Many gases, such as room air, are composed of several gasses (in the case of room air, primarily nitrogen, oxygen, and several trace gasses). Partial pressure is the amount of pressure that each gas contributes. To find the total pressure of a gas mixture, one would find the sum of all partial pressures of each individual gas. 

Gas exchange in the alveoli occurs by the process of simple diffusion. The blood that enters the lung capillaries is relatively low in oxygen and high in , in comparison to the room air that is drawn into the alveoli during respiration. The separation between the capillaries and the alveolar epithelium is thin enough that these gasses can exchange across their pressure gradients by the process of simple diffusion.

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

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.

The S2 heart sound (sometimes referred to as the "dub" in "lub-dub") occurs in diastole, during the closing of the aortic and pulmonary valves. When pressure within the aorta and pulmonary arteries exceeds pressure within the heart, the cups of the valves fill with blood and snap shut, causing the "dub" sound.

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.

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.