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• The immune system defends the body by destroying or neutralizing pathogens.
• The lymphatic system transports excess fluids to the bloodstream and filters pathogens.

Functional Anatomy

• The lymphatic system drains excess interstitial fluid and transports it to the bloodstream as lymph.
• Blockage of lymph drainage leads to lymphedema.
• The lymphatic system houses phagocytic cells and lymphocytes for tissue fluid cleaning and absorbs fats from the intestine via lacteals, forming chyle.

Structure

• Lymphatic system defends the body against environmental hazards and internal threats and includes vessels, cells, tissues, and organs.
• Lymph vessels carry lymph from peripheral tissues to the venous system, starting with lymphatic capillaries.

Lymph Capillaries

• Lymph capillaries are present in almost every tissue and organ and plentiful like blood capillaries.
• They are absent in areas lacking blood supply (cornea) and in the central nervous system and bone marrow.
• Lymphatic capillaries are blind-end tubes, have larger diameters, thinner walls, flattened lumens, lower resistance, and mini-valves.
• Mini-valves permit entry of fluids, proteins, viruses, bacteria, and cell debris, and prevent their return to intercellular spaces.
• Lymph flows from capillaries into collecting vessels with valves, towards the body's trunk.

Lymph Trunks

• Lymph trunks are formed by the convergence of lymph collecting vessels.
• Jugular trunks: located in the neck, drain the head.
• Subclavian trunks: located in the shoulders, drain the arms.
• Bronchomediastinal trunks: located in the chest, drain the thoracic cavity and lungs.
• Lumbar trunks: located in the lower back, drain the pelvis and lower limbs.
• Intestinal trunk: located in the abdomen, drains the walls of the digestive organs.
• Blockage of lumbar or subclavian trunks by worms causes Elephantiasis.

Lymph Ducts

• Lymph ducts are formed by the merger of lymph trunks.
• The right lymphatic duct drains the right side of the head, arm, shoulder, and thoracic cavity, emptying into the right subclavian vein and results from a merger of jugular, subclavian, and bronchomediastinal trunks.
• The thoracic duct ascends along the left vertebral column, collecting lymph from the bronchomediastinal, subclavian, and jugular trunks, and drains the left side of the head, arm, shoulder, thoracic cavity, abdomen, pelvic region, and both legs, emptying into the left subclavian vein.
• It features the cisterna chyli at its base, which receives lymph from the lumbar and intestinal trunks.

Organization of Immune Function

• Barrier defenses: skin and mucous membranes preventing pathogenic invasion.
• Innate immune response: rapid, non-specific response involving specialized cells and soluble factors.
• Adaptive immune response: slower, specific, effective response controlled by lymphocytes.
• Lymphopoiesis: lymphocyte production occurs in red bone marrow, thymus, and peripheral lymphoid tissues.
• White blood cells can be divided into phagocytic cells, lymphocytes, and granular WBCs.

Lymphocytes

• Lymphocytes account for 20-30% of circulating leukocytes, with most residing in lymph organs.
• B cells: 10-15% of circulating lymphocytes, responsible for antibody-mediated immunity.
• When stimulated by an antigen, B cells differentiate into plasma cells.
• Plasma cells: produce and secrete antibodies, containing a large amount of rough endoplasmic reticulum.
• T cells: approximately 80% of circulating lymphocytes, provide cell-mediated immunity.
• Natural Killer (NK) cells: 5-10% of circulating lymphocytes, part of non-specific defenses, use cytotoxic granules to attack infected cells and cancer cells called immunological surveillance.

Primary/Secondary Lymphoid Organs

• Red bone marrow generates blood cells starting in the yolk sac during embryonic development, a function later taken over by the spleen, liver, and finally, bone marrow.
• Thymocytes are immature T cells that mature in the thymus gland.
• The thymus produces thymosins to support T cell development and body defenses.
• The thymus is large in childhood but diminishes after puberty in a process called involution, weighing less and correlating with disease susceptibility by age 50.
• The thymus is divided into lobes by a capsule and further into lobules by septa, each containing a dark cortex and a lighter medulla dominated by thymic corpuscles.
• Naive lymphocyte has left the primary organ and entered a secondary lymphoid organ, fully functional but without having met the antigen necessary to respond to.
• Lymph Nodes - range from 1 mm to 25 mm and are kidney bean in shape, located in the cervical, axillary, and inguinal areas.
• Lymph flow in nodes: afferent vessels transport lymph into the node, which penetrates the capsule opposite the hilum; Afferent vessels deliver lymph to the subcapsular space, a mesh of reticular fibers, macrophages, and dendritic cells; Lymph then flows in the outer cortex, containing B cells; then flows through the lymph sinuses to the deep cortex, dominated by T cells; Lymph continues into the medullary sinuses containing B and plasma and is finally drained by the efferent lymphatic vessels exiting at the hilum.
• Lymph node antigens are at least 99% removed from the lymph and swollen lymph nodes are called buboes.

Spleen

• The spleen is the largest lymphoid organ.
• It filters blood, removes abnormal red blood cells, stores iron, and initiates immune responses.
• Located along the stomach's lateral border, attached by the gastrosplenic ligament is the spleen.
• It features a smooth outer diaphragmatic surface and has a capsule containing collagen and elastin fibers
• The spleen medial surface (hilum ) includes two areas: a gastric location for the stomach and another renal for the kidney.
• Trabeculae radiate from the hilum, containing blood vessels.
• It is composed of red pulp (containing red blood cells) and white pulp (resembling lymphoid nodules).
• Splenic phagocytes engulf damaged or infected cells in circulating blood due to the spleen unusual circulatory arrangement,

Lymph Nodules and MALT

• Lymph nodules are densely packed; they contain reticular connective tissue instead of a fibrous capsule.
• They include the palatine, pharyngeal, and lingual, and tubal tonsils in the pharynx, with tonsillitis occurring upon infection and swelling.
• Mucosa-associated lymphoid tissue (MALT) protects the epithelial linings of the digestive, respiratory, urinary, and reproductive tracts and has several types, including appendicitis.
• Aggregated lymphoid nodules (Peyer's patches) are found in the small intestine.
• Bronchus-associated lymphoid tissue (BALT) is located along the bronchi.
• Lymphoma originates from lymphoid cells or tissues.
• Hodgkin's lymphoma is characterized by Reed-Sternberg cells and is linked to the Epstein-Barr virus.
• Non-Hodgkin's lymphoma includes at least 61 other types.

Innate Immune Response Characteristics

• Innate defenses function from birth, are non-specific, localized, don't have memory, and attack infections at the entry point
• Innate immunity includes physical, cellular, and chemical defenses.

Physical Barriers of Innate Immunity

• Physical barriers keep organisms outside of the body.
• Skin's stratified squamous epithelium and keratin prevent entry.
• Hairs provide protection against abrasion and hazardous materials.
• Sweat glands flush the skin.
• Secretions contain defensins, lysozymes, and antibodies.
• Sebaceous glands secrete sebum to lubricate the skin and create an arid environment for microorganisms.
• Mucous membranes act as epithelial linings, supported by tight junctions and a basal lamina
• They trap microorganisms, secrete antimicrobial chemicals, and use cilia, and MALT.

Cellular Defenses of Innate Immunity

• Cellular defenses: cells attack infections at the site of entry.
• The phagocytic engulf pathogens and cell debris.
• They use diapedesis (emigration) to leave capillaries and positive chemotaxis to be attracted to infection chemicals.
• During phagocytosis, adherence occurs as phagocyte receptors bind to the target's surface.
• After attachment, the phagocyte may destroy or promote destruction of the target itself by activating T and B cells.
• There are various types of phagocytic cells: neutrophils (abundant, mobile, phagocytize debris and bacteria where there is injury), eosinophils (less abundant, engulf pathogens coated with antibodies), and monocytes (give rise to free and fixed macrophages).
• Free macrophages travel to the site of injury and fixed macrophages reside in specific tissues (i.e., Kupffer cells in liver).
• NK cells detect and destroy abnormal or infected cells by immunological surveillance.
• Steps include NK cells recognizing the abnormal cell, secretory vesicles with perforins travel to the surface, perforins are released and create pores, and the target cell disintegrates.

Chemical Defenses of Innate Immunity

• Chemical defenses destroy organisms, label them, prevent reproduction, or stimulate immune cells.
• Interferons are cytokines secreted by lymphocytes, macrophages, and infected tissues to protect healthy cells by triggering antiviral protein production.
• Alpha interferons enhance resistance and attract NK cells, Beta interferons slow inflammation, and Gamma interferons stimulate macrophage activity.
• The complement system (11 proteins) assists antibodies through the classical and alternative pathways.
• The classical pathway is rapid and involves complement proteins attaching to antibodies bound to antigens and the alternative pathway defends bacteria and parasites.
• The pathways enhance lysis, opsonization, phagocytosis, and histamine release.
• Inflammatory Response: is the localized tissue-level response to injury or infection.
• Tissue damage induces inflammation, leading to release of “alarm chemicals".
• Mast cells and basophils release histamine and heparin, causing increased blood flow (vasodilation) and permeability, leading to exudate and swelling (edema).
• Fibrin formation occludes lymph vessels. Leukocytosis WBC production and positive chemotaxis attract phagocytes.
• Signs: redness, heat, swelling, and pain.
• Pyrogens elevate body temperature, speeding metabolism, repair, and defense activity.
• Fever (above 37.2° C) increases metabolic rate.
• Increased body temperature may inhibit bacterial and viral growth but high temperatures denature proteins stopping immune response.

Adaptive Response Characteristics

• Adaptive defenses develop after exposure, are specific, systemic, have memory, versatile, and have tolerance.
• T lymphocytes provide cell-mediated immunity and B lymphocytes provide antibody-mediated immunity
• T cells are produced in bone marrow and mature in the thymus and T lymphocytes can not directly detect antigens and the antigen must be processed and presented
• Antigen occurs with glycoproteins on the surface and are called major histocompatibility complexes or MHC proteins
• Class I MHC are one every human cell and Class II MHC proteins are only on macrophages, dendritic cells and other phagocytic cells.
• Macrophages phagocytize organisms then process the antigen and expose it on surface of its own cell in combination with the Class II MCH protein.
• The T cells with a special CD4 marker differentiate to form TH(Helper) and Memory TH cells that secrete cytokines that alert other B and T lymphocytes
• Helper T cells guide and locate immune cells by positive chemotaxis.
• Virus infected body cells alert the body and take the normal peptides of the virus and incorporate with MCH proteins.
• Typical cells possess MHC Class I proteins that only stimulate cells with the CD 8 markers.
• CD 8 cells differentiate to form TC cells, TH cells and Memory TC cells.
• The Cytotoxic T cells (TC) recognize the antigen and destroy the sick cell by perforins to disrupt metabolism, apoptosis to trigger cell death and lymphotoxins to release.

T-Cell Types

• Helper T cells stimulates the all immune response and other immune cell types join
• Cytotoxic T cells attach virus infected cells and cancer cells
• Suppressor T cells shut down activity of T cells and B cells
• Memory T cells responds to future responses of same pathogen by secreting suppression faction

Adaptive B-lymphocites

• Adaptive immunity or in B-lymphocites produced in the red bone marrow
• Humoral Immunity - B lymphocytes attack the infections while circulating in body fluids (blood/lymph)
• B Lymphocytes in both fluids directly recognize their antigens then expands

Antiboty Structure

• Antibodies are consists of one pair of heavy chains on the interior and exterior light chains
• Four chains are held by disulfide bonds
• Each chain has a constant region of amino acid sequence and a variable region where sequence is unique
• The free tips of the segments form the region to bind to antigen

Antibody Free Tips

• Antibodies can interact on its site which is can be done by an enzyme
• Small amino acids are binding at the protein site with great specificity
• Antibody binds with its corresponding binding it makes an complex
• Anitbodies don’t bind to the entire antigen bit on the portion of the surface

Antigen Types

• Complete Antigen has two binding sites to bind on each molecule.
• Partial Antigen does not cause B-cell activation but binds to carrier molecules for complete function

Antibody Classes(Immunoglobins)

• There are five classes of antibodies and are determined by a chain but specificity is determine when bounding.
• IgA - Primary secretion for muscus tears breast milk, semen
• IgD - Binds B-cells for antigens in extracellular binds and proliferation
• IgE- Attaches of the surface to basophilis and starts the infmallatory by histamine and heparin.
• IgG - 80% of Antibodies for against viruses etc that are monomers can cross
• IgM - Pentamer after antigen and accelerated during concentration declines

B-Lymphocytes

• B lymphocytes prepares to undergo when encountering in the fluids which is Called Sensitization.
• Antibodies proliferate form a clone in this first expose called primary response
• During this time the antibody level doesn’t peak during the first week
• Clones mature and differentiate into two types: Plasma B cells and Memory B- cellls

Immune Response

• Infection Memory b-Cells generate more of the efficient response which is 2nd response for increasing antibodies when the the expose occurs
• Active- human make own antibodies for its defense
• Naturally Acquired- when it response naturally
• Artificially Acquired active immunity – exposed by the antigen of the immune system and vaccines
• Passive- short term by someone else
• Naturally Acquired- mother milk
• Artificially Acquired Active Immunity- Given to create a produce for Gamma Globulin

Immune Verse

• Immune system attack pathogens to trigger
• Complement Activation- trigger enhance
• Opsonization coats pathogens become more effective.
• Phagocytosis coats to attract
• Precipitation/Agglugtation- Close together and clumps
• Neutralization- Binding cell to protect
• Prevents adhesion- blocks cell Inflammation - Stimulaitng cell to protect

System Disorders

• Deficent numbers of immune system cells
• Sever combined immunodeficiency- disease from genetic order of b and T cells.
• Acquired- destorys cells decreasing mediated immunity by AIDS due to diseases. Allergies triggers reaction
• Immediate hyper starts and lasts till the hour.
• Subacute hypersensitivity occurs within the hours is in the hours
• Delayd hypersensitivity can occur during the first weeks . Antibodies Autoimmune Antibodies makes cells again.

Graft

• Graft Rejection tissue isn’t compatible form transplant for rejection
• Auto-Tissues same person
• Iso -Identical twins
• Allo-Non identical
• Xene- Different Species