The Circulatory System
Blood is one of the most researched liquids of the body that circulates through the heart, arteries, veins, and capillaries (that will be explained further in the text), performing various functions. Despite being 78% water, this red color pigmented substance contains four distinct components, which are plasma, red blood cells, white blood cells (leucocytes), and platelets (Shikha, 2020). Plasma is the fluid matrix in which other cells and substances are floating. Red blood cells or “erythrocytes” are disc-shaped cells intended to carry oxygen. They have an iron-containing red pigment called “hemoglobin” (Shikha, 2020). Leukocytes are white cells necessary for body protection. Finally, “thrombocytes” or platelets are colorless cells of different forms that are needed for blood coagulation.
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Besides the above-mentioned components, blood carries to body tissues the following, vital for any living organism substances: nourishment from food digestion, electrolytes such as salt, minerals, potassium, chloride, and others (Shikha, 2020). It also carries hormones such as testosterone, estrogen, cortisol, and thyroid, vitamins, antibodies, heat, and even oxygen people breath in with air while bringing out carbon dioxide formed in the breathing process and waste matter (‘Unit 3 – The Circulatory and Lymphatic Systems’, no date). It is possible to outline functions of blood in living organisms which are: transport of the mentioned components, body temperature and pH maintenance, body fluid electrolytes regulation, and removal of toxins from the body.
The human heart is considered to be one of the vital organs without which the functioning of an organism is impossible. It is the size of a fist, built of muscular tissues, and located behind and left of the breastbone (Hoffman, 2021). The main function of the heart is pumping blood through arteries and veins, which are a part of the cardiovascular system, to other organs, tissues, and cells (‘Unit 3 – The Circulatory and Lymphatic Systems’, no date). It also has a web of nerve tissues that run through in order to conduct complex signals responsible for contraction and relaxation.
The human heart is composed of four chambers which are the right atrium, the right ventricle, the left atrium, and the left ventricle, respectively. It also has four valves: tricuspid, pulmonary, mitral, and aortic (Michigan Medicine, 2019). The first two of them are intended to move blood from the upper to lower chambers, while the other two are responsible for transferring blood to the lungs and other parts of the body.
It is possible to outline how the heart is pumping the blood, revealing the process of its operating at the same time. Non-oxygenated blood from organs is received by the right atrium through the body’s veins, superior vena cava, and inferior vena cava in particular. Then, it is pumped through the tricuspid valve to the right ventricle (Michigan Medicine, 2019). Further in the process, blood is moved to the lungs through the pulmonary valve by the right ventricle to make it oxygenated (Michigan Medicine, 2019). After that, the left atrium pumps oxygenated blood through the mitral valve to the last chamber. Finally, the left ventricle transfers blood enriched with oxygen to the rest of the blood through the aortic valve.
Structure of Arteries, Veins and Capillaries
The net of arteries, veins, and capillaries are vessels the blood runs through. Arteries are necessary for enriching organs with oxygen and other elements contained in this red-pigmented liquid. They are composed of three layers that form a structure called the “artery wall.” Tunica intima or tunica interna is epithelium surrounded by connective tissue basement membrane whose fiber is elastic (‘Classification & Structure of Blood Vessels,’ no date). The middle layer is called “Tunica media,” and it is built of muscle tissue intended to support the artery and assist in blood pressure regulation. “Tunica externa” is the last, outermost layer that attaches the artery to the surrounding tissue and is composed of elastic and collagenous fibers.
Veins carry blood with a low oxygen content back to the heart and consist of the same three layers as arteries: tunica adventitia, tunica media, and tunica intima. However, these layers are modified to comply with less pressure, and therefore, they have less smooth muscle and connective tissue (‘Unit 3 – The Circulatory and Lymphatic Systems’, no date). Finally, capillaries which distribute blood to organs and are smaller than other vessels, consist of a single layer of endothelial cells.
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Double Circulation System
Double circulation is the system of blood movement in the body that most mammals, including humans, have. It involves the separated flows of oxygenated and deoxygenated blood (PMF IAS Team, 2016). As it was explained previously, the human heart has four chambers, 2 of which, the right atrium and right ventricle, receive oxygen-poor blood with a large amount of carbon dioxygen and two of which, left atrium and left ventricle, receive oxygen-rich blood.
There are two types of circulation in humans referred to as “double circulation system,” which involves pulmonary circulation and systemic circulation. Pulmonary circulation involves the lungs, deoxygenated blood is transported to which through the pulmonary artery after passing the right atrium and the right ventricle (PMF IAS Team, 2016). There, the blood is oxygenated, carbon dioxide is removed, and the red-pigmented liquid is carried to the left atrium and then to the left ventricle (PMF IAS Team, 2016; ‘Unit 3 – The Circulatory and Lymphatic Systems’, no date). Systemic circulation involves all systemic organs and tissues, as oxygenated blood goes to tissues through the aorta, where it becomes oxygen-poor and is carried to the right atrium and then to the right ventricle.
The Cardiac Cycle
The Cardia cycle is referred to as the period of time that begins with the contraction of the atria and ends with ventricular relaxation. The moment of contraction when the heart pumps blood into circulation is called systole, while the moment of relaxation when the chambers are filled with blood is called diastole (Pollock & Makaryus, 2020). The atria and ventricles undergo both of the stages, so it is vital for them to be coordinated to ensure the efficiency of blood pumping.
Atrial systole is the moment when the pressure inside it rises (when the containment of blood inside the atria is approximately 20-30% of the general amount), and blood is pumped by contraction into the ventricles. The systole lasts about 100 milliseconds and ends before the ventricular one (Pollock & Makaryus, 2020). Ventricular systole involves two phases: an isovolumic contraction that makes blood flow back toward the atria and closes the tricuspid and mitral valves. In the second phase, called the ventricular ejection phase, the contraction of the muscles raises the pressure making it greater than the one in the aorta, which pumps blood from the heart (Pollock & Makaryus, 2020). Ventricular diastole is the period of relaxation that lasts 430 milliseconds in total, which is divided between the isovolumic ventricular relaxation phase when pressure begins to fall and late ventricular diastole when pressure within the ventricles drops below the pressure in the atria.
There is a set of specific diseases of the circulatory system that can occur. Myocardial infarction (MI) is one of the most famous ones, and it is a blockage of blood flow that results in the muscle tissue of a coronary artery death. In other words, this disease is called “a heart attack,” and it may result in the death of a victim, or substantial cardiac rehabilitation might be necessary to strengthen the remaining muscle tissue (Sullivan, 2018). The symptoms of MI are pain in the chest, discomfort, pain that radiates from the jaw, shoulder, arm, or back, shortness of breath, sweating, nausea, irregular heartbeat, or unconsciousness.
The other disease, mitral prolapse, occurs when the flaps of the mitral valve tear away because of the disease. It starts a process called “prolapse” that results in leakage and backward flow of blood called “regurgitation.” This disorder is not acute, but a lifelong one, so many people may not know about their condition. The symptoms are an irregular heartbeat, also referred to as arrhythmia, dizziness, difficulty breathing, and fatigue.
Myocardial ischemia is a disease that occurs when blood flow to the heart is severely reduced that deprives the organ of sufficient oxygen obtaining. It is usually the result of blockage of coronary arteries. And ischemia can lead to abnormal heart rhythms and even a heart attack. The symptoms are neck, jaw, shoulder, or arm pain, a fast heartbeat, shortness of breath, nausea, sweating, and fatigue.
The Respiratory System
Functions of the respiratory system
The respiratory system or breathing system is intended for the exchange of gases (primarily, oxygen contained in the air and carbon dioxide) facilitation. Therefore, the first key function of it is inhalation and exhalation, referred to as the breathing process or pulmonary ventilation. The air is inhaled through two cavities, which are nasal and oral ones, moved through organs which will be discussed in detail further in the text, directly to lunges (Healthline Editorial Team, 2021). The air is exhaled back in the same way. The ventilation is triggered by changes in the pressure in the lunges caused by changes in the volume of air inside.
The other function is called external respiration or, in other words, the exchange of gases between the lungs and the bloodstream, which, as explained above, is vital for delivering oxygen to all organs, tissues, and cells. This process involves sacs called alveoli that are responsible for diffusing air to capillaries and diffusing carbon dioxide from them (‘Unit 5 – The Respiratory System’, no date). Internal respiration is the other level of gases exchange that happens between the bloodstream and body tissues. Oxygen is delivered to cells, and waste carbon dioxide is removed by diffusing from the tissues into red blood cells and plasma. Then, the deoxygenated blood is moved to the lungs for gas release.
The next key function is called phonation that implies the creation of sounds through air vibrating. It is done by structures in the upper respiratory tract during exhalation. Vocal cords are pushed together during speaking, and the air passing between makes them vibrate, which creates sounds (Healthline Editorial Team, 2021). Finally, the respiratory system is also responsible for chemical sensation, also known as smelling or olfaction. In the cavities, there are nervous system receptors that contact with chemicals in the air and send a signal to the brain that is perceived by neurons. Therefore, the respiratory system is necessary for life-supporting function fulfilling, enabling people to speak and distinguish different smells.
Structure of the organs of the respiratory system
The human respiratory system consists of a set of organs intended to participate in the mentioned above functions fulfilling. Some of the parts of the system are the nose and nasal cavity that is air-filled space behind the nose divided by the septum (Ratini, 2019). The other vital organ is the mouth that is a cavity inside the skull, which includes, with respect to breathing and phonation functions, lips, tongue, and teeth. The throat or pharynx behind both oral and nasal cavities is tubes that go to the stomach and lungs, connecting the nose and mouth to the breathing passages (Ratini, 2019). Voicebox or larynx is a tubular structure connected to the trachea and intended to produce sound by two folds of elastic tissue, called vocal cords, inside.
The trachea or windpipe is the next organ of the respiratory system, and it has a tube-like structure that connects the larynx and bronchi. The diaphragm is an upward curved organ that is formed of muscle and fibrous tissue intended to separate thoracic and abdominal cavities. Its contraction increases the volume of the thoracic cavity where the heart and lungs are located, assisting the breathing process. Lungs are a pair of organs located in the chest and covered by the pleura that is a thin layer of tissue (Ratini, 2019). It is intended to protect the lungs and be a lubricant for the smooth slipping of these organs, as they always expand and contract to take breaths. Lungs have tubular branches called bronchi that are divided into smaller branches known as bronchioles and end with air sacs called alveoli (Ratini, 2019). Alveoli are layers of cells that contain blood vessels known as capillaries, whose function was explained previously.
Internal and external respiration
Internal organs, cells, and tissues require oxygen and the removal of carbon dioxide. Internal respiration is referred to as the gas exchange between blood and the metabolizing tissue. It is known that the partial pressure of oxygen is lower than carbon dioxide (Panawala, 2017). It enables defusing of oxygen from the blood to tissues vice versa, with respect to removal of carbon dioxide, until the equilibrium on both sides of the membrane of tissue. Simultaneously, external respiration is the gas exchange that occurs in the lungs, and it is called so because oxygen is taken from outside of the body and transferred to the blood through the pulmonary capillaries, whose functioning was explained previously. The defusing is also ensured by the difference in partial pressure of these two gases, oxygen, and carbon dioxide, both of which are moved by red cells of the blood.
It is possible to outline several key differences, summarizing ones between internal and external respiration. In the first situation, the partial pressure of oxygen in the blood is reduced from 100 mmHg to 40 mmHg, while in the second one, it is increased from 40 mmHg to 100 mmHg (Panawala, 2017). External respiration involves breathing and attaching oxygen to hemoglobin, while internal one does not. However, internal respiration involves three stages: glycolysis, Krebs cycle, and oxidative phosphorylation instead, and sometimes do not need oxygen to occur (Panawala, 2017). Finally, external respiration is the physical mechanism of getting oxygen inside the body, while the internal one is a chemical one, as many reactions are provoked by oxygen or require it.
Role of the intercostal muscles and diaphragm
Breathing is an automatic process controlled by the respiratory center and supported even during sleep or a state of unconsciousness. Intercostal muscles and diaphragm are necessary for the function as the lungs do not have skeletal muscles to help them expand and contract (Dezube, 2021). The diaphragm is formed of muscle tissue attached to the lower part of the rib cage and the spine. As it contracts, the length and diameter of the chest cavity are increased, and therefore, the lungs are expanded as well (Dezube, 2021). Simultaneously, the intercostal muscles assist in breathing by elevating the rib cage. They consist of three layers, which are external, internal, and innermost ones, that are combined in order to fill the spaces between ribs.
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There is a broad spectrum of diseases associated with the respiratory system. One of the most well-known is asthma, which is a long-term condition or a chronic disease (Ratini, 2021). It affects the lungs and makes airways inflamed and narrow, causing difficulty breathing. The characteristic of asthma is inflammation of the bronchial tubes complimented with sticky sections inside them, which causes a feeling of airways being tightened or filled with mucus (Ratini, 2021). There are three determinants of the presence of asthma, which are airway blockage, expressed as the difficulty for air to pass through (Ratini, 2021). Then, it is inflammation expressed as red and swollen bronchial tubes in the lungs, which even can damage them, and finally, airway irritability, as sensitive airways tend to overreact even because of slight triggers as dust. The following symptoms may indicate the presence of the condition: coughing that strengthens at night or in the morning, wheezing during breathing, shortness of breath, pain or pressure in the chest, and trouble sleeping.
The other common disease is pneumonia, which is a lung infection, which can be relatively mild or severe. It occurs when the infection causes alveoli in the lungs to be filled with fluid that results in not diffusing enough oxygen in the bloodstream. The disease can affect one or both lungs at the same time. The ones who have a weak immune system are vulnerable to this condition as it is caused by bacteria, viruses, or fungi, and the one who has it can spread it to others. Lifestyle habits such as smoking, drinking, not eating properly can increase chances of being affected by pneumonia.
This disease s associated with a set of indicators that can assist in the determination of its presence. The symptoms of pneumonia include chest pain during breathing or coughing, cough that produces mucus, loss of appetite and fatigue, fever, sweating, and chills, nausea and diarrhea, and shortness of breath (Robinson, 2020). There are also complicators of pneumonia, which are bacteremia that implies the spread of bacteria by blood, severe trouble breathing that might result in the necessity of a breathing machine for life-supporting (Robinson, 2020). Moreover, fluid buildup between the layers of tissue can arise and even become infected, and finally, a pocket of pus inside the lungs, known as lung abscess, can arise.
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