Immune Cells & Lymphoid Organs

*The answer is E.* Splenic cords (of Billroth) are the sites in which abnormal RBCs are removed from circulation.

A 12-year-old African-American girl presents with anemia and a large percentage of her peripheral erythrocytes appear sickle-shaped. Genetic testing reveals homozygosity for sickle cell disease. In which of the following sites will the abnormal RBCs be removed from the circulation? a. Thymic cortex b. Periarteriolar lymphoid sheathes of splenic white pulp c. Medullary sinuses of lymph nodes d. Thymic medulla e. Splenic cords (of Billroth)

*The answer is A.* Most lymphocytes (about 90%) enter lymph nodes and diffuse/nodular lymphatic tissue through specialized postcapillary venules termed high endothelial venules (HEVs). HEVs are lined by cuboidal endothelial cells. They express an array of cell adhesion molecules (selectins and addressins) that mediate leukocyte binding and transendothelial migration (diabedesis). In lymph nodes, HEVs are located primarily in the deep cortex, a T-cell-rich region of the lymph node. Upon arrival in a lymph node, T cells meander in the deep cortex, while B cells migrate to the cortex. Immunohistochemical assays are used routinely to localize B- and T-cell populations in primary and secondary lymphoid organs. None of the other regions of the lymph node are characterized by the presence of HEVs.

A 22-year-old woman presents with a 3-day history of sore throat. Her temperature is 38.7°C (103°F). Physical examination reveals inflamed tonsils and swollen cervical lymph nodes. Trafficking of blood-borne lymphocytes to regional lymph nodes in this patient involves cell migration through high endothelial venules (HEVs). These specialized postcapillary venules are located primarily in which of the following regions of the patient's lymph nodes? (A) Deep cortex (B) Medullary sinus (C) Nodular cortex (D) Subcapsular sinus (E) Trabecular sinus

*The answer is A.* The oval identifies a region of the spleen that is filled with venous sinuses separated by thin cords. The splenic cords are difficult to visualize by light microscopy; they are composed of reticular cells and reticular fibers and may include a variety of acute and chronic inflammatory cells. Together, splenic cords and sinuses are referred to as red pulp. Circulation of blood through red pulp allows macrophages to remove senescent or defective RBCs and filter the blood for pathogens. None of the other choices describe histologic features of red pulp in the spleen.

A 26-year-old man ruptures his spleen in a motorcycle accident and requires an emergency splenectomy to control internal bleeding. The surgical specimen is examined in the pathology department (shown in the image). Which of the following histologic features best characterizes the region of the spleen indicated by the oval? (A) Cords and venous sinuses (red pulp) (B) Periarteriolar lymphoid sheath (PALS) (C) Splenic capsule and visceral peritoneum (D) Splenic lymphoid nodules (white pulp) (E) Trabecular connective tissue

*The answer is A.* Blood flow through the spleen is complex. In brief, the branches of splenic and trabecular arteries that enter the white pulp of the spleen are termed central arteries. Lymphocytes surround the central artery and its branches, forming a periarteriolar lymphatic sheath (PALS). The central artery continues into the red pulp of the spleen where it gives rise to multiple, small penicillar arterioles. These arterioles form sheathed capillaries that empty blood directly into splenic cords. The open circulation of blood in the spleen, from sheathed capillaries to splenic cords to venous sinuses, provides an opportunity for macrophages to remove senescent RBCs.

A 35-year-old woman with systemic lupus erythematosus undergoes a partial splenectomy to control her autoimmune hemolytic anemia. The surgical specimen is examined by a multiheaded microscope in the pathology department. For the surgical specimen described, identify the blood vessels indicated by the arrows. (A) Central (B) Cortical (C) Penicillar (D) Splenic (E) Trabecular

*The answer is A.* The double arrow identifies a secondary lymphoid nodule within the white pulp of the spleen. The germinal center is surrounded by a mantle of small lymphocytes. Red pulp immediately adjacent to the white pulp is referred to as the marginal zone. Th1 lymphocytes (choice D) interact with B cells and mediate delayed hypersensitivity reactions (e.g., poison ivy). Th2 lymphocytes (choice E) interact with eosinophils and mast cells, and mediate hypersensitivity responses to parasitic infestations and allergens. Although the other cells are found in diffuse and nodular lymphatic tissue, they do not form germinal centers in lymphoid follicles.

A 35-year-old woman with systemic lupus erythematosus undergoes a partial splenectomy to control her autoimmune hemolytic anemia. The surgical specimen is examined by a multiheaded microscope in the pathology department. Which of the following cells is expected to be most abundant in the region of the white pulp indicated by the double arrow (shown in the image)? (A) B lymphocytes (B) Dendritic cells (C) Macrophages (D) Th1 lymphocytes (E) Th2 lymphocytes

*The answer is D.* Examination of the photomicrograph reveals medullary cords within an open medullary sinus. A fine meshwork of reticular fibers and reticular cell processes crisscrosses this lymphatic sinus. As lymph filters through the lymph node, antigens and antigen-presenting cells provide signals to lymphocytes to coordinate their activation, proliferation, and maturation. Mature plasma cells leave the cortex of the node. They populate medullary cords and secrete antibodies. Antibodies (immunoglobulins) are subsequently delivered to the blood through the right lymphatic trunk or the left thoracic duct. Antibodies are targeting molecules that initiate humoral and/or cellular mechanisms of cytotoxicity. None of the other regions/structures exhibit histologic features of a medullary sinus.

A 55-year-old woman with breast cancer undergoes a modified radical mastectomy with axillary lymph node dissection. Another axillary lymph node obtained from the patient is examined in the pathology department. What is the appropriate name for the region indicated by the asterisk? (A) Cortical sinus (B) Efferent lymphatic vessel (C) Medullary cord (D) Medullary sinus (E) Trabecular sinus

*The answer is A.* Multiple afferent lymphatic vessels penetrate the capsule of lymph node. Lymph that is delivered to the subcapsular sinus flows through trabecular and medullary sinuses, before being drained by an efferent lymphatic vessel located at the hilum of the lymph node. The image shows an afferent lymphatic vessel located outside the capsule. None of the other structures exhibit the morphology of afferent lymphatic vessels near the periphery of a lymph node.

A 55-year-old woman with breast cancer undergoes a modified radical mastectomy with axillary lymph node dissection. The resected lymph nodes are carefully examined for evidence of malignant disease (shown in the image). For the surgical specimen described, identify the structure indicated by the asterisk. (A) Afferent lymphatic vessel (B) Cortical sinus (C) Efferent lymphatic vessel (D) Precapillary arteriole (E) Precapillary venule

*The answer is E.* Lymph nodes are characterized by the presence of subcapsular, trabecular, and medullary sinuses that provide channels for the circulation of lymph. The arrows identify a trabecular sinus that appears to be penetrating the cortex of the node (shown in the image). Trabecular sinuses drain to central medullary sinuses. Trabeculae are composed of dense connective tissue. They are continuous with the capsule and provide a framework for lymph node architecture. None of the other regions/structures exhibit histologic features of a trabecular sinus.

A 55-year-old woman with breast cancer undergoes a modified radical mastectomy with axillary lymph node dissection. The resected lymph nodes are carefully examined for evidence of malignant disease (shown in the image). Identify the region of the lymph node indicated by the arrows. (A) Lymphatic vessel (B) Medullary cord (C) Medullary sinus (D) Subcapsular sinus (E) Trabecular sinus

*The answer is C.* The corona of small lymphocytes that surrounds the germinal centers in secondary lymphoid follicles is referred to as the mantle zone. These small lymphocytes include resting T and B cells. Immunohistochemical labeling assays are used to distinguish between these lymphocyte subpopulations. In addition to lymphocytes, nodular lymphatic tissue is characterized by the presence of follicular dendritic cells that trap antigenic debris for uptake by antigen-presenting cells. None of the other histologic features exhibit the morphology of the mantle zone in a secondary lymphoid nodule.

A 59-year-old man with adenocarcinoma of the large intestine undergoes a right hemicolectomy. Microscopic examination of the surgical specimen reveals lymphatic tissue in the lamina propria of the distal ileum (shown in the image). For the surgical specimen described, what is the appropriate name for the corona of lymphocytes that surrounds the germinal centers of these lymphoid follicles? (A) Cortical matrix (B) Lymphoid sheath (C) Mantle zone (D) Primary cortex (E) Secondary center

*The answer is B.* The lymphoid nodules shown in the image exhibit central, pale stained germinal centers that are filled with proliferating B lymphocytes (plasmablasts). These secondary lymphoid follicles (nodules) are similar in morphology to the nodule present in the thyroid gland. The distal ileum is characterized by the presence of multiple lymphatic nodules, referred to as Peyer patches. These aggregates of nodular lymphoid tissue play a crucial role in regulating immune surveillance of the gut flora. Specialized epithelial microfold (M) cells sample antigens present in the lumen of the gut and transport them to the underlying lymphoid tissue to stimulate immune activation or anergy (tolerance). None of the other structures exhibit the morphology of a germinal center in a secondary lymphoid follicle.

A 59-year-old man with adenocarcinoma of the large intestine undergoes a right hemicolectomy. Microscopic examination of the surgical specimen reveals lymphatic tissue in the lamina propria of the distal ileum (shown in the image). Identify the area indicated by the arrows. (A) Diffuse lymphatic tissue (B) Germinal center (C) Medullary sinus (D) Periarteriolar sheath (E) Primary lymphoid follicle

*The answer is B.* The formation of germinal centers for B-cell proliferation in each node's cortex causes swelling.

A 6-year-old boy is brought to the clinic where his mother reports that was bitten by a neighbor's dog two days earlier. The child's right hand is lacerated between the thumb and index finger and this area is inflamed but healing. The doctor's examination reveals small but painless swellings beneath the skin inside the right elbow and arm pit and he explains to the mother that these are active lymph nodes enlarged in response to the infection in the hand. What has produced the swelling? a. Increased flow of lymph through the nodes' afferent lymphatics b. Formation of germinal centers for B-cell proliferation in each node's cortex c. Arrival of antigen-presenting cells in each node's medulla d. Enlargement and increased activity of the nodes' high endothelial venules e. Increased thickness of each node's paracortex

*The answer is B.* The image shows an efferent lymphatic vessel in the medulla near the hilum of a lymph node. Most lymphocytes leave lymph nodes through a common efferent lymphatic channel. Afferent lymphatic vessels (choice A) enter lymph nodes by penetrating the outer capsule. A large afferent lymphatic vessel is visible along the right side of this specimen (shown in the image). Unlike lymphatic channels, a medullary sinus (choice C) would contain medullary cords. Similarly, blood vessels (choices D and E) would contain WBCs and RBCs.

A 69-year-old man with high-grade prostatic adenocarcinoma receives radiation and chemotherapy, but eventually expires. The patient's para-aortic lymph nodes are examined at autopsy for evidence of malignant disease (shown in the image). Identify the channel/space indicated by the arrows. (A) Afferent lymphatic vessel (B) Efferent lymphatic vessel (C) Medullary sinus (D) Precapillary arteriole (E) Precapillary venule

*The answer is B.* The image shows secondary lymphoid follicles near the periphery of a lymph node. The follicles are separated from the capsule by a subcapsular sinus. Germinal centers within secondary lymphoid follicles frequently contain follicular dendritic cells. These large cells have multiple, hair-like processes that intercalate B lymphocytes to support their maturation. Follicular dendritic cells express cell surface Fc receptors that bind antigen-antibody (immune) complexes and store them for weeks (and even years). Follicular dendritic cells do not qualify as antigen-presenting cells (APCs), because the antigens they trap are not internalized and processed for display by MHC molecules; rather, the antigens are merely retained at the cell surface for "inspection" by passing lymphocytes. Dendritic cells (choice A) are typically located in T-cell-rich areas of the deep cortex. None of the other cells display histologic features of follicular dendritic cells.

A mediastinal lymph node is collected at autopsy and examined in the pathology department (shown in the image). The germinal centers of these secondary lymphoid follicles contain nonimmune cells with thin, hairlike processes that intercalate maturing B lymphocytes. Name these nonimmune cells of the reticular meshwork. (A) Dendritic cells (B) Follicular dendritic cells (C) Langerhans cells (D) Macrophages (E) Reticular cells

*The answer is E.* Most lymphocytes in the periarteriolar lymphoid sheath (PALS) are T cells. Thus, PALS are similar in function to the deep cortical region in lymph nodes; both are said to be thymus-dependent lymphoid zones. The mechanisms whereby T lymphocytes exit the blood and congregate around the central artery and its branches are poorly understood. Although the other cells listed are found in diffuse and nodular lymphatic tissue, they are not the principal component of PALS in the spleen.

A microscopic field of the specimen reveals a diffuse halo of cells surrounding a central arteriole (shown in the image). Identify the cells that constitute this periarteriolar lymphoid sheath. (A) B lymphocytes (B) Macrophages (C) Memory B lymphocytes (D) Plasma B cells (E) T lymphocytes

*The answer is A.* The histologic feature identified in the image represents a remnant of epithelial tissue derived from third and fourth pharyngeal pouches during embryonic development. These structures are referred to as Hassall corpuscles. They are a distinguishing feature of the medulla of the thymus. Hassall corpuscles are composed of concentric whorls of type VI epithelioreticular cells. Six functionally distinct populations of epithelioreticular cells have been described. These cells provide a framework for thymocytes and regulate crucial aspects of T-cell education. Herring bodies (choice B) are dilated terminal axons of neurons in the posterior pituitary. Mallory bodies (choice C) represent precipitated intermediate filament protein in the hepatocytes of chronic alcoholics. Meissner and Pacinian corpuscles (choices D and E) are tactile receptors in the dermis of the skin.

A neonate with TORCH syndrome develops respiratory insufficiency and expires. A lobule of the thymus is examined at autopsy (shown in the image). The structure indicated by the arrow shows concentric layers of epithelial cells derived from pharyngeal pouches during embryogenesis. Name this distinctive histologic feature of the medulla of the thymus. (A) Hassall corpuscle (B) Herring body (C) Mallory body (D) Meissner corpuscle (E) Pacinian corpuscle

*The answer is A.* T lymphocytes are preferentially located in the paracortex of lymph nodes, whereas B lymphocytes are found in lymphoid nodules located in lymph nodes, tonsils, and the spleen.

After their maturation in the thymus and release into the circulation, T lymphocytes migrate preferentially to which of the following sites? (A) Paracortex of lymph nodes (B) Cortical lymphoid nodules of lymph nodes (C) Hilus of lymph nodes (D) Lymphoid nodules of the tonsils (E) Lymphoid nodules of the spleen

*The answer is B.* The image shows a channel embedded in connective tissue between thymic lobules. The channel is filled with a monomorphic population of small lymphocytes (presumably thymocytes). The absence of red blood cells within the vessel lumen (see image of Question 9 for comparison) suggests that it is a lymphatic channel. Because the thymus lacks afferent lymphatic channels, this channel most likely represents an efferent channel. Efferent lymphatic vessels accompany blood vessels and nerves through the subcapsular and trabecular connective tissue. None of the other channels describe the morphology of lymphatic vessels in the thymus.

Cortical thymocytes are examined at high magnification in the histology laboratory. Further examination of the specimen reveals numerous thymocytes clustered within a channel that courses through connective tissue between adjacent lobules (shown in the image). What is the appropriate name for this channel? (A) Afferent lymphatic vessel (B) Efferent lymphatic vessel (C) Medullary sinus (D) Postcapillary venule (E) Precapillary arteriole

*The answer is D.* The spleen filters the blood. It removes pathogens and initiates immune response. The spleen also removes senescent and defective RBCs and retrieves iron from hemoglobin. The average life span of circulating RBCs is 120 days. With each pass through the red pulp of the spleen, RBCs must deform so as to squeeze through parallel stacks of long endothelial cells (so-called stave cells) that line the venous sinuses. This open circulation (from sheathed capillaries, to splenic cords, to venous sinuses) provides an opportunity for macrophages to remove RBCs that may be fragile or stiff. Macrophages also have receptors for phosphatidylserine molecules that appear on the outer leaflet of the RBC lipid bilayer following membrane damage. Kupffer cells (choice C) are resident macrophages in the liver. None of the other cells remove defective RBCs from the circulation in the spleen.

During a hematopathology conference you are asked to list and discuss functions of the spleen. Which of the following cells removes senescent and defective RBCs from the circulation in the spleen? (A) Dendritic cells (B) Endothelial cells (C) Kupffer cells (D) Macrophages (E) Reticular cells

*The answer is B.* As mentioned above, negative selection of immature T lymphocytes takes place in the medulla of the thymus during infancy and childhood. In this protected environment, MHC-restricted thymocytes encounter a variety of self-antigens that are displayed on the surface membranes of epithelioreticular cells. Up-regulation of self-antigens (e.g., insulin) on the surface of thymic reticuloepithelial cells is controlled by the autoimmune regulator (AIRE) gene product—a transcription factor. Thymocytes that are self-reactive undergo programmed cell death (negative selection). Macrophages (choice D) remove the residual apoptotic bodies of these self-reactive thymocytes. None of the other cells regulate T-cell education in the thymus.

During a hematopathology conference, you are asked to discuss mechanisms of T-cell "education" in the prepubertal thymus. Which of the following cells regulates negative selection of self-reactive thymocytes in the medulla of the thymus by expressing a wide variety of tissue-specific genes? (A) Dendritic cells (B) Epithelioreticular cells (C) Langerhans cells (D) Macrophages (E) Reticular cells

thymic medulla

Hassall's corpuscle is a diagnostic feature of what

Correct answer: A macrophage in the subcapsular sinus of a lymph node. Note the large size, eccentric nucleus, and cell inclusions.

Identify the cell indicated by the black arrow. An endothelial cell of a high endothelial venule A rod cell of a splenic sinus An epithelial reticular cell A macrophage A reticular cell A dendritic cell A plasma cell A T-lymphocyte

The asterisk marks a splenic cord. Note the presence of hemosiderin-laden macrophages which can help identify the cords, also note that you can see the outlines of the sinuses with the nuclei of lining cells (rod cells) jutting INTO the lumen of each sinus.

Identify the cell marked by the black arrow: A splenic sinus A splenic cord A lymph node medullary sinus A lymph node medullary cord The thymic cortex The thymic medulla

A macrophage in the subcapsular sinus of a lymph node. Note the large size, eccentric nucleus, and cell inclusions.

Identify the cell marked by the black arrow: An endothelial cell of a high endothelial venule A rod cell of a splenic sinus An epithelial reticular cell A macrophage A reticular cell A dendritic cell A plasma cell A T-lymphocyte

Correct answer: A T-lymphocyte. First, recognize that these images are from a thymus. The lighter area represents thymic medulla, not a germinal follicle. The morphology of the cell in question is such that it could only be a lymphocyte - although generally one cannot tell B and T-cells apart in routine H&E sections, you should be able to recognize this tissue as THYMUS where there generally are very few B-cells (the functional significance of these B-cells in the thymus is currently unknown).

Identify the cell marked by the black arrow: An endothelial cell of a high endothelial venule A rod cell of a splenic sinus An epithelial reticular cell A macrophage A reticular cell A dendritic cell A plasma cell A T-lymphocyte

Correct answer 2. A chondroblast in hyaline cartilage. It is OVOID and not yet surrounded by a lacuna. Therefore, it is a CHONDROBLAST. Osteogenic progenitors are located in the connective tissue perichondrium.

Identify the cell whose nucleus is marked by the black arrow. Chondrocyte Chondroblast Osteogenic progenitor cell Osteocyte Connective tissue fibroblast

Correct answer 2. Autonomic ganglion neuronal cell bodies between two layers of smooth muscle cells. The image depict a myenteric plexus or Auerbach's plexus.

Identify the cells indicated by the arrows in the below micrograph. Dorsal root ganglion neurons Autonomic ganglion neurons Satellite cells Schwann cells Intrafusal muscle fibers (cell)

Correct answer 2. The yellow arrows indicate canaliculi that extend from an osteocyte in a lacuna.

Identify the indented regions indicated by the yellow arrows. Lacunae Canaliculi Haversian canals Volkmann's canals Howship's lacunae

Correct answer 5. The bracket indicates the STRATUM CORNEUM of the epidermis.

Identify the layer indicated by the black bracket. The reticular layer of the dermis The papillary layer of the dermis The stratum basale of the epidermis The stratum granulosum of the epidermis The stratum corneum of the epidermis

The asterisk marks a splenic cord. Note the presence of hemosiderin-laden macrophages which can help identify the cords, also note that you can see the outlines of the sinuses with the nuclei of lining cells (rod cells) jutting INTO the lumen of each sinus.

Identify the location of the black asterisk. A splenic sinus A splenic cord A lymph node medullary sinus A lymph node medullary cord The thymic cortex The thymic medulla

Correct answer 2. Elastin and fibrillin. Most likely this image depicts the inner elastic lamina (IEL) of a muscular artery.

Identify the molecular components that form the structure that is indicated by the arrow in the TEM. Type IV collagen and laminin Elastin and fibrillin Type I collagen Smooth muscle cell cytoplasm Endothelial cell cytoplasm

Neonatal thymus high cell density of dark, lympatic cells in the cortex and the lighter stained areas of medulla also, there is a lobular organization young individual bc no areas of adipose cells are present GERMINAL CENTERS ARE NEVER PRESENT IN THE THYMUS

Identify the organ and explain the reason

Correct answer 4. Can readily regenerate and/or proliferate via cell division. The tissue shown is smooth muscle; all of the other responses apply to skeletal muscle (well, choice 3 actually applies to both cardiac AND skeletal muscle).

Identify the statement that is true about the predominant tissue depicted in this slide. It contracts rapidly and voluntarily. It interacts directly with nerves via motor end plates. It consists of regularly arranged sarcomeres. It can readily regenerate and/or proliferate via cell division. ALL of the above statements are true.

Correct answer 4. Like the sarcoplasmic reticulum in skeletal muscle cells, caveolae sequester and release calcium ions in smooth muscle cells.

Identify the structures that are functionally analogous to caveolae in smooth muscle cells. The transverse portion of intercalated disks in cardiac muscle The lateral portions of intercalated disks in cardiac muscle The Z lines in skeletal muscle cells The sarcoplasmic reticulum in skeletal muscle cells The T tubules in skeletal muscle cells

Correct answer 5. None of the above statements are true - the yellow outline encloses secretory cells of a SEBACEOUS gland. These cells secretes lipid-rich SEBUM by a HOLOCRINE mechanism.

Identify the true statement(s) about the cluster of cells enclosed by the yellow outline on the slide. They produce ceramide. They secrete in an apocrine manner. The secrete in an eccrine (or merocrine) manner. All of the above statements are true. None of the above statements is true.

Correct answer 4. This layer is the RETICULAR LAYER of the dermis and consists primarily of a coarse network of type I collagen fibers (which is why the term "reticular" is used here). Type III collagen is primarily found in the PAPILLARY layer of the dermis.

Identify the true statement(s) about the tissue layer indicated by the black line. It is where melanocytes usually reside. It contains cells densely packed with keratin tonofilaments. consists primarily of type III collagen fibers. consists primarily of type I collagen fibers. All of the above statements are true, None of the above statements are true.

Correct answer: venule. Note the size of the vessel (compared to the erythrocytes it contains) and the relative thinness of the vessel wall. Also a comparison with the nearby arteriole identifies it as a venule.

Identify the vessel that is indicated by the black arrow. Muscular artery Mid-size vein Arteriole Venule Capillary

Correct answer:B An individual with thymic aplasia would have no T-cells, so the most dramatic change would be in the deep cortex, which is the T-cell rich zone of a lymph node. The outer cortex would still contain primary follicles since they are B-cell rich, although there wouldn't be many secondary follicles with germinal centers due to a lack of T-cell help. The medulla wouldn't change much. Of course, the prognosis for this individual would not be good as he/she would be highly susceptible to infections.

In an individual with thymic aplasia (failure of the thymus to develop), which region of a lymph node shown would you expect to be attenuated? A B C ALL of the above NONE of the above

correct answer 3. A Haversian system (osteon) - this is a longitudinal section of compact bone showing LONGITUDINAL profiles of osteons consisting of concentric lamellae surrounding central Haversian canals (also in longitudinal profile). The canals that run PERPENDICULAR to the Haversian canals and it do NOT have any concentric lamellae organized around them are nutrient or Volkmann's canals.

In this section of ground bone, identify the area indicated between the two purple lines. Outer circumferential lamellae Interstitial lamellae A Haversian system (osteon) A Volkmann's canal Inner circumferential lamellae

Answer: D

In this section of heart tissue, which of the brackets correctly demarcates the endocardium? A B C D

*The answer is C.* T lymphocytes mature and become immunocompetent in the cortex of the thymus, whereas B lymphocytes do so in the bone marrow. After an antigenic challenge, lymphocytes proliferate and differentiate in various lymphoid tissues

In which of the following sites do lymphocytes become immunocompetent? (A) Germinal center of secondary lymphoid nodules (B) White pulp of the spleen (C) Thymic cortex (D) Red pulp of the spleen (E) Paracortex of lymph nodes

Correct answer 5. In all of the listed cellular structures (Answers 1 to 4). Myoepithelial cells are found in the acini and ducts of mammary glands and in the acini of eccrine and apocrine sweat glands. Note that they are NOT found in sebaceous glands (not needed since these glands secrete in a holocrine manner).

In which places/structures can myoepithelial cells be found? In active mammary gland acini In inactive mammary gland ducts In eccrine sweat gland acini In apocrine sweat gland acini In all of the above cellular structures In none of the above cellular structures

Darker stained areas bc dense lymphatic cells that might have germinal centers

Is white pulp stained darker or light? why

- the connective tissue capsule and darkly stained cortical versus a lighter and less densely populated medullar region - might find germinal centers in the cortex

List ways to identify a lymph node

*The answer is C.* The thymus normally develop less functionality and increasing amounts of adipose tissue with age.

Many immune-related cellular activities are often impaired in aged patients. Which lymphoid organ(s) normally develop less functionality and increasing amounts of adipose tissue with age? a. Axillary lymph nodes b. Lingual tonsils c. Thymus d. Splenic white pulp e. Splenic red pulp

1. Letter A labels the reticular dermis, so named because of the network of coarse, type I collagen fibers (Letter B indicates the papillary dermis). 2. Letter C labels Meissner's corpuscles, which are mechanosensory receptors that respond primarily to light touch and low frequency stimuli. 3. Letter D labels the ductal portions of sweat glands that are lined with a stratified cuboidal epithelium consisting of small, darkly staining cells. It is most likely an eccrine sweat gland duct given its proximity to a nearby acinus ('F') which is clearly eccrine (based on the small lumen). 4. Letters C AND E label both Meissner's AND Pacinian corpuscles, which are sensory receptors that are innervated by myelinated axons of dorsal root ganglion cells. 5. NONE of the letters labels an apocrine sweat glands as none is present in this tissue section ('G' is a venule).

Match the text descriptions below with the appropriately feature that is labeled by a letter in the tissue section. Some labeled features may be referred to once, more than once, or not at all. If the description refers to something NOT labeled on the slide, answer "NONE." Reticular dermis Which structure(s) respond(s) to light touch and low frequency stimuli An eccrine sweat gland duct Which structure(s) is/are innervated by a neuron, whose cell body is in a dorsal root/sensory ganglion An apocrine sweat gland secretory acinus

*The answer is C.* The photomicrograph provides a low magnification view of a lymph node. This secondary lymphoid organ is composed of a peripheral cortex and a pale stained, central medulla. Numerous lymphatic nodules are present in the cortex. The hilum, seen on the lower right side of the image, provides a region for blood vessels and an efferent lymphatic channel to enter and/or exit the lymph node. Lymph nodes filter the lymph, removing macromolecular antigens, and they provide a microenvironment for antigen-driven activation of B and T lymphocytes. None of the other lymphoid organs exhibit the distinctive morphology of a lymph node.

Primary and secondary lymphoid organs are examined in the histology laboratory. Identify the organ shown in the image (low magnification). (A) Bone marrow (B) Lingual tonsil (C) Lymph node (D) Spleen (E) Thymus

*The answer is E.* Primary lymphoid organs generate immature B and T lymphocytes; these organs include the bone marrow and thymus. Secondary lymphoid organs provide an environment for antigen stimulation and clonal selection; these organs include (1) diffuse and nodular lymphoid tissue; (2) lymph nodes, and (3) spleen. The image shows the distinctive lobular architecture of the thymus. The lobules are separated by connective tissue trabeculae that originate from a thin capsule. Each lobule is composed of a dark-stained cortex (cortical cap) and a light-stained medulla. The medullary regions are continuous. The cortex and medulla are populated by T lymphocytes (thymocytes) at various stages of differentiation. Reticuloepithelial cells form an extensive meshwork that organizes thymocytes and regulates their growth and development. At low magnification, thymic lobules look like secondary lymphoid follicles with germinal centers (choices B and C); however, lymphoid follicles in mucosa-associated lymphoid tissue are not separated by trabeculae, and lymph nodes have subcapsular, trabecular, and medullary sinuses. The thymus undergoes atrophy after puberty and is replaced by adipose tissue (thymic involution). None of the other lymphoid tissues/organs exhibit the distinctive lobular morphology of the prepubertal thymus.

Primary and secondary lymphoid organs are examined in the histology laboratory. Identify the organ shown in the image (low magnification). (A) Bone marrow (B) Lingual tonsil (C) Lymph node (D) Spleen (E) Thymus

*The answer is D.* The image shows a low magnification section through the spleen. Examination of the specimen reveals scattered splenic lymphoid nodules (white pulp) surrounded by small venous sinuses (red pulp). A dense connective tissue capsule encloses the spleen from which numerous trabeculae penetrate the parenchymal tissue. The spleen filters the blood, removing aged and defective RBCs. The spleen also provides a microenvironment for generating immune responses to blood-borne antigens. None of the other lymphoid organs display red and white pulp.

Primary and secondary lymphoid organs are examined in the histology laboratory. Identify the organ shown in the image (low magnification). (A) Bone marrow (B) Lymph node (C) Peyer patch (D) Spleen (E) Thymus

*The answer is D.* The major complex containing iron, occurs most actively in the spleen.

Recycling of iron and heme, the major complex containing iron, occurs most actively in which lymphoid organ(s)/tissue(s)? a. Lymph nodes b. Peyer's patches c. Tonsils d. Spleen e. Lymphatic vessels

Correct answer 4. All of the first three statements are true as the image depicts an epiphyseal growth plate with the zone of proliferation marked by the yellow bracket.

Select the answer that best describes the area indicated by the yellow bracket. It contains proliferating chondrocytes. It contains type II collagen fibers in its matrix. It is NOT present in adult bone (bone that is no longer growing in length) ALL of the above statements (1 to 3) are true None of the above statements are true

*The answer is D.* The arrow identifies dense connective tissue in the capsule of the spleen. The capsule and associated trabeculae of the spleen are populated by myofibroblasts. These contractile cells are believed to provide tension on the red pulp to accommodate changes in blood flow and discharge reserves of RBCs as needed. Myofibroblasts also synthesize a variety of extracellular matrix molecules. None of the other cells have been identified in the capsule of the spleen.

The capsule of the spleen is known to contain which of the following connective tissue cells? (A) Dendritic cells (B) Epithelioreticular cells (C) Follicular dendritic cells (D) Myofibroblasts (E) Reticular cells

Correct answer: It is re-entering the bloodstream in a splenic sinus. The presence of blood elements (e.g. platelets) OUTSIDE the vessel should identify this tissue as spleen, leaving only choices 5. and 6.. 5. is incorrect because there generally are no afferent lymph vessels in the spleen. 1. is incorrect because the endothelium is not 'high' - also leukocyte homing in a lymph node is usually restricted T and B-cells and monocytes. 2. is incorrect because medullary sinuses are LYMPHATIC sinuses, not blood sinuses. 3. is incorrect because there are no afferent lymph vessels in the thymus. 4. is possible, but highly unlikely. Mature T-lymphocytes may enter circulation via INTRAVASATION into venules in the thymus. Eosinophils and other granulocytes generally only LEAVE the circulation; they don't re-enter (except in the spleen where all blood cells leave the bloodstream and have to re-enter via the sinuses).

The electron micrograph shows an eosinophil traversing a vessel wall. What is the most likely process happening? It is entering the deep cortex of a lymph node via a high endothelial venule. It is re-entering the bloodstream in a lymph node medullary sinus. It is entering the thymic medulla via an afferent lymph vessel. It is exiting the thymic medulla via intravasation into a medullary venule. It is entering splenic white pulp via an afferent lymph vessel. It is re-entering the bloodstream in a splenic sinus.

Correct answer 3. Muscular artery. Note the well-defined inner elastic lamina and the thickness of the smooth muscle layer forming the tunica media.

The image depicts the wall of a cardiovascular component. Identify that component. Heart ventricle Heart atrium Muscular artery Elastic artery Mid-size or large vein Large lymphatic vessel

Correct answer: This is a mid-size or large vein. Note the cross section of a longitudinal smooth muscle bundle in the tunica adventitia.

The image shows the wall of a component of the cardiovascular system. Identify this component. Heart ventricle Heart atrium Muscular artery Elastic artery Mid-size or large vein Large lymphatic vessel

capsule then cortex (darker area): - nodular cortex (outer cortex) is rich in B cells - inner cortex or paracortex is rich in T cells then medulla -- medullar cords are rich in B cells

The lymph node can be divided into the cortex and medulla regions. Where do you expect to find mostly B and where mostly T cells?

Correct answer 1. Schwann cells as the images depict a myelinated nerve in Panel A and an unmyelinated nerve in Panel B.

The nuclei indicated by the arrows in Panel A and labeled "N" in the electron micrograph in Panel B (which is a high magnification view of the boxed area in panel A) belong to which type of cell? Schwann cells Smooth muscle cells Fibroblasts of the perineurium Dorsal root (sensory) ganglion neurons Autonomic ganglion neurons

*The answer is D.* Plasma cells are antigen-presenting cells that secrete immunoglobulins.

The plasma cell A. differentiates from T-lymphocytes following antigenic stimulation B. destroys foreign cells by inserting perforins in their membranes C. contains abundant smooth endoplasmic reticulum D. secretes immunoglobulins

*The answer B.* The spleen plays a major in in the destruction of abnormal red blood cells.

The spleen: A. contains numerous germinal centers in the red pulp B. plays a major role in the destruction of abnormal red blood cells C. is the primary erythropoietic organ of the fetus during the last third of pregnancy D. is essential to life E. has sinusoids lined by phagocytic cells

Correct answer 5. Brackets A, B, and C. As a heart valve leaflet is formed by a fold of the endocardium, the entire AV valve is part of the endocardium.

This TEM micrograph depicts an A-V valve leaflet. Which bar/letter marks the endocardium? Bracket A Bracket B Bracket C Brackets A and B Brackets A, B, and C

Macrophages are the major APCs in the tonsil and the spleen (although the spleen also has dendritic cells that do this to some extent as well). In the lymph node, dendritic cells are the major antigen presenters, although macrophages in the medullary sinuses also do this to some extent as well.

What are the major antigen presenting cells of the tonsil, spleen and lymph node?

Correct answer 2. The inner circumferential lamella is labeled. Note the location of the bone marrow.

What histological structure does the yellow bracket indicate? An interstitial lamella An inner circumferential lamella An outer circumferential lamella The periosteum The endosteum

These are the stellate shaped fibroblasts found in the lymph node that are involved in making reticular (type III collagen) fibers. They are NOT the same as the epithelial reticular cells found in the thymus: epithelial reticular cells s are true epithelial cells derived from the endodermal lining of the third pharyngeal pouch in the embryo (the third pouch is what gives rise to the thymus) whereas reticular cells, like most connective tissue fibroblasts, are derived primarily from mesoderm.

What is a fiber associated reticular cell?

The thymus is entirely composed of T cells, epithelial reticular cells and some macrophages. Occasionally another type of cell will get into the thymus, but it does not belong there. The thymus consists of a cortex and medulla with no germinal centers. Immature T cells are found at the edges of the cortex. As they mature, they migrate deeper into the cortex and eventually leave as mature naïve T cells through the venules of the medulla. In the lymph node, the cortex is made of primary follicles of resting B cells and secondary follicles with germinal centers. The germinal centers are where B cells are undergoing clonal expansion, after binding antigen and receiving T cell help. Most T cells are located deeper in the cortex. Antigen-stimulated helper T cells are formed when antigen is presented to them by dendritic cells (and possibly macrophages), deep in the cortex. B cells also bind their antigen in this region. B cells entering the lymph node travel through the cortex to a follicle. If they have bound antigen in the cortex, they attract antigen-stimulated T helper cells to the follicle, where T cell help occurs. T cell help in the spleen occurs in the PALS. Close to, if not touching, the PALS are follicles of resting B cells, a clone of which may give rise to a germinal center upon proper stimulation.

What is the distribution of B cells and T cells in the lymphatic tissue?

5. Tight junctions in the perineurium.

What type of cell junction plays an important role in the FUNCTION of the connective tissue layer indicated by the arrows? Gap junction Desmosome Hemidesmosome Zonula adherens or adherent junction Tight junction

Hyaline cartilage contains fibers made primarily of type II collagen only. Fibrocartilage contains type II collagen but also contains abundant type I collagen. Elastic cartilage contains type II collagen and elastic fibers.

What type of collagen is found in the cartilage types

*The answer is A.* B cells give rise to both memory and effector cells and is primarily associated with humoral immunity.

Which cell type gives rise to both memory and effector cells and is primarily associated with humoral immunity? a. B lymphocyte b. NK cell c. Macrophage d. T lymphocyte e. Reticular cell

*The answer is E.* All secondary (peripheral) lymphoid organs contain lymphoid nodules.

Which description is true of all secondary (peripheral) lymphoid organs? a. Capable of antigen-independent lymphopoiesis b. Contain crypts c. Contain epithelial-reticular cells d. Lack connective tissue capsules e. Contain lymphoid nodules

*The answer is A.* All lymphoid tissues and organs produce lymphocytes.

Which function is carried out by all lymphoid tissues and organs? a. Filtration of lymph b. Filtration of blood c. Extramedullary hemopoiesis d. Production of lymphocytes e. Destruction of old erythrocytes

Correct answer 5. All of the statements are TRUE. Note that statement 3 is TRUE. The matrix of fibrocartilage does contain type II collagen and some hyaluronan (of course, there's also a lot of type I collagen (just because type 1 collagen wasn't mentioned does NOT make the statement incorrect).

Which of the following statement(s) is/are true about fibrocartilage? It is present in intervertebral disks. It usually inserts into bone. It contains a matrix of type II collagen and hyaluronan. It has high tensile strength. ALL of the above.

*The answer is D.* Hassall corpuscles are located in the thymic medulla.

Which of the following statements concerning Hassall corpuscles is true? A. They are located in the thymic cortex of young individuals B. They are located in the thymic cortex of older individuals C. They are derived from mesoderm D. They are located in the thymic medulla E. They are derived from T memory cells

*The answer is B.* Epithelial reticular cells of the medulla congregate to form Hassall (thymic) corpuscles.

Which of the following statements concerning the thymus is true? (A) Lymphoid nodules form much of the thymic cortex. (B) Epithelial reticular cells form Hassall corpuscles. (C) T cells migrate into the medulla, where they become immunologically competent. (D) Most T cells that enter the thymus are killed in the medulla. (E) Macrophages are essential components of the blood-thymus barrier.

Excess activation of these cells may result in hypocalcemia (low blood calcium levels). The activation of osteoclasts results in higher blood calcium levels. Low blood calcium levels will trigger the release of parathyroid hormone (PTH), which will induce the formation of new osteoclasts.

Which of the following statements regarding the cells indicated by the black arrows is INCORRECT? They are derived from hematopoietic progenitor cells. They secrete collagenase. They are involved in remodeling ALL bones, whether formed via endochondral OR intramembranous ossification. Excess activation of these cells may result in hypocalcemia (low blood calcium levels). NONE of the above (i.e. ALL of the above statements are CORRECT).

Answer: 1 -- Smooth muscle cells are not found in the tunica intima.

Which statement regarding vascular smooth muscle cells is NOT true? They are especially abundant in the tunica intima of some mid-size blood vessels. They produce reticular and elastic fibers in the tunica media of large elastic arteries. If present in the tunica media of any blood vessel, they are oriented circularly. They may be present as longitudinal bundles in the tunica adventitia of large veins.

The cell is a mature erythrocytes/RBC which expresses ABO antigens that determine an individual's blood type.

Which statement(s) is/are true about the cell marked by the black arrow in the transmission electron micrograph below? It does not function properly in individuals with NADPH oxidase deficiency. It in normal individuals constitutes approximately 70% of total blood volume. It transports the bulk of blood CO2 as carboxyhemoglobin. It is derived from a lymphoid progenitor cell. It expresses ABO antigens that determine an individual's blood type. All the above statements are true.

The cell indicated is a basophil, which comprises less than 1% of circulating leukocytes.

Which statement(s) is/are true about the cell marked by the black arrow? It comprises less than 1% of circulating leukocytes. It produces platelets. It is derived from a lymphoid progenitor cell. It can leave the bloodstream and differentiate into a tissue macrophage. It secretes IgE antibodies.

The structures marked by the arrows are platelets/thromocytes, which are derived from a myeloid progenitor cell.

Which statement(s) is/are true about the histological structures indicated by the arrows. They express ABO antigens that determine an individual's blood type. They primarily contain enzymes that regulate blood pH. They are derived from a myeloid progenitor cell. They contain enzymes that produce oxygen radicals. They contain granules of insoluble fibrin

Correct answer 1. The bone spicule arose by intramembranous ossification.

Which statement(s) is/are true about the structure indicated by the yellow arrow. It arose via intramembranous ossification. It arose via endochondral ossification. It is comprised primarily of calcified cartilage. It is undergoing extensive remodeling as evidenced by numerous osteoclasts on its surface. It is in a secondary center of ossification.

*The answer is C.* The palatine tonsil is partly encapsulated and covered by nonkeratinized stratified squamous epithelium.

Which structure is partly encapsulated and covered by nonkeratinized stratified squamous epithelium? a. Appendix b. Lymph node c. Palatine tonsil d. Peyer's patch e. Thymic (Hassal's) corpuscle

*The answer is B.* T-lymphocyte precursors arise in the bone marrow, enter the circulatory system, and populate the thymus during fetal development. These multipotential lymphoid stem cells migrate to the cortical region of the thymic lobules. Here, they undergo T-cell receptor gene segment recombination and mutation to generate a heterogeneous population of thymocytes—each bearing a unique cell surface antigen receptor. Unlike surface immunoglobulins on B lymphocytes, T-cell receptors bind antigens that are presented by proteins encoded by the major histocompatibility complex (MHC). None of the other lymphoid organs provide a microenvironment (niche) for T-cell receptor gene assembly.

You are invited to give a research seminar on current topics in immunology. During your presentation, you are asked to explain key steps in lymphocyte differentiation. T-cell receptor gene rearrangement takes place in which of the following anatomic locations? (A) Bone marrow (B) Cortex of the thymus (C) Fetal liver (D) Mantle zone of secondary lymphoid follicles (E) Medulla of the thymus

This is the spleen

identify the organ depicted by this image Spleen Tonsil Thymus Lymph node Gut-associated lymphoid tissue

Correct answer 2. The tissue is cardiac muscle. Note the striations, branched fibers, intercalated discs, and centrally-located nuclei.

identify the tissue Skeletal muscle Cardiac muscle Smooth muscle Epimysium Dense regular connective tissue (tendon)

Correct answer 1. Hyaline cartilage is highly resistant to compression. It does NOT always have a perichondrium (as in articular cartilage). Its matrix consists of type II collagen and hyaluronan, and it is NOT found in the pinna of the ear and epiglottis (elastic cartilage is found there).

identify the true statement about the cartilage It is highly resistant to compression. It is ALWAYS completely invested by a fibrous perichondrium. It contains a matrix of type I collagen fibers and hyaluronan. It is found primarily in the pinna of the ear and the epiglottis. ALL of the above statements are true.

dense irregular connective tissue

the capsule of the spleen and the trabeculae are made of what tissue type?

The lymph node is composed of follicles surrounding medullary cords and sinuses. A feature that is characteristic of the lymph node is the post capillary, high endothelial venule. You can occasionally see lymphocytes migrating from the blood into the lymph node if you examine the walls of these vessels. In the palatine tonsil you can see large follicles and a stratified squamous epithelium. One feature of the lymphoid tissue of the tonsil and MALT in general is that its follicles have a "starry sky" appearance. This comes from the numerous, light staining macrophages present, along with lymphocytes and plasma cells, in the germinal centers of the tonsil. The spleen consists of areas of red and white pulp. The spleen can be identified by looking for deep staining areas of white pulp surrounding central arteries. These areas are known as the periarterial lymphatic sheath (PALS for short). Germinal centers of the spleen often run along the PALS. The thymus is unique in that it is the only lymphoid organ with no germinal centers. Germinal centers are made up of B cells that are proliferating and preparing to become plasma cells. You should never see B cells in the thymus. It is a place for the maturation of T cells, which then leave the thymus and enter other lymph tissues. The thymus is composed of lobules. One easily recognizable feature of the thymic medulla is the presence of Hassall's corpuscles. The function of these corpuscles is uncertain, although they do secrete IL-4 and IL-7 and therefore certainly influence the development of the thymus and T-cell maturation.

what are some defining characteristics of each of the lymphoid organs

Though it is easy to differentiate between compact and spongy bone at a gross level, at the microscopic level the main difference is the presence or absence of osteons. Grossly, compact bone has a dense appearance and is found, for example, on the outer surfaces of the long bones of the body. As the name implies, spongy bone is shaped like a sponge. The spaces within the sponge-shaped framework are filled with bone marrow. Compact bone, microscopically, is made of numerous osteons, whereas spongy bone is composed of sheets of lamellar bone and does not contain osteons.

what distinguishes between compact and spongy bone

the marginal zone represents the transition between white and red pulp primary site of antigen presentation in the spleen marginal zone surrounds mantle zone

what is impt about marginal zone

Spleen

what organ is this Spleen Tonsil Thymus Lymph node Gut-associated lymphoid tissue

Osteoid is the organic matrix of bone, not yet mineralized, that is laid down by osteoblasts (which also facilitate its mineralization).

what's an osteoid

4. Indicated is the AV bundle or bundle of His. It conducts the action potential from the A-V node to the ventricular myocardium.

which statement is true They synthesize and maintain components of the cardiac skeleton. They initiate contraction of atrial myocardium. They attach to atrioventricular valve leaflets via chorda tendinae. They conduct action potentials from the A-V node to the ventricular myocardium. They contract vigorously when stimulated and therefore contributes significantly to overall cardiac output.

only the germinal centers in the nodules are enriched in B cells the rest of the white pulp especially the PALS is rich in T cells

which white pulp area(s) is/are rich in B cells and which are rich in T cells?

With their dark staining nuclei and little cytoplasm, the abundant T lymphocytes in the cortex give the thymus a dark color. The thymic medulla has far fewer lymphocytes in it and so stains much lighter.

why is the thymic medulla lighter than the cortex