Lesson 24: Human Health and Disease (3

Lesson 24: Human Health and Disease (3.4.3)

PATHOGENS AND HUMAN HEALTH

The human body is truly an amazing machine. Normally the body functions perfectly without any problems and adapts to great variety of situation. The human body even has the ability to repair itself after injury and fight off attacking microorganisms. If this does not seem amazing, consider the fact that all this happens automatically, with you completely unaware that it is even happening.

Other microorganisms enter the body and attempt to infect the body causing disease. A disease is a condition where an organism experiences impaired function often with detrimental symptoms. A symptom is the response of the body to a disease and often is an indicator used to diagnose the type of disease.

Several factors like genetics, age or nutrition, can lead to diseases in humans. In this chapter we will examine the structure of viruses, mutation of viruses, bacteria and other microorganisms. We will examine how humans contact disease and how the body fights diseases.

PATHOGENS

Microorganisms, or tiny organisms, that cause disease are often called pathogens. A pathogen is a specific microorganism that causes a specific disease. Communicable, or infectious, diseases are diseases that can easily be spread from one person to another through contact or proximity. Communicable disease can be spread through the air, water, soil or animal such as mosquitoes. A pathogen can be a bacteria, virus, fungi or protists. It is important to note that viruses are still considered pathogens even though they are not technically microorganisms.

VIRUSES

A virus is a small particle that contains proteins and hereditary materials (DNA OR RNA), but is not alive. The virus is surrounded by a protein coat, or capsid. A virus particle cannot eat, metabolize food and can only reproduce inside a cell. Outside the cell, a virus particle does nothing and remains inactive. Viruses are cell specific, meaning they can only infect a cell if the capsid of the cell can fit into the receptor site in the host cell membrane. You can think of it like a lock and key, the virus has one of several thousand possible keys that may fit the lock on the surface of the cellular membrane. Figure 24.2 illustrates a virus that infects bacteria known as a bacteriophage virus.

Once the virus attaches to the cell, the protein coat falls away and disintegrates then it releases its hereditary material into the cell. The hereditary material (DNA or RNA) then uses the host cell’s machinery to make more viral particles. The cell takes one of two viral cycles – a lytic or lysogenic pathway.

LYTIC CYCLE

The virus uses its tail fibers to attach to the cell’s outer membrane, insert its genetic material into the host cell then, uses the host genetic material to generate many new viruses in approximately 20 seconds. The particles become very numerous in the cell and breaks out (lyse) then each viral particle infects new cell.

LYSOGENIC CYCLE

The virus inserts its genetic material into the host cell. The virus becomes incorporated into the host cell’s DNA. When the cell divides, it replicates not only its own DNA, but the DNA (or RNA) of the virus particle as well. Some diseases that are caused by a virus are listed table 24.1.

Table 24.1 Some Examples of Diseases Caused by Pathogens

Name of Disease / Symptoms / Causative Agent
Diseases causes by Viruses / Name of Viruses
AIDS / Flu-like at first, fever and opportunistic infections, weight loss / HIV
Influenza / Flu-like symptoms including headaches, body aches, tiredness, and fever
Small pox / Flu-like at first, fever, rash, in the form of pustules, around mouth spreading to entire body. / Variola major
Chicken pox / Fever, itchy open sores forming a rash on the skin. / Varicella zoster
Diseases caused by Bacteria / Type of Bacteria
Strep throat / Painful sore throat, white patches on the back of the throat, and fever / Streptococcus bacilli
Food poisoning / Fever, chills, severe diarrhea, vomiting and stomach cramping / Salmonella
Limes disease / Flu-like symptoms, headaches / rickettsea bacteria (vector -Ticks)
Plague / Fever, muscle aches, stomach pains, vomiting and eventually blood begins to seep into tissues turning them black / Yersinia pestis
Diseases Caused by Protists / Name of protists
Malaria / Fever, Pain in joints / Plasmodium
African Sleeping Sickness / Asymptomatic at first, sleeping / Trypanosoma (vector - tse fly)
Amoeboid dysentery / Severe stomach pain, diarrhea, Vomiting of blood (if serious) / Entamoeba histolytica
Cholera / Profuse watery diarrhea and vomiting / Vibrio cholera
Diseases caused by worms / Type of worms
Elephantiasis / Local inflammation, enlargement and thickening of the skin / Falarial worm (Wuchereria Bancrofti
Round worm disease / Blistering of skin and crippling of limbs / Guinea worms

PROTISTS

Some volunteers that work in undeveloped countries are taught to only drink purified water in the prevention of diseases such as cholera and amoebic dysentery, both caused by protists. Documentations have been made since 1834 on water borne outbreaks in Sweden. Protists are a unique group of often unicellular or colonial organisms. Many animal-like and fungus-like protists can cause human diseases including African sleeping sickness, amoebic dysentery, malaria and yellow fever. Some protists require animal intermediate called a vector to transmit the disease. A mosquito carries the protists that cause both African sleeping sickness and malaria.

PARASITES

A parasite is any organism that benefits by living on or in another organism (host). The parasite usually causes harm to the host. Often the association between a parasite and its host can continue over a long period of time, where the host slowly becomes weakened but does not die. Parasites can be unicellular protists or multicellular invertebrates. Some human parasites include: mites, head lice, tapeworms, round worms, pin worms, Loa loa, liver flukes, ticks, fleas and many more. Parasites are often treated by the administration of specialized drugs, a toxic chemical, designed to kill the offending parasite. Serious infections can cause death.

FUNGI

If you will recall fungi are multicellular, non-photosynthetic organisms that feed by absorbing their food and therefore called saprobes. Fungi cause serious infections and diseases including ergoptyism or St. Anthony’s Fire obtained through poisons released into the grasses or grains that they feed upon. Poisons released by fungi cause other diseases including athlete’s foot, ring worms and yeast infections.

Activity

This activity examines how quickly communicable diseases can spread. Before class began, your teacher spread “germs” (made of glow-in-the-dark powder or crushed white or fluorescent chalk) throughout your classroom. These germs were located on desks, chairs, the floor and other classroom surfaces. Under a black light you can see these “germs” glow. Make some observations about who might become sick after their exposure to these germs. Collect data about possible “sick” students and create a graph showing the results of this experiment.

NOTE: This activity is best conducted near the end of the class period. Be sure to sprinkle more chalk/powder before each new class arrives. Black out windows and draw shades to really see results. Glow-in-the-dark powder and black lights can be purchased online or at a local hobby store.

LUNG CANCER

People with a family history of cancer are at a higher risk for developing it; but they may or may not ever get cancer. Just because a person’s genes put them at a higher risk for developing cancer, does not mean they will get cancer. On the flip side, just because a person’s genes do not put them at a higher risk for developing cancer does not mean this person cannot or will not ever develop cancer. In the case of cancer, genes are only one factor determining cancer. A person’s environment may also play a role. It is difficult to say a person developed cancer simply because of their genes or because of their environment; more than likely it was a combination of the two that lead to cancer. For example, smoking can lead to lung cancer (lung tissue is destroyed by toxic chemicals), even if an individual does not have a family history of lung cancer. A person who smokes inhales many harmful toxic chemicals and carcinogens (chemicals that may cause cancer) with each puff of their cigarette. A person who inhales second hand smoke is at risk of developing lung cancer as well. Someone who is at a higher risk for lung cancer because of family history may never develop it simply because they did not smoke or inhale second hand smoke.

OTHER FACTORS AFFECTING HEALTH

NUTRITION

If an organism is in good health it is more likely to fight off disease and remain healthy. People who make healthy life choices throughout their lives are healthier and often avoid chronic or age related diseases like diabetes, arthritis, cancer or heart disease. Nutrients are substances needed by organisms to carry out life functions. Nutrients include things like carbohydrates, fats, proteins, nucleic acids, vitamins and trace minerals. Table 24.2 summarizes some common nutrients and their sources.

Table 24.2 Vitamins for Optimal Health

Vitamin / Source / Deficiency
Vitamin C / Citrus, tomatoes, cantaloupes / Hair loss, tooth loss & bleeding easily, gum disease - scurvy,
Vitamin D / Milk, soy milk and cereal / Bone loss or thinning of bones, Rickets (curved, bowlegs).
Vitamin A
/ Carrots, corn, and other yellow vegetable / Loss of sight, degenerative eye disease and night vision
Folic Acid / Cereals, grains and pasta / Spina bifida
Calcium / Green leafy vegetables,
broccoli, and dairy products / strong bones and teeth, muscles maintenance, proper heart rate, and blood pressure
Vitamin K / green leafy vegetables, parsley, dairy products, eggs, soy, avocados, kiwi / Blood clotting

IMMUNE RESPONSE

The first line of defense in the immune system is the skin and mucus membranes.

The second line of defense is the inflammatory response that takes place when the body reacts to damage tissue by injury or infections. For example, a pathogen may enter the body though a cut. The damaged cells release several chemicals, one of which is histamine. Histamine causes capillaries to expand and blood flow to increase, which causes inflammation (swelling) in the damaged area. The purpose of the inflammatory response is to localize the infection, allow the body to destroy the pathogen and repair the damaged tissue. Specialized white blood cells (WBC) called phagocytes are capable of surrounding foreign particles called antigens. An antigen can be a virus, bacteria, toxin or pieces of these foreign substances. Pollen can act as an antigen to individuals that show allergies in response to inhaling pollen grains.

The third line of defense is a cellular and chemical system that comes immediately into play if infectious agents make it past the surface defenses. Specialized white blood cells are involved in the defense against diseases. T–Cells (so called because they mature in the thymus gland) are types of WBC that differentiate into cytotoxic T and Helper T cells (see Table 24.3). Other important types of white blood cells are B-lymphocytes (so called because they mature in the bone marrow). When B- cells attach, antigen Helper T- cells stimulate B cells to differentiate into memory cells and plasma cells (see table 24.3). The second line includes the production of antibodies by the plasma cells which leads to types of immunity.

Table 24.3 Types of Immune cells

Immune Cell / Function of Immune cell
Macrophages / Large WBC that engulf antigens and destroy them
T Lymphocytes / Bind to B cells/antigen complex and stimulate the production of plasma cells or memory cells through differentiation
Helper T Cells / Recognize virus and attack these particles
Cytotoxic killer T – Cells / Releases chemicals onto antigens to destroy them
Plasma cells / Stimulates the production of specific antibodies
Memory cells / Retain or remember the antigens that have enter the body for quick immune response on second exposure.

Table 24.4 Types of Immunity

Active / Immunity acquired when the body produces its own antibodies when a person contracts a disease such as chicken pox
Passive / Immunity passed to a host and is short lived
Natural / Immunity acquired through body fluids, for example, from the mother through breast milk
Artificial immunity / Immunity acquired through receiving a vaccine

Lesson 24 Review: Pathogens and Environmental Health Factors

A. Define the following

AIDS parasite symptom second line of defense toxins

virus disease pathogen first line of defense histamine

bacteria protists nutrients diet and exercise pathogen

third line of defense

B. Choose the best answer.

1. What is a response of the body to a disease as indicated by a fever, cough, runny nose or

swollen lymph glands?

A.  diagnosis C. symptom

B.  pathogen D. behavior

2. What type of food listed below would be considered the healthiest

A. pizza C. caramel dipped apple slices

B. fried chicken fingers D. broiled chicken breast

3. Which activity below would be considered the healthiest?

A. chewing tobacco C. eating chips while watching TV

B. walking a distance to the store D. drinking soft drinks every night with dinner

4. Which of the following is a needed mineral that promotes good health.

A. pepsin B. potassium

B. ADP D. ATP

5. Which line of defense in the immune system is responsible for producing antibodies?

A. first line of defense C. inflammatory response

B. second line of defense D. third line of defense

C. Complete the following exercises

1. Why would a person at risk for a heart attack not want to consume too much vitamin K?

2. How is active immunity different from passive immunity?