Major Organs
The Heart The heart is a vitally important organ made of strong muscle tissue and is protected by the rib cage. It is about the size of your fist and sits slightly to the left of the middle of your chest.
The heart is one of the only organs in the circulatory system but it is one of the most important organs in your entire body. This essential organ consists of four hollow chambers: two atria (plural form of atrium) on top and two ventricles below them. These chambers work like pumps. Their job is to push blood through the body. The blood flows into the heart through the atria and out through the ventricles. At the exit of each of the chambers there is a valve that ensures that the blood flows in the correct direction when it is leaving. Below, I have added a diagram and some very helpful YouTube videos to assist with your understanding of the heart and its functions! |
Other important aspects of the circulatory system are arteries, veins, and capillaries. Although these are not organs, they are key elements of this system. Other organs from other systems that help the circulatory system carry out its functions are the brain and the lungs.
The brain is from the nervous system and is the control center of the entire body. The brain sends messages to all of the parts of the body including the heart, which is the major organ in the circulatory system. Without the brain, this system would not be able to function. Another important organ to the circulatory system are the lungs. The lungs are part of the respiratory system and deliver oxygen to the blood so that it can be pumped through the arteries by the heart and delivered to the rest of the body. These are just two examples of how organs and organ systems are interdependent. This just means that they rely on each other to carry out their proper functions. |
Blood Vessels
Picture a tree. A tree begins with the trunk and then separates into the strongest and most sturdy branches. Gradually, the branches branch out and get thinner and smaller until the very small tips. You can relate formation of the blood vessels to the layout of a tree. Imagine the heart as the trunk. The blood vessels closest to the heart are like the thickest branches; they are the arteries and veins, the most durable. These large vessels then branch out and become smaller with thinner walls until they are eventually tiny capillaries.
There are three types of blood vessels: Arteries, veins, and capillaries. Each type of vessel performs a specific function in the circulation of blood through the human body.
The arteries are the vessels that carry nutrient and oxygen-rich blood away from the heart and deliver it to all of the parts of the body. They have the strongest walls because they must contain the high pressure oxygen-filled red blood cells. The thickest artery is the largest blood vessel in the entire body; the aorta. This is the artery connected to the left ventricle that takes freshly oxygenated blood away from the heart. It begins the width of a quarter and then branches out into smaller arteries.
The thickest vein in the human body is about the width of a pencil and has much less sturdy walls than an artery. The veins receive blood from the capillaries after the capillaries have delivered all of the oxygen and nutrients to the body parts and removed the waste (the carbon dioxide). The blood that the veins carry is oxygen deprived and full of carbon dioxide. This blood is pumped back to the heart through the veins where the cycle can begin again. (For details on this process, see the "Functioning as a System" heading above.)
Last but certainly not least, there are the capillaries. These are the tiny vessels that wire the arteries to the veins. The oxygen-rich blood is carried to the capillaries by the arteries and then their semi-permeable walls allow them to deliver the oxygen and other nutrients in the blood to all of the organs and tissues. During this process they also take in any wastes (like carbon dioxide) that the organs and tissues need to get rid of. Capillaries are able to exchange food, oxygen, and wastes between blood cells and body cells through gas exchange and diffusion. Below you will find diagrams and an excellent video outlining this process.
There are three types of blood vessels: Arteries, veins, and capillaries. Each type of vessel performs a specific function in the circulation of blood through the human body.
The arteries are the vessels that carry nutrient and oxygen-rich blood away from the heart and deliver it to all of the parts of the body. They have the strongest walls because they must contain the high pressure oxygen-filled red blood cells. The thickest artery is the largest blood vessel in the entire body; the aorta. This is the artery connected to the left ventricle that takes freshly oxygenated blood away from the heart. It begins the width of a quarter and then branches out into smaller arteries.
The thickest vein in the human body is about the width of a pencil and has much less sturdy walls than an artery. The veins receive blood from the capillaries after the capillaries have delivered all of the oxygen and nutrients to the body parts and removed the waste (the carbon dioxide). The blood that the veins carry is oxygen deprived and full of carbon dioxide. This blood is pumped back to the heart through the veins where the cycle can begin again. (For details on this process, see the "Functioning as a System" heading above.)
Last but certainly not least, there are the capillaries. These are the tiny vessels that wire the arteries to the veins. The oxygen-rich blood is carried to the capillaries by the arteries and then their semi-permeable walls allow them to deliver the oxygen and other nutrients in the blood to all of the organs and tissues. During this process they also take in any wastes (like carbon dioxide) that the organs and tissues need to get rid of. Capillaries are able to exchange food, oxygen, and wastes between blood cells and body cells through gas exchange and diffusion. Below you will find diagrams and an excellent video outlining this process.
Major Tissues
Epithelial Tissue
This is a type of protective tissue that covers the entire body. It is made up of closely packed cells in one or more layers. Epithelial tissue found inside the body is called endothelium. Epithelial tissue usually sits on top of a thin layer of connective tissue, called the "basement membrane." In the circulatory system, epithelial tissue can be found in the structure of the arteries, veins, and capillaries, and it also covers the heart.
Muscle Tissue
Muscle tissue is made up of muscle cells which are able to contract, whether it is involuntarily or on demand. This is the tissue that enables us to move our whole body, or just certain parts. Muscle tissue also creates involuntary movement inside our bodies in every organ system. The main organ of the circulatory system, the heart, is considered a muscle and therefore is largely made up of muscle tissue.
Nervous Tissue
The nervous tissue's main function is to react to stimuli and send impulses to various organs around the body. This type of tissue is made up of neurons, a specialized type of cell. These cells are highly responsive which means that they react quickly to stimuli. The nervous tissue is made up of nerve cell fibres embedded in connective tissue (described in next paragraph). This tissue is important to the circulatory system because it helps the brain to transmit messages to all of the components of the circulatory system. Without this tissue, the circulatory system would not function!
Connective Tissue
Connective tissue is sometimes referred to as the "glue" that holds the body together. It is the most common and plentiful type of tissue in the entire body. The connective tissue consists of widely spread cells and its job is to connect, support, or surround other tissues and organs. The connective tissue is what makes up the structure of not only the circulatory system, but all of the other organ systems as well. This tissue can be found in the walls of arteries, veins, and capillaries, and, of course, in the makeup of the heart.
Major Cells
The major cells of the circulatory system can all be found in the blood. The following paragraphs will outline red blood cells, white blood cells, and platelets.
Red Blood Cells
Red blood cells make up about 45% of the blood. These cells look similar to a doughnut without the middle punched out all the way. This shape is called a biconcave disc. Red blood cells contain a substance called hemoglobin. Hemoglobin are small molecules found within the red blood cells that give the blood its rich red colour. Red blood cells are produced in the bone marrow and then released into the blood stream once they have matured. Their life span is about three or four months. Once they have aged or become damaged they are removed from the bloodstream by the spleen. The most important job of the red blood cells is to transport oxygen and other nutrients to all of the parts of the body and to get rid of wastes in the body, such as carbon dioxide.
As these cells pass by the lungs, the carbon dioxide that they are carrying diffuses into the lungs and in return, some oxygen diffuses into the red blood cells. They are then transported all around the body through the arteries and give nutrients to organs and tissues by using diffusion. As oxygen diffuses out of the red blood cells, carbon dioxide from the organs and tissues diffuses into the red blood cells. The red blood cells then carry the carbon dioxide back to the lungs, diffusion occurs, and the cycle begins again.
Below I have added a quick link to the video that I posted above (see YouTube video under "Blood Vessels" section). This video shows diffusion and gas exchange and will help improve your understanding of the job of the red blood cells!
As these cells pass by the lungs, the carbon dioxide that they are carrying diffuses into the lungs and in return, some oxygen diffuses into the red blood cells. They are then transported all around the body through the arteries and give nutrients to organs and tissues by using diffusion. As oxygen diffuses out of the red blood cells, carbon dioxide from the organs and tissues diffuses into the red blood cells. The red blood cells then carry the carbon dioxide back to the lungs, diffusion occurs, and the cycle begins again.
Below I have added a quick link to the video that I posted above (see YouTube video under "Blood Vessels" section). This video shows diffusion and gas exchange and will help improve your understanding of the job of the red blood cells!
Blood Doping and Red Blood Cells
Blood doping is considered a performance enhancing process and is frowned upon in athletic competitions worldwide. Blood doping is when an athlete removes some of the blood from their body a few weeks prior to a competition. During these weeks, their body replenishes the blood that they lost. Then, just before the competition, they inject the blood back into their body, giving themselves an irregularly high level of red blood cells in the bloodstream. More red blood cells means more oxygen which in turn gives the athlete a higher endurance and more stamina. This is a very dangerous and unsanitary process that will result in immediate disqualification from competition due to the fact that it gives you an advantage over the other competitors.
White Blood Cells
White blood cells only make up about 2% of your blood, although they have an extremely important job. These cells help the body defend itself against infections and diseases by discovering and fighting germs and bacteria. The lifespan of white blood cells are anywhere from seven to fourteen days. There are three types of white blood cells and each type helps defend against certain diseases. These cells find harmful cells, surround them, and then attack them from all angles.
Platelets
Platelets are small blood cell fragments that help mend wounds by causing blood to clot. When a tissue is cut and bleeding, platelets build up over the wound and work with proteins nearby to form a web which eventually hardens to create a scab, preventing any more blood loss.
Plasma- The Last Component of the Blood
53% of the blood is plasma, which is a yellowy coloured substance that gives the blood a liquid consistency. This liquid is mostly water but also contains dissolved sugars and calcium.