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Experiment and Analasys: Cardiovascular System

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The Cardiovascular system supplies oxygen and metabolic substrates to the tissues of the body and “removes the products of the metabolism”. The superior vena cava supplies deoxygenated blood to the right atrium, this connects to the right ventricle via the tricuspid valve. This valve inhibits the backflow of blood, as do the other valves. The pulmonary vein supplies oxygenated blood to the left atrium, this connects to the left ventricle via the bicuspid valve. The semi-lunar valves are in the pulmonary artery, which leaves the right ventricle, and the aorta, which leaves the left ventricle.

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The sinoatrial node (SAN) is the heart’s pacemaker and is located in the wall of the right atrium. A surge of electrical excitation travels across the left and right atrium making them contract. This electrical activity reaches the atrioventricular node (AVN), transferring the activity through the Purkinje fibres. These fibres run through the septum and inside the walls of both ventricles, the activity causes them to contract. A stethoscope can be used to listen to heart beats. Electrocardiograms are used to check the hearts rhythm and electrical activity, the electrode pads acting as sensors detecting electrical signals from the heart.

The blood vessels have layered walls which surround the lumen that contains the blood. Veins carry deoxygenated blood back to the heart from the capillaries. Arteries carry oxygenated blood from the heart to the capillaries. The capillaries facilitate the exchange of substances in the blood and interstitial fluid. The capillary endothelium allows cells from different tissues to uptake oxygen and nutrients and expel waste. 

Heart contractions control blood pressure, this is the pressure which blood exerts on blood vessel walls. Found in the carotid sinus, mechanoreceptors known as Baroreceptors have the function of detecting the pressure changes in the blood. This is done by retaliating to change in arterial wall tension.  This pressure is highest in arteries and lowest in veins. The auscultatory, automatic and palpatory methods can be used to measure blood pressure. The first two methods can determine both systolic and diastolic levels, the third only the systolic pressure.

The blood pressure of three subjects using the auscultatory, automatic and palpatory methods. The automatic method tends to provide more accurate results, although most of the values obtained from the auscultatory method are close to it. However, the second subject’s results display a larger difference. This may be due to human error, or the Korotkoff sounds may not have been heard clearly or due to the subject moving whilst the measurement was being taken. As shown in table 4, exercise has an effect on blood pressure. 

This is shown by the fact that each method displayed a rise in blood pressure once after exercise. However, the increase wasn’t large. This may be due to the subject not performing very intensive exercise, but it still showed that exercise has an effect on blood pressure. The first heart sound is caused by the shutting of both the mitral and tricuspid valves. 

The second sound is due to the shutting of the aortic and pulmonic valves. The first sound is slightly louder than the second one (MedEdu, No Date). The results displayed a third sound being heard after exercise, this can be attributed to the sudden increase in blood flow from the left atrium into the left ventricle. When this sound was observed, the first sound was heard decreasing in intensity whilst the second sound increased (MedEdu, No Date).

As depicted above, ECG traces consist of different positions which are P and T waves. T waves represent the repolarization of the ventricle. They also consist of QRS complexes, these indicate the different events occurring during the cardiac cycle. The ECG trace collected was different to that seen on the standard ECG, due to the fact that the PQRST points were harder to identify from the experimental trace. The P and T waves were the most difficult to identify. 

This was due to the fact that the waves were not defined as clearly as they are on the standard ECG, as there was no straight line in between the positions. The sinoatrial node (SAN), is a pacemaker and is located in the wall of the right atrium. The SAN is made up of a bundle of myocytes, generating electrical impulses which set both the heart’s rhythm and rate. These electrical impulses move through the heart and cause it to contract.

Potassium ions are at higher concentrations in the intracellular space and the sodium ions are in higher concentrations extracellularly. This concentration gradient for both ions is maintained by the Na-K ATPase pump, these use active transport to pump sodium out of and potassium into the cell. This concentration gradient causes an electrical potential over the myocyte membrane. 

If the potassium concentration increases in the extracellular area, the concentration gradient across the membrane declines, this further lowers the resting threshold potential. This causes a decline in the rate of the sodium channels opening, causing the myocardial conduction to slow. This leads to a longer PR interval and thus a wider QRS complex.

Heart rate is controlled by the autonomic nervous system, comprised of the parasympathetic and sympathetic nervous system. The sympathetic nervous system increases heart rate, whilst the parasympathetic decreases heart rate. Factors such as stress and caffeine may cause a temporary increase in heart rate. 

Exercise also causes a rise in heart rate and it will stay risen until the exercise stops. The results showed that standing up led to an increase in heartbeats. Laying down, the heart can pump blood around the body with more ease. As when stood gravity pulls in opposition to the blood flowing above the heart, making the heart work harder to ensure it’s able to work against the effect of gravity.

Both the systolic and diastolic pressures increased once the subject had performed intensive exercise. Systolic pressure is the pressure in the blood vessels caused by the heart beating. Diastolic pressure is the blood vessel pressure in between the beating of the heart. The systolic pressure increases after exercise, as the muscles used during the exercise require more oxygen, so more respiration occurs. 

Therefore, the heart has to pump faster in order to supply the oxygen needed. Baroreceptors, in the carotid sinus mechanoreceptors, detect the pressure changes in the blood. This is done by retaliating to change in arterial wall tension. Baroreflex mechanism is a quick response to an increase or decrease in blood pressure.

The kidneys remove waste fluid by blood filtration, using osmosis to remove excess water from the blood, by using a balance of potassium and sodium to absorb it. However high sodium levels in the bloodstream disturb this balance, preventing the kidneys absorbing the excess water. This causes a build-up of fluid raising blood pressure, leading to a strain on the kidneys, arteries, heart and brain.

In conclusion, the experiment displayed that posture and exercise have an effect on the rate at which the heart beats and on blood pressure. The results showed that exercise led to an increase in both heart rate and blood pressure, and that changing posture (standing to sitting) causes an increase in the rate at which the heart beats.

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