Introduction to Immunity

Question 1

Functions of the lymphatic system

Answer 1

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

Question 2

three major functions of lymphatic system

Answer 2

Tissue drainage

Fat transport

Trapping of foreign material

Question 3

Layers of the immune system

Answer 3

The immune system is in a continual battle with environmental pathogens including bacteria, viruses, fungi and parasites

Question 4

4 layers of protection of the immune system

Answer 4

Mechanical defences
Chemical defences
Cellular defences
Inflammatory response

Question 5

Mechanical Defences - The skin

Answer 5

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

Question 6

Mechanical Defences - Mucous membranes

Answer 6

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

Question 7

Mechanical Defences - The mucociliary escalator

Answer 7

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

Question 8

Chemical Defences - Hydrochloric acid

Answer 8

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

Question 9

Chemical Defences - Lysozyme

Answer 9

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

Question 10

Chemical Defences - Lactobacillus and the Female Reproductive Tract

Answer 10

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

Question 11

Chemical Defences - Dysbiosis in the Female Reproductive Tract

Answer 11

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

Question 12

Cellular Defences - Leukocyte populations

Answer 12

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

Question 13

Leukocyte are broadly divided into 2 populations

Answer 13

Granulocytes

Agranulocytes

Question 14

Granulocytes

Answer 14

cytoplasm is rich in prominent granules.

Question 15

Agranulocytes

Answer 15

These have fewer granules in their cytoplasm.

Question 16

three major granulocytes

Answer 16

Neutrophils, Basophils and Eosinophils

Question 17

two major types of agranulocyte

Answer 17

Monocytes and Lymphocytes

Question 18

Neutrophils

Answer 18

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

Question 19

Basophils

Answer 19

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

Question 20

Eosinophils

Answer 20

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

Question 21

Monocytes

Answer 21

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

Question 22

Monocytes and wandering macrophages

Answer 22

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

Question 23

Lymphocytes

Answer 23

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

Question 24

Inflammation

Answer 24

a normal response to irritation, infection or injury

Question 25

5 cardinal signs of inflammation

Answer 25

Redness
Swelling
heat
pain
Loss of function

Question 26

cellular and chemical nature of inflammation and role of the inflammatory response

Answer 26

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

Question 27

Mast cells

Answer 27

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

Question 28

Limiting the spread of infection

Answer 28

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