Relationship between Blood and Lymph Circulation

Blood Flow and Pressure

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Arterial and venous bloodMost of the blood is kept in the veins because they expand (largest distensibility) to occupy more blood.

The velocity of blood flow in the veins increases due to the greater total cross-sectional area of veins over capillaries.

Arteries contain fewer blood compared to veins because of their restricted distensibility.

Blood moves in the arteries by the direct pressure created by the heart.

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Movement of blood in veins

Muscle Pump:Contracting muscles compress veins and bush blood to the heart.

Respiratory Pump:During inspiration, intra-thoracic pressure is reduced and abdominal pressure is increased. This increases the venous return by increasing the venous flow from the abdominal viscera to the heart and lungs.

Veino-Constriction:In the abdominal viscera, cause increase in the venous flow during exercise.

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Blood capillaries

Due to constrictions of the arterioles and the presence of the precapillary sphincter blood reach the capillariesin a decreased pressure.

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The velocity of the blood flow is related to the total cross-sectionalarea of the type of the blood vessel. For example:

Cross-sectional area Velocity

Aorta 2.5 cm 240 cm/secArteries 30 cm2 10 – 40 cm/secArterioles 40 cm 20.1 cm/secCapillaries 2500 cm2 Less than 0.1 cm/secVeinules 250 cm2 0.3 cm/secVeins 80 cm2 0.3 to 5 cm/secVena Cavae 8 cm2 5 to 20 cm/sec

Velocity of Blood Flow

Distribution of blood in the circulatory system

• Heart 3%• Pulmonary circulation to lungs 10%• Systemic circulation 87%

• Arteries 17%• Capillaries 5%• Veins 65%

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Lymphatic circulation

Lymphatic system is formed of the lymph and lymph nodes.

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Lymphatic system has 3 basic functions:

- Transports interstitial fluid back to the blood.

- Transports absorbed fat from the intestine to blood.

- Provides immunological defense against microbes.

Formation of lymph

The high blood pressure at the arterial capillary region and the osmosis cause the plasma to be filtered into the intercellular space and called intercellular fluid.

Some of this fluid returns directly to the blood capillaries at the venous region. The remaining part enters the lymphatic capillaries.

Absorbed fats, proteins, interstitial fluid and microorganisms enter the lymphatic capillaries and are referred to as lymph.

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Lymph transportLymphatic capillaries are closed-end capillaries found in the intercellular spaces of the organs.

From the lymphatic capillaries the lymph is carried to large ducts called lymph ducts.

The lymph ducts are similar to the veins in their structure, having the same three layers andvalves to prevent backwards flow.

Lymph ducts contract to facilitate the flow of the lymph.

Blood capillaries

Interstial Fluid

LymphCapillaries

Lymph Ducts

High pressure

Large Circ.Veins

Lowpressure 9

The lymph ducts pass through lymph nodes where filtration of the lymph from germs takes place.

The filtration takes place by lymphocytes which are part of the immune system of the body.

Relation between lymphatic and circulatory systems

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The lymph ducts empty in the general circulation at the neck region.

Thus all lymph products are delivered back to the circulation.

Circulatory changes during exercise

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Rest Ex.

Heart 250 1250

Viscera 1250 1250

Kidneys 1000 1000

Bones 250 250

Brain 750 1000

Sk. Muscles

1000 21250

Blood pressure

The most important variables that affect blood pressure are heart rate, stroke volume and total peripheral resistance.

An increase in any one of these parameters will produce an increase in the blood pressure.

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The contraction of the heart produces the pressure necessary for the blood flow around the body.

Blood pressure in different vessels of the systemic circulation

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Blood pressure measurement

Stethoscope

Sphygm

omanometer

Cuff

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Measurement of blood pressure

Blood pressure is usually measured by sphygmomanometers in mmHg .

The rubber bladder is inflated and pinch the brachial artery. When air is released the first sound is heard just at systole and continue till the pressure reach diastole and the sound disappear because of the normal flow.

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Measurement of blood pressure

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Pulse pressure and mean arterial pressure

The pulse pressure is produced because of the rise of pressure from diastolic to systolic. The pulse pressure value is the difference between the systolic anddiastolic pressure.

PP = SP – DP

For example: 120 mmHg – 80 mmHg = 40 mmHg

The mean arterial pressure is the average arterial pressure during the cardiac cycle.

In the cardiac cycle diastole is longer than systole. Mean arterial pressure can be approximated by adding one third of the pulse pressure to the diastolic pressure.

Mean arterial pressure = diastolic pressure + 1/3 pulse pressure

For example: 80 mmHg + (40 x 1/3) = 93 mmHg

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