The miracles of blood – Part II

 Second in a Series

Dr. Charles E. Crutchfield, III

Blood is one of the most interesting and complex substances known to humankind. Last week we discussed the ability for blood to deliver oxygen to tissues and muscles for growth and performance. In the past, our blood was also associated with “emotions.” If someone was passionate or short-tempered, they were called “hot-blooded.” If someone was mean or lacked emotion, they were called “cold-blooded.”

We have come to learn that blood is much different and more complex than this. This week will talk about blood’s ability to deliver nutrients to every cell, tissue and organ in the body.


In review, blood has six basic functions

  1. Delivering oxygen to cells and muscles to kept them running at their peak and allowing them to produce energy
  2. Delivering nutrients to every cell to keep them healthy and growing
  3. Acting as a major player in our immune system and defending the body
  4. Transporting waste products away from cells so the body can expel them
  5. Performing messenger functions: the transport of hormone signals from one tissue or organ to another
  6. Regulating core body temperature and maintenance of body fluid levels

More blood facts

  • Blood makes up approximately seven to eight percent of the weight of a human body.
  • Plasma, the yellow liquid that makes up a large part of the fluid of blood, contains water, nutrients, proteins, glucose, gases, hormones and electrolytes.
  • Red blood cells are produced in the bone marrow and have a lifespan of about 120 days.
  • Blood delivers vital substances to our cells, but it also removes waste products.

Blood pressure

One of the main signs of life for humans is blood pressure. Blood pressure is the amount of pressure exerted on blood vessel walls when there is a sufficient volume of blood flowing through the circulatory system. Unfortunately, high blood pressure can have a negative impact on health, so it is important for people to keep their blood pressure within a healthy range.

Blood as a transport system

Blood transports vital substances to the cells and takes waste products away. Some of the products blood delivers are chemical and protein messengers from other parts of the body, commonly known as hormones. In this way, blood allows all the cells in the body to communicate with the other cells in the body.

Some organs can sense the presence of certain materials in the blood and release other messengers (hormones) into the blood that can have profound effects on the way our body functions. Many hormonal organs and the brain can use these messengers to precisely regulate and control how the body functions. An excellent example is the release of insulin, by the pancreas, to control the levels of sugar in the blood.


The yellow liquid part of the blood, known as plasma, contains all the materials that are the breakdown products of what we eat. The nutrients are absorbed from the food breakdown in our intestines after we eat. The nutritional make-up of plasma is never the same and changes several times per day.

Nutritionally, plasma contains fats, sugars and proteins. These are delivered throughout the body as fuel, building materials for growth and replenishment, and additional fuel for storage, commonly known as “body fat.”


We really are what we eat.

There is a new science that studies the different products in our blood after we eat. It is called metabolomics. Interestingly, the thousands of products in our plasma after eating are a result of what we eat and, importantly, our genetics.

Our genes determine how we process and break down the food we eat in our diets. Different people, having eaten the same meal, will have a slightly different metabolomic profile in their blood.

Some metabolomic profiles may produce plasma high in free fatty acids. This type of profile has been associated with inflammation, and inflammation is bad for the body’s overall health. So, metabolomics allows us to find out what happens to the food we eat and how it affects us.

Being loaded with all these breakdown food products, our blood is, in a sense, very nutritious. This is evidenced by the insects and other creatures that crave our blood such as mosquitos, leeches and lice.

Oddly, in the Roman days, people, especially people who were old or ill, would try to actually lick the wounds of recently killed gladiators to get the nutrients and “vital blood” of these young, strong and healthy gladiators.


Another interesting fact about blood is that it wasn’t until the early 1600s that we discovered that blood circulates. Before then, it was believed that the body made a fresh supply of blood daily. Dr. Harvey did an experiment that measured about 9-10 liters of blood being pumped by the heart every hour, meaning 240 liters being pumped daily. It would be impossible for the human body to make 240 liters of blood daily! Therefore, blood must circulate.

In fact, to transport our blood, the body contains almost 60,000 miles of blood vessels. That is enough to wrap around the earth almost 2½ times!

Blood vessels are of an ingenious design. Scientists have come to realize that their gently curving shapes are marvels of engineering, allowing blood to flow smoothly and not clot. This knowledge is invaluable for heart and vascular surgeons.

Our vascular system allows blood to travel to every organ, every tissue and every cell in our body, delivering a rich payload of oxygen and nutrients. The vasculature system is also involved in allowing our blood to defend us and expel waste products.

We will discuss our blood’s ability to defend and protect us next week.


Charles E. Crutchfield III, MD is a board certified dermatologist and Clinical Professor of Dermatology at the University of Minnesota Medical School. He also has a private practice in Eagan, MN. He received his M.D. and Master’s Degree in Molecular Biology and Genomics from the Mayo Clinic. He has been selected as one of the top 10 dermatologists in the United States by Black Enterprise magazine. Dr. Crutchfield was recognized by Minnesota Medicine as one of the 100 Most Influential Healthcare Leaders in Minnesota. He is the team dermatologist for the Minnesota Twins, Vikings, Timberwolves, Wild and Lynx. Dr. Crutchfield is an active member of both the American and National Medical Associations.


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