IB MYP Biology factors affecting human health Study Notes

IB myp 4-5 Biology – Notes- All Topics

Topic :Cells-Tissues

Topic :Cells– Weightage : 21 % 

All Questions for Topic : Tissues,Organs,System,Structure and Function,Life processes,Factors affecting human health,Vaccination

Topic :Interaction between organism-Pathogens/Parasites,Predator/Prey

Topic :Interaction between organism– Weightage : 21 % 

All Questions for Topic : Pathogens/Parasites,Preadator/Prey,Food chains and webs,Competition,Speciation and Extinction

Concepts of Health and Illness

According to the World Health Organization (WHO), a healthy life is not just a life without disease. A healthy life presents a complete sense of well-being including physical, mental and social well-being.

The physical, mental and social states of a person are in continuous interaction. Therefore, a change or alteration in any of the three could cause an imbalance leading to disease.

Four main factors should be considered when talking about being healthy and free of diseases.

  • a) A healthy environment, that is to say, an environment for example, without pollution, noise, dangerous animals and violence.
  • b) Healthy habits and life style.
  • c) Hereditary factors and age.
  • d) A Health system that can help prevent the appearance of illness.

What is an illness?

When a part of our body is altered and cannot carry out its functions normally, we say that we are ill. An ill person will show a series of symptoms of the disease. These symptoms are subjective and only the patient perceives them. Some include feeling dizzy, tired or in pain. Signs, on the other hand are more objective and can be seen/measured by others, such as: fever, vomiting, swollen areas, sudden rises or drops of blood pressure, abnormal parameters in blood tests or electrocardiograms etc.

There are many different diseases. Some are physical diseases, others are mental and others social. We must classify diseases into different groups in order to study them. There are different criteria we could use for disease classification; however, we will focus on two: the cause or agent which provokes the disease, and by how often we suffer the illness:

Classification of illnesses

There are two basic types of diseases: Infectious and non-infectious. 

Infectious diseases are those caused by other living organisms, which are called pathogens (or pathogenic organisms), usually micro-organisms such as bacteria or viruses. An infectious disease is passed on from one individual to another. For example AIDS, or the flu.

Non-infectious diseases may have a number of causes, but are not caused by a pathogen. A non-infectious disease is not passed on from one individual to another. For example, cancer or depression.

Classification of diseases by how often we suffer them:

Some diseases are acute, meaning that they happen in a limited time span, such as the flu. However, others are chronic, developing slowly and often lasting for the rest of someone’s life, such as arthritis. 

Sporadic diseases, which happen occasionally. E.g. Heart attack, blood clot (thrombus or stroke), etc. 

Endemic diseases being those that only affect a particular area. E.g. malaria, in tropical regions.

 when large numbers of people suffer it in a short period of time. E.g. The flu at certain times of the year. If an epidemic spreads throughout many countries or even world-wide, it is called a pandemic (E.g. AIDS).

Timeline of New and Emerging Infectious diseases 
Infectious diseases

Infectious diseases (Some background of interest: Heterotrophic organisms can be: symbiotic – if they live in association with another organism; saprophytes (or saprotrophs) – if they feed on dead organic matter in decomposition; and parasites – they live on the body of a host and cause it some harm).

As mentioned above infectious diseases are caused by a living organism (pathogen), usually a micro-organism, or by a substance (a toxin) released by it. Remember, that not all bacteria are pathogenic. Bacteria are unicellular prokaryotic organisms. Most of them are saprophytes or symbiotic organisms, and only a few species are parasitic, causing diseases. 
There are even some bacteria which are beneficial to humans, such as those found in our digestive track, which help with the formation of faeces and the production of vitamins.

Types of pathogenic micro-organisms

* Some bacteria cause diseases (as most of them are saprophytes or symbiotic organisms, and only a few species are parasitic). Some diseases caused by bacteria are: pneumonia, tuberculosis, salmonella, tetanus, cholera and diphtheria.

* Some protozoans (unicellular organisms) such as PlasmodiumPlasmodium, which causes malaria, or Trypanosoma which causes sleeping sickness.

* Fungi. Can be unicellular or multicellular organisms, and the illnesses caused by fungi are called mycosis. E.g. .Athlete’s foot, candidiasis (oral or genital thrush), seborrhoeic dermatitis.

* Viruses: Diseases caused by a virus are called virosis. Viruses are not considered ‘alive’ as they are not made of cells, and they cannot survive and reproduce outside the cells of their host. A typical virus has genetic material and a protein coat, and sometimes there is a lipid layer that envelopes the protein coat. They do not have any cellular structure. All viruses are pathogens, being responsible for many of the most serious human diseases. Some important viral diseases are: the flu, measles, AIDS, and rubella.

How are infectious diseases passed on from one individual to another?

Infectious diseases are contagious as the micro-organisms that provokes them are passed on from one individual to another. There are six different ways by which infectious diseases can be transmitted:

Direct contact. Such as sexual transmitted diseases (STD’s) e.g. syphilis.
Objects. Such as a handkerchief, a glass, saliva etc. e.g. tetanus
Water. Such as cholera.
Contaminated foods. Such as salmonella.
Air. Such as the flu.

Transmission vectors, which are animals that do not have the disease but transmit it, by introducing in a healthy individual of another species the micro-organism that causes the disease. E.g. Malaria is transmitted by the mosquito Anopheles, which carries the parasite Plasmodium. Also sleeping sickness, caused by the parasite Trypanosoma, which is transmitted by the tsetse fly.

Preventing infectious illnesses

Infectious illnesses can present a big risk to our health. That is why is important to try to prevent them by having a healthy lifestyle and making sure that we get vaccinated against certain diseases.

  • Having a healthy lifestyle would include having a good hygiene, following a healthy diet, avoiding any drug use, including medication that is not prescribed by a doctor, getting enough rest, having regular medical check ups, etc. All these habits will boost your immune system and keep it in good shape. 
  • Vaccination consists of introducing dead, weakened or partially weakened microbes into a healthy organism so the healthy organism will produce antibodies against them. If a person gets in contact with these microbes again the organism will ‘remember’ (acquired immunity) them and produce specific defences fairly quickly which will stop the infection from happening.  
How to cure infectious illnesses

The most important treatments include: 

Serum therapy or serotherapy Based on the injection of antitoxins or serum containing specific antibodies which have been produced by another person or animal to an ill patient who may need them quickly, for example in the case of having tetanus or rabies.  

Drug therapy: Based on the administration of chemical substances or medicines. These are drugs that act against microbes. The most important of those are antibiotics. 

Antibiotics are antimicrobial substances produced naturally or artificially which is only active against bacteria and some type of fungi. They should never be taken for a viral infection. It is also important to remember that you should not take them unless it’s necessary and prescribed by a doctor as bacteria become resistant to them, which makes them less effective or even useless. It is also important to follow the doctor’s prescription properly in terms of (with regard to) dosage and duration of the treatment in order to avoid increasing the resistance of bacteria to them.

Non-infectious diseases

Diseases that originate by other causes that are not micro-organisms. These diseases usually have more than one cause, ranging from the environment to the person´s genes and lifestyle. The most important are:

* Diseases that affect the normal functioning of systems or apparatus, such as coronary heart diseases or respiratory diseases.

*Traumatic diseases, such as sport injuries, or domestic, traffic or work accidents.

* Endocrine and metabolic diseases: these are caused by excessive or deficient secretion of a hormone or by malfunctions in the metabolic reactions within the body’s cells. Examples include some forms of obesity and diabetes.

* Deficiency diseases: a poor diet may deprive the body of some essential substances; such as anaemia (iron deficiency) or goitre (iodine deficiency).

* Psychological / mental disorders changes in the working of the brain may lead to abnormal behavior, such as. Schizophrenia, depression, anorexia and bulimia.

* Genetic diseases  which are present at birth and are caused, at least in part, by a genetic disorder (the affected person’s genes), e.g. certain types of blindness. Those diseases caused by a genetic defect that a person inherits from their parents are called hereditary diseases. Some of this type of diseases can be limited or prevented by adopting certain healthy habits.

* Cancer: It is a type of disease where a group of cells show uncontrolled and rapid division, invading and destructing other tissues, and sometimes metastasise (spread to other locations in the body via lymph or blood).giving rise to a mass of abnormal cells known as a tumour, that invade and kill other cells.

There are 2 types of tumours:

  • Benign tumours:  which are self-limited, and do not invade or metastasise.
  • Malignant tumour or cancer:  when the cells divide with no limit and extend to other organs (metastasis).

To prevent cancer, here is some advice for you to take:

-Have healthy life habits.
 -When you reach a certain age, ensure you have regular medical

How to prevent non-infectious illnesses.

How to prevent no infectious illnesses
As with infectious diseases having a healthy lifestyle will help you prevent  non-infectious diseases. Some of these are stated below:

* Do not smoke. Do not do drugs (alcohol is a drug).

* Avoid excessive sun exposure without protection.

* Have a healthy diet. 

* Have regular medical check-ups after you reach middle age.

* Regular exercise.

* Get enough rest. Avoid too much stress.

* Always follow safety instructions. 

*Avoid polluted environments.

The body’s defence against disease

The body’s defence against disease: our immune system.

As we come in contact with pathogenic micro-organisms,sporadically, they don’t always enter our body and/ or develop into an illness. We have an immune system that helps us fight diseases. There are two main types of defences against disease:

* External or passive: Avoiding the entrance of the pathogen inside the organism.

Physical barriers, such as the skin or mucus secreting cells.

Biochemical barriers, such as the enzymes in our tears, or the acid in our stomach.

Ecological barriers, such as the intestinal flora.

Mechanical barriers, such as mucus.
* Internal or active: organisms or pathogens that have crossed the external defences and are inside the body are removed or destroyed by white blood cells, which form part of the immune system. These potential pathogens have particles on their surface called antigens, and these are recognised and destroyed by phagocytes (unspecific immune response) and by antibodies (specific immune response).

In unspecific response, phagocytes (type of white blood cells) engulf and destroy the pathogen with digestive enzymes. There are many phagocytes present in areas of the body likely to suffer infection. E.g. the exposed surfaces of the lungs.

In specific response B-lymphocytes (type of white blood cells) produce specific antibodies, protective proteins specific to one antigen. These antibodies are able to recognise the antigens found on the surface of pathogens, bind to them and facilitate their destruction by other cells.

Addictive substances

Tobacco, alcohol and other drugs can not only be addictive, but very harmful for our systems putting our life at risk. As mentioned before, many drugs are used as medicine and need to be used as prescribed by doctors to avoid any problems. However, there are also drugs that people consume just to feel good, which can damage physical and mental health and are often illegal. Some of these include: tobacco, alcohol, THC( cannabis), cocaine, amphetamines and hallucinogenic substances among others.

The effects of drugs

The drugs that people use to feel good act on the central nervous system, and usually create tolerance and addiction.

When a person uses a drug often, their body gradually develops resistance to the action of the drug and adapts to it; this is called tolerance. As a person develops tolerance to a particular drug, he/she will need to increase the dosage of the drug in order to obtain the same effect.

Also, as a person uses a drug over and over, his/her body may require the drug in order to function properly, this is known as addiction to the drug. The lack of this drug causes disorders and serious symptoms. When a person is addicted to a drug, taking the drug becomes a life priority. Drug addiction has two components:

*  Physical dependence: A lack of drugs affects the functions of certain organs. The effects include vomiting, shaking, intense sweating, diarrhoea, aches and pains, etc. These symptoms are referred to as abstinence syndrome or craving. (craving: very strong desire for something).

*  Psychological dependence: Drugs change the way the brain works and give users a sense of pleasure and well-being that ends as soon as they stop using them. When a drug addict is not taking the drug he/she feels uneasy anxious and dissatisfied.

The consequences of drug use

Short term health consequences: These are mainly related to the intoxication produced by the presence of high levels of the drug in the body. The effects will vary according to the type of drug and dosage ranging from drunkenness, convulsions, high blood pressure, abnormally high heart rate, even coma or death. Drug users are also at higher risk of suffering accidents, as their perception of reality is altered.

Medium and long term consequences: Most drugs damage the nervous system and cause some type of dementia, psychosis and/or behavioural disorders. In many cases, they also cause damage to the liver, and the respiratory and circulatory systems. When the drug is injected, the risk of transmitting infectious diseases such as HIV or hepatitis B also increases.

Social consequences: Drug addiction causes many social problems to drug addicts, as they gradually lose interest in their studies, work, friends and family, becoming a pest to society.  It as well causes problems to society, as they may do whatever is necessary to obtain the drug (often expensive)

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