Appreciating Blood

As blood flows from the heart through arteries, capillaries and veins, this amazing substance keeps us alive. The beautiful red color of blood is due to the iron in hemoglobin, the molecule in red cells that carries oxygen.

Blood delivers oxygen, hormones and nutrients to body cells and picks up waste products from them.  White blood cells contain the many elements of the immune system.  Blood helps to control body temperature.  It carries a clotting system to control blood loss after injury. 

As blood travels throughout the body, its red cells deliver oxygen to all body cells and remove carbon dioxide.  After returning to the heart, blood travels to the lungs, giving off carbon dioxide and picking up fresh oxygen. Blood picks up digestive products from the intestines and carries them to cells for metabolism/energy production.  At the same time, it removes waste products from cells and delivers them to the kidneys for excretion.  All this is happening at great speed – a red blood cell will circulate through the body and return to the heart every 60 seconds. 

Have you ever wondered why your skin will bleed when pricked with something as tiny as a pin?  There is a capillary exceedingly close to every cell in the body. Capillaries are the smallest and most numerous blood vessels in the body, with an inner diameter just wide enough for a red cell to squeeze through.  It is estimated that there are 25,000 miles of capillaries in an adult human body.

Blood vessels help to regulate body temperature by dilating close to the skin when we are overheated, as in a hot flash or after exercise.  Heat is thereby lost to the outside air.  When we are cold, blood vessels in the skin constrict, saving warmth in our core. (Shivering also helps to create more heat.)

We have 6-8 liters of blood in our adult bodies, or about 10 pints.  About 45% of this is cells, and 55% plasma.  Plasma is a watery tissue containing dissolved proteins (albumin, globulin and fibrinogen), glucose, blood fats, clotting factors, electrolytes, hormones and carbon dioxide.  It is the protein reserve for the body.

Red and white blood cells and platelets are produced in the bone marrow of our ribs, sternum, vertebrae and pelvis.   We produce billions of blood cells a day, to replace those that have a short life.  Red blood cells live 120 days, and white cells a much shorter time. Platelets are small clear cell fragments that are essential in preventing blood loss by forming a plug at the site of an injury.  Blood components come from stem cells - undifferentiated biological cells that can become specialized - in the bone marrow they give rise to red cells, white cells and platelets.

The blood clotting system consists of numerous factors that circulate continuously through the body in an inactive form. When platelets make a plug to stop bleeding, a substance called fibrin starts to form a clot, and the many  other clotting factors are activated in a chain reaction called the coagulation cascade.

This has been a simple explanation of the functions of blood, probably familiar to all readers.  In a subsequent column I will write a more detailed description of the immune system. In the meantime, here are some ideas for keeping your blood working well for you.

Avoid blood-born diseases such as Hepatitis B and C and AIDS by never sharing a needle, and practicing safe sex with condoms with any new partner.

Have a complete blood count (CBC) when you see your doctor, to test for anemia (this is especially important for women with heavy periods).  Eat iron containing foods and take an iron supplement if needed.  There are forms of anemia that do not require iron, but may require B vitamins.  Find out; don’t guess.  It’s important.

Breath deeply, exercise and keep good posture to fully oxygenate your blood.  Don’t smoke.  In addition to damaging your lungs, smoking constricts your blood vessels and impedes circulation to your heart, your limbs and your vital organs.

If you are taking a blood thinner such as Coumadin, aspirin, Pradaxa, or similar new anti-coagulants, keep something on hand that helps to stop bleeding from nosebleeds, small cuts or external injuries.  Several products are available on line and in pharmacies without a prescription, containing a powder that causes blood to coagulate.  You sprinkle it on the wound, or introduce it into your nose with an applicator, and then apply pressure.  I am familiar with a product called QR – it is quite helpful with small cuts or nosebleeds.  It should not be used if stitches are necessary, a wound is infected, or if bleeding is arterial.  For gushing arterial bleeding, apply direct pressure with a clean cloth or bandage, and get emergency help at once. 

Sadja Greenwood, MD    Past columns on this blog.  Check out my novel, Changing the Rules, at the Grand Hotel, Uniquities, the Stinson Beach and Point Reyes Book Stores, and Amazon.

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Go to Health: Tomatoes All Year!


You might not expect that the latest on the benefits of tomatoes would come from the Lapland Central Hospital in Finland. Despite their short growing season, Finns are said to love tomatoes when they can get them. Finnish researchers studied what blood factors (from diet) were associated with a lowered risk of stroke in men, expecting to find correlations with levels of vitamins E and A. Instead, they found that men in the highest quartile of serum lycopene had a 55- 59% lower risk of stroke than those in the lowest quartile. Alpha and beta carotene, vitamin E and A were not associated with stroke risk.






Researchers at the College of Nursing, University of Kentucky, found that patients with heart failure who had the highest intake of tomatoes in their diet had longer times between adverse cardiac events.






Studies from Chungbuk National University in Korea found that tomato extract added to the diets of mice caused weight loss, despite a high-fat diet. Total cholesterol and LDL cholesterol were also reduced.






Studies from the University of Talca in Argentina found that rats supplemented with tomato extract had a reduction of platelet clumping, which would reduce blood clotting and improve blood flow.






Recent Canadian studies have looked at post menopausal women between 50 and 60 who were given lycopene-rich tomato juice, lycopene supplements or a placebo for 4 months. They were tested for blood markers of osteoporosis. Those taking tomato juice or lycopene were found to have reduced levels of bone breakdown compared to those given placebo. Subsequently, these researchers studied women who were told to restrict their intake of tomatoes or lycopene; in this study bone markers for osteoporosis were significantly increased.






U.S. studies from the 1990’s looking at male health professionals showed that frequent intake of tomato products was associated with a reduced risk of prostate cancer. Because further studies could not confirm this finding, Harvard researchers did a careful re-analysis in 2002 and again found a moderately reduced risk.






Tomatoes, which originated in South America and were first cultivated in Mexico, are clearly loved all around the world. Enjoy them! Do not start taking a lycopene supplement after reading this column. Excess intake of single carotenes may be counterproductive. There are many factors in tomatoes besides lycopene that can be healthy. Do start eating more tomato products while waiting for the ripe ones to come back into season. Tomato paste and low sodium organic Very Veggie are great choices – you can find them in our local stores in glass containers – free of BPA (Bisphenol A) and other chemicals. You can preserve homemade tomato sauce when they are in season; people lacking the time or expertise for home canning can simply freeze them. Here’s a great website from the University of Nebraska on easy ways to preserve tomatoes - http://food.unl.edu/web/preservation/freezing-tomatoes.






The beneficial compounds in tomatoes are best absorbed when eaten with fat, so include a healthy oil, such as olive oil, in your cooking or on your salad. Be careful of the high sodium content in many commercial tomato soups and sauces. You probably know that watermelon is also a good source of lycopene.






Next month I’m going to write about the amazing abilities of silkworm cocoons to keep vaccines and antibiotics cool, even in areas of extreme summer heat. This could be a great boon to immunization programs in Africa and Southeast Asia. Stay tuned!


Sadja Greenwood MD back issues sadjascolumns.blogspot.com