Lymphatic system

• Pathogens

  • Microscopic organisms that cause disease
  • Viruses
  • Bacteria
  • Fungi
  • Parasites
  • Each attacks in a specific way
• Lymphatic system (lymphoid system)

  • Protects us against disease
  • Lymphatic system cells respond to
  • Environmental pathogens
  • Toxins
  • Abnormal body cells, such as cancers
  • Lymphocytes
  • Part of the immune response
  • Identify, attack, and develop immunity to specific pathogens
• Immune system

  • Immunity
  • The ability to resist infection and disease
  • All body cells and tissues are involved in production of immunity
  • Not just lymphatic system
• Components of lymphatic system

  • Lymph
  • A fluid similar to plasma but without plasma proteins
  • Lymphatic vessels, drains into ducts
  • Carry lymph from peripheral tissues to veins
  • Lymphoid tissues and lymphoid organs
  • Scattered throughout body
  • Lymphoid cells
  • Lymphocytes, phagocytes, and other cells
• Components of Lymphatic System

  • Lymphocytes are produced in
  • Primary lymphoid tissues and organs
  • Red bone marrow and thymus
  • Lymphocytes are activated in
  • Secondary lymphoid tissues and organs
  • Tonsils, MALT, lymph nodes, and spleen
• Functions of lymphatic system

  • Produce, maintain, and distribute lymphocytes and other lymphoid cells
  • Return excess fluid to bloodstream
  • Maintain normal blood volume, lymph helps collect and put it back into venous system
  • Transport hormones, nutrients, and wastes
• Lymphatic vessels (lymphatics)

  • Carry lymph — interstitial fluid that has entered lymphatic vessels 
  • From peripheral tissues to venous system
• Lymphatic capillaries

  • Differ from blood capillaries in several ways
  • Closed at one end rather than forming a tube
  • Have larger luminal diameters
  • Have thinner walls
  • Have flat or irregular outline in sectional view
  • Endothelial cells loosely bound together
  • Overlap of endothelial cells acts as one-way valve
  • Allows fluids, solutes, viruses, and bacteria to enter
  • Prevents their return to intercellular spaces
• Lymph capillaries

  • arteriole portion transitions into venule portion, sort of like one loop circuit
  • lymph always flows up towards the heart, enters in peripheral regions of the body and heads up towards lymphatic vessels, which also contain one way valves to keep fluid from back flowing
  • overlap section, flap would close over gap and prevent it from leaking out
• Components of Lymphatic System

  • Lymph flows
  • From lymphatic capillaries to larger lymphatic vessels containing one-way valves
  • Lacteals
  • Special lymphatic capillaries in small intestine
  • Transport lipids from digestive tract
• Lymphatic vessels

  • Superficial lymphatics 
  • Deep lymphatics
  • Larger vessels that accompany arteries and veins
  • Located in skin, mucous membranes, and serous membranes lining body cavities
  • Join to form large lymphatic trunks that empty into two major collecting vessels
  • Thoracic duct
  • Right lymphatic duct
• Thoracic duct

  • Base expands to form cisterna chyli, which receives lymph from
  • Right and left lumbar trunks
  • Intestinal trunk
  • Inferior segment collects lymph from
  • Left bronchomediastinal trunk
  • Left subclavian trunk
  • Left jugular trunk
  • Empties into left subclavian vein
• Right lymphatic duct (much smaller)

  • Collects lymph from (right head, neck and thoracic area)
  • Right jugular trunk
  • Right subclavian trunk
  • Right bronchomediastinal trunk
  • Empties into right subclavian vein
• Components of Lymphatic System

  • Lymphedema (thin, low pressure, extra weight can block)
  • Blockage of lymph drainage from a limb
  • Causes severe swelling
  • Interferes with immune system function
  • Lymphoid cells
  • Immune system cells and supportive cells in lymphoid tissues
  • Lymphocytes
  • Make up 20–40% of circulating leukocytes
  • Most are stored, not circulating
• Types of lymphocytes

  • T cells
  • Thymus-dependent
  • B cells
  • Bone marrow – derived
  • NK cells
  • Natural killer cells
• Components of Lymphatic System

  • Lymphoid tissues
  • Connective tissues dominated by lymphocytes
  • Lymphoid nodules (lymphatic nodules)
  • Areolar tissue with densely packed lymphocytes
  • Germinal center contains dividing lymphocytes
  • Distributed in
  • Lymph nodes
  • Spleen
  • Respiratory tract (tonsils)
  • Along digestive, urinary, and reproductive tracts
• Five tonsils in wall of pharynx

  • Pharyngeal tonsil (adenoid)
  • Left and right palatine tonsils
  • Two lingual tonsils
  • Tonsillitis
  • Inflammation of tonsils, especially palatine tonsils
• Components of Lymphatic System

  • Mucosa-associated lymphoid tissue (MALT)
  • Lymphoid tissues associated with digestive system
  • Aggregated lymphoid nodules
  • Clustered deep to intestinal epithelial lining 
  • Appendix (vermiform appendix)
  • Contains a mass of fused lymphoid nodules
• Lymphoid organs

  • Include
  • Lymph nodes
  • Thymus
  • Spleen
  • Separated from surrounding tissues by a fibrous connective tissue capsule
• Lymph nodes

  • Trabeculae
  • Bundles of collagen fibers
  • Extend from capsule into interior of lymph node
  • Hilum
  • Shallow indentation where blood vessels and nerves reach lymph node
• Lymph nodes

  • Afferent lymphatics
  • Carry lymph from peripheral tissues to lymph node
  • Efferent lymphatics
  • Leave lymph node at hilum
  • Carry lymph to venous circulation
• Lymph flow through nodes

  • From subcapsular space
  • Contains macrophages and dendritic cells
  • Through outer cortex
  • Contains B cells within germinal centers
  • Through paracortex (dominated by T cells)
  • Through the core (medulla)
  • Organized into medullary cords
  • Contains B cells and macrophages
  • Finally, into efferent lymphatics at hilum
• Lymph node function

  • Purify lymph before return to venous circulation
  • Remove 99% of antigens
  • Antigens released due to infection
  • Enter lymph and stimulate macrophages and lymphocytes in lymph nodes
  • Are also carried by dendritic cells to lymph nodes
  • Lymphoid tissues and lymph nodes
  • Monitor peripheral infections
  • Respond before infections reach vital organs
• Components of Lymphatic System

  • Lymph nodes of gut, trachea, lungs, thoracic duct
  • Protect against pathogens in digestive and respiratory systems
  • Largest lymph nodes
  • In groin, axillae, and base of neck
  • Swell in response to infection
  • Lymphadenopathy
  • Chronic or excessive enlargement of lymph nodes
  • May indicate infections or cancer
• Thymus

  • Located in mediastinum
  • Atrophies after puberty, important in early life immunity and helps us develop it
  • Diminishing effectiveness of immune system
  • Divided into two thymic lobes
  • Septa divide lobes into smaller lobules
• Components of Lymphatic System

  • Thymic lobule
  • Dense outer cortex
  • Pale central medulla
  • Lymphocytes
  • Divide in cortex
  • Migrate into medulla
  • Mature T cells leave thymus by medullary blood vessels
• Components of Lymphatic System

  • Epithelial reticular cells
  • Surround lymphocytes in cortex
  • Form layered structures in medulla known as thymic(Hassall’s) corpuscles
  • Maintain blood thymus barrier in cortex
  • Absent in medulla
  • Thymic hormones
  • Thymosin — an extract from thymus containing several hormones
  • Promotes development and maturation of T cell
• Functions of the spleen

  1. Removal of abnormal blood cells and other blood components by phagocytosis

  2. Storage of iron recycled from red blood cells

  3. Initiation of immune responses by B cells and T cells

  • In response to antigens in circulating blood
• Anatomy of the spleen

  • sits upper left quadrant, below diaphragm protected by ribs
  • Attached to stomach by gastrosplenic ligament
  • Contacts diaphragm and left kidney
  • Splenic veins, arteries, and lymphatic vessels
  • Communicate with spleen at hilum

  Histology of the spleen

  • Cellular components within capsule make up pulp
  • Red pulp contains many red blood cells
  • White pulp resembles lymphoid nodules
• Spleen function

  • Phagocytes and other lymphocytes in spleen
  • Identify and attack damaged and infected cells in circulating blood
  • Splenectomy (very vascular, prone to rupture, difficult to repair, can live without it just more prone to infection)
  • Removal of a severely ruptured spleen
• immunity vs immune response****

  • Immunity
  • Ability to resist and defend against infectious organisms and other damaging substances
  • Resistance
  • Ability of body to maintain immunity
  • Immune response
  • Body’s reaction to infectious agents and other abnormal substances
• Two types of immunity

  • Innate (nonspecific) immunity
  • Always works the same way
  • Against any type of invading agent
  •  Adaptive (specific) immunity
  • Protects against specific pathogens
  • Depends on activities of lymphocytes
  • Develops after exposure to environmental hazards
  • immune system retains memory of it, if we come across it again, our immune system recognizes it and goes to destroy the pathogen before we develop the infection
• Lymphocytes

  • B cells, T cells, and NK cells
  • Lymphocyte distribution
  • Tissues maintain different T cell and B cell populations
  • Lymphocytes wander through tissues
  • Enter blood vessels or lymphatics for transport
  • Can survive many years
• Lymphocyte production

  • Also called lymphocytopoiesis, involves
  • Bone marrow
  • Thymus
  • Peripheral lymphoid tissues
  • Hemocytoblasts in bone marrow
  • Divide into two types of lymphoid stem cells
• Lymphoid stem cells

  • Group 1
  • Remain in bone marrow and develop with help of stromal cells
  • Produce B cells and NK cells
  • B cells differentiate with exposure to interleukin-7
  • Group 2
  • Migrate to thymus
  • Develop in environment isolated from blood (so does not contact interleukin-7)
  • T cells differentiate with exposure to hormones
• three types of lymphocytes

  • Immune surveillance: NK cells attack foreign cells, body cells infected, and cancer cells
  • secrete chemicals that lyse plasma
  • Antibody mediate immunity: stimulated B cells can differentiate into plasma cells which produce and secrete antibodies that attach to pathogens
  • cell mediate immunity: mature T cell, cytotoxic T cells, attack and destroy foreign cells or body cells infected by viruses
• T cells and B cells

  • Migrate throughout body
  • To defend peripheral tissues
  • Retain their ability to divide
  • Essential to immune system function
• Innate (nonspecific) defenses

  • Block or attack any foreign substance or pathogen
  • Cannot distinguish one pathogen from another
  • Include:
  • Physical barriers: keeps hazardous out
  • Phagocytes: engulf pathogens and cell debris
  • Immune surveillance: destruction of abnormal cells by NK
  • Interferons: chemical messengers coordinate defence
  • Complement: circulating proteins assist in antibodies in the destruction
  • Inflammation: localized response to limit spread of infection or injury
  • Fever: speeds up tissue metabolism and the activity of defenses
• Physical barriers

  • Outer layer of skin
  • Hair
  • Epithelial layers of internal passageways
  • Secretions that flush away materials
  • Sweat, mucus, and urine
  • Secretions that kill or inhibit microorganisms
  • Containing enzymes, antibodies, or stomach acid
• Phagocytes -

  • Attack and remove dangerous microorganisms
  • Microphages
  • Neutrophils and eosinophils
  • Enter peripheral tissues to fight infections
  • Macrophages
  • Large phagocytic cells derived from monocytes
  • Distributed throughout body
  • Make up monocyte–macrophage system (reticuloendothelial system)