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Endothelia

The epithelial cells lining the urogenital tract, blood vessels, lymphatic vessels, and certain other tissues are known as endothelia . These tightly packed cells provide a particularly effective frontline barrier against invaders. The endothelia of the blood-brain barrier , for example, protect the central nervous system (CNS), which consists of the brain and the spinal cord. The CNS is one of the most sensitive and important areas of the body, as microbial infection of the CNS can quickly lead to serious and often fatal inflammation. 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.

  • Describe how the mucociliary escalator functions.
  • Name two places you would find endothelia.

Mechanical defenses

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 ( [link] ).

A diagram of a person. An arrow from the eye points to a larger image that shows eyelashes, the eyelid and tear ducts. An arrow from the abdominal region shows a larger kidney are ureter. An arrow from the groin region shows a larger urethra.
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.
  • Name two mechanical defenses that protect the eyes.

Microbiome

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. difficile infections is fecal transplantation , which involves the transfer of fecal material from a donor (screened for potential pathogens) into the intestines of the recipient patient as a method of restoring the normal microbiota and combating C. difficile infections.

[link] provides a summary of the physical defenses discussed in this section.

Physical Defenses of Nonspecific Innate Immunity
Defense Examples Function
Cellular barriers Skin, mucous membranes, endothelial cells Deny entry to pathogens
Mechanical defenses Shedding of skin cells, mucociliary sweeping, peristalsis, flushing action of urine and tears Remove pathogens from potential sites of infection
Microbiome Resident bacteria of the skin, upper respiratory tract, gastrointestinal tract, and genitourinary tract Compete with pathogens for cellular binding sites and nutrients
  • 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.g., urination, tears)
  • The resident microbiota provide a physical defense by occupying available cellular binding sites and competing with pathogens for available nutrients.

Fill in the blank

The muscular contraction of the intestines that results in movement of material through the digestive tract is called ________.

peristalsis

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______ are the hair-like appendages of cells lining parts of the respiratory tract that sweep debris away from the lungs.

cilia

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Secretions that bathe and moisten the interior of the intestines are produced by _______ cells.

goblet

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Short answer

Differentiate a physical barrier from a mechanical removal mechanism and give an example of each.

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Identify some ways that pathogens can breach the physical barriers of the innate immune system.

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Questions & Answers

full life cycle of plasmodium parasite
Emmah Reply
what are ways of handling sharps
namugenyi Reply
never recap or bend a sharp objects
benita
describe the process of platelet formation
Joy Reply
what is parasitic helminths
Sadiya Reply
list three categories of symbiotic relationships.
mary Reply
what's the difference between microbial intoxication and infectious diseases
dranimva Reply
microbial intoxication results when a person ingests a toxin or a poisonous substance that has been produced by a microbe while infectious disease results when a pathogen colonize the body and subsequently cause disease.
mary
weighing balance is needed in lab of microbiology for weighing?
amna Reply
It is mainly used for media preparation and product testing purpose.
Nakaweesi
thank you for your joining
nuur
what is microbiology
Shamsuddeen Reply
study of living organisms that are too small to be visible with naked eye
Marah
yes
Ahmed
microbiology is the study of microscopic organisms, either unicellular(single cell), multicellular( cell colony), or acellular (lacking cell).
munachimso
is the word Atypical or a typical bacteria. .am confused pliz help
MUWANGUZI Reply
typical bacteria
Zulpha
okay thank you what does that mean
MUWANGUZI
atypical means that it has some characters from bacteria not all characters ...but tybical means that it has all the characters that bacteria have
Reham
thank you Zulpha
MUWANGUZI
some examples please
MUWANGUZI
thank you Reham
MUWANGUZI
1) typical bacteria contain a cell wall whereas atypical bacteria usually do not contain a cell . 2) typical bacteria can be either Gram-positive or Gram-negative while atypical bacteria remain colorless with Gram staining. 3) cells of typical bacteria are large ,while cells of the atypical small
Marah
Example of atypical : Mycoplasma pneumoniae , chlamydophila pneumoniae , legionella
Marah
what is micro biology
Jauharah Reply
is the study of organisms which can't be viewed by our necked eyes
Egumat
Because it preexisting causing secondary infection after collateral damage of normal microbota
Rafaa Reply
combinations of drugs that can't be taken together and why
Grace Reply
Antagonism: the combined action is less than that of the more effective agent when used alone). All these effects may be observed in vitro (particularly in terms of bactericidal rate) and in vivo والله اعلم
Lenovo
....fermentros have 1-15litre capacity
AMAR Reply
which of the following microorganisms are classified as eukaryotic?
Semugab Reply
how do I see the list?
Melissa
what are the choices?
Melissa
dear tell us the choices
MUWANGUZI
mr semugab give us the list please
Nambi
Fungi
munachimso
what are the new discoveries of microorganisms
Ezibon Reply
bacteriology,viriology,micrology
Egumat
Practice MCQ 3

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Source:  OpenStax, Microbiology. OpenStax CNX. Nov 01, 2016 Download for free at http://cnx.org/content/col12087/1.4
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