Smorgasbord Health -The Circulatory System -60,000 mile long network.

As we get older our bodies require more and more maintenance to keep essential functions and systems working efficiently. What worked for us at 20, 30 and even 50 is not necessarily enough once we get over 60 or older. Our circulatory system is not an optional extra but a critical and essential pathway throughout our body that carries our lifeblood. Without that lifeblood our organs die and within a few minutes the core of our being.. the brain dies.  In this series of updated posts from 18 months ago I will be covering both the network and the blood that it carries.

Our blood is fascinating and whilst we only see with the naked eye, under a microscope it is teeming with life.. most of which is essential to our own.  But before moving onto the blogs about the blood that flows through our body, a couple of articles on the system that carries it.

We have all suffered from bruising at some point in our lives which is when damage occurs to the blood vessels closest to the skin, but damage can also occur deep inside our bodies that can be extremely serious. Today a look a the structures themselves and next time how these arteries and veins can be damaged.

Depending on our age, the average adult has between 60,000 and 100,000 miles of blood vessels should they be laid end to end. Enough to circle the world 7 times. Our blood will travel around our bodies and achieve around the 12,000 miles each day. That is 500 miles an hour. There are an average of 8 pints of blood or 4.7 litres in an adult and this has to carry all the nutrients and oxygen we need to live around the body to keep our major organs alive.

A blockage in this 60,000 plus miles of blood vessels can be catastrophic as even a few minutes of lack of oxygen to a vital organ such as the heart or brain will cause a heart attack or stroke.

I have covered the results of blockages in the blood flow on the brain and the heart in previous blogs, but we rarely consider this amazing system that feeds those organs unless we cut ourselves or notice a bruise.

Maintaining the health of our blood vessels is fundamental to our health and the network needs a combination of oxygen, specific nutrients and exercise to keep them flexible and clear of debris.

Today I will talk about the structural aspects of the system and then over the next few blogs I will cover the common health issues of the vessels and the nutrients needed to keep them healthy.

How does blood circulate?

There are really two circulatory systems working in the body, the pulmonary and the systemic. Apart from the major veins and arteries there are also millions of smaller blood-vessels that form an interconnecting pathway throughout the body.

In the diagram below the blue is oxygen poor blood and the red is the oxygen rich blood.

pul-circ no labels

In the pulmonary system de-oxygenated blood is taken from the heart to the lungs where it is replenished with oxygen before making the return journey back to the heart. The oxygenated blood leaves the heart in the systemic circulatory network and taken to every single part of the body.

Although the circulation in our bodies is a closed system, the blood in the circuit begins its journey around the body in the left ventricle of the heart into the aorta. The blood at this point is oxygen-rich and full of nutrients and hormones as well as other substances necessary for us to function.

The coronary arteries split off and the aorta passes upward before doubling back on itself in an arch. From this arch the two main arteries to the head split off (left and right carotid arteries) and the main arteries for the arms (brachial). The aorta descends down the chest and into the abdomen where it branches off to the liver, intestines, and each kidney before dividing into the left and right iliac arteries, which supply blood to the pelvis and the legs. From there the blood passes into the arterioles and capillaries to feed the interior of organs and outlying areas of the body and remove any waste.

After passing through these tiny blood-vessels the blood is passed into the veins starting its return journey in small vessels called venules which are similar in size to the arterioles. It then makes its way back to the heart via the veins, which are close to the skin and visible at most times to the naked eye. These are the veins that contain valves to ensure the blood travels in only one direction.

All the veins in the body eventually merge into two very large blood-vessels called the superior vena cava and the inferior vena cava. The first collects the blood from the head, arms and neck and the second the blood from the lower half of the body. This blood then passes back into the heart and out to the lungs where it is re-oxygenated and returned to the heart to begin the process all over again.

What is the structure of the different blood-vessels?

Arteries are subjected to enormous pressure with each strong heartbeat and they therefore have to be thick walled and muscular. The outer layer of the artery (tunica adventitia) is a loose fibrous sheath filled with tiny blood-vessels that supply nutrients to the artery walls. Beneath this is an elastic sheath covering the muscular layer (tunica media) that gives the artery its strength. There is an internal elastic area covering the lining (tunica intima) of the blood-vessel.

 Artery 1

The thick elastic and muscular walls are vital if the system is to work efficiently and the blood is to be pushed around the entire body.

When you take your own pulse you will be measuring the force of each heartbeat as it is transmitted through the arteries and it is a very useful diagnostic tool for a doctor when determining any heart or circulatory problems you might be experiencing.

Veins are similar to arteries in the way that they circulate and when they both service major organs they often run in parallel. The major differences in the two blood-vessels are structural to enable them to perform their own individual roles in the circulatory system.

Veins have much thinner and more flexible walls that can expand to hold large volumes of blood. The pressure of blood returning to the heart is much lower than that in the arteries and its movement requires the use of valves in the veins to prevent the blood going backwards in the system.

The smallest capillaries only measure about eight- thousandths of a millimetre and are barely wider than a single blood cell. These minute vessels are thin and porous allowing the nutrients, oxygen rich blood and waste to pass between the circulatory system and the cells freely.

Capillaries also have another vital role in the body and this is in their ability to help regulate our body temperature. When the body is hot the capillaries in the skin expand to allow more blood to reach the surface of the skin and be cooled. When we experience extreme cold our circulatory system closest to the skin will begin to shut down forcing our blood to the centre of our bodies to ensure that our hearts and lungs are protected.

The capillaries nearest the skin are the most vulnerable to cuts, and when we bruise it is the damage to these small blood-vessels just under the skin which cause the discolouration. During our lifetime, any damage is usually repaired but as we age this ability lessens and capillaries collapse and leave the purple patches behind that are commonly seen on the arms and legs of the very elderly.

After passing through the capillaries and having completed the job of providing oxygen and nutrients from the tips of our toes to the scalp tissues the blood returns to the heart in the veins.

Are there any interruptions to the smooth flow of blood in our system?


At some stage, food that we have consumed must be processed and the nutrients extracted and waste removed. Part of this process involves the intestines and the liver. When blood leaves the intestines it does not flow directly back to the heart but diverts into the liver or hepatic portal system of veins. Once in the liver this enriched blood passes through the liver cells in special capillaries called sinusoids before passing back into the veins which transport it to the inferior vena cava and then to the heart.

What if we suffer damage to one system or another?

As blood loss and loss of circulation to a part of the body can be fatal, we do have an emergency diversion system that takes over in some areas. In the arms and the legs for example, damage to one artery stimulates another in the same branch to widen to allow more blood to pass through it, maintaining circulation.

During the fight or flight response, when adrenaline has been released, during intense activity or after eating, other mechanisms come into play. If you suddenly become more active blood vessels in the leg will increase in size and those in the intestine shut down so that you get the power where you need it. When you eat a meal the reverse process occurs – with blood being directed to the intestines. This is why it is advisable not to exercise too soon after eating a large meal as you will interrupt this major part of the digestive process.

Is blood in equal amounts in the two systems?

The blood is not evenly distributed in the two systems. If you were to take a snapshot of the circulatory system you would find approximately 12% to 15% in the arteries and veins in and around the lungs. About 60% will be in the veins and 15% in the arteries with 5% in the capillaries and 10% in the heart. It will also be travelling at different speeds in the various parts of the system leaving the heart quickly at around 30 cm per second and slowing down considerably in the capillary system. It speeds up again in the veins until it reaches the heart travelling around 20 cm per second.

Where is our circulation controlled from?

There are a number of the systems governed by certain parts of the brain such as hypothalamus. In the case of our circulation there is a small area in the lower part of the brain which is in charge called the vasomotor centre. The vasomotor centre receives messages from the pressure sensitive nerves in the aorta and carotid arteries and if necessary the centre sends out messages to the arterioles that will expand or constrict to control and maintain correct levels.

Next time the damage that can occur in our blood vessels that can cause problems in the blood flow.

©sallycronin Just Food For Health 2009