The Journey of Blood
The circulatory system (cardiovascular system) consists of the heart and the blood vessels running through the whole body. Amongst the vessels we have arteries, the ones carrying blood away from the heart, and veins, the ones carrying blood towards it.
The system of blood vessels are like a tree. There are bigger ones branching into smaller and smaller vessels. The biggest ones called the aorta (main artery) that break up to smaller ones, leading to the capillary network, the ones with the smallest branches.
As the image to the left shows, there are two circulatory systems in the human body, the Pulmonary and the Systemic circulation. The systemic circulation provides organs, tissues and cells with blood, whereas the pulmonary system is the one that is linked to the lungs, therefore responsible for carbon-dioxide elimination and oxygen intake.
We find 4 chambers in the heart. Left/right atrium, the two upper chambers of the hears, and left/right ventricle, the two lower chambers of the heart. The journey of blood starts when the hear relaxes between two heart beats, then as the top part of the heart contracts (the heart is built of many layers of involuntary muscles), pushing the blood from the top chambers to the bottom chambers which then expand. There are valves between the top and bottom chambers, making sure that the blood only goes one way in the system.
After the bottom ventricles, the ejection period happens, when by the contraction of the bottom of the heart the blood gets pumped into the main arteries. The one from the right ventricle travels into the pulmonary artery, that goes toward the lung, as it carries the carbon-dioxide rich blood to re-oxygenate. The one in the left ventricle enters the systemic circulation carrying oxygenated blood (and other vital nutrients) to provide the organs, tissues and cells with the necessary gas and nutrients. As earlier discussed, these big vessels then break into smaller ones that turn into capillaries where the gas exchange happens. Once the blood from the right ventricle has been re-oxygenated it enters the pulmonary vein that carries blood to the left atrium.
In the systematic circle, as the blood exits from the left ventricle it enters the Aorta (main artery) and carries oxygen to the organs, tissues and cells. Once the oxygen has been passed to these parts and carbon-dioxide been taken up, the blood enters to the Vena cava (main vein) to then bring the blood back to the right atrium so then the process can start from the beginning.
Inhalation and how breath is drawn in
We draw air into our bodies by inhaling into our lungs. The lungs sits in the thoracic cavity, surrounded by the ribcage and the diaphragm muscle at the bottom. The lungs are made of a spongy material, and covered with capillaries for gas exchange of oxygen and carbon-dioxide.
There is a respiratory control center at the base of our brain that controls our breathing, sending signals for through our nervous system to the involved muscles (diaphragm, intercostal muscles, abdominal muscles and neck muscles) to contract and relax. This does not require our attention and happens without us needing to be aware of it.
As we breathe in, air enters into our body through our nose and mouth, travels through the windpipe to the lungs. As this happens, the diaphragm stretches down, the intercostal muscles in-between the ribs stretch out to increase the space in the chest cavity (pulling the ribs up and out at the same time).
The air reaches the bronchial tubes and then enter the alvioli (air sacks). These air sacks have very thin layer of walls that allow gas exchange through them as previously described, in the capillaries the carbon-dioxide rich blood gets re-oxygenated and then travels back to the left atrium. In the red blood cells we find haemoglobin that carries the oxygen to different parts of the body.
How age, gender, posture effects breathing
New born babies breathe around 30-60 times a minute. Their breaths slows down and around age 3 they only breathe 22-40 times a minute. From age 6-12 kids have their resting breath rate round 18-30/minute, and between age 13-19 it’s even lower, around 12-16 times/minute as this is when most humans reach their peak fitness. But as we age, breath/minute Strat to increase again. In adulthood it’s 12-20 times/minute, around age 65 it’s 12-28 times/minute and above age 80 it is 10-30 times/minute. Of course these are vague values, because there are multiple factors affecting the resting breath rate, but in general it describes how the human body is breathing more frequently when very young or in elder age compared to when we are at our peak fitness.
The rate of breathing is determined by the lungs and heart. Men are capable to achieve higher heart rate, which effects the amount of oxygen that the lungs and heart can deliver to the body. In addition to this, men have larger heart and lung capacity compared to women, thus under strain (for example physical exercise) the breathing capacity in women is limited compared to that of men. The input and output with regards to breathing are different between the sexes due to structural and functional distinctions.
Posture also has affect on our breathing. When we maintain a healthy alignment of the body, the shoulders fall back, the spine reaches up straight allowing the ribs to be able to fully expand as well as the diaphragm muscle to come down as it is designed. But when we are rounding our beck and leaning forward with our upper bodies, bringing our shoulders towards our chest, we are limiting the thoracic cavity’s expansion and squashing the diaphragm as well. This will decrease the breath capacity, decrease the amount of oxygen that we are able to draw in, therefore leads to increased breath rate or even panting. It is important to support our spine by engaging the right spinal extensors as well as draw the shoulders back and the shoulder-blades down.
The interrelationship between the heart and lungs (as well as the respiratory and cardiovascular system)
The heart and the lungs together work to carry oxygen to all parts of our bodies; organs, tissues and cells. As a result of the contraction of the heart, the blood is being circulated in both the pulmonary and systemic circulation as previously described. Although when we look at the relationship between the heart and lungs it’s important to mention that there is only direct contact between the pulmonary circulation and the lungs.
The deoxygenated blood is being collected from all parts of our body and travels into the right atrium in the top of the heart. As the heart contracts blood passes from the right atrium into the right ventricle and then gets pumped into the pulmonary artery. This is the major artery of the pulmonary circulation that then branches into smaller arteries and eventually capillaries in the lungs. Here happens the oxygenation of the blood through the thin walls of the capillaries and alveoli (the air sacs of the lungs). Haemoglobin found in the red blood cells attract oxygen molecules from the fresh air that is in the lunges at this time. Then this oxygenated (and waste depleted) blood then travels back towards the heart in the pulmonary vein where it enters the left atrium. By further contraction of the heart this blood is sent to the left ventricle and is sent to the rest of the body.
So if we want to summarise the relationships, the heart is the main engine that is responsible for the circulation of blood in the cardiovascular system and the lungs are the major organs of the respiratory system that are responsible for re-oxygenating this blood by drawing air in.