UK GCSE level age ~14-16, ~US grades 9-10 Biology revision notes re-edit 16/05/2023 [SEARCH]

 Body defences: 1. Cleanliness, dangers of 'unclean' situations and types of pathogens

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INDEX of biology notes on the body's defence mechanisms against infections from pathogens

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(1) Cleanliness and pathogens

(1a) Starting with a historic note on cleanliness

Be aware that our bodies provide a good environment for many microbes to live and multiply at our expense and can make us ill once they are inside our body.

Our bodies need to be capable of stopping most microbes from getting in and dealing with any microbes which do get in.

A simple example of how science works - cleanliness reduces the incidence of infection!

Appreciate the contribution of Semmelweiss in controlling the rate of patient infection to solving modern problems with the spread of infection in hospitals.

Semmelweis worked in Vienna General Hospital in the 1840s and witnessed large numbers of women dying after childbirth from a puerperal fever disease.

He thought that the staff of the hospital were spreading the disease via unwashed hands.

After instructing doctors and nurses to wash their hands in an antiseptic solution, the mortality rate was considerably reduced.

Although Semmelweis didn't realise it at the time, the antiseptic solution was killing the infecting bacteria.

Apparently, when he left the Vienna hospital, the practice of washing hands in the antiseptic solution was relaxed, and the death rates rose again!

With the advent of new strain of bacteria today, there is now an even greater need for emphasis on hospital hygiene than ever before - so, if on a hospital visit, PLEASE WASH YOUR HANDS in the antiseptic gel provided.

(1b) What types of dangers are there? Types of pathogens

Reminders

Communicable/transmissible diseases are those in which the pathogen is passed from one host to another.

A non-communicable/non-transmissible disease cannot be passed from one host to another.

Microorganisms or microbes that cause infectious disease are called pathogens.

These pathogens can only be seen under a microscope and fine details of their structure might only be seen using a powerful electron microscope.

Bacteria, viruses and fungi can be harmless or harmful

They are very beneficial e.g. in our gut, or they

may reproduce rapidly inside the body and may produce poisons (toxins) that make us feel ill.

(i) What is a bacteria?

Bacteria and certain protozoa are very small cells which can rapidly reproduce by cell division in your body making you feel ill by damaging your body's cells and producing toxins - poisons produced as a by-product of the bacteria's cell chemistry.

They can be seen under a light microscope.

Diseases such as tuberculosis, whooping cough and cholera.

(ii) What is a virus?

Viruses are NOT cells and much smaller than bacteria, but damage the cells in which they reproduce. Viruses replicate by invading a cell and using the cell's genetic machinery to reproduce themselves ie copies of the original virus.

The virus 'invaded' cell then bursts releasing lots of new viruses which go on to invade more healthy cells. The cell damage makes you feel ill as your body (temporarily) fights back to make as many good cells as it can to replace those destroyed by the virus.

The structure of viruses can only be studied using the power of an electron microscope.

Diseases such as flue, HIV, meningitis, pneumonia and herpes are caused by viral infections.

(iii) Fungi

Fungi can also be pathogens and includes microorganisms like yeasts and moulds (so don't eat mouldy food!).

Athletes foot and ringworm are caused by a fungus.

How do our bodies defences work to counteract pathogens?

The body has two different types of barriers to protect itself against pathogens - bacterium, virus or fungus.

Our body has physical and chemical adaptations for protecting itself against pathogens.

You may well ask, where do the pathogens come from?

They are all around us, but hopefully in very low concentration!

They can be in the air, water or in soil.

Pathogens can enter the body through an accidental cut or graze of the skin.

Bacteria and fungi can be in contaminated food and so ingested.

Bacteria and viruses, unfortunately, are readily transmitted by humans!

When we cough or sneeze we spray into the air thousands of tiny moisture droplets, which may contain pathogens like bacteria or viruses, which we inadvertently breathe in. That is why, if at all possible, you should take care to cough or sneeze into a tissue and dispose of it carefully in a bin.

Microbes will try to enter through any openings in the body.


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