Our brand-new six-part ‘Systems the life’ collection looks at the gastrointestinal tract and starts through the mouth and also oesophagus. It comes through a self-assessment for this reason you can test your understanding after analysis it


Abstract

The gastrointestinal tract (gut) operation from the mouth come the anus. Digestion, a mechanical and chemical process, starts when food beginning the mouth, where it is chewed through the teeth, moistened by saliva and broken under by enzymes. Once a food bolus is formed, the goes under the pharynx and triggers the swallowing reflex. It then passes through the oesophagus, where 2 sphincters prevent its regurgitation into the pharynx and also mouth, and also regurgitation the acidic gastric juices right into the oesophagus. The mouth and oesophagus space commonly affected by conditions that impair digestion, together as dental candidiasis and gastro-oesophageal reflux disease. This article, the very first in a six-part collection on the cradle tract, looks at the mouth and oesophagus.

You are watching: The function of the uvula is to prevent food from entering the

Citation: knight J et al (2019) Gastrointestinal street 1: the mouth and also oesophagus. Nursing Times ; 115: 6, 51-55.

Authors: john Knight is associate professor in biomedical science; Nikki Williams is associate professor in respiratory tract physiology; Yamni Nigam is professor in biomedical science; every at the university of Human and also Health Sciences, Swansea University.

This post has been double-blind peer reviewed

Introduction

The cradle (GI) tract, likewise called the gut, is a muscular tube about 9m (30 feet) in length, running from the mouth come the anus. Its duty is come mechanically and also chemically malfunction foods from three major food teams – carbohydrates, proteins and fats – into basic components that have the right to be soaked up by the body. The produces various hormones that play a function in regulation digestion, appetite and satiety (feeling of being sated) and is residence to myriad micro-organisms (mostly bacteria) that are vital to health. These kind a large part of the human being microbiome – the ecosystem the billions of bacteria, viruses and fungal cells that live on or in the body.


This collection of six articles describes the anatomy and also physiology the the GI tract and also some that its typical pathologies; part 1 focuses on the mouth and also oesophagus.

The mouth

The mouth is the opening of the GI street - that anatomy is shown in Fig 1. The receives food, tastes it and also prepares it because that swallowing (as well as play a key role in vocalisation). The typical volume of the adult mouth is 72ml in men and also 55ml in ladies (Nascimento et al, 2012).

The mouth is inside wall by mucous membranes and consists of two significant regions:

Vestibule – the space between the inner surface ar of the cheeks/lips and the teeth;Oral cavity proper – the room beyond the teeth, largely occupied by the tongue, where food is chewed and also mixed v saliva before being swallowed.

*

Source: Peter Lamb


Tongue and also sense of taste

The tongue is a muscle the measures around 10cm and also weighs 60-70g. The is anchored posteriorly come the hyoid bone via tiny muscles and attached to the floor the the mouth by a thin flap that tissue, the lingual frenulum. That surface has actually a turbulent texture brought about by small extensions called papillae, which aid to tight food as it is moved around the mouth and mixed through saliva. The papillae save taste buds, which in turn contain gustatory cells the act as taste receptor (Kikut-Ligaj and also Trzcielinska-Lorych, 2015).


During mastication (chewing), saliva solubilises food, permitting food-derived molecule to communicate with the taste receptors. This receptors space activated and also nerve impulses space relayed to the gustatory cortex of the brain, wherein they are regarded as distinctive tastes.

Five significant tastes have been identified: salty; sweet; sour; bitter; and also umami – a savoury taste connected with glutamate-rich foods, such as fish, cured meat and mushrooms (Kurihara, 2015).

Many textbooks attribute a map of the tongue showing where every taste is perceived however these room misleading, as the different taste receptor types are distributed throughout the tongue (Chamma et al, 2018).

The sense of taste is intimately connected to olfaction (sense of smell) – which is why food can not be tasted effectively if the nose is blocked. As quickly as the olfactory apparatus detects the smell of food, the parasympathetic nervous system is activated and also stimulates the outstanding glands to release extra saliva, preparing the mouth to get it. As soon as food enters the mouth, mechanical and chemical cradle starts.

Both olfaction and also taste decrease v age, which have the right to make eating less enjoyable and also lead to diminished appetite. In particular, the capacity to taste salt reduce with period (Mauk, 2010) so older human being often include extra salt to food to reclaim the flavour. This deserve to increase plasma salt levels, possibly exacerbating problems such together hypertension or kidney condition (Nerbass et al, 2018).


Dentition

Adults typically have 32 teeth, which room evenly distributed in between the upper and also lower jaws (Fig 1). The teeth comprise:

Eight incisors – flat, chisel-like this that bite right into food and break that into tiny manageable pieces;Four canines – sharp, fang-like teeth just external the incisors that grip and tear food;Eight premolars – small teeth between the canines and molars that grind up and also cut into food;Eight molars – square this in the rear of the mouth that grind food to boost its surface ar area;Four wisdom this – extra molars that commonly erupt ~ the age of 18 years; lock are regularly removed if troubles occur during the eruption procedure or if they press the other teeth the end of alignment due to the fact that the dental cavity is also small.

Teeth are greatly composed the a bony material (dentine) extended by a class of white enamel (the hardest material in the human body). Their central portion, the pulp cavity, is written of living tissue – greatly blood vessels and sensory nerve endings. As teeth are, primarily, cutting and grinding tools, they room susceptible to erosion together a result of wear and also tear and also exposure come acidic foodstuffs (Wang and also Lussi, 2012).

Mastication

Mastication is brought out by the teeth, if the tongue moves food in the direction of the premolars and also molars. If teeth room missing, the gums can likewise chew food, back this calls for much more effort. This loss is, therefore, associated with diminished food intake, i beg your pardon may bring about nutrient deficiencies (Sahyoun et al, 2003). Chewing mechanically not only makes food less complicated to swallow but likewise increases the surface ar area that is easily accessible to the digestive enzymes, thereby improving chemical digestion.

The term of mastication varies according come the food being chewed: soft foods items require less time in the mouth 보다 denser foods, such together meats or easy cooked vegetables. Chewing involves three phases known as the chewing cycle:

Opening – in i beg your pardon the mandible (lower jaw) is depressed;Closing – in i m sorry the mandible is elevated;Occlusal – as soon as the maxillary (upper)and mandibular (lower) teeth are in contact with each other.

With age, the variety of mastication cycles required to adequately chew a mouthful that food before swallowing the changes; this boosts by around three cycles every 10 years (Peyron et al, 2004). This may be due to a reduced grinding surface area (missing teeth) and/or lessened efficiency and also strength the the muscles associated in mastication.

Salivary glands

The mouth has three pairs of salient glands (Fig 2), every innervated through the parasympathetic branch that the autonomic worried system:

Sublingual glands – located below the tongue;Submandibular glands – located listed below the mandible;Parotid glands – situated to the next of the earlobes.

*

Source: Peter Lamb


The salient glands consistently produce little amounts the saliva to save the mouth moist (basal secretion); in a typical 24-hour period 0.5-1.5L the saliva is secreted. Eating induces a far-ranging increase in saliva production (induced secretion). The submandibular glands do many of the basal secretion and also the parotid glands space the significant contributors to cheap induced by the visibility of food, while the sublingual glands just produce about 5% that both basal and induced saliva cheap (Navazesh and Kumar, 2008). The volume of saliva the is produced can be raised or diminished according t0 the nature that the food.

The outstanding glands develop a glycoprotein referred to as haptocorrin (transcobalamin I), which binds to vitamin B12 to safeguard it native the acidic secretions that the stomach (Morkbak et al, 2007). The movement and also absorption the vitamin B12 in the gut will certainly be explored in part 2, component 4 and component 5.

Saliva is also produced by the serous glands that the uvula, a estimate from the soft palate that avoids food entering the sleep cavity during swallowing (Fig 2).

Saliva

Saliva is an aqueous systems (Carpenter, 2013) consisting of water (99.5%), mucus, bicarbonate ions, two digestive enzymes – amylase and lipase (or lingual lipase) – and also lysozyme. The pH that saliva varies in between 6.2 and also 7.4, through a neutral pH of 7.0 recognised together optimal because that dental health (Baliga et al, 2013). The bicarbonate ion in saliva act together a chemistry buffer, neutralising mountain in the mouth to defend the teeth from erosion. Sugar-free chewing gum can protect the this as it encourages saliva production, which reduces mountain in the mouth.

The cradle enzymes begin the process of chemical digestion. Salivary amylase start digesting carbohydrates, breaking starch (long straight chains of glucose) right into maltose, a disaccharide do of 2 glucose units (Fig 3a). This is why, after having actually been chewed, a piece of white bread might taste sweet. Salient lipase starts digesting fats, break them down right into fatty acids and glycerol (Fig 3b). It attributes optimally in ~ a pH of about 4, so it will not work at that maximal performance until getting to the acidic atmosphere of the stomach (see part 2).

Lysozyme, an enzyme found in most body fluids, is component of the non-specific immune defences and acts together a general antimicrobial, attacking and breaking under bacterial cabinet walls. In the mouth, it starts to death certain varieties of bacteria in food, prior to further sterilisation occurs in the mountain secretions of the stomach.


*


Swallowing

Towards the finish of mastication, the tongue and roof the the mouth gather and also shape the chewed food into a pellet dubbed a bolus. Moisture and also mucus bind and also coat the bolus before it is pushed towards the back of the mouth and also into the oropharynx (anterior part of the throat). As the bolus get the posterior pharyngeal wall, the swallowing reflex (deglutition) is triggered.

Swallowing involves precisely combination muscular contractions. The pharynx walls contract around the bolus, while the epiglottis (a cartilaginous flap-like portion of the larynx) closes end the airway, preventing food indigenous entering the trachea and bronchial tree. The bolus is then funnelled, through the top oesophageal sphincter, right into the oesophagus (Fig 4).


*

Source: Peter Lamb


Common mouth conditions

Oral candidiasis

Candida albicans is a yeast usually living harmlessly ~ above the skin, in the GI tract and also on mucous membranes such together those that the mouth, nose, sinuses and also reproductive tract. However, in specific circumstances it multiplies rapidly, resulting in oral candidiasis (thrush), the most typical oral infection. A common trigger is the usage of broad-spectrum antibiotics, i m sorry wipe the end the ‘friendly’ bacteria, such together lactobacillus, that commonly outcompete, or sluggish the growth of, C. Albicans.

At-risk groups include people with diabetes, in who excess sugar have the right to encourage quick proliferation of C. Albicans, and also patients who space immunosuppressed (Singh et al, 2014). Smoking and xerostomia (see below) are additional risk factors (Singh et al, 2014).

Oral candidiasis manifests as white spots the can progressively extend and also fuse to cover huge regions that the dental cavity and tongue. The affected areas often feel an extremely sore and also swallowing deserve to be difficult and/or painful. Occasionally, dental candidiasis may expand to the oesophagus and also yeast may even enter the bloodstream, resulting in a hazard of sepsis or widespread systemic infection. In most cases, the condition can be fixed using topical antifungal preparations such together nystatin.

Xerostomia and dysphagia

Xerostomia (abnormally dried mouth) is increasingly common with age and often affects human being who breathe through the mouth, together this causes moisture come evaporate. Determinants such as lessened saliva production, insufficient fluid intake, high alcohol consumption and also poorly regulated diabetes can result in, or compound, xerostomia.

Insufficient saliva production is a usual side-effect of countless medications, consisting of diuretics, particular antidepressants, opioids and also many antihypertensives (Bartok, 2011). Xerostomia has been presented to be much more likely in patients who take an ext than 4 prescription drugs every day (Yellowitz and also Schneiderman, 2014). Persistent xerostomia is connected with an boosted risk of dry, cracked and also split lips, dental candidiasis, mouth ulcers and dental caries; the is therefore detrimental to oral health, and also poor oral health and wellness is connected with poorer basic health.

As moisture in the mouth dram a key role in forming and lubricating food boluses, patients with xerostomia may additionally have dysphagia (impaired swallowing), which boosts the danger of aspiration that food into the airways. Dysphagia is report to influence 26.7% of people aged ≥76 years, with those who have neurological disease, heart fail or lung an illness being an especially at threat (Smithard, 2015).

Patients with xerostomia and/or dysphagia need mindful assessment and also will frequently require referral to a speech and also language therapist. The nurse’s duty includes:

Ensuring patients are well hydrated;Maintaining humidity about the bed (particularly in ~ night);Keeping dried and/or crumbly foods items to a minimum.

Medications the stimulate saliva production and also saliva substitutes might need to be taken into consideration (Villa et al, 2014).

The oesophagus

The oesophagus (gullet), approximately 25cm in length, connect the mouth to the stomach via the pharynx (Fig 4). The oesophagus walk not develop digestive enzymes, however it go secrete large amounts that mucus the act together a lubricant, ensuring the smooth transit that the food bolus.

After having actually been swallowed, the food bolus passes with the top oesophageal sphincter (UOS), extending the oesophageal wall and triggering peristalsis (see below). The UOS close the door rapidly and also tightly to prevent regurgitation of food right into the pharynx and mouth. The transit time that food v the oesophagus varies according to components such together age, health and also the nature of the food consumed, but is typically 6-15 seconds (Maurer, 2015).

Once the food bolus reaches the lower part of the oesophagus, the lower oesophageal sphincter (LOS) dilates, permitting it to pass right into the stomach. The LOS (also dubbed the cardiac sphincter due to its proximity come the heart) close the door as shortly as the bolus beginning the superior section of the stomach to stop regurgitation of extremely acidic gastric juices right into the oesophagus. A variety of conditions – because that example, hiatus hernia – deserve to lead to bad closure the the LOS and result in mountain reflux (see part 2).

The oesophagus is the very first portion the the GI street in i beg your pardon the four layers that the gut wall – the mucosa, submucosa, muscularis and also serosa – room recognisable (Fig 5). Each has actually a distinct structure and role.


*

Source: Peter Lamb


Mucosa

The mucosa, the within lining the the gut, is in direct call with the food gift digested. That is a mucous membrane affluent in mucus-producing goblet cells. The mucus they develop lubricates the gut, ensuring the smooth transit of food. It likewise coats the mucosa to safeguard it against digestive enzymes and stomach mountain (which may otherwise erode the gut wall). If mucus production is reduced, this protective barrier may be lost, bring about the formation of ulcers (see part 2 and part 3).

The mucosa is folded so it uses a larger surface area. In regions of the gut wherein nutrients room absorbed, such as the ileum, it has even much more folds and extends right into finger-like projections dubbed villi, i beg your pardon massively rise the surface area. The mucosa additionally has small collections of lymphoid organization (Peyer’s patches) the trap pathogens, helping to keep the gut free from infection (Fig 5).

Submucosa

The submucosa, located immediately below the mucosa, is created of dense, rarely often, rarely connective tissue that is rich in blood vessels, nerves and lymphatic vessels that prolong into the mucosa. It additionally contains mucus-secreting glands, which relax mucus into the gut, adding to the mucus the is secreted through the goblet cell of the mucosa.

Muscularis

The muscularis, the main muscular class of the gut, is composed of two layers of involuntary smooth muscle:

An inner great of circular muscle fibres in concentric rings approximately the gut;An outer layer the longitudinal muscle fibres running along the gut wall.

The muscularis is responsible because that the peristaltic waves that propel food along the GI tract. Peristalsis entails highly coordinated, rhythmic contractions that the circular and longitudinal muscle class of the gut. The waves are motivated by a dense network of autonomic nerve fibres – the myenteric plexus (or Auerbach’s plexus) – i beg your pardon innervates both class of the muscularis. This network, also known together the enteric worried system, is so complex, it is often explained as a ‘second brain’ or ‘gut brain’ (Schneider et al, 2019).

Serosa

The serosa, the external epithelial layer of the gut, is written of a slim layer that collagenous connective organization overlain by a single layer of squamous (thin and flat) epithelial cells. This serous membrane produce a thin, watery secretion (serous fluid) the helps avoid abrasion and friction throughout movement that the body and gut wall.

Common oesophageal conditions

Gastro-oesophageal reflux disease

Most people have experienced the uncomfortable sensation of heartburn the occurs as a an outcome of gastric (acid) reflux. This regularly happens after eating a big meal that overstretches the stomach and forces the LOS come open, or after eat spicy food that irritates the LOS, bring about it to dilate. When gastric reflux i do not care chronic, there is a peril that prolonged exposure come stomach mountain will cause severe and painful inflammation, and also erosion to the mucosal lining the the oesophagus – this is a common condition referred to as gastro-oesophageal reflux disease (GORD).

In addition to leading to heartburn, gastric reflux is connected with regurgitation that gastric secretions into the mouth, possibly damaging the teeth, causing poor breath and also pain or an obstacle when swallowing (NHS Inform, 2019). If untreated or poorly managed, ongoing gastric reflux can lead come the development of oesophageal ulcers, which can make swallowing exceedingly painful.

GORD have the right to be effectively managed using antacids or drugs that block the manufacturing of acid in the stomach, such together histamine (H2) antagonists or proton pump inhibitors. Patients through gastric reflux and/or GORD need to be encouraged to eat smaller, more-frequent meals and also avoid root cause such as spicy foods, fat foods, chocolate and also coffee (NHS, 2017). These basic measures may assist them keep an adequate food intake, if the medications might promote healing.

Barrett’s oesophagus

Continual wake up of the oesophageal mucosa have the right to lead come epithelial cells undergoing abnormal structural alters (metaplasia). Abnormal epithelial cell are easily recognisable under a microscope, as they show up tall and column-shaped together opposed to your normal level (squamous) appearance. Metaplastic changes occur most frequently at the junction between the oesophagus and stomach, and also are usually figured out during endoscopy (Graham et al, 2016).

The existence of this abnormal cells is dubbed Barrett’s oesophagus and also patients v the condition are at greater risk that oesophageal cancer; 1-5% of people with Barrett’s oesophagus develop oesophageal cancer (Cancer research study UK, 2016a). Patients require mindful monitoring and management of gastric reflux symptoms.

Oesophageal cancer

Oesophageal cancer accounts for approximately 3% of cancers in the UK; that is most commonly diagnosed in civilization in your 60s and 70s, guys being at better risk 보다 women. Various other risk components are obesity, high alcohol consumption, smoking, GORD and Barrett’s oesophagus (NHS, 2016).

See more: Is Jennifer Carpenter Related To Karen Carpenter, Jennifer Carpenter Anorexia

Many civilization do not experience symptoms until the disease is progressed and tumour masses begin to interfere v food transit. Common symptoms include dysphagia, regurgitation, pain, heartburn and weight lose (NHS, 2016). Although treatments for oesophageal cancer have improved, the outlook for those v advanced condition is poor, v only roughly 4% surviving for ≥5 years (CRUK, 2016b).