Chapter 21- Immune system Flashcards
Immune system
not an organ system, but a cell population that inhabits all organs and defends the
body from agents of disease
Lymphatic System Functions
-fluid recover
-immunity
-lipid absorption
Fluid recovery
- Fluid continually filters from the blood capillaries into the tissue spaces
- Blood capillaries reabsorb 85%
- 15% (2 to 4 L/day) of the water and about half of the plasma proteins enter the lymphatic system and then are returned to the bloo
Immunity
- Excess filtered fluid (lymph) picks up foreign cells and chemicals from the tissues
- Passes through lymph nodes where immune cells stand guard against foreign matter
- Activates a protective immune response
Lipid absorption
- Lacteals in small intestine absorb dietary lipids that are not absorbed by the blood capillaries
Lymphatic capillaries (terminal lymphatics)
-Lymphatic capillaries penetrate almost all body tissues, except cartilage, cornea, bone, and bone marrow.
-They have a closed-end structure with endothelial cells overlapping like roof shingles.
-Anchoring filaments attach the cells to surrounding tissue.
-Large gaps between cells allow bacteria and cells to enter.
-Valve-like flaps in the endothelium open with high interstitial fluid pressure and close when it’s low
Right lymphatic duct
receives lymph from right
arm, right side of head and thorax; empties into
right subclavian vein
Thoracic duct
larger and longer, begins as a sac in abdomen called the cisterna chyli
cisterna chyli
receives
lymph from below diaphragm, left arm, left side of head, neck, and thorax; empties into left
subclavian vein
subclavian vein
collect from thoracic duct
flow of lymph
Lymph flows at low pressure and slow speed, driven by rhythmic contractions of lymphatic vessels (stimulated by vessel stretching), skeletal muscle and thoracic pumps, arterial pulsations, and the suction effect of rapidly flowing blood in subclavian veins, with valves preventing backflow. Exercise greatly enhances lymphatic return
lymphatic cells
-neutrophils
-natural killer cells
-T lymphocytes
-B lymphocytes
-dendritic cells
-reticular cells
neutrophils
antibacterial
Natural killer (NK) cells
large lymphocytes that attack and destroy bacteria,
transplanted tissue, host cells infected with viruses or that have turned cancerous
T lymphocytes (T cells)
mature in thymus, helper, cytotoxic, and regulator
B lymphocytes (B cells)
activation causes proliferation and differentiation into
plasma cells that produce antibodies
Dendritic cells
branched, mobile antigen-presenting cells (APCs) found in epidermis, mucous membranes, and lymphatic organs; alert immune system to pathogens that have breached the body surface
Reticular cells
branched stationary APCs that contribute to the stroma (connective tissue framework) of a lymphatic organ
Macrophages – VERY important cell
- Large, avidly phagocytic cells of connective tissue
- Develop from monocytes or other macrophages
- Phagocytize tissue debris, dead neutrophils, bacteria, and other
foreign matter - Process foreign matter and display antigenic fragments to certain
T cells alerting immune system to the presence of the enemy - Become antigen-presenting cells (APCs) when they do this
Lymphatic nodules (follicles)
- Dense masses of lymphocytes and
macrophages that congregate in response
to pathogens - Constant feature of the lymph nodes,
tonsils, and appendix - Aggregated lymphoid nodules: dense
clusters in the ileum, the distal portion of
the small intestine
Lymphatic Organs
-Lymphatic organs are anatomically well-defined
-Have connective tissue capsule or partial capsule that separates lymphatic
tissue from neighboring tissues
Primary lymphatic organs
- Red bone marrow and thymus
- Site where T and B cells become immunocompetent (become mature): able to
recognize and respond to antigens
Secondary lymphatic organs
- Lymph nodes, tonsils (patches of lymphatic tissue but distinct), and spleen
- Immunocompetent cells populate these tissues
Histology of Red Bone Marrow
- Soft, loosely organized, highly vascular
material - Separated from osseous tissue by
endosteum of bone - As blood cells mature, they push their
way through the reticular and
endothelial cells to enter the sinus and
flow away in the bloodstream
Thymus
- Houses developing lymphocytes
- Secretes hormones regulating their activity
- Bilobed organ located in superior mediastinum between sternum and aortic arch
- Degeneration (involution) with age
- Produce signaling molecules thymosin, thymopoietin, thymulin, interleukins, and
interferon
functions of lymph node
-Cleanse the lymph
-Act as a site of T and B cell activation
Cervical lymph nodes
Deep and superficial group in the neck (drain head and neck)
Axillary lymph nodes
Concentrated in armpit (receive lymph from upper limb and female breast)
Thoracic lymph nodes
In thoracic cavity (receive lymph from mediastinum, lungs, and airway
Inguinal lymph nodes
in the groin and receive lymph from the entire lower limb
Popliteal lymph nodes
Occur on the back of the knee (receive lymph from the foot and leg proper)
examples of lymph nodes
-cervical lymph nodes
-axillary lymph nodes
-thoracic lymph nodes
-inguinal lymph nodes
-popliteal lymph nodes
Lymphadenitis
swollen, painful node responding to foreign antigen
Lymphadenopathy
collective term for all lymph node diseases
staging cancer; lymph nodes
- Metastasizing cells easily enter lymphatic vessels and tend to lodge in the first
lymph node they encounter - Multiply there and eventually destroy the node - swollen, firm, and usually painless
- Cancer cells tend to spread to the next node downstream
- Treatment of breast cancer is lumpectomy, mastectomy, along with removal of
nearby axillary nodes (which can cause lymphedema
Tonsils
-patches of lymphatic tissue located at the entrance to the pharynx
-Guard against ingested or inhaled pathogens
-Covered with epithelium
-Have deep pits: tonsillar crypts lined with
lymphatic nodules
Three main sets of tonsils
-Palatine tonsils
Pair at posterior margin of oral cavity, largest
Most often infected
-Lingual tonsils
Pair at root of tongue
-Pharyngeal tonsil (adenoids)
Single tonsil on wall of nasopharynx
Spleen pulp
Red pulp: sinuses filled with erythrocytes
White pulp: lymphocytes, macrophages
surrounding small branches of splenic artery
Spleen - functions
- Healthy red blood cells (RBCs) come and go
- For old, fragile RBCs, spleen is “erythrocyte graveyard”
- Blood cell production in fetus (and very anemic adults)
- White pulp monitors blood for foreign antigens and keeps
an army of monocytes for release when needed - Stabilizes blood volume through plasma transfers to
lymphatic system
-Spleen is highly vascular and vulnerable to trauma and
infection - Ruptured spleen requires splenectomy, but this leaves
person susceptible to future infections, premature death
First line of defense
skin and mucous membranes
(innate immunity)
Second line of defense
-several innate defense
mechanisms (innate immunity
-Leukocytes and macrophages, antimicrobial proteins
(complement and interferon), natural killer cells, inflammation, and fever
-Innate immunity has local effect, is non-specific, and lacks memory
Third line of defense
- B-cells, plasma cells memory B-
cells; T-cells – helper T, cytotoxic T, regulator T and
memory T (adaptive immunity)
-Defeats a pathogen and leaves the body with a
“memory” of it so it can defeat it faster in the
future (memory B-cells and memory T-cells)
Neutrophils
wander in connective tissue killing bacteria using phagocytosis and
digestion and by producing a cloud of bactericidal chemicals
Eosinophils
guard against parasites, allergens (allergy-causing agents), and other pathogens; kill tapeworms and roundworms by producing superoxide,
hydrogen peroxide, and toxic proteins; phagocytize antigen–antibody complexes
Basophils
secrete chemicals that aid mobility and action of other leukocytes
* Leukotrienes: activate and attract neutrophils and eosinophils
* Histamine: a vasodilator, which increases blood flow
* Heparin: inhibits clot formation that would impede leukocyte mobilit
Lymphocytes
T, B, and NK cells
* Circulating blood contains: 80% T cells; 15% B cells; 5% NK cells
* Many diverse functions: NK cells are part of innate immunity, all others are part of adaptive immunity; helper T cells function in both
Monocytes
emigrate from the blood into connective tissues and
transform into macrophages
Macrophage system
all the body’s avidly phagocytic cells,
except leukocytes
Wandering macrophages
-actively seek pathogens
-Widely distributed in loose connective tissue
Fixed macrophages
phagocytize only pathogens that come to them
* Microglia—in central nervous system
* Alveolar macrophages—in lungs
* Stellate macrophages—in liver
Interferons
Interferons are proteins secreted by virus-infected cells to alert neighboring cells and protect them from infection. They bind to receptors on nearby cells, activating second-messenger systems that trigger the production of antiviral proteins to break down viral genes or prevent replication. Interferons also activate natural killer (NK) cells and macrophages, which destroy infected and malignant cells before viruses can spread.
complement system
The complement system is a group of over 30 proteins, mainly made by the liver, that support both innate and adaptive immunity. These proteins circulate in an inactive form and are activated by pathogens, enhancing inflammation, immune clearance, phagocytosis, and cytolysis. Activation occurs through the classical, alternative, or lectin pathways.
four mechanisms of pathogen destruction
-inflammation
-immune clearance
-phagocytosis
-cytolysis
fever
Fever, or pyrexia, is an abnormal rise in body temperature caused by factors like infections, trauma, or drug reactions. It’s an adaptive defense that enhances interferon activity, speeds up tissue repair by boosting metabolism, and inhibits the reproduction of bacteria and viruses
inflammation
inflammation is a local defensive response to tissue injury from trauma or infection, aiming to limit the spread of pathogens, remove damaged tissue debris, and initiate repair. Its key signs are redness, swelling, heat, pain, and sometimes loss of function
1st phase of inflammation
Inflammation involves mobilizing defenses through local hyperemia, where vasoactive chemicals cause vasodilation and increase capillary permeability. Selectins help leukocytes stick to vessel walls (margination), allowing them to exit the bloodstream (diapedesis) and enter tissues (extravasation).
containment and destruction of pathogens
Pathogen containment and destruction involve fibrinogen forming clots to wall off microbes, while heparin prevents clotting at the injury site. Pathogens are trapped in fluid pockets and attacked by antibodies and phagocytes, with neutrophils quickly arriving through chemotaxis to target the infection.
tissue cleanup and repair
Monocytes arrive within 8–12 hours, becoming macrophages that clean up by engulfing bacteria, dead cells, and neutrophils. Edema aids cleanup by promoting lymphatic drainage, while pus forms from dead neutrophils, bacteria, and debris.
Antigen
An antigen is any molecule that triggers an immune response, such as proteins, polysaccharides, glycoproteins, or glycolipids, helping the body distinguish self from foreign molecules. Epitopes are specific regions of antigens that stimulate immune responses, while haptens are small molecules that become antigenic only when bound to a host macromolecule, as seen with substances like cosmetics, detergents, and poison ivy.
immuglobulin
Immunoglobulins (Ig) are antibodies, which are defensive gamma globulins found in blood plasma, tissue fluids, body secretions, and some leukocyte membranes. There are five types based on the structure of their C region: IgA, IgD, IgE, IgG, and IgM.
IgA
-plasma; mucus, saliva, tears, milk, and intestinal secretions
-Provides passive immunity to newborns
IgD
-B cell transmembrane antigen receptor
-Thought to function in B cell activation by antigens
IgE
-transmembrane protein on basophils and mast cells
-Stimulates release of histamine and other chemical mediators of inflammation and allergy;
anaphylaxis
IgG
-constitutes 80% of circulating antibodies
-Crosses placenta to fetus, secreted in secondary immune response, complement fixation
IgM
-plasma and lymph
-secreted in primary immune response, agglutination, complement fixation
T cells
T cells are born in the red bone marrow, educated in the thymus, and then deployed to perform immune functions. In the thymus, cortical epithelial cells stimulate the development of surface antigen receptors, making T cells immunocompetent. They undergo positive selection for antigen recognition and negative selection to eliminate self-reactive cells, either by clonal deletion (cell death) or anergy (unresponsiveness). Only 2% of T cells pass the tests and are deployed to lymphatic tissues throughout the body
Cortical epithelial cells
release chemicals that stimulate maturing T cells to
develop surface antigen receptors
immunocompetent
capable of recognizing
antigens presented to them by APCs (they have passed the positive selection
test)
B cells
B cells develop in the red bone marrow, where fetal stem cells differentiate into B cells. Similar to T cells, B cells that react to self-antigens undergo anergy or clonal deletion. Self-tolerant B cells produce surface receptors, rapidly divide, and generate immunocompetent clones before leaving the bone marrow to colonize lymphatic tissues, but they do not go through the thymus.
Antigen-Presenting Cells (APCs)
T cells need antigen-presenting cells (APCs) like dendritic cells, macrophages, reticular cells, and B cells to recognize antigens, as T cells cannot do so on their own. APCs use MHC proteins as “identification tags” to display fragments of engulfed pathogens. If a T cell encounters an APC displaying a foreign antigen, it initiates an immune response, while self-antigens are ignored. This process is coordinated by chemical messengers called interleukins.
Cytotoxic T (TC) cells: killer T cells (T8, CD8, or CD8+)
- “Effectors” of cellular immunity; carry out attack on enemy cells
- Respond to nucleated cells with non-self antigen on the MHC-I protein
Helper T (TH) cells: (T4,CD4, CD4+
- Help promote TC cell and B cell action and innate immunity
- Respond to APCs with non-self antigen on the MHC-II protein
Regulatory T (TR) cells: T-regs
Inhibit multiplication and cytokine secretion by other T cells; limit immune
response; like TH cells, TR cells can be called T4, CD4, CD4+
Memory T (TM) cells
- Descend from the cytotoxic T cells
- Responsible for memory in cellular immunity
T cell activation
1.Antigen Recognition: T cells recognize antigens presented by APCs.
2.Costimulation: A second signal ensures proper activation of T cells (checkpoint).
3.Clonal Selection: T cells proliferate, increasing their numbers.
4.Attack:
TC (Cytotoxic T) cells destroy infected or foreign cells.
TH (Helper T) cells secrete interleukins, activating NK cells, B cells, cytotoxic T cells, and triggering inflammation.
Memory T cells are formed for future immune responses
Destruction of a Cancer Cell by Cytotoxic T Cells
- Perforin and granzymes — kill cells
in the same manner as NK cells - Interferons — inhibit viral replication
and recruit and activate macrophages - Tumor necrosis factor (TNF) — aids
in macrophage activation and kills
cancer cells
Clonal Selection and Ensuing Events of the Humoral Immune Response
1) Antigen Recognition
* Antigen binds to receptors on B cells
2) Antigen Presentation
* B cell displays antigen to TH cell which then secretes interleukin
3) Clonal selection
* increase in number of B cells
4) Differentiation
* plasma cells and memory B cells
5) Attack
* plasma cells produce antibodies
four mechanisms for humoral attack
Neutralization: Antibodies block the pathogenic region of the antigen.
Complement Fixation: Antibodies activate the complement system, triggering inflammation, phagocytosis, or cytolysis.
Agglutination: Antibodies bind to multiple cells, clumping and immobilizing them.
Precipitation: Antigen-antibody complexes form and are cleared by the immune system or phagocytized by eosinophils
hypersensitivity
Hypersensitivity is an excessive immune response to antigens that are normally harmless. It includes alloimmunity (reactions to transplanted tissue), autoimmunity (immune attacks on the body’s own tissues), and allergies (reactions to environmental antigens like pollen, dust, foods, and certain drugs).
Four kinds of hypersensitivity
Hypersensitivity is classified into four types based on the immune response. Type I (acute) causes rapid reactions like allergies, asthma, and anaphylaxis, while Types II and III (subacute) are antibody-mediated with a slower onset (1–3 hours) and longer duration (10–15 hours). Type IV is a delayed, cell-mediated response that does not involve antibodies
autoimmune diseases
Autoimmune diseases occur when the immune system fails to distinguish self-antigens from foreign ones, producing autoantibodies and self-reactive T cells that attack the body’s tissues. This can result from cross-reactivity (antibodies targeting similar self-antigens, e.g., rheumatic fever), abnormal exposure of self-antigens (like sperm crossing the blood-testes barrier), or structural changes in self-antigens due to viruses or drugs.
immunodeficiency disease
Immunodeficiency occurs when the immune system fails to respond effectively. Severe Combined Immunodeficiency Disease (SCID) is a hereditary condition marked by the absence of T and B cells, leaving individuals highly vulnerable to infections and often requiring protective isolation. Acquired Immunodeficiency Syndrome (AIDS), caused by HIV, destroys helper T (TH) cells, weakening innate, humoral, and cellular immunity, with an incubation period of several months to 12 years.
