Histology of the Blood & Vascular Tissue

*The answer is C.* The peripheral blood smear shows reactive (antigen-stimulated) large lymphocytes. Naïve lymphocytes encounter antigen-presenting cells (macrophages and dendritic cells) in the secondary lymphoid organs. In response to this cell-cell interaction, they become activated and circulate in the vascular system, before they are recruited to a peripheral tissue. The lymphocytes in the peripheral smear shown in the image appear reactive, because they are larger than normal circulating lymphocytes and have more cytoplasm. They are commonly seen in viral infections, including infectious mononucleosis, and they are usually of T-cell lineage. None of the other leukocytes display the distinctive nuclear and cytoplasmic features of activated lymphocytes.

A 19-year-old woman presents with 5 days of fever (38°C/101°F) and sore throat. She reports that she has felt fatigued for the past week and has difficulty swallowing. Physical examination reveals cervical lymphadenopathy. A peripheral blood smear is examined. Identify the leukocytes shown in the image. (A) Basophils (B) Eosinophils (C) Lymphocytes (D) Monocytes (E) Neutrophils

*The answer is A.* These proliferative stem cell colonies are committed to the erythrocyte pathway of differentiation. Erythroid hyperplasia is typically seen in people living (or climbing) at high altitude. Low oxygen tension evokes the production of erythropoietin by the kidneys, which promotes the survival and proliferation of erythroid progenitor cells in the bone marrow. Hyperplasia is defined as an increase in the number of cells in an organ or tissue. Like hypertrophy, it is often a response to trophic signals or increased functional demand and is commonly a normal process. None of the other cells undergo physiological hyperplasia in response to low oxygen tension.

A 24-year-old mountain climber suffers massive trauma during an expedition to the Himalayan Mountains and expires. Examination of the patient's bone marrow at autopsy reveals colonies of hematopoietic stem cells (arrows, shown in the image). These proliferative "burst-forming units" are committed to which of the following pathways of stem cell differentiation? (A) Erythrocyte (B) Granulocyte (C) Lymphocyte (D) Megakaryocyte (E) Monocyte

*The answer is D.* The blood smear displays elliptical erythrocytes, as well as a normal segmented neutrophil. Neutrophils are the most abundant leukocyte present in the peripheral blood (40 to 73 relative %). Hereditary elliptocytosis (HE) refers to a heterogeneous group of inherited disorders involving the erythrocyte cytoskeleton, all of which feature an abnormality within the cytoskeleton. HE usually manifests as a mild normocytic anemia; however, many patients are asymptomatic. None of the other cells display the distinctive polymorphonuclear morphology of segmented neutrophils.

A 25-year-old pregnant woman comes to the obstetrician for a prenatal check up. Routine laboratory testing reveals a mild anemia with serum hemoglobin of 9.4 g/dL (normal reference range = 12 to 15 g/dL). Examination of a peripheral blood smear reveals elliptical erythrocytes (shown in the image). The pathologist asks you to identify the normal leukocyte in the center of the field. (A) Eosinophil (B) Monocyte (C) Basophil (D) Neutrophil (E) Lymphocyte

*The answer is C.* In addition to having central pallor, the patient's red blood cells appear significantly smaller than the nucleus of a small lymphocyte (visible in the image). The blood smear shows microcytic, hypochromic (pale) erythrocytes that are characteristic of iron deficiency anemia caused by inadequate uptake or, more often, excessive loss of iron. Women who have menorrhagia, especially those who consume restricted diets, are especially prone to iron deficiency anemia. Hyperchromic cells (choice A) display increased pigmentation. Macrocytic cells are larger than normal (choice B). Normocytic cells (choice D) display normal size and shape. Poikilocytes (choice E) are abnormally shaped erythrocytes.

A 25-year-old woman with a history of heavy menstrual periods complains of chronic fatigue. Examination of a peripheral blood smear suggests iron deficiency anemia (shown in the image). Which of the following terms appropriately describes the morphology of the patient's erythrocytes? (A) Hyperchromic (B) Macrocytic (C) Microcytic (D) Normocytic (E) Poikilocytic

*The answer is E.* This photomicrograph reveals plasma cells (arrows) and macrophages within stromal connective tissue of the endometrium. Plasma cells are mature antibody-producing B lymphocytes. They are much larger than resting lymphocytes and frequently oval in shape. A few macrophages are also visible (arrowheads). The presence of plasma cells and macrophages in a surgical biopsy or autopsy specimen provides histologic evidence of chronic inflammation. Inflammation has historically been referred to as either acute or chronic, depending on the persistence of the injury, clinical symptoms, and the nature of the inflammatory response. The cellular components of chronic inflammation are lymphocytes, antibody-producing plasma cells, and macrophages. The chronic inflammatory response is often prolonged and may be associated with aberrant repair (i.e., fibrosis). None of the other inflammatory cells exhibit the distinctive cytologic features of plasma cells.

A 34-year-old woman complains of excessive menstrual bleeding and pelvic pain of 6 months' duration. An endometrial biopsy is obtained (shown in the image). Identify the cells marked by the arrows. (A) Basophils (B) Eosinophils (C) Macrophages (D) Monocytes (E) Plasma cells

*The answer is E.* Thrombosis and hemostasis are regulated by the activation of circulating platelets and plasma clotting factors. Platelets are small cytoplasmic fragments of megakaryocytes with a life span of about 10 days. They play a critical role in maintaining the integrity of the cardiovascular system. Platelets bind to exposed fibrillar collagen at sites of endothelial cell injury and degranulate, releasing growth factors (PDGF) and vasoactive mediators (serotonin and thromboxane A2). Activated platelets also provide a substrate for the conversion of fibrinogen to insoluble fibrin. The fibrin strands are cross-linked to form a mesh that traps platelets and cells. This intravascular hemostatic plug is appropriately referred to as a thrombus.

A 35-year-old construction worker sustains a laceration on the palmar surface of her left hand. The wound is cleaned, sutured, and wrapped with sterile gauze. Which of the following formed elements of the blood initiates thrombosis and hemostasis in this patient's wound? (A) Erythrocytes (B) Granulocytes (C) Lymphocytes (D) Monocytes (E) Platelets

*The answer is C.* From top to bottom, there is plasma, buffy coat, and packed erythrocytes that result from centrifugation.

A 35-year-old woman's physician orders laboratory blood tests. Her fresh blood is drawn and centrifuged in the presence of heparin as an anticoagulant to obtain a hematocrit. From top to bottom, the fractions resulting from centrifugation are which of the following? a. Serum, packed erythrocytes, and leukocytes b. Leukocytes, erythrocytes, and serum proteins c. Plasma, buffy coat, and packed erythrocytes d. Fibrinogen, platelets, buffy coat, and erythrocytes e. Albumin, plasma lipoproteins, and erythrocytes

*The answer is D.* The peripheral blood smear shows a mature eosinophil, with a trilobed nucleus and numerous red (eosinophilic) cytoplasmic granules. Eosinophils are granulocytes that are derived from a common myeloid progenitor cell in the bone marrow. They are particularly evident during allergic-type reactions and parasitic infestations. For example, infections with Trichinella are accompanied by eosinophilia, and skeletal muscle is typically infiltrated by eosinophils. Trichinosis is produced by the roundworm Trichinella spiralis. After mating, the females liberate larvae into the circulation. The larvae can invade almost any tissue but survive only in skeletal muscle in an encapsulated form. Elevated serum levels of creatine kinase indicate muscle cell necrosis. The other cells do not exhibit distinctive red granules that are the cytologic hallmark of eosinophilic granulocytes.

A 38-year-old man presents with myalgia (muscle pain), low-grade fever, and swelling of the right calf. The patient reports recently attending a Fireman's pig roast. Laboratory data show elevated serum levels of creatine kinase. The peripheral blood smear is shown in the image. Identify the leukocyte in the center of this field. (A) Basophil (B) Eosinophil (C) Monocyte (D) Neutrophil (E) Plasma cell

*The answer is E.* Neutrophils play a role in the formation of pus. Neutrophils are cells with polymorphic, multiple lobed nuclei.

A 43-year-old anatomy professor is working in her garden, pruning rose bushes without gloves, when a thorn deeply penetrates her forefinger. The next day the area has become infected. She removes the tip of the thorn, but there is still pus remaining at the wound site. Which of the following cells function in the formation of pus? a. Cells with spherical nuclei and scant cytoplasm b. Biconcave cells with no nuclei c. Cells with bilobed nuclei and many acidophilic cytoplasmic granules d. Very small, cell-like elements with no nuclei but many granules e. Cells with polymorphic, multiply lobed nuclei

*The answer is C.* Surgical disruption of the left arm's lymphatic drainage by removal of lymph nodes caused the lymph edema.

A 43-year-old woman notices a lump in her left breast which upon pathological examination of a needle biopsy is diagnosed as stage 3 adenocarcinoma of the mammary gland. She elects to have a single mastectomy and the surgeon also removes several axillary lymph nodes to be examined to determine the tumor's state of metastasis. The patient recovers well from the surgery, but at a 6-month followup visit at the clinic her upper left arm is seen to be swollen and the surgeon prescribes a bandage wrap for "lymph edema." This condition likely resulted from which of the following? a. Angiogenesis from arterial branches that brought blood to the left breast b. Growth of cancer cells and blockage of lymphatic drainage from the left arm c. Surgical disruption of the left arm's lymphatic drainage by removal of lymph nodes d. Surgical damage to the thoracic duct during lymph node removal e. Hypertrophy of the vessels in the upper arm to accommodate blood otherwise flowing to the left breast

*The answer is C.* Renal cell carcinomas often secrete erythropoietin, a 34-kDa glycoprotein that regulates erythropoiesis. This hormone stimulates the growth of erythrocyte progenitors in the bone marrow by inhibiting a default pathway of programmed cell death (apoptosis). Increased hematocrit in this patient is the result of bone marrow hyperplasia affecting burst-forming and colony-forming units of the erythroid lineage. The cellular and molecular mechanisms responsible for hyperplasia relate to the control of stem cell viability and cell proliferation. The other hormones do not regulate erythropoiesis.

A 54-year-old woman smoker complains of intermittent blood in her urine. Urinalysis confirms hematuria. The CBC reveals increased hematocrit. A CT scan of the abdomen reveals a 3-cm renal mass, and a CT-guided biopsy demonstrates a renal cell carcinoma. Which of the following tumor-derived hormones is responsible for increased hematocrit in this patient? (A) Aldosterone (B) Angiotensin (C) Erythropoietin (D) Renin (E) Thrombopoietin

*The answer is E.* An effusion represents excess fluid in a body cavity. Purulent effusions (and exudates) contain a prominent cellular component. Neutrophils respond to bacterial infections and would be expected in this patient's pleural effusion. Basophils (choice A) are the least numerous WBC in the peripheral blood. Eosinophils (choice B) respond to parasitic infestations and certain allergies. Lymphocytes (choice C) and monocytes (choice D) are chronic inflammatory cells.

A 58-year-old woman with a 3-day history of pneumococcal pneumonia develops a purulent effusion involving her right pleural cavity. Aspiration of this fluid will reveal an abundance of which of the following inflammatory cells? (A) Basophils (B) Eosinophils (C) Lymphocytes (D) Monocytes (E) Neutrophils

*The answer is E.* This disease process initially involved injury to the endothelial cells.

A 62-year-old African American man presents with exerciseinduced angina. His serum cholesterol is 277 mg/dL (normal < 200), LDL is 157 (normal < 100), HDL is 43 (normal > 35), and triglycerides 170 (normal < 150). His body mass index (BMI) is 34 and his coronary risk ratio is 6.84 (normal < 5). Cardiac catheterization reveals an occlusion of the left anterior descending and the origin of the right coronary artery. This disease process initially involved which one of the following? a. Smooth muscle cell proliferation b. Formation of an intimal plaque c. Intimal thickening through addition of collagen and elastin d. Adventitial proliferation of fibroblasts e. Injury to endothelial cells

*The answer is B.* The problems with blood distribution in this patient's leg are most likely associated with arterioles

A 66-year-old man diagnosed with type II diabetes 10 years earlier presents with an aching pain in the muscles of his lower extremities. He says the pain is relieved by rest and worsened by physical activity. His lower limbs appear cold, pale, discolored, and he has a sore on the skin of his left heel. He has a weak tibial pulse on both sides and poor skin filling from dermal capillaries. The problems with blood distribution in this patient's leg are most likely associated with what vascular structures? a. Veins and venules b. Arterioles c. Branches of the aorta d. Lymphatic vessels e. Ventricles

*The answer is D.* Failure of the left ventricle leads to chronic passive congestion of the lungs. Blood leaks from the congested pulmonary capillaries into the alveoli. Alveolar macrophages degrade these extravasated RBCs and accumulate intracellular hemosiderin (ferritin-derived iron storage pigment). These hemosiderin-laden phagocytes are called "heart failure" cells. They can be identified in histologic sections using the Prussian blue stain for iron. In addition to removing pathogens and necrotic debris, macrophages take up and process microbes and present antigens to lymphocytes. These cells can also differentiate into dendritic cells, which are highly efficient antigen-presenting cells. Macrophages are derived from circulating blood monocytes. None of the other cells are progenitors for the mononuclear phagocyte system.

A 69-year-old woman with a history of ischemic heart disease is hospitalized for shortness of breath. Physical examination shows marked jugular venous distension, hepatomegaly, ascites, and pitting edema. The patient subsequently dies of cardiorespiratory failure. Histologic examination of the lungs at autopsy reveals iron-laden macrophages filled with the remnants of extravasated erythrocytes. These so-called "heart failure" cells are derived from which of the following peripheral blood cells? (A) Basophils (B) Eosinophils (C) Lymphocytes (D) Monocytes (E) Neutrophils

*The answer is D.* Inflammation has historically been referred to as either acute or chronic, depending on the persistence of the injury, clinical symptoms, and the nature of the inflammatory response. The cellular components of chronic inflammation are lymphocytes, antibody-producing plasma cells, and macrophages. Macrophages are a principal source of growth factors and are recognized for their phagocytic functions. During healing of the lung, macrophages enter the alveolar air spaces to remove inflammatory debris. The chronic inflammatory response is often prolonged and may be associated with aberrant repair (i.e., fibrosis). Basophils (choice A) and eosinophils (choice B) do not respond to S. Pneumoniae. Lymphocytes (choice C) and plasma cells (choice E) are not phagocytes.

A 70-year-old man presents with fever, shaking chills, and shortness of breath. The patient exhibits grunting respirations, 30 to 35 breaths per minute, with flaring of the nares. The sputum is rusty yellow and displays polymorphonuclear leukocytes (neutrophils). The patient is successfully treated with antibiotics. Which of the following inflammatory cells will infiltrate the patient's respiratory alveoli during the recovery to remove necrotic debris? (A) Basophils (B) Eosinophils (C) Lymphocytes (D) Macrophages (E) Plasma cells

*The answer is D.* Inflammation is the response of the microvasculature to a pathologic insult. It is characterized by the movement of (1) fluid and (2) leukocytes from blood into the injured tissue. Neutrophils are the cellular hallmark of acute inflammation. These phagocytes exit the blood to clear debris and begin the process of wound healing. Lobar pneumonia refers to consolidation of an entire lobe, whereas bronchopneumonia signifies scattered solid foci in the same or several lobes. Basophils (choice A) are precursors of tissue mast cells. Lymphocytes (choice B) and plasma cells (choice E) are mediators of chronic inflammation; they provide antigen-specific immunity to infectious diseases. Tissue macrophages (choice C) are chronic inflammatory cells derived from circulating blood monocytes; they secrete numerous cytokines to regulate wound healing.

A 75-year-old woman presents with a 3-day history of productive cough, fever, and shortness of breath. Her temperature is 38°C (101°F). An x-ray film of the chest shows consolidation of both the lungs, and sputum cultures are positive for Streptococcus pneumoniae. The patient develops respiratory insufficiency and expires. Her lungs are examined at autopsy (shown in the image). Which of the following inflammatory cells is most abundant in the alveolar air spaces of this patient? (A) Basophils (B) Lymphocytes (C) Macrophages (D) Neutrophils (E) Plasma cells

*The answer is A.* The bone marrow aspirate shows progenitor cells at various stages of differentiation and maturation. The arrows identify three large cells filled with red (eosinophilic) granules. These eosinophils will leave the bone marrow and circulate with a life span of 8 to 12 hours but may survive for days within target tissues. They are characteristic of hypersensitivity reactions, as well as allergic and asthmatic responses. Eosinophils contain preformed mediators of inflammation. They express cell surface IgA receptors and contain intracellular granules filled with eosinophil major basic protein (MBP), a carbohydrate-binding protein that provides a powerful defense against worm-like parasitic infestations (helminths). None of the other hematopoietic cells exhibit large eosinophilic granules.

A bone marrow aspirate is obtained from a 50-yearold woman with B-cell lymphoma (shown in the image). Identify the hematopoietic cells indicated by the arrows. (A) Eosinophils (B) Lymphocytes (C) Macrophages (D) Monocytes (E) Neutrophils

*The answer is B.* Megakaryocytes in the bone marrow mature into multilobed giant cells by a number of endomitotic cell divisions. After reaching a certain size and ploidy, megakaryocyte cytoplasm is released into bone marrow sinusoids in long, platelet containing ribbons. After their release from the bone marrow, platelets circulate with a life span of about 10 days. They help maintain the integrity of the vascular endothelium by initiating thrombosis and delivering growth factors that stimulate tissue regeneration and repair. Platelets can be observed in a peripheral blood smear (examined at high magnification) as small (2 to 3 μm) anucleate particles.

A bone marrow biopsy is obtained from a 5-year-old boy recently diagnosed with lymphoblastic leukemia (shown in the image). Identify the normal hematopoietic cell indicated by the arrow. (A) Macrophage (B) Megakaryocyte (C) Monocyte (D) Myelocyte (E) Reticulocyte

*The answer is E.* Eosinophils contain factors for destruction of helminthic parasites and for modulating inflammation.

A differential cell count of a blood smear from a patient with a parasitic infection is likely to reveal an increase in the circulating numbers of which cell type? a. Neutrophils b. Lymphocytes c. Monocytes d. Basophils e. Eosinophils

*The answer is E.* The peripheral blood smear shows a maturing neutrophil surrounded by erythrocytes (red blood cells). Neutrophils are the most abundant white blood cells (WBC, leukocyte) found in the peripheral blood. These acute inflammatory cells are phagocytes (cells that devour); they exit the circulatory system at sites of tissue injury or infection to remove pathogens and necrotic debris. Neutrophils exhibit variation in size and nuclear morphology. As they leave the bone marrow, neutrophils exhibit a horseshoe-shaped nucleus and are referred to as "band cells." As they mature in the peripheral blood, their nuclei become lobulated (segmented). Mature, segmented neutrophils are commonly referred to as polymorphonuclear leukocytes. The nuclei of mature segmented neutrophils have two to four lobes joined by thin strands of chromatin. Neutrophils are loaded with granules that contain enzymes (e.g., myeloperoxidase and collagenase) and antimicrobial peptides (e.g., lysozyme and defensin). B lymphocytes produce antibodies (choice A). Platelets regulate coagulation and hemostasis (choice B). Fibroblasts synthesize collagen (choice C). Upon degranulation, mast cells release histamine (choice D).

A peripheral blood smear from a 20-year-old woman is examined in the clinical laboratory. Which of the following describes the primary function of the leukocyte shown in the image? (A) Antibody production (B) Coagulation and hemostasis (C) Collagen biosynthesis (D) Histamine release (E) Phagocytosis

*The answer is C.* The peripheral blood smear shows a large lymphocyte and a basophilic granulocyte (arrow, shown on the image). The basophil has a bilobed nucleus and contains large, basophilic granules. Basophils and tissue mast cells express cell surface receptors for the Fc domain of IgE. When IgE-primed basophils and mast cells encounter multivalent antigens, their Fc receptors are clustered in the plane of the membrane. This clustering event triggers degranulation and the release of a variety of inflammatory mediators (e.g., histamine). Histamine is a primary mediator of increased vascular permeability during inflammation. Histamine binds specific H1 receptors in the vascular wall, inducing endothelial cell contraction, gap formation, and local edema. Basophils do not have cell surface receptors for the other immunoglobulin classes.

A peripheral blood smear from a 22-year-old man is examined in the clinical laboratory (shown in the image). The leukocyte identified by the arrow has cell surface receptors for which of the following types of immunoglobulin? (A) IgA (B) IgD (C) IgE (D) IgG (E) IgM

*The answer is E.* The peripheral blood smear shows a large, agranular cell with a markedly indented nucleus. This kidney-shaped nuclear morphology is the hallmark of circulating monocytes. The nuclear indentation is filled with membranes of the Golgi apparatus and centrioles. Monocytes are the progenitors of the mononuclear phagocyte system. Monocytes exit the circulation and migrate into all tissues and organs to become resident macrophages. Examples include alveolar macrophages, bone osteoclasts, and liver Kupffer cells. In response to inflammatory mediators, they also accumulate at sites of acute and chronic inflammation. Macrophages recognize, internalize, and digest foreign materials, microorganisms, and cellular debris. This process is termed phagocytosis, and the effector cells are known as phagocytes. None of the other mechanisms of inflammation describe the primary function of macrophages. The peripheral blood smear shown in the image also reveals numerous platelets.

A peripheral blood smear from a 28-year-old woman is examined in the clinical laboratory (shown in the image). Which of the following describes the primary function of the leukocyte indicated by the arrow after it exists the blood? (A) Antibody production (B) Collagen biosynthesis (C) Complement activation (D) Histamine release (E) Phagocytosis

*The answer is C.* The peripheral blood smear shows a small lymphocyte with a dark spherical nucleus and scant blue cytoplasm. Lymphocytes are the principal mediators of antigen-specific immunity. B and T lymphocytes originate in the bone marrow. T cells are educated as to self-/nonself-antigenicity in the thymus. Together, B and T lymphocytes constitute about 30% of total peripheral blood leukocytes. Most lymphocytes in the peripheral blood are immunocompetent; they have been sensitized to a target and are in transit from one tissue to another. T and B cells are indistinguishable by light microscopy. B cells secrete immunoglobulins (antibodies), whereas T cells either lyse target cells or secrete cytokines. Cytokines (signaling molecules) produced by helper T lymphocytes include interferon-γ, TGF-β, and a variety of interleukins. None of the other immunological responses describe the principal function of lymphocytes.

A peripheral blood smear from a 30-year-old man is examined in the pathology department. Which of the following describes the primary function of the leukocyte shown in the image? (A) Collagen biosynthesis (B) Complement activation (C) Cytokine secretion (D) Histamine release (E) Phagocytosis

*The answer is C.* When a sample of blood to which anticoagulants have been added is centrifuged, the volume of packed erythrocytes is referred to as the hematocrit. The normal hematocrit for women is 35% to 45% (v/v). The normal hematocrit for men is slightly higher (39% to 50%). Increased hematocrit in this patient reflects hemoconcentration, secondary to fluid loss (severe diarrhea). This hematologic condition, termed relative polycythemia, is characterized by decreased plasma volume with a normal red cell mass. When patients suffer from burns, vomiting, excessive sweating, or diarrhea, they not only lose fluid but also suffer electrolyte disturbances. Systemic blood pressure falls with continuous dehydration, and declining perfusion eventually leads to death. None of the other percentages falls within the reference range for normal hematocrit in women.

An 18-year-old woman complains of fever and severe diarrhea for 3 days. Her temperature is 38°C (101°F). The CBC reveals an increased hematocrit, most likely caused by dehydration and hemoconcentration, secondary to diarrhea. Which of the following represents a normal hematocrit reading for this patient? (A) 10% (B) 20% (C) 40% (D) 60% (E) 80%

*The answer is C.* Concentric elastic lamellae with fenestrated membranes are characteristic of the tunica media of conducting arteries (elastic arteries).

Concentric elastic lamellae with fenestrated membranes are characteristic of the tunica media of A. large veins B. venules C. conducting arteries D. distributing arteries E. lymphatic vessels

*The answer is E.* Blood is an amazing connective tissue that delivers nutrients and oxygen to cells and removes metabolic waste. Blood also provides a transport mechanism for hormones and other signaling molecules. Blood consists of formed elements (cells and platelets) and a protein-rich fluid termed plasma. Most plasma proteins are synthesized in the liver. In addition to albumin and immunoglobulins (e.g., IgG and IgM), plasma contains numerous clotting factors. During blood coagulation, fibrinogen (a 340- kDa glycoprotein) is converted to insoluble fibrin, forming an adherent intravascular clot (thrombus). Without anticoagulants, blood removed from the circulation will clot spontaneously. Once the fibrin clot is removed, the fluid that remains is referred to as serum. None of the other laboratory procedures describe a method for converting plasma to serum.

During a 4th year elective rotation in blood bank/transfusion medicine, you are asked to discuss differences between blood, plasma, and serum. You explain that blood plasma is converted to serum using which of the following laboratory procedures? (A) Addition of heparin anticoagulant (B) Centrifugation to remove the buffy coat (C) Heat inactivation of complement (D) Precipitation of immunoglobulins (E) Removal of the insoluble fibrin clot

*The answer is A.* Formed elements in the blood include platelets, red blood cells (erythrocytes), and white blood cells (leukocytes). Of these, erythrocytes are the most abundant formed elements in the peripheral blood (normal reference range = 3.7 to 5.2 × 1012/L). There are approximately 1,000 times more RBCs than WBCs (choices B, C, and D). RBCs are 10 times more abundant than platelets (choice E). Platelets are nonnucleated (anucleate) cytoplasmic fragments derived from megakaryocytes in the bone marrow. RBCs are anucleate cells devoid of common intracellular organelles. Basophils are the least abundant leukocytes in the peripheral blood.

During clinical rounds, the attending physician asks you to discuss basic principles of hematology. Which of the following is the most abundant formed element in the blood? (A) Erythrocytes (B) Granulocytes (C) Lymphocytes (D) Monocytes (E) Platelets

*The answer is D.* Capillaries do not have any smooth muscle.

During light microscopic examination of a tissue, you note a vessel that has no smooth muscle but a large amount of connective tissue at its periphery. Which of the following vessels are you examining? a. Arteriole b. Venule c. Elastic artery d. Capillary e. Large vein

*The answer is A.* Monocytes are large cells with usually distinctly indented or C-shaped nucleus.

Examination of a normal peripheral blood smear reveals a cell more than twice the diameter of an erythrocyte with a kidney-shaped nucleus. There cells are < 10% of the total leukocytes. Which of the following cell types is being described? a. Monocyte b. Basophil c. Eosinophil d. Neutrophil e. Lymphocyte

1. *A.* Neutrophils are the predominant cells in pus. 2. *C.* Basophilic leukocytes contain receptors for IgE 3. *B.* Eosinophilic leukocytes

For Questions 1-3, select one of the following A. neutrophilic leukocytes B. eosinophilic leukocytes C. basophilic leukocytes D. erythrocytes E. platelets 1. Predominant cell in pus in acute staphylococcal infection 2. Plasma membranes contain receptors for IgE 3. Numbers often increase in parasitic infections

*The answer is C.* The tunica media is most likely affected by malformed fibrillin.

Individuals with Marfan syndrome have mutations in the fibrillin gene and commonly experience aortic aneurisms. What portion of the arterial wall is most likely to be affected by the malformed fibrillin? a. Endothelium b. Tunica intima c. Tunica media d. Tunica adventitia e. Vasa vasorum

*The answer is D.* Lymphatic capillaries anastomose freely to form networks.

Lymphatic capillaries A. are fenestrated to permit rapid passage of cells into their lumens B. have well developed zonulae occludens C. are surrounded by a well-developed basal lamina D. anastomose freely to form networks E. help to remove excess interstitial fluid from the gray matter of the brain.

*The answer is C.* The proximal portion of a central channel is known as a metarteriole, whereas its distal portion is the thoroughfare channel. Blood from metarterioles may enter the capillary bed if their precapillary sphincters are relaxed. If the precapillary sphincters of metarterioles are constricted, blood bypasses the capillary bed and flows directly into thoroughfare channels and from there into a venule.

Metarterioles, vessels interposed between arterioles and capillary beds, (A) function to control blood flow into arterioles. (B) possess a complete layer of smooth muscle cells in their tunica media. (C) possess precapillary sphincters. (D) receive blood from thoroughfare channels. (E) possess valves to regulate the direction of blood flow

*The answer is C.* Vasa vasorum are the small blood vessels that serve the walls of elastic and muscular arteries with oxygen and nutrients just as the coronary arteries provide for the walls of the heart.

Vasa vasorum function in a way that is similar to (A) AV valves. (B) semilunar valves. (C) coronary arteries. (D) elastic arteries. (E) metarterioles.

*The answer is C.* Just as the heart wall is supplied with its own coronary vasculature for nutrients and O2, large vessels usually have vasa vasorum, which supply the walls of large blood vessels.

Vasa vasorum serve a function analogous to that of which of the following? a. Valves b. Basal lamina c. Coronary arteries d. Endothelial diaphragms e. Arterioles

*The answer is D.* Monocytes are the precursor to microglia and most antigen-presenting cells

What cell in circulating blood is the precursor to microglia and most antigen-presenting cells? a. Eosinophil b. Basophil c. Lymphocyte d. Monocyte e. Mast cell

*The answer is D.* The approximate life span of a circulating erythrocyte is 120 days, which is about 4 months.

What is the approximate life span of a circulating erythrocyte? a. 8 days b. 20 days c. 5 weeks d. 4 months e. 1 year

*The answer is B.* Elastic fibers are abundant in the aorta.

Where are elastic fibers abundant? A. Tendon B. Aorta C. Bone D. Fibrocartilage E. Adipose tissue

*The answer is B.* Carbohydrates of the erythrocyte cell surface is primarily responsible for determining blood type.

Which biochemical component of the erythrocyte cell surface is primarily responsible for determining blood type (eg, the A-B-O system). a. Fatty acid b. Carbohydrate c. Nucleic acid d. Protein e. Cholesterol

*The answer is B.* Basophils contain heparin and histamine.

Which cell type has cytoplasmic granules that contain heparin and histamine? a. Eosinophils b. Basophils c. Lymphocytes d. Monocytes e. Neutrophils

*The answer is B.* Continuous capillaries are most common in the brain and muscle.

Which description is true of continuous capillaries? a. Unusually wide lumens b. Most common in both brain and muscle c. Abundant fenestrations d. Lack a complete basement membrane e. Phagocytic cells often seen inserted in the intercellular clefts

*The answer is D.* T lymphocytes differentiate outside of the bone marrow; they mature in the thymus.

Which of the following blood cells differentiate outside of the bone marrow? a. Neutrophils b. Basophils c. Eosinophils d. T lymphocytes e. Megakaryocytes

*The answer is A.* Pericytes are spider-shaped stem cells help stabilize capillary walls, control permeability, and play a role in vessel repair. They secrete many ECM components and form their own basal lamina, fusing with the basement membrane of endothelial cell.

Which of the following is true of pericytes? a. Are associated with the basal lamina of capillary endothelial cells b. Have similar histological features as contractile cells of the myocardium c. Form a layer of cells joined by gap junctions d. Are terminally differentiated e. Capable of forming multinucleated muscle fibers

*The answer is D.* The smooth endothelial lining of intact, healthy capillaries inhibits clot formation. Capillaries do not control blood pressure.

Which of the following statements about healthy, intact capillaries is true? (A) They control blood pressure. (B) They are lined by a simple columnar epithelium. (C) They have a smooth muscle coat. (D) They inhibit clot formation. (E) Satellite cells share their basal lamina

*The answer is D.* The muscular artery possesses a distinct internal elastic lamina. Elastic arteries possess an incomplete internal elastic lamina, whereas capillaries, arterioles, metarterioles and veins do not possess an internal elastic lamina.

Which one of the following possesses a distinct internal elastic lamina? (A) Capillary (B) Metarteriole (C) Arteriole (D) Muscular artery (E) Vein