DIGESTION IN ORAL CAVITY AND STOMACH
Many people spend a third of their time consciously trying to control how to get food into their digestive tracts and another third thinking about how that food is doing when it gets into their digestive tracts and another third of their time consciously trying to control how to get their food intake out of their digestive tracts. However, once food is swallowed, the conscious ability to control the passage of food is almost completely lost. When the food reaches the point of elimination some conscious control is again reestablished in the digestive system. The gastrointestinal track or as people call it, the digestive system, has the main purpose of break down food, both solid and fluid into sustenance for the various tissues and systems in the body. A normal digestive tract squeezes the utmost benefit from what it eats. Feces are the products left over when the body has selected everything that is of use from the food that has been eaten.The digestive system distance ranges from the mouth to the bottom of the trunk, which when we look at it, seems like no more than two or three feet, but is really about
From the moment the three main types of food-carbohydrates, fats and proteins-enter the mouth, they are exposed to chemical and mechanical actions that begin to break them apart so that they can be absorbed through the intestinal walls into the circulatory system.
Taste Receptors A very large number of molecules elicit taste sensations through a rather small number of taste receptors. Furthermore, it appears that individual taste receptor cells bear receptors for one type of taste. In other words, within a taste bud, some taste receptor cells sense sweet, while others have receptors for bitter, sour, salty and umami tastes. Much of this understanding of taste receptors has derived from behavioral studies with mice engineered to lack one or more taste receptors.
The pleasant tastes (sweet and umami) are mediated by a family of three T1R receptors that assemble in pairs. Diverse molecules that lead to a sensation of sweet bind to a receptor formed from T1R2 and T1R3 subunits. Cats have a deletion in the gene for T1R2, explaining their non-responsiveness to sweet tastes. Also, mice engineered to express the human T1R2 protein have a human-like response to different sweet tastes. The receptor formed as a complex of T1R1 and T1R3 binds L-glutamate and L-amino acids, resulting the umami taste.
The bitter taste results from binding of diverse molecules to a family of about 30 T2R receptors. Sour tasting itself involves activation of a type of TRP (transient receptor potential) channel. Surprisingly, the molecular mechanisms of salt taste reception are poorly characterized relative to the other tastes.
Taste is a chemical sense which is detected by special structures called taste buds, of which we all have about 10,000, mainly on the tongue with a few at the back of the throat and on the palate. Taste buds surround pores within the protuberances on the tongue’s surface and elsewhere. There are four types of taste buds: these are sensitive to sweet, salty, sour and bitter chemicals. All tastes are formed from a mixture of these basic elements.
Many different tastes can be distinguished because of the combination of taste and the more discriminating sense of smell. The sense of smell is estimated to be about 10,000 times more sensitive than the sense of taste. The two senses are very closely related. It is usually correct to say that one smells more flavours than one tastes. When the nose fails, from a bad cold for instance, 80% of the taste ability is lost. Loss of taste without loss of smell is pretty rare, but “dry mouth” can contribute because taste buds can only detect flavour when food is dissolved in saliva. Taste can also be lost as a result of damage to the taste buds themselves or damage to the cranial nerves that carry taste sensations to the brain. Full sensory appreciation of food also involves its appearance, its consistency, and its temperature.
The picture of the tongue shows the areas where different types of taste are detected.
Green represents the area where sweet taste is interpreted.Blue interprets salty tastes. Red detects sour tastes and yellow picks out the bitter tastes.
Observation of the Tongue Observation of the tongue, also known as tongue diagnosis, is an important procedure in diagnosis by inspection. It provides primary information for the Chinese physicians to make diagnosis.
Physiology of the tongue. The tongue directly or indirectly connects with many zang – fu organs through the meridians and collaterals. The deep branch of Heart Meridian of Hand – Shaoyin goes to the root of the tongue ; the Spleen Meridian of Foot – Taiyin traverses the root of the tongue and spreads over its lower surface ; the Kidney Meridian of Foot – Shaoyin terminates at the root of the tongue. So the essential qi of the zang – fu organs can go upward to nourish the tongue, and pathological changes of the zang – fu organs can be reflected by changes in tongue conditions. This is why the observation of the tongue can determine the pathological changes of the internal organs.
1. Heart and lung
2. Spleen and Stomach
3. Kidney
4. Liver and gallbladder
Observation of the tongue includes the tongue proper and its coating. The tongue proper refers to the muscular tissue of the tongue, which is also known as the tongue body. The tongue coating refers to a layer of ” moss ” over the tongue surface, which is produced by the stomach qi. A normal tongue is of proper size, soft in quality, free in motion, slightly red in color and with a thin layer of white coating which is neither dry nor over moist.
The tongue is divided into four areas, namely, tip, central part, root and border. The tip of the tongue often reveals the pathological changes of the heart and lung ; its border reveals those of the liver and gallbladder ; its central part reveals those of the spleen and stomach ; and its root reveals those of the kidney. This method of diagnosing the pathological changes of the zang – fu organs by dividing the tongue into corresponding areas is clinically significant.
Function Saliva keeps the mouth and other parts of the digestive system moist.
Saliva also helps break down carbohydrates (with salivary amylase, formerly known as ptyalin) and lubricates the passage of food down from the oropharynx to the stomach.
Saliva also has elements that help to neutralise the acid responsible for tooth decay; this is called buffer action (antacid).
The antibacterial properties within saliva help to sustain a neutral balance and prevent the development of germs.
A summary is provided in the following table.
Salivary glands are innervated by the parasympathetic and sympathetic branches of the autonomic nervous system.
Histology
The glands are enclosed in a capsule of connective tissue and internally divided into lobules. Blood vessels and nerves enter the glands at the hilum and gradually branch out into the lobules.
There are 3 main types of cells that are found in the major salivary glands:
1. Serous cells, which are pyramidal in shape and are joined to usually form a spherical mass of cells called acinus, with a small lumen in the centre. Serous demilunes are found in the submandibular gland.
2. Mucous cells are usually cuboid in shape and organised as tubules, consisting of cylindrical arrays of secretory cells surrounding a lumen. These cells produce glycoproteins that are used for the moistening and lubricating functions of saliva.
3. Myoepithelial cells surround each secretory portion and are able to contract to accelerate secretion of the saliva.
In the duct system, the lumens formed by the secretory cells empty into intercalated ducts, which in turn join to form striated ducts. These drain into ducts situated between the lobes of the gland (called interlobar ducts or excretory ducts).
The main duct of the salivary glands ultimately empties into the mouth.
Salivary glands are innervated, either directly or indirectly, by the parasympathetic and sympathetic arms of the autonomic nervous system.
· Parasympathetic innervation to the salivary glands is carried via cranial nerves. The parotid gland receives its parasympathetic input from the glossopharyngeal nerve (CN IX) via the otic ganglion, while the submandibular and sublingual glands receive their parasympathetic input from the facial nerve (CN VII) via the submandibular ganglion.
· The sympathetic nervous system affects salivary gland secretions indirectly by innervating the blood vessels that supply the glands.
Digestion begins in the mouth. A brain reflex triggers the flow of saliva when we see or even think about food. Saliva moistens the food while the teeth chew it up and make it easier to swallow. Amylase, which is the digestive enzyme found in saliva, starts to break down starch into simpler sugars before the food even leaves the mouth. The nervous pathway involved in salivary excretion requires stimulation of receptors in the mouth, sensory impulses to the brain stem, and parasympathetic impulses to salivary glands.
Swallowing your food happens when the muscles in your tongue and mouth move the food into your pharynx. The pharynx, which is the passageway for food and air, is about five inches (5″) long. A small flap of skin called the epiglottis closes over the pharynx to prevent food from entering the trachea and thus choking. For swallowing to happen correctly a combination of 25 muscles must all work together at the same time. Salivary glands also produce an estimated three liters of saliva per day.
The esophagus (also spelled oesophagus/esophagus) or gullet is the muscular tube in vertebrates through which ingested food passes from the throat to the stomach. The esophagus is continuous with the laryngeal part of the pharynx at the level of the C6 vertebra. It connects the pharynx, which is the body cavity that is common to both the digestive and respiratory systems behind the mouth, with the stomach, where the second stage of digestion is initiated (the first stage is in the mouth with teeth and tongue masticating food and mixing it with saliva).
After passing through the throat, the food moves into the esophagus and is pushed down into the stomach by the process of peristalsis(involuntary wavelike muscle contractions along the G.I. tract). At the end of the esophagus there is a sphincter that allows food into the stomach then closes back up so the food cannot travel back up into the esophagus.
Histology
The esophagus is lined with mucus membranes, and uses peristaltic action to move swallowed food down to the stomach.
The esophagus is lined by a stratified squamous epithelium, which is rapidly turned over, and serves a protective effect due to the high volume transit of food, saliva, and mucus into the stomach. The lamina propria of the esophagus is sparse. The mucus secreting glands are located in the submucosa, and are connective structures called papillae.
The muscularis propria of the esophagus consists of striated muscle in the upper third (superior) part of the esophagus. The middle third consists of a combination of smooth muscle and striated muscle, and the bottom (inferior) third is only smooth muscle. The distal end of the esophagus is slightly narrowed because of the thickened circular muscles. This part of the esophagus is called the lower esophageal sphincter. This aids in keeping food down and not being regurgitated.
The esophagus has a rich lymphatic drainage as well.
he stomach is a thick walled organ that lies between the esophagus and the first part of the small intestine (the duodenum). It is on the left side of the abdominal cavity, the fundus of the stomach lying against the diaphragm. Lying beneath the stomach is the pancreas. The greater omentum hangs from the greater curvature.
A mucous membrane lines the stomach which contains glands (with chief cells) that secrete gastric juices, up to three quarts of this digestive fluid is produced daily. The gastric glands begin secreting before food enters the stomach due to the parasympathetic impulses of the vagus nerve, making the stomach also a storage vat for that acid.
The secretion of gastric juices occurs in three phases: cephalic, gastric, and intestinal. The cephalic phase is activated by the smell and taste of food and swallowing. The gastric phase is activated by the chemical effects of food and the distension of the stomach. The intestinal phase blocks the effect of the cephalic and gastric phases. Gastric juice also contains an enzyme named pepsin, which digests proteins, hydrochloric acid and mucus. Hydrochloric acid causes the stomach to maintain a pH of about 2, which helps kill off bacteria that comes into the digestive system via food.
The gastric juice is highly acidic with a pH of 1-3. It may cause or compound damage to the stomach wall or its layer of mucus, causing a peptic ulcer. On the inside of the stomach there are folds of skin call the gastric rugae. Gastric rugae make the stomach very extendable, especially after a very big meal.
The stomach is divided into four sections, each of which has different cells and functions. The sections are: 1) Cardiac region, where the contents of the esophagus empty into the stomach, 2) Fundus, formed by the upper curvature of the organ, 3) Body, the main central region, and 4) Pylorus or atrium, the lower section of the organ that facilitates emptying the contents into the small intestine. Two smooth muscle valves, or sphincters, keep the contents of the stomach contained. They are the: 1) Cardiac or esophageal sphincter, dividing the tract above, and 2) Pyloric sphincter, dividing the stomach from the small intestine.
After receiving the bolus (chewed food) the process of peristalsis is started; mixed and churned with gastric juices the bolus is transformed into a semi-liquid substance called chyme. Stomach muscles mix up the food with enzymes and acids to make smaller digestible pieces. The pyloric sphincter, a walnut shaped muscular tube at the stomach outlet, keeps chyme in the stomach until it reaches the right consistency to pass into the small intestine. The food leaves the stomach in small squirts rather than all at once.
Water, alcohol, salt, and simple sugars can be absorbed directly through the stomach wall. However, most substances in our food need a little more digestion and must travel into the intestines before they can be absorbed. When the stomach is empty it is about the size of one fifth of a cup of fluid. When stretched and expanded, it can hold up to eight cups of food after a big meal.
Gastric Glands There are many different gastric glands and they secret many different chemicals. Parietal cells secrete hydrochloric acid and intrinsic factor; chief cells secrete pepsinogen; goblet cells secrete mucus; argentaffin cells secrete serotonin and histamine; and G cells secrete the hormone gastrin.
Disorders of the Stomach Disorders of the stomach are common. There can be a lot of different causes with a variety of symptoms. The strength of the inner lining of the stomach needs a careful balance of acid and mucus. If there is not enough mucus in the stomach, ulcers, abdominal pain, indigestion, heartburn, nausea and vomiting could all be caused by the extra acid.
Erosions, ulcers, and tumors can cause bleeding. When blood is in the stomach it starts the digestive process and turns black. When this happens, the person can have black stool or vomit. Some ulcers can bleed very slowly so the person won’t recognize the loss of blood. Over time, the iron in your body will run out, which in turn, will cause anemia. There isn’t a known diet to prevent against getting ulcers. A balanced, healthy diet is always recommended. Smoking can also be a cause of problems in the stomach. Tobacco increases acid production and damages the lining of the stomach. It is not a proven fact that stress alone can cause an ulcer.
Histology of the human stomach Like the other parts of the gastrointestinal tract, the stomach walls are made of a number of layers. From the inside to the outside, the first main layer is the mucosa. This consists of an epithelium, the lamina propria underneath, and a thin bit of smooth muscle called the muscularis mucosa.
The submucosa lies under this and consists of fibrous connective tissue, separating the mucosa from the next layer, the muscularis externa. The muscularis in the stomach differs from that of other GI organs in that it has three layers of muscle instead of two. Under these muscle layers is the adventitia, layers of connective tissue continuous with the omenta.
The epithelium of the stomach forms deep pits, called fundic or oxyntic glands. Different types of cells are at different locations down the pits. The cells at the base of these pits are chief cells, responsible for production of pepsinogen, an inactive precursor of pepsin, which degrades proteins. The secretion of pepsinogen prevents self-digestion of the stomach cells.
Further up the pits, parietal cells produce gastric acid and a vital substance, intrinsic factor. The function of gastric acid is two fold 1) it kills most of the bacteria in food, stimulates hunger, and activates pepsinogen into pepsin, and 2) denatures the complex protein molecule as a precursor to protein digestion through enzyme action in the stomach and small intestines. Near the top of the pits, closest to the contents of the stomach, there are mucous-producing cells called goblet cells that help protect the stomach from self-digestion.
The muscularis externa is made up of three layers of smooth muscle. The innermost layer is obliquely-oriented: this is not seen in other parts of the digestive system: this layer is responsible for creating the motion that churns and physically breaks down the food. The next layers are the square and then the longitudinal, which are present as in other parts of the GI tract. The pyloric antrum which has thicker skin cells in its walls and performs more forceful contractions than the fundus. The pylorus is surrounded by a thick circular muscular wall which is normally tonically constricted forming a functional (if not anatomically discrete) pyloric sphincter, which controls the movement of chyme.
Control of secretion and motility The movement and the flow of chemicals into the stomach are controlled by both the nervous system and by the various digestive system hormones. The hormone gastrin causes an increase in the secretion of HCL, pepsinogen and intrinsic factor from parietal cells in the stomach. It also causes increased motility in the stomach. Gastrin is released by G-cells into the stomach. It is inhibited by pH normally less than 4 (high acid), as well as the hormone somatostatin. Cholecystokinin (CCK) has most effect on the gall bladder, but it also decreases gastric emptying. In a different and rare manner, secretin, produced in the small intestine, has most effects on the pancreas, but will also diminish acid secretion in the stomach.
Gastric inhibitory peptide (GIP) and enteroglucagon decrease both gastric motility and secretion of pepsin. Other than gastrin, these hormones act to turn off the stomach action. This is in response to food products in the liver and gall bladder, which have not yet been absorbed. The stomach needs only to push food into the small intestine when the intestine is not busy. While the intestine is full and still digesting food, the stomach acts as a storage for food.
Esophagus The esophagus is the portion of the GI tract that connects the pharynx to the stomach. It is a muscular tube approximately
the stomach, the esophagus passes through the diaphragm by means of an opening called the esophageal hiatus. The esophagus is lined with a nonkeratinized stratified squamous epithelium; its walls contain either skeletal or smooth muscle, depending on the location. The upper third of the esophagus contains skeletal muscle, the middle third contains a mixture of skeletal and smooth muscle, and the terminal portion contains only smooth muscle. Swallowed food is pushed from the oral to the anal end of the esophagus (and, afterward, of the intestine) by a wavelike muscular contraction called peristalsis.
Movement of the bolus along the digestive tract occurs because the circular smooth muscle contracts behind, and relaxes in front of, the bolus. This is followed by shortening of the tube by longitudinal muscle contraction. These contractions progress from the superior end of the esophagus to the gastroesophageal junction at a rate of 2 to
The lumen of the terminal portion of the esophagus is slightly narrowed because of a thickening of the circular muscle fibers in its wall. This portion is referred to as the lower esophageal (gastroesophageal) sphincter. After food passes into the stomach, constriction of the muscle fibers of this region help prevent the stomach contents from regurgitating into the esophagus. Regurgitation would occur because the pressure in the abdominal cavity is greater than the pressure in the thoracic cavity as a result of respiratory movements. The lower esophageal sphincter must therefore remain closed until food is pushed through it by peristalsis into the stomach.
Stomach
The J-shaped stomach is the most distensible part of the GI tract. It is continuous with the esophagus superiorly and empties into the duodenum of the small intestine inferiorly.
The functions of the stomach are to store food, to initiate the digestion of proteins, to kill bacteria with the strong acidity of gastric juice, and to move the food into the small intestine as a pasty material called chyme.
Swallowed food is delivered from the esophagus to the cardiac region of the stomach ( fig. 18.5 ). An imaginary horizontal line drawn through the cardiac region divides the stomach into an upper fundus and a lower body, which together compose about two-thirds of the stomach. The distal portion of the stomach is called the pyloric region. The pyloric region begins in a somewhat widened area, the antrum, and ends at the pyloric sphincter. Contractions of the stomach churn the chyme, mixing it more thoroughly with the gastric secretions. These contractions also push partially digested food from the antrum through the pyloric sphincter and into the first part of the small intestine.
The inner surface of the stomach is thrown into long folds called rugae, which can be seen with the unaided eye. Microscopic examination of the gastric mucosa shows that it is likewise folded. The openings of these folds into the stomach lumen are called gastric pits. The cells that line the folds secrete various products into the stomach; these cells form the exocrine gastric glands .
Gastric glands contain several types of cells that secrete different products:
1. mucous neck cells, which secrete mucus (these supplement the surface mucous cells, which line the luminal surface of the stomach and the gastric pits).
2. parietal cells, which secrete hydrochloric acid (HCl);
3. chief (or zymogenic ) cells, which secrete pepsinogen, aninactive form of the protein-digesting enzyme pepsin;
4. enterochromaffin-like (ECL) cells, found in the stomach and intestine, which secrete histamine and 5-hydroxytryptamine (also called serotonin ) as paracrine regulators of the GI tract;
D cells, which secrete the hormone somatostatin.
In addition to these products, the gastric mucosa (probably the parietal cells) secretes a polypeptide called intrinsic factor, which is required for the intestinal absorption of vitamin B 12 . Vitamin B 12 is necessary for the production of red blood cells in the bone marrow (see the next Clinical Application box). Also, the stomach has recently been shown to secrete a hormone named ghrelin. Secretion of this newly discovered hormone rises before meals and falls after meals.
This may serve as a signal from the stomach to the brain that helps regulate hunger
The exocrine secretions of the gastric cells, together with a large amount of water (2 to 4 L/day), form a highly acidic solution known as gastric juice.
Experimental method of studying of stomach secretion (Method of Basov – during the operation on dogs put the fistula in stomach. It connect stomach with the external environment. During eating the stomach juice go out through this fistula, but it has food and saliva. Method of Pavlov – method of “imaging eating” – during the operation on dogs put 2 fistulas: in esophagus and stomach. During eating the food go out through the esophagus fistula, that is way we have only juice. Method of Geydengine – a little stomach – to apart a little part of stomach, in which cut n.vagus. In this case we may to study humoral stimulation. Method of Pavlov – to separate little stomach from whole organ by 2 layers of mucous. In this case presents all regulatory mechanisms.)
c) Clinical method of stomach investigation (Gastroscopy, stomach sound, ultrasonic investigation, electrogastrography, pH-metry, determine helycobacter pylory.)
About
To stimulate production of duodinum gormon – secretin.)
Phases of stomach secretion
a) Cephalic phase (This phase caused by nervous system. It has conditional and unconditional reflexes. Conditional reactions caused by appearance of food, it smell and other stimulus, which are connect with food. Unconditional influences have parasympathetic. Parasympathetic components of unconditional influences beginning from receptors of tongue and other receptors of the oral cavity. From these receptors impulses pass through the fibers of nervus trigeminus, nervus facialis, nervus glossopharyngeus, nervus vagus to the medulla oblongata. Impulses return to stomach by nervus vagus. Except neuron influences this phase has humoral influences – brunch of nervus vagus produce gormon gastrin. These phase is very shortly.)
b) Stomach phase (These phase depend from quantity of food, which are present in stomach. It has vago-vagal reflexes (by mean of central nerves system) and local – peripheral reflexes, which are closed in stomach walls. Duration of these phase is longer and quantity of juice is much. It has humoral mechanisms too (production of gastrin and histamin).
c) Intestine phase (Presence of food in the upper portion of small intestine can cause the stomach to secrete small amount of gastric juice. This probably results of gastrin are also released by the duodenal mucosa in response to distension or chemical stimuli of the same type as those that stimulate the stomach gastrin mechanism.)
1. Digestion in the small intestine
a) Role of duodenum in the digestive system (There are two secretor functions of pancreas – external and internal. The external secretor function of pancreas means that exsogenic cells of pancreas and ducts cells produce pancreatic juice. It helps to hydrolyzed protein to peptides and amino acids, carbohydrates to monosaccharides, lipids to the fat acids and glycerine. It neutralizes acidic chymus, which come from stomach.)
b) External secretor function of pancreas (The external secretor function of pancreas means that exsogenic cells of pancreas and ducts cells produce pancreatic juice).
c) Composition and property of pancreas juice (Quantity of pancreatic juice per day – 1,5–
d) Regulation of pancreas secretion (Regulation act by complex of neuro-humoral mechanisms. There are three phases of pancreatic secretion: cephalic, stomach and intestine. The first stage caused by act of nervous influences. Nervus vagus realizes this effect by means of conditioned and unconditioned reflexes. Secretion begins after 1-2 minutes of food. This juice consists of enzymes, small quantity of water and ions. Sympathetic influences have a trophic role. During the second phase there are two kinds of influences: nervous and humoral, for example, gastrin from stomach. The third phase caused by chymus contents. The main is humoral factors. In that time secrete 2 hormons – secretin and cholecystokinin-pancreasemin. Secretin stimulates production of a big quantity of juice with a high concentration of hydro carbonates and a small quantity of enzymes in ducts cells. Cholecystokinin-pancreasemin stimulates production of a less quantity of juice with a big concentration of enzymes in acinars cells.)
e) Bile production and bile secrete (Secretion of bile occur all time and increase by influences of bile acids, cholecystokinin-pancreasemin, secretin. Bile secretion in the duodenum depends from take food. It depends of nervus vagus and humoral influences – concentration of cholecystokinin-pancreasemin, secretin, fats.)
f) Composition of bile, their role in digestive processes (Composition: bilirubin, bile acids, cholesterol, leukocytes, some epitheliocytes, cristalls of bilirubin, calcium, cholesterol. The role of bile: 1. Neutrolyze the stomach acid; 2. Inhibit he act of stomach proteases; 3. Increase the activity of pancreatic lipase; 4. Emulgate the lipids; 5. Increase the absorption of fat acids, vitamins K, D, E; 6. Increase tone and motor function of intestines; 7. Decrease the activity of intestine microflora.)
g) Composition and properties of intestine juice (Composition of intestine juice: mucus, enzymes – peptidase, saccharase, maltase, lactase, lipase, immunoglobulins, leukocytes; epitheliocytes (
h) Cavity and membrane hydrolyses of substances (On the glicocalix of micro fibers present enzymes, which are adsorbed and digest small molecules of nutritive substances – membrane hydrolyses of substances. Cavity hydrolyses of substances provide by enzymes, which are in intestine space.)
OTHER AUTONOMIC REFLEXES AFFECTING BOWEL ACTIVITY
Aside from the duodenocolic, gastrocolic, gastroileal, enterogastric, and defecation reflexes, several other important nervous reflexes can affect the overall degree of bowel activity. These are the peritoneointestinal reflex, reno-intestinal reflex, vesicointestinal reflex, and somato-intestinal reflex. All these reflexes are initiated by sensory signals that pass to the prevertebral sympathetic ganglia or to the spinal cord and then are transmitted through the sympathetic nervous system back to the gut. And they all inhibit gastrointestinal activity.
The peritoneointestinal reflex results from irritation of the peritoneum, it strongly inhibits the excitatory enteric nerves and thereby causes intestinal paralysis. The renointestinal and vesicointestinal reflexes inhibit intestinal activity as a result of kidney or bladder irritation. Finally, the somato-intestinal reflex causes intestinal inhibition when the skin over the abdomen is irritatingly stimulated.
