non-specific immune responses

• What is the first line of defence?

  skin

  mucous membranes

  expulsive reflexes

  chemical secretions
• How is skin a defence mechanism?

  • Skin posses an outer layer of dry, dead, hardened cells filled with keratin
  • Keratin is a tough fibrous protein
  • This layer of cells acts as a physical barrier to pathogens
  • There are secretions of sebum that contain fatty acids which have antimicrobial properties
• Mucous membranes as a defence mechanism?

  • Mucous membranes line the gut, airways and reproductive system
  • The mucous membrane consists of epithelial cells and mucus-secreting cells like goblet cells
  • Mucus contains lots of glycoproteins with long carbohydrate chains. These chains are what make mucus sticky
  • Viruses, bacteria, pollen and dust float about in the air that we breathe in
  • Mucus in the airways (trachea, bronchi and bronchioles) can trap these particles
  • The particles are then moved towards the back of the throat by cilia
• Expulsive reflexes as a defence mechanism?

  • When a pathogen irritates the lining of an airway it can trigger an expulsive reflex; a cough or sneeze
  • Both a cough and sneeze result in a sudden expulsion of air. This expelled air contains secretions from the respiratory tract along with the foreign particles that have entered
• Chemical secretion of lysozymes as a defence mechanism?

  • Lysozymes are antimicrobial enzymes that breakdown the cell wall of bacteria
  • These special enzymes are found in body fluids such as blood, tears, sweat, and breast milk
• Chemical secretions of hydrochloric acid as a defence mechanism?

  • Hydrochloric acid is produced by the cells that line the stomach
  • The acid creates a low pH inside the stomach which helps to kill any bacteria that has been ingested alongside food
  • The cells of the gut secrete mucus to prevent being damaged by hydrochloric acid
• What are the second line of defence mechanisms?

  • Blood clotting
  • Inflammation
  • Wound repair
  • Phagocytosis
• What is blood clotting?

  • When the body is wounded it responds rapidly
  • A break in the mucous membranes or skin membranes causes the release of molecules that trigger a chemical cascade which results in blood clotting
  • Blood clotting prevents excess blood loss, the entry of pathogens and provides a barrier (scab) for wound healing to occur
  • The chemical cascade involves a large number of steps and several plasma proteins
  • A small initial stimulus is amplified to produce a large amount of fibrin so that the wound is quickly sealed
• What is inflammation?

  • The surrounding area of a wound can sometimes become swollen, warm and painful to touch; this is described as inflammation
  • It occurs via chemical signalling molecules which cause the migration of phagocytes into the tissue and increased blood flow
  • Body cells called mast cells respond to tissue damage by secreting the cell signalling molecule, histamine
  • Histamine stimulates many responses:
  • one is Vasodilation increases blood flow through capillaries
  • another is phagocytes leave the blood and enter the tissue to engulf foreign particles
• What are cytokines?

  • Cytokines are cell-signalling compounds that stimulate inflammation and an immune response
  • They are small proteins molecules
  • Interleukins are a group of cytokines
  • Interleukin 1 (IL-1) and interleukin 6 (IL-6) promote inflammation
  • IL-1 targets the brain, causing drowsiness and fever
• Wound repair- second line of defence?

  • A scab is formed as a result of blood clotting
  • Underneath this scab, there are stem cells that divide by mitosis to heal the wound
  • Wound healing occurs in a number of overlapping stages:
  • New blood vessels form
  • Collagen is produced
  • Granulation tissue forms to fill the wound
  • Stem cells move over the new tissue and divide to produce epithelial cells
  • Contractile cells cause wound contraction
  • Unwanted cells die
• What are expulsive reflexes?

  when the body attempts to force foreign substances out

  e.g irritation of mucous membranes in nostrils causes sneezing

  irritation of ciliated epithelium in respiratory tract causes coughing
• What are ways the non-specific immune system responds to infection?

  inflammation

  phagocytosis

  digestive action of lysozymes

  skin /mucuos mems
• Outline the process of inflammation?

  1 damaged vessels release histamines, causing vasodilation

  2 blood flow and permeability of blood vessels increase

  3 white blood cells and plasma move into the infected tissue
• How does blood clotting occur?

  1 blood platelets form a plug and release chemicals that enhance clotting e.g thromboplastin

  2 prothrombin changes into thrombin, its active form

  3 fibrinogen changes into insoluble fibrin which covers the wound
• How does phagocytosis destroy pathogens?

  1 phagocyte moves towards pathogen which may have been marked by opsonins

  2) phagocyte engulfs pathogen via endocytosis to form a phagosome

  3)phagosome fuses with with lysosome to form a phagolysosome

  4) lysozymes digest pathogen

  5) phagocyte absorbs the products from pathogen
• What is the role of antigen-presenting cells (APCs)?

  1 macrophage displays antigen from pathogen on its surface after absorbing the products in phagocytosis

  2) enhances recognition by T helper cells, which cannot directly interact with pathogens/antigens in body fluid

  3) APCs secrete cytokines that are involved in stimulating the specific immune response
• What is the difference between the non-specific immune response and the specific immune response?

  Non-specific immune response is the immediate, general defense mechanism against any pathogen, while specific immune response is a targeted response that is tailored to a specific pathogen.
• What are lysozymes?

  digestive enzymes

  found in lysosomes, as well as many secretions e.g tears and mucus

  can damage bacterial cell walls, causing osmotic lysis
• What structures/cells are involved in preventing the entry of pathogens into the body?

  goblet cells

  mucous membranes

  platelets

  skin
• Which cells or structures act as a physical barrier to the entry of pathogens?

  platelets

  skin
• Which cells or structures are involved in phagocytosis?

  antigen-presenting cells

  lysosomes

  neutrophils

  phagosomes
• What is the function of epithelial cells in the airways of mammals in the defence against pathogens?

  goblet cells secrete mucus

  mucus traps pathogen

  cilia sweep mucus

  cytoskeleton (microtubules) moves cilia
• What line of defence is blood clotting?

  primary
• What is the role of opsonin during phagocytosis?

  opsonin binds to antigen on pathogen and assists binding to phagocyte
• How is the structure of a neutrophil specialised?

  lobed nucleus

  many mitochondria

  many lysosomes

  well-developed cytoskeleton

  has specific receptors
• What is the role of cytokines in phagocytosis?

  attract phagocytes (cell-signalling)
• What is the role of opsonins in phagocytosis?

  bind to pathogens / antigens increasing recognition by phagocytes
• What are expulsive reflexes?

  Expulsive reflexes are involuntary (happen automatically) muscle contractions that help to expel substances from the body, such as coughing, sneezing, and vomiting.

  A sneeze happens when the mucous membranes in the nostrils are irritated by things such as dust or dirt.

  A cough stems from irritation in the respiratory tract.

  Both coughing and sneezing are an attempt to expel foreign objects, including pathogens.
• What is a blood clot?

  a mesh of fibrin fibres(protein fibres)
• What is the role of blood clots?

  to plug wounds to prevent pathogen entry and blood loss
• How are blood clots formed?

  by a series of chemical reactions that occur when platelets are exposed to damaged vessels
• What are signs of inflammation?

  swelling, pain, heat and redness
• How can inflammation be triggered?

  tissue damage: the damaged tissue releases molecules which increase the permeability of the blood vessels, so they start to leak fluid into the surrounding area

  this causes swelling and helps to isolate any pathogens that may have entered the damaged tissue

  the molecules also cause vasodilation, which increases the blood flow to the affected area, making the area hot and brings WBCs to the area to fight off any pathogens.
• what type of defence is the skin?

  a non-specific defence, as it defends against all pathogens not just one
• how does the defence act as a defence?


  the skin provides a waterproof covering for the whole body, it makes it difficult for pathogens to penetrate unless a wound is present
• why is it important that open wounds are cleaned and properly protected?

  to prevent exposure to infection
• how are mucous membranes a defence?


  mucous membranes produce sticky mucous that traps bacteria/pathogens inside the body

  cilia waft this mucous away to be removed from the body
• what does irritation of the mucous membranes cause?


  expulsive reflexes, such as coughing and sneezing, which force the mucous (which contains the pathogen) out of the body
• when does blood clot?

  if it's exposed to air in a process called coagulation

  this clotting creates a seal if the skin is broken, which reduces blood loss and the chances of infection by pathogens