Jonah Patel
The human body has a two-line defence system against pathogens (germs) that make you sick. The first line of defence includes physical and chemical barriers that are always ready and prepared to defend the body from infection. These include the skin, tears, mucus, stomach acid, urine flow, and 'friendly' bacteria.
| Characteristics | Values |
|---|---|
| First line of defence | External physical barriers |
| Skin | |
| Sweat | |
| Saliva | |
| Tears | |
| Mucus | |
| Stomach acid | |
| Urine flow | |
| 'Friendly' bacteria | |
| White blood cells (neutrophils) | |
| Second line of defence | Internal physical barriers |
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What You'll Learn
Skin
The skin is the largest organ in the body and acts as the first line of defence against pathogens (germs) that make you sick. Pathogens include bacteria, viruses, toxins, parasites and fungi.
The skin is part of the body's first line of defence, which includes physical and chemical barriers that are always ready and prepared to defend the body from infection. Other physical barriers include tears, mucus, cilia, stomach acid, urine flow, 'friendly' bacteria and white blood cells called neutrophils.
If the first line of defence is broken, the second line of defence within the body is activated.
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Stomach acid
The stomach is lined with a thick layer of mucus that protects it from the acid. This mucus layer is continuously produced and renewed, ensuring that the stomach is not damaged by its own acid. The mucus also contains bicarbonate ions, which act as a buffer to neutralise the acid and maintain the stomach's pH at a level that is optimal for digestion.
In addition to its role in digestion, stomach acid is an important part of the body's defence system. It helps to kill bacteria and parasites that may be present in food or water. The low pH of stomach acid can denature proteins, breaking down the cell walls of bacteria and making them unable to survive in the acidic environment. This helps to prevent infections and illnesses caused by harmful microorganisms.
However, it is important to note that stomach acid can also be harmful to the body if it is too high or too low. Conditions such as acid reflux and gastroesophageal reflux disease (GORD) can occur when stomach acid backs up into the oesophagus, causing heartburn and other symptoms. On the other hand, low stomach acid production can lead to nutrient deficiencies and an increased risk of infection. Therefore, maintaining the right balance of stomach acid is crucial for overall health and well-being.
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Urine flow
The body's first line of defence against pathogens is its physical and chemical barriers, which include skin, tears, mucus, cilia, stomach acid, urine flow, 'friendly' bacteria and white blood cells called neutrophils.
The kidneys are two bean-shaped organs located on either side of the spine, just below the rib cage. They are responsible for filtering the blood and removing waste products, which are then excreted from the body in the form of urine. The kidneys also play a crucial role in maintaining the body's fluid balance, electrolyte levels, and blood pressure.
The ureters are two thin tubes that carry urine from the kidneys to the bladder. They are about 10-12 inches long and connect to the bladder at the ureteric orifices. The bladder is a hollow, muscular organ located in the pelvis. It stores urine until it is full, at which point it sends a signal to the brain that it needs to be emptied. The bladder then contracts, forcing the urine out through the urethra.
The urethra is the tube through which urine exits the body. In females, the urethra is short and located near the vagina, while in males, it is longer and passes through the penis. The urethra is also used to expel semen during ejaculation.
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Tears and mucus
The body's first line of defence is a two-line defence system against pathogens (germs) that make you sick. Pathogens include bacteria, viruses, toxins, parasites and fungi. The first line of defence includes physical and chemical barriers that are always ready and prepared to defend the body from infection. These include the skin, tears, mucus, cilia, stomach acid, urine flow, ‘friendly’ bacteria and white blood cells called neutrophils.
Mucus is a slimy substance that lines the nose, throat, intestines and reproductive tract. It traps microbes that we come into contact with as we breathe and eat, preventing them from entering the body. Mucus also contains antibodies and enzymes that help to destroy any pathogens that may be present.
Together, tears and mucus work to protect the body from infection and keep the eyes and respiratory system healthy. They are an important part of the body's defence system, acting as a first line of defence against pathogens. They help to trap and destroy unwanted microorganisms, and prevent them from entering the body and causing harm.
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'Friendly' bacteria
The body's first line of defence against pathogens (germs) includes physical and chemical barriers such as skin, tears, mucus, cilia, stomach acid, urine flow, 'friendly' bacteria and white blood cells called neutrophils.
Friendly bacteria are microorganisms that live all over the skin and mucous membranes. They are part of the body's first line of defence against invading pathogens. Mucous membranes line the nose, throat, intestines and reproductive tract and trap microbes we come into contact with as we breathe and eat.
Friendly bacteria help to maintain a healthy balance of microorganisms in the body. They compete with harmful bacteria for nutrients and space, and they also produce substances that inhibit the growth of harmful bacteria. In addition, friendly bacteria stimulate the production of antibodies and enhance the activity of white blood cells, which are an important part of the body's second line of defence.
Probiotics are live microorganisms that are similar to friendly bacteria. They are often referred to as "good" bacteria and are available as dietary supplements. Probiotics are thought to help restore the natural balance of bacteria in the gut, which may be disrupted by illness or antibiotics.
Prebiotics are non-digestible food components that selectively stimulate the growth of friendly bacteria in the gut. They act as a source of fuel for these beneficial bacteria, promoting their growth and activity. Prebiotics can be found in foods such as garlic, onions, leeks, asparagus, artichokes and bananas.
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Frequently asked questions
The body's first line of defence against pathogens (germs) is its external physical barriers, such as skin, sweat, saliva and tears.
If the first line of defence is broken, the body's second line of defence is activated. This includes white blood cells called neutrophils.
Pathogens are microorganisms that cause disease. They include bacteria, viruses, toxins, parasites and fungi.
The body's first line of defence includes physical and chemical barriers that are always prepared to defend the body from infection. For example, stomach acid kills bacteria and parasites that have been swallowed, and urine flow flushes out pathogens from the bladder.
The three lines of defence in the immune system are like defensive tiers in football, where the first line of defence represents the biggest and best defence, and the second and third lines act as backup.
