Heart

Increased epinephrine, released either by the adrenal medulla or by myocardial innervation, increases contractility in the heart, which in turn increases stroke volume.

Deoxygenated blood from the body flows through the superior and inferior vena cava into the right atrium of the heart. From there it enters the right ventricle, then is ejected into the lungs via the pulmonary arteries. The blood is oxygenated in the lungs, then flows through the pulmonary veins into the left atrium, then into the left ventricle to be pumped back out into the body.

Blood in the right atrium must pass through the tricuspid valve to enter the right ventricle. The mitral valve is between the left atrium and the left ventricle. The semilunar valves are located at the base of the aorta and the pulmonary trunk, also known as the aortic valve and pulmonary valve. The foramen ovale is a type of shunt that exists in the fetal heart. It's presence in an adult patient is a form of congenital heart defect.

Cardiac output (CO) is the measure of the amount of blood that is able to circulate through the heart in one minute. It is found by multiplying the stroke volume times the heart rate, in beats per minute. The ejection fraction, another important measure of cardiac function, is not considered when calculating cardiac output.

The S1 heart sound (sometimes referred to as "lub") is caused by the sudden snapping-shut of the tricuspid and mitral valves during systole, when the heart contracts and tension on the chordae tendinae is released. No sound is produced on the opening of these or any other valves in the heart.

The contraction rate for the heart is set by the cells of the sinoatrial node, also known as the pacemaker cells of the heart. These cells have membranes that are especially permeable to ions, and are able to depolarize on their own at a rate of 70-100 beats per minute. All the other areas listed do have their own spontaneous contractility, but their rates are slower than that of the sinoatrial node. Thus, the sinoatrial node is the pacemaker in a healthy heart.

Depolarization is able to travel in a uniform wave through myocardium due to the presence of gap junctions. These junctions allow the depolarizing current to be transmitted directly from cell to cell in the heart. Striation in cardiac muscle is a feature of contraction, created by overlapping thick and thin contractile filaments. Desmosomes are strong fiber-like anchors between myocardial cells, and T-tubules, while an important part of depolarization, are not responsible for the rapid inter-cellular communication that occurs as a result of the presence of gap junctions.

The vagus nerve provides the main parasympathetic innervation of the heart. The recurrent laryngeal nerve, a branch of the vagus nerve, innervates the majority of the intrinsic muscles of the larynx. The cardiac nerve is part of the sympathetic innervation of the heart.

The majority of blood supply to the left atrium and left ventricle is provided by the left coronary artery. The septal branches and left circumflex artery are smaller divisions of this main artery. The posterior descending artery supplies the posterior one-third of the interventricular septum.

The nurse is most likely palpating the abdominal aorta. This vessel is large, generally 2.5-4 cm in diameter, and a strong pulse can often be felt on palpation. The femoral artery is also an area where a pulse may be felt, but it is only palpable in the mid-inguinal point of the inner thigh. The exterior iliac artery branches off of the abdominal aorta below the umbilicus, and the inferior mesenteric artery is a minor artery and is not generally palpable on examination.