19 In this section of a healing bone fracture, which of the following best describes the cell at the arrow? A. Apoptotic cell B. Bone-lining macrophage C. Dividing osteoblast D. Necrotic cell E. Typical osteoblast Explanation: The correct answer is A. Apoptosis refers to programmed cell death, and in this situation, appears to be a means for the elimination of unneeded osteoblasts as the extracellular matrix is reshaped and the healing process continues. Two basic morphologic features of apoptosis are seen in this cell. First, cytoplasmic blebbing, in which round, elongated structures (blebs) extend from the main cell body, is evident. Some blebs appear as though in clusters. Second, nuclear blebbing, in which the nucleus shows the same irregular type of blebs or protrusions, is apparent. This cell does not have features of a macrophage (choice B) such as lysosomes, or a heterogeneous cytoplasm. Ribosome-filled blebs are not features of macrophages. No chromosomes are present, hence this cannot be a dividing cell (choice C). Cytoplasmic and nuclear blebbing are not features of necrosis (choice D). In necrosis, nuclei are washed out (karyolysis), markedly compact (pyknotic), or fragmented (karyorrhexis). A typical osteoblast (choice E) is seen to the left of the blebbing cell. This cell has extensive rough endoplasmic reticulum and a Golgi apparatus with elliptical and round granules. 20 Which of the following products do the cells indicated above produce? A. Alkaline phosphatase B. Hydrochloric acid C. Immunoglobulin D. Major basic protein E. Mucus F. Surfactant G. von Willebrand's factor H. Zymogen Explanation: The correct answer is F. This is a photomicrograph of lung alveolar walls or septa. Type II pneumocytes are cuboidal-like with round nuclei and a washed-out or foamy cytoplasm. This cytoplasmic appearance is due to the lipid content. Lamellar bodies (secretory granules) of these cells contain a complex of phospholipids, proteins, and carbohydrates known as surfactant. Alveolar macrophages are also present in the lumen of the alveolus. Osteoblasts, which produce alkaline phosphatase (choice A), might be confused with these cells. However, osteoblasts line bone and have more of an epithelial-lining appearance. Hydrochloric acid (choice B) is produced by gastric parietal cells. Such cells are interspersed among protein producing cells. Other HCl producing cells are found in the body, but not in the alveolar wall environment. Immunoglobulins (choice C) are secreted by plasma cells, which are connective tissue cells. The cells in the micrograph are attached to a basal lamina. Major basic protein (choice D) is produced by eosinophils. These cells do not have the nuclear features of eosinophils. Mucus cells (choice E) would give a similar cytoplasmic appearance; however, nuclei of such cells are usually shaped quite differently. The indicated cells are not flat (squamous) enough to be confused with endothelial cells. Such cells produce von Willebrand's factor (factor VIII, choice G), and may be seen surrounding vessels in the alveolar walls. Zymogen granules (choice H) would not give this type of appearance with a typical H&E stain. 28 A cardiovascular physiologist is performing experiments using a new alpha1 adrenergic agonist to determine the amount of vasoconstriction the new drug can produce compared with a phenylephrine control. Which of the labeled structures is the cellular target of both of these drugs? A. A B. B C. C D. D E. E Explanation: The correct answer is E. Arrow E points to a smooth muscle cell in the media of the arteriole. Alpha1 agonists stimulate alpha1 receptors present on the smooth muscle, which leads to an increase in intracellular calcium via phosphatidylinositol hydrolysis. This increase in calcium is necessary for smooth muscle contraction. Arrow A indicates an endothelial cell located in the intima of the arteriole. Nitric oxide, also known as endothelial cell relaxing factor (EDRF), is produced from arginine by endothelial cells. A muscarinic agonist can lead to the evolution of NO, producing vasodilatation. Arrow B indicates a polymorphonuclear leukocyte in the bloodstream. Arrow C indicates the basal lamina underlying the endothelium. Arrow D indicates the arteriolar adventitia. 29 What is the primary function of the cell pointed to in the figure above? A. It produces low-molecular weight polypeptides B. It secretes bactericidal enzymes C. It secretes lipases D. It secretes mucins E. It secretes pepsinogen Explanation: The correct answer is B. The drawing depicts the histology of the small intestinal villus and crypts. The arrow points to a Paneth cell. Paneth cells are unique to the small intestine. They are found at the base of the crypts of Lieberkühn in the small intestinal villi, and have many secretory granules that contain enzymes with bactericidal activity. The enteroendocrine cells of the stomach produce low-molecular weight polypeptides (choice A). There are no lipase-secreting cells in the small intestine (choice C). Lipases are secreted by cells in the salivary glands, stomach, and exocrine pancreas. So, even if you did not know that the arrow pointed to Paneth cells, you should have eliminated this choice based on the fact that the small intestine does not secrete lipase. The goblet cells of the small intestinal villi are responsible for producing protective glycoproteins called mucins (choice D). After secretion, they are hydrated and become a mucous layer that protects the intestinal epithelium. There are many goblet cells depicted in this figure, but they are not located at the bases of the crypts. Pepsinogen (choice E) is secreted by the chief cells of the stomach. 31 A 29-year-old man with reactive airway disease undergoes endobronchial biopsy. The biopsy material is prepared for light microscopy as well as electron microscopy. The cell pictured above in an electron micrograph stains reddish purple with toluidine blue. The cell depicted is most likely a(n) A. alveolar macrophage B. histiocyte C. mast cell D. type II pneumocyte Explanation: The correct answer is C. The mast cell has uniform-sized, spherical granules that contain material arranged in a scroll-like pattern. In some granules, as many as five scrolls in cross or longitudinal section can be seen. The cell membrane is irregular with several long microvilli, allowing for an increased number of binding sites for IgE. The nucleus characteristically has a considerable amount of heterochromatin, and in this section, a nucleolus is evident. Collagen fibrils are also scattered around the cell, another indicator that it is a mast cell, since mast cells are found in the connective tissue extracellular matrix. An alveolar macrophage (choice A) has a cytoplasm containing heterogeneous granules. It is larger in size than this cell and has a more irregular surface. Histiocytes (choice B) or connective tissue macrophages have heterogeneous granules of different sizes, and the cells are also much larger. Type II pneumocytes (choice D) contain granules, but they are not this abundant. The granules or lamellar bodies are larger and contain stacks (lamellae) of dense plate-like material, the phospholipid or surfactant. The arrangement also resembles the EM appearance of myelin. The type II pneumocyte is related by junctions to type I cells and other type II cells, which are not seen in this micrograph. 32 Which of the labeled structures is responsible for the secretion of renin? A. A B. B C. C D. D E. E Explanation: The correct answer is C. This question required that you know two pieces of information: (1) renin is secreted from the juxtaglomerular (JG) cells; and (2) the location of the JG cells in a picture that includes both the glomerulus and the juxtaglomerular apparatus. Remember that renin is responsible for converting angiotensinogen to angiotensin I, which is subsequently converted to angiotensin II in the lungs by an important enzyme appropriately called angiotensin-converting enzyme. Angiotensin II helps preserve blood pressure both by its potent vasoconstrictor properties and by its ability to stimulate aldosterone secretion from the adrenal cortex. The label for choice A points to the glomerular basement membrane. The label for choice B points to the epithelium of Bowman's capsule. The label for choice D points to the macula densa cells, which are thought to sense sodium concentration in the distal convoluted tubule. The label for choice E points to the Polkissen cells. Their function is unknown. 44 A 25-year-old man presents with a 4-cm mass above the clavicle. Chest X-ray demonstrates marked mediastinal widening. Excisional biopsy of the supraclavicular mass demonstrates areas with the appearance shown in the photomicrograph above. The large cell (indicated with the arrow) is most likely which of the following? A. Langhans cell B. LE cell C. Mott cell D. Reed-Sternberg cell E. Touton cell Explanation: The correct answer is D. The cell illustrated is a Reed-Sternberg cell. These cells characteristically are neoplastic giant cells with a bilobed mirror-image nucleus that may have large ("owl-eyes") nucleoli surrounded by a clear halo. Most commonly, these cells are associated with Hodgkin's disease, but it is worth knowing that in real life, a surprising variety of other lymphomas and some other diseases may have at least occasional ReedSternberg look-alikes. For that reason, the diagnosis of Hodgkin's disease often requires confirmatory immunohistochemical staining. The Langhans cell (choice A) is a giant cell with peripherally arranged nuclei found in granulomas. The LE cell (choice B) is a degenerating neutrophil seen in lupus erythematosus in in vitro preparations. The Mott cell (choice C) is a "constipated" plasma cell filled with immunoglobulins, producing a grapecluster appearance to the cell. Mott cells are seen in multiple myeloma and some parasitic infestations. The Touton giant cell (choice E) has distributed nuclei and is found in tumors other than Hodgkin's lymphoma.