These enzymes are chemical barriers. The nose has internal hairs, which act as a physical barrier to infection. Cells in the nose produce mucus. This traps pathogens before they can enter the lungs. When the nose is blown, mucus is removed and any pathogens are trapped within it. The trachea runs from the nose towards the lungs. The cells that line the trachea also have hairs called cilia , which are much smaller than those in the nose.
These are called ciliated cells. The ciliated cells waft their hairs in a motion like a Mexican wave at a football match and move mucus and pathogens upwards towards the throat where it is swallowed into your stomach. Other cells called goblet cells create the mucus in order to trap pathogens.
The production of mucus in your airways is a physical barrier. Go to the footer. Functions of Tears and how they work. Functions of Tears After blinking, a film of tear fluid coats the surface of the eye at a certain thickness, and is maintained for a while.
Preventing dryness Tears prevent dryness by coating the surface of the eye, as well as protecting it from external irritants. Supplying oxygen and nutrients to the eyes There are no blood vessels on the surface of the eye, so oxygen and nutrients are transported to the surface cells by tears.
Preventing infection Foreign bodies that enter the eye are washed out by tears. Moreover, tears contain a substance called lysozyme, which has an antibacterial action, and works to prevent invasion and infection by microbes. Healing damage to the surface of the eye Tears contain components that heal damage to the surface of the eye.
Creating a smooth surface on the eye Tears lubricate and smooth the surfaces of our eyes so that light is refracted correctly, enabling us to see clearly. Two-layer Structure of Tears Maintaining tear structure is important for the tears covering our eyes to function normally. The cell junctions in the blood vessels traveling through the CNS are some of the tightest and toughest in the body, preventing any transient microbes in the bloodstream from entering the CNS.
This keeps the cerebrospinal fluid that surrounds and bathes the brain and spinal cord sterile under normal conditions. In addition to physical barriers that keep microbes out, the body has a number of mechanical defenses that physically remove pathogens from the body, preventing them from taking up residence. We have already discussed several examples of mechanical defenses, including the shedding of skin cells, the expulsion of mucus via the mucociliary escalator, and the excretion of feces through intestinal peristalsis.
Other important examples of mechanical defenses include the flushing action of urine and tears, which both serve to carry microbes away from the body.
The flushing action of urine is largely responsible for the normally sterile environment of the urinary tract, which includes the kidneys, ureters, and urinary bladder.
Urine passing out of the body washes out transient microorganisms, preventing them from taking up residence. The eyes also have physical barriers and mechanical mechanisms for preventing infections. The eyelashes and eyelids prevent dust and airborne microorganisms from reaching the surface of the eye. Any microbes or debris that make it past these physical barriers may be flushed out by the mechanical action of blinking, which bathes the eye in tears, washing debris away Figure 6.
Figure 6. Tears flush microbes away from the surface of the eye. Urine washes microbes out of the urinary tract as it passes through; as a result, the urinary system is normally sterile. In various regions of the body, resident microbiota serve as an important first-line defense against invading pathogens.
Through their occupation of cellular binding sites and competition for available nutrients, the resident microbiota prevent the critical early steps of pathogen attachment and proliferation required for the establishment of an infection. For example, in the vagina , members of the resident microbiota compete with opportunistic pathogens like the yeast Candida. This competition prevents infections by limiting the availability of nutrients, thus inhibiting the growth of Candida , keeping its population in check.
Similar competitions occur between the microbiota and potential pathogens on the skin, in the upper respiratory tract, and in the gastrointestinal tract. As will be discussed later in this chapter, the resident microbiota also contribute to the chemical defenses of the innate nonspecific host defenses.
The importance of the normal microbiota in host defenses is highlighted by the increased susceptibility to infectious diseases when the microbiota is disrupted or eliminated. Treatment with antibiotics can significantly deplete the normal microbiota of the gastrointestinal tract, providing an advantage for pathogenic bacteria to colonize and cause diarrheal infection. In the case of diarrhea caused by Clostridium difficile , the infection can be severe and potentially lethal.
One strategy for treating C. Which of the following constantly sheds dead cells along with any microbes that may be attached to those cells? Which of the following uses a particularly dense suite of tight junctions to prevent microbes from entering the underlying tissue? Skip to main content. Innate Nonspecific Host Defenses. Search for:. Physical Defenses Learning Objectives Describe the various physical barriers and mechanical defenses that protect the human body against infection and disease Describe the role of microbiota as a first-line defense against infection and disease.
Every Rose Has its Thorn Mike, a gardener from southern California, recently noticed a small red bump on his left forearm. Think about It Describe how the mucociliary escalator functions. Name two places you would find endothelia. Think about It Name two mechanical defenses that protect the eyes. Think about It List two ways resident microbiota defend against pathogens. Key Concepts and Summary Nonspecific innate immunity provides a first line of defense against infection by nonspecifically blocking entry of microbes and targeting them for destruction or removal from the body.
The physical defenses of innate immunity include physical barriers, mechanical actions that remove microbes and debris, and the microbiome, which competes with and inhibits the growth of pathogens. The skin, mucous membranes, and endothelia throughout the body serve as physical barriers that prevent microbes from reaching potential sites of infection.
Tight cell junctions in these tissues prevent microbes from passing through. Microbes trapped in dead skin cells or mucus are removed from the body by mechanical actions such as shedding of skin cells, mucociliary sweeping, coughing, peristalsis , and flushing of bodily fluids e. Multiple Choice Which of the following best describes the innate nonspecific immune system?
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