CH. 21: The Immune System Flashcards
What is the lymphatic system?
An extensive network of one-way lymphatic vessels, lymphatic tissues and organs
What is the function of the lymphatic system?
Return of excess fluid (3 liters/day)
Defense against disease using lymphocytes at the lymph nodes
Transportation of absorbed fats by lymphatics moving filtered proteins to the venous fluids (too big for capillaries)
Return of filtered proteins because filtered proteins cannot return back into the capillaries so they are returned through the venous fluids via lymphatics
No unique functions of its own (has to work with other systems)
What are lymph and its components?
An interstitial fluid that moves into lymphatic capillaries due to pressure gradient during the capillary exchange
-15% of fluid does not get reabsorbed back into the capillaries
-Blood is not returned as much as it was filtered out, so it goes through the lymphatic vessels
Components:
-Water & dissolved solutes
-Few proteins
-Foreign materials (cellular debris, pathogens, metastasized cancer cells)
What are lymphatic capillaries and its components?
Are initial lymphatics located at the terminal end of the lymphatic system
Components:
-Blind-ended
-Intertwined with the capillary bed
-Interspersed throughout areolar connective tissue except in red bone marrow and CNS
-Absent in avascular tissue
What is the structure of lymphatic capillaries?
Larger than capillaries
Lack of a basement membrane
Possess free-edged overlapping endothelial cells serving as one-way mini valves to allow fluid into the capillary
Anchoring filaments hold the endothelial cells in place to prevent lymphatics from collapsing due to excessive interstitial fluid hydrostatic pressure (HPif)
What happens when you move lymph into lymphatics?
The pressure drives function where interstitial fluid hydrostatic pressure (HPif) forces fluid between endothelial cells, and internal hydrostatic pressure forces endothelial cells together preventing fluid outflow to ECF
Escaped proteins, cellular debris, & pathogens are shunted to lymphatics because the openings are larger than capillary pores (following the direction of bulk flow)
What are lymphatic vessels and their components?
Vessels that are formed by the convergence of the lymphatic capillaries
Superficial lymphatics are adjacent to superficial veins, and deep lymphatic vessels are adjacent to both deep arteries and veins
Posses all 3 vessel tunics and one-way valves
Lacks a pump so it relies on the skeletal and respiratory pump to drive pulsatile movement of blood in nearby arteries. The rhythmic contraction of lymphatic smooth muscle also helps with lymph flow
What are lymphatic trunks and their components?
They form the union of lymphatic vessels and are named for the region of the body from which they collect lymph
Paired Trunks (right & left)
-Jugular: head and neck
-Subclavian: upper limbs, breasts, & superficial thoracic wall
-Bronchomediastinal: deep thoracic structures
-Lumbar: lower limbs, pelvis, and abdominopelvic wall
Unpaired Trunks
-Intestinal: most abdominal structures
What are lymphatic ducts and their components?
They are where lymph empties into the venous circulation
Consists of right lymphatic duct and thoracic duct
What are the components of the thoracic duct?
Larger of the two ducts and is responsible for the rest of the body extending from the left subclavian and jugular veins and consist of the cisterna chyli at the end of the duct
Cisterna Chyli
-Receives from vessels that drain the small intestine, intestinal trunk, and from lumbar trunk
-Lipid-rich lymph (chyle)
What are primary lymphatic structures?
Involved in the formation and maturation of lymphocytes
Includes the red bone marrow and thymus
What are secondary lymphatic structures?
House lymphocytes and other immune cells following their formation
Provide the site where an immune response is initiated
Includes the lymph nodes, spleen, tonsils, lymphatic nodules, and MALT
What are red bone marrow and its components?
They are found in between trabeculae in selected portions of spongy bone
In adults, it includes flat bones of the skull, vertebrae, ribs, sternum, ossa coxae, and proximal epiphysis of the humerus & femur
Responsible for hematopoiesis:
-T-cells: must migrate from bone marrow to thymus to complete maturation
-B-cells: mature in the bone marrow
What are the thymus and its components?
Composition:
-Lobules are composed primarily of the epithelium to secrete hormones (thymopoietin & thymosins) that participate in T-cell maturation
-Infiltrated with T-cells at various stages of maturation
The most important function is early in life and continues to grow until puberty and regresses into adulthood (thymic tissue is replaced by adipose tissue)
What is the structure of the thymus?
Two fused lobes surrounded by a connective tissue capsule
Extensions of the capsule (trabeculae) subdivide the lobes into lobules
Lobules are arranged by the outer region (cortex) and inner region (medulla)
Blood-thymus barrier prevents entry of bloodborne pathogens into the cortex and premature activation of the immature T-cell
What is the difference between macrophages, dendritic cells, and immune cells within the secondary lymphatic structures?
Macrophages - phagocytize foreign substances
Dendritic Cells - capture antigens & bring them to the lymph nodes
Immune cells - are enmeshed within a reticular extracellular matrix
How are the secondary lymphatic structures are organized?
Organized into either an organ or an aggregate of lymphatic nodules in the presence/absence of a dense irregular CT capsule
Complete CT capsule = organ
-Lymph nodes and spleen
Incomplete or absent capsule = other lymphatic structure
-Tonsils, MALT, and diffuse lymphatic nodules
What are lymph nodes and their components?
Clusters that receive lymph from selected body regions or individually throughout the body
-Most are embedded in CT and not readily observed
-Large clusters are found near the body surface in the axillary, inguinal, and cervical regions
Functions to filter the lymph before it returns to the bloodstream
-Macrophages in the node destroy microorganisms and other cellular debris to prevent them from entering the bloodstream
-Monitor for the presence of antigens and mount attacks against them
What is the lymph node structure?
Capsule
Outer cortex
Inner medulla
Cortical and Medullary sinuses
What are the components of the capsule of the lymph node?
It is a dense fibrous enclosure made of trabeculae
Trabeculae
-connective tissue strands that extend from the capsule to divide the node into compartments
What are the components of the outer cortex of the lymph node?
It is the activation and proliferation site of lymphocytes that is divided into the lymphatic nodules
Lymphatic Nodule
-Composed of reticular fibers
-Activation/proliferation site for B-cells in inner germinal centers
-Outer mantle zone contains T-cells, macrophages, and dendritic cells
What are the components of the inner medulla of the lymph node?
It is the center of most portion of the node
Consists of medullary cords
-CT extension from the lymphoid tissue of the cortex
-Supports B-cells, T-cells, and macrophages
What are the components of the sinuses in the lymph node?
The lymph capillary system allows the lymph to be exposed to the cells in the node that is lined with macrophages
Includes cortical and medullary sinuses
How does lymph flow through the nodes?
- Afferent Lymphatic Vessels
-Numerous - Sinuses (cortical and medullary)
-Macrophages remove foreign debris
-Lymphocytes come into contact with foreign debris and become activated
-Cortical Sinus initiates B-cell activation and proliferation
-Medullary Sinus is where B-cells & T-cells enter the circulation to sites of infection - Efferent Lymphatic Vessel
-Only one per many afferent vessels because lymph flows slow down in the node to allow the cells within the node to be exposed longer to the lymph and perform their protective function
-Originates from the hilum
Lymph nodes move through a series of nodes (in a cluster) and the same lymph is repeatedly screened for unwanted materials
What is the spleen and its components?
It is the largest lymphatic organ that is responsible for fighting any invading germs in the blood
Located:
-On the left side of the abdominal cavity
-Curves around the anterior aspect of the stomach
-Lies lateral to left kidney
-Posterolateral side (diaphragmatic surface) lies against the diaphragm
The medial side is concave and contains the hilum (blood vessels and nerves)
What is the spleen strcuture?
CT capsule
Trabeculae responsible for subdividing spleen into white and red pulp
Populated with lymphocytes and macrophages
What is the structure of the white pulp of the spleen?
Spherical structures of T-cells, B-cells, & macrophages resiting on reticular fibers
Each structure surrounds a branch of the splenic artery (central artery)
Involved in immune function of the spleen
What is the function of the red pulp in the spleen?
Surrounds white pulp
Consists of B-cells, macrophages, erythrocytes, and platelets residing on splenic cords consisting of reticular fibers (platelet reservoir)
Splenic sinuses are associated with red pulp for permeable capillaries to drain into small venules
What are the functions of the spleen?
Immune surveillance and response by having macrophages remove debris and foreign matter (white & red pulp)
Is a blood cleanser by extracting aged and defective RBCs and platelets from circulation (red pulp)
Is a reservoir for platelets (red pulp)
Responsible for erythrocyte production in the fetus during the first 5 months of development
What is the direction of flow of the spleen?
- Splenic artery
- Central arteries (white pulp)
- Sinusnoids (red pulp)
- Venules
- Splenic vein
What are the tonsils and their components?
They are the simplest lymphatic organs with incomplete connective tissue capsule
Three Pairs of Tonsils:
-Pharyngeal
-Palatine
-Lingual
Functions to help protect against ingested or inhaled foreign substances
What are the three pairs of tonsils?
Pharyngeal
-Posterior wall of the nasopharynx
-Also referred to as adenoids
Palatine
-Posterolateral region of the oral cavity
Lingual
-Posterior third of the tongue
What is the structure of the tonsils?
Tonsillar Crypts
-Invaginated outer edges
-Increases surface to entrap bacteria and particulate matter
-Presents antigens to the lymphocytes for heightened immunity
Lymphatic Nodules
-Contain loosely scattered lymphocytes and some contain germinal centers
What is lymphatic nodules?
They are small oval clusters of lymphatic cells with incomplete/absent CT capsules (some have an extracellular matrix)
Diffuse lymphatic nodules are scattered and found within every body organ
Function to localized to destroy bacteria and generate “memory” T cells for long-term immunity
What is MALT?
Mucosa-associated lymphatic tissues (MALT) are located within lamina propria of the mucosa of the GI, respiratory, genital, and urinary tract
If located in the small intestine, they are called Peyer patches
Functions to defend against foreign materials in mucosal membranes
What are the components of the right lymphatic duct?
Responsible for the upper right quadrant of the body
Receives lymph draining from the right:
-Head & neck (jugular)
-Upper limb (subclavian)
-Thorax
What are infectious agents and their categories?
Organisms that cause damage to the host organism (pathogenic)
Categories:
-Bacteria
-Viruses
-Fungi
-Protozoans
-Multicellular parasites
What are bacterias and their components?
They are prokaryotic, microscopic, single-celled organisms enclosed in a capsule
They are named based on the shape
-Spherical (cocci)
-Rod-like (bacilli)
-Coiled (spirilla)
Certain kinds produce a disease (can be extracellular or intracellular parasites or produce enzymes or toxins). Some examples are:
-Tuberculosis
-Syphilis
-Lyme disease
-Salmonella
-Anthrax
What are viruses and their components?
They are NOT a cell but is composed of DNA or RNA with a protein capsid. They are obligate intracellular parasite and uses cells to replicate. It ultimately kills the infected cells
Examples:
-Common cold
-Influenza
-Polio
-Chickenpox
-Herpes
-HIV
What are fungi and their components?
They are eukaryotic cells with cell walls. They produce spores and release proteolytic enzymes. These include mold, yeasts, and multicellular fungi
Examples:
-Superficial (ringworm, athlete’s foot)
-Mucosal (vaginal yeast infections)
-Internal (histoplasmosis)
What are protozoans and their components?
They are eukaryotic cells without a cell wall and could be either intracellular or extracellular parasites
Examples:
-Malaria
-Toxoplasmosis
-Giardiasis
-Amoebiasis
What are multicellular parasites and their components?
They are nonmicroscopic parasites that live in the host and use nutrients provided by the host
Examples:
-Tapeworms
-Flukes
-Hookworms
-Pinworms
What are prions and their components?
Small infectious proteins that cause disease in nervous tissue and are spread by consuming infectious meat
Examples:
-Bovine spongiform encephalopathy (mad cow disease)
What is the immune system and the defense components?
It provides resistance to disease by including immune cells, plasma proteins, and cytokines (hormone-like chemicals)
Intrinsic Defense Components:
-Innate Immune Component is non-specific and fast
-Adaptive Immune Component is specific and slow
What are the primary locations of immunocytes?
Most leukocytes are not circulating in the blood so they are found at either:
-Lymphatic tissue
-Select organs
-Epithelium of the skin and mucosa
-Connective tissue
What types of immunocytes are found in the lymphatic tissues?
T-cells, B-cells, macrophages, & NK cells in secondary lymphatic structures
What types of immunocytes are found in select organs?
Specifically named macrophages in specific tissues
Permanent Resident = fixed macrophages
Migrating Macrophage = wandering macrophages
What types of immunocytes are found in the epithelium of the skin and mucosa?
Dendritic cells (from monocytes) are phagocytic cells that engulf pathogens and then migrate to lymph tissue to present antigens
What types of immunocytes that are found in the connective tissue?
Mast cells are abundant in skin and mucosa or respiratory, GI, and urogenital tract
What are cytokines and their components?
They are small soluble proteins produced by immune cells. They function to:
-Means of communication between cells
-Control development and behavior of effector cells
-Regulate inflammatory response
-Serve as a weapon of destruction
In the mode of action, they are:
-Released by a cell to bind to a receptor on the target cell to activate a signal cascade
-Can be an autocrine, paracrine, or endocrine signal
Relatively short half-lives
What are the four classes of cytokines?
Interleukins (ILS) regulate immune cells
Tumor Necrosis Factors (TNFs) destroy tumor cells
Colony-Stimulating Factors (CSFs) stimulate leukopoiesis
Interferons (INFs) are anti-viral and pro-inflammatory agents
What is innate immunity?
They are born defenses to protect against non-specific substances
It prevents entry of potentially harmful substances which is the 1st line of defense (external) through skin and mucosal membranes
It responds non-specifically to a wide range of harmful substances after entering the body as the 2nd line of defense
-Cellular (activities of neutrophils, macrophages, and NK cells)
-Chemical (interferons and complement)
-Physiological (inflammation and fever)
How does the skin prevent the entry of pathogens?
Epidermis is a heavily keratinized epithelial membrane acting as a physical barrier to most microorganisms
Mucosa is structurally modified to trap and move invading particles away from the internal environment. They also produce acids and enzymes
Secrete a variety of antimicrobial substances
-IgA: binds to foreign particles
-Lysozyme, Defensins, & Dermicidin: antibacterial and antifungal substances
-Sebum: biotoxic and creates a low pH that inhibits bacterial growth
Mucus traps microorganisms to prevent them from spreading
Other pathogen removals:
-Skin slough off
-Saliva washes materials away and contains antibacterial enzymes
-Lacrimal fluids
-Urine
