Factor VII deficiency
pH 7.4 PCO2
E. Gastroesophageal Reflux Disease
C. Achalasia D. Scleroderma
Nausea and Vomiting
Vomiting, with its precursor warning signs of nausea and retching, is mainly a protective re-flex, but also an important symptom. Chronic vomiting causes severe disorders.
The vomiting center, located in the medulla oblongata (→A, top), is reached, among others, via chemosensors of the area postrema on the bottom of the 4th ventricle (chemosensor trig-ger zone [CTZ]), where the blood–brain barrier is less tight. CTZ is activated by dopamine ago-nists such as apomorphine (therapeutic emet-ic), by numerous drugs or toxins, for example, digitalis glycosides, nicotine, staphylococcal enterotoxins as well as hypoxia, uremia, and diabetes mellitus. The CTZ cells also contain re-ceptors for neurotransmitters (e.g., epineph-rine, serotonin, GABA, substance P), allowing neurons access to the CTZ.
However, the vomiting center can also be ac-tivated without mediation by the CTZ, such as during unphysiological stimulation of the or-gans of balance (kinesia [motion sickness]). In addition, diseases of the inner ear (vestibule), such as Ménièreʼs disease, cause nausea and vomiting.
The vomiting center is activated from the gastrointestinal tract via vagal afferents:
◆on overstretching of the stomach or damage to the gastric mucosa, for example, by alco-hol;
◆by delayed gastric emptying, brought about by autonomic nervous efferents (also from the vomiting center itself), by food which is difficult to digest as well as by blockage of the gastric exit (pyloric stenosis, tumor), or of the intestine (atresia, Hirschsprungʼs dis-ease, ileus) (→p. 168);
◆by overdistension and inflammation of the peritoneum, biliary tract, pancreas, and in-testine.
Finally, visceral afferents from the heart may also cause nausea and vomiting, for example, in coronary ischemia. Nausea and vomiting are common during the first trimester of preg-nancy (vomitus matutinus). Exceptional distur-bances (see below) due to the vomiting may oc-cur (hyperemesis gravidarum). Psychogenic vomiting occurs mostly in (nonpregnant) young women, brought about by sexual con-flicts, problems in the home environment, loss
of parental attention, etc. Vomiting can be pre-cipitated deliberately by putting a finger into the throat (afferent nerves from touch sensors in the pharynx). It may occasionally provide re-lief, but frequent vomiting by patients with bu-limia (→p. 30) may lead to serious conse-quences (see below).
Finally, exposure to radiation (e.g., in the treatment of malignancy) and raised intracrani-al pressure (intracraniintracrani-al bleeding, tumors) are important clinical factors in precipitating nau-sea and vomiting.
The consequences of chronic vomiting (→A, bottom) are brought about by diminished food intake (malnutrition) and by loss of gastric juice, together with the loss of swallowed sali-va, drinks, and sometimes also of small-intesti-nal secretions. The result is hypovolemia. Re-lease of ADH, initiated by the vomiting center, favors retention of water; the excessive loss of NaCl and relatively small loss of H2O leads to hyponatremia which is exacerbated by in-creased excretion of NaHCO3. The latter is a re-sponse to a nonrespiratory alkalosis. This situa-tion results from the parietal cells of the stom-ach passing one HCO3–ion for each H+ion se-creted into the lumen. While the H+ ions (10–100 mmol/L gastric juice) are lost with the vomit, and therefore do not use up any HCO3–to buffer them in the duodenum, HCO3– accumulates in the organism. The alkalosis is made worse by hypokalemia; K+is lost both with the vomit (food, saliva, and gastric juice) and the urine. The hypovolemia leads to hyper-aldosteronism, during which K+excretion in-creases in the course of increased absorption of Na+[→pp. 106 and 132 ff]).
The act of vomiting and the vomit cause fur-ther damage, namely gastric rupture, tears in the esophageal wall (Mallory–Weiss syn-drome), dental caries (due to acid), inflamma-tion of the oral mucosa, and aspirainflamma-tion pneu-monia are the most important potential conse-quences.
152
6Stomach,Intestines,Liver
Plate6.4NauseaandVomiting
153 Delayed
gastric emptying
Medulla oblongata
Mallory-Weiss syndrome Esophageal rupture
Chronic
Loss of Na+
Loss of K+ Loss of H+
Apomorphine, nicotine, digitalis, uremia,
bacterial toxins, hypoxia,
etc. Chemoreceptor trigger zone (area postrema)
Intestinal obstruction Inflammation and overtension of peritoneum, bile passages, pancreas, intestine, etc.
Vomiting center
(reticular formation)
(see below)ADH
Vomiting
Food uptake
Compen-satory Loss of gastric juice
Gastric rupture Damage of teeth
Heavy
meal
NaHCO3
excretion HCl
K+ excretion
Distension
Motion sickness, vestibular disease Intracranial pressure
Aspiration of HCl, pepsin Pneumonia
Psychogenic
Breathing arrested
Abdominal squeeze
Hypo-kalemia
Hypo-natremia
Hypo-volemia
Nonresp.
alkalosis Warning signs
Inflammation
Renin Angiotensin II
Malnutrition Aldosterone
[HCO3] in blood (see above)ADH H2O
excretion [Na+] in plasma Pregnancy
Exposure to radiation
Nausea Pallor
Wide pupils Flow of saliva
Outbreak of sweat
Retching A. Causes and Consequences of Vomiting
Gastritis (Gastropathy)
Simplifying the situation somewhat, one can differentiate three main types of gastritis:
◆erosive and hemorrhagic gastritis
◆nonerosive, chronic active gastritis
◆atrophic (fundal gland) gastritis
(As complete inflammatory reaction is often absent in many cases of gastritis, the term gas-tropathy is now often used.)
Erosive and hemorrhagic gastritis (→A 1) can have many causes, for example:
◆intake of nonsteroidal anti-inflammatory drugs (NSAIDs), whose local and systemic mucosa-damaging effect is described in greater detail on p. 158;
◆ischemia (e.g., vasculitis or while running a marathon);
◆stress (multi-organ failure, burns, surgery, central nervous system trauma), in which the gastritis is probably in part caused by is-chemia;
◆alcohol abuse, corrosive chemicals;
◆trauma (gastroscope, swallowed foreign body, retching, vomiting, etc.);
◆radiation trauma.
This type of gastritis can quickly produce an acute ulcer (e.g., through stress or NSAIDs;
→p. 158), with the risk of massive gastric bleeding or perforation of the stomach wall (→A 1).
Nonerosive, chronic active gastritis (type B;
→A 2) is usually restricted to the antrum. It has become increasingly clear in the last decade that its determining cause is a bacterial coloni-zation of the antrum withHelicobacter pylori, which can be effectively treated with antibiot-ics (see also ulcer;→p. 156 ff). Helicobacter colonization not only diminishes mucosal pro-tection, but can also stimulate antral gastrin liberation and thus gastric juice secretion in the fundus, a constellation that favors the de-velopment of chronic ulcer.
A further type, reactive gastritis, (→A 4) oc-curs in the surroundings of erosive gastritis (see above), of ulcers or of operative wounds.
The latter may partly be caused after opera-tions on the antrum or pylorus by enterogastric reflux (reflux gastritis), resulting in pancreatic and intestinal enzymes and bile salts attacking the gastric mucosa. On the other hand, the al-kaline milieu of the intestinal juice counteracts
gastrin release and is also a hostile medium for Helicobacter pylori. (For similar reasons, Helico-bacter colonization is less common in atrophic gastritis.)
Atrophic (fundal gland) gastritis (type A;
→A 3), most often limited to the fundus, has completely different causes. In this condition the gastric juice and plasma usually contain au-toantibodies (mainly immunoglobulin G, infil-trates of plasma cells, and B lymphocytes) against parts and products of parietal cells (→A, upper right), such as microsomal lipo-proteins, gastrin receptors, carboanhydrase, H+/K+-ATPase, and intrinsic factor (IF). As a re-sult, the parietal cells atrophy with the effect that acid and IF secretion falls markedly (achlorhydria). IF antibodies also block the binding of cobalamines to IF or the uptake of IF–cobalamin complexes by cells in the ileum, ultimately resulting in cobalamine deficiency with pernicious anemia (→blood, p. 38). In atrophic gastritis more gastrin is liberated in response to this, and the gastrin-forming cells hypertrophy. Hyperplasia of the enterochromaf-fin-like (ECL) cells occurs, probably as a conse-quence of the high level of gastin. These cells carry gastrin receptors and are responsible for producing histamine in the gastric wall. This ECL cell hyperplasia can sometimes progress to a carcinoid. However, the main danger in atrophic gastritis is extensive metaplasia of the mucosa which, as a precancerous condi-tion, may lead to carcinoma of the stomach.
Except for Helicobacter pylori, gastritis is only rarely caused by a specific microorganism such as Mycobacterium tuberculosis, cytomega-lovirus, or herpes virus, or by fungi (e.g., Candi-da albicans). However, these gastritides are not uncommon in immunocompromised patients (AIDS, immunosuppression with organ trans-plantation, etc.).
154
6Stomach,Intestines,Liver
Plate6.5Gastritis
155 4
2 3
1
H+
Helicobacter pylori infection
Autoantibodies IF
Atrophic fundal gland gastritis
(Type A) Chronic active
antral gastritis (Type B)
Acid secretion normal or increased
(Chronic) gastric and duodenal ulcer Erosive and
hemorrhagic gastritis
Acute ulcer
Reactive gastritis
Carcinoid Carcinoma
Epithelial metaplasia
ECL-cell hyperplasia G-cell hyperplasia
Cobalamine deficiency
Long-term
Gastrin receptor Carbonic
anhydrase
H+/K+ -ATPase
Parietal cell
Lumen
Gastrin secretionAcid
Pepsinogen secretionIF
Cobalamine absorption
Bleeding
Perforation
Gastrin
Pernicious anemia NSAIDs,
alcohol Multi-organ failure, burns
Trauma Ischemia
K+ A. Gastritis
Ulcer
The H+ions in gastric juice are secreted by the parietal cells that contain H+/K+-ATPase in their luminal membrane, while the chief cells enrich the glandular secretion with pepsinogen (→A). The high concentration of H+ (pH 1.0–2.0) denatures the food proteins and acti-vates pepsinogens into pepsins which are endo-peptidases and split certain peptide bindings in food proteins.
The regulation of gastric secretion (→A 1) is achieved through neural, endocrine, paracrine, and autocrine mechanisms. Stimulation is pro-vided by acetylcholine, the postganglionic transmitter of vagal parasympathetic fibers (muscarinic M1 receptors and via neurons stimulating gastrin release by gastrin-releasing peptide [GRP]), gastrin (endocrine) originating from the G cells of the antrum, and histamine (paracrine, H2receptor), secreted by the ECL cells and mast cells of the gastric wall. Inhibi-tors are secretin (endocrine) from the small in-testine, somatostatin (SIH; paracrine) as well as prostaglandins (especially E2and I2), transform-ing growth factorα (TGF-α) and adenosine (all paracrines and autocrines). The inhibition of gastrin secretion by a high concentration of H+ ions in the gastric lumen is also an important regulatory mechanism (negative feedback;
→A 1, left).
Protection of the gastric and duodenal mu-cosa. Because the acid–pepsin mixture of gas-tric secretion denatures and digests protein, the protein-containing wall of the stomach and duodenum has to be protected from the harmful action of gastric juice. The following mechanisms are involved in this (→A 2):
a A gel-like mucus film, 0.1–0.5 mm thick, protects the surface of the gastric epithelium.
The mucus is secreted by epithelial cells (and depolymerized by the pepsins so that it can then be dissolved).
b The epithelium secretes HCO3–ions that are enriched not only in the liquid layer directly over the epithelium, but also diffuse into the mucus film, where they buffer H+ions that have penetrated from the gastric lumen. Pros-taglandins are important stimulants of this HCO3–secretion.
c In addition, the epithelium itself (apical cell membrane, tight junctions) has barrier
proper-ties that largely prevent the penetration of H+ ions or can very effectively remove those H+ ions that have already penetrated (Na+/H+ ex-change carrier only basolaterally). These prop-erties are regulated, among others, by the epi-dermal growth factor (EGF) contained in saliva and bound to receptors of the apical epithelial membrane. Glutathione-dependent, antioxida-tive mechanisms are also part of this cytopro-tection.
d Finally, good mucosal blood flow serves as the last“line of defense” that, among other ac-tions, quickly removes H+ions and provides a supply of HCO3–and substrates of energy me-tabolism.
Epithelial repair and wound healing. The fol-lowing mechanisms repair epithelial defects that occur despite the protective factors listed above (→B, bottom left):
◆The epithelial cells adjoining the defect are flattened and close the gap through sideward migration (→p. 4) along the basal membrane.
This restitution takes about 30 minutes.
◆Closing the gap by cell growth takes longer (proliferation;→p. 4). EGF, TGF-α, insulin-like growth factor (IGF‑1), gastrin-releasing pep-tide (GRP), and gastrin stimulate this process.
When the epithelium is damaged, especially those cell types proliferate rapidly that secrete an EGF-like growth factor.
◆If ultimately the basement membrane is also destroyed, acute wound healing processes are initiated: attraction of leukocytes and macro-phages; phagocytosis of necrotic cell residua;
revascularization (angiogenesis); regeneration of extracellular matrix as well as, after repair of the basement membrane, epithelial closure by restitution and cell division.
The danger of epithelial erosion and subse-quent ulcer formation exists whenever the pro-tective and reparative mechanisms are weak-ened and/or the chemical attack by the acid–
pepsin mixture is too strong and persists for too long (→A 3 and B, top). Gastric and duode-nal ulcers may thus have quite different causes.
Infection withHelicobacter pylori (H. pylori) is the most common cause of ulcer. As a conse-quence, administration of antibiotics has been shown to be the most efficacious treatment in most ulcer patients not receiving nonsteroidal 156
"
6Stomach,Intestines,Liver
Plate6.6UlcerI
157 a
b
c
d
HCO3
H+
H+ H+
H+ H+
H+
Ulcer 3 Danger of ulcer
2 Mucosal protection
Prostaglandins
Buffering:
HCO3 + H+® CO2 + H2O
(in saliva)EGF
pH1 pH7
Blood supply Pepsin
Gastric lumen Mucus Surface epithelium
pH3
Helicobacter pylori Secretion of gastric juice
HCO3 secretion Cell formation Blood perfusion
Pepsin
Protein digestion
Tubular gland
Parietal cell Chief cell
Acetylcholine Gastrin Histamine
see 2 below Pepsin
Vagus n.
Longitudinalmuscles Circularmuscles Submucosa Mucosa
1 Formation of gastric juice
Gastrin
Mucosal blood perfusion Epithelial barrier HCO3 secretion Mucus film
PGE2
SIH
Secretin PGI2 AdenosineTGFa M1 receptors H2 receptors A. Gastric Juice Secretion, Mucosal Protection and Risk of Ulcer
anti-inflammatory drugs (NSAIDs; see below).
H. pylori probably survives the acidic environ-ment of the mucus layer because it possesses a special urease. The bacterium uses this to pro-duce CO2and NH3, and HCO3–and NH4+, respec-tively, and can thus itself buffer H+ions in the surroundings. H. pylori is transmitted from per-son to perper-son, causing inflammation of the gas-tric mucosa (gastritis, especially in the antrum;
→p. 154). A gastric or duodenal ulcer is ten times more likely to develop in such cases than if a person does not suffer from gastritis of this kind. The primary cause of such an ulcer is a disorder in the epitheliumʼs barrier func-tion, brought about by the infection (→A, B).
It is likely that, together with this ulcer for-mation due to the infection, there is also an in-creased chemical attack, as by oxygen radicals that are formed by the bacteria themselves, as well as by the leukocytes and macrophages tak-ing part in the immune response, or by pepsins, because H. pylori stimulates pepsinogen secre-tion.
The fact that infection of the gastric antrum also frequently leads to duodenal ulcer is prob-ably related to gastrin secretion being increased by the infection. As a result, acid and pepsino-gen liberation is raised and the duodenal epi-thelium is exposed to an increased chemical at-tack. This causes metaplasia of the epithelium, which in turn favors the embedding of H. pylo-ri, leading to duodenitis and increased meta-plasia, etc.
A further common cause of ulcer is the in-take of nonsteroidal anti-inflammatory drugs (NSAIDs;→p. 154), for example, indometha-cin, diclofenac, aspirin® (especially in high doses). Their anti-inflammatory and analgesic action is based mainly on their inhibitory effect on cyclo-oxygenase, thus blocking prostaglan-din synthesis (from arachidonic acid). An unde-sirable effect of NSAIDs is that they systemical-ly block prostaglandin synthesis also in gastric and duodenal epithelia. This decreases HCO3– secretion, on the one hand (weakened mucosal protection;→B, top left), and stops inhibition of acid secretion, on the other (→A 1). In addition, these drugs damage the mucosa locally by non-ionic diffusion into the mucosal cells (pH of gastric juice << pKaʼ of the NSAIDs). During in-take of NSAIDs an acute ulcer may thus develop after days or weeks, the inhibitory action of
these drugs on platelet aggregation raising the danger of bleeding from the ulcer.
Acute ulcers also occur if there is very severe stress on the organism (stress ulcer), as after major surgery, extensive burns, and multi-or-gan failure (“shock”). The main cause here is probably impaired blood flow through the mu-cosa correlated with high plasma concentra-tions of cortisol.
Often psychogenic factors favor ulcer devel-opment. Strong emotional stress without an outward “safety valve” (high cortisol levels) and/or disturbed ability to cope with“normal”
stress, for example, in oneʼs job, are the usual causes. Psychogenically raised secretion of gas-tric acid and pepsinogen, as well as stress-re-lated bad habits (heavy smoking, antiheadache tablets [NSAIDs], high-proof alcohol) often play a part.
Smoking is a risk factor for ulcer develop-ment. A whole series of moderately effective single factors seem to add up here (→B). Alco-hol in large quantities or in high concentration damages the mucosa, while moderate drinking of wine and beer increases gastric secretion through their nonalcoholic components.
Rare causes of ulcer are tumors that auto-nomically secrete gastrin (gastrinoma, Zollin-ger–Ellison syndrome), systemic mastocytosis, or basophilia with a high plasma histamine concentration.
Apart from antibiotics (see above) and (rare-ly necessary) surgical intervention, the treat-ment of ulcer consists of lowering acid secre-tion by blocking H+/K+ATPase (→p. 155, right above). Treatment with antacids acts partly by buffering the pH in the lumen, but also has fur-ther, as yet not fully understood, effects on the mucosa.
158
"
6Stomach,Intestines,Liver
Plate6.7UlcerII
159 Bile salts,
pancreatic enzymes O2 radicals
Stress (shock, burns, operation)
Gastritis
Psychogenic components
Barrier function disturbed
H+ secretion Pepsinogen secretion
Chemical aggression Prostaglandin
synthesis Indomethacin, diclofenac,
acetylsalicylic acid, etc.
Helicobacter pylori infection
Gastrinoma, Smoking etc.
Ulcer Rapid restitution
through migration
Blood perfusion Mucosal
protection
Epithelial damage
Granulation, angiogenesis, restitution of basal membrane Covering defect
through cell division Wound
Smoking
Smoking
Wound healing Smoking
Radiograph: Treichel J. Doppelkontrastuntersuchung des Magens, 2nd ed. Stuttgart: Thieme; 1990