Topic 6.3Defence against infectious disease

Topic 6: Human Health and Physiology

A pathogen in an organism or virus that causes disease.

Some diseases are caused by genetic defects, others by environmental stresses – not all

diseases are infections.

What is a pathogen?

Patho = disease Gen = Producer A pathogen is an organism or virus

that causes a disease. Why aren’t viruses called

organisms?? Organisms are living things. What

are the characteristics of living things?

Characteristics of living things

Properties of life Cellular Respiration Reproduction Metabolism Homeostasis Heredity Responsiveness Growth and development

Viruses infecting living cells

Viruses are not living organisms

Viruses do not Grow Have homeostasis Metabolize

Viruses do Infect cells and use the cell to make

more viruses Cause disease in many organisms

Viruses

Viruses are micro organisms consisting of a strand of DNA or RNA surrounded by a protein coat

They enter cells and hijack the cells machinery to make more viruses.

They then burst out of the host cell, destroying or damaging it.

Other pathogens

Bacteria Fungi Protozoa Animals Prions

Flip over to I-biology ppt

Antibiotics

Major medical improvement Produced by fungi and bacteria Work on bacteria but… Cannot be used on viruses

antibiotics block specific metabolic pathways found in bacteria, but not eukaryotic cells

because viruses reproduce using the host cell (eukaryotic) metabolic pathways, they are unaffected by antibiotics

antibiotics have produced great benefits world-wide in the control of bacterial diseases

Staphylococcus infections controlled STD's, such as gonorrhea and syphilis controlled

antibiotic resistance has evolved in bacterial populations

In what form can pathogens enter the body?

6.3.3 Outline the role of skin and mucous membranes in defence against pathogens

Skin

Unbroken skin provides a fantastic barrier against pathogens trying to enter the body

Sebum (oil) waterproofing You do not need to

learn the parts of this diagram.

Mucous Membranes (and other non-specific immunity)

Lungs – Mucous membranes and cilia

Stomach – Acid

Urethra – mucus membranes + urine is sterile

Eyes – tears contain lysozymes

Vagina – mucous membranes and acid

Anus – mucous membranes

Anywhere on the body that is not protected by skin has its own method of protection.

Infection!

This occurs if pathogens do get inside the body.

The proteins on the surface of a pathogen are immediately recognised as “foreign”.

Phagocytes (a type of leucocytes) will ingest the pathogen by phagocytosis.

Phagocytosis

Phagocytes

Phagocytes are found in the blood and in body tissues such as the lungs.

After phagocytes engulf pathogens, they destroy them with digestive enzymes found in lysosomes.

Phagocytosis

damage to tissues allows invasion across 1st line of defense microbes successfully invade body fluids or tissues damaged cells release histamine and other chemicals

initiating inflammation

phagocytes attracted to site by chemotaxis toward histamine phagocytes recognize microbes as foreign by antigen

recognition variety of phagocytic cells: neutrophils (small phagocytic

& macrophages (large phagocytic)

phagocytes endocytotically engulf microbes,which are digested by enzymes held in lysosomes digested microbe fragments are displayed on cell

membrane phagocytes with microbe fragments displayed =

antigen-presenting cells

antigens and antibodies

antigen: a molecule recognized as foreign by the immune system; it elicits an immune response; usually a foreign protien

antibody: =immunoglobulin a globular glycoprotein recognizes an antigen by its complementary shape and charge thus allowing it to attach to the antigen specifically marking it for attack by the immune system

Antibodies Also known as immunoglobulins Globular glycoproteins The heavy and light chains are

polypeptides The chains are held together by

disulphide bridges Each antiboby has 2 identical antigen

binding sites – variable regions. The order of amino acids in the variable

region determines the shape of the binding site

How Antibodies work? Some act as labels to identify

antigens for phagocytes Some work as antitoxins i.e. they block

toxins for e.g. those causing diphtheria and tetanus

Some attach to bacterial flagella making them less active and easier for phagocytes to engulf

Some cause agglutination (clumping together) of bacteria making them less likely to spread

Type Number of ag binding sites

Site of action Functions

IgG 2 BloodTissue fluidCAN CROSS PLACENTA

Increase macrophage activityAntitoxinsAgglutination

IgM 10 BloodTissue fluid

Agglutination

IgA 2 or 4 Secretions (saliva, tears, small intestine, vaginal, prostate, nasal, breast milk)

Stop bacteria adhering to host cellsPrevents bacteria forming colonies on mucous membranes

IgE 2 Tissues Activate mast cells HISTAMINEWorm response

Lymphocyte with antigens

http://student.ccbcmd.edu/courses/bio141/lecguide

Blood types

Where do antibodies come from?= Lymphocytes

Produce antibodies B-cells mature in bone marrow then

concentrate in lymph nodes and spleen

T-cells mature in thymus B and T cells mature then circulate in

the blood and lymph Circulation ensures they come into

contact with pathogens and each other

White Blood cellsWBC (Lymphocytes) are made in the bone marrow.

The cells divide and mature into 2 types:

T Lymphocytes B Lymphocytes

Develop in the thymus gland Develop in the bone marrow lymph nodes

Plasma ɞ cells have a different shape receptor on its membrane. There are about 10 million kinds in your body at any one time! Each can detect any antigen of a pathogen. Once activated they divide very fast (clone) and start to secrete specific antibodies. Antibodies slowly removed from blood and lymph. Memory ɞ cells remember antigens and can turn into Plasma ɞ if re-infected.

The Humoral (Antibody) ResponseThe Cell-Mediated Resopnse

Foreign, mutant or infected cells are identified as ‘non-self’ by surface antigens.T helper cell recognises antigens andalerts the other T cells.Killer (Cytotoxic) cells attack with perforinor nitric oxide. T memory cells rememberthe antigen for a later attack.T suppressor cells switch off T and B cellsafter attack over.

HIV

HIV is a virus that specifically attacks the T lymphocytes.

This means the number of lymphocytes decreases.

Less antibodies are made. Predict the consequences…

http://www.sumanasinc.com/webcontent/animations/content/hiv.html

http://www.avert.org/

http://www.un.org/ecosocdev/geninfo