Blood and Lymphatic Tissue PDF

Blood and Lymphatic tissue ANAT2441: Histology JOYCE EL-HADDAD [email protected] @orientatewithjoyce Lecture Outline - Function of blood - formation of blood - Formed elements of blood - Lymphoid organs Learning Outcomes 1. To identify the cellular components of blood and understand their...

Blood and Lymphatic tissue ANAT2441: Histology JOYCE EL-HADDAD [email protected] @orientatewithjoyce Lecture Outline - Function of blood - formation of blood - Formed elements of blood - Lymphoid organs Learning Outcomes 1. To identify the cellular components of blood and understand their functions. 2. To describe the tissue morphology of a lymph node and the features of the cortex, medulla, trabeculae, medullary cords and sinusoidal system. Centrifuged blood sample Plasma composition Plasma ~55% Water 92% Transports organic and inorganic molecules, cells, platelets, and heat Plasma proteins 7% Other solutes Buffy coat <1% 1% Platelets Blood clot formation and tissue repair White blood cells Neutrophils (60 -70%) Monocytes (3-10%) Red blood cells Eosinophils (1-4%) Red blood cells ~45% Lymphocytes (20 -40%) Basophils (0 -1%) LM of bone marrow obtained via needle biopsy from the medullary cavity L typi Two are a (Ba) stain lymp has cyto (RBC elem a un and with bico 690 Blood • • • Blood is specialized connective tissue Consists of cells that circulate in a fluid known as plasma Average volume of blood ~ 4-6 L depending on body composition Function of blood is: o to transport oxygen and nutrients to the lungs and tissues. o form blood clots to prevent blood loss o carry cells that are immune in nature o deliver waste products to the kidneys and liver, which filter and clean the blood. 168 Blood and Bone Marrow Blood formation (Haemopoiesis) Timeline Main source of Haemopoiesis PE RBC First few weeks of gestation Yolk sac 6 weeks of development Liver and spleen 6-7 months of fetal life Bone marrow LM of a bone marrow smear at low (Above) and high (Right) magnifications. The smear, made from a bone marrow aspirate, shows details of hematopoiesis. Hematopoietic cells of the erythroid lineage at different stages of development in B include a proerythroblast (Pr), basophilic erythroblast (BE), and early polychromatophilic erythroblast (PE). Mature erythrocytes (RBC) and two unidentifiable cells (arrows) are also seen. Above: 8×; Right: 2000×. Wright’s. Pr BE https://radiopaedia.org/articles/yolk-sac He Childhood Bone marrow (most of the skeleton) Adult life Bone marrow (axial skeleton, femur, LM of a bone marrow biopsy specimen at low (Above) and high (Right) magnifications. The solid core of tissue contains bone marrow and humerus) and bony trabeculae (arrows). Normal bone marrow consists of a heter- FC Bo ogeneous population of cells in various stages of differentiation. Clusters of tightly packed hematopoietic cells (He) sit between large adipocytes (FC) and bony trabeculae (Bo). Adipocytes look empty because of lipid extraction during specimen preparation. Above: 8×; Right: 200×. H&E. 7.11 METHODS OF STUDYING BONE MARROW Smears and trephine needle biopsy (for preparation of bone than smears for elucidating cell details but provide a panoramic view of bone marrow and its normal architecture. They are also Haemopoiesis • Bone marrow is the site of haematopoiesis after birth. Because most blood cells are short-lived, they need continuous replacement. • All mature blood cells derive from pleuripotential stem cells in bone marrow • Colony-forming unit (CFUs) committed to erythroid lineage production contain progenitor cells known as colony-forming unit-erythrocytes (CFU-E). In other words, these are the cells that turn into the erythrocytes. • Granulocyte and monocyte cell lines develop from one progenitor cell known as the colony-forming unitgranulocyte-monocyte (CFU-GM). In other words, these are the cells that turn into the leukocytes. • Cells of the lymphocyte lineage are generated from colony-forming unit-lymphocytes (CFU-L). • Progenitor cells for megakaryocytes produce colonies that contain colony-forming unit-megakaryocytes (CFU-Me). En Erythrocytes (red blood cells) • • • • • • Anucleated biconcave discs A biconcave shape provides a large surface area for primary functions like transporting O2 from lungs to tissues and returning CO2 from tissues to lungs for elimination The iron containing protein hemoglobin in RBCs accounts for their red color Highly flexible and malleable as they travel in narrow capillary lumina 99% of formed elements of blood and have a lifespan in circulation of 120 days RBCs lose their nucleus at the end stages of erythropoietic development in bone marrow. * RBC * 5µm Electron micrograph (EM) of an erythrocyte in the lumen of a capillary. The RBC lacks organelles. Its uniformly granular density is due to the presence of hemoglobin. An endothelium (En) surrounds the capillary, sectioned transversely. Note how the RBC completely fills the lumen. 11,500×. RBC 2µm 7.3 ULTRASTRUCTURE AND FUNCTION OF ERYTHROCYTES RBCs are anucleate biconcave discs that are highly flexible and malleable as they travel in narrow capillary lumina. They make up 99% of the formed elements of blood and have a lifespan in circulation of about 120 days. Numbers of RBCs per liter of blood usually average 5 × 1012 in men and 4.5 × 1012 in women. In the human embryo, RBCs are initially nucleated, up to 7 weeks of gestation. During final stages of erythropoietic development in bone marrow, RBCs lose the nucleus and almost all organelles except the cytoskeleton and then enter the circulation. Because RBCs lack a nucleus but have a plasma membrane, they are more containing protein hemo color. Hemoglobin rapid jugated protein containi globin. Heme is a porphy of hemoglobin in whole 12-16 g/dl for females. S abnormalities, including occur in humans. C A deficiency of RBCs and types of which exist. Corr Immune System LYMPHOCYTES Function: provide defense of the body against invasion of foreign material from both outside and inside the body A Neutrophil. Ne Neutrophils • Neutrophils are the most numerous leukocytes and constitute 60%-70% of the leukocyte count. • The nucleus has a distinctive morphology and many forms (polymorphonuclear leukocytes), with a clump-like pattern and three to five lobes connected by fine chromatin strands. • Immature neutrophils show only slight nuclear lobulation; older cells have more, dark-staining lobes. A Neutrophil. • • • RBC Blood and Bone Marrow B Neutrophils are actively motile and function outside the circulation. After they develop in bone marrow, they stay in the bloodstream for 8-12 hours. Neutrophil numbers increase in acute bacterial infections. 161 Ne Ne RBC * C RBC GC LMs of neutrophils in blood smears. The young neutrophil (Ne) in A has a U-shaped, darkly stained nucleus. The neutrophil in B is more mature; its * Eosinophils • Eosinophils make up a small proportion of leukocytes in peripheral blood: 1%-4% of the leukocyte count. • Eosinophils circulate in the bloodstream for 6-8 hours; once they migrate to connective tissues, their lifespan is 8-10 days. • Their nucleus is typically bilobed. • Cytoplasm extremely eosinophilic. 162 Blood and Bone Marrow Eosinophil. • The cells phagocytose antigen-antibody complexes and parasites, and elevated cell numbers occur in parasitic infections and allergic responses such as hay fever and asthma. Eo RBC LM of an eosinophil in a blood smear. The distinctive, closely packed eosinophilic granules fill the cytoplasm of the eosinophil (Eo). The usually bilobed nucleus has an irregular shape. This granular leukocyte has a larger diameter than that of the erythrocytes (RBC). 1350×. Wright’s. Basophils • The least numerous leukocytes, account for less than 1% of the leukocyte count • The nucleus is often irregular in shape or bilobed. • Distinctive specific granules that are intensely basophilic and fill the cytoplasm. • Basophils closely resemble mast cells of connective tissue • Basophil. .The motile basophils are involved in allergic reactions and increase in number in many clinical conditions such as hay fever, urticaria (hives), chronic sinusitis, and some leukemias. • Blood and Bone Marrow Ba RBC An elevated basophil count in peripheral blood rarely occurs in most benign conditions. An increasing basophil count can suggest worsening of disease SG LM of a basophil in a blood smear. The easily recognized basophil (Ba) has many large basophilic specific granules that are blue. The nucleus, being masked by the granules, is less evident. The erythrocytes (RBC) are smaller than the basophil. 1200×. Wright’s. Monocytes • Monocytes are agranular leukocytes that are immediate precursors to cells of the monocytemacrophage system (aka Mononuclear Phagocytic System) • They usually circulate in the bloodstream for only 1-3 days and perform almost all functions outside the circulation. These actively motile cells enter connective tissues to become macrophages (or phagocytes). Monocyte. • Each cell has a nucleus that varies in form and may have an oval, kidney, or horseshoe shape Blood and Bone Marrow LM of a monocyte in a blood smear. A monocyte (Mo) nucleus is highly indented and less densely stained than that of lymphocytes. Throughout the light blue cytoplasm are many faintly stained granules, so the cytoplasm looks dusty. The monocyte is twice as large as the erythrocytes (RBC). 1350×. Wright’s. Mo RBC 1 Platelets Blood and Bone Marrow opoiesis 169 Thrombocytopoiesis (Megakaryocytopoiesis) poietic Cell Cell Hematopoietic Stem Cell CFU-Meg blast Megakaryoblast 166 Blood and Bone Marrow Platelets. Promegakaryocyte RBC hocyte Thymus • Platelets are motile cytoplasmic fragments enveloped by a plasma membrane • They arise from megakaryocytes in bone marrow and appear as plate-like structures without nuclei. • Platelets play a major role in blood coagulation Pl Megakaryocyte En 1µm T-Lymphocyte Platelets EM of two platelets and part of an erythrocyte (RBC) in the lumen of a blood vessel. The platelets (Pl) contain several dense, membrane-bound granules. One platelet seems to adhere (arrows) to the vessel’s endothelium (En). 15,000×. Pl T-Lymphocyte Platelets T-Lymphocyte nce, main cell types seen in bone marrow smears topoiesis (center, right), and megakaryocyesemble lymphocytes. Except for megakaryocytes, es, nuclear density increases, and special features cific granules (eosinophilic, basophilic, or on rate and survival and maturation of progenitor Pl En Lymphocytes Lymphocytes Organs B Cells* T Cells* NK cells Dendritic cells (antigen presenting cell) Diffuse Lymphatic Tissue (S) Lymph Nodes (S) Spleen (S) Thymus (P) Bone Marrow (P) P= Primary lymphatic organ S = Secondary lymphatic organ * Plus different types of these cells. Lymphocytes - B cells are more numerous than T cells - B cells > Plasma cells > production and secrete of antibodies - T cells recognise invaders, activate the immune response, kill infected or abnormal cells, coordinate immune functions, and establish immunological memory to provide long-term protection against recurring threats. Take home: Smooth cytoplasm = low/no activity Rough/grainy cytoplasm = high activity – protein synthesis Lymphocytes When lymphocytes are active, that is when their morphology will change e.g. Plasma “Clockface” nucleus • Heterochromatin: tightly packed form of DNA (dark) • Euchromatin: loosed packed form of DNA (light) • Activated B cell > plasma B cells that is secreting antibodies B vs T cell Plasma B cell Cytotoxic T cell Lymphoid Organs qDiffuse Lymphatic Tissue (S) qLymph Nodes (S) qSpleen (S) qThymus (P) Diffuse Lymphatic Tissue • Mucosal Associated Lymphoid Tissue (MALT) • Initiate immune responses to specific antigens encountered along all mucosal surfaces – enlarge. • Not enclosed by a connective tissue capsule • Located in the underlying lamina propria of epithelial lining Different locations, different name: NALT - Nasal Associated Lymphoid Tissue BALT - Bronchus Associated Lymphoid Tissue GALT - Gut Associated Lymphatic Tissue Think about the epithelial lining covering the nasal cavity, upper resp tract and GIT Lymphatic follicles in the ileum Transport gut lumen organisms and particles to immune cells across the epithelial barrier. Most numerous in the ileum of the small intestine LYMPH NODES: Function In lymph vessel pathways “filter” (surveillance) lymph Immune - detect infections from peripheral tissues • skin, respiratory tract, gastrointestinal tract, etc. Return interstitial fluid to circulation Primary or secondary? LYMPH NODES: Structure Location throughout the entire body - concentrated in axilla, groin, lung, gastrointestinal tract mesenteries Small (1 mm - 2 cm) encapsulated organ. In lymph vessel pathways “filter” lymph • Afferent - towards node (A - arrives at the node) • Efferent - away from node (E - exits the node) LYMPH NODES 1 Afferent lymphatic vessel 2 Subcapsular sinus 3 Trabecular sinus 4 Medullary sinus 5 Efferent lymphatic vessel Afferent lymphatic vessels → subcapsular sinus → trabecular sinuses → medullary sinuses → efferent lymph vessel (hilum) @orientatewithjoyce @orientatewithjoyce @orientatewithjoyce • High endothelial venules (HEVs) are different from regular blood vessels. • They have a high endothelial cell layer with cuboidal or columnar morphology, as opposed to the flat endothelial cells found in typical capillaries. • This specialized endothelium allows for interactions between lymphocytes and endothelial cells, which is essential for lymphocyte extravasation (leakage).