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Friday, April 12, 2019

The Circulatory System

          The Circulatory System





The Circulatory System





The body is made up of a series of systems that control different functions, such as the respiratory system to breathe, the digestive system that helps us break down the food we eat, the nervous system that allows us to think and react to the environment around us. And the system responsible for supplying blood to all parts of our body through the action of the heart is the cardiovascular system (CVS), also called the circulatory system (CS)


Overview of  the Circulatory System


Most of the cells of the human body are not in direct connect with the outer environment, so depend on the circulatory system to serve as a transport service. Two fluids are relied, which move through the circulatory system: Blood and Lymph. The heart, the blood, the blood vessels of the cardiovascular system. Lymph nodes, lymph nodes and lymphatic vessels of the lymphatic system. The cardiovascular and lymphatic systems collectively form the circulatory system

Two main circulation / transport systems in the body:

  • The circulatory system / The cardiovascular system: including, the heart as the pump, and circulating fluid
  • The lymphatic system: an open system that returns excess materials to the blood in the tissue spaces
  • The circulatory system works in combination with the lymphatic system, they are directly connected to each other

Fluid = blood = lymph (containing white blood cells)

All organs and tissues in the body need oxygen. This requirement is met by the constant flow of blood that carries oxygen. The cardiovascular system is responsible for ensuring that blood flow is constant, allowing every cell in the body to have access to oxygen. Without a properly functioning CVS, our cells could not function properly. CVS has a number of parts that control blood flow. These components are: blood, heart, blood vessels


The structure and functions of the circulatory system


The circulatory system includes the cardiovascular system which carries the blood and the lymphatic system which distributes the lymph throughout the body. CS, which is a network of blood vessels that carries water, electrolytes, nutrients in the form of amino acids, hormones, enzymes, lymph (fluid that contains white blood cells), antibodies, gas (oxygenated blood) to all tissues, cells, organs and transports metabolic waste to the kidneys, liver and skin and carbon dioxide to the lungs. This maintains homeostasis (capillaries, venules and veins) and stabilizes body temperature and PH levels. Contributes to the body's defenses (the immune system), to the coagulation process

The lymphatic system is considered part of the circulatory system, whose main purpose is to circulate the lymphatic fluid from the tissues and protect it from infections

The main function of CVS is to pump blood throughout the body. The heart (the central organ of the system) pumps about 5 liters of blood through the cardiovascular network to the vital organs. The function of the heart is to act as a pump. By pushing blood into the blood vessels, the blood vessels transport the blood to all the different parts of the body before it returns to the heart to start the cycle again. Blood carries oxygen from the lungs to all the parts of the body. It is also responsible for transporting waste such as carbon dioxide, which is then removed from other systems in the body

Interactions with another system:

• Nervous system: the brain regulates the heart rat and blood pressure
• Respiratory system: gas exchange in the lungs (carbon dioxide and oxygen)


Overview of the cardiovascular system 


The main components of the cardiovascular system are: blood, heart, blood vessels and the main goal of the cardiovascular system is to pump nutrient and oxygen-rich blood to all parts of the body

• Heart: the muscle pump that circulates blood through the heart, lungs (pulmonary circulation) and the rest of the body (systemic circulation)

Blood: Fluid consist of elements, such as, erythrocytes, thrombocytes, leukocytes and plasma. It is a specialized body fluid that supplies the vital substances to the body's cells (oxygen, food, salts, hormones) and disposal of the  metabolic waste products (carbon dioxide, urea, lactic acid) away from those same cells. Blood circulates through the body through the blood vessels by the pumping action of the heart muscle

• Arteries: a branched system of vessels that transports blood from the left and right ventricles of the heart to all parts of the body; carries blood away from the heart

• Veins: vessels that carry blood from peripheral tissues to the heart

• Capillaries: microscopic blood vessels that link the arterioles to the venules, facilitating the passage of fluids containing oxygen and nutrients to cell bodies and the disposal of accumulated waste and carbon dioxide


The organization of the cardiovascular system


The cadoivascular system can be divided into further categories in the pulmonary, systemic and coronary circulation according to the pathways that the blood takes. Pulmonary circulation, as the name suggests, involves the transfer of blood to and from the heart and lung. In this circulation, deoxygenated blood is transported to the lungs and freshly oxygenated blood is returned to the left side of the heart. Systemic circulation takes care of the whole body and heart, so that oxygen and blood circulate in the tissues and the deoxygenated blood returns to the right part of the heart. Coronary circulation means the blood that circulates in the heart itself


Pulmonary Circulation:

When blood is oxygen-free and contains waste materials, such as carbon dioxide, deoxygenated blood enters two large veins called venae cavae into the right atrium of the heart (lower chamber), which then contracts (systole) and pushes blood into the right ventricle (upper chamber) through the tricuspid valve (right atrioventricular valve). The right ventricle contracts by forcing fluid out through the semilunar pulmonary valve into the pulmonary artery and lungs, resulting in gas exchange. Oxygenated blood is returned to the left atrium through the pulmonary veins, which is pumped into the left ventricle of the heart and expelled through the aorta, the largest artery in the body (to resist high pressures), to the other arteries. portions of the body

There are numerous valves in the heart and in the exchange of oxygen and carbon dioxide. During breathing, gas exchange takes place in the alveoli where oxygen passes into the bloodstream while carbon dioxide and other waste products are expelled. In the pulmonary circulatory system, the pulmonary artery is responsible for the transport of deoxygenated blood from the heart to the lungs. The pulmonary vein carries blood, which rich with the oxygen to the heart. The oxygenation and deoxygenation procedures occur synchronously at the alveolar-capillary interface in the deep pulmonary airways

• Veins around the body that prevent reflux, sealing the vessels when the heart expands (diastole), causing lower upward pressure


Systemic Circulation:

High blood pressure is exerted when it is removed from the aorta into the left ventricle to pass throughout the body. Within this flow, the blood will absorb the nutrients obtained from digestion, which is then used to provide fuel for energy and storage. The waste is eliminated through the liver and then expelled from the body. The walls of the container are smooth enough to allow for easy flow and strong enough to withstand the high flow pressure. Eventually, the deoxygenated blood that carries the waste product returns to the heart. Due to the greater distance to carry, the left ventricle muscle is stronger and provides enough pressure for the blood to circulate more


Coronary Circulation:

Oxygenated blood circulates through the heart through the coronary arteries, while deoxygenated blood is transported to the lungs through the heart veins. The coronary circulatory system is basically the systemic circulatory system, in the sense that blood is supplied to the heart but through the coronary arteries. The heart and coronary arteries are analogous to the organs of the human body and the cardiovascular network of the arteries


The physiology of the cardiovascular system


Heart: (A tireless pump)


The Circulatory System



Despite its small size, the heart is the most active organ of the body: throughout its life, the muscle fibers that make it up contract without releasing blood throughout the body, with an average frequency of 70 contractions per minute. Due its complex system of cavities and valves, the heart muscle is a massive machine that pumps 2.5 million liters of blood every year

The heart has three layers or coatings:

  • Endocardium: The inner lining of the heart
  • Myocardium: The muscular intermediate layer of the heart
  • Pericardium: The external membranous sac that surrounds the heart

The external aspect of the heart:

The heart is a small organ (10-12 cm in diameter, with an average of 300 g) housed in the rib cage, between the lungs. Its surface is divided by grooves, along which the coronary arteries and veins extend, responsible for the blood circulation of the heart muscle. These grooves correspond to the boundaries between the atria and ventricles

The Cardiac (heart) Muscle:

The heart is essentially made up of the myocardium (or muscle heart), which forms a thick wall of striated muscle fibers. The endocardium, the internal surface of the myocardium, is lined with a thin layer of cells similar to those that cover blood vessels. The heart muscle is wrapped in the epicardium, a thin membrane that forms the innermost leaflet of the pericardium

Four cavities, four valves:

The heart is made up of two parts, separated by the septum, which do not communicate directly with each other. Each part of the heart is made up of two chambers: an atrium and a ventricle. The atrium is the compartment that receives blood from the veins (caval veins for the right atrium, pulmonary veins for the left atrium), while the larger volume ventricle expels the blood to the arteries (pulmonary trunk for the right ventricle), aorta for the left ventricle). These four chambers are equipped with valves designed to prevent blood reflux when the heart contracts. There are atrioventricular valves (tricuspid and mitral), located between the atria and ventricles, and semilunar valves (pulmonary and aortic), located at the exit of the ventricles

The cardiac cycle:(A remarkably regular rhythm)

Myocardial contractions obey a regular cycle that has three different stages. Each cycle is triggered by the cells of the heart muscle in particular, called authoritative because they are capable of generating and propagating electrical impulses. These cardiac stimulators are essential because the correct functioning of the cardiovascular system depends on the regularity and coordination of the movements of the heart


The cardiac cycle:

It takes about 0.8 seconds for a flow of 70 ml of blood to enter the heart, pass and expelled to the arteries. This cycle comprises a resting phase (diastole) and two contraction phases (The systole)

The Diastole:

Muscle rest phase, the diastole is characterized by general dilatation. The blood from the veins enters the atria and then, by opening the atrioventricular valves, flows directly into the ventricles, which fill up to 70% of their capacity

The arterial system:

When they contract, the atria expel the blood they contain, which ends up filling the ventricles. This first muscle contraction is called atrial systole

The ventricular system:

Ventricular systole refers to the contraction of the ventricles. Atrioventricular valves, closed, it prevents blood from flowing back to the atria, while the semilunar valves open to allow blood to flow into the pulmonary trunk and aorta

Cardiac conduction:



The Circulatory System



Although nerve or hormonal messages can change your heart rate, it is basically dictated by some myocardial cells, which have the ability to spontaneously depolarize and to emit electrical impulses from 70 to 80 times per minute. This stimulation spreads throughout the myocardium, where it subsequently triggers the contraction of the atria and ventricles. Located on the wall of the right atrium, the sinoatrial node (1) is the starting point of heart excitement When cells depolarize (on average every 0.8 seconds), they generate an electrical action potential. Spreading rapidly from one cell to another from the internodal (2), this influx causes the atria to contract. After reaching the atrioventricular node (3), borrow the bundle of His (4) (or atrioventricular bundle), which is the only electrical path between the atria and ventricles. The impulse descends along the interventricular septum, reaches the apex of the heart and then spreads rapidly to the muscle mass of the ventricles through the Purkinje fibers (5). The ventricles contract nearly 0.16 seconds after the atria


Blood vessels



The Circulatory System



There are three major categories of blood vessels: arteries, veins, and capillaries. Blood circulates throughout the body through its pathways. The circulatory system is known as the closed system because blood is always contained in the heart or blood vessels, always flowing in one direction. The path is the same

• Heart (ventricles) → arteries → arterioles → target organ (capillaries) → veins → heart (atrium)

I. Arteries: carry blood (rich in oxygen) from the heart to the body
II Capillaries: very small blood vessels that allow the exchange of gas (oxygen and carbon dioxide), water, nutrients and waste products to and from the blood
III. Veins: bring blood (low in oxygen) to the heart


The Circulatory System



Blood circulates throughout the human body, with the exception of some highly localized areas, such as tooth enamel or the cornea of ​​the eyes. To move, the blood borrows two types of blood vessels, arteries and veins, which differ in their anatomy, but above all in their respective roles in the cardiovascular system

Arteries:

Arteries are a branched system of vessels that carries blood from the heart to all parts of the body. In a normal state, arteries are elastic tubes that rise and carry blood in pulsating waves. All arteries have a pulse, which reflects the rhythmic beat of the heart; however, some points are commonly used to control the frequency, rhythm and conditions of the arterial wall. The heart has its own set of arteries to supply you with blood called coronary arteries

The potent pumping of the heart exerts pressure on the walls of the arteries as blood flows through them, leading them to expand. This rhythmic expansion and contraction of the blood vessels can be perceived as the pulse (or heart rate) and can be measured as the blood pressure (BP). However, it is important to remember that the strength of the blood on the blood vessels is what creates the BP

Capillaries:

Formed by a thin layer of endothelial cells covered by a basal membrane, capillaries are very small blood vessels: they are only 0.3 to 1 mm long and their diameter does not exceed 0.01 mm. The extreme thinness of its wall promotes exchanges between the blood and the outside. It is through this pathway that oxygen and nutrients are distributed to the tissues and that carbon dioxide, due to cellular metabolism, is transported away

1. Arterioles branch out into very small blood vessel networks: capillaries. These have a very large surface and thin walls that are thick in a single cell (epithelial)
2. It is in the capillaries that exchanges between blood and body tissues take place
3. The capillaries are also tight. This slows down the blood and allows it to spread. In most capillaries, blood cells must flow into a file
4. Tissue fluid forms in the capillaries when their walls lose

Capillary circulation:

The blood flow in the capillary networks depends on the oxygen requirement of the tissues. A resting muscle requires less blood than an active muscle. These are the precapillary sphincters that control blood flow in the capillaries by contracting or relaxing

• When the muscle is at rest, several sphincters contract, cutting the blood entering the capillaries
• Relaxation The relaxation of the precapillaries of the sphincter allows the blood to supply the active muscle of the capillary networks

Veins:

Veins collect blood from the capillaries and restore it to the heart. Since they are further away from the heart, the blood pressure in these vessels is much lower than in the arteries. All veins carry low oxygen (low oxygen) blood to the heart, where the cycle can repeat itself

1. After leaving the capillaries, the blood enters a network of small venules that feed on the veins. These, in turn, bring blood back to the atria of the heart
2. Like arteries, the walls of the veins are lined with epithelium and contain smooth muscles. The walls of the veins are thinner and less elastic than the arteries, but they are also more flexible
3. Veins tend to run between the muscle blocks of the body and closer to the surface than the arteries
4. The larger veins contain valves that preserve the direction of the flow of the blood. This is important where blood must flow against gravity
5. The blood flow in the veins is favored by the contractions of the skeletal muscles, in particular those of the arms and legs. When the muscles contract, they squeeze against the veins and help force the blood to return to the heart. Again, this is known as secondary circulation


Blood circulation in the veins: 

Because of their reduced ability to contract, the veins have difficulty returning blood to the heart. This difficulty occurs mainly in the lower extremities, where Blood flow opposes gravity. Due to its contractions, the skeletal muscles that facilitate blood circulation through the veins. In fact, when they contract, the muscles compress the venous walls and force the valves above them to open to allow blood to flow to the heart. The valves under the muscles prevent the blood from flowing because they can only open one way. This process defined as "venous pump" or "muscle pump"

Blood flow speed:

Blood flows more slowly in the capillaries than in the larger vessels. This slowdown allows exchanges between blood and tissues





The physiology of the lymphatic system: (drainage and cleaning of body fluids)



The Circulatory System




The lymphatic system is jointly connected to the cardiovascular system. Every day, the plasma leaves the blood capillaries and accumulates in the tissues, where it forms the interstitial fluid. Through its network of vessels, the lymphatic system drains this fluid (which is later called lymph) and prevents swelling of the tissues. The lymph gets rid of infectious agents in the lymph node system and is then reintroduced into the cardiovascular system. Other organs like the spleen, thymus and tonsils, they play a role similar to that of the lymph nodes without being directly related to the lymph


Lymph Drainage

The lymphatic system consists of a one-way network that collects about three liters of lymph per day in the different tissues of the body. After being evacuated from the lymphatic capillaries, the lymph passes through the filtering nodes and is then led to two main channels: the right lymphatic canal, which drains the higher right quarter of the body, and the thoracic duct, which receives the lymph. from the rest of the body. These two vessels meet and then open into the subclavian vein, through which they return the lymph to the cardiovascular system


Lymphatic Vessels 

Present throughout the organization, except the central nervous system and the superficial part of the skin, the lymphatic vessels run along the blood vessels. Lymphatic capillaries are formed by an extremely thin and permeable membrane, which allows the interstitial fluid to penetrate with a simple pressure. The bacteria, it contains are then evacuated and then destroyed by white blood cells


Lymphatic filtering blood

located behind the stomach, the spleen is composed of two types of tissue: the red pulp, rich in red blood cells and the white pulp, which forms small masses of lymphocytes along the arteries. In addition to its role in immune defense, the spleen filters the blood by destroying depleted red blood cells. It is also an important blood tank


Lymphatic gangles

After being drained from the lymphatic vessels, the lymph passes through the ganglia, specialized organs, rich in white blood cells (lymphocytes and macrophages), which filter and clean. Very numerous, these small organs with a diameter of 1 to 25 mm are arranged in groups along the vessels, mainly in the armpit (axillary lymph nodes), in the neck (cervical nodes), in the groin (inguinal node) and in the intestine (intestinal nodes)


Diseases of the cardivascular system


Now that you understand the structure and normal function of CVS, we will discuss some important diseases that occur as a result of CVS problems. Alterations in any part of CVS, including conditions discussed in the previous section, such as chamber or heart valve defects and arrhythmias such as atrial fibrillation, can contribute to the development and severity of diseases that ultimately prevent blood from circulating properly in all parts of the body

Cardiovascular disease (CVD) includes a group of heart and blood vessel disorders, including:

• Coronary heart disease (CHD)

• Heart attack

• Angina

Arrhythmias (Heart rhythm disorders)

• Aorta disease and Marfan syndrome

• Heart muscle disease (cardiomyopathy)

Heart failure

Hypertension (High blood pressure)

• Cerebrovascular disease (cerebrovascular accident)



  • Stroke
  • Transient ischemic attack (TIA)
  • Aneurysms
  • Vascular dementia
  • Subarachnoid hemorrhage



• Peripheral vascular disease (poor blood supply to the extremities)

• Heart valve disease


• Pericardial disease

• Rheumatic heart disease (heart damage from bacterial infection)

• Congenital heart disease (heart defect present at birth)

• Deep vein thrombosis and pulmonary embolism (blockages of blood flow due to blood clots)

Coronary and cerebrovascular diseases (cerebrovascular accidents) represent the majority of CVD cases


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