to hypoxia (pulmonary hypoxic vasconstriction). This is an adaptive mechanism that causes blood to shunt away from regions of the lung that are poorly ventilated (e.g. because of airway obstruction) to areas that are beter ventilated. In other organs, vasodilation generally occurs in response to hypoxia.

Question 60

A boy and a girl set of wins is beginning to undergo puberty at age 14. In the development of their reproductive systems, wich of the following characteristics is similar for spermatogenesis and oogenesis?

Answer 60

DNA replication during meiosis The actual process of manipulation of DNA and chromosomes during meiosis is very similar to spermatogenesis ad oogenesis. However, the processes also differ in many other respects. In oogenesis, the process of meiosis begins before birth and arrests between birth and puberty in prophase I. In contrast, spermatogenesis does not begin until puberty. The egg retains a large volume of cytoplasm whereas nearly all of the cytoplasm is strepped during formation of a sperm. As noted above, in oogenesis, meiosis is arrested in prophase I, which is conseqeuntly very prolonged in the female. In spermatogenesis, meiosis is completed in a much shorter time. Both the egg and the sperm have mitochonddria but those of the sperm are let outside when the sperm nucleus enters the egg and consequently do not contribute to the mitochondrial genome of the fetus. Instead, the mitochondria are transmitted from the egg to the fetus. Traits coded for by mitochondrial DNA are therefore inherited in a matrilineal fashion.

Question 61

Pathologist is looking at slides of a lung that were removed during autopsy of a woman who died of lung cancer. On examination of the slide, the doctor orients herself to the respiratory zone of the lung. She identifies this area by which structure.

Answer 61

Type I epithelial cells There are two zones in the lung, the conducting zone (where there is no gas exchange) and the respiratory zone (where there is gas exchange). Of all of the structures listed, only type I epithelial cells are located in the respiratory zone. Type I epithelial cells are the primary sructural cells of the alveola wall. Type II epithelial cells, also located in the alveoli, produce surfactant.

Question 62

28 y/o decides to donate kidney to his brother with renal failure, after HLA typing suggests he would be a suitable donor. He is admitted to the hospital, and his right kidney is removed and transplanted into has brother. Which of the following indices would be expected to be decreased in the donor after full recovery from the operation.

Answer 62

Creatinine clearance Because creatinine is reely filtered by the glomerulus, but not secreted or reabsorbed to a significant extent, the renal clearance of creatinine is approximately equal to the glomerular filtration rate. In fact, creatinine clearance is commonly used to assess renal function in the clinical setting. When a kidney is removed, the total glomerular filtration rate decreases because 50% of the nephrons have been removed, which causes the creatinine clearance to decrease. In turn, the plasma creatinine concentration increases until the rate of creatinine excretion by the kidneys is equal to the rate of creatinine production by the body. Recall that creatinine excretion = GFR x plasma creatinine concentration. Therefore, creatinine excretion is normal when GFR is decreased following removal of a kidney because the plasma concentration of creatinine is elevated. Creatinine is a waste product of metabolism. Creatinine production is directly related to the muscle mass of an individual, but is independent of renal function.

Question 63

49 y/o woman comes to the clinic complaining of fatigue. She denies fever, vomiting, or diarrhea, but physical examination shows dry mucous membranes. Her blood pressure is 90/60 mm Hg. Laboratory studies show a plasma sodium level of 129 mEq/L and a potassium level of 5.5 mEq/L. Which of the following is the most likely cause of her hyponatremia?

Answer 63

Addisons disease Addison disease, or primary adrenal insufficiency, is caused by destruction of adrenal cortical tissue. As a consequence of the loss of mineralocorticoids, there is reduced ability to retain sodium and excrete potassium. (Recall that aldosterone acts on the renal collecting duct to promote resorption of Na+ and secretion if K+.) Hence, this patient has hyponatremia and hyperkalemia. Low plasma sodium is accompanied by hypovolemia, signs of dehydration, and hypotension.

Question 64

32 y/o man is on a high-protein low carbohydrate diet because he has heard that this will help him build muscle. Which of the following peptides needs to be released to increase the secretion of pancreatic enzymes into the small intestine so that he can digest these types of meals?

Answer 64

Cholecystokinin The release of cholecystokinin is stimulated by the presence of peptides, aino acids, or fatty acids int he small intestine. Cholecystokinin acts on the pancreas to stimulate secretion of pancreatic enzymes that aid in the digestion of these compounds.

Question 65

Study of renal function, the urine flow rate of an experimental animal is 2.0 ml/min, the glomerular filtration rate is 100 ml/min, and renal plasma flow is 500 ml/min. During this time, substance X is infused, and a steady state is achieved. The afferent arteriolar concentration of X is 100 mg/dL, the efferent arteriolar concentration is 120 mg/dL, and the renal vein concentration is 102 mg/dL. From these data, you can conclude that X is?

Answer 65

Not filtered or secreted If a substance is not filtered, its concentration int he efferent arteriole will be greater than the concentration in the afferent arteriole by an amount equal to the fraction of water filtered into the glomerulus. In this case, the filtration fraction (FF = glomerular filtration rate/renal plasma flow ) = 100/500 = 20%, so efferent arteriolar concentration equals 120 mg/dL. All the filtered water except for that amount necessary to sustain urine flow is reabsorbed back into the peritubular capillaries, and so it is present in the renal vein. In this case, the fractional excretion of water ( = urine flow rate/glomerular filtration rate) =2/100 = 2% so renal vein concentration is 2% greater than afferent arteriolar concentration, giving a renal vein concentration of 102 mg/dL. Note that answering this question did not require any calculations. The numbers are used in the discussion only to highlight the general concepts you should have recognized: the relationship between a substances concentration in the afferent arteriole vs the efferent arteriole provides information about filtration of the substance. The concentration of the substance in the afferent arteriole vs the renal vein provides information about the secretion of that substance.

Question 66

A med student is studying pancreatic function on a computer simulated patient. The student is trying to understand the insulin secretion pattern in the pancreatic cells. The student is presented with a list of substances that affect insulin secretion. She clicks on a substance and inds that it directly inhibits the patients insulin secretion. This response was most likely caused by which of the following substances.

Answer 66

Alpha2 - adrenergic agonist Alpha2-receptor agonists directly inhibit pancreatic insulin secretion. Beta2 - adrenergic agonists stimulated insulin secretion. Cholecystokinin is a hormone that causes not only gallbladder contraction, but also insulin secretion from the pancreas. Pancreatic glucagon release acts as a paracrine stimulus for insulin secretion. Muscarinic activity in the gastrointestinal tract enhances secretion of insulin from the pancreas.

Question 67

A patient placed on a ventilator in the intensive care unit has an anatomic dead space of 150ml. If the ventilator has a dead space of 350ml and a rate of 20/min, which tidal volume should be selected for the ventilator to provide an alveolar ventilation of 6L/min.

Answer 67

800 mL Recall that total ventilation is equal to alveolar ventilation plus dead space ventilation. This can be expressed mathematically as: Vt x n = Va x n + Vd x n, where Vt = tidal volume va = the volume of alveolar gas in the tidal volume Vd = dead space n = respiratory frequency to calculate answer solve for Vt. Realize that dead space is combined dead space of the patient and the ventilator. : 150ml + 350ml = 500ml Do not forget to check units you need to convert 6L/min to 6000ml/min (Vt x 20/min ) = (6000ml/min) + (500ml 20/min (Vt x 20/min) = 16,000 ml/min Vt = 800ml

Question 68

55 y/o woman stopped menstruating approximately 3 months ago. Worried that she may be pregnant she decides to have a pregnancy test. The result is negative. Which of the following series of test results will confirm that the woman is postmenopausal?

Answer 68

Increased LH, Increased FSH, decreased estrogen During menopause, there is a loss of functioning follicles in the ovaries such that GnRH stimulated LH and FSH secretion do not result in normal estrogen secretion. The low estrogen levels can not inhibit gonadotropin secretion in a negative-feedback fashion, resulting in very high levels of LH and FSH.

Question 69

A child falls and bumps her head on the floor. Tissue factor is exposed beneath the endothelium of traumatized blood vessels. Which of the following procoagulant proteins binds to tissue factor and initiats the clotting cascade.

Answer 69

Factor VII The extrinsic pathway of clotting begins iwth tissue factor binding to factor VII or factor VIIa. All other clotting proteins require proteolytic cleavage to become active, however, Factor VII has a low level of activity in its inactive form and can act with tissue factor and phospholipids to initiate the clotting cascade. In the extrinsic pathway, FActor VII cleaves Factor X to Xa, which acts in concert with Factor V to cleave prothrombin to thrombin. the final step in the coagulation pathway is the cleavage of fibrinogen to fibrin by thrombin. Fibrin polymerizes and cross-links, thereby forming a hemostatic net of insoluble protein.

Question 70

A 63 y/o man with essential hypertension has gone several weeks without taking his meds. He arrives at the emergency department after falling on his outstreched right hand. He has a heart rate of 90min and a blood pressure of 170/115 mm Hg. Which of the following is most likely to be decreased in the skeletal muscles of his legs?

Answer 70

Adenosine levels The skeletal muscles of the body have a normal blood flow even when blood pressure si chronically elevated. Organs and tissues in which the vasculature has primarily a nutritive function (e.g. brain, heart, and skeletal muscle) regulate their blood flow in accordance with the metabolic needs of the tissues. These tissues exhibit short term autoregulation of blood flow such that the increase in flow caused by an elevated arterial pressure is minimized by constriction of the arterioles. The constriction is caused in part by decreased levels of adenosine (an endogenous vasodilator) in the tissues. The rate of aenosine production in a tissue is a function of its metabolic rate, which is not affected significantly by an increase in systemic pressure. When blood flow to the muscle increases, the adenosine is literally washed from the muscle, lowering the tissue levels of adenosine. The decrease in adenosine concentration causes small arteries and arterioles in the muscle to constrict, and this increase in resistance maintains blood flow at a normal rate in the face of increased arterial pressure. venous oxygen of concentration does not decrease in the skeletal muscles of hypertensives because blood flow is maintained at an adequate level to meet the nutritional demands of the muscles.

Question 71

A man with normal lungs overdoses on secobarbital, causing hypoventilation. He is brought to a hospital where the barometric pressure is 500 mm Hg. Alveolar Pco2 rises to 80 mm Hg, and the respiratory exchange ratio is 1.0. Assuming that the patients condition remains unchanged, what percentage of inspired O2 will return his alveolar Po2 to normal (100 mg Hg).

Answer 71

40 The patient is hypoventilating because of the effects of barbiturates on respiration. This questionn requires the use of the alveolar gas equation. : PAo2 = PIo2 - PAco2/R Where PAo2 = the partial pressure of alveola O2 PIo2 = the partial pressure of inspired O2 PAco2 = the partial pressure of alveolar CO2 R = respiratory exchange ratio. PAo2 = 100 PAco2 = 80 R = 1 now solve for PIo2. PIo2 = 180 mm Hg. PIo2 = Fo2 x (PB - PH2O) , where Fo2 is the fraction of inspired O2 and PB is the barometric pressure, PH2O is the water vapor pressure in the airways and always remains constant at 47 mm Hg. Solving for FO2 180 = FO2 x (500 - 47) FO2 = 0.40

Question 72

The clearance of several substances was measured at a constant glomerular filtration rate and constant urine flow rate, but at increasing plasma concentration of the substance. Under these conditions, cearance will increase at high plasma concentrations for which of the following substances?

Answer 72

Phosphate Clearance of a substance will change with increasing plasma concentration if that substance is secreted or reabsorbed by a facilitated mechanism. As the concentration of the substance increases, the transporter becomes saturated, and its contribution to excretion changes, changing the clearance. If the substance is reabsorbed by a facilitated mechanism, clearance will eventually increase ith increasing plasma concentrations. Approximately 80% of filtered phosphate is reabsorbed in the proximal tubule by a sodium-phosphate cotransporter, which is a facilitated mechanism.

Question 73

In the clotting process, as the hemostatic plug develops, fibrin polymerizes into monomeric threads that are held together by noncovalent bonds. Which clotting protein increases the strength of the clot by cross-linking the newly formed fibrin threads?

Answer 73

Factor XIII Fibrinogen is cleaved by thrombin twice as it is activated to form fibrin. The initial cleavage caues it to polymerize, and the second causes it to branch. Thrombin also activates Factor XIII to XIIIa, which cross-links the fibrin strands and strengthens the clot.

Question 74

26 y/o man receives a concussion from a car accident. The brain edema that follows causes compression of the cerebral arteries to such an extent that he needs to be placed on mchanical ventilation to control his breathing. His respiratory drive is diminished mainly because of decreased?

Answer 74

Arterial Pco2 acting through central chemoreceptors. The most important factor in the control of minute to minute ventilation is arterial Pco2, which influences chemoreceptors located near the ventral surface of the medulla. As arterial Pco2 rises, CO2 difuses rom cerebral blood vessels into the CSF. Carbonic acid is formed and dissociates into bicarbonate and protons. Protons directly stimulate these central chemoreceptors, resulting in hyperventilation. Hyperventilating reduces the Pco2 in the arterial blood and subsequently in the CSF. Peripheral chemoreceptors located in the carotid and aortic bodies respond to increasses in PCO2 but are less important than the central chemoreceptors. It is estimated that when a normal subject hyperventilates in response to inhalation of CO2, less than 20% of the response can be attributed to the peripheral receptors. However, they respond more quickly than their central counterparts and are thought to play a role in regulating ventilation after abrupt changes in PCO2.

Question 75

A contruction worker has a serious accident in which his rib cage and abdominal muscles becoe completely paralyzed. He is still able to breathe, however, because his diaphragm continues to contract. At which level might his spinal cord injury have occured?

Answer 75

C7 Trauma to the lower cervical cord (at C7 for example) can cause the pattern described int he question since the lesion is below the origin of the phrenic nerve, but above the origin of the nerve that innervates the muscles of the rib cage and abdomen. C2 Trauma high in the neck at C2 above the origin of the phrenic nerve (C3-C5 nerve roots) would cause diaphragmatic paralysis as well. Lesion at L3 would spare all of the accessory respiratory muscles, as well as the diaphragm. Lesion at T5 would spare part of the accessory muscles of the rib cage.

Question 76

49 y/o mildly obese man with no history of heart disease is prescribed a diet and an aerobic exercise regimen. Which of the following is most important for maintaining adequate cardiac output during exercise?

Answer 76

Increased heart rate and stroke volume

Question 77

A woodworker operating a bandsaw accidently injures his wrist severing hsi radial artery and producing severe hemorrhage. As he loses blood his body tries to compensate for the developing hypotension by increasing sympathetic outflow. The postganglionic signals carrying the impulses to constrict his arterioles are transmitted along wihich of the follwing fibre types?

Answer 77

C Fibers. There are two systems currently used for classifying nerve fibers. The first system groups both sensory and motor fibers together, describing A-a, A-B, A -y, A-gamma, B, and C fibers.

Question 78

35 y/o man complains of dificulty eating food and drinking liquids. History reveals he can swallow the food but feels as though what he eats and drinks does not go anywhere after swallowing. Recently begun to voit undigested food and he has a cough that wakes him from sleep at nightitme. He has lost 5lb of weight within the past month without trying to lose weight. Laboratory studies are normal. A barium swallow shows dilation of the distal esophagus with a tapered end. Which of the following is the most likely cause of his disorder?

Answer 78

A defect in the neural network of the myenteric plexus. The patient has achalasia. Symptoms of this disorder include dysphagia for solids and liquids, chest pain, vomiting of undigested food, and weight losss. Symptoms of aspiration, such as coughing at nighttime, pneumonia, and dyspnea, can also be present. On barium swallow study, his esophagus has the classic "bird beak" appearance. This disorder is caused by the failure of the lower esophageal sphincter to relax during a swallow due to damage to the neural network o the myenteric plexus in the lower two thirds of the esophagus. The myenteric plexus cannot transmit a signal to cause relaxation of the lower esophageal sphincter as food approaches this area during the swallowing process. This causes the musculature of the lower esophagus to be spastically contracted, leading ot the rentention of swallowed food.

Question 79

1 week old infant has a coarctation of the aorta just distal to the subclavian arteries. The blood pressure distal to the constriction is 50% lower than normal. Which of the following is increased in this infant?

Answer 79

Plasma levels of angiotensin II The aorta is constricted at a point beyond the arterial branches to the head and arms but proximal to the kidneys. Collateral vessels in the body wall carry much of the blood flow to the lower body, and the arterial pressure in the lower body is about 50% lower compared with the pressure in the upper body. The lower than normal pressure at the level of the kidneys causes renin to be secreted and angiotensin to be formed. The angiotensin causes salt and water retention so that within a few days to weeks the arterial prssure in the lower body (at the level of the kidneys) increases to normal, but in doing so, the blood pressure in the upper body has increased to hypertensive levels. the kidneys are no longer ischemic when the lbood pressure has increased, therefore, renin secretion decreases and the formation of angiotensin returns to normal levels. Blood flow in the lower body is lower than normal at this early stage of aortic coarctation. However, blood flow can be normal above and below the constriction if the body is able to compensate fully. The decrease in blood pressure at the level of the kidney causes the glomerular filtration rate to decrease. Increase plasma levels of angiotensin II causes salt and water retention thus salt and water excretion are decreased.

Question 80

A research physiologist decides to use a marker to measure the volume of total body water in a volunteer medical student. Which of the following substances would he most likely use?

Answer 80

Tritium Antipyrine and tritium are both markers for total body water.

Question 81

73 y/o woman has mild hemoptysis, dyspnea, orthopnea, and paroxysmal nocturnal dyspnea. She has a low pitched, rumbling diastolic murmur, produced by a stenotic valve, that is accentuated by exercise. The murmur is heard best at the apex when she lies in the left lateral recumbent position. In normal patients, which of the following points on a left ventricular pressure volume loop (pic below) represents the opeing of the affected valve?

Answer 81

A The our corners of the pressure/volume loop represent points of aortic/mitral valve openings or closings. Aortic stenosis produces a dramatic systolic murmur, whereas a mitral stenosis produces a diastolic murmur. The mitral valve opens at the beginning of diastole, when the left ventricle is at its lowest pressure. Point B represents ventricular filling. Pressure in the left ventricle gradually increases as blood begins to enter it from the left atrium during diastolic ventricular filling. Point C represents the closing of the mitral valve. Point D represents isovolumetric contraction. It occurs when the left ventricle contracts in response to ventricular filling but has not yet achieved enough pressure to force open the aortic valve. Point F represents systolic ejection. It occurs after the aortic valve opens (E)., allowing the left ventricle to pump its blood volume into the aorta, consequently decreasing left ventricular volume. Point G, represents the closing of the aortic valve at the end of systole. Point H, is in the middle of isovolumetric relaxation.

Question 82

65 y/o woman receives 3 liters of 0.9% saline following a minor surgical procedure. This results in increased right atrial filling and conctraction. Which of the following is most likely to be secreted in response?

Answer 82

Atrial natriuretic factor (ANF) Atrial stretch results in secretion of atrial natriuretic factor (ANF), a polypeptide hormone that increases urinary sodium excretion and therefore decreases intravascular volume to maintain homeostasis. None of the remaining answer choices are appropriate, physiologic responses to increased atrial filling. Aldosterone causes sodium retention by increasing sodium and water reabsorption in the distal convoluted tubule. This leads to an increased intravascular volume.

Question 83

67 y/o woman muscle weakness, freaquent urination, and increased thirst. Blood pressure is 180/90 mm Hg. On prior visits she has been normotensive. Laboratory studies show that sshe is hpernatremic and hypokalemic. A CT scan of the abdomen shows a nodule on her left adrenal gland. What is the most likely mechanism for her disorder?

Answer 83

Excessive tubular sodium reabsorption this patient has symptoms of primary hyperaldosteronism caused by an adrenal adenoma. Symptoms for this are hypertension, muscle weakness, polyuria, polydipsia, edema, hypokalemia, hypernatremia, and metabolic alkalosis. The adrenal adenoma is secreting excess aldosterone, leading to increased sodium reabsorption and increased potassium secretion in the cortical collecting tubules. This increases intravascular volume, thus causing hyptertension. With an excess of aldosterone, renin amounts are actually decreased due to negative feedback caused by excess aldosterone or by the excess extracellular fluid volume and increased arterial pressure.

Question 84

Medical school professor is using tape recorded heart beats for lecture on heart sounds. He draws an atrial pressure tracing on the board for correlation. The first tape played has normal first and second heart sounds. The second heart sound would correspond to which of the following points on an atrial pressure tracing.?

Answer 84

v wave The second heart sound and the v wave both occur during isovolumetric relaxation. The onset of the a wave occurs during atrial systole and coincides with the fourth heart sound, if present. The onset of the c wave coincides with the first heart sound and evolves into the x descent during rapid ejection. It does not correspond to any heart sounds The y descent occurs during rapid filling and does not correspond to any heart sounds.

Question 85

A 65 y/o woman with renal failure presents for hemodialysis she is foujd to be anemic and is given a dose of erythropoietin along with her usual vitamin and mineral supplements. Erythropoietin stimulates which of the following intermediates in hematopoiesis?

Answer 85

Colony forming units-erythroid (CFU-E) The colony forming unit-erythroid (CFU-E) is a unipotential stem cell that develop from a burst forming unit-erythroid (BFU-E), which develops eventually from the multipotential stem cell. The BFU-E is somewhat responsive to erythropoietin but the CFU-E is completely dependent on erythropoietin. Erythropoietin is normally released from the kidney in response to hypoxic or anemic conditions. Its half-life is about 3-6 hours, clinically, it takes 5 days to see reticulocyte formation in the peripheral blood following erythropoietin administration.

Question 86

Accident at work resulting in severe hemorrhage, machinist rushed to emerg. Which of the following sets of autonomic responses would be predicted in regards. to an increse or decrease in heart rate, increase or decrease in bowel sounds and pupil diameter.

Answer 86

Heart rate increased, bowel sounds decreased, pupil diameter dilated. This is simpl a question about baroreceptor reflexes. The reflex response that would be anticipated after a decrease in blood pressure (e.g. after a hemorrhage) would be an increase in sympathetic outflow and a decrease in parasympathetic outflow. As a result, heart rate would increase, gastrointestinal motility would decrease, and the pupils would dilate.

Question 87

in a tissue capillary, the interstitial hydrostatic pressure is 2 mm Hg, the capillary hydrostatic pressure is 25mm Hg, and the interstitial oncotic pressure is 7 mm Hg. If the net driving force across the capillary wall is 3 mm Hg favoring filtration, what is the capillary oncotic pressure?

Answer 87

27 mm Hg The net driving force for fluid across a capillary wall is given by the following equation: Driving force = (hydrostaticc - hydrostatici) - (oncoticc - oncotici) where hydrostatic i = interstitial hydrostatic pressure Hydrostaticc = capillary hydrostatic pressure oncotici = interstitial oncotic pressure oncoticc = capillary oncotic pressure. Therefore. : 3 = (25 - 2) - (x-7). Simplifying, 3 - 23 - x + 7 x = 27

Question 88

A medical student volunteers to have his lung volumes and capacities measured for his organ physiology laboratory class. He is connected at the end of a normal expiration to a spirometer containing a known concentration of helium. He is instructed to breathe seeral times until the helium has equilibrated between the spirometer and his lungs. Calculations are made to determine the amount of air in his lungs when he was connected to the spirometer, which is called the ?

Answer 88

Functional residual capacity

Question 89

78 y/o woman has mean arterial pressure of 120 mm Hg and a heart rate of 60/min. She has a stroke volme of 50ml, cardiac output of 3000 ml/min, and a right atrial pressure of 0 mm hg. What is the total peripheral resistance (in mm Hg/ml/min) in this woman?

Answer 89

.04 The total peripheral resistance (TPR) is equal to the pressure gradient across the circulation (mean arterial pressure - right atrial pressure) divided by the cardiac output. Thus, TPR = 120/3000 = .04 mm Hg/ml/min. The ABC rule is useful in remembering the relation between pressure (P), flow (Q), and resistance (R) because P = QR (note the alphabetical order). Note that knowedge of heart rate and stroke volume is not required to solve this problem because cardiac output is provided.

Question 90

23 y/o man with diabetes mellitus has a glomerular filtration rate (GFR) significantly greater than normal, especially when he consumes excessive amounts of sweets. A decrease in which o the following parameters would tend ot increase the glomerular capillary hydrostatic pressure?

Answer 90

Afferent arteriolar resistance A decrease in the resistance of the aferent arteriole ( i.e. arteriolar dilation) directly increases glomerular capillary hydrostatic pressure by lessening the drop in blood pressure that normally occurs along the vasculature proximal to the glomerulus. Recall that the aferent arteriole is upstream from the glomerulus, the efferent arteriole is downstream from the glomerulus. The glomerular capillary hydrostatic pressure is the deterinant of glomerular filtration rate most subject to phyysiologic control.

Question 91

A woman goes to a restaraunt for a freinds birthday and eats a large meal. AFter meal a certain hormone is stimulated by acid entering her duodenum. This hormone inhibits stomach motility and stimulates bicarbonate secretion from the pancreas. Which of the following hormones is structurally related to the hormone in question?

Answer 91

Glucagon The hormone in question is secretin. Acid entering the duodenum stimulates its secretion by the S cells in the duodenal lining. It inhibits stomach motility and stimulates bicarbonate secretion from teh pancreas. Glucagon, secretin, and vasoactive peptide (VIP) are all structurally related.

Question 92

With time, blood stored in a blood bank tends to become relatively depleted of 2,3 -diphosphoglycerate (2,3 -DPG) What efect does this have on the hemoglobin-oxygen dissociation curve?

Answer 92

Shifts the cuve to the let, so that the hemoglobin has an increased oxygen affinity. 2,3-DPG is produced in red cells by a variation on the glycolytic pathway, and levels diminish when glycolyssis by the red cells slows. The depeletion of 2,3-DPG is stored blood causes a conformation change in the Hb moleucle, which increases the affinity of the molecule for oxygen. This is expressed as a shit in the Hb-dissociation curve to the left. This is helpful in the picking up of oxygen by hemoglobin in the lungs, but it can be very problematic in the release of oxygen form the blood in tissues. This is not just a theoretical point: considerable efort has been expended in developing improved solutions for storing packed red cells and methods for "restoring" older stored cells so that the 2,3-DPG levels are adequate. In practice, in otherwise reasonably healthy patients, older transfused blood will quickly regenerate 2,3-DPG when placed in the glucose-containing environment of the serum, however, even transiently decreased 2,3-DPG levels in a severely compromised patient can be dangerous.

Question 93

A researcher attaches a video camera to his microscope so that he can observe all of the stages of spermatogenesis. He is specifically interested in observing the process of crossing over. This particular process occurs during the meiotic division of which of the following cells?

Answer 93

Primary Spermatocytes Crossing over, a transposition of genetic information, occurs during the first meiotic (reduction) division, when the primary spermatocytes divides to form two secondary spermatocytes. This division does not consist of separation of sister chromatids after DNA replication, but rather involves the separation of previously paired, homologous chromosomes. Crossing over occurs during prophase of Meiosis I.

Question 94

Answer 94

Estrogen Estrogen levels peak at the end of the follicular phase of the menstrual cycle, creating positive feedback to the hypothalams and pituitary gland. This increases the number of GnRH spikes per 24 hours, cuasing a surge of both follicle-stimulating hormone (FSH) and luteinizing hormone (LH). It is the surge of LH, in combination with the high estrogen levels, that induces ovulation. FSH levels peak at ovulation Gonadotropin-releasing hormone is released in pulses, not in a continuous pattern as is estrogen. LH levels peak at ovulation Progesterone peaks during the premenstrual phase of the cycle. It is represented by the solid line on the graph.

Question 95

30 year old woman with menorrhagia visits her gynecologist. She is evaluated for possible iron-deficiency anemia. Her hemoglobin is 10g/dl, hematocrit is 36%, red blood cell cout is 4.0 million/ul, and mean cell diameter is 7.5um. What is the patients mean corpuscular volume (MCV)

Answer 95

90 fL MCV is calculated by the following formula. (Hct x 10) / red blood cell count Hemoglobin and mean cell diameter are not needed for this calculation. The remaining answer choices are incorrect calcs. Although patients with menorhagia (excessive menstrual bleeding) are at risk for iron-deficiency anemia (which is associated with microcytosis (MCV \< 85), this patient has not developed this complication. Her MCV is in the normal range.

Question 96

To celebrate the end of the semester, a college student goes on an alcohol binge. She drinks day and night for 3 days straight. During this period her urinary flow rate increased from 1 to 10ml/min. This increase in urinary flow rate will significantly increase the clearance of ?

Answer 96

Urea Urine flow rate is controlled primarily by antidiuretic hormone (ADH), which regulates the amount of pure water retained in the urine. ADH also controls the reabsorption of urea in the papillary dollecting duct. High urine flow rates indicate low ADH, which would increase urea clearance. In contrast, low urine flow rates indicated high ADH, which would result in a greater reabsoption of urea and a lower urea clearance.

Question 97

66 y/o woman complains of fatigue to her physician. Her pulse is 80/min and her hematocrit is 32%. Ultrasoud shows and end-systolic volume of 65 ml and and end-diastolic volume of 115ml. Which of the following is the ejection raction in this woman?

Answer 97

0.43 Ejection fraction is an index of contractility equal to the ratio of stroke volume to end-diastolic volume. The stroke volume is equal to the difference between the amount of blood in the ventricle prior to systole (end-diastolic volume) and the amount of blood in the ventricle at the end of systole (end-systolic volume). Because the end-diastolic volume is 115ml and the end-systolic volume is 65ml, the stroke volum eis 115-65 = 50 ml . The ejection raction is calculated as 50ml/115ml = 0.43. Ejection raction (normal value = 0.65) can be estimated by radionuclide angiography or echocardiography and is frequently depressed in systolic heart failure, even when the stroke volume itself is normal.

Question 98

Answer 98

A Glucose is freely filtered by the glomerular capillary membrane and totally reabsorbed in the Proximal tubule under normal conditions. Therefore, the concentration of glucose is highest in the fluid leaving the bowman capsule. The concentration of glucose is essentially zerio in the thin descending limb of loop of henle, distal convoluted tubule, cortical collecting tubule, and medullary collecting tubule.

Question 99

30 y/o woman given 0.1g inulin intraenously. One hour later the plasma inulin concentration is 1 mg/100ml. Which of the following is the extracellular fluid volume (in liters) of this woman (assuming that urinary loss of inulin is insignificant.

Answer 99

10L The volume of a fluid compartment can be measured by placing a substance into the compartment, allowing it to disperse evenly throughout the compartment, and then measuring the extent to which the indicator is diluted in the fluid. The volume of a compartment can be determined using the follwoing formula. Volume of compartment = Quantity of indicator substance administered / Concentration of indicator in compartment. The extracellular fluid volume can be measured using inulin as the indicator: 0.1g inulin was administered intravenously and the concentration of inulin in the compartment was 1 mg/100ml an hour later (when inulin had dispersed evenly in extracellular fluid compartment) Extracellular fluid volume = 0.1 g / 1 mg/100 = 100 mg / 1mg 0,1L = 10 L

Question 100

62 y/o man tingling in his feet and difficulty with balance. He has a mean corpuscular volume of 130 fl. A peripheral blood smear shows six-lobed neutrophils and macro-ovalocytes. Which of the following conditions is associated with a lifelong requirement for parenteral administration of the vitamin deficient in this patient? I. pernicious anemia II. removal of colon III. removal of gallbladder Iv. removal of ileum v. removal of jejunum VI. removal of stomach

Answer 100

I, IV, VI The question tests your knowledge of how vitamin B12 is normally absorbed. In summary, parietal cells in the gastric lining secrete a glycoprotein called intrinsic factor into the gastric lumen. This protein binds to vitamin B12, protecting it from degradation and allowing for its eventual absorption. At the level of the ileum, B12 bound to intrinsic factor is actively reabsorbed. Therefore, a loss of inhtrinsic factor or of its reabsorption site, the ileum, would lead to the need for lifelong injection of vitamin B12, Removal of the stomach would obviously lead to loss of intrinsic factor. Pernicious anemia is actually an autoimmune disease that targets the gastric epithelium. In many cases, patients have autoantibodies against intrinsic factor, preventing the absorption of ingested vitamin B12. Removal of the colon, jejunum, or gallbladder would not affect reabsorption of intrinsic factor or B12, A total absence of bile (which occurs with bile duct blockage, bu not with cholecystectomy) may lead to malabsorption of fat-soluble vitamins such as ADEK bt not B12.