Circulatory System - NCLEX-PN

Macrophages consume bacteria, cancer cells, and cellular debris via phagocytosis. Once these elements are within the cell, the macrophage is able to use lysosomes to break them down and prepare them for release into the blood as waste, which will eventually be excreted.

Platelets are small cell fragments that play an important role in hemostasis, or clot formation. Once activated, platelets release clotting factors that recruit more platelets till a clot is formed and bleeding stops.

Diapedesis, also known as leukocyte extravasation, is the process by which white blood cells move into and out of blood vessels. This process includes four stages: chemoattraction, rolling adhesion, tight adhesion, and endothelial transmigration. This process is integral in the delivery of white blood cells to sites of infection and in their return into the blood stream to mobilize and facilitate the excretion of waste.

Neutrophils, eosinophils, and basophils are all granulocytes, meaning they contain visible granules within their cytoplasms. These granules contains acids and antimicrobial enzymes, and are released at the site of infection. Monocytes and lymphocytes are agranulocytes, meaning they do not contain granules in their cytoplasm but rather destroy foreign proteins by other means, such as phagocytosis and cytotoxicity.

Platelets are derived from megakaryocytes, cells produced in bone marrow, kidney, liver, and spleen, with large, lobed nuclei. Platelets are formed within the cell and then released into plasma. Erythrocytes (mature red blood cells), plasma cells (a type of B cell) and progranulocytes (precursors to neutrophils, basophils, and eosinophils) take no part in the creation of platelets, which are fragments of cells, not whole cells.

The average adult body contains 4.5-6 liters of blood, depending on size and gender. Blood volume (BV) can be calculated by the following formula, given the hematocrit (HC) and plasma volume (PV):

The three main types of proteins in the blood are albumin, globulin, and fibrinogen. Major histocompatibility complex is not a free plasma protein, but rather a class of proteins found on the surface of all nucleated cells (MHC class I) and on the surface of certain immune cells known as antigen-presenting cells (MHC class II). They play an important part in immune function by displaying foreign antigens for communication between leukocytes.

The only anucleate blood cells are erythrocytes, or red blood cells. These cells are created with nuclei, but each daughter cell will then lose its nucleus in order to create more suface area for hemoglobin to bind oxygen and for easier passage through narrow capillaries.

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.

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.

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 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.

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.

Sympathetic innervation will decrease the heart rate, which will automatically decrease the cardiac output

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.