Review Sheet Exercise 6 Cardiovascular Physiology Essay

Heart valves ensure one way blood flow through heart. The atrioventricular (AV) valves lie between the atria and the ventricles prevents the back flow of blood in to the atria while the ventricles contract. Chordae tendinae anchor AV values to papillary muscles. The left AV valve, the mitral or bicuspid valve consists of two cusps of endocardium. The right atrioventricular valve, the tricuspid valve, has three cusps. The second sets of valve are the semilunar valves. The pulmonary semilunar valves lie between the right ventricle and pulmonary trunk. Aortic semilunar valves lie between ventricle and the aorta. Semilunar valves prevent the backflow of blood into the ventricle.

The resting heart rate fluctuates over time because it is under control of the autonomic nervous system and the fluctuations are a result of the sympathetic and parasympathetic systems trying to balance each other out.

R E V I E W S H E E T 30 Anatomy of the Heart

The natural “pacemaker” of the heart is the initiating electrical conductor to start each heartbeat which is identified as the sinoatrial node located in the right atrium of the heart and signals for atrial contraction (Levine & Miller, 2008). The electricity travels then to the atrioventricular node that signals for ventricular contraction. The Bundle of His receives this signal and the electrical impulse is split down the septum of the heart to each ventricle. The impulse then terminates in the purkinje fibers following contraction of the ventricles (http://www.emedicine.medscape.com/article/1922987-overview#a4). This process is repeated with every

The heart serves an important purpose within the body, pumping blood throughout the circulatory system to supply all parts of the body with vital nutrients and molecules. It pumps oxygen and nutrient rich blood to be exchanged for carbon dioxide, which is then pumped to the lungs and eliminated from the body. The movement of blood throughout the body is due to the heart’s ability to push blood along the circulatory system at a steady, unfaltering rate. This rate, known as heart rate, is regulated and can be altered at a moment’s notice by signaling within the body and heart itself. In vertebrates, the autonomic nervous system controls and regulates heart rate. The autonomic nervous system is divided into two subunits, the sympathetic nervous system and parasympathetic nervous system. The parasympathetic nerve that innervates the heart is the vagus nerve. In this laboratory experiment, the regulation of heart rate was observed by studying a certain breed of turtle, the Red-eared Slider (Trachemys scripta elegans). Both chemical and electric signaling can influence the components of the nervous

In the normal conduction of the heart the electrical impulse starts in the SA node, also called the pacemaker of the heart. The electrical impulse travels through the right atrium and through the Bachmann’s bundle into the left atrium. This stimulates the atria to contract. Next the signal travel to the AV node. The AV node slightly delays the signal. This delay is needed for the heart to beat properly. Without this delay the atria and ventricles would beat at the same time. The electrical signal then travels to the Bundle of His where it is split into the signals going to the right and left ventricle. The signal

Meaning The Sa node and Av node work together, forcing blood into the ventricles, which contract, forcing the blood to leave from the left side of the heart. The blood that enters the right side of the heart enters through veins as it is under less pressure. Blood with co2 in it will exit the right side of the heart through the pulmonary artery to the lungs where gaseous exchange occurs.

FIGURE 4: Effect of atrial extrastimulation on preexcitation. A: Manifest preexcitation during normal sinus rhythm (NSR) with HV interval value of -11 msec. Atrial extrastimulation (AES) increased the degree of preexcitation (HV interval value of -64 msec). B: An earlier coupled AES produced more pronounced preexcitation with HV interval value of -93 msec. C: A more premature AES produced full preexcitation with the His bundle activated retrogradely , with VA conduction over the AVN & an echo beat (atrioventricular reentry) (Issa et al, 2012).

The electrical impulses then arrive at another group of cells called the atrioventricular (AV) node. This node is located near the tricuspid valve (between the right atrium and right ventricle. The signals pause at the AV node while the ventricles fill with blood. Once they have filled, the signals are released in order to spread throughout the lower chambers, causing them to contract and push blood outward.

The ability of the heart to contract stems from its possession of the SA node (Sino atrial node) also called the pacemaker as it generates the hearts own electrical signal and allows it to contract and pump blood to the rest of the body. This gives the heart a special feature making it the only organ that is capable of working outside the body if provided with enough oxygen.

“An electrical signal from the ventricles causes an early heart beat that generally goes unnoticed”

The SA node is the primary pacemaker of the heart. It starts the heartbeat by spontaneously contracting, causing the rest of the heart to contract in a wave.

Myogenic hearts contract spontaneously. Myogenic hearts are found in vertebrates and molluscs. In vertebrates a specialized region of cells called the sinoatrial (SA) node, acts as the pacemaker for

3. Refractoriness – this prevents heart muscle from responding to a new stimulus while the heart is still in a state of contraction due to an earlier stimulus, and thus, helps to preserve heart rhythm. Irritability is lowest during refractory period. During the absolute refractory period, the heart muscle will not respond to any stimulus however, strong;during the relative refractory period, the heart muscle slowly regains irritability.

The hearts role is to pump oxygenated blood to every cell in the body by having a continuous beat. Throughout time the heart has created mystery, however current technology has solved most of the mystery, there still remains an enchantment and eagerness to learn more.