Page 150 - Color Atlas Of Pathophysiology (S Silbernagl Et Al, Thieme 2000)

Nausea and Vomiting
Vomiting, with its precursor warning signs of sexual conflicts, problems in the home envi-
nausea and retching, is mainly a protective ronment, loss of parental attention, etc. Vom-
reflex, but also an important symptom. iting can be precipitated deliberately by put-
Chronic vomiting causes severe disorders. ting a finger into the throat (afferent nerves
The vomiting center, located in the me- from touch sensors in the pharynx). It may
dulla oblongata (→ A, top), is reached, among occasionally provide relief, but frequent
others, via chemoreceptors of the area po- vomiting by patients with bulemia (→ p. 26)
strema on the bottom of the 4th ventricle may lead to serious consequences (see be-
(chemoreceptor trigger zone [CTZ]), where low).
the blood–brain barrier is less tight. CTZ is Finally, exposure to radiation (e.g., in the
Liver activated by dopamine agonists such as apo- treatment of malignancy) and raised intra-
cranial pressure (intracranial bleeding, tu-
morphine (therapeutic emetic), by numer-
Stomach, Intestines, glycosides, nicotine, staphylococcal entero- cipitating nausea and vomiting.
mors) are important clinical factors in pre-
ous drugs or toxins, for example, digitalis
toxins as well as hypoxia, uremia, and dia-
The consequences of chronic vomiting
(→ A, bottom) are brought about by dimin-
betes mellitus. The CTZ cells also contain re-
ished food intake (malnutrition) and by loss
ceptors for neurotransmitters (e.g., epineph-
rine, serotonin, GABA, substance P), allowing
of gastric juice, together with the loss of
However, the vomiting center can also be
also of small-intestinal secretions. The result
is hypovolemia. Release of ADH, initiated by
activated without mediation by the CTZ,
6 neurons access to the CTZ. swallowed saliva, drinks, and sometimes
such as during unphysiological stimulation the vomiting center, favors retention of wa-
of the organs of balance (kinesia [motion ter; the excessive loss of NaCl and relatively
sickness]). In addition, diseases of the inner small loss of H 2 O leads to hyponatremia
ear (vestibule), such as Ménière’s disease, which is exacerbated by increased excretion
cause nausea and vomiting. of NaHCO 3 . The latter is a response to a non-
The vomiting center is activated from the respiratory alkalosis. This results from the
gastrointestinal tract via vagal afferents: parietal cells of the stomach passing one
+
–
– on overstretching of the stomach or dam- HCO 3 ion for each H ion secreted into the
+
age to the gastric mucosa, for example, by lumen. While the H ions (10–100 mmol/L
alcohol; gastric juice) are lost with the vomit, and
–
– by delayed gastric emptying, brought therefore do not use up any HCO 3 to buffer
–
about by autonomic nervous efferents them in the duodenum, HCO 3 accumulates
(also from the vomiting center itself), by in the organism. The alkalosis is made worse
food which is difficult to digest as well as by hypokalemia; K + is lost both with the
by blockage of the gastric exit (pyloric ste- vomit (food, saliva, and gastric juice) and
nosis, tumor), or of the intestine (atresia, the urine. The hypovolemia leads to hyperal-
+
Hirschsprung’s disease, ileus) (→ p.156); dosteronism, during which K excretion in-
– by overdistension and inflammation of the creases in the course of increased absorption
+
peritoneum, biliary tract, pancreas, and of Na [→ p. 98 and 122 ff]).
intestine. The act of vomiting and the vomit cause
Finally, visceral afferents from the heart may further damage, namely gastric rupture, tears
also cause nausea and vomiting, for example, in the esophageal wall (Mallory–Weiss syn-
in coronary ischemia. Nausea and vomiting drome), dental caries (due to acid), inflam-
are common during the first trimester of mation of the oral mucosa, and aspiration
pregnancy (vomitus matutinus). Exceptional pneumonia are the most important potential
disturbances (see below) due to the vomiting consequences.
may occur (hyperemesis gravidarum). Psy-
140 chogenic vomiting occurs mostly in (non-
pregnant) young women, brought about by
Silbernagl/Lang, Color Atlas of Pathophysiology © 2000 Thieme
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