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Structure of a tooth. The part above the gums (gingiva) is called the crown, the part below the gingiva is the root. The very top of the crown is a thick enamel, this is very thick at the region above the gingiva and much thinner in the root. The next layer in is the dentin and this is equally thick in both the crown and root. In the very center is the pulp which contains the pulp canal (root canal) and nerve and blood vessels. The root sits mainly in the bone region. There is a small space where the tooth extends past the gingiva, this is called the gingival crevice.
The tooth has a visible crown with an outer layer of enamel, a layer of dentin, and an inner pulp. The root, hidden by the gums, contains the pulp canal (root canal). (credit: modification of work by Bruce Blaus)

Microbes such as bacteria and archaea are abundant in the mouth and coat all of the surfaces of the oral cavity. However, different structures, such as the teeth or cheeks, host unique communities of both aerobic and anaerobic microbes. Some factors appear to work against making the mouth hospitable to certain microbes. For example, chewing allows microbes to mix better with saliva so they can be swallowed or spit out more easily. Saliva also contains enzymes, including lysozyme , which can damage microbial cells. Recall that lysozyme is part of the first line of defense in the innate immune system and cleaves the β-(1,4) glycosidic linkages between N-acetylglucosamine (NAG) and N-acetylmuramic acid (NAM) in bacterial peptidoglycan (see Chemical Defenses ). Additionally, fluids containing immunoglobulins and phagocytic cells are produced in the gingival spaces. Despite all of these chemical and mechanical activities, the mouth supports a large microbial community.

  • What factors make the mouth inhospitable for certain microbes?

Anatomy and normal microbiota of the gi tract

As food leaves the oral cavity, it travels through the pharynx, or the back of the throat, and moves into the esophagus , which carries the food from the pharynx to the stomach without adding any additional digestive enzymes. The stomach produces mucus to protect its lining, as well as digestive enzymes and acid to break down food. Partially digested food then leaves the stomach through the pyloric sphincter , reaching the first part of the small intestine called the duodenum . Pancreatic juice, which includes enzymes and bicarbonate ions, is released into the small intestine to neutralize the acidic material from the stomach and to assist in digestion. Bile, produced by the liver but stored in the gallbladder , is also released into the small intestine to emulsify fats so that they can travel in the watery environment of the small intestine. Digestion continues in the small intestine, where the majority of nutrients contained in the food are absorbed. Simple columnar epithelial cells called enterocytes line the lumen surface of the small intestinal folds called villi . Each enterocyte has smaller microvilli (cytoplasmic membrane extensions) on the cellular apical surface that increase the surface area to allow more absorption of nutrients to occur ( [link] ).

The small intestines with increasing magnification. A) is a diagram and b), c), and d) are micrographs of each magnification. The micrograph of the larges magnification shows a pink region on the bottom with a deeply waved darker pink region at the surface; the top of the image is clear. There are some darker patches in the bottom layer labeled Peyer’s patches. The diagram sows a tube lined with three layers of muscle; blood vessels connected to the outside of the tube. A cutout of the tube shows circular folds along the diameter of the tube. These folds contain deeply lobed villi. The empty space in the tube is labeled lumen. The next layer of magnification is one of the vili. The micrograph is filled with pink layers folding back and forth. The diagram shows two folds. The surface of the fold is covered with absorptive cells and some goblet cells. Between the folds is further indent labeled intestinal crypt. Inside the folds are capillaries, arteries, and lymphatic vesicles. At the very bottom of the structure (below the blood and lymph vessels, are a few duodenal glands. The final close-up shows finger-shapes in a row on the surface of a cell. These are labeled microvilli (brush border) on the diagram.
(a) The structure of the wall of the small intestine allows for the majority of nutrient absorption in the body. (b) Villi are folds in the surface of the small intestine. Microvilli are cytoplasmic extensions on individual cells that increase the surface area for absorption. (c) A light micrograph shows the shape of the villi. (d) An electron micrograph shows the shape of the microvilli. (credit b, c, d: Modification of micrographs provided by the Regents of University of Michigan Medical School © 2012)

Questions & Answers

reactions if viruses to physical and chemical agents?
All viruses contain the following two components: 1) a nucleic acid genome and 2) a protein capsid that covers the genome. Together this is called the nucleocapsid. In addition, many animal viruses contain a 3) lipid envelope. The entire intact virus is called the virion.
assume you have performed a gram stain on a sample of pus from a patients urethra. you see red, nucleated cells and purple rods. what can you conclude
Petty Reply
Study of micro organisation which we cannot see with naked eye...
shyam Reply
Despite their bad reputation, microbes are mostly beneficial or have a neutral effect on our lives. Microbiology is the scientific study of these microorganisms. Microorganisms are those organisms that are too small to see with the naked eye and include things like bacteria, fungi, and viruses.
not 'things'...'organisms' like bacterias, viruses and fungi
simi, it's not bacterias but bacteria which is the plural form of the word while bacterium is the singular of it
bacterium is obvio in a singular form but plural of bacterium is bacterias
Richard is right it's bacterium which is the singular form and plural is bacteria. *Bacterias* doesn't exist.
what is microbiology?
Sandeep Reply
what is microbiology
is the study of small microorganisms that can't be viewed by our naked eyes under a microscope
it's the study of microbes their classification, diversity, their cellular structure and processes, their applications and interaction with other organisms.
what is EMP pathway
which organism is implicated in meningoencephalitis
Peter Reply
Herpes virus
which mold is called dairy mold?
Geotrichum candidum
which infectious agent is the smallest
spore or virus
prion ....it is a single protein in a misfolded form..there is also a theory based on it
yup...m sry
yes it can be turned as a virus
which gram positive bacteria is responsible for food poisoning?
prion is not a living organism yet it is infectoois why
prions are virus like organism. and it is a misfolded protein that may cause disease to us.
Clostridium perfringens, B.cereus
Who is the father of the biology
I have one more question. . that who is the father of botany and medicine? ? can any one tell
define polar bond in simple way
Rashmi Reply
when there is formation of positive and negative poles i.e. one atom is +ve and other is -ve which further results in the dipole moment. Such bond is know as polar bond. It is a convalent bond only.
Hi everyone, is these site only about microbiology? I want a site which I can download articles on hematological and biochemical profile
Peter Reply
I think it is only about micro biology.
so whats happening
I am about to enter school and am going for MCB
Olugbenga Reply
What is DNA damage and repair
Sree Reply
removal of nucleotide bases from DNA is damage n addition or insertion of bases in DNA is repair.
replication is a term related to generation of new DNA from a parental DNA.
role of microorganism as pathogens
Parteek Reply
to live inside the host body, reproduction n destroy the immune system of host body.
what is replication
please give me ans
replication is a term related to generation of new DNA from parental DNA.
difference between endotoxin and exotoxin
Binkheir Reply
toxins released inside the cell or a body is endotoxin n toxins released outside the cell or a body is exotoxin.
Generally, exotoxins are produced by gram positive bacteria and endotoxins are the integral part of the cell wall of gram negative bacteria. But some gram negative bacteria can also produced exotoxins such as E.coli.
Yeah u r ryt aakarti exotoxins screted by gram postive bacteria nd secreted by cell surface and they are secondary metabolites ....On the other hand endotoxin released by gram negtive bacteria nd released inside the cell (lipopolysaccharide) ..
Heat stable lipopolysaccharides to be exact.
please I want the names of bacteria and the diseases they cause.
Ibrahim Reply
there are many we classify it according to their shapes gram negative or gram positive
so u may refer the book u guess or by when u want I can do a list for you and send u here
please do a list for me
I have the lost but it's too much to type ..
MSc entrance prepare books and questions LA etha base pani irukum..
Guhan Reply
kushal always prescott is the imp book to follow.search some objective mcqs books based on your syllabus
deepthi Reply
I want to clear entrance of ms university so I have no more idea so my preparation is based on my bachlor studies.
what are the opportunistic infection in aids stage
certain cancer or pneumonia 🤔
penicillium crysogenum
Kushal Reply
Practice MCQ 2

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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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