Basic anatomy of exocrine glands and lymphatic organs
The average gland is composed of simple cuboidal epithelial cells that form grape-shaped structures called acini (although others are tube-shaped). These grape-shaped structures are where the secretions are produced. The liquids produced by these cells next enter a duct, which can be made of simple cuboidal or columnar eipthelial cells. The outside of the gland is surrounded by dense connective tissue capsule. The connective tissue extends inwards forming trabeculae (or septa), which can divide the organ into different lobes.
The average lymphatic organ is surrounded by a dense connective tissuecapsule. The connective tissue extends inwards forming trabeculae. Inside the organ, clusters of white blood cells suspended within reticular connective tissue form germinal centers (or nodules) where the white blood cells filter cellular debris and scan body fluids for pathogens. If they detect a pathogen, they multiply and release inflammatory signals starting from the lymphatic organ, and then migrate through the body's connective tissues looking for more pathogens.
The major function of salivary glands is to produce saliva, which helps to maintain the health of the oral mucosa and teeth, as well as assist in mastication. Acinar epithelial cells transcribe and translate long mucous proteins on the rough endoplasmic reticulum, modify them in the golgi apparatus to form large glyco-proteins, and secrete them. These cells also pump electrolytes from their cytoplasm into the lumen of the acinus, which, along with the glycoproteins, attract water by osmosis. Other molecules can be secreted to become a part of saliva, but these components make saliva moist, but sticky enough to adhere to all surfaces of the oral cavity and not sink to the floor of the mouth.
The mucous component of saliva helps it to adhere to all surfaces of the oral cavity. Buffers within saliva help to maintain a stable pH, despite the acidity or alkalinity of different foods, and the acidity of certain oral bacterial secretions. Buffers and electrolytes can also help disrupt the formation of bacterial biofilms, which otherwise allow bacteria to adhere to teeth. The watery nature of saliva helps to moisten food and the oral mucosa, assisting in mastication, speech and swallowing. Watery saliva helps to limit the population of oral bacteria. People swallow saliva even when they are not eating, and this flushes a percentage of oral microorganisms down to the stomach, where certain death awaits in the form of Hydrochloric Acid and a powerful protein-destroying enzyme called pepsin. The enzymes salivary amylase and lysozyme are produced by acinar cells to serve a similar purpose, breaking covalent bonds within the cell walls of viruses and bacteria. I suppose if you chewed for long enough, salivary amylase could help digest carbohydrates in food, but no one chews for long enough for that to happen. Therefore, salivary amylase should not be considered a digestive enzyme. It is an anti-microbial enzyme that helps limit oral microbiome populations.
The dental pellicle is a coating of glycoproteins from saliva on the surface of teeth. It normally prevents excess deposits of Ca2+PO43-. It also helps prevent deminerization of enamel. Either depositing bumps, or eroding crevices allows bacteria to adhere to teeth and avoid being washed into the stomach. However, saliva also contains the minerals that produce calculus.
Histology of salivary glands
Serous acini produce more watery secretions. These are composed of simple cuboidal epithelium. Serous acini tend to stain more faintly using a traditional H&E stain, because they make fewer mucous proteins.
Mucous acini secrete more glycoproteins, making their secretion thicker and stickier. These are made of a simple columnar epithelium. Mucous acini tend to stain a little darker using a traditional H&E stain, because they make more mucous proteins.
Muco-serous acini produce secretions halfway inbetween the first two in consistency. These look like mucous acini under the microscope, with an additional bonnet of myo-epithelial cells. These cells contract like smooth muscle cells. For most epithelial cells, the actin and myosin genes are not highly expressed, except by epithelial stem cells, which may need to migrate to a different area to help repair a wound. Myo-epithelial cells, on the other hand, use some of the DNA instructions for making and organizing actin and myosin that are usually only transcribed by muscle cells, making them appear similar to smooth muscle. However, these cells have an epithelial lineage-- they differentiated from an epithelial stem cell, not from a Mesenchymal Stem Cell or myoblast.
All three secretions wind up mixing in the oral cavity to produce saliva, therefore memorizing which type of acinus does what is fairly academic. These secretions reach the oral cavity by way of different types of ducts, which can be identified under the microscope by their different type of epithelial cells. I know of no clinical significance to the types of ducts or their cells, which makes identifying the ducts by type an academic exercise. You can do it, but why would you?
Parotid duct papillae by D Rosenbach, is liscensed CC BY SA 3.0
The parotid glands drain into the oral cavity by way of the parotid (or Stensen) ducts. The ducts travel through the masseter muscle and enters the oral cavity at a papillae usually located lateral to the 2nd maxillary molar.
Mumps by Photo CDC/NIP/Barbara Rice, is in the Public Domain CC 0
Mumps is a viral infection tha tcauses swelling of the Parotid glands. Vaccination has reduced the number of mumps cases in the US by over 99%, however mumps outbreaks still occur, often in high-density living areas (such as college dormitories), quite possibly aided by fraudulent misinformation campaigns against the MMR vaccine.
Carruncula sublingularis by Hellerhoff, is liscensed CC BY SA 3.0
The sub-lingual and sub-mandibular glands have ducts that share an entrance on the floor of the mouth at the sub-lingual caruncle. The sub-lingual gland also has numerous smaller ducts that open onto the floor of the mouth.
Nicotinic stomatitis by DVIDS is in the Public Domain CC0
Numerous minor salivary glands are located throughout the oral cavity. They are normally not visible, unless the oral mucosa is hyperkeratinized. Luckily, no one has bothered to name these glands or their ducts, except for the von Ebner salivary glands, which are minor salivary glands associated with the circumvallate lingual papillae. The minor salivary glands are predominatly mucous, with exceptions, which helps their secretions to stick to the roof and sides of the oral cavity.
Hyposalivation, or decreased saliva production, can be caused by certain diseases, medications, cancer treatments, and aging. It may result in xerostomia, or dry mouth. Reduced saliva can decrease the healing ability of the oral mucosa, leading to sores. Reduced saliva also removes some of the limits to growth placed on the oral microbiome, leading to infections and caries. Reduced taste can also be a consequence, which patients might compensate for by flavoring their food with excessive levels of salt. Using Monosodium Glutamate (MSG) to enhance both flavor and saliva production is a significantly safer option, despite fears of the non-existant "Chinese Restaraunt Syndrome".
The electrolcytes in saliva can precipirate and form salivary gland stones, or sialoliths. Large sialoliths may block the duct of one of the salivary glands, which stops the secretion-- but not the production-- of saliva. As a result, saliva builds up in the gland, causing swelling and possibly inflammation. Blockage of a minor salivary gland produces a swelling within the oral mucosa known as a mucocoele, while blockage of a major salivary gland produces a ranula.
Ranula human by Ph0t0happy is liscensed CC BY SA 3.0
Own work by hellerhoff, is in liscnensed CC BY SA 3.0
Sialography
Sialoliths may be felt by technicians. Alternately, an image of the blockage known as a sialograph may be taken by injecting a radio-opaque dye as far into the salivary gland duct as it will go. Usually, sialoliths can be removed with minimal discomfort.
Background image Own work by Goran tek-en, is liscensed CC BY SA 3.0
Lymphatic drainage of the teeth
Fluid travels to the teeth via capillaries. As plasma exudes from the capillaries, it becomes ECF. Lymphatic vessels collect this fluid, at which point it is called lymph, and return it to the circulatory system. Lymphatic vessels are more permeable than capillaries, having mini-valves on their edges, which allow solids to enter the lymphatic vesselm including cellular debris, microorganisms, and cancer cells. The lymphatic vessels are connected to a number of Lymmph nodes, which clean up the debris and mount an immune reponse against the microorganisms and cancer cells. Knowing the pathway of these lymphatic vessels can help identify periodontal disease by the inflammation triggered in the down-stream lymph nodes.
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Lymph nodes
Lymph nodes are found throughout the body. Larger clusters of lymph nodes can be found in the neck, in addition to a few other places. Lymph nodes are composed primarily of reticular connective tissue, which provides support for resident clusters of white blood cells. Afferent lymphatic vessels bring lymph to the node, while efferent vessels drain lymph towards the circulatory system.
Lymph nodes serve two major functions. One is to clear and cellular debris before lymph reaches the circulatory system, becoming blood plasma again. Two is to identify pathogens and begin an inflammatory response. If this occurs, white blood cells begin to multiply within the node and begin secreting inflammatory molecules.
Tonsillar tissue
Tonsillar tissue is similar to lymph nodes, except there are no lymphatic vessels, and one end of the tissue remains un-encapsulated. Clusters of white blood cells can be found in germinal centers, suspended within reticular connective tissue.
The tonsils
There are 4 major tonsils located in the oral cavity and pharynx: lingual, palatine, pharyngeal and tubal. These tonsils form a ring, called Waldeyer's ring, which serves to identify pathogens that are either ingested or inhaled, and begin an immune response before they reach deeper locations, such as the lungs or stomach.
Clinical applications of lymphatic system histology
own work by James heilman MD, is liscensed CC BY SA 3.0
Lymphadenopathy of lymph nodes
In the absence of infection, lymph nodes are soft and cannot be felt. However, if the white blood cells detect a pathogen, they undergo cell division and release inflammatory molecules. This leads to lymph nodes becoming palpable, possibly visibly swollen, and likely sensitive to the touch.
The mandibular incisors drain into sub-mental lymph nodes. The sub-mental lymph nodes and the rest of the teeth (other than maxillary 3rd molars) drain into sub-mandibular lymph nodes. The submandibular lymph nodes then drain into superior deep cervical nodes. Swelling of some or all of these lymph nodes can indicate active periodontal disease.
own work by James heilman MD, is liscensed CC BY SA 3.0
Lymphadenopathy of tonsillar tissue
Tonsillar tissue can also become inflamed. When it does, the increased number of white blood cells may be visible as white-ish patches within the inflamed tonsil(s).
The para-nasal sinuses are spaces within the frontal, sphenoid, ethmoid and maxillary bones that surround the nasal cavity. The maxillary, frontal and spehnooid sinus connect to the nasal cavity via small passageways. The paranasal sinuses are lined with pseudostratified epithelium. This epithelium produces mucus which can trap pathogens and debris. With the aid of cilia, these harmful agents are remove them from the body. Within the nasal cavity are 3 bumps called nasal conchae, which divide the nasal cavity into three winding spaces called the nasal meatuses.
Clinical applications of para-nasal sinus histology
own work by James heilman MD, is liscensed CC BY SA 3.0
Inflammation within the para-nasal sinuses
When the para-nasal sinuses become inflamed (known as sinusitis), the small ducts leading to the nasal sinuses may become obstructed. The increase in fluid that accompanies inflammation will then have nowhere to drain, leading to pressure within the sinuses. Furthermore, one response of goblet cells to inflammatory signals is to produce more mucous proteins, which again will have nowhere to drain.
Figure 1 by by Gina Roque-Torres, is liscensed CC BY 4.0
The posterior maxillary teeth lie close to (or partly within) the maxillary sinuses. Therefore, if inflammation occurs within these sinuses, it can cause discomfort to the significantly more-senitive teeth. Furthermore, sinus infections may be able to spread to the posterior maxillary teeth.
