1. Blood Flow Regulation By
Dr. Khurram Irshad

2. Objecctives
To describe the mechanisms responsible for the regulation of Blood Flow to different tissues

3. Why Do We Need to Regulate Blood Flow ?

4. Mechanisms of Blood Flow
Acute Control
Rapid changes in diameter of arterioles, metarterioles and precapillary sphincters occurring within seconds to minutes leading to increase or decrease in blood flow.

6. Slow changes in flow over the period of days, weeks or even months.
Long Term Control
Slow changes in flow over the period of days, weeks or even months.
This is brought about by
- Increase or decrease in size of organ
- Increase or decrease in No. of blood vessels supplying the organ

7. Acute Control of Blood Flow
Local Metabolic factors
Myogenic response
Humoral Factors

8. Local Metabolic Factors responsible for Acute control of blood flow
Lack of oxygen according to the tissue needs
It will lead to locally accumulation of
- Adenosine
- carbondioxide
- Adenosine phosphate compounds
- histamin
- K +
- H +
(Vasodilator Theory)

9. Lack of Oxygen and Nutrient will directly lead to Vasodilation
Glucose
Vitamin C
Vitamin B
Thiamine
Niacin
Riboflavin

10. Special Mechanisms for Acute Blood Flow Control in Specific Tissues
Kidney’s
Tubuloglomerular feed back
Brain
Heart

11. Vasodilation and Vasoconstriction in Arteries when there is change in microvasculature
- EDRF (endothelium derived relaxing factor)
- NO

12. Examples of Acute Blood Flow Control
Reactive Hyperemia
Active Hyperemia

13. Long Term Control of Tissue Blood Flow
Change in Tissue vascularity
(Oxygen requirement is important factor)
Angiogensis (growth of new blood vessels)
Collateral circulation

14. HUMORAL REGULATION Vasoconstrictor agents
- Epinephrine and norepinephrine
- Angiotensin
- Vasopressin
- Endothelin

15. Vasodilator Agents
- Bradykinin
- Histamin