circulation

1. SPLANCHNIC CIRCULATION

2. 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

3. 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.

4.  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.

5.  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)

6. Types of regulations
 Regulation:
 1)intrinsic regulation
 2)extrinsic regulation

7. Regulation
 1)intrinsic regulation
1. Local metabolic control & myogenic control
2. Local reflexes
3. Locally produced vasoactive substances
 2)extrinsic regulation
1. Sympathetic innervations
2. Circulatory vasoactive substances
3. Systemic hemodynamic changes

8. 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

9. Intrinsic regulation cont’d
 Local reflexes: occurs as a response of the
presence of luminal contents
 Locally produced vasoactive substances
1) gastrin
2) secretin
3) cholecystokenin

10. 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 vc
Beta adrenoreseptors results in vd
Adrenaline is predomenantly active on alpha
receptors thus vascular resistance in the
intestine.

11. Factors affecting the
splanchinic circulation
1) glandular secretion
2) motility
3) oxygen availability local VD
4) Peptide hormones
eg: gastrin
secretin
cholecystokenin
kenin

12. 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?

13. 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.

14. Importance of sympathetic
vasoconstriction:
Shutting off splanchenic circulation during
exercise when inc, blood flow is needed by the
skeletal muscle
1. 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

15. Thank you