Lymphatic and Immune Systems

Lymphatic vs Immune System

• The lymphatic system is a true organ with immune cells concentrated in areas such as the lymph nodes
• The immune system is not a true organ, it is a population of cells found in organs throughout the entire body
• The immune system defends the body from agents of disease like fungi, bacteria, and toxins

Lymphatic System Functions

• It is a network of organs and vein-like vessels which:
  • Recovers tissue fluid and directs it to the bloodstream
  • Inspects fluid for disease agents
  • Activates immune responses

Lymphatic System Composition

• Lymph nodes
• Spleen
• Thymus
• Tonsils
• Red bone marrow (produces blood cells)

Main Functions of the Lymphatic System

• Fluid recovery moves fluid from blood capillaries into tissues
  • Capillaries can reabsorb about 85% of fluids
  • Excess fluid if returned to the bloodstream
  • Fluid is composed of 2-4L of water and ¼ - ½ lb. of plasma proteins
• Immunity picks up foreign cells and chemicals from the tissues for the bloodstream to pass through lymph nodes via immune cells and creates immune responses to pathogens
• Lipid absorption occurs in the small intestine, where fats are not absorbed by blood capillaries

Lymph

• Lymph is recovered fluid
• contains macrophages, mobile white blood cells, hormones, bacteria, viruses, and even cancer cells.
• Lymph is a colorless fluid, similar to plasma, but with less protein
  • Lymph comes from lymphatic vessels
  • Lymph can be milky from lipids after a meal
  • Lymph nodes always contain lymphocytes

Lymphatic Vessels

• Lymphatic vessels transport lymph throughout the body
• Lymphatic tissues are composed of lymphocytes and macrophages that populate organs
• Lymphatic organs are responsible for concentrating immune cells

Tissue Fluid Route

• Tissue fluid returns to the bloodstream
• Tissues exist throughout the body

Lymphatic Capillaries

• Lymphatic capillaries are similar to blood capillaries, but closed on one end
• They penetrate every tissue except cartilage, bone, bone marrow, and the cornea
• Cells are not joined by tight junctions
• Gaps allow for bacteria and lymphocytes to access tissue fluid
• Fluid flow in lymphatic capillaries has low pressure, much like veins, using valves to prevent backflow

Collecting Vessels

• Lymphatic capillaries merge into collecting vessels found alongside veins and arteries
  • Receive and filter lymph
  • Immune cells monitor for foreign antigens and phagocytize bacteria

Lymphatic Trunks

• Lymphatic trunks converge from collecting vessels

Lymphatic Trunk Locations

• Jugular
• Subclavian
• Broncho mediastinal
• Intercostal
• Intestinal
• Lumbar

Collecting Ducts

• Lymphatic trunks converge into 2 collecting ducts, which are the largest lymphatic vessels

Right Lymphatic Duct

• The right lymphatic duct:
  • Receives lymph from the right arm, right side of the head, and the thorax
  • Drains into the right subclavian vein

Thoracic Ducts

• Thoracic ducts:
  • Receives lymph from the left arm, both legs, the opposite side of the head, and the thorax
  • Drain into the left subclavian vein

Subclavian Veins

• Subclavian veins are an important part of the lymphatic system

Lymphoid Cells

• Lymphoid cells are the immune cells of the lymphatic system and are:
  • Produced through lymphopoiesis
  • Hemocytoblasts develop into lymphoid stem cells, becoming lymphocytes

Lymphocytes

• T cells
  • Mature in the thymus and are activated by thymus hormones
  • Make up 80% of circulating lymphocytes

T Cell types

• Cytotoxic (Tc)- attack foreign cells
• Helper T (TH)-promote the action of cytotoxic cells and play key roles in innate immunity
• Regulatory T (Tr) – Limits the immune response and down regulates cytotoxic cell (Tc) activity after a pathogen has been defeated
• Memory T (TM) – for cellular immunity

B Cells

• B Cells are differentiable plasma cells that are connective tissue and secrete antibodies
  • Y-shaped soluble proteins containing antigen-binding sites and most antibodies have two sites
  • Colonize same organs as T cells and are found in lymph nodes, spleen, bone marrow, and mucous membranes
  • APCs/Antigen-presenting cells display antigens of foreign cells with major histocompatibility complex (MHC) proteins
    • Alert the immune system of a foreign antigen
  • Communicate with other leukocytes through cytokines
  • Develop memory B cells to remember antigens

Continuation of B Cells

• Antibodies (aka Immunoglobulins) produce proteins against specific antigens
  • Tag pathogen for destruction
  • Good defense against viruses, bacteria, toxins, and yeast spores

Actions of Antibodies

• Neutralization - the antibody physically covers a pathogen and makes it ineffective
• Agglutination (Clumping) - antibody clumps with foreign cell antigens and is especially effective on bacterial cells
• Precipitation - forms antigen-antibody complex, in which the antibody becomes insoluble and precipitates out of body fluids. Precipitated complexes engulfed and eliminated by phagocytes.

NK Cells

• Natural killer cells – migrate throughout the body and attack and destroy pathogens
  • Invade bacteria, transplanted tissues and host cells infected with viruses become cancerous cells
  • Neutrophils - Aggressively antibacterial
  • Macrophages - Phagocytic cells that come from Monocytes

Monocytes

• Phagocytize tissue debris, dead neutrophils, old red blood cells, bacteria, and foreign material
• Display Antigens to T cells and APC’s (antigen presenting cells)
• Dendritic Cells - Arise from Monocytes found in the epidermis, mucous membranes, and lymphoid organs
  • Branched projections increase surface area and exposure to antigens
  • Alert the immune system if pathogens breach the body surface

Lymphoid Tissue

• Lymphoid tissue is connective tissue dominated by lymphocytes that engulf foreign matter and migrate toward the body to activate immune responses
• Loosely scattered in the mucous membrane compacting the cell populations in lymphatic organs
• MALT (Mucosa-associated lymphoid tissue): collection of tissues in the respiratory, urinary, digestive, and reproductive tracts.
• Lymphoid nodules: masses of lymphocytes in areas where pathogens try to invade tissues. Constantly found in small intestine & the appendix

Adaptive Immunity

• Two types of adaptive immunity:
• Humoral immunity: B cells employ antibodies and tag pathogens for destruction by extracellular viruses, yeasts, protozoans, toxins, venoms, allergens, foreign erythrocytes
• Cellular immunity: T cells directly attack and destroy pathogens residing inside human cells, such as intracellular viruses, bacteria, yeasts, protozoans, cancer cells, parasitic worms, cells from transplants

Lymph Nodes

• Lymph nodes act like checkpoints for lymph in the body and number around 450 in adults
• Found in areas:
  • Cervical
  • Axillary
  • Abdominal
  • Inguina
  • Thoracic
  • Pelvic

Lymphatic Organs

• Lymph nodes that clean lymph may contain:
  • Bacteria, antigens, or other harmful matter
  • Macrophages phagocytize foreign matters
  • Lymphocytes responding to any antigens
  • Site of T and B cell activation

Tonsils

• Tonsils at the entrance of the pharynx and serve as the first line of defense against inhaled pathogens with three main sets
  • Pair of palatine tonsils (posterior oral cavity)
  • Pair of lingual tonsils (not of tongue & close to your palate/roof of mouth)
  • One pharyngeal tonsil (posterior wall of the pharynx and through the nose)
• Tonsillitis is an infection of the tonsils needing surgical removal

Spleen

• The Spleen is the largest mass of lymphoid tissue and is very fragile and tears easily, therefore produce blood cells
  • Acts as blood reservoirs for adults
  • Recycles blood cells and filter blood
  • Activates lymphocytes & macrophages
  • Two types of tissue: red pulp and white pulp

Red Pulp vs White Pulp

• Red pulp: contains erythrocytes and produces blood cells in the fetus. In severe anemia, the spleen can produce blood cells in adults. In healthy adults the spleen acts as a blood reservoir.
• White pulp: in adult spleens get rid of old blood cells and macrophages phagocytize bacteria & act like lymph nodes and macrophages when foreign antigens are detected

Thymus

• The Thymus is part of the endocrine lymphatic and immune systems
  • Large in infants until puberty when it begins to shrink replacing fat (involution)
  • Houses developing lymphocytes, secreting thymosin & thympoetin to stimulating T lymphocytes
  • T cells will deplete in blood & tissues if the Thymus is removed from a new born

Red Bone Marrow

• Red bone marrow contains soft, gelatinous tissue in central cavities of long bones (femur and humerus)
  • Involved in hemopoiesis and immunity
  • A supplier of lymphocytes to the immune system

Immune System Barriers

• Immune System barriers:
  • Epithelial physical barriers such as the skin and mucous membrane (impenetrable to most pathogens)

Leukocytes

• Leukocytes contain macrophages, antimicrobial proteins, NK cells, used in inflammation
  • Types of Lekocytes: white blood cells
  • Neutrophils that circulate blood for 6-10 hours and enter connective tissue to destroy bacteria
  • Phagocytosis (engulf microbes) through Respiratory burst to degrade internalized particles. They have a short life span that limit damage
  • Eosinophils found in mucous membranes (respiratory and gastrointestinal tracts) for parasites and allergies & phagocytes engulfing foreign matter and promotes inflammation

Lymphocytes

• Lymphocytes:
  • Mast cells that regulate vasodilation, innate & adaptive immune responses, angiogenesis, and venom detoxification
  • Basophils- act as short one to two day fighters that are less than 1% of circulating white blood cells and help respond to bacteria, cancer, leukocytes, and inflammatory responses
  • Release histamine (vasodilation) & Heparin (anticoagulant)

Lymphocyte Types

• Lymphocytes make up the second most white blood cells in the body and:
  • T cells – 80%
  • B cells – 15%
  • NK cells – 5%
• Mainly found in circulation for adaptive immunity
• Monocytes help circulate blood for 1 to 3 day periods and migrate toward CT to:
  • Macrophages help phagocytize microorganisms & remove dead cells stimulating the activity of other immune cells
  • Dendrite boost immune responses by presenting antigens to other immune cells

Adaptive Immunity

• Adaptive immunity mechanisms destroy pathogens and leave the body with the memory of pathogens
  • First and second lines of defense

Types of Immunity

• Immunity can be:
  • Local, where it fights pathogens at the point of invasion
  • Nonspecific, fighting a broad array of pathogens
• Memory immunity lacks prior pathogens such as mosquito bites
• Adaptive immunity is the third line of defense that depends on and responds to the environment
• Interferons form the second line of defense; certain cells secrete proteins when infecting viruses telling neighboring calls

Fever

• Fever:
  • Second line of defense that has an abnormal elevation of body temperature above 37.2 degrees Celsius or 99 degrees Fahrenheit
  • Caused by trauma, infections, drug reactions, and brain tumors which supports Interferon Activity
    • Inhibits reproduction of bacteria and viruses & elevates metabolic rate, as well as accelerates tissue repair
      • Low-grade fever- 100-101 F
      • Intermediate grade fever- 102 F
      • High-grade- 103-104 F
    • Dangerous high grade- over 104 F that has a change in metabolic pathways and denaturation of proteins, possible seizures, leads to irreversible brain damage at fever and high as 106F and death if over 108F

The lymphatic system, a network of organs and vessels, recovers tissue fluid and activates immune responses. Its composition includes lymph nodes, spleen, thymus, tonsils, and red bone marrow. In contrast, the immune system defends the body from disease agents and is a population of cells found throughout the body.