The cardiovascular system or the circulatory system is an organ system that passes nutrients, electrolytes, gases, hormones, blood cells, nitrogenous wastes, etc. to and from the cells in the body and helps stabilize body temperature and pH to maintain homeostasis. The main components of the circulatory system are the heart, the blood, and the blood vessels.
Cardiology is that branch of medicine which deals with the diagnosis and treatment of heart diseases. Cardiologists investigate patients with suspected heart disease. Cardiologists should not be confused with cardiac and cardiothoracic surgeons who are surgeons that perform cardiac surgery - operative procedures on the heart and great vessels.
Adults have approximately 60,000 miles of blood vessels – arteries, arterioles, veins, and venules. By moving blood throughout this network of vessels, the cardiovascular system supplies all cells of the body with oxygen and nutrients and removes carbon dioxide and other waste products.
BLOOD VESSELS
Blood vessels are part of the circulatory system that transports blood throughout the body. There are 3 major types of blood vessels
• Arteries – carry blood away from the heart
• Veins – carry blood towards the heart
• Capillaries – smallest blood vessels where exchange of water and chemicals between blood and body tissues happen.
The arteries and veins have the same basic structure with their walls having three layers from the inside to the outside –
• Tunica intima – thinnest internal layer
• Tunica media – the middle thick layer made of vascular smooth muscles
• Tunica adventitia – the outer connective tissue layer
The capillaries consist of just a layer of endothelium and occasional connective tissue. Many regions of the body receive blood supplies from two or more arteries. The points where these arteries merge are called arterial anastomoses. Arterial anastomoses allow tissues to receive blood even after one of the arteries supplying blood has been blocked.
Arteries are thick-walled vessels that carry blood away from the heart. Aorta that comes out of the heart is the largest artery. Blood flows in the arteries as it is propelled forward by the pumping heart. As the arteries continue on their path away from the heart, they branch into smaller vessels called arterioles.
Arterioles have thinner walls than the art Arterioles have thinner walls than the arteries and are composed almost entirely of smooth muscle with very little elastic tissue. The arterioles end up in capillaries.
Capillaries are the smallest of the blood vessels and the thin walls allow for the exchange of materials between the blood and the tissue surrounding the body cells.
The capillaries connect the arterioles to the beginnings of the venules. Venules are the smaller veins that collect the deoxygenated blood from the cells for transport back to the heart. The venules branch into larger vessels known as veins.
Veins have thinner walls than the arteries. Blood moves in the veins due to contraction of the skeletal muscles. The valves within the veins support the flow of blood in one direction and prevent backflow of blood.
THE HEART
The heart is the center of the circulatory system. It lies within the mediastinum, in the thoracic cavity cradled between the lungs, just behind the sternum. The area of the chest covering the heart is the precordium. The heart is a muscular organ for pumping blood through the blood vessels by repeated, rhythmic contractions. This seemingly tireless organ beats about 100,000 times a day. It is basically a clenched fist shaped organ weighing less than a pound.
The heart is cone-shaped, with the broader upper portion called the base and the narrower lower tip called apex. The apex of the heart is located between the fifth and sixth ribs on a line perpendicular to the midpoint of the left clavicle.
The heart is enclosed by a thin, double-walled, membranous sac called the pericardium. The pericardium has 2 layers
- Parietal pericardium: the outer fibrous sac providing strength
- Visceral Pericardium: the inner serous membrane forming a thin, tight covering over the heart surface
- Between these 2 layers is a small space – the pericardial cavity containing a fluid that lubricates the surface of the heart and reduces friction during cardiac muscle contraction – the pericardial fluid
The heart wall itself consists of 3 layers –
- The epicardium: The outermost serous membrane, almost sequestered with the serous visceral pericardium
- The myocardium: The middle muscular membrane that consists of the muscles of the heart that contract and relax
- The endocardium: The innermost thin endothelial membrane which forms the inner lining of the heart Externally, 2 prominent grooves are visible on the surface of the heart:
- The coronary sulcus (atrioventricular groove) marks the junction of the atria and ventricles.
- The anterior interventricular sulcus and posterior interventricular sulcus mark the junction of the ventricles on the front and back of the heart, respectively.
INTERNAL ANATOMY OF THE HEART
The heart functions as 2 pumps working simultaneously to move blood to all the sites of the body. The interior of the heart is divided into 4 chambers – right and left the atria are the receiving chambers and the right and left ventricles are the pumping chambers. The common wall separating the right and left heart is the septum (the interatrial septum dividing the atria and the interventricular septum dividing the ventricles)
- Superior vena cava – from the superior part of the body
- Inferior vena cava – from the inferior part of the body
- The coronary sinus – from the myocardium
The left atrium
The left atrium receives oxygenated blood from the lungs through 4 veins – 2 from each lung. When the ventricles relax, the blood from the left atrium moves into the left ventricle through the left atrioventricular valve – the bicuspid valve having only 2 cusps. The bicuspid valve is also called the mitral valve.
The left ventricle
The left ventricle is larger than the right ventricle and much more muscular. Blood received from the left atrium is pumped out of the left ventricle into the aorta and then on into the arteries leading to all parts of the body through the aortic semilunar valves, again having 3 cusps.
• When the left ventricle contracts, the left AV valve closes and prevents blood from moving back into the right atrium. As in the right AV valve, the chordae tendineae prevent overextension of the left AV valve.
• When the left ventricle relaxes, the initial backflow of blood in the aorta closes the aortic semilunar valve and prevents the return of blood to the left ventricle Along with the above valves, 2 additional passageways are present in the fetal heart:
• The foramen ovale is an opening across the interatrial septum. It allows blood to bypass the right ventricle and the pulmonary circuit, while the nonfunctional fetal lungs are still developing. The opening, which closes at birth, leaves a shallow depression called the fossa ovalis in the adult heart.
• The ductus arteriosus is a connection between the pulmonary trunk and the aorta. Blood that enters the right ventricle is pumped out through the pulmonary trunk. Although some blood enters the pulmonary arteries (to provide oxygen and nutrients to the fetal lungs), most of the blood moves directly into the aorta through the ductus arteriosus
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