BSC1011 Advanced Biology
Tuesday, January 17, 2012
The heart weighs 300 grams and is shaped like a grapefruit and has two atria, two ventricles, and four valves receive blood from both venae cavae and the four pulmonary veins, and throw it into the aorta and pulmonary trunk. The heart pumps blood to 9 liters per day, making from 60 to 160 beats per minute. The heart is covered with a dense fibrous membrane - the pericardium, forming serous cavity filled with liquid, which prevents friction when it decreases. The heart consists of two pairs of chambers - the atria and ventricles, which act as separate pumps. The right half of the heart "pumps" venous-rich carbon dioxide blood through the lungs, it is - a small circulation. The left half throws oxygenated blood that is passed from the lungs into the systemic circulation. Venous blood from the upper and lower hollow vein enters the right atrium which consist of the “superior vena cava” which is a smaller vein that circulates de-oxygenated blood from the upper half of the body to the right atrium and the “inferior vena cava” which is a larger vein that circulates de-oxygenated blood from the lower half of the body to the right atrium. Four pulmonary veins deliver arterial blood to the left atrium.
Atrioventricular valves are of special thin papillary muscles and tendinous filaments attached to the ends of the sharp edges of valves. These structures are fixed valves and prevent them from "falling through" (prolapse) back into the atrium during ventricular systole. The left ventricle is formed by thick muscle fibers than the right ventricle because it is opposed to higher pressure of blood in the systemic circulation and should make greater efforts to overcome it during systole. “Located on the right dorsal side of the heart is the “tricuspid valve” also known as the right atrioventricular valve. Generally the “tricuspid valve” has three papillary muscles and leaflets and connected by the chordae tendineae” (Levick, 2010). “A bicuspid aortic valve (BAV) is most commonly a congenital condition of the aortic valve where two of the aortic valvular leaflets fuse during development resulting in a valve that is bicuspid instead of the normal tricuspid configuration. Normally the only cardiac valve that is bicuspid is the mitral valve (bicuspid valve) which is situated between the left atrium and left ventricle. Cardiac valves play a crucial role in ensuring the unidirectional flow of blood from the atrium to the ventricles, or the ventricle to the aorta or pulmonary trunk” (Levick, 2010). Between the ventricles and extending from them aorta and pulmonary trunk are semilunar valves. The heart is located in the chest behind the breastbone and in front of the descending part of the aortic arch and esophagus. It is fixed to the central muscle bundle diaphragm. Both sides are located in one lung. At the top are the major blood vessels, and place the division into two main tracheal bronchus.
During diastole atrial, blood flows from the upper and lower hollow vein into the right atrium, and the four pulmonary veins into the left atrium. Flow increases during inspiration, when the negative pressure inside the chest helps to "suction" of blood to the heart, as the air in the lungs. Normally, it can manifest respiratory (sinus) arrhythmias. Atrial systole ends, when the excitation reaches the atrioventricular node and extends along the branches of bundle branch block, causing ventricular systole. Atrioventricular valves quickly slammed shut, tendon fiber and ventricular papillary muscles prevent them from screw driving (prolapse) into the atrium. The venous blood fills the atria during diastole and ventricular systole. Blood in the vessels is not distributed evenly throughout the circulatory system. At any given time, approximately 12% of the blood in...