MCAT Biology - Ch 9

T cell antigen receptors are different from antibodies because: A. T cell receptors must interact with antigen uniquely presented by other cells but not with free antigen B. T cell receptors bind various cytokines C. T cell receptors bind complement proteins to lyse cells D. T cell receptors are mediators of allergic reactions

A

Which of the following statements about antibodies is true? I. Antibodies are produced by B cells II. Antibodies only recognize peptide antigens III. Antibodies can mark an antigen for destruction by killer T cells A. I only B. II only C. I and II D. I and III

A

What would happen if gap junctions in the heart were blocked, but voltage-gated ion channels remained functional?

An action potential could exist, but not be transmitted to neighboring cells

How strong is atrial compared to ventricular contraction?

Atrial contraction is much weaker

Blood pressure is directly proportional to cardiac output and peripheral resistance. Which of the following will raise blood pressure? A. Consumption of a large meal because it increases the heart rate B. Exercise because it increases cardiac output C. Sizable blood loss because it increases epinephrine levels due to the fear response D. A localized allergic reaction because it causes fluid loss to the tissue at the site

B

The cardiac cycle is divided into systole and diastole, during which the ventricles contract and relax, respectively. During systole, blood is ejected from the ventricles and is pumped into either the aorta or pulmonary artery. The pressure in the ventricles rapidly increases; however, the volume of the blood in the ventricles initially remains unchanged. This is referred to as isovolumetric contraction. Which of the following is the most likely reason for isovolumetric contraction? A. Decreased ventricular contractility due to over-stretching of cardiac sarcomeres B. The pressure in the aorta is initially greater than that of the left ventricle C. The pressure within the pulmonary vein is initially lower than that of the right ventricle D. The action potential that propagates through the bundle of His and Purkinje fibers has not yet depolarized all of the ventricles

B

Which one of the following best describes the mechanism by which production of specific antibody is achieved in response to antigen exposure? A. Immature B cell clones expressing several different antibody genes select for one gene and turn off expression of others B. Antigen stimulates proliferation of a specific B cell clone expressing a single antibody protein that recognizes that antigen C. The variable regions of antibody proteins on an immature B cell clone form a pocket around the antigen, and the antibody genes are recombined to fit the bound antigen D. Antibody light and heavy chains are mixed on each B cell's surface in different combinations to produce different antigen recognition

B

Individuals affected with DiGeorge syndrome have a T cell deficiency due to congenital lack, or incomplete development, of the thymus. Based on this statement, individuals affected with this syndrome will: A. Have normal humoral immunity B. Have normal cell-mediated immunity C. Be susceptible to infection D. Be resistant to infection

C

What are the names of the two portal systems in the body? A. The pancreatic and the hypothalamic-hypophyseal B. The pancreatic and the renal-urinary C. The hepatic and the hypothalamic-hypophyseal D. The hepatic and the renal-urinary

C

Will the absolute refractory period, during which a cell will not fire an action potential, be longer in cardiac or neuronal cells?

Cardiac cells

Blood flows: A. From the lungs into the right atrium, since the right side of the heart deals with deoxygenated blood B. From the right ventricle to. the right atrium, since the atrium is a low-pressure chamber C. From the right atrium to the left ventricle, since the right side of the heart deals with deoxygenated blood and the left side must pump blood to the body D. From the lungs into the left atrium and from there to the left ventricle, since the left side of the heart deals with oxygenated blood

D

Cardiac output is influenced by which of the following? I. Nervous input II. Hormones III. Blood pressure A. I only B. II only C. I and II only D. I, II, and III

D

Hepatitis B is an inflammatory disease of the liver. While the virus itself is relatively benign, the body's attempt to eradicate it causes unwanted liver inflammation. Which of the following blood test results could be from an individual who has been vaccinated against Hepatitis B and does not have an active infection?

D

The ductus arteriosus is a shunt in the fetal circulation that diverts a portion of the blood from the pulmonary circulation into the aorta. Failure of the ductus arteriosus to close shortly after birth results in a condition referred to as a patent ductus arteriosus and, in severe cases, the generation of a left-to-right shunt. A left-to-right shunt would result in all of the following EXCEPT: A. Increased mixing of oxygenated blood with deoxygenated blood B. Decreased blood flow into the systemic circulation C. Increased blood flow into the pulmonary circulation D. Decreased vascular pressure in the pulmonary circulation

D

Which one of the following is true during systole? A. The bicuspid valve is open B. Blood does not flow through the aortic valve C. Both semilunar valves are closed D. Pressure in the atria is low, and thus the atria fill with blood from the vena cava and pulmonary veins

D

Which one of the following will increase cardiac output? A. Blocking sodium leak channels in the sinoatrial node B. Stimulation of the heart by the parasympathetic nervous system C. Significant dehydration due to prolonged exercise in the heat D. Contraction of smooth muscle in the walls of the large veins

D

Which is longer: systole or diastole?

Diastole

Albumin is produced in the liver. Alcoholics with diseased livers make insufficient amounts of albumin, and thus have insufficient plasma oncotic pressure. What result would you predict?

Edema of the entire body

In fish, blood passes from the heart to the gills and then to the rest of the body. Why have mammals evolved a separate circulation for the lungs?

Fish capillaries must have a very high pressure, having 2 separate circulations solves this problem

What would occur if capillaries throughout the circulatory system were made more permeable?

Fluid would be lost from the plasma into tissues, decreasing blood volume and cardiac output

If the hypothalamic-hypophysial portal circulation is severed, how does this affect the function of the pituitary?

Hormones must take a longer route and will be diluted and degraded before they reach the pituitary

How would an increase in stroke volume change blood pressure?

Increase BP

What is the difference between ischemia and hypoxia?

Ischemia: wastes build up Hypoxia: wastes are adequately removed

Does hemoglobin have higher affinity for oxygen in the tissues or in the lungs?

Lungs

If the arterioles in a large part of the systemic circulation dilate, how will this affect cardiac output?

More blood will flow through the tissues so cardiac output increases

Can a T helper cell become activated after encountering a foreign particle floating in the blood?

No, T helpers are only activated by antigen presented on MHC II

Would an antibody against a cytoplasmic bacterial protein help the immune system to remove the bacteria?

No, antibodies are soluble in plasma

Myoglobin is a molecule with a structure very similar to hemoglobin, but with a single subunit that has one binding site. Does myoglobin display cooperativity in oxygen binding?

No, cooperativity requires more than one binding site

If the arterioles constrict in a tissue, will material diffuse through the wall of the arterioles into the tissue?

No, exchange between blood and tissues occurs at the capillaries

If a T cell is specific for an antigen, does that mean it releases antibodies that bind to the antigen?

No, only B cells make antigens, T helpers can activate B cells or T killers to destroy it

Do all of the arteries of the body carry oxygenated blood?

No, pulmonary arteries carry deoxygenated blood

In general, every cell of the body is said to possess the same copy of the genome. Is this true in the immune system?

No, recombination during development of B and T cells makes an exception to this rule

Does ACh always inhibit postsynaptic cells?

No, the receptor type determines if it is stimulatory or inhibitory

Vaccination against some viruses is ineffective in preventing future infection, while it is highly effective against other viruses. Does the failure of vaccination to protect against some viruses indicate a failure in the ability to produce memory cells?

No, the virus might have mutated

Do ligand-gated ion channels propagate action potentials in cardiac muscle?

No, they may help create threshold depolarization but do not propagate an AP

What valve prevents blood flow between the left ventricle and the right ventricle?

None, ventricles are separated by interventricular septum

Why don't potassium leak channels cause spontaneous action potentials in neurons or muscle cells?

Potassium leak channels allow potassium to leave the cell, down a gradient, polarizing the membrane (opposite of sodium channels)

At a given PO2, which has a higher % saturation: tense or relaxed hemoglobin?

Relaxed since it has a higher affinity

Why might tense, stressed people have high blood pressure?

Tension/stress stimulate the sympathetic nervous system

During exercise a significant amount of lactic acid is produced by fermentation in muscles that are not receiving adequate oxygen. Despite this increase in lactic acid, the pH of the blood does not change dramatically. Why not?

The HCO3- buffer system prevents pH change

An overweight child weighing 110 pounds, a female athlete weighing 110 pounds, and an elderly man weighing 110 pounds all require a cardiac output of about 5 L/min. But the child and the old man have a stroke volume of 1/16 L, while the athlete's stroke volume is 1/9 L. How can the child and the old man supply enough blood to their bodies?

The athlete's heart rate will be much lower

The mitral valve must withstand enormous pressures. What would happen if it ruptured?

The left ventricle would pump blood in both directions, results in elevated pulmonary blood pressure and pulmonary edema

Since the ventricles are ultra-high pressure chambers, why is it necessary to put valves between them and the arteries?

The ventricles are only pressurized while contracting, have a low pressure when they are not contracting

Which is larger: the cardiac output of the right ventricle or the left ventricle?

They are equal

Will the strength of contraction by cardiac muscle be affected by the extracellular concentration of calcium ions?

Yes, a significant portion of the calcium that stimulates contraction comes from the extracellular pool

If binding of oxygen is cooperative, is it saturable?

Yes, binding will be saturable at a high concentration since there are a limited number of binding sites

If the antigen binding site is small, can antibodies recognize large proteins as antigens?

Yes, they can recognize small parts of the protein, not the entire protein