Blood Vessels and Vasculature
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MCAT Biology › Blood Vessels and Vasculature
Where would one find the most deoxygenated blood?
Pulmonary arteries
Left atrium
Left ventricle
Aorta
Femoral artery
Explanation
The circulatory system follows both the systemic and pulmonary circuits. Deoxygenated blood is returned from the systemic circuit through the vena cavae into the right atrium. It then goes into the right ventricle after passing through the tricuspid valve. From the right ventricle it enters the pulmonary circuit through the pulmonary artery, which carries deoxygenated blood from the right ventricle to the lungs, where it gets oxygenated. From the lungs it goes through the pulmonary veins into the left atrium. From the left atrium it goes into the left ventricle through the mitral valve, and is returned to the systemic circuit through the aorta.
Deoxygenated blood would be found in mostly in systemic veins, including the vena cavae, pulmonary arteries, and the right side of the heart. Oxygenated blood would be found in systemic arteries, such as the femoral artery, pulmonary veins, and the left side of the heart.
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?
Central vein
Hepatic artery
Portal vein
Bile duct
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.
Nutrients absorbed in the small intestine follow which of the following pathways before entering the tissues of the body?
Hepatic portal circulation -> liver -> vena cava -> heart
Liver -> hepatic portal circulation -> vena cava -> heart
Vena cava -> heart -> hepatic portal circulation -> liver
Vena cava -> heart -> liver -> hepatic portal circulation
Explanation
It is important to remember that these nutrients go through the liver before entering the general circulation. Amino acids and carbohydrates are absorbed through the intestine's epithelial cells into the hepatic portal circulation, then to the liver, through the inferior vena cava, and finally into the heart. From the heart, these nutrients are pumped from the left ventricle to the rest of the body's tissues.
Hemoglobin is the principal oxygen-carrying protein in humans. It exists within erythrocytes, and binds up to four diatomic oxygen molecules simultaneously. Hemoglobin functions to maximize oxygen delivery to tissues, while simultaneously maximizing oxygen absorption in the lungs. Hemoglobin thus has a fundamentally contradictory set of goals. It must at once be opitimized to absorb oxygen, and to offload oxygen. Natural selection has overcome this apparent contradiction by making hemoglobin exquisitely sensitive to conditions in its microenvironment.
One way in which hemoglobin accomplishes its goals is through the phenomenon of cooperativity. Cooperativity refers to the ability of hemoglobin to change its oxygen binding behavior as a function of how many other oxygen atoms are bound to the molecule.
Fetal hemoglobin shows a similar pattern of cooperativity, but has unique binding characteristics relative to adult hemoglobin. Fetal hemoglobin reaches higher saturation at lower oxygen partial pressure.
Because of cooperativity, adult and fetal oxygen-hemoglobin dissociation curves appear as follows.
Beyond its ability to carry oxygen, hemoglobin is also effective as a blood buffer. The general reaction for the blood buffer system of hemoglobin is given below.
H+ + HbO2 ←→ H+Hb + O2
The hemoglobin gene can be the site of catastrophic genetic changes, one of which is the change seen in sickle cell anemia. In this disorder, hemoglobin mutations cause red blood cells to take on a sickled appearance. These cells are less able to flow freely in the blood through tight spaces. Which of the following vessels is most likely to be the site of accumulation of these misshapen cells?
Capillaries
Veins
Venules
Arteries
Arterioles
Explanation
With morphological changes, cells are most likely to be caught in regions with the smallest cross sectional area. Though capiallary beds have the highest TOTAL cross sectional area of any vessel bed in the body, individual capillaries are smaller than any other type of blood vessel. The result is that misshapen red blood cells, such as those in sickle cell anemia, can easily get stuck in capillaries.
Which of the following incorrectly matches the type of blood with the vessel or structure carrying it?
Oxygenated blood—pulmonary artery
Oxygenated blood—left atrium
Deoxygenated blood—inferior vena cava
Deoxygenated blood—right ventricle
Oxygenated blood—pulmonary vein
Explanation
Arteries always carry blood away from the heart. Most carry oxygenated blood, but the pulmonary artery carries deoxygenated blood from the right ventricle to the lungs so that it can reoxygenated and sent back to the heart.
Which of the following vessels has the highest concentration of oxygen?
Pulmonary veins
Pulmonary arteries
Superior vena cava
Skeletal capillaries
Inferior vena cava
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.
Edema is a condition caused by a build-up of fluid in the interstitium.
Which of the following is associated with edema?
Increased blood vessel wall permeability
High plasma albumin
Increased plasma oncotic pressure
Decreased hydrostatic pressure
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.
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?
The pulmonary artery
The left atrium
The pulmonary veins
The gastric artery
The superior vena cava
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.
What characteristics of arteries and veins allow the heart to pump blood strong enough to travel through the body against gravity without backing up?
One-way valves in veins; compliance in thick-walled arteries
Small diameters
One-way valves in arteries; compliance in thick-walled veins
One-way valves in veins; elasticity in thin-walled arteries
One-way valves in arteries; elasticity in thin-walled veins
Explanation
Areteries need to be thick and able to withstand strong, sudden increases in pressure because they recieve blood more directly from the heart. The aorta in particular is very thick and able to expand with a large increase in blood volume. "Compliance" is the word that decsribes a vessel's ability to do this. Veins are thin and collapsable, and contain one-way valves to prevent blood from flowing backwards as it moves against gravity towards the heart.
In extremely cold temperatures, which of the following is most directly responsible for constricting blood flow to the skin in order to preserve heat?
Arterioles
Arteries
Capillaries
Venules
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.