regional circulation prof. k. sivapalan. 2013 regional circulation 2 regional blood flow. every...

Regional Circulation

Prof. K. Sivapalan

2013 Regional Circulation 2

Regional blood flow.

• Every organ has specific functions to perform.• The blood flow to each organ will vary

depending on the functional state of the organ, metabolic requirements and general conditions.


Pulmonary circulation.

• Pressure: 25 / 10 mm Hg.• Thickness of the wall of Pulmonary artery is only

30 % compared to aorta and arterioles also contain less muscles.

• 1000 ml of blood in pulmonary vessels when erect.• When erect, base of the lungs are at the level of the

heart.• When lying, most of the lungs are below heart level.• When lying 400 ml more accumulates.


Pulmonary circulation ctd.• Bronchial vein opens into the pulmonary vein resulting in

2 % deoxygenated blood mixing with oxygenated blood.• Capillaries form baskets around alveoli and their

diameter is 8μ.• Abundant lymphatics.• No tissue fluid formation in alveoli:

– Pressure less than oncotic pressure.– Surfactant.

• Function – gas exchange, filtration of clots, etc.


Splancnic circulation.• Blood flow through liver [1500 ml per min.].• From portal vein [1L] and hepatic artery to hepatic vein through

sinosoids.• Sympathetic: vasoconstriction• Reduces during heavy exercise and hemorrhage.• Parasympathetic: vasodialatation.• Vasoactive intestinal peptide from intestine dialates.• Blood flow doubles after meals.• Congestive cardiac failure: enlarged liver, necrosis around

central vein.• Cirrhosis of the liver [fibrosis]: acytis due to portal

hypertension.


Cerebral circulation.• Precapillary anastomosis between arteries are minimal

and not effective and so arteries in brain are known as end arteries.

• If they are occluded, the area supplied by them will result in ischemia and infraction.

• Deep veins empty into Venus sinuses in dura and internal carotid vein.

• Blood from eye and nose also drain into internal carotid vein.


Exchange of substances in cerebral vessels.

• Blood brain barrier: tight junctions in endothelium & pia mater [choroid epithelium] or end feet of astrocytes applied to endothelium.

• No fenestrations in capillaries.• Only water, CO2 and O2 cross BBB.

• Cerebrospinal fluid formed in choroid plexus.

• Astrocytes feed neurons.


Cerebral blood flow.• Cranium contains brain [1400 g.], blood

[75 ml], CSF [75 ml, 550 ml/d].• Flow: 750 ml/min. [54 ml/100 g.]• Kept constant by,

– Cranium.– Auto regulation [negligible VMC effect].– Cushing reflex- ↑ ICP → ↓ blood flow →

ischemia → + VMC, +CIC, ↑BP• Regional flow within the brain is affected

by metabolites.• Serious reduction of systemic blood

pressure reduces blood flow.• No blood for 1 minute – faint, 5 minutes:

serious damage to cortical areas. Further ischemia – death.


Coronary circulation.

• Coronary arteries arise from sinuses behind two cusps of aortic valves.

• Veins →coronary sinus →right atrium.

• Interior parts of ventricles drain directly into chambers, into left heart as well.

• Arteries anastomose to a certain extent. It can be improved by exercise.


Coronary flow.

• At rest: 250 ml/min. (84 ml/100g/min.) oxygen extraction 70 – 80 %.

• Left ventricle is responsible for ejection resulting in higher tissue pressure than the aortic pressure in systole.

• Flow in left coronary artery is highest during diastole.


Regulation of coronary flow.

• Mechanical factors.– Left ventricle- during systole intra muscular tension

compresses arteries and therefore blood flows only during diastole.

• Metabolites:– Hypoxia, hypercapnoea, acidity, potassium ions, lactic

acid, adenine nucleotides, adenosine- vaso dilators.• Neural:

– α constriction. [ in muscle, ↑force, metabolites → dilatation]

– β dilatation


Abnormalities of coronary flow.• Atherosclerosis is deposition of fatty material

below intima, calcification, damage to intima, etc.• This narrows the lumen and prevents dilatation

and promotes thrombosis which can block completely.

• When this occur in coronary arteries, angina pectoris and myocardial infarction can occur.

• Risk factors: over eating, diabetes, smoking, lack of exercise, stress.

• Alcohol – dilator but promotes atherosclerosis. ? benefit to heart.

• Aspirin 150 mg daily, glyceryl trinitrin and other drugs better care.


Cutaneous circulation.• Function of skin: heat loss and protection.• Flow 1 to 150 ml/min/100g.• Cutaneous vaso dilatation in hot and

constriction in cold under thermoregulatory center.

• Extreme cold, arterio-venus anastomosis shunt blood in fingers, toes, palm and ear lobes.

• Prolong exposure to cold – exhaustion of smooth muscles, vaso dilatation and bleeding [frost bite]

• Subdermal venous plexus- reservoir of blood.


Control of flow.

• Vasomotor tone – constriction.• Circulating catacholamines- constriction.• Thermoregulatory influence over rides

baro receptor influences. [blanket and shock]

• Local metabolites – dilatation.• Reactive hyperaemia- after occlution.• Dilatation caused by alcohol.


Response to injury.

• Mild stroke-– white reaction. – [Mechanical stimulation to

pre capillary sphincters.]• Deeper stroke- triple

response:– Red reaction [ cap.

Dilatation.]– Wheal [cap. Permeability]– Flare. [art. Dilatation]

• Axon reflex.


Capillary circulation.

• Contain 5 % of the blood.• Active blood [exchange].• Transition time – 1 -2 sec.

– Pre capillary sphincters- controlled by local metabolites.

• Fluid exchange.• Pulse pressure from 5 → 0.

[pulsatile → non pulsatile]


Special capillaries.

Liver – sinusoids.

Brain – BBB.

Kidney – glomerular tuft and vasa recta.


Uterus.

• 8 x 5 x 3 cm, 70 grams.

• Pregnancy – well developed uterus and fetus.

• Uterine artery develops and blood flow increases more than 20 times.


Placental circulation.• The placenta has to provide

oxygen and nutrients to and remove wastes from the fetus.

• Umbilical vein and artery form villi covered with chorion.

• Inter villus space is filled with maternal blood.

• Arterioles open into and venules drain the blood from this space. [no capillaries]

• This increases cardiac output but reduces peripheral resistance.

• Pulse pressure increases.


Fetal respiration.

• Gas exchange through placenta.• Fetal Hb % = 18 g/100 ml.• Fetal hemoglobin attaches to oxygen at

lower partial pressure than adult Hb.


Fetal circulation.• Umbilical vein: 80 % saturated.• Venous blood from lower body: 26 %

saturated.• IVC: 67 % saturated.• Left atrium gets IVC blood through

foramen ovale.• Upper body gets this blood through

aorta.• SVC [60 % saturated] drains into right

ventricle through the atrium and goes to lower body and placenta through ductus arteriosus [lung high resistance]

• Pressure in pulmonary artery is higher than in aorta.

• 55% of cardiac out put goes to placenta.


Change at birth.

• Placental circulation cut.

• Foramen ovale is closed [left atrial pressure rises, umbilical vein closed]

• Ductus arteriosus is closed as lungs expand and draw blood in.

regional circulation prof. k. sivapalan. 2013 regional circulation 2 regional blood flow. every...

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