Humans

The Respritory System 

 

 

The circulatory system is the system that circulates blood and lymph through the human body. The human body has a closed circulatory system meaning the blood is carried in vessels rather than filling the body cavities such as insects. The main organ in the circulatory system is the heart, which acts as a pump for blood traveling to the top and bottom of the body and to the lungs. The heart is a 4-chambered organ made mostly of muscle tissue help. As blood is circulated around the body and the oxygen from the blood is deposited to the surrounding tissues, it makes its way back to the heart to be pumped to the lungs and become oxygenated. A human heartbeat is myogenic meaning made by muscle rather than made by a nerve impulse. There are two nodal regions in the heart that control the way it beats. The first is the Sino-atrial node, which is like a humans natural pacemaker; the second is the Atrioventricular (AV) node, which electrically connects the SA node and Purkinje fibers. These electrical currents causing the heart to beat are ultimately caused by the human nervous system. Neurons such as the Parasympathetic neuron and the Sympathetic neuron control the heart rate and blood pressure. The blood from the top half of the body enters the heart through the superior vena cave, and the blood from the lower half of the body enters the heart through the inferior vena cava. From here the blood flows into the right atria/atrium through diastole. The blood is then forced through the AV valve, which is held in place by the chordae tendinae because of the high pressure its put under. It then enters the right ventricles which pumps blood through the pulmonary systemic circuits. As the atrium relaxes, the ventricles will contract (systole) forcing the blood through the semilunar valve and into the Pulmonary Artery. The Pulmonary Artery pushes the blood from the heart to the right and left lung to then be oxygenated and pushed back to the heart to be circulated around the rest of the body. The blood from the lungs enters the heart through the pulmonary vein and enters the left atria/atrium (diastole). From here the blood flows into the left ventricles and as the left atrium relaxes the left ventricle contracts (systole) causing the blood to be pushed through the aorta to the top and bottom of the body where it then circulated allowing for oxygen to be distributed to the bodies tissues. During circulation blood travels through the arteries to the arterioles and then through the capillaries, on its way back to the heart it travels from the capillaries to the venules and into the veins. It’s hard for the blood to get from the bottom of the body e.g. the feet back to the heart because of gravity wanting to push it back down. This is why the veins have specialized valves that shut not allowing the blood to flow back down towards the feet aiding the circulation of the blood back to the heart. This is why it is important that humans move their skeletal muscles, in order to aid blood flow through the body. Human blood is made up of four different components, plasma, red blood cells, white blood cells and platelets. Red blood cells carry oxygen throughout the body depositing it to surrounding tissues. It also carries carbon dioxide out of the body and into the atmosphere. White blood cells aid in fighting off infections and helps the immune system fight diseases and sickness in the body. Plasma is a liquid substance that carries nutrients and carbon dioxide as bicarbonate ions in the blood. Lastly platelets help the blood to clot if damaged, this forms things such as scabs (Biology 11, 2011).