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