blood VESSELS 

Blood vessels are the bodies highways that allow blood to flow quickly and efficiently from the heart to every region of the body and back again. The names of blood vessels from the heart to capillaries and back to the heart are in order : aorta | arteries | arterioles | capillaries | venules | veins | vena cava

As the blood vessels leave the heart, and spread through the body, they become smaller and smaller in diameter while at the same time there are more and more branching vessels. Because the increase in number of vessels, the surface areas of the vessels increase, allowing for diffusion of gas and nutrients to and from tissues. The total surface area of capillaries is the largest even though the diameter of the capillaries is the smallest. As the capillaries becomes venules, the diameter increases while the total surface area decreases.

• ARTERIES - Carry oxygenated blood away from the heart (except the pulmonary artery, which carries deoxygenated blood away from the heart to the lungs) They Have thicker, more elastic and muscular walls, allowing stretch to accommodate the pressure. They can contract or expand to regulate the flow of blood. In this way the body controls how much blood flows to different parts of the body under varying circumstances. 

• VEINS - Carry deoxygenated blood to the heart (except the pulmonary vein, which carries oxygenated blood from the lungs to the heart.) They have thinner walls and can’t constrict. Many veins particularly ones in the arms and legs have valves, to ensure that blood only flows in one direction, back to the heart. They open when the blood flows toward the heart and close when blood might flow backward ie due to gravity. Compression of  veins by muscular contraction helps squeeze blood back to the heart. just as squeezing a toothpaste tube ejects toothpaste, the powerful calf muscles for example are particularly important, forcefully compressing the deep veins in the legs with every step.

• CAPILLARIES - are the smallest and thinnest of the blood vessels and the most common they can be found running throughout almost every tissue of the body. Capillaries carry blood very close to the cells of the tissues of the body, in order to exchange gases, nutrients and waste products.

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blood PRESSURE

Blood pressure is the pressure of blood in your arteries. This figure changes throughout the day on exertion, stress, fear , meditation. E.g. 120/80 

- Systolic pressure: This is the highest level of your blood pressure – when your heart beats and contracts to pump blood.

- Diastolic pressure: This is the lowest level of your blood pressure – when your heart relaxes between beats.

Blood pressure is determined by two factors:

1 CARDIAC INDEX - the volume of blood pumped by the heart per minute, determined by : 

• Heart rate (The number of heart beats per minute.} The average resting heart rate is usually between 60 and 80 bpm. But some athletes have resting heart rates as low as 30 to 40 bpm.

• Stroke volume index (the volume of blood pumped by the heart with each beat (scaled for body size) This is determined by; the filling pressure of the heart at the end of diastole; the inherent vigour of contraction of the heart muscles during systole; and the pressure against which the heart must work to eject blood during systole. Physical exercise may increase stroke volume, resulting in a lower (resting) heart rate. Reduced heart rate prolongs ventricular diastole (filling), increasing end-diastolic volume, and ultimately allowing more blood to be ejected. Lack of regular exercise = decreased heart stroke volume so heart rate increases to achieve need of cardiac output. Exercise makes the heart and blood vessels more robust, more resilient, and more responsive to the stresses of life.

2  PERIPHERAL RESISTANCE - the resistance of the arterial vessels to blood flow, determined by :

• Autonomic activity. The sympathetic NS is activated during stressful situations (fight or flight) and acts on the capillaries by constricting them increasing resistance and so blood pressure. The parasympathetic nervous system activated during yoga, (rest and digest) relaxes the capillaries and reduces peripheral resistance and overall blood pressure.

• Blood viscosity (increased viscosity increases resistance.)

- Hypertension - High blood pressure = strain on system 140/90mmHg 

Doesn’t often show symptoms but can lead to heart disease, heart attacks, strokes, heart failure, kidney disease.

- Hypotension  - Low blood pressure = less than 90/60mmHg. It does not always cause symptoms, but may cause lightheadedness or dizziness, feeling sick, blurred vision, generally feeling weak, confusion, fainting.

YOGA &

the cv system

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Stress itself magnifies all the risk factors for heart disease. When you’re chronically stressed, your blood pressure and cholesterol goes up because of the increase in cortisol. Yoga is a natural relaxant which calms the mind and soothes the nervous system reducing our stress response and its harmful effects. Studies found that yoga is linked to the reduction of key risk factors for heart disease, including lower body mass index (BMI), weight loss, improved cholesterol levels, lower blood pressure, and reduced heart rate. 

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Standard medical advice for people whose blood pressure is controlled on medication is to engage in exercise and other healthy activities that a person with normal blood pressure would do. This means all of yoga, including inversions if introduced gradually. In fact, inversions trigger several reflexes that temporarily reduce blood pressure, so theoretically, regular practice may enhance treatment of your high blood pressure. Note, however, that people whose high blood pressure is not under control should bring the pressure down first by other means before practicing inversions.

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Yoga for those with low blood pressure, that involves sudden changes in posture — can trigger symptoms, including dizziness, blurred vision, and nausea. That doesn’t mean someone with hypotension shouldn’t practice, be cautious of the pace, without bending and rising quickly to an upright position. Yoga can be beneficial in helping with hypotension, as it helps improve blood circulation.

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Above all, yoga gives us the opportunity to actually begin to pay attention to ourselves, to have self-recognition and understanding of who we are, which is most valuable. With yoga we start to look at the heart as part of the organic process of healing the whole self.

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