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19Anatomy, Physiology, and Selected Pathologies of the Gastrointestinal Tract
emerged as potential alternatives to conventional surgical treatment.
These options can be categorized into three groups:
1. Radiofrequency energy delivery to the esophagocardiac junction
2. Injection of nonabsorbable inert material into the wall of the cardia
3. Endoluminal suturing.
Despite very promising concepts, it is still a matter of debate as to
whether these techniques may really gain a role in gastroesophageal reflux
disease management
[3,4].
2.2.5.2 Implants
The first implant was clinically evaluated about 30 years ago. The
so-called Angelchik prosthesis had a sausage-like form filled with silicone.
Though effective in preventing reflux, it frequently had foreign bodyrelated side effects like perforation and mig ration. Soon it became obsolete. A new implant is a ring with magnetic beads (LINX). Although the
first reports are promising, some concerns exist in regard to the typical
problem of the perforation of foreign bodies
[5].
2.2.5.3 Electrical Stimulation
Though electrical stimulation of the lower esophageal sphincter is quite
an old idea, only now are the first devices commercially available.
Two electrodes attached to the sphincter deliver electrical impulses
produced by a subcutaneously implanted pacemaker. This principle appears
to be effective, although little is known about the mode of action
[6].
Achalasia can be relieved either by endoluminal dilatation of the LES
or by dissecting the sphincter muscle. The design of dilatation devices still
needs improvement (e.g., pressure control to avoid the risk of perforation). Electrical stimulation could be at least conceivable.
In case of cancer , radical surgical resection is the treatment of choice.
Different techniques are available. Most commonly, the right thorax has to be
opened to get access to the esophagus. When it is cut out, its former function
is restored either by a gastric pull-through or by a colonic segment.
Esophagectomy is major surgery and should be only performed in particularly
experienced and well-equipped centers. In early cases, innovati ve technologies
are now available to avoid classical resection. Early cancer can be locally
excised. In rare cases, local destruction by thermo-ablation may be justified.
For advanced, otherwise inoperable stages, various types of stents are provided to ove rcome the obstruction. If food intake is completely impossible,
enteral nutrition can be maintained by a “percutaneous endoscopic gastrostomy” (PEG) (see Chapter 8.4.2: Percutaneous Endoscopic Gastrostomy).
20 Biomedical Engineering in Gastrointestinal Surgery
Table 2.1 Esophagus: selected diseases/disorders and BME aspects
Disease/disorder Therapy BME aspects
Gastroesophageal
reflux disease
Achalasia Balloon dilatation, surgery
Cancer Surgical resection Stents, robotic surgery
Medical treatment or
surgery (fundoplication)
(cardiomyotomy)
Chemotherapy Endoluminal resection
Radiotherapy Ablation
Antireflux implants
Sphincter stimulation
Endoluminal augmentation
Balloon dilatation
stimulation?
Over many decades it was attempted to create artificial substitutes of
the esophagus. Up to now, none of these experimental designs has been
successful and the clinical need is comparatively low (
Table 2.1).
Self-evidently, this list of esophageal disorders is not complete.
Esophageal function is also impaired by diverticles (outpouching of the
wall), motility disorders, etc., but these diseases are of low BME relevance.
2.3 STOMACH
2.3.1 Anatomical Description
The stomach is the section of the GI tract between the esophagus and the
duodenum, located beneath the diaphragm, in the center and to the left
of the abdomen (
is denominated “lesser curvature” and the left one as “greater curvature.”
The stomach is usually closed to the esophagus by the lower esophageal
sphincter, which opens during swallowing, belching, or vomiting.
Further more, temporary “transient” relaxations occur.
The region between the stomach and the esophagus is called the esophagogastric junction or “cardia.” The stomach is divided into three parts:
the proximal (fundus), the middle (corpus), and the distal third (antrum)
(
Fig. 2.4B). The frontier between the stomach and the adjacent duode-
num is marked by the so-called “Pylorus.” This is another functional
sphincter region which regulates the transit of ingested food into the
small bowel.
The gastric wall consists of a strong muscular layer and a relati vely thick
mucosa. The latter is able to produce both highly concentrated hypochloric
acid as well as mucus which protects the gastric wall from self-digestion.
Fig. 2.4A). It is a hollow, curved organ. The right edge
Anatomy, Physiology, and Selected Pathologies of the Gastrointestinal Tract
Figure 2.4 (A) The stomach is localized in the epigastrium—beneath the rib
arches and the space between the sternum and the navel. (B) For practical
reasons, it is divided into three sections. The upper (oral) part relaxes during
food intake to augment the volume. The distal part produces strong, rhythmic
contraction and transports the food via the pylorus into the duodenum. From
M. Scholle.
21
2.3.2 Functional Task
Themaintaskofthestomachistotakeuptheingestedfoodandto
deliver it in adequate quantities into the small bowel. However,
preprocessing is included as well. Gastr ic acid production reduces
bacterial contamination and prepares digestion. Furthermore, mechanical alteration takes place, induced by continuous rotation in the
distal part of the stomach (“antral mill”). Whereas the proximal twothirds part has mainly a receptive function, the distal par t is mechanically active.
However, the stomach is more than just a “food bag” with some
motor activity. It is proven that the distension of the proximal stomach
influences via hormonal control the degree of satiety—or hunger.
In addition, an electr ical pacemaker is assumed to exist in the fundus/
fornix region which stimulates the electromechanical phenomena
like the antral motility and the digestive waves of the distal stomach,
the duodenum, small and large bowel. Many of these aspects are
still poorly understood. A better understanding of physiological and
22 Biomedical Engineering in Gastrointestinal Surgery
pathological processes would be fundamental to design better therapeutic tools.
2.3.3 Disorders and Diseases
Historically, acid-related disorders were of outstanding importance. Peptic
gastric ulcers led to perforation and bleeding. Due to the detection of
Helicobacter pylori and the availability of cheap proton pump inhibitors, the
significance of peptic ulcer disease decreased. Nevertheless, ulcer bleeding
or perforation are still severe problems worldwide. They frequently
require emergency surgery. Endoscopic treatment has become an option
as well
dence has declined as well. Major parts or even the whole s tomach
have to be removed, resulting in a more or less significant reduction of
quality of life afterward. A better understanding of tumor biology
could help in the future. In many instances a too radical resection
could be avoided if it were possible pre- or intraoperatively to assess
whether lymph nodes are inflicted or not (precise “staging”). If the
tumor is still localized, i.e., not inflicting adjacent structures like lymph
nodes, local excision is sufficient and radical resection is not required.
If intraoperative tissue differentiation were possible a big step toward
individualized surgery would be achieved.
Gastric motility disappears which leads to emptying disturbances.
Electrical stimulation can be helpful (see Chapter 14: Visceral Surgery of
the Future: Prospects and Needs).
target of bariatric surgery.
[7].
The number one problem today is gastric cancer, although its inci-
Less frequently gastric motility disorders occur, such as gastroparesis.
Due to its essential role in food intake, the stomach is also a particular
The main aim is to reduce the reservoir capacity.
2.3.4 Biomedical Engineering Aspects
Gastric bleeding was formerly a clear indication for emergency surgery.
Due to the rapid development of endoscopic techniques and technology,
they can now be stopped in the majority of cases by injecting techniques,
the application of clips, or by banding. Further refinement of the technology could make surgery completely avoidable.
23Anatomy, Physiology, and Selected Pathologies of the Gastrointestinal Tract
Perforation is still today a case for the surgeon. However, the first
promising approaches are underway to occlude the hole by means of specially designed endoluminal clips or sutures (see Chapter 8.4.1:
Gastrointestinal Bleeding).
The standard answer to gastric cancer is radical surgical resection.
However, this is changing gradually today. Early cancer can be excised
endoscopically using sophisticated new dissection techniques. Even full
wall resection could become mature for routine clinical use if reliable
occlusion techniques are provided.
In advanced cases, palliation can be improved by stenting techniques
or PEG.
Gastroparesis is an emptying disorder of the stomach due to motility
impairment. Bizarre dilatation of the stomach is the consequence. In
advanced cases, partial resection is recommended, but the results are poor.
Gastric electrostimulation could become helpful
[8].
Morbid obesity: The stomach is a key target of biomedical engineering
approaches to cure morbid obesity. Currently, there are a large variety of
surgical procedures to reduce food intake which can be subdivided into
restrictive (limitating the quantity of food during a meal), malabsorptive,
or combined. One example of a restrictive approach is the so-called “gastric band.” It is positioned like a belt around the upper part of the stomach. A similar restrictive effect is achieved by a so-called “gastric sleeve”
operation. Large parts of the stomach are removed and only a narrow
tube is left. In malabsorptive surgery, a bypass is created between the
stomach and the distal ileum. Thus, a considerable length of the small
bowel is excluded from digestion. Usually, they are significant surgical
interventions, and the results are not completely satisfying.
Many efforts are focused upon internal (endoscopic) solutions
[9].
One popular approach is to position an inflatable balloon into the gastric
lumen. The large volume of the balloon reduces the internal gastric volume for further food intake.
Another approach is gastric stimulation
[10]. The idea is to modify
the gastric motility by electrical impulses delivered by a dedicated pacemaker. Many questions are still to be answered.
BME will play a major role in the treatment of these very frequent
diseases. A closer cooperation between researchers, clinicians, and engineers would certainly help to identify innovative, less invasive treatment
options (
Table 2.2).
24 Biomedical Engineering in Gastrointestinal Surgery
Table 2.2 Stomach: selected diseases/disorders and BME aspects
Disease/
disorder
Bleeding Surgical hemostasis Clipping
Perforation Surgical excision and
Cancer Radical surgical
Gastroparesis Medical treatment Gastric pacemaker
Morbid
obesity
Therapy BME aspects
Injection technique
Banding
Endoscopic closure using specially
closure
resection
Chemotherapy
(Radiotherapy)
Partial gastric resection
Sleeve resection Gastric band
Gastric bypass Endoluminal restriction techniques
designed clips
Local excision with specially
designed clips
Endoscopic submucosal dissection
(ESD)
Stenting
PEG
Gastric balloon
Implantable deviation devices
Gastric electrostimulation
2.4 DUODENUM AND SMALL INTESTINE
2.4.1 Anatomical Description
The next part of the alimentary tract is the small bowel, which is subdivided into the duodenum, the jejunum, and the ileum (
The duodenum—directly adjacent to the stomach—has a smaller
diameter than the stomach (13 cm under nor mal conditions) and is
roughly C-shaped.
It is fixed t o the retroperitoneum. Only after the duodenojejunal
flexure does the small intestine become mobile. The duodenum is
localized in close vicinity to the pancreas, the caval vein, and the liver.
The distinct S-shaped transit into the jejunum is denominated the
duodenojejunal flexure.
Whereas the border between the duodenum and the jejunum is
anatomically rather clearly defined, it is not easy to define where the jejunum ends and where the ileum begins. The length of these sections of
the alimentary tract varies considerably, depending upon the physiological
state. Usually, a length of about 23 meters is quoted in the literature.
Fig. 2.5).
Anatomy, Physiology, and Selected Pathologies of the Gastrointestinal Tract
Figure 2.5 The duodenum: This part of the small intestine deserves special mention
because of its specific anatomical and physiological features. From M. Scholle.
25
This is significantly more than is needed, since it is known from surgical
experience that as little as 120 cm is sufficient to guarantee normal
digestion (
Fig. 2.6).
The end of the small intestine is clearly defined. It is the orifice into
the large bowel. It is called the ileocecal (or Bauhin’s) valve.
The microscopical aspects of the jejunum and the ileum are rather
homogenous: The inner mucosal layer, the muscular layer (longitudinal
and circular), and the peritoneum.
2.4.2 Functional Task
As soon as the acidic gastric content leaves the stomach, it is immediately
neutralized by the alkalic bile/pancreatic juice mixture injected into the
intestinal lumen via the Vater papilla.
The preprocessed intestinal content is now digested in the jejunum
and ileum. All valuable components like fats, sugars, and proteins are
extracted and delivered via the portal vein system to the liver. A complicated motility pattern with forward and backward transportation leads
to a prolonged contact time with the intestinal mucosa to increase the
effectiveness of absorption. The uptake of lipids, including fat soluble
26
Biomedical Engineering in Gastrointestinal Surgery
Figure 2.6 The small intestine: (A) The colon is the frame of the convolute of small
bowel loops; (B) The stomach and parts of the colon removed: Beginning with the
duodenum, the small intestine is now visible in its whole length; (C) The distal ileum
joins with the colon: Bauhin’s valve. From M. Scholle.
vitamins, is enhanced by bile acids, whereas pancreatic enzymes are
responsible for the digestion of proteins, etc.
2.4.3 Disorders and Diseases
As compared to the other sections of the GI tract, the duodenum and the
small bowel are relatively “peaceful” areas. Cancer is rare. In the duodenum, peptic ulcers may cause bleeding or perforation. Basically, they are
treated in a similar way as described for gastric ulcers.
A major problem is duodenal obstruction due to pancreatic cancer or
distal cancer of the stomach. Gastric outlet obstruction would lead to
starvation, often accompanied by bile duct obstruction with jaundice. The
27Anatomy, Physiology, and Selected Pathologies of the Gastrointestinal Tract
classical approach is to create a deviation from the stomach into the small
intestine (gastroenteric anastomosis) and a so-called hepaticojejunostomy,
i.e., an anastomosis between the bile duct system and the small bowel.
Bleeding can occur in the small bowel and this is often difficult to
localize.
The Meckel’s diverticulum is a structural (anatomical) disorder.
It is more or less a large bulge of the distal ileum as a remnant of the
yolk stalk. It often mimics appendicitis.
Last but not least obstructions of the jejunum are frequent in the case
of gastroenteritis regionalis (Crohn’s disease), a nonbacterial inflammation
process. This disease is still not yet completely understood. Medical treatment is always the first option. However, surgery may become necessary
in case of fistula or stenosis.
It is postulated that disorders of the small intestine may be the cause of
a broad range of dysfunctional syndromes of the alimentary tract. Up until
now, our knowledge of normal intestinal motility has been very limited;
the real significance is still unknown.
2.4.4 Biomedical Engineering Aspects
Duodenal obstruction is currently increasingly often treated by stenting of
the bile duct and the duodenum. Much has still to be improved, but there
is no doubt that so-called palliation in the case of noncurable pancreatic or
bile duct cancer will become a domain of nonsurgical interventions
Advanced BME enabled the surgeons/gastroenterologists to explore
the last white spot on the gastrointestinal map—the small bowel.
Around the year 2000, the first capsule was provided by the industry
for visual exploration of the whole gastrointestinal tract (see Chapter 5.7.8:
Wireless Capsule Endoscopy). Soon, specially designed endoscopes became
available which allowed to promote the tip of the endoscope actively by
sophisticated balloon techniques (see Chapter 5.7.2.6.2: Enteroscopy,
“Deep Endoscopy”). Thus, endoluminal therapeutic procedures became
possible which had been unthinkable before. Argon beaming of bleeding
angiodysplasia as well as balloon dilatation of stenosis are now on the
threshold of clinical maturity (
Tab le 2 . 3 ).
Maybe, BME aspects can also contribute the “crux medicorum” of
so-called dysfunctional abdominal syndromes. If motility disturbances
are really the cause, electrical stimulation could, theoretically, become a
promising approach.
[11].
28 Biomedical Engineering in Gastrointestinal Surgery
Table 2.3 Duodenum and small intestine: selected diseases/disorders and BME
aspects
Disease/disorder Treatment BME aspects
Bleeding (duodenum) See Table 2.2
Perforation
(duodenum)
Obstruction
(duodenum)
Obstruction
(small intestine)
Bleeding
(small intestine)
Intestinal dysfunction Medical treatment Electrostimulation
Bilioenteric and gastroenteric
anastomosis
Segmental resection Double balloon
Surgical hemostasis Capsule endoscopy
See Table 2.2
Stenting
PEJ
dilatation
for localization
Enteroscopy for
hemostasis
2.5 COLON AND RECTUM
2.5.1 Anatomical Description
The colorectum is the last part of the alimentary tract. It begins with the
ileocolic valve (“valvula Bauhini”) and terminates with the anal sphincter.
Its general outline resembles an M or inverted U (with the exception of
the rectosigmoid) (
The length of the colon is not more than about one fourth of the
length of the small intestine. As compared to the small bowel it is less
mobile and its position is much more constant. Two subdivisions, however, may vary considerably in shape and length and localization: the
transverse and the sigmoid colon (
The external appearance of the large bowel is quite characteristic:
three long itudinal muscle bands (“taenia”) shorten the bowel thus producing the typical pouches (“haustra”) separated by transverse furrows.
The inner diameter of the colon decreases gradually from about 5 cm at
its beginning in the cecum to about 2.5 cm in the sigmoid. If the colon is
empty and in a contracted state, the lumen is very small, but it is capable
of great increase.
The last part of the GI tract—the rectum—deserves special notice.
The length is defined as 15 cm and divided into the upper, middle, and
lower third, which encompasses the anus.
The anorectum (
the pelvic floor
Fig. 2.7).
Fig. 2.8).
Fig. 2.9) is part of the complex anatomical region of
[13].