Blood also picks up cellular wastes and byproducts, and transports them to various organs for removal. For instance, blood moves carbon dioxide to the lungs for exhalation from the body, and various waste products are transported to the kidneys and liver for excretion from the body in the form of urine or bile. Many types of WBCs protect the body from external threats, such as disease-causing bacteria that have entered the bloodstream in a wound.
Other WBCs seek out and destroy internal threats, such as cells with mutated DNA that could multiply to become cancerous, or body cells infected with viruses. When damage to the vessels results in bleeding, blood platelets and certain proteins dissolved in the plasma, the fluid portion of the blood, interact to block the ruptured areas of the blood vessels involved.
This protects the body from further blood loss. Recall that body temperature is regulated via a classic negative-feedback loop. If you were exercising on a warm day, your rising core body temperature would trigger several homeostatic mechanisms, including increased transport of blood from your core to your body periphery, which is typically cooler. As blood passes through the vessels of the skin, heat would be dissipated to the environment, and the blood returning to your body core would be cooler.
In contrast, on a cold day, blood is diverted away from the skin to maintain a warmer body core. In extreme cases, this may result in frostbite. Blood also helps to maintain the chemical balance of the body. Proteins and other compounds in blood act as buffers, which thereby help to regulate the pH of body tissues.
Blood also helps to regulate the water content of body cells. Bottom: erythrocytes RBCs , which consist of hematocrit volume of erythrocytes. You have probably had blood drawn from a superficial vein in your arm, which was then sent to a lab for analysis.
Some of the most common blood tests—for instance, those measuring lipid or glucose levels in plasma—determine which substances are present within blood and in what quantities. Other blood tests check for the composition of the blood itself, including the quantities and types of formed elements.
One such test, called a hematocrit , measures the percentage of RBCs, clinically known as erythrocytes, in a blood sample.
It is performed by spinning the blood sample in a specialized centrifuge, a process that causes the heavier elements suspended within the blood sample to separate from the lightweight, liquid plasma Figure 1.
Because the heaviest elements in blood are the erythrocytes, these settle at the very bottom of the hematocrit tube. Located above the erythrocytes is a pale, thin layer composed of the remaining formed elements of blood.
These are the WBCs, clinically known as leukocytes, and the platelets, cell fragments also called thrombocytes. This layer is referred to as the buffy coat because of its color; it normally constitutes less than 1 percent of a blood sample.
Above the buffy coat is the blood plasma, normally a pale, straw-colored fluid, which constitutes the remainder of the sample. Figure 1. The cellular elements of blood include a vast number of erythrocytes and comparatively fewer leukocytes and platelets. Plasma is the fluid in which the formed elements are suspended. A sample of blood spun in a centrifuge reveals that plasma is the lightest component.
It floats at the top of the tube separated from the heaviest elements, the erythrocytes, by a buffy coat of leukocytes and platelets. Hematocrit is the percentage of the total sample that is comprised of erythrocytes. Depressed and elevated hematocrit levels are shown for comparison. The volume of erythrocytes after centrifugation is also commonly referred to as packed cell volume PCV.
In normal blood, about 45 percent of a sample is erythrocytes. The hematocrit of any one sample can vary significantly, however, about 36—50 percent, according to gender and other factors.
Normal hematocrit values for females range from 37 to 47, with a mean value of 41; for males, hematocrit ranges from 42 to 52, with a mean of The layer containing the leukocytes and platelets is referred to as the buffy coat because of its color; it normally constitutes less than 1 percent of a blood sample.
Above the buffy coat is the blood plasma, normally a pale, straw-colored fluid matrix, that constitutes the remainder of the sample. The hematocrit test allows one to measure the volume of erythrocytes after centrifugation and the result is also commonly referred to as packed cell volume PCV.
In normal blood, about 45 percent of a sample is erythrocytes. The hematocrit of any one sample can vary significantly, ranging from 37—52 percent based on sex and other factors. Normal hematocrit values for females range from 37 to 47 percent, with a mean value of 41 percent; for males, hematocrit values range from 42 to 52 percent, with a mean of 47 percent.
The percentage of other formed elements, the leukocytes and platelets, is extremely small so it is not normally considered with the hematocrit. Thus the mean plasma percentage is the percent of blood that is not erythrocytes: for females, it is approximately 59 percent or minus 41 percent , and for males, it is approximately 53 percent or minus 47 percent. When you think about blood, the first characteristic that probably comes to mind is its color. Blood that has just taken up oxygen in the lungs is bright red, and blood that has released oxygen in the tissues is a more dusky red.
This is because hemoglobin is a pigment that changes color depending upon the degree of oxygen saturation. Blood is viscous and somewhat sticky to the touch. It has a viscosity approximately five times greater than water.
The viscosity of blood has a dramatic impact on blood pressure and flow. Consider the difference in flow between water and honey. The more viscous honey would demonstrate a greater resistance to flow than the less viscous water.
The same principle applies to blood. Although the surface of blood vessels is relatively smooth, as blood flows through them, it experiences some friction and resistance, especially as vessels age and lose their elasticity, thereby producing heat.
This accounts for its slightly higher temperature. The pH of blood averages about 7. At an average pH of 7. Blood contains numerous buffers that contribute to the regulation of pH. Blood constitutes approximately 8 percent of adult body weight. Adult males typically average about 5 to 6 liters of blood. Females average 4 to 5 liters.
Like other fluids in the body, plasma is composed primarily of water; in fact, it is about 92 percent water. Dissolved or suspended within this water is a mixture of substances, most of which are proteins. There are literally hundreds of substances dissolved or suspended in the plasma, although many of them are found only in very small quantities. About 7 percent of the volume of plasma—nearly all that is not water—is made of proteins. These include several plasma proteins proteins that are unique to the plasma , plus a much smaller number of regulatory proteins, including enzymes and some hormones.
In addition to proteins, plasma contains a wide variety of other substances. These include various electrolytes, such as sodium, potassium, and calcium ions; dissolved gases, such as oxygen, carbon dioxide, and nitrogen; various organic nutrients, such as vitamins, lipids, glucose, and amino acids; and metabolic wastes.
All of these non-protein solutes combined contribute approximately 1 percent to the total volume of plasma. When more than a few drops of blood are required, phlebotomists perform a venipuncture, typically of a surface vein in the arm. They perform a capillary stick on a finger, an earlobe, or the heel of an infant when only a small quantity of blood is required. An arterial stick is collected from an artery and used to analyze blood gases. After collection, the blood may be analyzed by medical laboratories or perhaps used for transfusions, donations, or research.
While many allied health professionals practice phlebotomy, the American Society of Phlebotomy Technicians issues certificates to individuals passing a national examination, and some large labs and hospitals hire individuals expressly for their skill in phlebotomy.
Medical or clinical laboratories employ a variety of individuals in technical positions:. They perform a wide variety of tests on various body fluids, including blood. The information they provide is essential to the primary care providers in determining a diagnosis and in monitoring the course of a disease and response to treatment. Medical laboratory assistants MLA spend the majority of their time processing samples and carrying out routine assignments within the lab.
Clinical training is required, but a degree may not be essential to obtaining a position. They are formed mostly in the red bone marrow not within the blood itself and one of them, platelets, are circulating fragments of a much larger cell so referring to them as cells even thrombocytes is a misnomer.
It is for this reason that this group is not labeled as cellular components of blood. Erythrocytes function to carry oxygen through the bloodstream so it may be delivered throughout the body. There are several different types of leukocytes that have unique functions contributing to the body's housekeeping and sickness fighting efforts.
Platelets function in helping to maintain blood volume a process called hemostasis by forming blood clots to prevent blood loss. Each category of formed element is covered in more detail in a dedicated section of this chapter.
Exit capillaries and move into tissues; lifespan of usually a few hours or days. Phagocytic; particularly effective against bacteria; Release cytotoxic chemicals from granules. Phagocytic cells; effective with antigen-antibody complexes; release antihistamines; increase in allergies and parasitic infections. Nucleus generally two-lobed but difficult to see due to presence of heavy, dense, dark purple granules. Lack abundant granules in cytoplasm; have a simple-shaped nucleus that may be indented.
Primarily specific adaptive immunity: T cells directly attack other cells; B cells release antibodies; natural killer cells are like T cells but nonspecific. Initial cells originate in bone marrow, but secondary production occurs in lymphatic tissue; several distinct subtypes; memory cells form after exposure to a pathogen and rapidly increase responses to subsequent exposure; lifespan of many years.
Very effective phagocytic cells engulfing pathogens or worn-out cells; also serve as antigen- presenting cells APCs for other components of the immune system.
Produced in red bone marrow; referred to as macrophages after leaving circulation. Cellular fragments surrounded by a plasma membrane and containing granules; purple stain. Formed from megakaryocytes that remain in the red bone marrow and shed platelets into circulation.
In addition to measuring the hematocrit, a very common blood test is a complete blood count or CBC with differential. A small amount of blood is taken and smeared onto a gridded microscope slide and then stained to allow for proper examination under a microscope. A trained technician will then view the blood under the microscope and count the numbers of each different type of formed element visible. The report includes numbers for each specific type of leukocyte for the differential portion, along with some other information about the sizes, shapes, and characteristics of each element.
Learn Site. What is Blood? Blood has five main functions. Oxygen is an essential ingredient in the aerobic cellular respiration carried out by the cells of the human body. We get oxygen from the air we inhale, and red blood cells transport this oxygen from the lungs to the rest of the body.
Carbon dioxide is produced as a waste product of cellular respiration, and it is deposited into the blood, so it can be brought to the lungs and exhaled. Blood transports hormones and nutrients throughout the body. As we digest food, the villi of the small intestines absorb nutrients into the blood. Blood also transports waste substances to the kidneys and liver, which remove them and process them for elimination. Blood regulates body temperature. When the body needs to warm up or cool down, the circulatory system plays an important role.
This is called vasodilation. Blood protects the body from pathogens. Some white blood cells are specialized to engulf bacteria and other pathogens through a process called phagocytosis. Blood clots to prevent blood loss at sites of injury. When a blood vessel tears, platelets in the area activate, connecting with other platelets to form a plug to prevent further blood loss. These platelets release enzymes that help a blood clot form.
Blood cells are produced within red bone marrow. There are five types of white blood cells: neutrophils, basophils, eosinophils, monocytes, and lymphocytes.
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