MCAT Biology : Lymph and Fluid Balance

Study concepts, example questions & explanations for MCAT Biology

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Example Questions

Example Question #1 : Lymphatic System

Which of the following systems is NOT directly aided by the lymphatic system?

Possible Answers:

Digestive system

Immune system

Cardiovascular system

Endocrine system

Correct answer:

Endocrine system

Explanation:

The lymphatic system has a variety of functions in the body. It collects excess interstitial fluid and returns it to the blood (cardiovascular system), it has lymph nodes that screen the lymphatic fluid for pathogens (immune system), and it reroutes fat digestates to the neck veins (digestive system). The lymphatic system does not aid the endocrine system, as hormones travel in the bloodstream.

Example Question #1 : Lymphatic System

Lymph in the thoracic duct __________.

I.  contains fluid and cells collected from the left hand

II.  contains chylomicrons collected from the intestine

III.  contains fluid and cells collected from the left leg

IV.  contains fluid and cells from the head and neck

V.  all of these are true

Possible Answers:

III

II

V

IV

I

Correct answer:

V

Explanation:

You either know the anatomy of lymphatic flow, or you don't and you need to review it. All statements are true. The thoracic duct is the major collecting point for lymph from both lower limbs, the intestine, and certainly the left arm and left side of the head and neck. It empties into the junction of the left subclavian vein and the left jugular vein, most commonly. The question did not ask you to argue about whether or not lymph from the right arm and right side of the head and neck rejoined the venous circulation through the thoracic duct or a smaller accessory thoracic duct on the right side, because this is somewhat variable.  

Example Question #1 : Lymph And Fluid Balance

The lymph collected from the majority of the body drains into the vena cava via what vessel?

Possible Answers:

Hepatic duct

Thoracic duct

Right lymphatic duct

Mammary duct

Correct answer:

Thoracic duct

Explanation:

It is important to know that the lymphatic system is an open system, meaning that it drains the interstitial fluid from the body and delivers it to the circulatory system in two different ways. The majority of the lymph drains from the body through the thoracic duct into the vena cava. The thoracic duct is also what drains fats collected in the liver and turned into chylomicrons.

Lymph from the head and right arm drains via the right lymphatic duct back to the vena cava, but this does not constitute the majority of lymph flow.

Example Question #4 : Lymphatic System

The lymph from the head, neck, and right arm drains into the vena cava via what duct?

Possible Answers:

Hepatic duct

Right lymphatic duct

Thoracic duct

Mammary duct

Correct answer:

Right lymphatic duct

Explanation:

It is important to know that lymph from the head, neck, and right arm drains via the right lymphatic duct into the vena cava, to be added to the venous circulation. The other important lymphatic duct is the thoracic duct, which drains lymph from the remainder of the body. 

Example Question #5 : Lymphatic System

During the course of a day, approximately three liters of plasma are filtered out of the capillaries, but are not reabsorbed into the vessels. This means that the volume of fluid stays in the interstitial space around the capillaries. 

What does the body do with this large volume of fluid?

Possible Answers:

It is transported to the kidney to exit the body as urine

It is absorbed into the lymphatic system

It exits the body as sweat

It stays in the interstitial space until the blood volume is decreased

Correct answer:

It is absorbed into the lymphatic system

Explanation:

Lymphatic fluid is formed by absorbing the excess plasma that has been filtered from the capillaries. This occurs because more plasma is filtered out of the capillaries than can be reabsorbed back into the capillaries. This leads to a net filtration of plasma into the interstitium. The role of the lymphatic system is to absorb this filtered plasma and return it to circulation via a duct into the right atrium. A failure to collect the extracellular fluids can lead to swelling of the extremities, known as edema.

When the lymphatic vessels collect fluid they also carry it through the lymph nodes, which house large populations of lymphocytes. These lymphocytes screen the blood for foreign antigens and can launch an immune response if pathogens are found.

Example Question #6 : Lymphatic System

What would you NOT expect to find in lymph fluid?

Possible Answers:

Water

White blood cells

Triglycerides

Red blood cells

Proteins

Correct answer:

Red blood cells

Explanation:

Lymph is a fluid that travels through its own kind of circulatory system. The lymphatic system as a whole helps maintain distribution of fluids and maintain blood composition. Plasma from blood leaks out of capillaries and gets collected and redistributed by the lymph system. It also transports other molecules, like proteins, triglycerides, and white blood cells. You would not expect to find a red blood cells in this fluid, as they do not leak out of veins and capillaries.

Example Question #7 : Lymphatic System

Which of the following is not a component of the lymphatic fluid?

Possible Answers:

Albumin

Water

Red blood cells

Chylomicrons

Correct answer:

Red blood cells

Explanation:

The lymph is collected in the periphery from the fluid that is not reabsorbed by oncotic pressure in the capillary beds. Proteins (including the main blood component albumin), chylomicrons (collected from enterocytes in the liver), and water are all parts of lymph. These components can exit the capillary walls in areas of significant hydrostatic pressure, and enter the lymph to avoid being trapped in the interstitium.

Red blood cells are too large to pass through capillary walls, and thus would not be released into the interstitium or absorbed into the lymphatic system.

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