Defences against Disease Flashcards
Non specific external defenses
May be physical (mechanical) or a chemical substance. This is sometimes known as the body’s first line of defence
1st line of defence
- The skin
- Ear
- Eyes
- Respiratory
- Gastrointestinal tract
- Urinogenital tract
The skin
Tough mechanical barrier, 0.5-4mm, thick. Pathogens cannot penetrate skin unless it is broken. It is continuously shed and fully replaced every approx 4 weeks.
Sweat contains
Contains the powerful anti-microbial enzyme, lysozyme (also found in tears, nasal secretions, tissue fluid and saliva.
Why cannot foreign substances establish themselves on skin
It is continually rubbed off and replaced by new cells. Skin contains sebaceous glands which produce an oily sebum (fatty acids resistant to bacteria)
The ear
Modified glands at the entrance to the auditory canal secrete cerumen (ear wax) which is thought to repel insects and inhibit bacterial growth.
The eyes
Eyes are protected by the brows, lashes and lids. Blinking prevents some harmful substances entering the eye.
Tears
Have a flushing action, washing out the eye. They also contain lysozyme, and salt.
Respiratory tract
Initial protection is provided by coarse hairs in the nostrils
Nasal fluids contain lysozyme
Microscopic cillia line the upper respiratory tract. These fine hairs beat rhythmically and sweep the mucous layer up the trachea and into the throat.(Coughed or swallowed)
Gastrointestinal tract
Gastric juices: HCL in stomach (avg pH 2)
Sticky mucous lining (anus)
Saliva contains lysozyme
The urinogenital tract in males
Flushing action of urine which tends to be slightly acidic at pH 6.
Vagina
Relies on a tough epithelium which is difficult for microbes to penetrate. Good bacteria and fungi secrete lactic acid which makes the vagina fluid acidic (PH 4) which discourages most microbes.
2nd line of defence
- Reflexes
- Inflammation
- Fever
- Phagocytosis
Reflexes
- Sneezing
- Coughing
- Vomiting
- Diarrhoea
Inflammation
When tissue is damaged mechanically, chemically or by infection, the infected area becomes hot, red and swollen.
Purpose of inflammation
- Reduce spread of pathogens
and prevent entry of more - Remove damaged tissue and cell debris
- Begin repair of damaged tissue
Four signs of inflammation
- Redness
- Swelling (odema)
- Heat
- Pain
Results of tissue injury
MAST cell (type of WBC) secretes
- Histamines
- Heparin
- Cytokines
Histamines being released
Vasodilation of blood vessels near injury
Heparin released
Prevents clotting in immediate area of injury
Cytokines being released
- Attract phagocytes (increased phagocytosis)
- Stimulate pain receptors
- Mitosis = new cells = repair
Inflammatory response
- Damaged tissue
- Releases chemicals including heparin and histamine by MAST cells
- Causes local blood vessels to dilate and become more permeable
- Increases fluid to tissues
- Defensive chemicals and cells move to damaged tissues
- Phagocytosis by wbc of pathogens and damaged tissue (pus may form)
- Mitosis of tissue cells to replace damaged cells
Fever
An increase in body temperature
How does a fever create an unfavourable environment
- Speeds up chemical reactions helping body cells to repair themselves.
- Inhibits replication and growth of pathogen
- Interferon activities are enchanced: decreased viral replication.
How a fever works
Pyrogens act on hypothalamus and increase your internal thermostat. The hypothamamus responds by:
- Making skeletal muscles shiver (increase heat)
- Vasoconstriction of blood vessels in skin (decrease in heat loss)
Crisis point
When the fever breaks (point called crisis) the person feels hot and appears flushed, skin vasodilation and profuse sweating takes place (increases heat loss)
Cells that are phagocytes in tissue
- Monocytes and macrophages
- Neutrophils
- Dendritic cells
Monocytes and macrophages
Monocytes leave blood and move to infected tissue. Differentiate into macrophages. They can repair as fixed residents (e.g alveoli)
Neutrophils
Most abundant leucocyte. 1st cell to move to tissues and destroying pathogens. Short life - fund in pus.
Dendritic cells
Ability to detect, engulf and process foreign particles. Assist within specific immunity.
Phagocytes
Mobile specialised white blood cells (leucocytes) that can engulf and destroy microbes or cellular material. They recognise microbes as ‘non self.’
Main function of lymphatic system
Collect fluid and return to circulatory system
Internal defence
The immune response
When foreign particles/organisms penetrate the non-specific defences, the body reacts by producing special cells from the lymphoid tissue.
- Antibody mediated (humoral)
- Cell mediated (cellular)
Antibody-mediated immunity (humoral)
- Involves the production of special proteins called antibodies and involves B cells
- Works against bacteria, toxins, viruses BEFORE they enter body cells. Even red blood cells from different blood groups.
- Resistance before microorganisms or substances enter a cell.
Cell-mediated immunity (cellular)
- Involves formation of special lymphocytes and involves T cells
- Resistance at the intracellular phase of infections
- Provides resistance to fungi or parasites
Immunological competence
As T and B cells mature they are able to identify chemical markers called antigens that distinguish self from non-self cells and specific pathogens that cause disease.
Antigen
A substance capable of causing a specific immune response. They are large molecules such as proteins, carbs. lipids or nucleic acids
Non self antigens
Foreign compounds that do trigger an immune response.
Antigens information
-Large molecules
- May be a protein, polysaccharide, nucleo-protein (nucleic acid and protein) or glycolipid
- Many anitgens are on the surface of foreign particles
- E.g pili, (projections) cell wall, proteins of outer membranes, flagella, etc
Antigen-presenting cells
Phagocytic cells that digest pathogens and present the non-self antigen to lymphocytes. Typically includes macrophages.
The antibody
A specialised protein made in response to non-self antigens. Also known as immunoglobins.
Function of antibody
Antibodies combine with the non-self antigen to form an “antigen-antibody complex.” They are specific as they combine only with particular antigens, which have specific active sites.
Results of antigen-antibody binding
Antigen is tagged for removal from the body. “CAPDIN”
CAPDIN (C)
- Coats bacteria: Antibody binds to a bacteria and promotes phagocytosis
CAPDIN (A)
- Agglutination: Clumping of bacteria, viruses on foreign blood cells by antibodies. Antigens are easier to be phagocytised.
CAPDIN (P)
- Precipitation: Of soluble antigens to make them insoluble (in solution). Antigens are easier to be phagocytized.
CAPDIN (D)
- Dissolves organisms
CAPDIN (I)
- Inactivate: An antibody combines with foreign enzymes or bacterial toxins or inactivates them by inhibiting reactions with other cells or compounds.
CAPDIN (N)
- Neutralisation: Of an antigen. Antibodies bind to viruses or toxins. Preventing entry into host cell
B-Lymphocytes
- Some activated B cells will become plasma cells and produce lots of antibodies
- These antibodies travel to the blood, lymph lining of gut and lungs
- Each B-cell has a specific antibody on it’s surface
- Other B-cells differentiate into memory cells
- They can also be stimulated to enlarge and divide by helper T-cells
- A helper T-cell is presented the antigen (via antigen presenting cell)
- Helper T-cells release cytokines-some of which activate the B-cells
- Originate and mature in bone marrow
T-cells
- Originate in bone marrow, mature in thymus gland
- Each T-cell is specific for a particular antigen.
- T cells do not respond to free antigen by to a cell bond antigen
- An infected cell alerts the immune system by displaying non-self protein fragments on it’s outer surface
- Killer, helper or T suppressor cells
Killer T-Cells
Leave the lymph node and migrate to the site of infection where they attack the infected cells directly by
- Lysing them
- Increasing phagocytosis
- Secrete substances to activate other lymphocytes
Helper T-Cells
Secrete cytokines, which activate B and killer T cells
Suppressor T-Cells
Regulate the activities of the other types of T-cells keeping them from causing excessive immune reactions that might be dangerous to the body.
Primary immune response
Response to an antigen the first time the antigen infects the body.
Secondary immune response
A more rapid response to a pathogen the second time it invaded the body, memory cells are activated. Antibody production increases, dramatically and in a much shorter time.
Types of acquired immunity
Can be acquired naturally or artificially.
Naturally acquired immunity
Person acquires immunity without human intervention.
Naturally acquired passive immunity
Via the placenta to unborn baby,
Antibodies via breast milk
Naturally acquired active immunity
Person gets antigen and manufactures own antibodies as a result of antigen attack
Artificially acquired immunity:
Person is given the antigen or antibodies that results in immunity
Artificially acquired passive immunity
Person receives antibody from another person. E.g. a person receives the antibody-rich portion of serum; short lived immunity
Artificially acquired active immunity.
Person recieves antigen in form of a vaccine and manufactures own antibodies (injection or oral serum)
