SPLANCHNIC CIRCULATION •Definition •Blood flow amount •Characteristics •Regulation •Factors affecting it Year 3 Medicine, UST Sana‘a, Spring 2010
Definition: Portal circulatory system + arterial blood flow into the liverPortal circulatory system:COP known amount of blood vessels of intestine spleen portal venous system liver
Main artery Main tributaries arteries Main areas supplied1. Coiliac trunk common hepatic (branches: Liver, parts of right gastric and stomach,dudenum and gastrodudenal) pancreas Splenic Spleen , parts of stomach and pancreas Lt gastric Parts of stomach and lower esophagus2.Superior mesenteric Inferiorpancreatinodudenal Small intestine, artery , Intestinal, iliocolic , right caecum,ascending colon, colic, middle colic most of the transverse colon, parts of duodenum and pancreas Left colic,segmoid,superior Descending and sigmoid3.Inferior mesenteric artery rectal colon, parts of transverse colon and rectum
Blood flow amount About 1100 ml of portal blood enters liver each minute Plus 350ml of blood from the hepatic artery enters liver each minute total blood flow = about 1450ml or 29% of the circulating blood flow. Oxygen consumption during rest is approximately 20-35% of the body‘s total needs.
Characteristics: The splanchnic blood flow participates in the regulation of circulating blood volume as well as the systemic blood pressure. In case of acute hypovolaemia, such as in case of hemorrhage, the splanchnic circulation becomes markedly reduced to be able to supply more vital or essential organs such as the brain and heart. The splanchnic circulation is also an important source of inflammatory mediators.
Characteristics continued: The blood flow to the mucosa is greater than that to the rest of the intestinal wall and it responds to changes in the metabolic activity (such as after meal, the blood flow doubles in the intestine and lasts up to 3 hours)
Types of regulations Regulation: 1)intrinsic regulation 2)extrinsic regulation
:Regulation 1)intrinsic regulation2. Local metabolic control & myogenic control3. Local reflexes4. Locally produced vasoactive substances 2)extrinsic regulation6. Sympathetic innervations7. Circulatory vasoactive substances8. Systemic hemodynamic changes
Intrinsic regulation(1 Local metabolic control: responds by local vasodilators eg. oxygen and cellular metabolism Myogenic control: a response caused by an increase in the vascular transmural pressure by arterial vasoconscriction These two are important for maintaining adequate blood flow for metabolic needs
Intrinsic regulation cont‘d Local reflexes: occurs as a response of the presence of luminal contents Locally produced vasoactive substances3) gastrin4) secretin5) cholecystokenin
Extrinsic regulation(2t Sympathetic nervous activity: this dec. blood flow by increasing the vascular resistance of the arteries and arterioles.e Circulatory vasoactive substances eg: catecholamineAlpha adrenoreceptors results in vcBeta adrenoreseptors results in vdAdrenaline is predomenantly active on alpha receptors thus vascular resistance in the intestine.
Factors affecting the splanchiniccirculationn glandular secretioni motilityi oxygen availability local VDA Peptide hormones eg: gastrin secretin cholecystokenin kenin
Factors affecting cont‘d5) Nervous control:2 Parasympathetic to stomach and lower colon . It blood flow and secretions .l Sympathetic causes vc and blood flow .but that last for few minutes then it return to normal ……….. WHY?
Factors affecting cont‘d This is because of a mechanism known as Auto regulatory escape ……… local vasodilators mechanisms elicited by ischemia- hence the activity of the vasodilator metabolites ……..returns blood flow to the GIT and muscles.
Importance of sympathetic:vasoconstriction1. Shutting off splanchenic circulation during exercise when inc, blood flow is needed by the skeletal muscle2. It causes strong vc of intestine and mesenteric artery which doesn‘t escape but blood volume and thus displaces large amount of the blood to other parts of the circulation