The Immune System Overview, Animation

The Immune System Overview, Animation

the immune system is the body’s defense
system it protects the body from disease-causing organisms called
pathogens the protection has several layers first invading pathogens meet
with a number of surface barriers which consist of physical chemical and
biological obstacles designed to keep them out the primary physical barrier is
the skin which covers the entire body body systems that are open to outside
environment such as the respiratory digestive urinary and reproductive
system each have their own mechanisms to prevent entrance of microbes mucous
membranes trap them sneezing or coughing reflex expels them while urine
mechanically flushes them out chemical barriers include stomach acid and
various antimicrobial substances in sweat saliva tears and other body fluids
the skin and mucous membranes are also heavily inhabited by the body’s normal
flora which competes with pathogens for nutrition and space providing biological
barriers if an organism manages to get past the surface barriers for example
via a splinter that pierces through the skin it will meet with the innate
component of the immune system which mounts an immediate but nonspecific
response if this fails to contain the infection another layer of Defense
called the adaptive or acquired immune response comes into play the adaptive
response takes longer to be activated but is more effective as it specifically
targets the invading pathogen it also leaves the body with a memory of the
pathogen so it can react faster the next time the same pathogen attacks the
major players of the immune system are the white blood cells or leukocytes all
leukocytes derive from hematopoietic stem cells in the bone marrow each of
them has different roles in the immune response
the first response of the innate immune system is inflammation resident
macrophages which constantly patrol body tissues ingest the pathogen and release
inflammatory chemicals called cytokines which attract other immune cells to the
site of injury: basophils, eosinophils, and mast cells release their own
cytokines amplifying inflammation cytokines dilate blood vessels
increasing blood flow and are responsible for clinical signs of
inflammation such as redness and swelling they act on endothelial cells
of blood vessels and serve as chemical cues for migration of neutrophils the
major phagocytes involved in first-line defense activated endothelial cells
attached to neutrophils in the flow slowing them down before getting them to
squeeze through the vessel wall neutrophils engulf bacteria and destroy
them with enzymes or toxic peroxides they may also release highly reactive
oxygen species in a phenomenon known as oxidative burst which kills pathogens
faster and more efficiently the neutrophils themselves however also die
in the process their debris forming pus on the injury site
the adaptive immune response starts with the so called antigen presenting cells
of which dendritic cells are most effective resident dendritic cells on
the site of infection swallow up pathogens cut them into pieces called
antigens and display them on their surface these dendritic cells are then
picked up by lymphatic capillaries and travel to lymph nodes where they present
the antigens to a matching t-cell the pathogen itself may also travel to a
lymph node where it may encounter a matching b-cell the match finding
process underlies the specificity of adaptive immune response t-cells and
b-cells exist in billions of variations each carries a unique surface protein
which acts like a key among these billions of keys only the ones that can
bind to or unlock the invading pathogen are activated activated T cells and B
cells undergo differentiation and proliferation called clonal expansion
this process produces memory cells ready for future infections by the same
pathogen and effector cells which include activated cytotoxic T cells and
plasma b-cells producing antibodies both of these are specific to the pathogen
antibodies and cytotoxic T cells then leave the lymph node for the blood
stream to be delivered to the site of infection antibodies attached pathogens
and either target them for destruction or neutralize them cytotoxic T cells
release toxins to kill infected host cells

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