Midterm 3 - Key

Fill in your scantron form as follows:

·         Write and bubble in your name in the upper left, last name first.

·         Follow any additional instructions provided in class.

·         Sign your form in the upper right.  By so signing, you are indicating that you have followed Creighton’s policy on academic honesty in taking this test.

Multiple choice:   As always, choose the best answer for each multiple-choice question.  Answer on your scantron form.  Each question is worth 3 points.

1.      Which of the following is not associated with the gastrointestinal tract?

a.       Absorption of food

b.      Digestion of food

c.       Excretion of waste products

d.      Motility

e.       All of the above are associated with the GI tract.

2.      If one of the stomach’s chief cells ruptured, and leaked all its contents into the interstitial space, then the surrounding cells

a.       would probably be damaged by the hydrochloric acid released by the cell.

b.      would not be damaged because the cells do not store the hydrochloric acid they make.

c.       would probably be damaged by the pepsin released by the cell.

d.      would not be damaged because the cells store pepsin in an inactive state.

e.       would probably be covered in mucus.

3.      The release of gastrin is inhibited most strongly by

a.       low pH in the stomach.

b.      high levels of pepsin in the stomach.

c.       high levels of peptides in the stomach.

d.      increased distention of the stomach.

e.       increased parasympathetic stimulation of the stomach.

4.      An inability to produce enterokinase would cause difficulty primarily in

a.       digesting proteins.

b.      digesting fats.

c.       absorbing amino acids.

d.      absorbing fatty acids.

e.       a and b

5.      The release of bicarbonate by the gastrointestinal system’s accessory organs is controlled primarily by

a.       bile.

b.      cholecystokinin.

c.       gastrin.

d.      secretin.

e.       an unknown chemical messenger.

6.      Fats that have been digested and absorbed first enter the bloodstream as

a.       free fatty acids.

b.      free fats.

c.       fatty acids packaged in chylomicrons.

d.      fats packaged in chylomicrons.

e.       These fats never enter the bloodstream.

7.      By definition, a portal system is a part of the circulation in which

a.       substances are absorbed.

b.      blood passes through the liver.

c.       blood passes through two sets of capillaries before returning to the heart.

d.      blood is shunted back to the heart.

e.       blood is shunted to an alternate dimension.

8.      Most of the total volume of water that enters the digestive tract comes from

a.       food and water intake.

b.      salivary secretions.

c.       secretions into the stomach.

d.      secretions into the small intestine.

e.       secretions into the large intestine.

9.      The primary advantage to storing energy in the form of fat is that

a.       fats can be mobilized more quickly than glucose.

b.      fatty acids can be converted into glucose as needed.

c.       fats have a high energy density.

d.      fats can also be used to build structural elements of cells.

e.       fat is nice and squishy.

10.  Which of the following tend to cause an increase in leptin levels?

a.       Increased amounts of stored fat.

b.      Overeating for a day or two.

c.       Increased exercise.

d.      Two of the above. (a and b)

e.       All of the above.

11.  The solutes that enter the nephron as part of the glomerular filtrate are

a.       sodium and glucose.

b.      sodium, glucose and urea.

c.       sodium, glucose, amino acids and urea.

d.      sodium, chloride, glucose, amino acids and urea.

e.       all substances small enough to pass through the pores in the glomerular walls.

12.  The glomerular filtration rate of an individual is 100 ml/min and the rate of final urine production is 1.0 ml/min.  If the substance nonsensiquine is found in the initial filtrate at a concentration of 1 mg/ml, and in the final urine at a concentration of 200 mg/ml, we know that

a.       nonsensiquine was secreted into the nephron.

b.      nonsensiquine was reabsorbed from the nephron.

c.       nonsensiquine was neither secreted nor reabsorbed.

d.      nonsensiquine is a waste product.

e.       nonsensiquine would precipitate out of the urine.

13.  The function of the concentration gradient in the renal medulla is

a.       to allow water to be absorbed from urine in the descending loop of Henle.

b.      to allow uptake of sodium from the urine in the ascending loop of Henle.

c.       to allow water to be absorbed from urine in the collecting duct.

d.      Two of the above.

e.       All of the above.

Note – I ended up giving credit on this question for any answer because so many people appeared to misunderstand it. The question means, “Why is it there?” not “How does it work?”.

14.  The maximum urine concentration that can be generated by the human kidney is about

a.       300 mOsm.

b.      800-1000 mOsm.

c.       1200-1400 mOsm.

d.      1800-2000 mOsm.

e.       2200-2400 mOsm.

15.  The reabsorption of glucose across the apical membrane of the proximal tubule of the nephron occurs via

a.       permeation.

b.      facilitated diffusion.

c.       an ATP-powered glucose transporter.

d.      cotransport with Na⁺.

e.       cotransport with K⁺.

16.  Anti-diuretic hormone is associated with

a.       aquaporin insertion into the collecting duct.

b.      increased sodium reabsorption from the distal tubule.

c.       increased vasoconstriction.

d.      Two of the above. (a and c)

e.       All of the above.

17.  Renin activates receptors in

a.       the kidneys.

b.      the liver.

c.       the lungs.

d.      the adrenal cortex.

e.       Renin does not activate any receptors.

18.  The direct trigger for increased release of atrial natriuretic factor is

a.       decreased blood osmolarity.

b.      increased sodium concentration.

c.       increased blood volume.

d.      increased blood pressure.

e.       increased filling of the atria.

I gave credit for “d” also, but note that the way in which this feedback system senses increased BP is because the atria fill (and hence stretch) more when BP is higher.

19.  In response to an increase in blood pressure above normal values, which of the following responses would most likely be seen?

a.       Increased cardiac output, increased vasoconstriction, increased aldosterone secretion.

b.      Decreased cardiac output, increased vasoconstriction, increased aldosterone secretion.

c.       Decreased cardiac output, decreased vasoconstriction, increased aldosterone secretion.

d.      Decreased cardiac output, increased vasoconstriction, decreased aldosterone secretion.

e.       Decreased cardiac output, decreased vasoconstriction, decreased aldosterone secretion.

20.  Other than bicarbonate, the important buffering substances in humans and other vertebrates include

a.       calcium.

b.      phosphate.

c.       proteins.

d.      Two of the above. (b and c)

e.       All of the above.

Short answer:  Write a concise answer to each of the following questions.  Your answers should fit in the spaces provided.  Diagrams must be accompanied by written explanations.  Each question is worth 8 points.

21.  Discuss the process of carbohydrate digestion and absorption.  Be sure to indicate where digestion takes place, the enzymes involved and their source, and the details of absorption.  You do not need to describe the control of these processes.

The digestion of complex carbohydrates begins in the mouth, where amylase is secreted as part of the saliva and begins to break down starches into sugars.  No further digestive enzymes affect the carbohydrates until the food (or chyme) enters the small intestine.  Here, additional amylase secreted by the pancreas further digests starches.  In addition, any disaccharides present are broken down into monosaccharides by enzymes [disaccharidases such as sucrase, maltase, etc.] located on the epithelial surface of the lumen.  Absorption takes place by secondary active transport, with sugars being cotransported with Na⁺ across the apical membrane, then moving by facilitated diffusion across the basolateral membrane.  From there the sugars enter the mucosal capillaries [and from there travel via the hepatic portal vein to the liver].

22.  These questions relate to the post-absorptive phase:

a.       Describe the activities of different tissue types during this phase with regard to fuel supply and use.

General tissue cells are metabolizing fatty acids for fuel.
Nervous tissue is using glucose for fuel [assuming it is still available].
The liver releases glucose produced from glycogen (via glycogenolysis) or from conversion of amino acids (gluconeogenesis) for use by the nervous system.  It may also release some fatty acids.
Adipose tissue (or fat cells) release fatty acids for use by general tissues.
[Muscle cells may use glycogen stores for energy as well as fatty acids.]

b.      If all the alpha cells of the pancreas were destroyed, how would these activities change, and why?

These cells produce the hormone glucagon, which promotes the release of glucose by the liver and also appears to promote fatty acid release by adipose tissue.  Without the promotion of these activities, fuel availability for the nervous system and for other tissues would be severely limited during the post-absorptive phase.

23.  For the proximal tubule of the nephron, describe what drives the reabsorption of water and urea. Is urea concentration in the fluid leaving the proximal tubule higher, lower or the same as in the glomerular filtrate, and why?

In the proximal tubule, a number of solutes, including sodium chloride and glucose, are reabsorbed by primary and secondary active transport.  As these substances leave the primary urine and enter the interstitial space, the osmolarity of the urine is slightly decreased while that of the ISF is slightly increased.  As a result, an osmotic pressure is generated that tends to reabsorb water from the proximal tubule.  As water is reabsorbed, the concentration of any solutes not being actively reabsorbed, including urea, increases due to the water loss.  As the concentration of urea increases beyond its normal value in the ECF, a concentration gradient is generated that favors the movement of urea from the urine into the ICF.  Because the nephron wall is somewhat impermeable to urea, the urea concentration does not come to equilibrium, and the urea concentration in the tubule remains higher than the concentration in the ECF, which is also the concentration that was seen in the initial filtrate.  Looked at another way, the amount of water reabsorbed is greater than the amount of urea reabsorbed, so the concentration of urea increases.

24.  Describe one of the two intrinsic (i.e. local) mechanisms in the kidney that normally result in the maintenance of a relatively constant glomerular filtration rate.

The two strictly intrinsic mechanisms that help control GFR are myogenic regulation and tubuloglomeric feedback

Myogenic regulation involves the ability of the afferent arteriole of the glomerulus to respond directly to an increase in blood pressure. Without regulation of some kind, increased BP would lead to an increase in GFR.  But the increased BP results in stretching of the walls of the afferent arteriole, and in response the smooth muscle of the arteriole tends to contract, causing vasoconstriction and thus reducing the GFR.  If BP increases, stretching of the arterioles decreases and vasodilation occurs.

Tubuloglomeric feedback involves the juxtaglomerular apparatus.  If GFR increases, the cells of the macula densa sense an increase in the rate of fluid flow through the distal tubule (sensed as an increase in the flow of Na⁺).  In response, the cells release a paracrine agent that diffuses to the adjacent afferent arteriole and causes vasoconstriction, reducing GFR.  If GFR is low, less paracrine agent is release, the arteriole vasodilates, and GFR increases.

25.  The following questions relate to the condition known as acidosis.

a.       Define a metabolic versus a respiratory acidosis, and provide one possible cause for each.

A respiratory acidosis is a condition in which there is an increased concentration of hydrogen ions (that i,s a lowered pH) in the ECF due to an excess of carbon dioxide.  The general cause is hypoventilation, which can result from conditions such as emphysema or asthma.

A metabolic acidosis is a decrease in pH from any cause other than a carbon dioxide increase.  Some causes are anaerobic metabolism (lactic acid buildup) and severe diarrhea.

b.      How could differentiate between these two forms of acidosis based just on variables measured in a blood sample?  Explain your answer.

The bicarbonate buffering system is active in both forms of acidosis, but shows a different pattern of change in bicarbonate levels in each case.  In a respiratory acidosis, increased levels of carbon dioxide lead to a shift from CO₂ + H₂O to H⁺ + HCO₃^-.  This shift is what actually causes the acidosis, and it also causes an increase in bicarbonate levels above the normal value.  In a metabolic acidosis, on the other hand, an increase in H⁺ ions is the initial disturbance.  This tends to move the buffering system from H⁺ + HCO₃^- to CO₂ + H₂O, decreasing the amount of bicarbonate below normal levels.  Thus a blood test that measured bicarbonate levels could distinguish between the two forms of acidosis.