First line of defence
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Expected Learning: To develop a comprehensive understanding of the first line of defence in the immune system. First Line of Defence. By Eden Aspinall and Theresa Hudson. Physical Barriers: Animals. Integumentary system (skin) is the main barrier, preventing pathogens from entering

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First Line of Defence

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First line of defence

  • Expected Learning:

  • To develop a comprehensive understanding of the first line of defence in the immune system.

First Line of Defence

By Eden Aspinall and Theresa Hudson

Physical barriers animals

Physical Barriers: Animals

  • Integumentary system (skin) is the main barrier, preventing pathogens from entering

  • Like a blockade?

  • Mucosal (mucus) membranes inhibits bacteria

  • Natural agents like sweat are secreted to eradicate bacteria

  • The body grows bacteria to provide a natural competitor for other bacteria.


First line of defence

Skin as

a Barrier

First line of defence

Joharn‘s yucky ear!


First line of defence

Natural Agents as a Barrier

Chemical barriers animals

Chemical Barriers: Animals

  • Certain white blood cells destroy invading microorganisms.

  • Sweat and fatty acids have properties that repel pathogens

  • The immune system produces substances and agents that are designed to attack the invading microorganisms.

  • Enzymes like lysozyme, found in tears and saliva ‘lyse’ or burst pathogenic substances

First line of defence

White Blood Cells as

a Barrier

First line of defence

Immune System as a Barrier

What about plants

What about plants?

  • What!? They have no immune system!?

    They actually don’t!!

    Many plants are resistant to pathogens and have several characteristics that protect them from infection from things such as insects and nematode worms.

Physical barriers plants

Physical Barriers: Plants

  • External covering of plants works like skin while repelling bacteria.

  • Plants have physical responses to prevent infection spreading such as ‘galls’

  • Galls, like scabs, form a sort of ‘cork’ when a plant is infected

  • These stop the parasite or infection from spreading throughout the plant.

  • Often, the stomata is a common ‘entry point’.

  • Thorns are another type of defence

Chemical barriers plants

Chemical Barriers: Plants

  • Produce chemicals that act as antibiotics.

  • Some leaves have high silicon content to prevent harmful pathogens.

  • Some trees produce oils or gum to repel or reduce infection

  • Resins, Tannins and Phenolic substances also help repel malevolent substances.

  • ‘The tale of the Ouchie Mouth’

First line of defence

Chemicals as a Barrier

Internal organs and tissue in the immune system

Internal Organs and Tissue in the Immune System

  • Bone marrow – Stem cells differentiate into a range of different cell types before leaving the bone marrow, mainly T cells and B cells

  • Thymus – T cells go through thymic selection and circulate in the bloodstream after maturing.

  • Spleen – B cells travel from the bone marrow into the spleen and mature.

More organs and tissues in the immune system

More Organs and Tissues in the Immune System

  • Lymph Vessels and Nodes

  • Other Lymphoid Tissue

  • ^Ears, eyes, gut etc.

Self and non self

Self and Non-Self

  • Materials made by the body’s own cells is called self.

  • Foreign material is called non-self.

  • When invaded by non-self material, the immune system is activated.

  • Self can be: blood cells, plasma, reproductive cells, etc.

  • Non-self can be: Toxins, dirt, bacteria, pollen etc.

Major histocompatibility complex

Major Histocompatibility Complex

  • MHC: A cluster of genes that encode information for the production of marker proteins on the surface of cells.

  • Two types of ‘markers’ in our bodies:Class 1 markers: Found on every cell except red blood cells. Class 2 markers: Found on Macrophages B and T cells.

How do they tell the difference

How do they tell the difference?

  • T and B cells recognise similar markers on other cells and ignore them, as they are not a threat

  • They respond to the foreign MHC markers on ‘invaders’.

  • Like if you saw someone in the enemy’s uniform sneaking around your camp

  • When they come into contact with foreign, or non-self material, they



  • Any foreign substance that causes the immune system to create antibodies against it

  • These activate the production of ‘antibodies’

  • ‘Self-antigens’ can also be found in immune cells. These are like ‘markers’

Homework reflection

Homework & Reflection

  • Reflection

    • Answer the multiple choice questions on the following slide.

  • Homework

    • Quick check pg. 250, questions 1 - 3

Reflection multiple choice

Reflection: Multiple Choice

  • Question 13

  • First-line defences that mammals have against invasion by disease-causing bacteria include

  • A. lysozymes.

  • B. interferons.

  • C. antibodies.

  • D. killer T cells.

Reflection cont d

Reflection cont’d

  • Question 19

  • First-line defence mechanisms in humans include

  • A. development of fever.

  • B. action of phagocytes.

  • C. use of antibiotics.

  • D. presence of cilia.

Reflection cont d1

Reflection cont’d

  • Question 8

  • Evidence that a vascular plant has an infectious disease includes the

  • A. drying out of root hairs during drought.

  • B. yellowing of leaves due to deficiency of iron.

  • C. presence of spores on fungal hyphae growing out of stomata.

  • D. presence of nitrogen fixing bacteria in the root nodules of legume plants.

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