Chapter 5 Integumentary Multiple Choice System Review Answers

xviii.four Leukocytes and Platelets

Learning Objectives

By the end of this section, you lot will be able to:

Classify and characterize leukocytes (white blood cells)

• Depict the full general characteristics of leukocytes
• Classify leukocytes co-ordinate to their lineage, their primary structural features, and their master functions
• Discuss the most common malignancies involving leukocytes
• Place the lineage, bones structure, and function of platelets

The leukocyte, usually known as a white blood cell (WBC), is a major component of the body's defenses against disease. Leukocytes protect the trunk against invading microorganisms and trunk cells with mutated DNA, and they clean upwards debris. Platelets are essential for the repair of blood vessels when impairment has occurred; they too provide growth factors for healing and repair. See Chapter xviii.3 Erythrocytes for a summary of leukocytes and platelets.

Characteristics of Leukocytes

Although leukocytes and erythrocytes both originate from hematopoietic stem cells in the bone marrow, they are very dissimilar from each other in many meaning means. For instance, leukocytes are far less numerous than erythrocytes: Typically there are only 5000 to 10,000 per µL. They are also larger than erythrocytes and are the only formed elements that are consummate cells, possessing a nucleus and organelles. And although there is just 1 type of erythrocyte, there are many types of leukocytes. Most of these types accept a much shorter lifespan than that of erythrocytes, some equally short every bit a few hours or even a few minutes in the example of acute infection.

I of the about distinctive characteristics of leukocytes is their movement. Whereas erythrocytes spend their days circulating within the claret vessels, leukocytes routinely leave the bloodstream to perform their defensive functions in the body'southward tissues. For leukocytes, the vascular network is a highway they travel and so exit to reach their destination. These cells are sometimes given distinct names depending on their function, such as macrophage or microglia, . As shown in Effigy 18.4.ane, they leave the capillaries—the smallest blood vessels—or other modest vessels through a procedure known as emigration (from the Latin for "removal") or diapedesis (dia- = "through"; -pedan = "to jump") in which they squeeze through side by side cells in a claret vessel wall.

One time they take exited the capillaries, some leukocytes will take upward fixed positions in lymphatic tissue, os marrow, the spleen, the thymus, or other organs. Others will move most through the tissue spaces very much like amoebas, continuously extending their plasma membranes, sometimes wandering freely, and sometimes moving toward the direction in which they are drawn by chemical signals. This alluring of leukocytes occurs because of positive chemotaxis (literally "movement in response to chemicals"), a phenomenon in which injured or infected cells and nearby leukocytes emit the equivalent of a chemic "emergency" call, attracting more than leukocytes to the site. In clinical medicine, the differential counts of the types and percentages of leukocytes present are oft key indicators in making a diagnosis and selecting a treatment.

Figure 18.4.i – Emigration: Leukocytes go out the blood vessel and then motion through the connective tissue of the dermis toward the site of a wound. Some leukocytes, such equally the eosinophil and neutrophil, are characterized every bit granular leukocytes. They release chemicals from their granules that destroy pathogens; they are also capable of phagocytosis. The monocyte, an agranular leukocyte, differentiates into a macrophage that then phagocytizes the pathogens.

Classification of Leukocytes

When scientists first began to observe stained claret slides, it quickly became axiomatic that leukocytes could exist divided into two groups, according to whether their cytoplasm contained highly visible granules:

• Granular leukocytes contain arable granules inside the cytoplasm. They include neutrophils, eosinophils, and basophils (you can view their lineage from myeloid stem cells in Affiliate 18.2 Production of Formed Elements).
• While granules are non totally lacking in agranular leukocytes, they are far fewer and less obvious. Agranular leukocytes include monocytes, which mature into macrophages that are phagocytic, and lymphocytes, which arise from the lymphoid stem cell line.

Granular Leukocytes

Nosotros will consider the granular leukocytes in order from nigh mutual to least common. All of these are produced in the red bone marrow and have a short lifespan of hours to days. They typically have a lobed nucleus and are classified according to which type of stain best highlights their granules (Figure 18.4.2).

Effigy eighteen.four.2 – Granular Leukocytes: A neutrophil has pocket-size granules that stain light lilac and a nucleus with two to five lobes. An eosinophil's granules are slightly larger and stain ruddy-orange, and its nucleus has two to three lobes. A basophil has large granules that stain night blue to royal and a two-lobed nucleus.

The most common of all the leukocytes, neutrophils will ordinarily comprise l–70 percentage of total leukocyte count. They are 10–12 µm in diameter, significantly larger than erythrocytes. They are chosen neutrophils because their granules show up most conspicuously with stains that are chemically neutral (neither acidic nor basic). The granules are numerous but quite fine and commonly appear calorie-free lilac. The nucleus has a distinct lobed appearance and may have two to 5 lobes, the number increasing with the age of the cell. Older neutrophils take increasing numbers of lobes and are ofttimes referred to as polymorphonuclear (a nucleus with many forms), or simply "polys." Younger and young neutrophils begin to develop lobes and are known equally "bands."

Neutrophils are rapid responders to the site of infection and are efficient phagocytes with a preference for leaner. Their granules include lysozyme, an enzyme capable of lysing, or breaking down, bacterial prison cell walls; oxidants such equally hydrogen peroxide; and defensins, proteins that bind to and puncture bacterial and fungal plasma membranes, and so that the cell contents leak out. Abnormally high counts of neutrophils indicate infection and/or inflammation, particularly triggered by leaner, but are besides establish in fire patients and others experiencing unusual stress. A fire injury increases the proliferation of neutrophils in order to fight off infection that tin can result from the destruction of the bulwark of the skin. Depression counts may be caused by drug toxicity and other disorders, and may increase an private's susceptibility to infection.

Eosinophils typically correspond 2–4 percent of total leukocyte count. They are also 10–12 µm in diameter. The granules of eosinophils stain all-time with an acidic stain known as eosin. The nucleus of the eosinophil will typically have two to three lobes and, if stained properly, the granules will have a distinct carmine to orangish color.

The granules of eosinophils include antihistamine molecules, which counteract the activities of histamines, inflammatory chemicals produced by basophils and mast cells. Some eosinophil granules comprise molecules toxic to parasitic worms, which can enter the torso through the integument, or when an individual consumes raw or undercooked fish or meat. Eosinophils are also capable of phagocytosis and are peculiarly effective when antibodies bind to the target and class an antigen-antibody circuitous. High counts of eosinophils are typical of patients experiencing allergies, parasitic worm infestations, and some autoimmune diseases. Depression counts may be due to drug toxicity and stress.

Basophils are the to the lowest degree mutual leukocytes, typically comprising less than one percent of the total leukocyte count. They are slightly smaller than neutrophils and eosinophils at 8–10 µm in diameter. The granules of basophils stain best with basic (alkaline) stains. Basophils contain large granules that pick upward a dark blue stain and are so common they may make it difficult to see the 2-lobed nucleus.

In general, basophils intensify the inflammatory response. They share this trait with mast cells. In the past, mast cells were considered to be basophils that left the circulation. Withal, this appears not to be the case, as the two cell types develop from dissimilar lineages.

The granules of basophils release histamines, which contribute to inflammation, and heparin, which opposes blood clotting. High counts of basophils are associated with allergies, parasitic infections, and hypothyroidism. Depression counts are associated with pregnancy, stress, and hyperthyroidism.

Agranular Leukocytes

Agranular leukocytes contain smaller, less-visible granules in their cytoplasm than practise granular leukocytes. The nucleus is simple in shape, sometimes with an indentation but without distinct lobes. There are two major types of agranulocytes: lymphocytes and monocytes (see Effigy i; chapter xviii.3).

Lymphocytes are the only formed element of blood that arises from lymphoid stem cells. Although they form initially in the os marrow, much of their subsequent development and reproduction occurs in the lymphatic tissues. Lymphocytes are the 2d most mutual type of leukocyte, bookkeeping for about 20–30 pct of all leukocytes, and are essential for the immune response. The size range of lymphocytes is quite extensive, with some authorities recognizing two size classes and others iii. Typically, the large cells are 10–14 µm and have a smaller nucleus-to-cytoplasm ratio and more granules. The smaller cells are typically half dozen–9 µm with a larger volume of nucleus to cytoplasm, creating a "halo" issue. A few cells may fall outside these ranges, at 14–17 µthousand. This finding has led to the three size range classification.

The iii major groups of lymphocytes include natural killer cells, B cells, and T cells. Natural killer (NK) cells are capable of recognizing cells that practise not express "self" proteins on their plasma membrane or that contain strange or aberrant markers. These "nonself" cells include cancer cells, cells infected with a virus, and other cells with atypical surface proteins. Thus, they provide generalized, nonspecific immunity. The larger lymphocytes are typically NK cells.

B cells and T cells, also called B lymphocytes and T lymphocytes, play prominent roles in defending the body against specific pathogens (disease-causing microorganisms) and are involved in specific immunity. One class of B cells (plasma cells) produces the antibodies or immunoglobulins that demark to specific foreign or aberrant components of plasma membranes. This is as well referred to as humoral (body fluid) immunity. T cells provide cellular-level amnesty by physically attacking foreign or diseased cells. A memory cell is a multifariousness of both B and T cells that forms later on exposure to a pathogen and mounts rapid responses upon subsequent exposures. Different other leukocytes, memory cells alive for many years. B cells undergo a maturation process in the bi marrow, whereas T cells undergo maturation in the thymus. This site of the maturation procedure gives rising to the name B and T cells. The functions of lymphocytes are complex and will be covered in detail in the affiliate roofing the lymphatic system and immunity. Smaller lymphocytes are either B or T cells, although they cannot exist differentiated in a normal blood smear.

Abnormally high lymphocyte counts are feature of viral infections also every bit some types of cancer. Abnormally low lymphocyte counts are characteristic of prolonged (chronic) illness or immunosuppression, including that acquired by HIV infection and drug therapies that ofttimes involve steroids.

Monocytes originate from myeloid stem cells. They commonly represent 2–8 percentage of the full leukocyte count. They are typically hands recognized past their large size of 12–xx µm and indented or horseshoe-shaped nuclei. Macrophages are monocytes that accept left the apportionment and phagocytize debris, foreign pathogens, worn-out erythrocytes, and many other expressionless, worn out, or damaged cells. Macrophages also release antimicrobial defensins and chemotactic chemicals that concenter other leukocytes to the site of an infection. Some macrophages occupy fixed locations, whereas others wander through the tissue fluid.

Abnormally high counts of monocytes are associated with viral or fungal infections, tuberculosis, and some forms of leukemia and other chronic diseases. Abnormally depression counts are typically caused by suppression of the bone marrow.

Lifecycle of Leukocytes

Most leukocytes have a relatively short lifespan, typically measured in hours or days. Production of all leukocytes begins in the bone marrow under the influence of colony-stimulating factors (CSFs) and interleukins. Secondary production and maturation of lymphocytes occurs in specific regions of lymphatic tissue known as germinal centers. Lymphocytes are fully capable of mitosis and may produce clones of cells with identical properties. This chapters enables an private to maintain immunity throughout life to many threats that accept been encountered in the past.

Disorders of Leukocytes

Leukopenia is a status in which too few leukocytes are produced. If this condition is pronounced, the individual may be unable to ward off disease. Excessive leukocyte proliferation is known as leukocytosis. Although leukocyte counts are loftier, the cells themselves are oftentimes nonfunctional, leaving the private at increased risk for illness.

Leukemia is a cancer involving an abundance of leukocytes. It may involve only one specific type of leukocyte from either the myeloid line (myelocytic leukemia) or the lymphoid line (lymphocytic leukemia). In chronic leukemia, mature leukocytes accrue and fail to dice. In acute leukemia, there is an overproduction of young, young leukocytes. In both conditions the cells do non office properly.

Lymphoma is a form of cancer in which masses of malignant T and/or B lymphocytes collect in lymph nodes, the spleen, the liver, and other tissues. As in leukemia, the malignant leukocytes practise non function properly, and the patient is vulnerable to infection. Some forms of lymphoma tend to progress slowly and reply well to treatment. Others tend to progress chop-chop and require aggressive treatment, without which they are rapidly fatal.

Platelets

Yous may occasionally run into platelets referred to every bit thrombocytes, just because this proper name suggests they are a type of jail cell, information technology is not accurate. A platelet is not a cell but rather a fragment of the cytoplasm of a cell chosen a megakaryocyte that is surrounded past a plasma membrane. Megakaryocytes are descended from myeloid stalk cells (see Chapter 18.2 Production of the Formed Elements) and are big, typically 50–100 µyard in diameter, and comprise an enlarged, lobed nucleus. As noted earlier, thrombopoietin, a glycoprotein secreted by the kidneys and liver, stimulates the proliferation of megakaryoblasts, which mature into megakaryocytes. These remain inside os marrow tissue (Figure xviii.4.3) and ultimately grade platelet-precursor extensions that extend through the walls of bone marrow capillaries to release into the apportionment thousands of cytoplasmic fragments, each enclosed past a bit of plasma membrane. These enclosed fragments are platelets. Each megakarocyte releases 2000–3000 platelets during its lifespan. Following platelet release, megakaryocyte remnants, which are little more than a cell nucleus, are consumed by macrophages.

Platelets are relatively modest, 2–4 µm in diameter, but numerous, with typically 150,000–160,000 per µL of blood. After inbound the circulation, approximately one-third migrate to the spleen for storage for later release in response to any rupture in a claret vessel. They so become activated to perform their primary part, which is to limit claret loss. Platelets remain but most 10 days, and so are phagocytized by macrophages.

Platelets are disquisitional to hemostasis, the stoppage of blood menses following damage to a vessel. They too secrete a variety of growth factors essential for growth and repair of tissue, especially connective tissue. Infusions of concentrated platelets are now being used in some therapies to stimulate healing.

Disorders of Platelets

Thrombocytosis is a status in which at that place are too many platelets. This may trigger germination of unwanted blood clots (thrombosis), a potentially fatal disorder. If at that place is an insufficient number of platelets, called thrombocytopenia, blood may not clot properly, and excessive bleeding may event.

Figure 18.iv.three – Platelets: Platelets are derived from cells called megakaryocytes.

Figure 18.4.4 – Leukocytes (Micrographs provided by the Regents of University of Michigan Medical Schoolhouse © 2012)

External Website

View University of Michigan Webscopes at
http://virtualslides.med.umich.edu/Histology/Cardiovascular%20System/081-2_HISTO_40X.svs/view.apml?cwidth=860&cheight=733&chost=virtualslides.med.umich.edu&listview=1&title=&csis=1 and explore the claret slides in greater item. The Webscope feature allows you to movement the slides as yous would with a mechanical stage. You tin increment and decrease the magnification. At that place is a chance to review each of the leukocytes individually after you have attempted to identify them from the first two blood smears. In addition, in that location are a few multiple choice questions.

Are y'all able to recognize and place the various formed elements? Yous volition need to do this is a systematic fashion, scanning along the epitome. The standard method is to apply a filigree, but this is not possible with this resource. Try constructing a elementary tabular array with each leukocyte type and so making a mark for each prison cell type y'all identify. Attempt to allocate at least 50 and perhaps as many every bit 100 different cells. Based on the percentage of cells that you lot count, do the numbers stand for a normal blood smear or does something announced to exist aberrant?

Chapter Review

Leukocytes function in trunk defenses. They squeeze out of the walls of blood vessels through emigration or diapedesis, then may move through tissue fluid or get attached to various organs where they fight against pathogenic organisms, diseased cells, or other threats to health. Granular leukocytes, which include neutrophils, eosinophils, and basophils, originate with myeloid stem cells, equally do the agranular monocytes. The other agranular leukocytes, NK cells, B cells, and T cells, arise from the lymphoid stem jail cell line. The most arable leukocytes are the neutrophils, which are first responders to infections, especially with bacteria. Almost 20–30 percentage of all leukocytes are lymphocytes, which are disquisitional to the body's defense confronting specific threats. Leukemia and lymphoma are malignancies involving leukocytes. Platelets are fragments of cells known equally megakaryocytes that dwell within the bone marrow. While many platelets are stored in the spleen, others enter the circulation and are essential for hemostasis; they also produce several growth factors important for repair and healing.

Interactive Link Questions

Figure 18.iv.4 Are you able to recognize and place the various formed elements? Y'all will need to practise this is a systematic manner, scanning along the image. The standard method is to use a grid, but this is not possible with this resource. Try constructing a simple tabular array with each leukocyte type and and so making a mark for each prison cell type you identify. Effort to classify at to the lowest degree l and perhaps equally many as 100 different cells. Based on the percentage of cells that you count, do the numbers correspond a normal claret smear or does something appear to exist abnormal?

Figure 18.4.4 This should appear to be a normal blood smear.

Review Questions

Critical Thinking Questions

1. One of the more mutual adverse furnishings of cancer chemotherapy is the destruction of leukocytes. Before his next scheduled chemotherapy treatment, a patient undergoes a blood examination called an absolute neutrophil count (ANC), which reveals that his neutrophil count is 1900 cells per microliter. Would his healthcare team exist likely to continue with his chemotherapy treatment? Why?

2. A patient was admitted to the burn unit of measurement the previous evening suffering from a astringent fire involving his left upper extremity and shoulder. A blood test reveals that he is experiencing leukocytosis. Why is this an expected finding?

Glossary

agranular leukocytes

leukocytes with few granules in their cytoplasm; specifically, monocytes, lymphocytes, and NK cells

B lymphocytes

(also, B cells) lymphocytes that defend the body against specific pathogens and thereby provide specific immunity

basophils

granulocytes that stain with a basic (element of group i) stain and store histamine and heparin

defensins

antimicrobial proteins released from neutrophils and macrophages that create openings in the plasma membranes to kill cells

diapedesis

(also, emigration) process past which leukocytes squeeze through next cells in a blood vessel wall to enter tissues

emigration

(also, diapedesis) process by which leukocytes squeeze through adjacent cells in a blood vessel wall to enter tissues

eosinophils

granulocytes that stain with eosin; they release antihistamines and are specially active confronting parasitic worms

granular leukocytes

leukocytes with abundant granules in their cytoplasm; specifically, neutrophils, eosinophils, and basophils

leukemia

cancer involving leukocytes

leukocyte

(also, white claret cell) colorless, nucleated blood cell, the chief function of which is to protect the body from disease

leukocytosis

excessive leukocyte proliferation

leukopenia

below-normal production of leukocytes

lymphocytes

agranular leukocytes of the lymphoid stem prison cell line, many of which function in specific immunity

lymphoma

form of cancer in which masses of malignant T and/or B lymphocytes collect in lymph nodes, the spleen, the liver, and other tissues

lysozyme

digestive enzyme with bactericidal backdrop

megakaryocyte

bone marrow prison cell that produces platelets

memory prison cell

blazon of B or T lymphocyte that forms afterwards exposure to a pathogen

monocytes

agranular leukocytes of the myeloid stalk jail cell line that broadcast in the bloodstream; tissue monocytes are macrophages

natural killer (NK) cells

cytotoxic lymphocytes capable of recognizing cells that do not express "self" proteins on their plasma membrane or that comprise foreign or abnormal markers; provide generalized, nonspecific amnesty

neutrophils

granulocytes that stain with a neutral dye and are the near numerous of the leukocytes; especially active against bacteria

polymorphonuclear

having a lobed nucleus, as seen in some leukocytes

positive chemotaxis

process in which a jail cell is attracted to move in the direction of chemical stimuli

T lymphocytes

(also, T cells) lymphocytes that provide cellular-level immunity past physically attacking foreign or diseased cells

thrombocytes

platelets, ane of the formed elements of blood that consists of cell fragments cleaved off from megakaryocytes

thrombocytopenia

status in which there are too few platelets, resulting in abnormal bleeding (hemophilia)

thrombocytosis

condition in which at that place are as well many platelets, resulting in abnormal clotting (thrombosis)

Solutions

Answers for Critical Thinking Questions

1. A neutrophil count below 1800 cells per microliter is considered abnormal. Thus, this patient's ANC is at the low end of the normal range and there would exist no reason to filibuster chemotherapy. In clinical practice, near patients are given chemotherapy if their ANC is above 1000.
2. Whatever severe stress can increase the leukocyte count, resulting in leukocytosis. A burn down is especially likely to increase the proliferation of leukocytes in order to ward off infection, a significant risk when the barrier function of the skin is destroyed.

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