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Chapter 2 (page 7)
gastroduodenal junction or affect the rate of gastric emptying. According to Wingate
(l987) it is uncertain whether the pylorus is indeed a sphincter; it depends on what is
meant by the term "sphincter". The limitation of language has not yet allowed a
comprehensive definition of the concept.
An illustrated medical dictionary (Dorland l988) again defines sphincter as a ringlike
band of muscle fibres that constricts a passage or closes a natural orifice; the pyloric
sphincter is said to be a thickening of the circular muscle of the stomach around its
opening into the duodenum.
It is clear that consensus has not been reached on the definition of "sphincter" in general
terms. It would appear, however, that the definition as stated in most medical
dictionaries is totally inadequate.
A time-honoured view is that a sphincter is a band of circular musculature which is
tonically contracted most of the time, creating a zone of sustained elevation of pressure
preventing flow of intestinal contents in either direction; it relaxes intermittently, usually
in reciprocity with an oncoming peristaltic wave, to allow flow. In this view a sphincter
functions more or less independently of the surrounding musculature and probably has a
As far as the pylorus is concerned, the question arises whether the pyloric ring should be
looked upon as a sphincter in the sense implied above. Is it a ring consisting totally or
almost totally of muscular fibres, or is it merely a constriction which impedes flow by its
narrowness and poor distensibility, as suggested by Stadaas and Aune (l970) and by
Another view of sphincters is that proposed by Thomas and Mann (l98l), who mention
the possibility of sphincteric zones acting in complex regulatory fashion. However, on
anatomical grounds it is difficult to accept the theory of reciprocal innervation, in which a
particular nerve stimulus is purported to produce opposite effects in the "sphincteric" and
the adjacent smooth musculature.
A third possibility is that a rather intricate sphincteric mechanism may exist at junctional
zones, e.g. the pyloroduodenal junction. In this instance localized rings of circular
musculature are inherent components of a muscular region or cylinder consisting of both
circular and longitudinal fibres, the entire structure functioning as a unit.
It is proposed to discuss these and related questions in more detail in subsequent chapters.
- Alumets J, Hakanson R, Sundler F, et al. VIP innervation of sphincters. Scand J
Gastroent l978, 13 (Suppl 49), 6 (abstract).
- Black's Medical Dictionary, edit Thomas WAR, A & C Black, London 29th ed,
- Didio LJA, Anderson MC. The "Sphincters" of the Digestive System. Williams
and Wilkins, Baltimore l968.
- Dorland's Illustrated Medical Dictionary, edit Taylor EJ, WB Saunders Co,
Philadelphia, 27th ed, l988.
- Edwards DAW, Rowlands EN. Physiology of the gastroduodenal junction. In:
Handbook of Physiology, Sect 6, Vol 4, Motility. Edit Code CF. The American
Physiological Society, Washington DC, l968, l985-2000.
- Gould Medical Dictionary. McGraw Hill, 3rd edit, New York l972, p 1444.
- Gray's Anatomy. 35th British Edition, ed Warwick R, Williams PL. Longman
Co, Edinburgh l973, p 1273.
- Mehta SJ, Kaye MD, Showalter JP. Is there a pyloric sphincter?
Gastroenterology l974, 66, 746 (abstract).
- Reeve DRE. Anatomy of the sphincters of the alimentary canal. In: Alimentary
Sphincters and their Disorders. Edit Thomas PA, Mann CV. MacMillan Publ, London
l98l, pp 1-26.
- Ruch TC, Patton HD. Physiology and Biophysics. WB Saunders Co, London
l973, pp 4, 18.
- Schulze-Delrieu K, Shirazi SS. Neuromuscular differentiation of the human
pylorus. Gastroenterology l983, 84, 287-292.
- Schulze-Delrieu K. Volume accomodation by distension of gastric fundus
(rabbit) and gastric corpus (cat). Dig Dis Sci l983, 28, 625-632.
- Shepro D, Belamarich F, Levy C. Human Anatomy and Physiology. Holt
Rinehart Winston Inc, New York l974, p 598.
- Stadaas J, Aune S. Intragastric pressure-volume relationship before and after
vagotomy. Acta Chir Scand l970, 136, 611-615.
- Stedman's Medical Dictionary. Williams and Wilkins, 22nd edit, Baltimore l972,
- Thomas PA, Mann CV. Alimentary Sphincters and their Disorders. MacMillan
Publ, London l98l, pp xi, 227-232.
- Wheater PR, Burkitt HG, Daniels VG. Functional Histology. Churchill
Livingstone, London l979, pp 184, 188.
- Williams I. Closure of the pylorus. Brit J Rad l962, 35, 653-670.
- Wingate DL. Functional disorders of the stomach and small bowel. Scand J
Gastroenterol l987, 22 (Suppl 128), 62-68.
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