The term blood volume refers to the total volume of blood in the body. Blood volume consists of the volume of blood plasma and the volume of cellular blood components.
What is blood volume?
The term blood volume refers to the total amount of blood in the body. The total amount of blood in the body is referred to as blood volume. Blood can be divided into two parts. First, there is the plasma volume. It corresponds to the blood volume without the blood cells. About 55 percent of the blood consists of blood plasma. 90 percent of the blood plasma in turn consists of water. The remaining 10 percent consists of dissolved substances. Important dissolved substances include electrolytes such as sodium, chloride, potassium, calcium, magnesium, bicarbonate and phosphates. Plasma proteins such as albumin, lipoproteins, immunoglobulins and fibrinogen are also components of blood plasma. Blood plasma also contains hormones and nutrients such as glucose. Likewise, breakdown products from metabolism are found in blood plasma. These include pyruvate, creatinine, uric acid and lactate. Forty-five percent of the blood volume is corpuscular components. Three cell types can be distinguished among the cellular components: red blood cells (erythrocytes), white blood cells (leukocytes) and platelets (thrombocytes). By far the largest proportion, four to five million cells per µl of blood, are red blood cells. The thrombocytes form the second strongest fraction with 150,000 to 300,000 cells. In contrast, there are only 4000 to 9000 leukocytes per µl. The total blood volume in adults is four to six liters. In women, 61 milliliters of blood can be expected per kilogram of body weight. For men, it averages 70 milliliters per kilogram of body weight. Depending on the organ or compartment, blood volume can be divided into cerebral, pulmonary, intrathoracic, extrathoracic, venous and arterial. The volume of blood that the heart pumps through the systemic circulation per minute is called cardiac output.
Function and purpose
However, blood volume can also be divided according to aspects of function. The central blood volume is that portion of the blood volume that is located in the area between the pulmonary valve and the aortic valve of the heart. Thus, central blood volume is the blood volume of the left atrium, right ventricle, and pulmonary circulation. Central blood volume is a critical manipulated variable of central venous pressure. Central venous pressure is the venous blood pressure measured at the central venous catheter. Central blood volume also serves as a blood depot for the left ventricle. When there is a mismatch between the pumping power of the two ventricles, the blood depot can rapidly increase the ejection output of the left ventricle so that the mismatch can be corrected. The circulating blood volume is the volume of blood that is actually circulating at the moment. Part of the blood volume is in the low-pressure system and another is used as a blood reservoir. The circulating blood volume is mainly used for transporting substances. The blood transports nutrients, vitamins and oxygen to the body cells. At the same time, it transports harmful substances or metabolic waste products from the cells to the excretory organs. Hormones also travel from the site of production to the target cells via the circulating blood volume. The circulating blood volume also plays a role in the body’s defense against infections. Circulating blood carries white blood cells to sites of infection. Peripheral blood volume is located in the periphery of the body. Due to its heat capacity, peripheral blood volume is particularly important in maintaining body temperature. An adequate and constant blood volume also plays an important role in maintaining blood pressure in the vessels. Without a constant blood volume, organs and tissues cannot be supplied with oxygen or nutrients.
Diseases and ailments
A decrease in blood volume is called volume contraction. Blood volume can decrease due to dehydration, which is dehydration. Dehydration can be caused either by inadequate fluid intake or by pathologically increased fluid loss. Diseases of the kidneys, high fever, breastfeeding, diarrhea and vomiting can result in severe fluid losses.Excessive reduction in blood volume is noticeable by thirst, dryness of skin and mucous membranes, and decreased urine output. Low blood pressure is also a characteristic symptom of dehydration. When 12 to 15 percent of body fluid is lost, hypovolemic shock occurs. However, hypovolemic shock can have other causes. Fluid can be lost from extensive burns, for example. Hemorrhagic shock is also hypovolemic shock. Hemorrhagic shock is caused by bleeding within the body. For example, hemorrhagic shock often occurs after gastrointestinal bleeding. Traumatic hemorrhagic shock is hemorrhagic shock that occurs as a result of a traumatic event. The amount of circulating blood volume decreases due to severe fluid loss. A blood loss of one liter can still be compensated. Arterial blood pressure remains largely normal. With greater fluid loss, blood pressure drops. In the initial stages of hypovolemic shock, blood pressure is still normal. The skin is cool, moist, and pale. In the second stage, the stage of incipient decompensation, systolic blood pressure drops to less than 100 mmHg. The jugular veins are collapsed, patients have severe thirst, and urine output is greatly reduced. In the third stage, systolic blood pressure is below 60 mmHg. The pulse can barely be felt and breathing is shallow. Patients become unconscious. Renal function fails completely. Hypovolemic shock requires intensive medical treatment as soon as possible. Otherwise, it can be fatal.
