Cardiovascular Anatomy and Physiology

Introduction

The cardiovascular system is a system that is closed and contained blood vessels as well as the heart. The heart pumps blood through blood vessels to body parts. Blood contains waste, nutrients and oxygen among other materials. The heart is about the size of a human fist (Welsh, 2013). It is cone-shaped and sits slightly shifted to the left side in a mediastinum which is located at the middle of the chest cavity. It sits on top of the diaphragm which are muscles that assist in breathing and which is located behind the sternum, in front of the vertebral column, protected by ribs (Coad & Dunstall, 2011). Blood vessel, on the other hand, is supplied all over body tissues and there are estimated to be 60,000 miles of vessels in the human body (McDowell, 2010). Blood transports; diseases causing virus, oxygen, nutrients, and hormones among other things. (Waugh & Grant, 2014). This essay will discuss the anatomy and physiology of the cardiovascular system, some of its components, and their functions as well as how the components work to coordinate the whole system.

Anatomy of the Heart

The heart is hollow and muscular organ that pumps blood via blood vessels by contractions which are rhythmic (Sherwood, 2015). It contains cardiac muscles which are involuntary muscle tissue. In addition, it has 4 chambers namely; the right and left atrium, and right and left ventricle. The cardiac muscles are self-exciting in contrast to skeletal muscles which require reflex nervous stimuli or conscious (Welsh, 2013). The rhythmic contraction occurs spontaneously through the heart rate frequency is determined by the hormonal influence i.e. Adrenaline. The heart is covered with thick muscular tissue known as myocardium which is composed of specialized cardiac cells. The muscles can contract as well as conduct electricity. Furthermore, Rhoades & Bell., (2012), states that the heart contains pericardium- a membranous sac which surrounds the heart. It prevents injury to the heart and acts as lubricant. Moreover, it has two layers which include the serous pericardium and fibrous pericardium. Serous is further divided into bilayers which are separated by a space known as the pericardial cavity. As mentioned earlier, the heart has two ventricles as well as two atriums. The right atrium contains blood with poor oxygen, while other atria contain blood which is oxygen rich. The atrium on the right, receive blood from vena cava. Left atria receive blood rich in oxygen from the right as well as left pulmonary vein. The ventricles collect blood from atria and plump it out of the heart. Right ventricle which pumps blood to the lungs while left ventricle to all body parts (Martini et al., 2012). Ventricles have thicker muscles compared to atria. At the centre of the heart, is the septum which separates the two upper chambers (left and right).

Moreover, the heart contains valves which control blood flow in the heart. They include atrioventricular valves (AV) with control flow of blood from the atria to ventricles and only one-way valves (Ojanguren, 2019). The right atrioventricular valves are also known as the tricuspid valve and have three flaps (Kam & Power, 2012). It’s based between the right ventricle and left ventricle and in addition, allows blood to the right ventricle from the right atria during diastole. Left AV- bicuspid on the other hand has two flips. It restricts backflow of blood to the left ventricle. On the other hand, semilunar valves resemble half-moon. Pulmonary semilunar valve is based between the right ventricle and pulmonary trunk. The aortic semilunar is placed between the aorta and right ventricle. The chordae attached to papillary muscles together form the subvalvular apparatus which prevent valves from collapsing.

Passage of Blood through the Heart

The atriums contracts at the same period while ventricles contract at similar time too. The heart functions like pumps pumping blood simultaneous. The right pump blood to pulmonary circulation while the left pumps to systemic circulation (Pace et al., 2014). Systemic circulation blood gets to the right atrium via the upper and lower vena cava. Right atria contracts and blood is forced via the tricuspid valve to the right ventricle. The ventricle contract forcing blood into pulmonary trunk and later pulmonary artery. Blood is taken to the lungs and supplied with oxygen.

The Circulatory System

This contains the arteries which are muscular vessel that transport blood away from the heart. Secondly are the arterioles which are small arteries which elongate and lead to capillaries which have a thick and smooth wall that is muscular (Wolf, 2013). Capillaries are little blood vessels in the body and are in contact with most tissues. Veins on the other and transport blood towards the heart; pulmonary vein transport blood that has oxygen blood from the heart while other veins transport blood with little oxygen from systemic circulation.

The Cardiovascular Pathways

The cardiovascular system contains a double circulatory system which is systemic circulation and pulmonary circulation. The pulmonary circuit involves pumping deoxygenated blood from the heart to lungs and blood rich of oxygen to the heart via the pulmonary artery and pulmonary vein respectfully. On the other hand, systemic circulation involves supplying oxygenated blood to body organs via the aorta and later to capillaries and body tissues. In tissues, cells consume oxygen and other components of blood. Deoxygenated and low nutrient blood is pumped back to the heart via vena cava. Lastly is the coronary circulation which supplies blood to and from the heart (Pace et al., 2014).

The Cardiac Cycle

This is the relaxation and contraction of the heart while pumping blood via the body. The cardiac cycle determines heart frequency. Resting human heart beats is approximate 70-75mps. The normal range is between 60 and 100 MPs ( Wieling & Karemaker, 2013). Every heartbeat involves ventricular systole, atrial systole as well as complete cardiac diastole. At the systole phase, systole is ignited by sinoatrial node electrical cells- heart pacemaker. It is a phase of contraction of the heart ventricles which occur between the first as well as second rounds of the cardiac cycle. It results to ejaculation of blood via the aorta. The phase lasts for 0.3 to 0.4 seconds (Rangayyan, 2015). It is initiated by a brief contraction period followed by a phase of ejaculation was blood leave the ventricles. At this phase, arterial pressure is between 90 to 120mm of mercury in human. On the other hand, diastole refers to the cardiac cycle where the heart undergoes heart muscle relaxation followed by blood rapid filling the heart chambers. It is followed by a duration of contraction myocardia. At this duration, arterial pressure is decreased to its minimum- 80mm of mercury in human (Lilly, 2012). Ventricular diastole comes again after blood is injected into the aorta.

The Intrinsic Conduction System

The heart has muscles with a network of nerve fibres coordinated to relax as well as contract to produce a wave-like heart’s pumping action. The heart has pacemakers which cause heartbeat. This is controlled by circulating adrenaline and autonomic nervous system. One of the pacemakers is the Sinoatrial node which is a tissue based in the right atria of the heart (Baruscotti et al., 2010). The SA is triggered by its ability to generate impulse faster than other areas of the pacemaker potential. The electrical impulse from the SA node triggers electrical series of events in heart and control myocardial contraction that pump blood out of the heart. The polarization as well as depolarization of the SA node and other hearts’ electrical platform creates a strong pattern of changes in voltage which can be determined by an electrocardiogram (Goldberger et al., 2017). The SA node cells are self-firing and charge and discharge to create impulses. Secondly is the atrioventricular node (AV). This is a tissue which conducts an electrical impulse from atria to ventricles. It receives impulses from atria through the crista terminalis and anterior septum. It is a discremental conductor which prevents rapid conduction to the ventricles in cases of atrial rhythm which are rapid. It delays the impulse by 0.1 seconds and spread it to the walls of ventricles (Peate & Nair., 2011). This ensures that atria are empty before contraction of ventricles. Supply of blood of the AV node mostly comes from the right coronary artery. Another pacemaker is Purkinje fibre which is located in the walls of the ventricles. The fibre is specialized in myocardial fibres which conduct electrical impulses enabling the heart to contract in a version which is coordinated (Levick, 2013). The fibres work with the SA node and the AV node to control heart rate. On ventricle contraction, the Purkinje fibre carries the contraction impulse from the right and left bundles branches to the ventricular myocardium. This initiate contraction forcing blood out of the heart-both systemic and pulmonary circulation. Some of the cardiovascular diseases include atherosclerosis which is a disease affecting blood vessels referred to hardening of arteries, circulatory shock which is a severe condition as a result of reduced circulation of blood, and stroke among others.

Conclusion

The cardiovascular system is a system that is closed and contained the heart and blood vessels. The system is involved in a series of activities such as transport of nutrient and hormones. Looking at the heart structure, it has four chambers, semilunar valves, atrioventricular valves while the ventricles are thick compared to atria. Blood in the heart passes via all chambers in a jetting mechanism, which ensures blood flows from one chamber to another. This then involves two circulation systems which include the systemic and pulmonary circulation. Pumping of blood involves the cardiac cycle which involves diastole and systole. To initiate a pumping mechanism, pacemakers are involved and include SA and AV nodes, the Purkinje fibre, pacemaker, and AV bundles among others.

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References

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