Archive for the ‘ L1-Regional Circulation ’ Category

L1- Regional Blood Flow

Regional Blood Flow

1.Pulmonary circulation

2.Coronary circulation.

3.Renal circulation.

4.Cerebral circulation.

5.Cutaneous circulation.



1) Pulmonary circulation

•It is concerned with passage of blood from the right ventricle ,through the lungs and then to the left atrium.

•It’s time is about 7 seconds at rest.

•It receives all the COP from the right ventricle.

Pulmonary vessels

•The lung are supplied with blood from two sources.

1- Pulmonary artery:

•It transmit venous blood from the right ventricle to the lung.

•It is divide into two pulmonary arteries right and left.

•They give multiple branches >>capillaries

•>>wall of the alveoli >>gas exchange.

2- The bronchial arteries:

•They arise from aorta, and supply mainly the bronchi and bronchioles.

•there are many anastomoses between the bronchial and pulmonary arteries.




Regulation of pulmonary circulation

1-Intrinsic regulation

•Decreased O2 tension leads to pulmonary Vasoconstriction.

2-Extrinsic mechanism:

•cardiac output. Increased COP increases pulmonary blood flow with slight increase in pulmonary BP.

•pulmonary capacity : can change to buffer excessive changes in pulmonary BP

•Pulmonary peripheral resistance

–Equals 1/6 of the systemic PR.

•Nervous factors

–Vagal stimulation produces dilatation of the pulmonary blood vessels.

–Sympathetic stimulation>>V.C of pulmonary blood vessels.


2) Coronary circulation


Coronary circulation

•The heart comprise 0.5% of the total body weight.

•It has a very high basal O2 consumption.


•The highest A-V O2 difference of major organs .

•Under resting condition it receives about 5% of the COP.

•All the capillaries are open all the time (there is no vasomotion).

•Most of the O2 is extracted from the blood as it passes through myocardial capillaries.

•Total coronary flow is greater in diastole than in systole.

•Increased heart rate  in normal subject:

•Increased cardiac work &decreased diastolic period  >>restrict coronary flow

•But at the same time there is increase metabolism>>dilatation of coronary vessels.

In heart with limited blood flow

•Such as in coronary insufficiency

•Increased heart may cause chest pain (angina).

•Because flow can not increase to meet the increased O2 demand.



Regulation of coronary blood flow

•Intrinsic mechanism:

–Oxygen demand is the major factor in local blood flow regulation.

–Oxygen lack causes vasodilatation.

•Extrinsic mechanism:

–Nervous factor.

–Mechanical factor.

–Chemical factor.

Nervous factor

•Sympathetic >>>>

vasoconstriction by direct mechanism.

Strong vasodilatation indirectly.

•Parasympathetic >>>>

Direct >> V.D.

Indirect >> V.C.

Chemical factors:


2.Long acting nitrates.

3.B blocker

4.Ca channel blockers.

Mechanical factors:

•The heart rate.

•Arterial blood pressure.

•Cardiac output.

Coronary artery disease:

•Angina pectoris.

•Myocardial infarction.

3) Renal Circulation

Renal Artery and its branches

-2 large renal arteries from abdominal aorta (one for each kidney)

-arise just inferior to origin of the Superior Mesenteric Artery between L1 and L2

-the left renal arises a little higher than the right

-the right artery is longer and passes posterior to IVC

-each artery divides into 5 segmental end arteries before entering the hilum into renal sinus

-the 5 segmental arteries are

  1. superior
  2. inferior
  3. posterior
  4. anterior
  • anterior superior
  • anterior inferior

-a segmental artery gives LOBAR ARTERIES to the pyramid

-these divide to provide 2-3 INTERLOBAR ARTERIES that travel between pyramids

-near the junction of the medulla and cortex arises ARCUATE ARTERIES at right angles

-from them arise INTERLOBULAR ARTERIES pass into the cortex

-then each interlobular artery give AFFERENT ARTERIOLES



Renal Capillaries

-and EA give both PERITUBULAR CAPILLARIES (cortical nephron) and VASA RECTA (juxtamedullary nephron)

Renal Vein


4) Cerebral Circulation

-the brain receive its arterial supply from the VERTEBRAL and INTERNAL CAROTID arteries

-they are interconnected in the cranial cavity by ARTERIAL CIRCLE OF WILLIS

1) 2 Vertebral Artery


-each vertebral artery arises from the 1st part of SUBCLAVIAN ARTERY at lower part of the neck


-it passes superiorly through the TRANSVERSE FORAMINA of the upper six cervical vertebrae

-enters the cranial cavity through the FORAMEN MAGNUM


-the two vertebral arteries fuse inferior to the pons and form BASILAR ARTERY


•before union

  1. Ant Spinal artery
  2. Post Spinal artery
  3. PICA

•after union

  1. AICA
  2. Internal Acoustic
  3. Pontine arteries
  4. Superior Cerebellar arteries

•teminal branches

  1. Post Cerebral arteries

2) Internal Carotid Artery


-arises as one of the two terminal branches of the COMMON CAROTID arteries in the neck


-it enters the cranial cavity via CAROTID CANAL


-it gives off :

  1. Ophthalmic artery
  2. Post Communicating artery
  3. Mid Cerebral artery
  4. Ant Cerebral artery

3) Circle of Willis

-lies at the base of the brain by the interconnecting vertebrobasilar and internal carotid systems of vessels

-it is formed by

  1. Ant Communicating artery connecting the left and right ant cerebral arteries
  2. 2 Post Communicating arteries connecting the internal carotid artery with the post cerebral artery