The digestive tract has tight junctions and goblet cells that secrete mucus but it generally does not have cilia like the respiratory tract. Instead, there is peristalsis or strong muscular contractions that propel the mucus out of the body along with feces. The goblet cells are always the cells in the body responsible for making mucus through secretory vesicles near the cell’s surface. The cells that line the urogenital tract, lymph vessels, and blood vessels are called endothelial cells. These are also the cells that make the blood-brain barrier, which prevents disease in the central nervous system. These cell junctions are the tightest in the body because they prevent serious infections from getting into the delicate tissues of the brain and spinal cord. There are other mechanical defenses besides skin sloughing and cilia movement. The urine provides a mechanical defense by flushing bacteria out of the urinary tract. Eyelashes, eyelids, and tears also prevent the invasion of bacteria in the eyes. Peristalsis is a mechanical defense system in the GI tract. The normal microbiome of the body will be a good line of defense against invading microorganisms. They compete for nutrients and occupy the area so pathogens can’t get into the body. Places where the microbiome is important include the vagina, the GI tract, the respiratory tract, and the skin. There are chemical contributions to the microbiome as well. The lack of a good microbiome plays a role in getting an opportunistic infection after taking an antibiotic.
CHEMICAL DEFENSE SYSTEMS The innate immune system has chemical defense mechanisms that also block pathogens. Some are produced in the human body itself, while others are produced by friendly microbes. The sebaceous glands secrete sebum that seals off the hair follicle the gland is attached to. There are bacteria in the microbiome that feed off of sebum to make a waste product called oleic acid, which is acidic and prevents bacterial contamination. The oleic acid is not endogenous to humans but is made by skin bacteria and fungi.
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