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Higher Human Biology
Unit 4
Immunology & Public Health
KEY AREA 1: Non-specific Defences
Higher Human Biology
We are going to build on the knowledge and skills that you developed during N5 and will
learn about the following Immunology & Public Health key areas : -
Key Area 1 – Non-specific Defences
Key Area 2 – Specific Cellular Defences
Key Area 3 – Transmission and Control of Infectious Diseases
Key Area 4 – Active Immunisation and Vaccination and the Evasion of Specific
Immune Responses by Pathogens
Physiology & Health Learning Intentions
KEY AREA 1 – Non specific Immune Response
a)Physical and Chemical Defences
b)Inflammatory Response
c)Phagocytes and Apoptosis by Natural Killer Cells
1a) Immune System Introduction
Pathogens are organisms that cause disease
The human body defends itself against pathogens, toxins (produced by living things) and cancer cells
through the immune system
Immunity is the ability of the body to resist infection by a pathogen or destroy the organism if it
succeeds in invading and infecting the body
First line of defence (Non-specific)
-Example 1: Skin to act as a physical barrier to pathogens
-Example 2: Secretion of stomach acids to kill microbes
-Example 3: Secretion of mucus by the trachea to trap microbes
Second line of defence (Non-specific)
-Example 1: Cellular Response: Phagocytosis
-Example 2: Cellular Response: Natural Killer Cells
Third line of defence (Specific)
-Example 1: Response by T-Lymphocytes from the Thymus Gland
-Example 2: Production of antibodies by B-lymphocytes from Bone Marrow
1b) Physical and Chemical Defences
The surface of the skin is composed of layers of closely packed epithelial cells which offer
physical protection against bacteria and viruses
Mucous membranes that line the digestive and respiratory tracts are also composed
of epithelial cells that form a protective physical barrier
Secretions from skin provide chemical defence against invasion:-
-Example 1: Sweat glands and sebaceous glands in the skin keep the skin at a pH that is too low for
most microbes to survive
-Example 2: Tears and saliva contain the enzyme Lysozyme which digests the cell walls of bacteria and
destroys them
-Example 3: Mucous membranes secrete sticky mucus which traps microbes
-Example 4: The epithelial lining of the stomach secretes acid which destroys microbes
1c) Inflammatory Response
When the body suffers a
physical injury such as a cut
and/or invasion by microbes, it
responds by a localised
defence mechanism called an
inflammatory response at the
affected site
1d) Inflammatory Response: Mast Cells & Histamine
Mast cells:- are produced from the same stem cells as white blood cells
- they are present in connective tissue throughout the body
- they release histamine
Histamine is a chemical that causes blood vessels to vasodilate (become
wider) and capillaries to become more permeable
After injury, mast cells are activated and release large quantities of
histamine resulting in blood vessels in the injured area undergoing
vasodilation and capillaries becoming more permeable
The additional blood supply makes the injured area red and inflamed, and it
swells up due to the stretched capillary walls becoming more permeable which
causes them to leak fluid into neighbouring tissues
1e) Cytokines
Cytokines are cell-signalling protein molecules secreted by many types of cell
including white blood cells that arrive at the site of injury/infection
During the inflammatory response, increased blood flow and permeability of
capillary walls bring about the following beneficial effects:-An accumulation of phagocytes to the damaged tissue as they are attracted by
cytokines. (Phagocytes engulf pathogens by Phagocytosis)
-Speedy delivery of antimicrobial proteins to the infected site (these proteins
amplify the immune response)
-Rapid delivery of blood-clotting chemicals (clotting elements) to the injured
area (Coagulation of blood stops the loss of blood, prevents further infection
and marks the start of the tissue repair process)
1f) Non-specific Response: Phagocytosis
1. Phagocyte detects surface antigen molecules present on
a pathogen(as being ‘foreign’ or non-self), and move
towards it.
2. Phagocyte engulfs the pathogen (bacterium) by infolding
of the cell membrane to create a vacuole.
3. Lysosomes, are cell organelles which contain digestive
enzymes, present in the phagocyte’s cytoplasm fuse with
the vacuole and release enzymes to digest the ‘foreign’
pathogen
4. The breakdown products are adsorbed by the phagocyte
5. Once the pathogen is digested the Phagocyte releases
cytokines which attract more phagocytes to the infected
area to continue the battle against the pathogens
6. Dead bacteria and phagocytes accumulate at the
infected site as a pus
1g) Apoptosis by Natural Killer (NK) Cells
1. NK Cells attack virus-infected cells and cancer cells in general
2. NK Cells releases molecules of a protein which forms pores in the target
cell’s membrane
3. The pores allow a “signal” molecule from the NK cell to enter the target cell
and trigger a genetically controlled series of events
4. The target cell then switches on a “suicide” gene, and “suicide” proteins are
released
5. “Suicide” proteins function as self-destructive (degradative enzymes) which
break down the cell’s DNA and vital proteins into useless fragments, causing
the cell to shrink and die
6. This process of programmed cell death is called apoptosis
After contact with a pathogen, Phagocytes and NK Cells release cytokines
which circulate in the bloodstream and stimulate the specific immune
response by activating lymphocytes
1h) Apoptosis by Natural Killer (NK) Cells
Physiology & Health Questions
KEY AREA 1 – Non specific Immune Response
1.Testing Your Knowledge 1 Page 311
2. Quick Quiz
Q’s 1 - 4