Page 85 - Clinical Anatomy

ECA2 7/18/06 6:42 PM Page 70

70 The abdomen and pelvis

through the bed of, the 12th rib. A finger is then passed upwards and for-
wards between liver and diaphragm to open into the abscess cavity. An
anteriorly placed collection of pus below the diaphragm can alternatively
be drained via an incision placed below and parallel to the costal margin.
Nowadays, intra-abdominal fluid collections can often be drained percuta-
neously under ultrasound or CT control.

The gastrointestinal tract

The stomach
The stomach is roughly J-shaped, although its size and shape vary consid-
erably. It tends to be high and transverse in the obese short subject and to be
elongated in the asthenic individual; even in the same person, its shape
depends on whether it is full or empty, on the position of the body and on
the phase of respiration. The stomach has two surfaces — the anterior and
posterior; two curvatures — the greater and lesser; and two orifices — the
cardia and pylorus (Fig. 51).
The stomach projects to the left, above the level of the cardia, to form the
dome-like gastric fundus. Between the cardia and the pylorus lies the body of
the stomach leading to a narrow portion, immediately preceding the
pylorus, which is termed the pyloric antrum. The junction of the body with
the pyloric antrum is marked by a distinct notch on the lesser curvature
termed the incisura angularis. The junction of pylorus with duodenum is
marked by a constriction externally and also by a constant vein (of Mayo)
which crosses it at this level.
The thickened pyloric sphincter is easily felt and surrounds the lumen of
the pyloric canal. The pyloric sphincter is an anatomical structure as well as a
physiological mechanism. The cardia, on the other hand, although compe-
tent (gastric contents do not flow out of your mouth if you stand on your
head), is not demarcated by a distinct anatomical sphincter. The exact
nature of the cardiac sphincter action is still not fully understood, but the
following mechanisms have been suggested, each supported by some
experimental and clinical evidence.

Fig. 51◊The stomach and
its subdivisions.