Lymphatic function during cirrhosis
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- Lymphatic function during cirrhosis
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Lymphatic function during cirrhosis
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[ID] => 554756
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[post_date] => 2024-12-23 18:29:03
[post_date_gmt] => 2024-12-23 23:29:03
[post_content] => Practice Passage (Question 1-6)
*This passage is the property of Khan Academy and has been reformatted into an AAMC-style interface in their entirety by MedLife Mastery. MedLife Mastery does not endorse and is not an affiliate of Khan Academy.
Cirrhosis of the liver is a progressive medical condition characterized by the replacement of healthy liver tissue with non-functional tissue, primarily fibrotic tissue. Major contributing factors to this condition are chronic alcoholism and hepatitis infection. One of the prominent manifestations of cirrhosis is ascites, which occurs when excess lymphatic fluid accumulates in the abdominal cavity, outside the organs. Researchers examining lymphatic dysfunction in cirrhosis performed the following studies.
Experiment 1a
Researchers compared the composition and flow rate of lymph between patients with and without cirrhosis. In the first phase of the study, X-ray computed tomography scans were taken of the thoracic duct, the largest lymphatic vessel in the body, responsible for draining lymph fluid from the lower extremities and abdomen into the bloodstream. The study found that among patients without cirrhosis, the thoracic duct had an average diameter of 5 mm. However, among patients with cirrhosis, the thoracic duct had an average diameter of 8 mm.
Experiment 1b
In the second phase of the study, 1 mL of lymphatic fluid was removed from the thoracic duct using a catheter. It was analyzed for protein content and red blood cells. It was found that among patients with cirrhosis, red blood cells made up 4% percent of the lymph, compared with 0% percent for patients without cirrhosis. Protein content among patients with cirrhosis was found to be approximately 6.4 g/dL compared with 6.7 g/dL for patients without cirrhosis.
Experiment 2
Researchers used an immunohistochemical stain for VEGFR3 (the receptor for VEGF-C, a pro-lymphangiogenic factor) to examine lymphatic vessels obtained from patients without cirrhosis, patients with compensated cirrhosis (without ascites), and patients with decompensated cirrhosis (with ascites). The results of their findings are shown in Figure 1.
Figure 1 Results of immunohistochemical stain for VEGFR3 in study groups
Experiment 2 and Figure 1 adapted from: Savneet Kaur et al. Nano-engineered VEGF-C ameliorates gut lymphatic drainage, portal pressure and ascites in experimental portal hypertension. https://www.medrxiv.org/content/10.1101/2020.12.24.20248815v1.full
[post_title] => Lymphatic function during cirrhosis
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[question] => Which elements normally help to push lymph forward through lymph vessels?
I. Valves
II. Skeletal muscle contraction
III. Pressure from the heart
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[answer] => 2
[description] => Reason for Correct Answer:
One primary function of the lymphatic system is to return excess extracellular fluid to the bloodstream. Smaller lymph vessels in the lower part of the body carry lymph fluid upwards towards the thoracic duct, which empties its contents into blood circulation.
Lymph vessels contain valves (I), which allow fluid to move in one direction but not the other, thus preventing backflow.
The contraction of skeletal muscles in the area (II) physically pushes lymph forward through lymphatic vessels.
The pressure produced by the heart (III) produces lymph, due to the flow of fluid through blood vessels and into surrounding tissues, but does not help the lymph travel through the lymphatic vessels to the thoracic duct.
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[each_answer] => A. I only
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[each_answer] => B. I and II only
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[each_answer] => C. II and III only
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[each_answer] => D. I, II and III
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[1] => Array
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[quiz_unique_key] => 1403770772
[question] => Which statement does NOT help to explain the results of Experiment 1b?
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[answer] => 2
[description] => Reason for Correct Answer:
Experiment 1b shows that patients with cirrhosis had red blood cells in their lymphatic fluid, whereas patients without cirrhosis did not; it also shows that patients with cirrhosis had lower protein content in their lymphatic fluid.
Choice A helps to explain why healthy patients have no red blood cells in their lymphatic fluid, whereas Choice C helps to explain why cirrhosis patients have red blood cells entering their lymphatic fluid from blood vessels.
Choice D helps to explain why patients with cirrhosis have lower protein content in their lymphatic fluid when liver function is impaired.
Choice B DOES NOT help to explain the results, because red blood cells ARE leaking into the lymphatic system/extracellular fluid in cirrhosis patients (the patients who have compromised blood vessels).
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[each_answer] => A. Healthy blood vessels do not allow red blood cells to leak out because the spaces between endothelial cells are too small.
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[each_answer] => B. Red blood cells are larger in diameter than the largest proteins and therefore less likely to leak out of compromised blood vessels.
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[each_answer] => C. Cirrhosis of the liver may compromise blood vessel walls leading to more leakage than usual.
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[each_answer] => D. Many of the proteins that end up in lymphatic fluid are produced in the liver.
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[2] => Array
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[quiz_unique_key] => 1403770772
[question] => Changes in lymphatic vessel diameter in cirrhosis patients indicate that:
[value] => Array
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[answer] => 1
[description] => Reason for Correct Answer:
The results of Experiment 1a show that the thoracic duct has a larger diameter in cirrhosis patients, and the results of Experiment 2 also show that lymph vessels, in general, have a larger diameter in cirrhosis patients.
Vessel walls can stretch over time in response to pressure and stress.
Blood pressure does not directly act on the walls of the thoracic duct because blood does not flow through the thoracic duct – only lymph does.
The thoracic duct and other vessels would increase in diameter to allow for an increased flow of lymph. One way in which this might happen is that an increased flow rate of lymph would put more pressure on the walls of the thoracic duct and stretch it out. This effect is similar to the way a hose fills up and stretches out when water flows through it. Over time, this pressure on the walls of the thoracic duct could cause it to grow in diameter.
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[each_answer] => A. these patients have a higher flow rate of lymph fluid.
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[each_answer] => B. these patients have higher blood pressure.
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[each_answer] => C. these patients have a lower flow rate of lymph fluid.
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[each_answer] => D. these patients have lower blood pressure.
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[quiz_unique_key] => 1403770772
[question] => Which effect likely contributes to the development of ascites in cirrhosis patients?
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[answer] => 1
[description] => Reason for Correct Answer:
Ascites is defined in the passage as “excess lymphatic fluid accumulat[ing] in the abdominal cavity, outside the organs.”
The answer choices refer to changes in lymphatic fluid and changes in fluid composition in the extracellular space. Keep in mind that lymphatic fluid is the fluid in the extracellular space/surrounding cells, with excess taken up by lymphatic vessels.
In cirrhosis, the liver’s impaired function leads to reduced production of proteins.
The passage describes a reduction in protein content in the lymphatic fluid, but cirrhosis would also cause a drop in blood protein concentration, particularly of the protein albumin.
Albumin is responsible for maintaining oncotic pressure in the blood vessels. When albumin levels decrease, the osmotic pressure in the blood decreases. As a result, more fluid moves from the blood vessels into the extracellular spaces/lymphatic fluid, leading to the development of ascites.
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[each_answer] => A. Decreased osmotic pressure in the blood due to decreased protein production in the liver allows more water to enter the extracellular fluid.
)
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[each_answer] => B. Decreased osmotic pressure in the lymphatic fluid due to decreased protein production in the liver allows more water to enter the extracellular space.
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[each_answer] => C. Increased osmotic pressure in the blood due to decreased protein breakdown in the liver allows less fluid to stay in the blood.
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[each_answer] => D. Increased osmotic pressure in the lymphatic fluid due to decreased protein breakdown in the liver causes more water to enter the extracellular space.
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[quiz_unique_key] => 1403770772
[question] => Which statement is most supported by the results in Figure 1?
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[answer] => 2
[description] => Reason for Correct Answer:
Figure 1 shows that, in cirrhosis patients, both the number and diameter of VEGFR3-positive lymphatic vessels are increased. In compensated cirrhosis patients (without ascites, according to the passage), this increase is not as severe as it is in decompensated patients (with ascites, according to the passage).
This suggests that dilated lymphatic vessels are a sign of worse lymphatic function, so Choice A cannot be correct.
The difference between compensated and decompensated patients in these graphs suggests that compensation mechanisms may somewhat improve lymphatic function, so Choice C cannot be correct.
However, the fact that compensated cirrhosis patients still have MORE numerous and dilated lymphatic vessels than normal patients indicates that compensation mechanisms DO NOT likely completely reverse damage to the lymphatic system in cirrhosis, so Choice D cannot be correct.
The data indicates that in decompensated cirrhosis, with ascites, there is an increased number and increased dilation of lymphatic vessels (compared to that seen in both normal patients and patients with compensated cirrhosis); this is likely caused by lymphatic pressure buildup due increases in fluid volume and well as restricted flow through the liver that is no longer compensated by other mechanisms.
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[each_answer] => A. The presence of dilated lymphatic vessels in compensated cirrhosis indicates improved lymphatic function compared to normal patients.
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[each_answer] => B. Increased number and increased dilation of lymphatic vessels is associated with ascites in cirrhosis patients.
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[each_answer] => C. Though compensation mechanisms counter some side effects of cirrhosis, they do not improve lymphatic function.
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[each_answer] => D. Compensation mechanisms fully reverse damage to the lymphatic system in patients with cirrhosis.
)
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[quiz_unique_key] => 1997864699
[question] => In patients with cirrhosis, which side effect is LEAST likely to result from direct damage to the liver?
[value] => Array
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[answer] => 4
[description] => Reason for Correct Answer:
To answer this question, you want to consider some basic functions of the liver:
The liver produces cholesterol, the precursor to sex hormones and vitamin D, so impairments to the liver could directly result in their impaired production.
The liver produces bile salts, which are stored in the gallbladder and released into the small intestine to aid in the digestion of fats. In cirrhosis, the bile salts can build up in the liver, and then the blood, due to impaired circulation from scarring in the liver.
The liver also metabolizes nutrients absorbed from the small intestine, so cirrhosis would impair this.
Electrolyte imbalances, which can affect nerve function, may occur in cirrhosis due to kidney dysfunction or complications related to the disease, but they are not primarily caused by direct liver damage. The liver’s central role in metabolism and detoxification is more directly related to options A, B, and C, making them more likely to be side effects of cirrhosis.
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[each_answer] => A. Impaired sex hormone and vitamin D production
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[each_answer] => B. Jaundice, or yellowing of the skin, from a build-up of bile
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[each_answer] => C. Fatigue and weakness due to impaired nutrient metabolism
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[each_answer] => D. Impaired nerve function due to electrolyte imbalances
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[554756|1] => B
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[554756|3] => A
[554756|4] => A
[554756|5] => B
[554756|6] => D
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Figure 1
