General Prerequisites:. Course Term:. Course Lecture Information:. Course Weight:. Course Level:. Assessment type: Written Examination. Course Overview:. Learning Outcomes:. Course Synopsis:. The following modules will not be taught in Reading List:. Physical Cell Biology, second ed. Rob Phillips et al. Garland Science. Humans, birds, and mammals have a four-chambered heart that completely separates oxygen-rich and oxygen-depleted blood, as is shown in Figure Fish have a two-chambered heart in which a single-loop circulatory pattern takes blood from the heart to the gills and then to the body.
Amphibians have a three-chambered heart with two atria and one ventricle.
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A loop from the heart goes to the pulmonary capillary beds, where gas exchange occurs. Blood then is returned to the heart. Blood exiting the ventricle is diverted, some to the pulmonary circuit , some to systemic circuit. The disadvantage of the three-chambered heart is the mixing of oxygenated and deoxygenated blood.
Some reptiles have partial separation of the ventricle. Other reptiles, plus, all birds and mammals, have a four-chambered heart, with complete separation of both systemic and pulmonary circuits. Figure Circulatory systems of several vertebrates showing the progressive evolution of the four-chambered heart and pulmonary and systemic circulatory circuits. The heart, shown in Figure 11, is a muscular structure that contracts in a rhythmic pattern to pump blood. Hearts have a variety of forms: chambered hearts in mollusks and vertebrates, tubular hearts of arthropods, and aortic arches of annelids.
Accessory hearts are used by insects to boost or supplement the main heart's actions. Fish, reptiles, and amphibians have lymph hearts that help pump lymph back into veins. The basic vertebrate heart, such as occurs in fish, has two chambers. An auricle is the chamber of the heart where blood is received from the body. A ventricle pumps the blood it gets through a valve from the auricle out to the gills through an artery.
Amphibians have a three-chambered heart: two atria emptying into a single common ventricle.
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Some species have a partial separation of the ventricle to reduce the mixing of oxygenated coming back from the lungs and deoxygenated blood coming in from the body. Two sided or two chambered hearts permit pumping at higher pressures and the addition of the pulmonary loop permits blood to go to the lungs at lower pressure yet still go to the systemic loop at higher pressures.
Biology and Mechanics of Blood Flows
The relationship of the heart and circulatory system to major visceral organs. Below: the structure of the heart. Establishment of the four-chambered heart, along with the pulmonary and systemic circuits, completely separates oxygenated from deoxygenated blood. This allows higher the metabolic rates needed by warm-blooded birds and mammals. The human heart, as seen in Figure 11, is a two-sided, four-chambered structure with muscular walls. An atrioventricular AV valve separates each auricle from ventricle.
A semilunar also known as arterial valve separates each ventricle from its connecting artery. The heart beats or contracts approximately 70 times per minute. The human heart will undergo over 3 billion contraction cycles, as shown in Figure 12, during a normal lifetime. The cardiac cycle consists of two parts: systole contraction of the heart muscle and diastole relaxation of the heart muscle.
Atria contract while ventricles relax. The pulse is a wave of contraction transmitted along the arteries. Valves in the heart open and close during the cardiac cycle. Heart muscle contraction is due to the presence of nodal tissue in two regions of the heart. The SA node sinoatrial node initiates heartbeat. The AV node atrioventricular node causes ventricles to contract. The AV node is sometimes called the pacemaker since it keeps heartbeat regular. Heartbeat is also controlled by nerve messages originating from the autonomic nervous system. The cardiac cycle. Blood flows through the heart from veins to atria to ventricles out by arteries.
Heart valves limit flow to a single direction. One heartbeat, or cardiac cycle, includes atrial contraction and relaxation, ventricular contraction and relaxation, and a short pause. Normal cardiac cycles at rest take 0. Blood from the body flows into the vena cava, which empties into the right atrium. At the same time, oxygenated blood from the lungs flows from the pulmonary vein into the left atrium.
The muscles of both atria contract, forcing blood downward through each AV valve into each ventricle. Diastole is the filling of the ventricles with blood. Ventricular systole opens the SL valves, forcing blood out of the ventricles through the pulmonary artery or aorta.
The sound of the heart contracting and the valves opening and closing produces a characteristic "lub-dub" sound.
Lub is associated with closure of the AV valves, dub is the closing of the SL valves. Human heartbeats originate from the sinoatrial node SA node near the right atrium. Modified muscle cells contract, sending a signal to other muscle cells in the heart to contract. The signal spreads to the atrioventricular node AV node. Signals carried from the AV node, slightly delayed, through bundle of His fibers and Purkinjie fibers cause the ventricles to contract simultaneously.
Figure 13 illustrates several aspects of this. The contraction of the heart and the action of the nerve nodes located on the heart. Heartbeats are coordinated contractions of heart cardiac cells, shown in an animate GIF image in Figure When two or more of such cells are in proximity to each other their contractions synch up and they beat as one. Animated GIF image of a single human heart muscle cell beating. An electrocardiogram ECG measures changes in electrical potential across the heart, and can detect the contraction pulses that pass over the surface of the heart.
Hemodynamics - Wikipedia
There are three slow, negative changes, known as P, R, and T as shown in Figure Positive deflections are the Q and S waves. The P wave represents the contraction impulse of the atria, the T wave the ventricular contraction. ECGs are useful in diagnosing heart abnormalities. Normal cardiac pattern top and some abnormal patterns bottom.
Cardiac muscle cells are serviced by a system of coronary arteries. During exercise the flow through these arteries is up to five times normal flow. Blocked flow in coronary arteries can result in death of heart muscle, leading to a heart attack. Blockage of coronary arteries, shown in Figure 16, is usually the result of gradual buildup of lipids and cholesterol in the inner wall of the coronary artery.
Occasional chest pain, angina pectoralis, can result during periods of stress or physical exertion. Angina indicates oxygen demands are greater than capacity to deliver it and that a heart attack may occur in the future. Heart muscle cells that die are not replaced since heart muscle cells do not divide.
Heart disease and coronary artery disease are the leading causes of death in the United States. Development of arterial plaque. Causes in most cases are unknown, although stress, obesity, high salt intake, and smoking can add to a genetic predisposition. Two main routes for circulation are the pulmonary to and from the lungs and the systemic to and from the body.
Pulmonary arteries carry blood from the heart to the lungs. In the lungs gas exchange occurs. Pulmonary veins carry blood from lungs to heart. The aorta is the main artery of systemic circuit.
The vena cavae are the main veins of the systemic circuit.