Lymphatic System Lecture Slides.pdf

Lymphatic System  Objectives List the functions of the Lymphatic System, the Lymphatic Vessels and the Cell Types. Describe the diffuse lymphatic tissue, GALT (Gut Associated Lymphatic Tissue), MALT (Mucosa Associated Lymphatic Tissue), BALT (bronchus-associated lym...

Lymphatic System  Objectives List the functions of the Lymphatic System, the Lymphatic Vessels and the Cell Types. Describe the diffuse lymphatic tissue, GALT (Gut Associated Lymphatic Tissue), MALT (Mucosa Associated Lymphatic Tissue), BALT (bronchus-associated lymphatic tissue) and the lymphatic nodules. Describe the histologic structures of the tonsils (palatine, pharyngeal and lingual tonsils). Explain the specific functions, components (stroma & parenchyma), histologic organization, and the histophysiology of the lymphatic organs.  Objectives List the functions of the Lymphatic System, the Lymphatic Vessels and the Cell Types. The lymphatics collect plasma continuously leaking out from blood vessels into the interstitial spaces and return this fluid, now called lymph, to the blood (after filtration). Lymph flows in only one direction and movement originates from rhythmic contractions of the smooth muscle cells. The lymphatics have an important function in regulating both immune and fluid homeostasis. Lymphatic Vascular System Main Function ❖To passively collect lymph Excess tissue fluid and proteins from the intercellular spaces of the connective tissue and return it into the venous portion of the blood vascular system. Lymph is a clear fluid and an ultrafiltrate of the blood plasma. Numerous lymph nodes are located along the route of the lymph vessels. ❖Lymph that flows through the lymph nodes is also exposed to the numerous macrophages that reside here. Engulf any foreign microorganisms and suspended matter. Lymphatic Vascular System ❖ Consists of lymph capillaries and lymph vessels. ❖ This system starts as blind-ending tubules or lymphatic capillaries in the connective tissue of different organs. Collect the excess interstitial fluid (lymph) from the tissues and return it to the venous blood via the large lymph vessels, the thoracic duct and right lymphatic duct. ❖ The endothelium in lymph capillaries and vessels is extremely thin Allows greater permeability. ❖The structure of larger lymph vessels is like that of veins except that their walls are much thinner. Lymphatic Vascular System ❖The lymph vessels also bring to the systemic bloodstream lymphocytes fatty acids (a.k.a lacteals) immunoglobulins ❖Lymph movement Contractions of surrounding skeletal muscles forces the lymph to move forward. Lymph vessels contain more valves to prevent a backflow of collected lymph. ❖Lymph vessels are found in all tissues except the central nervous system, cartilage, bone and bone marrow, thymus, placenta, and teeth.  Lymphatic Vascular System Lymphatic capillaries are thin-walled vessels that begin as blind-ended channels adjacent to capillary beds where they collect lymph. 1. They are composed of a single layer of attenuated endothelial cells that lack fenestrae and fasciae occludentes. They possess a sparse basal lamina. 2. Lymph enters these leaky capillaries via spaces between overlapping endothelial cells. 3. Small lymphatic anchoring filaments between the surrounding connective tissue and the abluminal plasma membrane assist in maintaining luminal patency in these delicate vessels.  Lymphocytes Lymphocytes can be classified into three major types based on their immunologic functions: B lymphocytes (B cells) T lymphocytes (T cells) Null cells B cells and T cells are the two main cell types found in lymphoid organs. Lymphocytes originate in the bone marrow and develop and mature in primary lymphoid organs. Immune Cells Macrophages Monocytes Neutrophils, Eosinophils, Basophils Dendritic cells Langerhans cells B cells - are both antigen- presenting and antigen- receiving cells.  Objectives Describe the diffuse lymphatic tissue, GALT (Gut Associated Lymphatic Tissue), MALT (Mucosa Associated Lymphatic Tissue), BALT (bronchus-associated lymphatic tissue) and the lymphatic nodules. https://www.histology.leeds.ac.uk/lymphoid/MALT.php  Objectives Describe the diffuse lymphatic tissue, GALT (Gut Associated Lymphatic Tissue), MALT (Mucosa Associated Lymphatic Tissue), BALT (bronchus-associated lymphatic tissue) and the lymphatic nodules.  Lymphatic nodules Are usually found in structures associated with the alimentary canal such as the tonsils, ileum, and vermiform appendix. GC  Objectives Pharyngeal Tonsils Describe the histologic Palatine Tonsils structures of the tonsils (palatine, pharyngeal and lingual tonsils). Lingual Tonsils Pharyngeal Tonsils Pharyngeal tonsil (g) Palatine Tonsils Palatine tonsil (g) Lingual tonsil (g) Identify this lymphatic tissue: a) Pharyngeal tonsil b) Palatine tonsil c) Lymph node d) Thymus  Organs of the Immune System Primary/ Secondary/ Central Peripheral Thymus ▪Lymph nodes Bone Marrow ▪Spleen ▪MALT: (mucosa-associated) GALT (gut-associated) NALT (nasal-associated) BALT (bronchus- associated) Urogenital Tract ▪CALT (cutaneous-associated) Blood/ Lymphatic System Bone Marrow Cross Section of a Portion of the Thymus Cross Section of a Portion of the Thymus FIGURE 9.7 Thymus gland (panoramic view). Stain: hematoxylin and eosin. Low magnification. FIGURE 9.8 Thymus gland (sectional view). Stain: hematoxylin and eosin. High magnification. Structure of the Spleen FIGURE 12.4. This low-power photomicrograph displays the smooth capsule (C) of a human spleen. Observe, that the spleen is not divided into a cortex and a medulla, instead it has red pulp (RP) and white pulp. Note the presence of a lymphoid nodule with a germinal center (GC) composed of B lymphocytes. The lymphoid nodule is invested by the T-cell–rich region of the spleen, known as the periarterial lymphatic sheath (PALS). The arrow points to the marginal zone located between the white pulp and the red pulp (132).  GALT Peyer’s patch in the ileum Lymphatic nodules Appendix Circulating Lymphocytes Meet Pathogens in the Draining Lymph Nodes Activation of adaptive immune response in a draining lymph node Circulating Lymphocytes Meet Pathogens in the Draining Lymph Nodes Clinical consideration: Edema ❖ Edema is a pathologic process resulting in an increased volume of tissue fluid. Edema may be caused by venous obstruction or decreased venous blood flow (e.g. in CHF) increased capillary permeability (due to injury) starvation excessive release of histamine obstruction of lymphatic vessels. Clinical consideration: Edema ❖It is common during pregnancy and in older persons. ❖Edema that is responsive to localized pressure (i.e., depressions persist after release of pressure) is called pitting edema. ❖Edema can be a symptom of a serious underlying disorder including heart disease, liver disease, or diseases of the thyroid, lymphatic system or the kidneys, with serious consequences. Clinical consideration: Venous Lymphedema ❖Lymphedema is obstruction of lymphatic vessels accompanied by swelling ❖Secondary lymphedema due to obstruction of venous flow Fig 2. This patient had onset of leg swelling from early adolescence. Lymphatic delay was noted on the right side but was normal on the left. Venogram showed bilateral iliac vein stenoses. Right limb venogram is shown with severe diffuse iliac vein stenosis. Note the normal caliber of the femoral vein. Seshadri Raju, James Brooke Furrh IV, Peter Neglén (2012) Diagnosis and Treatment of Venous Lymphedema. 55(1), 141–149.  Afferent lymphatic vessels -convey lymph on the convex surface of the capsule. Efferent lymphatic vessels – lymph away Lymph Nodes 1mm FIGURE 12.2 This photomicrograph of a human lymph node demonstrates that the capsule (C) of the node is surrounded by adipose tissue. The capsule sends trabeculae (T) into the substance of the node. Note the presence of the subcapsular and paratrabecular sinusoids (S) as well as the germinal centers (GC) of the lymphoid nodules. The paracortex (PC) is evident between the cortex and the medulla (132). Clinical consideration: HIV infection ❖ Lentivirus from the retroviridae two RNA copies (genomic and mRNA) ❖Infects primarily CD4+ immune cells and other types Immune dysfunction and systemic disease Immune depletion of CD4+ T cells over the course of years Latent infection, viral reservoirs and systemic viral spread (CNS, GI, lymph nodes) Untreated chronic infection leads to acquire immunodeficiency syndrome (AIDS) CD4+ below 200cell/mm3 Clinical consideration: Treatment against HIV infection ❖Antiretroviral treatment (ART) with HIV-specific targets Non-nucleoside and nucleoside analogs Viral protease inhibitors ❖Combination of different classes (combined antiretroviral therapy; cART) High mutagenic rate Accessory viral proteins ❖ Anti-HIV vaccines are limited Clinical Considerations: DiGeorge syndrome ❖Also referred to as congenital thymic aplasia, is characterized by the congenital absence of the thymus and parathyroid glands, resulting from abnormal development of the third and fourth pharyngeal pouches. 1. This syndrome is associated with abnormal cell-mediated immunity but relatively normal humoral immunity. 2. It usually results in death from tetany or uncontrollable infection. Appendicitis Acute Tonsilitis Non-Hodgkin’s Lymphoma Hodgkin’s Lymphoma