splanchnic circulation
DESCRIPTION
This is a presentation about splanchinc circulation.Done by year 3 medical students at the University of Science and Technology, Sana'a, Republic of Yemen.Spring semester of 2010.TRANSCRIPT
SPLANCHNIC CIRCULATION
Year 3 Medicine, UST Sana’a, Spring 2010
•Definition•Blood flow amount•Characteristics•Regulation•Factors affecting it
Definition: Portal circulatory system + arterial blood
flow into the liver Portal circulatory system: COP known amount of blood
vessels of intestine spleen portal venous system liver
Main arteryMain tributaries arteries
Main areas supplied
1. Coiliac trunk
2.Superior
mesenteric artery
3.Inferior mesenteric artery
common hepatic (branches: right gastric and gastrodudenal)
Splenic
Lt gastric
Inferiorpancreatinodudenal , Intestinal, iliocolic , right colic, middle colic
Left colic,segmoid,superior rectal
Liver, parts of stomach,dudenum and pancreas
Spleen , parts of stomach and pancreas
Parts of stomach and lower esophagus
Small intestine, caecum,ascending colon, most of the transverse colon, parts of duodenum and pancreas
Descending and sigmoid 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 regulation 1. Local metabolic control & myogenic
control2. Local reflexes3. Locally produced vasoactive substances 2)extrinsic regulation1. Sympathetic innervations2. Circulatory vasoactive substances3. Systemic hemodynamic changes
1)Intrinsic regulation
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 substances
1) gastrin 2) secretin3) cholecystokenin
2)Extrinsic regulation
1. Sympathetic nervous activity: this dec. blood flow by increasing the vascular resistance of the arteries and arterioles.
2. Circulatory vasoactive substances eg: catecholamine
Alpha adrenoreceptors results in vcBeta adrenoreseptors results in vdAdrenaline is predomenantly active on alpha
receptors thus vascular resistance in the intestine.
Factors affecting the splanchinic circulation
1) glandular secretion2) motility 3) oxygen availability local VD
4) Peptide hormones eg: gastrin secretin cholecystokenin kenin
Factors affecting cont’d
5) Nervous control:i. Parasympathetic to stomach
and lower colon . It blood flow and secretions .
ii. 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 vasoconstriction:
1. Shutting off splanchenic circulation during exercise when inc, blood flow is needed by the skeletal muscle
2. 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
Thank you