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.

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.

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 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.

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.

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 atrioventricular (AV) node is located in the lower intratrial septum and receives impulses from the sinoatrial node. The sinoatrial node is termed the pacemaker of the heart and is located in the wall of the right atrium. It initiates normal heart beats and is innervated by the vagus nerve, which helps control the rate of impulses. Once an impulse causes the atria to contract, it travels to the atrioventricular node. Once the AV node receives the impulse, cellular mechanisms initiate a delay. This prevents simultaneous atrial and ventricular systole, allowing the ventricles to receive the blood exiting the contracted atria. Following the delay, the impulse travels from the AV node to the bundle of His.nThe bundle of His is a pathway for electrical signals to be transmitted to the ventricles. The Purkinje fibers spread through the myocardium and distribute electical stimuli to cause contraction of the ventricular myocardium. The bundle branches supply the two ventricles with electrical stimuli. 

The heart has the beta-1 receptor on its surface. When norepinephrine binds to beta-1 receptors on the heart, the effect is an increase in heart rate. In patients with a heart problem, increasing the heart rate might exhaust the heart and provoke heart failure. By blocking this receptor with a beta blocker, agonists to the beta-1 receptor cannot increase the heart rate.   

As mentioned in the passage, carbonic anhydrase inhibitors will prevent the reabsorption of sodium and water at the proximal tubule. By preventing water reabsorption, the blood volume decreases. Lowering the blood volume will lower the blood pressure. The heart is constantly pushing blood against a pressure. The higher the blood pressure is, the more work the heart will have to do to push the blood out. Therefore, by lowering the blood pressure, the heart does not have to work as hard.