Systems of the Human Body 3: Protection, Reproduction and Cooperation

Science, Grade 6


Table Of Contents: Systems of the Human Body 3: Protection, Reproduction and Cooperation

1. Disease and the Body's Defense

2.1. Pathogens and Disease
A pathogen is an organism that can cause disease. Viruses, bacteria, fungi and parasites are examples of pathogens that can cause infection at a number of different locations in the body.
2.2. How Diseases Spread
Once a pathogen infects the body, our defense mechanisms work to destroy it. However, there is always the chance that a pathogen can spread from the initial site. It can multiply and invade surrounding tissues and the bloodstream, causing problems in many parts of the body. Pathogens can also be transmitted from one human to another through the air, via skin-to-skin contact, or on surfaces such as door handles.
2.3. Body Defense against Pathogens
You encounter a wide variety of pathogens every day, but your body is protected from them by different defense systems. A naturally existing barrier, such as your skin, is one type of defense against disease. Inflammation is another general defense system that is activated when pathogens enter the body. A third type of defense is the immune response, which is a very specific cellular response to disease.
2.4. Natural Barriers to Disease
The human body protects itself with non-specific defense systems that react naturally and automatically to invading organisms. Your skin, with its layers of protective tissue, is a very strong, watertight barrier to environmental pathogens. Another example is in your respiratory tract, where mucus and cilia help trap pathogen particles and move them up to your throat, so you can cough and expel them.
2.5. Inflammation
Sometimes pathogens are able to move past natural barriers and enter the body. When body cells are damaged, then inflammation occurs. The signs of inflammation (heat, swelling, redness and pain) reflect the body’s general response to an injury or pathogen.
2.6. Inflammation and Repair
Inflammation occurs when there is an injury or introduction of anything foreign into your body. When you cut your skin, blood vessels widen to increase blood flow. This enables an explosive increase in the number of white blood cells in the area of injury. These white blood cells, called neutrophils, engulf any foreign material. All of these reactions provide the early stages for wound repair. At the same time, the body’s immune response is also activated.
2.7. Specific Protection from Disease
When challenged by disease or infection, the cells of our body’s immune system go into high gear to protect us from illness. Immune system cells called lymphocytes can distinguish between different kinds of pathogens and have specific reactions to fight against and destroy each type of pathogen.

2. Pause and Interact

3.1. Review
Use the whiteboard tools to complete a concept map of the body's different defenses against pathogens.

3. The Immune Response

4.1. What Is an Antigen?
An antigen is a molecule that the immune system can recognize as either part of the body or as foreign to the body. Pathogens have antigens on the surface of their cells. These antigens, or marker molecules, signal the body's immune system that there is a foreign invader.
4.2. How Does the Immune System Work?
The immune system works in two ways. One type of white blood cell produces antibodies against specific antigens that lead to the destruction of the pathogens. Another type of white blood cell reacts directly against pathogens to destroy them.
4.3. Antibodies
Antibodies are proteins that bind to specific molecules called antigens, which are present on the cells of invading organisms. Once antibodies bind to antigens, the pathogen is marked for destruction. Some antibodies make it easier for macrophages to destroy the pathogens. A macrophage cell can engulf an invading pathogen and secrete enzymes to destroy it.
4.4. B Lymphocytes
In the immune system’s response, the white blood cells that produce antibodies are called B lymphocytes. Each type of B lymphocyte produces only one kind of antibody. Antibodies help destroy and remove pathogens. For example, when you suffer from strep throat caused by bacteria, your body produces anti-strep antibodies that lead to the removal of the bacteria.
4.5. T Lymphocytes
T lymphocytes are another type of white blood cell that reacts against pathogens through direct cell contact or by release of chemicals that are toxic to the pathogen. For example, T lymphocytes can attach to cancer cells and release chemicals that poke holes in and kill the cancer cells.
4.6. Lymphocyte Location
B and T lymphocytes are scattered together all over the body, especially in the lymph nodes and spleen, which function as focal points for fighting pathogens in the body.
4.7. Lymph Node Protection
Lymph nodes are small kidney bean shaped filtration structures rich in lymphocytes and macrophages. Lymph nodes monitor foreign materials, and are found throughout the body. For example, when you suffer from a sore throat, the lymph nodes below your chin become larger as the white blood cells work to fight off the bacteria or virus.
4.8. Role of the Spleen
The role of the spleen is similar to a lymph node except that it filters blood, while lymph nodes filter other fluid. Like lymph nodes, the spleen is full of B and T lymphocytes and macrophages. These cells help clear the blood of foreign materials and old or abnormally-shaped red blood cells.

4. Pause and Interact

5.1. Review
Compare and contrast B and T lymphocytes. Fill in the table using the whiteboard text tool.
5.2. Immune System
Click on the Terms button. Then click and drag each term to the correct box. Use the reset button to clear the terms and start over. Use the gear button to customize the draggable terms.

5. Illness, Immunity and Allergies

6.1. When the Immune System Is Overwhelmed
Although your body has several levels of defense and an amazing immune response, you still experience sickness. This happens when cancer or the infectious agent, such as in pneumonia, grows beyond what our immune and inflammatory systems can fight, and illness wins out.
6.2. Immunization: Passive Immunity
There are ways in which our system can be boosted or immunized to protect us from pathogens. In cases of passive immunity, specific antibodies are injected into the bloodstream. For example, a person infected with rabies is injected with anti-rabies antibodies to acquire immunity. Another example of passive immunity happens naturally in a developing fetus as antibodies are passed from mother to fetus across the placenta.
6.3. Immunization: Active Immunity
Active immunization happens when a person receives an injection of weakened antigens in the form of a vaccine. The vaccine stimulates the B and T lymphocytes, and antibodies are produced. If the immunized person is exposed to or infected with that specific pathogen again, the immune system is ready to defend the body against the challenge. Each year many people are immunized with a flu vaccine to avoid the spread of a particular type of influenza.
6.4. Allergic Response
A person with allergies has an immune system that is hypersensitive to certain materials. When the immune system reacts or overreacts to materials such as dust, pollen, latex or certain foods, we call this an allergic reaction. Exposure to these materials, or allergens, produces an exaggerated response that can sometimes even threaten someone’s life.
6.5. Staying Healthy and Preventing Disease
Keeping healthy requires a combination of maintaining healthy defense systems and reducing our exposure to those materials that can make us sick. Frequent hand washing is a way to kill germs that can easily spread from person to person and reduce the risk of infection.

6. Pause and Interact

7.1. Review
Compare and contrast passive and active immunity. Fill in the table using the whiteboard text tool.

7. Skin - Physical Protection

8.1. Skin Barrier and Production of Vitamin D
The skin provides a watertight physical barrier that protects us from injury, infection and dehydration. In the presence of ultraviolet light, skin cells also produce vitamin D, which helps in calcium absorption and maintaining strong bones.
8.2. Skin and Temperature
The skin is rich in blood vessels that constrict to conserve heat when the temperature is cold. These blood vessels will enlarge and increase blood flow to release body heat when the temperature is hot. Sweat glands within the skin will also release secretions, called perspiration, in response to heat. Sweat quickly evaporates to create a cooling effect.
8.3. Cell Structure of the Skin
Skin is made up of an outer layer of tightly packed cells called the epidermis and an inner layer of connective tissue with nerves and blood vessels called the dermis.
8.4. The Epidermis
The epidermis has many layers of cells that are constantly being replaced. Within the epidermis, pigmented cells known as melanocytes release varied amounts of melanin. Skin pores on the surface of the epidermis are openings to sweat glands. These pores are most numerous in the palms of the hands and in the armpits.
8.5. Skin Growth and Repair
The epidermis of our skin grows throughout our lifetime. Epidermal cells live for about two weeks. The outer layer of dead epidermal cells is sloughed off and replaced by an inner layer of growing cells. If injured, the epidermis can grow back to repair the damage, such as when someone suffers from a cut.
8.6. Skin Support: The Dermis
The dermis is the underlying layer of the skin that provides the blood supply and contains the nerves that give us our sense of touch. The dermis also contains sweat glands, hair follicles and oil glands.
8.7. Skin Cancer
Cells of the epidermis are susceptible to the challenges of our environment, including the potentially damaging rays of the Sun. Melanoma is a type of skin cancer that can develop from overexposure to ultraviolet rays. The chance of developing melanoma can be reduced through the use of high SPF lotions and protective clothing.
8.8. Importance of Healthy Skin
Your skin is important for your survival. It protects you from your environment, which is full of potentially dangerous bacteria, viruses and fungal organisms. People suffering from serious burns often lose a layer of skin. These burn victims are at significant risk for infection and death until healed due to the loss of this all-important physical barrier.

8. Pause and Interact

9.1. Review
Use the whiteboard text tool to describe the composition of the epidermis and the dermis.
9.2. The Skin
Click on the Terms button. Then click and drag each term to the correct box. Use the reset button to clear the terms and start over. Use the gear button to customize the draggable terms.

9. Reproduction--Continuing the Species

10.1. Sex Cells
Both males and females produce sex cells. When sex cells combine during the process of fertilization, a new offspring is produced. Females release a single egg, or ovum, during a monthly reproductive cycle. Males produce millions of sperm cells. These cells are stored so they can be released as part of the fertilization process.
10.2. Fertilization
The moment of fertilization occurs within the female reproductive tract when a single sperm cell enters an egg. The nuclear material of the egg and sperm combine to form a zygote, which is the earliest stage of human embryonic development.
10.3. Sperm Production
The male reproductive system is designed to continuously produce sperm through a type of cell division called meiosis that occurs within the male's testes. Each sperm is a specialized cell that develops a tail known as a flagellum. This tail gives the cell the ability to “swim,” an important function in the process of fertilization.
10.4. Testes
Sperm are produced in the male’s testes and carried through a series of tubules. The sperm are nourished and supported by secretions from accessory glands such as the prostate. Within the testes, specialized cells release the hormone testosterone, which is important in the process and rate of sperm production. Testosterone also controls the development of adult male physical characteristics, such as facial hair and a deep voice.
10.5. Female Reproductive System
The organs of the female reproductive system are designed to support the growth and release of a single egg from the ovaries during a monthly cycle. The egg is released through uterine tubes, called the oviducts, into the uterus. The uterus is made up of an inner glandular wall and an outer muscular wall, both important in nurturing a developing fetus and helping move the fetus, through muscular contractions, during birth.
10.6. Female Reproductive Hormones
Female reproductive processes are controlled by different hormones. For example, the follicle-stimulating hormone is released by the pituitary gland to control the growth and release of the egg from the ovary. During this early stage of the cycle, the ovaries release estrogen and progesterone hormones to stimulate the growth of the inner lining of the uterus, in case fertilization occurs.
10.7. Menstruation
If an egg is released but not fertilized, then pregnancy does not occur. Hormone levels signal the breakdown of the inner lining of the uterus. This excess tissue and blood pass out of the body in a process known as menstruation. Then the monthly cycle starts all over again.
10.8. Egg Fertilization
If an egg is fertilized within the female, the embryo will adhere to the inner lining of the uterus, establishing a connection through which the mother can nourish the fetus through pregnancy. The embryo is supported by the nutrient-rich blood vessels of the placenta. As the embryo grows into a fetus, the ovaries continue to produce hormones that keep the connection between fetus and mother very strong.
10.9. Human Implantation and Early Development
The zygote begins dividing and developing into a multicellular embryo as it travels down the oviduct toward the uterus. The embryo then attaches to the inner lining of the uterus and begins to grow rapidly. From this point, through the 8th or 9th week, there are many cell divisions and changes as the embryo shows signs of a developing nervous system and other organ systems.
10.10. Human Fetal Development and Birth
From the ninth week of development until birth, the growing human is referred to as a fetus. After approximately nine months, a human infant is born. A number of dramatic changes occur in an infant’s lungs and circulatory system to allow the baby to breathe and circulate blood completely on his or her own. Previously, the baby was totally dependent on the mother through the umbilical cord connection with the placenta. At birth, this physical connection ends as the baby moves into another stage of the human life cycle.

10. Pause and Interact

11.1. Review
Use the whiteboard text tool to complete the table.
11.2. The Male Reproductive System
Click on the Terms button. Then click and drag each term to the correct box. Use the reset button to clear the terms and start over. Use the gear button to customize the draggable terms.
11.3. The Female Reproductive System
Click on the Terms button. Then click and drag each term to the correct box. Use the reset button to clear the terms and start over. Use the gear button to customize the draggable terms.

11. Systems Working Together

12.1. Link between Cardiovascular and Respiratory Systems
The lungs contain a very extensive network of capillaries. Oxygen moves through the walls of the alveoli into the capillaries and blood. Carbon dioxide and water move in the opposite direction, through the walls of the capillaries into the alveoli. In this gas exchange process, oxygen-poor blood is replenished with oxygen, and carbon dioxide moves into the lung space to be exhaled.
12.2. Links between Digestive, Nervous and Muscular Systems
A constant dietary source of carbohydrates is important for the functioning of vital organs. Skeletal muscles and brain neurons require carbohydrate (glucose) as a source of cellular energy. When glucose runs low in muscles, you become fatigued. When it happens with neurons of the brain, you feel light-headed, dizzy and confused.
12.3. Organ Systems During Exercise
During exercise your muscles contract to move your skeleton in different directions and at different speeds. Your heart rate tends to increase as you exercise because this activity requires a constant delivery of oxygen to your tissues. You breathe harder to get rid of excess carbon dioxide and to deliver even more oxygen. Your brain neuron activity is a virtual firestorm of activity as you work to consciously and subconsciously control all aspects of body movement.
12.4. Healthy Habits, Healthy Organs
To maintain overall body health, it is important to make sure your vital organs are functioning normally. Your lungs should be clear of pollutants, and your blood vessels should not be thickened with excess fat. Your heart needs to be fit and efficient. Reduction in stress will also benefit your body systems by keeping stress hormones at a minimum.

12. Vocabulary Review

13.1. Vocabulary Matching Review

13. Virtual Investigation

14.1. Infection and Inflammation
Your immune system responds quickly when your body is threatened by potentially dangerous foreign invaders, such as bacteria and viruses. In this investigation, you are provided with three scenarios. For each scenario you will identify and select the cells that are involved with the body's defense systems and watch animations that illustrate how the cells work together to fight against foreigner invaders.Click on the more info button for background information about the different types of cells that help your body respond to foreign invaders (pathogens) and allergens.

14. Assessment

15.1. Human Body 3