Blood and Immunity

Question 1

Describe lymphatic vessels and nodes.

Answer 1

Lymphatic vessels are closely related with the circulatory system and absorb excess interstitial fluid and transport the lymph to ducts that drain it into the bloodstream. Lymphatic nodes are gland and organs in the lymphatic system that facilitates immune defence by producing lymphocytes.

Question 2

Identify the composition of lymphatic vessels and nodes.

Answer 2

Lymphatic vessels are continuous with lymphatic capillaries and are lined by flattened endothelial cells, and have 2 additional layers: middle smooth muscle cell and outer connective tissue layer. Lymph nodes have a cortex that is the outer layer and contains a branching system to route lymph from afferent lymphatic vessels to the medulla, which is the inner core containing medullary cords and lymph sinuses spanned by crisscrossing fibres which act as a filter for the passage of lymph from the cortex to the efferent lymphatic vessels.

Question 3

Describe lymph fluid.

Answer 3

Lymph fluid (AKA interstitial fluid) is a colourless fluid that surrounds all body tissues, and is a collection of extra fluid that drains from cells and tissues, is filtered through lymph nodes, and drained back into the bloodstream.

Question 4

Discuss the origin of lymph fluid.

Answer 4

Lymph fluid derives from blood plasma as fluids pass through capillary wall at the arterial end. As it accumulates, it is picked up and removed by lymphatic vessels.

Question 5

Discuss how the lymphatic vessels contribute to homeostasis.

Answer 5

They maintain interstitial fluid homeostasis by absorbing accumulating fluid from blood vessels and returning it to the bloodstream.

Question 6

Describe the route of lymph fluid from the tissues back to systemic circulation.

Answer 6

Lymph is collected from cells and tissues in the blood vessels of the systemic and pulmonary circuits, and collected into the lymphatic capillaries, filtered in the lymph nodes, moved through lymphatic vessels, and back into systemic circulation.

Question 7

Identify factors that promote lymph fluid movement through lymphatic vessels.

Answer 7

Respiratory pump moves lymph fluid during inspiration when intrathoracic pressure drops and intraabdominal pressure increases. Movement of the diaphragm forces lymph fluid from vessels in the abdomen (when pressure is highest) and into thoracic lymph vessels (when pressure is lowest), efficiently moving lymph fluid against gravity. Contraction of smooth muscle layer squeezes lymph forward. Skeletal muscles contract and compress lymph vessels which propels lymph forward. One-way valves prevent back flow of lymph.

Question 8

Define afferent and efferent vessels and discuss why their arrangement is important to immunity.

Answer 8

Afferent (meaning toward) vessels bring unfiltered fluids from the body into the lymph node where they are filtered. Efferent (meaning away from) vessels carry clean fluid away and back to the bloodstream, where it helps form plasma.

Question 9

Discuss the lymph nodes role in homeostasis.

Answer 9

Site of lymphocyte production and storage, as well as lymph fluid filtration.

Question 10

Discuss the physiological functions of the thymus, spleen and Peyer’s patches.

Answer 10

Thymus is critical for formation of T-cells. Spleen filters blood through white pulp, and it exits via splenic vein, exposing pathogens to immune cells. Peyer’s patches contain lymphocytes and other immune cells that protects and maintains mucosal integrity of digestive tract, preventing entry of pathogens into the body.

Question 11

Describe the anatomy of the thymus, spleen and Peyer’s patches.

Answer 11

Thymus is located in young mammals in cranial portion of the thoracic cavity, within the mediastinum, and after puberty it shrinks over the lifespan and is replaced by connective and adipose tissues. Spleen near the stomach in the upper left portion of the abdomen, and contains 2 sections: white pulp which houses lymphocytes, and red pulp that stores red blood cells. Peyer’s patches are lymphoid tissue closely associated with the small intestine (specifically the ileum), and are elongated.

Question 12

Identify the constituents of blood.

Answer 12

45% solid portion (formed elements) and 55% liquid portion termed plasma. Formed elements consist of red blood cells, platelets and white blood cells.

Question 13

Identify the components that are transported throughout the body by blood.

Answer 13

Nutrients, oxygen, wastes, carbon dioxide, hormones, growth factors, immune cells, and heat.

Question 14

Describe the morphology of red blood cells and state the importance to physiology.

Answer 14

Biconcave shape that are packed with haemoglobin. The shape increases surface area to allow for more oxygen binding, haemoglobin molecules are closer to the ell surface, which aids in oxygen binding, and confers the ability to bend and squeeze through tight places like capillary networks.

Question 15

Discuss erythropoiesis.

Answer 15

The process by which red blood cells are produced. Red bone marrow, located in the long bones of mammals, respond to the hormone erythropoietin (EPO) by increasing rate of RBC production. Decreased oxygen tension in blood signals the kidney to release EPO. Step-wise differentiation of a progenitor cell termed the erythroblast.

Question 16

Describe role of hemoglobin.

Answer 16

Hemoglobin is a large, oxygen-binding protein that provides RBCs with their characteristic red colour, and circulate oxygen throughout the body.

Question 17

Describe the ABO system of red blood cell antigens.

Answer 17

Red blood cells contain antigens on their cell surface that are recognized by immune system. ABO system is group of antigens used to determine blood type. Type A refers to a person that only contains ‘A’ antigens on their RBC surface; type B refers to only ‘B’ antigens on their RBC surface; type AB can have both ‘A’ and ‘B’ antigens on RBC surface; type O don’t have ‘A’ or ‘B’ antigens.

Question 18

Discuss blood type matching and agglutination reactions.

Answer 18

If blood types don’t match, the recipient’s immune system will react to the unknown antigens found on the cell surface in a process called agglutination. Agglutination is when the recipient antibodies attach to the donor’s red blood cells, causing them to clump together.

Question 19

Discuss erythropoietin function in erythropoiesis.

Answer 19

Erythropoietin is a hormone produced and secreted by the kidney, which stimulates the production and differentiation of RBCs.

Question 20

Identify factors that lead to erythropoietin release.

Answer 20

Low level of oxygen in the blood; blood loss, lung disease, and higher altitudes.

Question 21

Define anucleate and discuss how that impacts cellular metabolism and lifespan of red blood cells.

Answer 21

RBCs are anucleate, meaning they have no nucleus. Without a nucleus, RBCs rely on anaerobic metbolism (glycolysis) for energy production, and they have a short lifespan of 120 days.

Question 22

Discuss the production of platelets.

Answer 22

Platelets (or thrombocytes) are small, fragments of cells, origination from the bone marrow as fragments from the larger megakarocyte. They are also anucleated.

Question 23

Identify the role of platelets in hemostasis.

Answer 23

Platelets transport serotonin and release it when activated, which extends the vasopasm to allow for effective thrombus (clot) formation. These activated platelets release various growth factors. Platelets then become sticky, forming a platelet plug.

Question 24

Describe the morphology of platelets.

Answer 24

When platelets come into contact with damaged inner endothelial linings of blood vessels, they activate by changing shape and become more stellate (star-like). Morphology change and other biochemical transformations makes them more sticky, and they begin to clump together forming a platelet plug.

Question 25

Identify common white blood cells and indicate their future.

Answer 25

Lymphocytes are involved in adaptive immunity, where B-cells produce antibodies and T-cells produce chemokines and directly lyse pathogens. Basophils produce histamine and heparin, which increase blood flow. Neutrophils are the first to arrive at infectious sites, they phagocytize bacteria, fungi and some viruses, and are a major population of WBCs. Eosinophils are involved in allergic reactions and defend against parasitic infections. Monocytes differentiate into macrophages in tissues, phagocytize bacteria, dead cells, and other cellular/tissue debris.

Question 26

Briefly describe the production of white blood cells.

Answer 26

White blood cells are produced in bone marrow from stem cell populations (myeloid and lymphoid stem cells) under the influence of various growth factors. Specific membrane receptors develop to react to different cytokines (autocrine regulators) and cause the production of different subtypes of white blood cells.

Question 27

Identify common innate immune defence mechanisms and discuss how they provide immune protection.

Answer 27

Innate (non-specific) immune system include general mechanisms for immune defence and include mechanical barriers (skin), chemical barriers (stomach juices), inflammation, phagocytosis, fever and natural killer (NK) cells. If pathogens enter the body, internal defence mechanisms are activated: macrophages and neutrophils ingest and destroy pathogens/toxic chemicals, NK cells destroy cells infected with viruses and, mast cells that release histamine and inflammatory mediators.

Question 28

Briefly describe inflammation, mechanical barriers, complement system, chemical barriers, phagocytosis, and fever.

Answer 28

Inflammation: swelling, redness and heat at site of infection due to invasion of immune cells and increased blood flow.
Mechanical Barriers: first line of defence by preventing entry of pathogens into the body by physically separating the external environment from the body’s internal environment; ex. skin, epithelial membranes of respiratory/digestive tract.
Complement System: part of innate immune system, and helps adaptive immune system clear pathogens from the body, by binding of antibodies to antigens, resulting in complement proteins being activated, promoting killing and phagocytosis of targeted pathogen.
Chemical Barriers: chemicals that will kill pathogens prior to entry into the body; enzymes that are released by lysosomes on the skin and acidity in the stomach and urinary tract.
Phagocytosis: engulfment of pathogens/particles into cells followed by enzymatic digestion by the cell’s lysosomes.
Fever: cytokines, released from leukocytes, will cause an increase in body temperature which triggers increased level of neutrophils and interferons which can help fight infection.

Question 29

Define specific immunity, antigens, haptens, epitope.

Answer 29

Specific Immunity: involves recognition of antigen (activates T and B cells), targets specific molecules/diseases by developing antibodies.
Antigens: foreign molecules that will stimulate and bind to antibodies.
Haptens: small organic molecules that can’t stimulate an immune response on its own; it needs to bind to a carrier protein to become immunogenic.
Epitope: part of the antigen that is recognized and bound by antibodies (antigenic determinant).

Question 30

Identify common antigens.

Answer 30

Infectious bacteria, viral particles, toxins, and cancer.

Question 31

Differentiate between class I and class II major histocompatibility complexes.

Answer 31

Class I MHC are found on all nucleated cells (not RBCs), and present polypeptides derived from proteins in cell’s cytoplasm and nucleus. Class II MHC are only found on antigen presenting cells (dendritic cells, macrophages, B lymphocytes). Cytotoxic T-cells are only activated by antigens presented with Class I MHC molecules , and helper T-cells are activated by antigen presenting cells with class II MHC molecules.

Question 32

Describe antigen recognition and processing by antigen presenting cells.

Answer 32

Antigen recognition is a complex procedure that requires processing by antigen presenting cells, which detect, engulf, digest, and present antigens on their surface using a group of proteins termed the major histocompatibility complex (MHC). T-cell become activated upon binding to the antigen:MHC complex. Activation of T-cells requires proper antigen processing and presentation, and it also specific to a particular antigen.

Question 33

Identify common antigen presenting cells.

Answer 33

Macrophages and dendritic cells.

Question 34

Discuss cell mediated immunity.

Answer 34

Cell mediates immunity requires cell to cell contact that T-cells make with antigen present cells. Facilitate by presenting foreign antigens in combination with MHC to T lymphocytes through antigen presenting cells. Results in the proliferation of cytotoxic cells, helper T-cells and release of cytokines that destroy target cells.

Question 35

Differentiate between cytotoxic and helper T-cells.

Answer 35

Cytotoxic T-cells (CD8 T-cells) proliferate when they are activated, and bind to cancer cells or virally infected cells which display non-self antigens. Once bound, they secrete perforin, which produces holes in the cells causing it to undergo programmed death. Helper T-cells (CD4 cells) respond to antigens by secreting chemical messengers called cytokines, which can activate other lymphocytes such as cytotoxic CD8 T-cells and B-cells to mediate immunity.

Question 36

Describe cell mediated destruction by cytotoxic T-cells.

Answer 36

Cell mediated immunity if a form of adaptive immunity. Upon presentation of a cell with a viral antigen and class I MHC, a cytotoxic T-cell will release perforins to perforate the target cell’s membrane. Followed by granzymes that will enter the cytoplasm and destroy DNA.

Question 37

Discuss how helper T-cells contribute to cell mediated immunity.

Answer 37

Helper T-cells bind to antigen presenting cells that present a viral antigen in combination with class II MHC. Activation causes secretion of lymphokines (cytokines) which helps in proliferation of cytotoxic T-cells.

Question 38

Indicate how human immunodeficiency virus (HIV) leads to acquired immunodeficiency syndrome.

Answer 38

HIV specifically targets the CD4 positive cell population in HIV positive individuals and eventually prevents activation of CD8 positive T-cells and B-cells resulting in life-threatening immune deficiency.

Question 39

Describe perforin mediate apoptosis.

Answer 39

Perforin is a protein, secreted by cytotoxic T-cells that are bound to viral cells that display non-self antigens, and produces holes in cells causing the infected/damaged cells to undergo programmed cell death (apoptosis).

Question 40

Describe humoral immunity.

Answer 40

Blood and lymph are body fluids (humours). Immunity that takes place within fluid compartments of body via B-cells.As antibodies that are secreted by activated B-cells diffuse through bodily fluids, this type of specific immunity is termed ‘humoral immunity’.

Question 41

Discuss how B-cells contribute to humoral immunity.

Answer 41

B-cells circulate through the lymphatic and circulatory system, waiting for exposure to an antigen. They produce antibodies in response to specific antigen exposure, and the B-cells proliferate then differentiate into plasma cells that produce 2,000 antibodies per second.

Question 42

Describe how antibodies mediate humoral immunity.

Answer 42

Antibodies recognize and serve as binding sites for antigens, and the binding triggers proliferation of antibody clones that become plasma and memory cells. Plasma cells will produce large amounts of antibodies identical to B-cell parent to combat specific antigen by activating complement immune system.

Question 43

Differentiate between primary and secondary immune responses.

Answer 43

Primary Immunes Response: immune response from exposure to a new pathogen/antigen; an infected person won’t be completely protected from the pathogen as the immune system needs to create antibodies specific to the pathogen that can take up to 5-10 days.
Secondary Immune Response: immune response that is mounted upon secondary exposure to a pathogen; antibody production is much faster due to memory lymphocytes and will reach maximal levels within 2 hours of infection; likely sufficient to precent development of disease.

Question 44

Identify constituents of blood plasma.

Answer 44

45% solid portion (formed elements) and 55% liquid portion (plasma). Formed elements consist of red blood cells, platelets, and white blood cells. Plasma consists of water, amino acids, proteins, carbohydrates, lipids, vitamins, hormones, electrolytes, and cellular wastes.

Question 45

Describe the process of hemostasis.

Answer 45

Hemostasis, the stopping of bleeding, attempts to avoid blood loss after vascular injury by vasospasm, platelet plug formation and blood coagulation. Upon damage, vasoconstriction of local smooth muscle is triggered, decreasing blood flow to injured area. Exposed collagen will trigger the aggregation of platelets to the site of the injury forming a sticky plug to prevent blood loss. Glycoproteins will bind to the exposed collagen fibres along with von Willebrand factors to form the plug. Upon binding, platelets are activated causing degranulation of secretory granules and release of ADP and thromboxane A2 to promote plug formation and serotonin to stimulate vasoconstriction. Activated platelets will also activate variety of plasma clotting factors that will lead to conversion of fibrinogen to fibrin, which will bind to platelets’ plasma membrane, strengthening the platelet plug.

Question 46

Identify components of a platelet plug.

Answer 46

Platelet cells, von Willebrand’s factor (protein), and fibrin.

Question 47

Discuss the intrinsic, extrinsic, and common coagulation pathways.

Answer 47

Intrinsic: starts when there is a trauma in blood or when blood is exposed to negatively charged surfaces, such as collagen (component of extracellular matrix outside the lumen of blood vessels); longer and slower pathway.
Extrinsic: initiated by tissue factors that are released from damaged tissues (outside of blood); shorter and more rapid pathway.
Coagulation Pathways: biochemical process that produces blood clots or thrombi (conversion of fibrinogen to fibrin).

Question 48

Identify common factors that induce coagulation.

Answer 48

Fibrinogen (Factor I), prothrombin (Factor II), proaccelerin (Factor V), and Stuart-Prower (Factor X).

Question 49

Discuss how coagulation is limited to the site of injury.

Answer 49

In undamaged blood vessels, endothelial lining physically separates collagen and platelet activators from blood, so platelets don’t stick together. Endothelium secretes nitric oxide and prostacyclin to inhibit platelet aggregation. Only at the site of injury with damaged endothelial lining, causes activation of platelets and coagulation is triggered. Fibrin will bind to thrombin to slow down positive feedback loop. During tissue repair, basophils and mast cells will secrete heparin (prevent formation of thrombin).

Question 50

Describe the tissue repair process at the site of blood clot.

Answer 50

Once clot is no longer needed, plasmin becomes activated from inactivated plasminogen and breaks down the fibrin network through a process called fibrinolysis. Tissue plasminogen activator (tPA), urokinase and lysosomal enzymes are examples of proteins that can activate plasminogen and begin the process of dissolving a blood clot. Tissue repair involves shrinking of clot, infiltration by fibroblast to synthesize new collagen and extracellular matrix, and formation of new blood vessels through angiogenesis.

Question 51

Describe the process of fibrinolysis.

Answer 51

Enzymatic degradation of blood clot following tissue repair. Factor XII activates plasma molecules kallikrein, which convert plasminogen to plasmin. Plasmin digests fibrin, causing dissolution of the clot.