The Heart and Vascular System for Phlebotomy

Concepts covering heart layers, the cardiac cycle, circulation, blood composition, hemostasis, and phlebotomy-specific equipment and procedures.

Pericardium

A thin, fluid-filled sac that surrounds the heart.

Epicardium

The thin outer layer of the heart.

Myocardium

The middle muscle layer of the heart.

Endocardium

The thin inner layer of the heart.

Cardiac cycle

One complete contraction (systole) and relaxation (diastole) of the heart, which lasts about $0.8$ second.

First heart sound ("lubb")

The sound produced when the ventricles contract and the AV valves close.

Second heart sound ("dupp")

The sound produced when the ventricles relax and the semilunar valves close.

Cardiac output

The volume of blood pumped by the heart in $1$ minute.

Pulmonary circulation

The circuit that carries blood from the right ventricle (RV) of the heart to the lungs and returns oxygenated blood to the left atrium (LA).

Systemic circulation

The circuit that carries oxygenated blood and nutrients from the left ventricle (LV) to body cells and returns deoxygenated blood to the right atrium (RA).

Venules

Small veins that join capillaries.

Capillaries

Microscopic, one-cell-thick vessels that connect arterioles and veins, serving as the site of gas exchange between blood and body tissues.

Antecubital fossa

A shallow depression in the arm anterior to and below the bend of the elbow; it is the site of major veins and the first choice for venipuncture.

Plasma

The liquid portion of blood ($55\%$ of volume) consisting of $90\%$ water, gases ($O_2$, $CO_2$, $N$), minerals ($Na$, $K$, $Ca$, $Mg$), proteins, and other substances.

Antigen

A carbohydrate or protein with a particular shape on the surface of red blood cells that determines blood type.

Antibodies

Proteins made by the body in response to foreign antigens, directed at the opposite blood type.

Agglutinate

To clump together; this occurs when red blood cells react to a blood transfusion of the wrong type.

Hemolyze

The process of rupturing red blood cells.

Serum

The fluid portion of blood remaining after clotting; it does not contain fibrinogen because it was used up in the clotting process.

Plasma (Specimen)

The fluid portion of whole blood separated from the cells by centrifugation; it contains fibrinogen and must be collected in an anticoagulant tube.

Hemostasis

The arrest or stoppage of bleeding after injury as a body response, involving vasoconstriction, platelet plug formation, blood clotting, and fibrinolysis.

Fibrinolysis

The ongoing process by which fibrin is dissolved, removing hemostatic clots from tissue as healing occurs.

Antiseptics

Substances that prevent sepsis (microorganisms or their toxins in the blood) and are safe on human skin, such as $70\%$ isopropyl alcohol.

Disinfectants

Chemicals used to remove or kill microorganisms on surfaces and instruments; they are not safe on human skin.

Anticoagulants

Substances that prevent blood from clotting by either precipitating calcium or inhibiting the formation of thrombin.

Ethylenediaminetetraacetic acid (EDTA)

A type of anticoagulant commonly found in lavender-top tubes.

Sodium citrate tubes

Light blue-top tubes containing a $9:1$ ratio of blood to anticoagulant that must be filled to within $90\%$ of volume for accurate results.

Clot Activators

Substances like glass (silica) particles, inert clays (Celite), or thrombin that provide more surface for platelet activation and enhance coagulation.

Thixotropic gel separator

A gel with a density between that of cells and serum/plasma that prevents cells from continuing to metabolize substances after centrifugation.

CLSI Order of Draw

The standard sequence for collecting blood tubes: 1. Blood culture (SPS), 2. Sodium citrate (Lt. Blue), 3. Serum tube (Red/SST), 4. Heparin (Green/PST), 5. EDTA (Lavender), 6. Sodium fluoride/potassium oxalate (Gray).