Heart - MCAT Biological and Biochemical Foundations of Living Systems

The semilunar valves refer to the aortic valve and pulmonary valve, both of which have three flaps. The atrioventricular valves separate the atria from the ventricles. The right side of the heart is separated by the tricuspid valve, while the left is separated by the bicuspid, or mitral, valve. The mitral valve is the only heart valve with two flaps.

The lungs remain non-functional in the developing fetus. Instead, the fetus receives oxygen via gas exchange between maternal and fetal circulation in the placenta. To prevent inefficient blood flow to the lungs, blood is shunted in two ways. The ductus arteriosus shunts blood directly from the pulmonary artery to the aorta, allowing it to bypass the pulmonary circuit. After birth, this duct quickly collapses to become the adult structure known as the ligamentum arteriosum. The second shunt is the foramen ovale, which allows blood to pass directly from the right atrium to the left atrium. In adults, this structure becomes the fossa ovalis.

The ductus venosus is not found in the heart, and is used to direct blood from the umbilical vein to the inferior vena cava. This allows the oxygenated blood (returning from the placenta through the umbilical vein) to bypass systemic circulation and enter directly into the heart. The heart can then direct the blood through circulation.

The correct answer is "it is striated." Similiar to skeletal muscle, cardiac muscle is striated. It has only one nucleus per cell, and its action is involuntary. Futhermore, it is composed of sarcomeres, which give it its striated appearance.

Systolic blood pressure measures the force of blood exiting the heart into the arteries during contraction. This can measure how strong the heart tissue is. Diastolic pressure indicates the pressure when the heart is relaxed. Healthy systolic blood pressue is 120mmHg, and diastolic is 80mmHg.

Oxygenated blood returning to the heart from the lungs enters the left atrium. It then goes to the left ventricle and out the aorta.

Cardiac output is defined as the volume of blood pumped per minute. The two factors that will directly affect the cardiac output will be stroke volume (volume pumped per beat) and heart rate (beats per minute).

Systole can apply to either te atria or the ventricles and refers to the period during which the chambers contract. Diastole, in contrast, described the period of relaxation. During diastole, blood fills the relaxed chambers. During systole, blood is forced out of the chambers as they contract. Systole and diastole are coordinated between chambers such that both atria contract together (atrial systole) and both ventricles contract together (ventricular systole) in a rhythm that allows coordinated filling and emptying of the chambers without backflow or disruption.

Note that systolic blood pressure refers to blood pressure during ventricular systole, and diastolic blood pressure to pressure during ventricular diastole.

The correct electrical path through the heart is the SA (sinoatrial) node, AV (atrioventricular) node, bundle of His (AV bundle), then purkinje fibers.

The sinoatrial node initiates the electrical signal and acts as the heart's natural pacemaker. Innervation from the parasympathetic nervous system is crucial in maintaining a normal heart rate from the SA node, but is not required to initiate electrical signals. The signal travels to the atrioventricular node and is briefly delayed, allowing the atria to finish contracting before initiaing ventricular systole. The signal travels down the bundle of His and is quickly distributed to the purkinje fibers, which initiate ventricular systole.

The tricuspid valve separates the right atrium from the right ventricle. The bicuspid valve (also known as the mitral valve) separates the left atrium from the left ventricle. The pulmonic valve separates the right ventricle from the pulmonary artery and the aortic valve separates the left ventricle from the aorta (these are known as the semilunar valves).

Cardiac output is the product of heart rate (HR) and stroke volume (SV). Heart rate is equal to beats per minute, while stroke volume is equal to volume per beat. The "beat" units cancel, and leave the cardiac output equal to volume per minute.

cardiac output = (beats/min) * (volume/beat) = volume/min.

The mitral (or bicuspid) valve is the atrioventricular valve that is located between the left atrium and left ventricle. Filling of the left ventricle requires that the valve stay open so that blood can enter into the ventricle from the left atrium. With ischemic damage to the valve, abnormal flow between the left atrium and ventricle will occur.

The aortic valve is located between the left ventricle and the aorta. The tricuspid valve separates the right atrium and right ventricle. The pulmonic valve is located between the right ventricle and pulmonary artery.

Electrical coupling of cells is mediated through gap junctions—ions are able to immediately flow through adjacent cells through these transmembrane protein channels. Cardiac muscle requires such syncytial connections in order to most effectivey synchronize muscle contraction.

Neurotransmitters, synaptic junctions, and cholinergic receptors would necessitate a nervous system communication, but the heart is electrically-coupled without neural mediation. Pressure receptors are not involved in cardiac muscle activity.

This a simple anatomy question. The mitral (bicuspid) valve lies between the left atrium and ventricle, therefore the answer must be the mitral valve. The tricuspid valve lies between the right atrium and ventricle.

The valve between the right atrium and ventricle is the tricuspid valve. The valve between the left atrium and ventricle is called the bicuspid, or mitral, valve. "Bicuspid" and "mitral" can be used interchangeably.

The pulmonary valve connects the right ventricle with the pulmonary artery, while the aortic valve connects the left ventricle with the aorta.

The correct answer is increased heart rate.

Cardiac output is the volume of blood pumped by the heart per minute. This volume can be calculated by using two other cardiac measures: heart rate and stroke volume. Heart rate is the number of strokes/contractions per minute, while stroke volume is the volume of blood ejected per beat.

The only way to increase cardiac output is to increase either the heart rate or to increase the stroke volume.

The heart beats automatically through stimulation from the sinoatrial node. The group of neurons found in this node depolarize in a coordinated, spontaneous manner to allow for the contraction of the atria and ventricles in the heart. Without the sinoatrial node, heart contraction may be possible, but it would not be regular and would require additional regulation.

Depolarization of the sinoatrial node specifically leads to atrial contraction. The signal is then transmitted through the atrioventricular node and bundle of His to the purkinje fibers, which coordinate the contraction of the ventricles.

After axons from the sinoatrial node flow through the atria to cause atrial contraction, the depolarization pauses in the atrioventricular node. Once the atrioventricular node depolarizes, the electrical signal travels though the bundle of His to the walls of the ventricles via purkinje fibers. The atrioventricular node initiates ventricular contraction, the bundle of His carries the signal, and the purkinje fibers allow for synchronized contraction of different regions of the ventricular wall.

The vagus nerve is a major nerve of the parasympathetic nervous system, responsible for mediating numerous responses in the body. In relation to the heart, the vagus nerve provides constant inhibition to the sinoatrial node, slowing the heart rate. The sinoatrial node naturally fires at about 80 to 100 beats per minute, while a healthy resting heart rate is closer to 60 due to innervation by the vagus nerve.

The radial nerve is located in the forearm; the femoral nerve is located in the thigh; the subcostal nerve is located along the lower ribs.

In a fetus, there are three fetal shunts: the ductus arteriosus, the ductus venosus, and the foramen ovale. Failure to fully close the foramen ovale during birth will allow blood to shunt directly from the right atrium to the left atrium, diverting the blood from the lungs. The ductus arteriosus also shunts blood away from the fetal non-functional lungs, allowing it to pass directly from the pulmonary artery to the aorta. Additionally, after birth, the ductus arteriosus becomes the ligamentum arteriosum.

Conversely, the ductus venosus is a structure in the fetus that diverts blood away from the fetal liver.