Introduction to Immunity Flashcards
Functions of the lymphatic system
The lymphatic system is the second circulatory system which runs in parallel to the cardiovascular system and carries a milky-coloured fluid called lymph
consists of lymphatic vessels, lymph nodes and two major lymphatic organs; the spleen and thymus gland
three major functions of lymphatic system
Tissue drainage
Fat transport
Trapping of foreign material
Layers of the immune system
The immune system is in a continual battle with environmental pathogens including bacteria, viruses, fungi and parasites
4 layers of protection of the immune system
Mechanical defences
Chemical defences
Cellular defences
Inflammatory response
Mechanical Defences - The skin
provides the major mechanical barrier to infection
the epidermis provides a robust mechanical barrier against environmental pathogens - rich in the tough, dense protein keratin which provides a high tensile strength.
The outer layer of cells (the cornified layer) is dead and the surface cells are continuously sloughing away, taking with them surface pathogens
Mechanical Defences - Mucous membranes
skin does not cover the entire surface of the body;
body cavities such as the mouth, nose or reproductive tract, opens out to the surface it is usually lined by a mucous membrane
mucous membranes are rich in goblet cells that produce sticky mucous which functions as a mechanical barrier, trapping particulates
Mechanical Defences - The mucociliary escalator
Lining the nasal cavity and upper portions of the bronchial tree is a specialised ciliated epithelium
this epithelial layer is rich in goblet cells which secrete
mucus
has a layer of specialised ciliated cells which continually move contaminated mucus upwards from the lungs to the throat where it is swallowed and enters the sterilising acidic secretions of the stomach
Chemical Defences - Hydrochloric acid
low pH - important for activating the digestive enzyme pepsin which initiates the digestion of proteins in the stomach
high acidity of the stomach is also essential for sterilising the food that is eaten.
All food will have bacterial, viral and fungal contamination since these pathogens are continually landing on the food from the atmosphere.
few pathogens can survive the internal pH of the stomach which functions as an effective sterilising chamber
Chemical Defences - Lysozyme
Most body fluids contain an enzyme called lysozyme
attacks the components of bacterial cell walls initiating lysis (bursting)
found in particularly high concentrations in sweat and the secretions that bath the eye
Since lysozyme is an effective antimicrobial, it can be added to wound dressings to help reduce infection at wound sites
Chemical Defences - Lactobacillus and the Female Reproductive Tract
The female reproductive tract is usually colonised by a population of “friendly bacteria” including lactobacillus species
Lactobacillus bacteria produce lactic acid which helps maintain an acidic pH within the vagina of around 3.9
This makes it difficult for other bacteria and yeast to colonise the female reproductive tract
Chemical Defences - Dysbiosis in the Female Reproductive Tract
The balance of healthy bacteria in the vagina can be disrupted (dysbiosis) by the use of strong soaps or depleted through the use of antibiotics
Loss of lactic acid-producing bacteria can allow the pH of the reproductive tract to drift towards neutral (pH of 7) which can allow pathogenic yeast such as Candida albicans to grow
If Candida albicans grows rapidly it can lead to the common fungal infection called thrush
Cellular Defences - Leukocyte populations
Leukocytes (white blood cells) are probably the most famous element of the immune system and circulate through the major tissues and organs patrolling for infection
Leukocyte are broadly divided into 2 populations
Granulocytes
Agranulocytes
Granulocytes
cytoplasm is rich in prominent granules.
Agranulocytes
These have fewer granules in their cytoplasm.
three major granulocytes
Neutrophils, Basophils and Eosinophils
two major types of agranulocyte
Monocytes and Lymphocytes
Neutrophils
most common leukocyte; account for 50-70% of the total leukocyte population
easily recognisable by their prominent multilobed nucleus
Neutrophils can trap pathogens in the blood or move out of the blood vessels into sites of infection
Neutrophils trap foreign material by phagocytosis (cell eating), in the tissues phagocytosis of pathogen by neutrophils and other phagocytes can result in the formation of pus
Basophils
rarest leukocyte; typically forming around 1% of the total leukocyte population
Basophils produce histamine which is one of the major mediators of inflammation
Basophils produce heparin; a natural anticoagulant which helps prevent the blood from clotting
Basophils circulate in the blood
Eosinophils
account for 2-4% of the total leukocyte population
play a key role in parasite destruction releasing enzymes onto the integument (skin) of the parasite to initiate killing
important in protecting against worm infestations such as thread worms and tape worms
Monocytes
recognisable by their crescent or kidney shaped nuclei
form between 2-8% of the total leukocyte population
circulate in blood for around 1-3 days before leaving the blood vessels and entering the solid organs and tissues
Once inside the tissues, monocytes mature into much larger cells called macrophages which wander through the interstitial spaces patrolling for infection
Monocytes and wandering macrophages
actively phagocytic and enter wound/infection sites to remove potential pathogens.
much larger cells than neutrophils,
can each trap large numbers of pathogen and contribute to pus formation at wound sites
Lymphocytes
agranular leukocytes accounting for around 20-30% of the total leukocyte population
found within the lymphatic system where they reside predominantly within the lymph nodes
produce antibodies which form a key element of specific immune responses.
large nucleus - occupies a large proportion of the cells interior with just a thin rim of cytoplasm usually present between the nucleus and the plasma membrane
Antibodies are Y-shaped molecules which bind to foreign material labelling it and marking it out for destruction by the immune system
Inflammation
a normal response to irritation, infection or injury
5 cardinal signs of inflammation
Redness Swelling heat pain Loss of function
cellular and chemical nature of inflammation and role of the inflammatory response
An inflammatory response is triggered whenever body tissues are injured
The major purpose of inflammation is to limit the spread of infection and prevent pathogens being disseminated outside the inflammatory site
Inflammation also ensures efficient removal and disposal of pathogenic material from the inflammatory site together with any damaged human tissue
Mast cells
key trigger cells in the inflammatory response; these cells synthesise and store histamine in the form of dark granules
When a tissue is injured mast cells degranulate releasing their histamine which initiates the inflammatory response
Limiting the spread of infection
cut to skin - potential pathogens will almost certainly be introduced
If bacteria are introduced at the wound site; they are now in an environment that is warm, rich in oxygen and dissolved nutrients and can begin to divide rapidly
resident mast cells degranulate and release histamine
