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Coronary Circulation


Coronary Circulation-via R. & L. coronary arteries.

1. endarteries but anastamosis can be seen in pathological conditions.

2. LAD most commonly involved in CAD.

3. 60-80 ml/100 gm/min or 250 ml/min

4. Maximum A-V O2 Difference & O2 extraction.

5. phasic i.e supply more during diastole, minimum during systole(zero in subendocardium), so more capillaries

6. autoregulation is present – adenosine (main metabolite), K+, H+, CO2

7. sympathetic stimulation increases and parasympathetic stimulation decreases coronary blood flow.

Cerebral circulation–Circle of Willis   

1. 50-60 ml/100 gm/min or 750 ml/min. O2 consumption: 49 ml/min

2. Autoregulation present.

3. Factors regulating cerebral blood flow (CBF):

a. Inc. pCO2 & dec.  pO2 cause vasodilatation & vice versa

b. Cerebral metabolism rate

c. Cerebral perfusion pressure: Mean arterial pressure – intracranial pressure

d. Blood viscosity

e. Temperature: Fall in temp. by 1o C decrease CBF by 5-7%

The Blood-Brain Barrier and Cerebrospinal Fluid

  1. The barrier between cerebral capillary blood and cerebrospinal fluid (CSF) is formed by cerebral capillary endothelium connected by tight junctions & Astrocytes
  2. Water easily diffuses across the BBB; nonionized drugs cross more readily than ionized drugs.
  3. Glucose, the primary energy source of the brain, requires carrier-mediated transport (GLUT 1 & 3)
  4. Except CO2, Creatinine, Cl- HCO3- & Mg2+ all substances are more in plasma as compared to CSF
  5. Most CSF is secreted by the choroid plexus (meningeal vessels). CSF fills the subarachnoid space and ventricles of the brain. Regulation of pressure is by absorption which occurs in arachnoid villi. (10% lymphatics also)
  6. Normal vol. 150 ml. Daily production 500 ml. Rate 0.2-0.3 ml/min
  7. Pressure 50-180 mm H2O  or 10 mm Hg. Below 68 mm absorption stops.In sitting more than lying.

Composition of CSF


292-297 mOsm/L


137-145 mmol/L (137-145 mEq/L)


2.7-3.9 mmol/L(2.7-3.9 mEq/L)


1.0- 1.5 mmol/L(2.1 – 3.0 mEq/L)


1.0-1.2 mmol/L(2.0-2.5 mEq/L)


116-122 mmol/L(1 16-122 mEq/L)

CO2 content

20-24 mmol/L(20-24 mEq/L


6-7 kPa (45-49 mmHg)




40-70 mg/dL


10-20 mg/dL


20-50 mg/dL


<5 per mL


60-70 percent


30-50 percent




  1. Regions lying outside BBB are: post. Pituitary, Area Protrema, OVLT & Subfornical Organ & Median eminence of hypothalamus Hepatic Circulation : 1500 ml/min, dual via portal vein (80%) % hepatic A. (20%)

Difference between Systemic & Pulmonary circulation

Systemic or greater circulation

Pulmonary or lesser circulation


high pressure & high resistance circulation (aortic pressure- 120/80 mm Hg & average capillary pressure 17)

low pressure & low resistance circulation

(pulmonary trunk pressure- 25/8 mm Hg &     average capillary pressure 7 )

Compliance relatively less

It is high-compliance system and The empty  vessels are ready to accommodate either acute or chronic increases in PBV (recruitment), with little or no increase in pulmonary arterial driving pressure.

Hypoxia causes vasodilatation (due to ATP sensitive K channels)

Hypoxia causes vasoconstriction (due to hypoxia sensitive K channels). Also decline in pH also produces vasoconstriction in the lungs, as opposed to the vasodilatation it produces in other tissues.

The mean velocity of the blood in aorta is about 40 cm/s.

The mean velocity of the blood in the root of the pulmonary artery is the same as that in the aorta. It falls off rapidly, then rises slightly again in the larger pulmonary veins.

Body responses to exercise


1. Muscle Blood flow: ­

a. At rest à 2-4ml/100g/min (650ml/min)

b. During maximal exercise à 90ml/l00g/min (20850 ml/min) 25 times of normal

c. Local mechanism blood flow (vasodilation) Po2, Co2 (H+ or pH) and accumulation of K+.

2. Systemic circulatory changes: ­

i. With the start of an isometric muscle contraction the heart rate rises, largely due to ed vagal tone. Strokevolume  changes relatively little

ii. Response to isotonic muscle contraction prompt increase in Heart rate and marked increase in stroke volume, and there is net fall in total peripheral resistance.


a. Cardiac out put: ­

  1. At rest -t 5.5 L/min
  2. During isotonic exercise →  35 L/min

b. Heart rate: ­

In children 200 or > beats/min

In adult rarely exceeds> 195 beats /min

→ In Elderly persons rise is even smaller.

Maximum HR is given by 220-age.so 200 is the best answer


3. Respiratory Response to Exercise

  1. At start of exercise ↑ ventilation due to psychic stimuli and afferent impulse from proprioceptors in muscles and tendons.
  2. Arterial O2 tension remains in normal range which is provided by :
    ↑↑ Ventilation, pulmonary blood blow (5.5 L/min at rest to as much as 20-25 L/min in exercise) CO
  3. Arterial PaCO2 either normal or low in moderate exercise and more vigorous exercise respectively therefore HCO3 levels of blood is either normal or low.
    1. Despite CO2 production in exercise, Arterial.PaCO2 remain normal or low, due to increased excretion of CO2 by lungs from 200 ml/min at rest to as much as 8000 ml/min.
  4. Other changes in exercise
    1. ↑ Body temp.
    2. ↑ Serum K+ level
    3. ↑ lactic acid
  5. In moderate exercise Arterial pH, PCO2 and PO2 remain constant (by increasing ventilation and CO)
  6. Effect of exercise on blood flow to various organs

Blood flow during rest ml/min Blood flow during exercise ml/min

Cardiac output









Skeletal muscle






Kidney, liver and GIT




  1. Effect on the CVS on changing posture from supine to the upright: -           
    1. Arterial blood pressure     →  decrease
    2. Central venous pressure    → decrease (3 mmHg)
    3. Heart rate                        →  increase (25)
    4. Abdominal and limb flow'  →  decrease by 25%
    5. Cardiac output                → decrease by 25%
    6. Stroke volume                    → decrease by 40%
    7. Abdominal and limb resistance   → increase
    8. Total peripheral resistance      → increase by 25%
    9. Small vein pressure                →  increase 10 min Hg
    10. Cerebral blood pool                 decrease by 400 ml

Note: Orthopnea never occurs in a normal person due to Reservoir function of pulmonary veins

  1. The pulmonary veins are an important blood reservoir because of their distensibility.
  2. When a normal individual lies down, the pulmonary blood volume increases by up to 400 mL, and when the person stands up this blood is discharged into the general circulation.
  3. This shift is the cause of the decrease in vital capacity in the supine position and is responsible for the occurrence of orthopnea in heart failure.    
  4. Orthopnea is due to increased distribution of blood to the pulmonary circulation while recumbent. Orthopnea is often a symptom of left ventricular heart failure and/or pulmonary edema.
  5. Mechanism: the Left heart's failure causes congestion of the Left atrium. the Pulmonary Vein and thus the lungs also will become congested. In a supine position this congestion is compounded with the ease by which blood can backflow from the atria , against blood coming back from the lungs. When one is sitting up, gravity helps to keep the congested blood from working as much against the blood returning from the lungs, allowing less congestion of the lungs itself and thus less difficulty breathing
Region Blood Flow AV Oxygen
O2 Consumption Percentage of Total body
ml min mL/100gm/min mL/min mL./l00 gm/min Cardiac Output O2 Consumption
Liver 1500 55 35 51 2.0 30 20.5
Kidneys 1250 420 15 18 6.0 25 7.5
Brain 750 54 65 49 3.0 15 19.5
Skin 450 13 25 12 0.3 9 5.0
Skeletal muscle 800 2-4 60 50 0.2 16 20.0
Heart muscle 250 84 100 27 10 5 10.0
Whole body 5000 8-10 50 250 0.4 100 100

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