U3 Immunity: Non-specific defences against disease Flashcards
What are non-specific defences against disease?
Defences of the body that act against all pathogens
What are the categories of non-specific defences against disease?
- External defences
- Internal defences
- Protective reflexes
What are the external non-specific defences against disease?
- Skin
- Mucus membranes
- Hairs
- Acids
- Lysozyme
- Cerumen
- Movement of fluid
How does the skin work as an external defence against disease?
- It’s a physical barrier that covers the outside of the body and stops the entry of microorganisms when it isn’t broken by cuts
- Large numbers of non-pathogenic bacteria live on the skin, occupying the area so potential pathogens find it difficult to become established
- Skin contains sebum: oily secretion produced by oil glands in skin which contains substances that kill some pathogenic bacteria
- Skin contains sweat: secreted on skin and contains salt that prevents the growth of microorganism
How do mucus membranes work as an external defence against disease?
- Mucus membranes line the openings in the skin
- Mucus is a slimy substance produced by mucus membranes which traps particles and therefore inhibits their entry into the body
- The digestive, urinary and reproductive tracts are protected this way
How do hairs work as an external defence against disease?
- Hairs line the mucus membranes in the nasal cavity, trachea and other passages
- The hairs have a beating motion which moves mucus containing trapped particles and microorganism towards the throat where it can be coughed out or swallowed
How do acids work as an external defence against disease?
- Stomach acids are strong and kill bacteria consumed with food or in mucus from the windpipe
- The vagina also has acid secretions that reduce the growth of microorganisms
How does lysozyme work as an external defence against disease?
- Lysozyme is an enzyme that kills bacteria
- Tears in the eyes, saliva and nasal secretions contain lysozyme
How does cerumen work as an external defence against disease?
- Cerumen is earwax
- It’s slightly acidic and contains lysozyme
- It protects the outer ear from bacteria
How does the movement of fluid work as an external defence against disease?
- The flushing action of body fluids helps keep some areas relatively free of pathogens
- This occurs in the urethra in the form of urine flowing through and having a cleaning action
What are the non-specific protective reflexes?
- Sneezing
- Coughing
- Vomiting
- Diarrhea
How does sneezing work as a protective reflex?
- Stimulus: irritation of walls of nasal cavity by toxic fumes or dust particles, which could be carrying microorganisms
- Sneezing is the forceful expulsion of air from the lungs which carries mucus and foreign particles out through the nose and mouth
How does coughing work as a protective reflex?
- Stimulus: irritation of lower respiratory tract (bronchi and bronchioles)
- Coughing is the forced removal of air from the lungs to remove an irritant by driving mucus and foreign matter out through the mouth
How does vomiting work as a protective reflex?
- Stimulus: psychological, excessive stretching of the stomach or bacterial toxins
- Vomiting is the contraction of the muscles of the abdomen and diaphragm, which expels the stomach contents
How does vomiting work as a protective reflex?
- Stimulus: irritation of small and large intestines by bacteria, viruses or protozoans
- Diarrhea occurs when the muscles of the intestines increase their contractions to remove irritants faster, causing water to not be absorbed and feces to be watery
What are the non-specific internal defences?
- Phagocytosis
- Inflammatory response
- Fever
- Lymphatic system
How does phagocytosis work as a non-specific internal defence?
- Organisms that penetrate external defences are attacked by phagocytes
- Phagocytes are specialised leucocytes (white blood cells) that engulf and digest microorganisms and cell debris, eliminating pathogens before an infection has a chance to take hold
What are the types of phagocytic cells?
- Monocytes and macrophages
- Neurophils
- Dendritic cells
What do monocytes and macrophages do?
- When a tissue becomes infected, monocytes leave the bloodstream and enter the tissue
- In the tissue they differentiate into macrophages
- The macrophages move through the tissue and destroy pathogens through phagocytosis or stay fixed in one place and destroy pathogens that come to them
What do neutrophils do?
- They are the first cells to move into tissue to destroy pathogens by phagocytosis
- They are important in killing pathogens inside cells
- When they die, they make up a large portion of the pus that forms after an infection
What do dendritic cells do?
- They do phagocytosis as well as detect, engulf and process foreign particles
- They use this information about the ingested particles to assist with specific immunity
What is inflamamtion?
An immune response to any damage to body tissue
What is the purpose of inflammation?
- To reduce the spread of pathogens by destroying them and preventing the entry of additional pathogens
- To remove damaged tissue and cell debris
- To begin repair of damaged tissue
What are the signs of inflammation?
- Redness
- Swelling
- Heat
- Pain
What stimulus the inflammatory response?
Damage to tissues
What are the steps of the inflammatory response?
- Mechanical tissue damage or local chemical changes occur
- Mast cells (specialised leucocytes) are activated by complement proteins
- The mast cells release histamine and heparin into the tissue fluid
- Histamine causes vasodilation, increasing blood flow through the area
- The walls of the blood capillaries become more permeable
- More fluid moves through the capillary walls into the tissue
- Heparin prevents clotting in the immediate area of the injury
- A clot of fluid forms around the damaged area to slow the spread of the pathogen into healthy tissue
- Complement system proteins and other chemicals released by mast cells attract phagocytes to the area
- The phagocytes actively consume microorganisms and debris by phagocytosis
- The abnormal conditions in the tissue stimulate pain receptors, so the person feels pain in inflamed area
- The phagocytes, now filled with bacteria, debris and dead cells, start to die
- Dead phagocytes and tissue fluid forms pus
- New cells are produced by mitosis
- Damaged tissue starts to repair
What is a fever?
An elevation of the body temperature above the normal level of 37°C
Why do fevers occur?
High body temperature
- Inhibits the growth of some bacteria and viruses
- Inhibits viral replication by allowing chemicals called interferons (proteins produced by immune cells to prevent the replication of a pathogen) to operate faster
- Speeds up the rate of chemical reactions, which helps body cells repair faster during infection
What happens when fever causes body temperature to get too high?
- It can cause convulsions and brain damage
- Death occurs when the body temperature reaches 45°C
How does a fever occur?
- Macrophages respond to the entry of a pathogen by ingesting it through phagocytosis
- The activated macrophages (as well as dendritic and epithelial cells) start secreting pyrogens into the blood
- Pyrogens travel to the hypothalamus and alter the body’s thermoreceptors to make them feel as if the body is cooler than it really is
- Thermoregulatory mechanisms (vasoconstriction and shivering) are initiated, which increase heat conservation and production to raise body temperature
- When the fever breaks (a point called the crisis), the body’s thermostat is reset to normal
What is the lymphatic system?
A system of vessels that drains excess fluid from the tissues
What does the lymphatic system consist of?
- A network of lymph capillaries joined to larger lymph vessels
- Lymph nodes located along the length of some lymph vessels
How does the lymphatic system work as an internal defence against disease?
- Lymph nodes occur at intervals along lymphatic vessels
- Each node contains masses of lymphoid tissue (cells which are criss-crossed by a network of fibres)
- Lymph entering the lymph nodes contains cell debris, foreign particles and microorganism that have penetrated the body’s external defences
- Some of these microorganisms may be pathogenic and could cause disease if not destroyed
- Larger particles (bacteria) are trapped in the meshwork of fibres as lymph flows through spaces in the nodes
- Macrophages ingest and destroy these particles by phagocytosis
- When infections occur, the formation of lymphocytes increases and the lymph nodes become swollen and sore
- Most lymphocytes are important in the specific immune response to a particular pathogen
