Human digestive system

Dental caries

Digestive system disease
The debris is colonized by bacteria and causes foul breath halitosis. Do I need to revert to Realplayer 14, or 13? Read More on This Topic. Try doing a clean REinstall of RealPlayer. They also produce normal droppings, which are not eaten. When the pyloric sphincter valve opens, chyme enters the duodenum where it mixes with digestive enzymes from the pancreas and bile juice from the liver and then passes through the small intestine , in which digestion continues.

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Other tonsillar tissue in the upper part of the pharynx and at the root of the tongue may be similarly involved. In diphtheritic pharyngitis, the membranous exudate is more diffuse than in other types of pharyngitis, it is tougher, and it extends over a much larger part of the mucous membrane of the mouth and nose. One of the complications of tonsillitis or pharyngitis may be a peritonsillar abscess , also called quinsy, adjacent to one tonsil; this appears as an extremely painful bulging of the mucosa in the area.

Surgical incision and draining are sometimes necessary if antibiotics are not given promptly. Cleft lip , also known as harelip, is a congenital deformity in which the central to medial lip fails to fuse properly, resulting in a fissure in the lip beneath the nostrils. Other disorders are related to an abnormal position of the teeth and the jaws, resulting in inefficient chewing , and to the absence of one or more of the salivary glands, which may lessen the amount and quality of saliva that they produce.

Neurological defects that provide inadequate stimulation to the muscles of the tongue and the pharynx can seriously impair chewing and even swallowing. Sensory-innervation defects may not allow the usual reflexes to mesh smoothly, or they may permit harmful ingestants to pass by undetected. The secretion of saliva is markedly diminished in states of anxiety and depression.

The consequent dry mouth interferes with speech, which becomes thick and indistinct. In the absence of the cleansing action of saliva, food debris persists in the mouth and stagnates, especially around the base of the teeth.

The debris is colonized by bacteria and causes foul breath halitosis. In the absence of saliva, swallowing is impeded by the lack of lubrication for the chewing of food that is necessary to form a bolus. The condition is aggravated in states of anxiety and depression when drugs that have an anticholinergic-like activity such as amitriptyline are prescribed, because they further depress the production of saliva.

The salivary glands are severely damaged and atrophy in a number of autoimmune disorders such as Sjögren disease and systemic lupus erythematosus.

The damage occurs partly by the formation of immune complexes antigen-antibody associations , which are precipitated in the gland and initiate the destruction. In these circumstances, the loss of saliva is permanent. As some of the salivary glands retain their function, they may be stimulated by chewing gum and by a parasympathomimetic agent such as bethanecol.

The production of saliva may be also impaired by infiltration of the salivary glands by pathological lymphocytes, such as in leukemias and lymphomas. In the early stages of these diseases, the glands swell and become painful. Excessive production of saliva may be apparent in conditions interfering with swallowing, as in Parkinson disease , or in pseudobulbar paralysis from blockage of small arteries to the midbrain regions. True salivary hypersecretion is seen in poisoning due to lead or mercury used in certain industrial processes and as a secondary response to painful conditions in the mouth, such as aphthous stomatitis certain ulcers of the oral mucosa and advanced dental caries.

Acute and painful swelling of salivary glands develops when salivary secretion is stimulated by the sight, smell, and taste of food but saliva is prohibited from flowing through an obstructed salivary duct.

Swelling and pain subside between meals. Diagnosis can be confirmed by X ray. Persistent swellings may be due to infiltration by benign or malignant tumours or to infiltration by abnormal white blood cells, as in leukemia.

The most common cause of acute salivary swelling is mumps. Difficulty in swallowing dysphagia may be the only symptom of a disorder of the esophagus. Sometimes dysphagia is accompanied by pain odynophagia , or pain may occur spontaneously without swallowing being involved. The esophagus does nothing to alter the physical or chemical composition of the material it receives, and it is poorly equipped to reject materials that have got past the intricate sensors of the mouth and throat.

Consequently, it is vulnerable to mucosal injury from ingestants as well as to materials that reflux into its lower segment from the stomach. Although the esophageal muscle coats are thick, the esophagus is not protected with a covering of serous membrane, as are neighbouring organs in the chest.

Congenital defects of the esophagus are most often seen in infancy, primarily as a failure to develop normal passageways. Infants born with openings between the esophagus and trachea cannot survive without early surgery. The lower end of the esophagus is subject to various developmental abnormalities that shorten the organ so that the stomach is pulled up into the thoracic cavity.

Abnormalities of the diaphragm may contribute to a similiar outcome. Inflammatory disorders of the esophagus result from a variety of causes, from the ingestion of noxious materials, the lodgment of foreign bodies, to a complex of events associated with reflux of gastric contents from the stomach into the lower esophagus. Inflammation resulting from surface injury by caustic substances is called corrosive esophagitis. When the problem is associated with reflux, the term peptic esophagitis is applied to inflammation involving both the mucous membrane and the submucosal layer.

A number of other diseases may cause inflammation of the esophagus, e. Fibrous scar tissue contracts over time. Consequently, when fibrous tissue develops around a tube, as in the esophagus, in response to inflammation, the contracting scar narrows the lumen, causing a stricture, and may eventually obstruct it completely.

Strictures are readily diagnosed by X ray or esophagoscope. Dysphagia is characterized by difficulty in swallowing caused by lesions, failure to transport a bolus through the esophagus, or mechanical obstruction by stricture, tumours, or foreign bodies in the esophagus. The neural arc of swallowing involves the medulla of the brain stem , the vagus 10th cranial nerves, and the glossopharyngeal, trigeminal, and facial nerves.

Consequently, dysphagia may also result from interference with the function of any part of this pathway. Thus, it occurs commonly, but usually transiently, in strokes. Dysphagia may be prominent in degenerative diseases of the central nervous system , especially of the ganglia at the base of the brain. In these circumstances, the behaviour of the smooth muscle of the pharynx and the upper esophageal sphincter is disturbed.

Most individuals can locate the site of dysphagia and the distribution of the pain with accuracy. A sense of food sticking or of pain on swallowing, however, may be felt to be in the throat or upper sternum when the obstruction or disease is in fact at the lower end of the esophagus.

The sensation may result from gastroesophageal reflux or from drying of the throat associated with anxiety or grief. Treatment is directed toward the cause of the disorder.

The nerves conveying the sense of pain from the esophagus pass through the sympathetic system in the same spinal cord segments as those that convey pain sensations from the muscle and tissue coverings of the heart. As a result, episodes of pain arising from the esophagus as a result of muscle spasm or transient obstruction by a medicine tablet or other object may be experienced in the chest and posterior thorax and radiate to the arms. This pain thus mimics pain of cardiac origin angina. The pain due to transient obstruction may be felt not only in the chest but also, through radiation to the back, between the shoulder blades.

It is very similar to pain from gallstones ; attacks last 10 to 30 minutes. In middle-aged and elderly persons, spontaneous and diffuse spasm of the smooth muscle of the esophagus causes considerable discomfort as well as episodes of dysphagia. The appearance of the esophagus seen on an X-ray screen while a barium bolus is swallowed resembles that of the outline of a corkscrew because of the multiple synchronized contractions at different levels of the spirally arranged smooth muscle.

The pain of esophageal spasm may be relieved by medications that relieve cardiac angina, especially nitroglycerin or nifedipine. Disorders of the motility of the esophagus tend to be either caused by or aggravated during times of stress.

Eating rapidly is another trigger, as this demands more precise and rapid changes in muscle activity than eating slowly. Achalasia , formerly called cardiospasm, is a primary disturbance in the peristaltic action of the esophagus that results in failure to empty the organ of its contents. The lower sphincteric portion of the esophagus does not receive its normal signal to relax and, over time, may become hypertonic, resisting stretching.

A cycle occurs in which the main portion of the esophagus slowly becomes distended, holding a column of fluid and food that it cannot propel downward to a lower esophageal sphincter that stays closed because of a failure in its neural system. In most persons with this disorder, there is a shortage or disease of ganglion cells of the myenteric plexus Auerbach plexus , or a disease of the network of nerves within the muscles of the esophagus, so that coordinated peristalsis becomes impossible.

In Chagas disease , parasites called trypanosomes invade the neural tissue and directly destroy ganglion cells. These organisms are not present in the temperate zones of the world, however, and the reason for ganglion cell degeneration in achalasia is generally unknown.

Effective treatment is achieved by destroying the ability of the lower esophageal sphincter of the esophagus to contract. This may be done by forcible dilatation, using a balloon, of the esophagus in the area that is tonically contracted.

The objective is to rupture the circular muscle at the site, and this is generally achieved with one or two dilatations. If this fails to overcome the contraction or if the contraction recurs, surgery is required that involves opening the abdomen and cutting through the circular muscles from the outside of the esophagus.

The disadvantage of both methods of treatment is that the anti-reflux mechanism is thereby destroyed. Consequently, if precautions are not taken, the individual may lose the symptoms and risks of achalasia but may develop the symptoms and signs of reflux peptic esophagitis.

In healthy individuals, reflux of gastric contents into the esophagus occurs occasionally. This causes the burning sensation behind the sternum that is known as heartburn.

Some of the refluxed material may reach the pharynx where it also may be felt as a burning sensation. Reflux is most likely to occur after large meals, especially if physical activity , including bending, stooping, or lifting, is involved.

In these circumstances, the esophagus responds with peristaltic waves that sweep the gastric contents back into the stomach, with relief of the heartburn. Persistent reflux symptoms are invariably due to inadequate functioning of the anatomical components, such as the lower esophageal sphincter, which keep the contents of the stomach below the diaphragm, delayed esophageal clearance of the refluxed material, and delayed emptying of the stomach.

The disorder can also be caused by obesity. Excessive fat on the trunk is almost always accompanied by large deposits of fat within the abdomen, especially in the mesentery the curtainlike structure on which most of the intestine is hung. Consequently, when intra-abdominal pressure is increased, such as in physical activity, there is insufficient room within the abdomen to accommodate the displacement of the organs, and the resulting pressure forces the stomach upward. The weak point is the centre of the diaphragm at the opening hiatus through which the esophagus passes to join the stomach.

The upper portion of the stomach is pushed through the hiatus, and the distortion of the position of the organs brings about impaired functioning of the anti-reflux mechanisms.

In the early stages the stomach may slide back into the abdomen when the increase in the intra-abdominal pressure eases, but eventually, if the circumstances are unchanged, the upper part remains above the diaphragm.

A common contributory cause of gastroesophageal reflux in women is pregnancy. As the uterus containing the developing fetus comes to occupy a large part of the abdomen, the effect is the same as in obesity. Because gravity is the only force that keeps the gastric contents within the stomach, if a hernia develops, the reflux and the symptoms from it will promptly occur when the individual lies down.

Persisting reflux of gastric contents with acid and digesting enzymes leads to chemical inflammation of the lining of the esophagus and ultimately to peptic ulceration. If inadequately treated, the process leads to submucosal fibrosis and stricturing, and, besides the symptoms of heartburn and regurgitation, the patient experiences pain on eating and swallowing.

The treatment of peptic reflux esophagitis includes losing weight, avoiding acidic and fatty foods and beverages, remaining upright for two to three hours after meals, giving up smoking, and raising the head of the bed high enough to discourage nocturnal gastroesophageal reflux.

Antacids are effective, as are medications that reduce the secretion of acid by the stomach, such as histamine receptor antagonists and proton pump inhibitors. If a stricture has formed, it can be dilated easily. If the disorder is not overcome with these conservative measures, surgical repair is performed through either the chest or the abdomen.

Some individuals with severe peptic reflux esophagitis develop Barrett esophagus , a condition in which the damaged lining of the esophagus is relined with columnar cells. These cells are similar to those lining the upper part of the stomach and are not the usual squamous cells that line the esophageal mucosa. In some persons in whom this transformation occurs, a carcinoma develops some 10 to 20 years later. The decision as to the treatment of a hiatal hernia by conservative means or by surgery is influenced by such factors as age, occupation, and the likelihood of compliance with a strict regimen.

There is a much less common form of hiatal hernia, called a paraesophageal hernia, in which the greater curvature of the stomach is pushed up into the thorax while the esophagogastric junction remains intact below the diaphragm. Such individuals experience dysphagia caused by compression of the lower esophagus by the part of the stomach that has rolled up against it. This rarer form of hernia is more dangerous, often being complicated by hemorrhage or ulceration, and requires relief by surgery.

Pouches in the walls of the structures in the digestive system that occur wherever weak spots exist between adjacent muscle layers are called diverticula. In the upper esophagus, diverticula may occur in the area where the striated constrictor muscles of the pharynx merge with the smooth muscle of the esophagus just below the larynx. Some males over 50 years of age show protrusion of a small sac of pharyngeal mucous membrane through the space between these muscles.

As aging continues, or if there is motor disturbance in the area, this sac may become distended and may fill with food or saliva. It usually projects to the left of the midline, and its presence may become known by the bubbling and crunching sounds produced during eating. Often the patient can feel it in the left side of the neck as a lump, which can be reduced by pressure of the finger. Sometimes the sac may get so large that it compresses the esophagus adjacent to it, producing a true obstruction.

Treatment is by surgery. Small diverticula just above the diaphragm sometimes are found after the introduction of surgical instruments into the esophagus. Boerhaave syndrome is a rare spontaneous rupture to the esophagus. It can occur in patients who have been vomiting or retching and in debilitated elderly persons with chronic lung disease.

Emergency surgical repair of the perforation is required. A rupture of this type confined to the mucosa only at the junction of the linings of the esophagus and stomach is called a Mallory-Weiss lesion. At this site, the mucosa is firmly tethered to the underlying structures and, when repeated retching occurs, this part of the lining is unable to slide and suffers a tear.

The tear leads to immediate pain beneath the lower end of the sternum and bleeding that is often severe enough to require a transfusion. The circumstances preceding the event are commonly the consumption of a large quantity of alcohol followed by eating and then vomiting.

The largest group of individuals affected are alcoholic men. Diagnosis is determined with an endoscope. Most tears spontaneously stop bleeding and heal over the course of some days without treatment.

If transfusion does not correct blood loss, surgical suture of the tear may be necessary. An alternative to surgery is the use of the drug vasopressin, which shuts down the blood vessels that supply the mucosa in the region of the tear. Esophageal tumours may be benign or malignant. Generally, benign tumours originate in the submucosal tissues and principally are leiomyomas tumours composed of smooth muscle tissue or lipomas tumours composed of adipose, or fat, tissues.

Malignant tumours are either epidermal cancers, made up of unorganized aggregates of cells, or adenocarcinomas, in which there are glandlike formations. In adult doves and pigeons, the crop can produce crop milk to feed newly hatched birds.

Certain insects may have a crop or enlarged esophagus. Herbivores have evolved cecums or an abomasum in the case of ruminants. Ruminants have a fore-stomach with four chambers. These are the rumen , reticulum , omasum , and abomasum.

In the first two chambers, the rumen and the reticulum, the food is mixed with saliva and separates into layers of solid and liquid material.

Solids clump together to form the cud or bolus. The cud is then regurgitated, chewed slowly to completely mix it with saliva and to break down the particle size. Fibre, especially cellulose and hemi-cellulose , is primarily broken down into the volatile fatty acids , acetic acid , propionic acid and butyric acid in these chambers the reticulo-rumen by microbes: In the omasum, water and many of the inorganic mineral elements are absorbed into the blood stream.

The abomasum is the fourth and final stomach compartment in ruminants. It is a close equivalent of a monogastric stomach e. It serves primarily as a site for acid hydrolysis of microbial and dietary protein, preparing these protein sources for further digestion and absorption in the small intestine.

Digesta is finally moved into the small intestine, where the digestion and absorption of nutrients occurs. Microbes produced in the reticulo-rumen are also digested in the small intestine.

Regurgitation has been mentioned above under abomasum and crop, referring to crop milk, a secretion from the lining of the crop of pigeons and doves with which the parents feed their young by regurgitation. Many sharks have the ability to turn their stomachs inside out and evert it out of their mouths in order to get rid of unwanted contents perhaps developed as a way to reduce exposure to toxins. Other animals, such as rabbits and rodents , practise coprophagia behaviours — eating specialised faeces in order to re-digest food, especially in the case of roughage.

Capybara, rabbits, hamsters and other related species do not have a complex digestive system as do, for example, ruminants. Instead they extract more nutrition from grass by giving their food a second pass through the gut. Soft faecal pellets of partially digested food are excreted and generally consumed immediately.

They also produce normal droppings, which are not eaten. Young elephants, pandas, koalas, and hippos eat the faeces of their mother, probably to obtain the bacteria required to properly digest vegetation. When they are born, their intestines do not contain these bacteria they are completely sterile. Without them, they would be unable to get any nutritional value from many plant components.

An earthworm 's digestive system consists of a mouth , pharynx , esophagus , crop , gizzard , and intestine.

The mouth is surrounded by strong lips, which act like a hand to grab pieces of dead grass, leaves, and weeds, with bits of soil to help chew. The lips break the food down into smaller pieces. In the pharynx, the food is lubricated by mucus secretions for easier passage. The esophagus adds calcium carbonate to neutralize the acids formed by food matter decay. Temporary storage occurs in the crop where food and calcium carbonate are mixed. The powerful muscles of the gizzard churn and mix the mass of food and dirt.

When the churning is complete, the glands in the walls of the gizzard add enzymes to the thick paste, which helps chemically breakdown the organic matter. By peristalsis , the mixture is sent to the intestine where friendly bacteria continue chemical breakdown.

This releases carbohydrates, protein, fat, and various vitamins and minerals for absorption into the body. In most vertebrates , digestion is a multistage process in the digestive system, starting from ingestion of raw materials, most often other organisms.

Ingestion usually involves some type of mechanical and chemical processing. Digestion is separated into four steps:. Underlying the process is muscle movement throughout the system through swallowing and peristalsis. Each step in digestion requires energy, and thus imposes an "overhead charge" on the energy made available from absorbed substances. Differences in that overhead cost are important influences on lifestyle, behavior, and even physical structures.

Examples may be seen in humans, who differ considerably from other hominids lack of hair, smaller jaws and musculature, different dentition, length of intestines, cooking, etc.

The major part of digestion takes place in the small intestine. The large intestine primarily serves as a site for fermentation of indigestible matter by gut bacteria and for resorption of water from digests before excretion. In mammals , preparation for digestion begins with the cephalic phase in which saliva is produced in the mouth and digestive enzymes are produced in the stomach. Mechanical and chemical digestion begin in the mouth where food is chewed , and mixed with saliva to begin enzymatic processing of starches.

The stomach continues to break food down mechanically and chemically through churning and mixing with both acids and enzymes. Absorption occurs in the stomach and gastrointestinal tract , and the process finishes with defecation.

The human gastrointestinal tract is around 9 meters long. Food digestion physiology varies between individuals and upon other factors such as the characteristics of the food and size of the meal, and the process of digestion normally takes between 24 and 72 hours. Digestion begins in the mouth with the secretion of saliva and its digestive enzymes. Food is formed into a bolus by the mechanical mastication and swallowed into the esophagus from where it enters the stomach through the action of peristalsis.

Gastric juice contains hydrochloric acid and pepsin which would damage the walls of the stomach and mucus is secreted for protection. In the stomach further release of enzymes break down the food further and this is combined with the churning action of the stomach. The partially digested food enters the duodenum as a thick semi-liquid chyme.

In the small intestine, the larger part of digestion takes place and this is helped by the secretions of bile , pancreatic juice and intestinal juice.

The intestinal walls are lined with villi , and their epithelial cells is covered with numerous microvilli to improve the absorption of nutrients by increasing the surface area of the intestine. In the large intestine the passage of food is slower to enable fermentation by the gut flora to take place.

Here water is absorbed and waste material stored as feces to be removed by defecation via the anal canal and anus. Different phases of digestion take place including: The cephalic phase occurs at the sight, thought and smell of food, which stimulate the cerebral cortex.

Taste and smell stimuli are sent to the hypothalamus and medulla oblongata. After this it is routed through the vagus nerve and release of acetylcholine. Acidity in the stomach is not buffered by food at this point and thus acts to inhibit parietal secretes acid and G cell secretes gastrin activity via D cell secretion of somatostatin. The gastric phase takes 3 to 4 hours. It is stimulated by distension of the stomach, presence of food in stomach and decrease in pH.

Distention activates long and myenteric reflexes. This activates the release of acetylcholine , which stimulates the release of more gastric juices. As protein enters the stomach, it binds to hydrogen ions, which raises the pH of the stomach. Inhibition of gastrin and gastric acid secretion is lifted.

This triggers G cells to release gastrin , which in turn stimulates parietal cells to secrete gastric acid. Gastric acid is about 0. Acid release is also triggered by acetylcholine and histamine.

The intestinal phase has two parts, the excitatory and the inhibitory. Partially digested food fills the duodenum. This triggers intestinal gastrin to be released. Enterogastric reflex inhibits vagal nuclei, activating sympathetic fibers causing the pyloric sphincter to tighten to prevent more food from entering, and inhibits local reflexes.

Protein digestion occurs in the stomach and duodenum in which 3 main enzymes, pepsin secreted by the stomach and trypsin and chymotrypsin secreted by the pancreas, break down food proteins into polypeptides that are then broken down by various exopeptidases and dipeptidases into amino acids.

The digestive enzymes however are mostly secreted as their inactive precursors, the zymogens. For example, trypsin is secreted by pancreas in the form of trypsinogen , which is activated in the duodenum by enterokinase to form trypsin.

Trypsin then cleaves proteins to smaller polypeptides. Digestion of some fats can begin in the mouth where lingual lipase breaks down some short chain lipids into diglycerides. However fats are mainly digested in the small intestine. In humans, dietary starches are composed of glucose units arranged in long chains called amylose, a polysaccharide.

During digestion, bonds between glucose molecules are broken by salivary and pancreatic amylase , resulting in progressively smaller chains of glucose. This results in simple sugars glucose and maltose 2 glucose molecules that can be absorbed by the small intestine. Lactase is an enzyme that breaks down the disaccharide lactose to its component parts, glucose and galactose. Glucose and galactose can be absorbed by the small intestine. Approximately 65 percent of the adult population produce only small amounts of lactase and are unable to eat unfermented milk-based foods.

This is commonly known as lactose intolerance. Lactose intolerance varies widely by ethnic heritage; more than 90 percent of peoples of east Asian descent are lactose intolerant, in contrast to about 5 percent of people of northern European descent.

Sucrase is an enzyme that breaks down the disaccharide sucrose , commonly known as table sugar, cane sugar, or beet sugar. Sucrose digestion yields the sugars fructose and glucose which are readily absorbed by the small intestine. Some nutrients are complex molecules for example vitamin B 12 which would be destroyed if they were broken down into their functional groups.

To digest vitamin B 12 non-destructively, haptocorrin in saliva strongly binds and protects the B 12 molecules from stomach acid as they enter the stomach and are cleaved from their protein complexes. After the B 12 -haptocorrin complexes pass from the stomach via the pylorus to the duodenum, pancreatic proteases cleave haptocorrin from the B 12 molecules which rebind to intrinsic factor IF. These B 12 -IF complexes travel to the ileum portion of the small intestine where cubilin receptors enable assimilation and circulation of B 12 -IF complexes in the blood.

There are at least five hormones that aid and regulate the digestive system in mammals. There are variations across the vertebrates, as for instance in birds. Arrangements are complex and additional details are regularly discovered. For instance, more connections to metabolic control largely the glucose-insulin system have been uncovered in recent years.

Digestion is a complex process controlled by several factors. In the mouth, pharynx and esophagus, pH is typically about 6. Saliva controls pH in this region of the digestive tract.

Salivary amylase is contained in saliva and starts the breakdown of carbohydrates into monosaccharides. Most digestive enzymes are sensitive to pH and will denature in a high or low pH environment. The stomach's high acidity inhibits the breakdown of carbohydrates within it. This acidity confers two benefits: In the small intestines, the duodenum provides critical pH balancing to activate digestive enzymes. The liver secretes bile into the duodenum to neutralize the acidic conditions from the stomach, and the pancreatic duct empties into the duodenum, adding bicarbonate to neutralize the acidic chyme , thus creating a neutral environment.

The mucosal tissue of the small intestines is alkaline with a pH of about 8.

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