The Vascularization of the Digestive Tract Studied by Scanning Electron Microscopy with Special Emphasis on the Teeth, Esophagus, Stomach, Small and Large Intestine, Pancreas, and Liver

The periodontal vessels in adult rats show a ladder-like pattern; in guinea pigs molars, by contrast, they present a honey-comb pattern. The vascular architecture in human teeth seems to be similar to that of rabbits. In guinea pigs, rats, rabbits and humans esophagus circumferential vessels give off perforating vessels. In human esophagus the number and diameter of the vessels in the submucous venous plexus decrease from proximal to distal. In the stomach the subepithelial capillary network shows a honey-comb pattern reflecting the arrangement of the gastric pits. A local portal system between the gastric glands and the surface mucosal cells for the transport of HCO3- ions has been suggested. In the small intestine of humans and rabbits the existence of a dual blood supply of the villus has meanwhile been established. It consists of pericryptal capillaries for the lower portion of the villus (tuft pattern) and a direct arterial supply up to the villus tip (fountain pattern). The colonic microvasculature closely resembles that of the stomach. In the pancreas the insulo-acinar portal system is physiologically significant in that it connects the venules draining the islets with the acini. Venous sphincters in the vascular system of the exocrine pancreas of the rat are of particular functional importance. The hepatic sinusoids are supplied both by the hepatic artery and the branches of the portal vein. The peribiliary plexus is supplied by the afferent vessels of the hepatic artery, the efferent vessels drain the plexus either into the sinusoids or into the lobular vein

Endoscopic injection sclerotherapy in the treatment of bleeding oesophageal varices in patients with portal hypertension due to alcohol-induced cirrhosis : an assessment of acute control of bleeding, prevention of recurrent bleeding and prognostic factors predicting early variceal rebleeding and death

The ideal treatment of portal hypertension and bleeding varices should be universally effective, safe, easy to administer and inexpensive. Currently no such treatment exists and the surgeon or physician is obliged to select the most appropriate intervention from a menu of currently available therapeutic options, none of which is ideal or applicable to all patients. The rational treatment of oesophageal varices depends on a clear understanding of the risks of rebleeding and the response to each specific intervention. The selection of the correct and appropriate intervention is critical and requires a comprehensive understanding of the relative efficacy and safety of each treatment compared to other competing options. In addition, the chosen intervention requires detailed knowledge of the criteria underpinning the correct selection of patients for treatment in order to maximize the therapeutic benefits of the appropriate choice while minimising the side effects of the treatment. The optimal management of bleeding oesophageal varices therefore requires a full appreciation of portal, gastric and oesophageal venous collateral anatomy, the pathogenesis and haemodynamic consequences of variceal bleeding and the utility of each available therapy at specific stages in the natural history of portal hypertension (Henderson 1998)

Clinical and haemodynamic studies in portal hypertension

Over the last 20 years, there have been significant advances in the management of portal hypertension, with the introduction of drug therapy and the transjugular intrahepatic portosystemic stent-shunt (TIPSS). This development continues at a strong pace as our understanding of the pathogenesis of portal hypertension deepens. There are 2 aims of this thesis:1. To study the haemodynamic effects of two novel vasoactive agents on the portal and systemic circulations.a. Carvedilol, a vasodilating non-cardioselective beta-blocker with op antagonism. The acute and chronic haemodynamic effects of this agent will be studied, with particular attention paid to patient tolerability.b. Losartan, an angiotensin II receptor antagonist. The chronic effects of this agent will be studied in patients with well compensated cirrhosis.These laboratory based studies will assist in determining the suitability of these agents for use in controlled clinical trials on patients at risk of variceal bleeding.2. TIPSS has been used extensively in the management of portal hypertension, particularly variceal bleeding. Two studies will be presented in this thesis aimed at answering the following questions.a. Is TIPSS effective for the management of gastric variceal bleeding? Gastric variceal bleeding is less common than oesophageal variceal bleeding, hence there are relatively few studies investigating the effect of TIPSS on bleeding gastric varices. This study will also compare gastric variceal bleeding with oesophageal variceal bleeding, and aim to correlate clinical outcomes with haemodynamic data.b. Is it necessary to continue portographic TIPSS surveillance indefinitely if variceal band ligation is combined with TIPSS for the prevention of oesophageal variceal rebleeding? This is the hypothesis for a randomised controlled trial comparing TIPSS alone with TIPSS plus variceal band ligation. This study will address 2 drawbacks of TIPSS, namely the need for long-term portographic to ensure TIPSS patency and hepatic encephalopathy