MCAT Biology : Blood Vessels and Vasculature

Study concepts, example questions & explanations for MCAT Biology

varsity tutors app store varsity tutors android store

Example Questions

← Previous 1 3

Example Question #1 : Blood Vessels And Vasculature

The liver primarily serves to help detoxify both endogenous and exogenous substances from the blood and intestines. Once blood from the intestines (delivered by the portal vein) or from the systemic circulation (delivered by the hepatic artery) enters the liver, it is filtered over liver cells called hepatocytes. Endogenous substances, such as bilirubin, and exogenous substances, such as drugs, are taken up by transporters on hepatocytes and undergo three phases of metabolism. The three phases allow the transported compound to be detoxified by a method of electron transfer (phase I), by addition of amino acid derivatives (phase II), and finally by exocytosis from the hepatocyte into the bile (phase III). The bile is then transported into the small intestine, and finally excreted from the body.

Amino acid derivatives are often taken from the Krebs cycle, added to sugar nucleotides, and transferred to molecules for detoxification. A common example of an enzyme responsible for this is UDP-glucuronosyl transferase.

The flow of substances through the liver follows the portal triad. The portal triad does not include which of the following structures?

Possible Answers:

Portal vein

Central vein

Bile duct

Hepatic artery

Correct answer:

Central vein

Explanation:

The passage details the passage of substances through the liver. The portal triad consists of the portal vein, hepatic artery, and bile duct. Blood from the intestines enters the liver through the portal vein and is filtered by hepatocytes on its way to the central vein that connects to the inferior vena cava and onto the rest of the venous circulation. The liver is thus able to filter out toxic metabolites before they reach systemic circulation.

Example Question #2 : Blood Vessels And Vasculature

Which of the following vessels has the highest concentration of oxygen?

Possible Answers:

Superior vena cava

Pulmonary veins

Pulmonary arteries

Skeletal capillaries

Inferior vena cava

Correct answer:

Pulmonary veins

Explanation:

The pulmonary veins have the greatest concentration of oxygenation, because they bring oxygenated blood from the lungs to the left atrium. They are the only veins that carry oxygenated blood.

Blood in the pulmonary arteries is deoxygenated and travels from the right ventricle to the lungs for gas exchange. Blood in the vena cavae is returning to the heart after systemic circulation, and is thus deoxygenated. Blood in the capillaries is a mixture of oxygenated and deoxygenated, but is always less oxygenated than the blood of the pulmonary veins.

Example Question #3 : Blood Vessels And Vasculature

Hemoglobin is the protein responsible for the transport of oxygen throughout the bloodstream. The saturation of hemoglobin can be graphed based on the pressure of oxygen. As the pressure of oxygen increases, the saturation of hemoglobin with oxygen will increase in a sigmoidal fashion. This oxygen dissociation curve can be shifted depending on the external conditions in the blood.

Where would hemoglobin have the lowest saturation percentage of oxygen?

Possible Answers:

The gastric artery

The pulmonary artery

The left atrium

The superior vena cava

The pulmonary veins

Correct answer:

The pulmonary artery

Explanation:

Keep in mind that the saturation percentage of hemoglobin depends on the pressure of oxygen. Before returning to the lungs, hemoglobin has given up the majority of attached oxygen to the body's tissues. As a result, the hemoglobin will be least saturated just before entering the lungs to become oxygenated once again. This is why the pulmonary artery will contain blood with the lowest saturation of hemoglobin.

The low partial pressure of oxygen in the pulmonary artery, compared to the high partial pressure of oxygen in the alveoli, generates the gradient for oxygen to enter the blood stream.

Example Question #2 : Blood Vessels And Vasculature

In extremely cold temperatures, which of the following is most directly responsible for constricting blood flow to the skin in order to preserve heat?

Possible Answers:

Arteries

Venules

Arterioles

Capillaries

Correct answer:

Arterioles

Explanation:

The arterioles feed into the capillaries, and control which tissues and parts of the body get more oxygenated blood. During cold weather conditions, the arterioles are activated in vasoconstriction of oxygenated blood to the capillary beds in the skin.

Example Question #31 : Circulatory System

Edema is a condition caused by a build-up of fluid in the interstitium.  

Which of the following is associated with edema?

Possible Answers:

High plasma albumin

Increased plasma oncotic pressure 

Decreased hydrostatic pressure 

Increased blood vessel wall permeability

Correct answer:

Increased blood vessel wall permeability

Explanation:

Increased blood vessel wall permeability can lead to edema. Edema is the result of abnormal fluid homeostasis; proper fluid homeostasis is achieved by balancing hydrostatic pressure and oncotic pressure in blood vessels. If hydrostatic pressure is greater than oncotic pressure in a blood vessel, fluid will filter out of the blood vessel and into the interstitium. The Starling Equation describes fluid movement across capillary membranes in relation to hydrostatic pressure and oncotic pressure within the blood vessel. 

Example Question #31 : Circulatory System

Which of the following areas in the general circulation has the lowest blood pressure?

Possible Answers:

Vena cavae

Venules

All of these have the same average blood pressure

Capillaries

Arteries

Correct answer:

Vena cavae

Explanation:

In the general circulation, the highest blood pressure is found in the aorta and the lowest blood pressure is in the vena cava. As this suggests, blood pressure drops in the general circulation as it goes from the aorta to the rest of the body. Pressure drops form the aorta to the arteries, the arteries to the arterioles, and the arterioles to the capillaries. Flow rate reaches a minimum in the capillaries before blood begins to pool in the venules. Pressure continues to drop from the venules to the veins to the vena cavae.

Example Question #32 : Circulatory System

Which of the following best describes the cause of diastolic blood pressure?

Possible Answers:

Elastic recoil of the aorta

The viscosity of blood

Venous pressure

Right ventricular contraction

Correct answer:

Elastic recoil of the aorta

Explanation:

Systolic blood pressure is generated by the contraction of the left ventricle and the ejection of blood into the aorta. As blood is ejected into the aorta, the aorta expands to accommodate the large volume of blood. The wall of the aorta then begins to recoil and pushes blood through the arteries. This is how blood pressure continues to stay elevated even when the heart is not contracted.

Right ventricular contraction causes blood to go into the pulmonary circulation, which is not measured with blood pressure testing. The viscosity of blood does not impact the pressure that is exerted on the wall of a blood vessel. Venous pressure is not typically measured, as it is much lower than arterial pressure and is relatively unaffected by heart contractions due to the narrowness of the preceding capillaries.

Example Question #33 : Circulatory System

Where is blood pressure the greatest?

Possible Answers:

Pulmonary veins

Capillaries

Arterioles

The aorta

Correct answer:

The aorta

Explanation:

Blood pressure tends to be the greatest near the heart, and decreases as blood flows to the capillaries. The pressure is greatest at the aorta and gradually decreases as blood moves from the aorta to large arteries, smaller arteries, and capillaries. The pressure is lowest in the venous system, which is why blood can pool in the veins and act as a "blood reservoir". Veins contain valves that allow them to pump blood back to the heart. 

Example Question #3 : Blood Vessels And Vasculature

The sympathetic nervous system is responsible for the "fight or flight" responses in the body. When innervated, the sympathetic nervous system will redirect blood from the digestive and excretory organs, and send the blood to the muscles of the body.

How is blood "redirected" to other areas of the body?

Possible Answers:

Sympathetic vasoconstriction of arterioles

Sympathetic vasodilation of arteries

Blood is redirected to the muscles by the heart

Sympathetic innervation of venule shunts

Parasympathetic innervation of venule shunts

Correct answer:

Sympathetic vasoconstriction of arterioles

Explanation:

The heart is incapable of selectively pumping blood to certain areas, nor can it manipulate the speed of blood flow through certain areas. Instead, the sympathetic nervous system can stimulate the smooth muscle surrounding arterioles to constrict. This constriction of arterioles allows blood to be redirected to other areas of the body where blood is needed. Venule shunts are important for counteracting gravity, but the lack of thick smooth muscle lining these vessels makes them ineffective at redirecting blood flow.

Example Question #35 : Circulatory System

Which of the following statements about capillaries is FALSE?

I.  The blood flow to a capillary bed can be interrupted by constriction of pre-capillary sphincters.

II.  There is a continuous, slow exudation of intravascular fluid into all capillary beds.

III.  Together with small arteries, capillaries constitute the "resistance bed" of an organ.

IV.  The blood in the distal capillaries of many tissues has a higher osmotic pressure than the blood in the same proximal capillaries.

V.  In the pituitary vascular portal system, capillaries take up releasing hormones from the hypothalamus.

Possible Answers:

II

III

IV

I

V

Correct answer:

II

Explanation:

Some—but not all—capillary beds experience transudation of fluid from the vessels. Recall that capillaries can be discontinuous (spaces between adjacent cells), completely closed with tight junctions between cells (as in the brain), or fenestrated (pores through their cytoplasmic membranes (as in the kidney). Closure of arteriolar pre-capillary sphincters can reduce or eliminate the blood flow to a region of tissue. This is why your fingers blanche in very cold weather. Although the arterioles are the major resistance vessels in a circuit, the capillary beds have some contribution. Transudation of fluids, but not large molecules such as protein, from inside to outside a capillary indeed raises the osmotic pressure of the remaining blood; this is Starling's Law, not to be confused with the Frank-Starling law of the heart.

Choice V is a true statement regarding the hypothalmo-hypophyseal portal system.

← Previous 1 3
Learning Tools by Varsity Tutors

Incompatible Browser

Please upgrade or download one of the following browsers to use Instant Tutoring: