H52 



HANDBOOK OF PHYSIOLOGY 



CIRCULATION II 



RELATION OF BLOOD FLOW TO FUNCTION 

 OF THE MESENTERIC ORGANS 



The influence of the blood flow on the function of 

 the mesenteric organs seems to be clearly established 

 in only one respect; namely, that a certain minimum 

 flow is essential for the maintenance of the integrity 

 of the cells. Whether or not the alimentary activities, 

 secretion, absorption, and motility, of the stomach, 

 intestine, and pancreas require an augmentation of 

 the blood supply above the basal level is the subject 

 of conflicting evidence, although most of the admit- 

 tedly scanty evidence indicates that, necessary or not, 

 there is an increase in blood flow through these or- 

 gans after the ingestion of a meal. 



Herrick et al. (77), in thermostromuhr studies in 

 the unanesthetized dog, observed that 1 to 2 hours 

 after taking a meal the cranial mesenteric artery flow 

 was increased to 50 to 60 per cent above control. 

 Since there were increases of similar magnitude in 

 flows through the femoral and carotid arteries at the 

 same time, they concluded that digestion caused a 

 general increase in cardiac output rather than a shift 

 of blood supply from other regions of the body to the 

 abdominal viscera. Reininger & Sapirstein (109) 

 used their K 42 method to demonstrate that there was 

 a similarly uniform increase of about 30 per cent in 

 blood flow to all parts of the body of the rat after 

 feeding. 



Brodie and co-workers (23, 24) measured the 

 oxygen uptake by segments of canine small intestine 

 and observed a 30 per cent increase during absorp- 

 tion of dilute salt solutions and a 60 per cent increase 

 during absorption of protein solutions. They reported 

 similar rises in blood flow, but this must be interpreted 

 in light of their use of the plethysmograph to make 

 the measurements. Lindseth (95) determined both 

 total intestinal segment flow and its partition among 

 the individual tissues in anesthetized fasted and fed 

 dogs. In upper jejunal segments, feeding produced no 

 significant change in total venous outflow but caused 

 a diversion of the flow through the mesentery to the 

 capillaries of the mucosa and submucosa. In the 

 ileum, there was a 25 to 30 per cent increase in total 

 flow, almost all of which went to the muscle, there 

 being essentially no change in that through the 

 absorbing mucosa. He also found no significant altera- 

 tion in the fraction of the total flow which passed 

 through arteriovenous anastomoses. 



Numerous attempts have been made to determine 

 the relation between blood flow and secretion by the 



gastric mucosa. Thompson & Vane (131) in their 

 studies with the perfused cat stomach observed 

 parallel changes in secretory rate and blood flow as 

 a consequence of sympathetic stimulation, epineph- 

 rine administration, and celiac arterial infusion of 

 histamine, and concluded that secretion could be 

 directly influenced by changing blood flow. Lim 

 et al. (94), on the other hand, in similar studies with 

 the dog found that histamine-induced secretion could 

 occur in face of a falling blood flow. Further, sodium 

 nitrite increased the blood flow without initiating 

 secretion. Cutting et al. (37) observed increases in 

 both parameters in the cat when given histamine or 

 pilocarpine. Pituitrin decreased blood flow and 

 volume secretion but had little if any effect on the 

 amount of acid produced. Warming the stomach or 

 the administration of erythrol tetranitrate increased 

 flow without stimulating secretion. Finally it has 

 been noted that vagal stimulation which induces 

 secretion has little or no effect of the total blood flow 

 through the stomach although it does cause mucosal 

 engorgement. There seems little doubt that the parie- 

 tal cells must require an increase in oxygen supply 

 during secretion. There are, however, a number of 

 ways by which this can occur without alteration in 

 the total gastric blood flow. Oxygen extraction can 

 rise, although the work of Peters & Womack (105) 

 indicates that such is not the case in the dog in re- 

 sponse to histamine injection or vagal stimulation. 

 Other possibilities include shifts of flow from arterio- 

 venous anastomotic channels, from other tissues, 

 or from other regions of the stomach to the fundic 

 mucosa. Experiments to measure the distribution of 

 blood flow to the different tissue and arteriovenous 

 channels in the basal and in the secretory states are 

 needed. It is the mucosal flow that is of real signifi- 

 cance and it may not vary in the same manner as 

 the total flow. On the basis of the evidence presently 

 available reasonable conclusions seem to be that 

 agents which decrease gastric blood flow below the 

 basal level prevent or at least markedly reduce 

 secretion, that increased blood flow does not of itself 

 initiate or augment secretion, and that whether or 

 not secretion is necessarily accompanied by an in- 

 crease in total gastric blood flow cannot be answered 

 definitely. 



The investigations on the relation of pancreatic 

 secretion to blood flow have been critically reviewed 

 recently by Tankel & Hollander (130). They pointed 

 out the contradictory nature of the evidence presently 



