Production of erythrocytes in the red bone marrow occurs at the staggering rate of more than 2 million cells per second. The most abundant formed elements in blood, erythrocytes are basically sacs packed with an oxygen-carrying compound called hemoglobin. Dissolved or suspended within this water is a mixture of substances, most of which are proteins. Like other fluids in the body, plasma is composed primarily of water. Depressed and elevated hematocrit levels are shown for comparison. Hematocrit is the percentage of the total sample that is comprised of erythrocytes. It floats at the top of the tube separated from the heaviest elements, the erythrocytes, by a buffy coat of leukocytes and platelets. A sample of blood spun in a centrifuge reveals that plasma is the lightest component. Plasma is the fluid in which the formed elements are suspended. The cellular elements of blood include a vast number of erythrocytes and comparatively fewer leukocytes and platelets. Not counting the buffy coat, which makes up less than 1% of the blood, we can estimate the mean plasma percentage to be the percent of blood that is not erythrocytes: approximately 55%.įigure 9.3 Composition of Blood. Taking synthetic testosterone can elevate it as well. One of the factors that determines hematocrit is testosterone levels, and so cisgender men tend to have higher hematocrits than cisgender women. The hematocrit of any one sample can vary significantly, however, by about 36–50 percent. In normal blood, about 45 percent of a sample is erythrocytes, which is referred to as the hematocrit. Above the buffy coat is the blood plasma, normally a pale, straw-colored fluid, which constitutes the remainder of the sample. Above the erythrocyte layer we see the buffy coat, a pale, thin layer of leukocytes and thrombocytes, which together make up less than 1% of the sample of whole blood. Erythrocytes are the heaviest elements in blood and settle at the very bottom of the tube. In the laboratory, blood samples are often centrifuged in order to separate the components of blood from one another (see the figure below). This fluid, which is mostly water, perpetually suspends the formed elements and enables them to circulate throughout the body within the cardiovascular system. The extracellular matrix, called plasma, makes blood unique among connective tissues because it is fluid. The cellular elements are referred to as the formed elements and include red blood cells (RBCs), white blood cells (WBCs), and platelets. The Composition (Anatomy) of Blood and the Functions of the Componentsīlood is a connective tissue made up of cellular elements and an extracellular matrix. Blood pressure is recorded as systolic pressure over diastolic pressure. Blood pressure is measured in mm Hg and is usually obtained from the brachial artery using a sphygmomanometer and a stethoscope. Turbulent blood flow through the vessels can be heard as a soft ticking while measuring blood pressure these sounds are known as Korotkoff sounds. The technique used today was developed more than 100 years ago by a pioneering Russian physician, Dr. Blood pressure is one of the critical parameters measured on virtually every patient in every healthcare setting. Blood pressure may be measured in capillaries and veins, as well as the vessels of the pulmonary circulation however, the general term ‘blood pressure’ refers to the pressure of blood flowing in the arteries of the systemic circulation. Blood Pressureīlood pressure is the force exerted by blood upon the walls of the blood vessels or the chambers of the heart. The arrows indicate the direction of blood flow, and the colors show the relative levels of oxygen concentration. The systemic circuit moves blood from the left side of the heart to the head and body and returns it to the right side of the heart to repeat the cycle. The pulmonary circuit moves blood from the right side of the heart to the lungs and back to the heart. Pulmonary veins then return freshly oxygenated blood from the lungs to the heart to be pumped back out into systemic circulation. In contrast, in the pulmonary circuit, arteries carry blood low in oxygen exclusively to the lungs for gas exchange. The blood returned to the heart through systemic veins has less oxygen, since much of the oxygen carried by the arteries has been delivered to the cells. Systemic arteries provide blood rich in oxygen to the body’s tissues. Physiology of the Blood Vessels and Blood Physiology of the Blood VesselsĪrteries and veins transport blood in two distinct circuits: the systemic circuit and the pulmonary circuit.
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