C3.2 Defence against disease Flashcards
What are pathogens
Pathogens are disease-causing organisms like viruses, bacteria, fungi and protists that result in disease upon entry into the body
[most not pathogenic to humans but have exceptions]
- pathogens use human tissues as food and shelter but their means of growth and secretions can cause us harm
NOS 1
meticulous observations can lead to break throughs
- 1854, major cholera outbreak in suburb of London, UK
- Vibio cholerae bacteria that causes cholera is found in faeces of infected Indivs
- common practice in 1800s to empty waste into areas in front of homes –> bacteria moved through soil and infected drinking well used by many
- a physician named JOHN SNOW suspected cholera was transmitted in water supplies
- he created a map of all known infections and found one particular well was used by all
- the well was closed –> number of cholera infections fell
- info & map by SNOW formed basis of modern epidemiology studies that trace outbreaks
NOS 2
In mid 1800s, physician IGNAZ SEMMELWEIS in Vienna, Austria studied a lethal diseases called childbed fever
- disease alrdy had alarming high rates of infection & death in Vienna maternity wards
- semmelweis noted a difference in infection rates btw 2 maternity wards
- one ward staffed by midwifes, one staffed by other physicians and medical students
- rate of infection & death much faster in physcians’ ward
- he eliminated specific differences btw 2 wards, besides who staffed them
- one difference which proved to be consequential is that physicians often carried out autopsies before childbirth
- he postulated that the physicians were carrying small “particles” that caused the disease from autopsies to pregnant women
- he ordered all to wash hands w chlorine solution before treating patients –> immediate improvement in infection rate
Lines of defence against pathogens
- First line of defence - surface barriers that prevent entry of pathogens into body
- skin, mucous membrane, secretions of skin & mucous membrane - Second line of defence - non-specific phagocytes & internal mechanisms that comprise innate immunity
- phagocytic leukocytes
- antimicrobial proteins
- inflammatory response
- fever - Third line of defence - specific lymphocytes that produce antibodies as part of adaptive immune response
- lymphocytes
- antibodies
- memory cells
Skin and mucous membrane as primary defence [physical & chemical barrier to pathogens]
Skin has 2 primary layers:
1. Dermis (underneath)
- sweat glands, capillaries, sensory receptors, dermal cells which give structure and strength to skin
2. Epidermis (top layer)
- constantly replaced as the underlying dermal cells die and move upwards
- layer of dead cells forms physical barrier against most pathogens bc it is not alive
- as long as skin is intact, we are protected from most pathogens
BUT pathogens can enter body through a few locations not covered by skin - these entry points are lined with tissue cells that form a mucous membrane
- cells of mucous membranes produce and secrete a lining of sticky mucus
- mucus traps incoming pathogens –> preventing them from reaching cells they can infect
- some mucous membrane tissues lined with cilia [hair-like extensions capable of wave-like movement –> movement carries trapped pathogens up and out of mucous-lined tissues like trachea]
Areas with mucous membrane
Trachea - tube that carries air to and from lungs
Nasal passages - tubes that allow air to enter nose then trachea
Urethra - tube that carries urine from bladder to outside
Vagina - reproductive tract leading from uterus to outside
Sealing of cuts in skin by blood clotting
Plasma proteins circulate in the blood plasma:
1. Prothrombin
2. Fibrinogen
they circulate in the blood plasma and remain inactive till events like bleeding occur
Cell fragments that circulate in bloodstream: Platelets
- they form in the bone marrow, along w RBC (erythrocytes) and WBC (leucocytes) but don’t remain as entire cells
- one breaks down into many fragments and each becomes a platelet –> they don’t have nucleus and hence has short cellular life span of 8-10days
Process of blood clotting
- when cells of blood vessels damaged, chemicals are released to stimulate platelets to adhere to damaged area –> forming a “plug”
- damaged tissue and platelets release chemicals called clotting factors that convert prothrombin to thrombin
- thrombin is an active enzyme that catalyses the conversion of soluble fibrinogen into relatively insoluble fibrin
- fibrin is a fibrous protein that forms a mesh-like network which helps stabilise platelet plug
- more and more cellular debris gets trapped in fibrin mesh –> stable clot is formed, preventing further blood loss & entry of pathogens
Innate immune system (First layer of human immunity)
- responds to broad categories of pathogens & don’t change during a person’s lifetime
- recognise things that belong and those that don’t belong in human body
- the molecules of foreign/ non self entities are called ANTIGENS which can trigger an immune response
- the innate immune system involves the activation of a group of leucocytes (WBC) called phagocytes which are able of engulfing invading materials by endocytosis
Adaptive immune response (Second layer of human immunity)
- develops over time & only after exposure to specific antigens of specific pathogens
- first exposure to specific antigen leads to series of cellular events culminating in molecules and cells that are longed lived and have ability to defend body against specific pathogen
- specific long-lived WBC formed during first exposure are memory cells
- upon second exposure to same pathogen, these specific memory cells are activated quickly –> very effective in fighting a pathogen
- adaptive immune response become more effective with age, as a person becomes exposed to more pathogens
Phagoctyes
They are leucocytes (WBC) capable of AMEOBOID MOVEMENT –> can purposefully extend sections of their plasma membrane, followed by cytoplasm and organelles
- phagocytes use this motion to squeeze their way through capillaries so that they can leave & enter bloodstream to move through body tissues
When phagocyte encounters something in body tissues that contain antigens –> sends out plasma membrane extensions to engulf foreign body in ENDOCYTOSIS
- hydrolytic enzymes of LYSOSYMES inside phagocyte digest potential invader
[this response is non-specific and hence innate immune response]
Lymphocytes
Continuously circulate in bloodstream & contained in
lymphatic system (lymph nodes)
- B-lymphocyte [B-cells]
- produce protein molecules called ANTIBODIES as part of adaptive immune response
- each type of B-lymphocyte can only synthesise a specific antibody [each antibody is diff bc its produced in response to a diff pathogen]
- each specific antibody recognises and binds to a specific antigen - ## T-lymphocyte [T-cells]
Antibodies
Y-shaped proteins
- at the end of each branch of the Y is a binding site
- binding site is where antibody attaches itself to antigen
- bc antigen is a protein on the surface of a pathogen, antibody attaches to pathogen
