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1. Identify the main structures and blood vessels of the human heart and explain their roles in maintaining circulation.
2. Discuss the structure of arteries, veins and capillaries in relation to their functions.
3. Explain the importance of a double circulation for humans

Superior vena cava

Superior vena cava- Superior vena cava is the great venous trunk that helps to return the de-oxygenated blood from the circulatory system to the right atrium. This vein receives the venous return form the upper portion of the body (overhead diaphragm) (Pappano and Wier 2012)..

Aorta- This largest artery of the body starts from the left ventricle and the oxygenated blood from the left ventricle is pushed into the blood circulation system with the help of aorta (Ussher and Drucker 2012).

Pulmonary artery- This artery transports the de-oxygenated blood from the right ventricle of heart to lungs and further makes the blood oxygenated (Ussher and Drucker 2012).

Pulmonary vein- This vein helps to carry oxygenated blood from lungs to the left atrium of the heart and further pump them to the circulatory system (Pappano and Wier 2012).



Structure of wall

Size of lumen

Presence of valves

How structure fits function


The primary function of the artery is to carry oxygenated blood and nutrients from heart to rest of the body (Boulpaep 2012).

The structure of artery is divided into three sections. the innermost layer is tunica intima (a squamous epithelium surrounded by a basement membrane), the middle layer is known as tunica media that helps to regulate artery diameter and flow of blood and the outermost layer is tunica adventitia that helps to attach the artery to tissues and maintain the structure

The size of lumen is shorter than that of veins but bigger than the capillaries. This is because to maintain the blood pressure and prevent the back flow of the blood  

Arteries do not have valves, as the blood pressure is very high in heart that helps to flow the blood in one direction only.

 As the pressure of blood is high in heart, and the lumen of arteries are small and the wall is thicker. This structure helps to maintain a good pressure in the artery and the bloods in one direction only without the presence of any valve (West 2012)


These vessels carries the deoxygenated blood from the circulatory system ti the heart (Boulpaep 2012)

The structure is also divided in three sections that is tunica intima, tunica media and tunica adventitia. However, the difference is presence of less smooth tissue and less connective tissue.   

The size of lumen is bigger than the artery as does not determine the blood pressure, further the lumen is bigger as the presence of valves prevent the back flow of blood and the blood need extra space to make the blood flow from the veins

Veins contains valves to stop the backflow of blood.

The wall structure is important for the flow rate for the collection of blood from the body circulation to the heart. As the blood pressure is low, to prevent back valves are present (West 2012).


 Capillaries exchanges the materials between blood and tissue cells (Boulpaep 2012).

The wall structure of capillaries are different from veins and arteries. The capillary wall is made up of single layer of endothelial cells that helps to diffuse materials into body.  

The lumen size is shorter than that of the arteries and veins. This is because the capillary is responsible for the exchange of nutrients, oxygen and other requiring materials in the tissue joints. Therefore, the blood flow need to be slower.

It does not possess any valve

 The structure of the capillary is important for ts function. As the capillary is responsible for diffusion of nutrients and food and blood exchange, the single epithelial layer of capillary helps to diffuse those materials (West 2012)

 Your heart is a single organ, but it acts as a double pump in the human body – Explain this important concept.

The heart is a single body part however, it pumps the blood in two different circuits and pumps oxygenated and de-oxygenated blood simultaneously. The perimary role of heart is to drive blood from the entire body to the lungs for oxygenaton and further pumping the oxygenated blood from the lungs ot the netire body. There are two circuits for blood flow, pulmonary circuit and systematic circuit. The pulmonary circuit involves right ventricle, lungs and left atrium. Through this circuit, the blood ggets pumped from right ventricle to the lungs, as it is deoxygenated blood and from the kungs to the left atrium, as it is the oxygenated blood. On the other hand, the systematic circuit involves left ventricle, the entire circulatory system and the right atrium. This circuit helps to desperse the oxygenated blood to the entire body and collectuon of deoxygenated blood from the system to the heart. After te cycle, the blood needing more oxygen are sent baxck to the heart through superior and inferior vena cava and then again the pulmonary circuit begins. this cycle runs 1000 times everyday for As the single organ helps to pump two different type of blood into two different circuit simultaneously, it is called as double pump.

a) Myogenic is a term that can be explained as a muscle or tissue that contracts on their own, without the help of brain or spinal cord related stimulus or external electrical stimulus. An example of such muscle is the human heart. The human heart is myogenic as it contracts without the help of external electrical impulse however; it contracts with the help of nerve impulse (generated by the Sino-Atrial node). However, the nerve impulse just helps to maintain the rate of heartbeat; it does not help to contract the heart or initiate muscle contraction.

  1. b) As the human heart is myogenic, it produces its own electrical impulse to pump the blood, there are 5 elements needed for the conduction pathway such as the sino-atrial (SA) node, the bundle of His, the Purkinje fibres , the atrio-ventricular (AV) node and the right and the left bundle branches.
  • The electrical stimuli is generated form the SA node at a regular rate and the rate is dependent on the need of stimulus or contraction by the atria. This creates a movement of retrenchment that disperses through the atria rapidly (Gaztañaga, Marchlinski and Betensky 2012).
  • After this, the electrical impulse reaches the AV node and this period is enough to pump the blood from atria to ventricle. As the ventricles are filled, the repolarisation of atria occurs and the electrical impulse moves through the AV node and bundle of His to Purkinje fibres. The Atria again starts filling.
  • This cycle occurs again as the 400 million myocardial cells starts contracting the ventricle to drive the blood out of the heart into the entire body and ventricular repolarization starts again.
  • Therefore, one heartbeat is comprised of three main events, atrial depolarisation, ventricular depolarisation and atrial and ventricular depolarisation.

Hence, these conductive tissues help the heart to create its own electrical impulse to pump blood from heart to the direction of lungs and again from heart to the direction of entire body simultaneously (Gaztañaga, Marchlinski and Betensky 2012).


c) The sound of heartbeat, lub-dub is caused by the closing and opening of the heart valves and pumping of blood through atria to ventricle and further to entire body. In a properly working heart, the blood can flow only in one direction and the valves present in the junction of each atria and ventricle. The valves work in exact co-ordination with the blood pumping action of heart and allows blood to flow in one direction. As the tricuspid and mitral valves closes, the sound ‘Lub’ is produced. Similarly as the aortic and pulmonary valves closes, it produces the ‘Dub’ sound. It should be noted that when one set of valves are closed; the other two valves are open to maintain proper blood flow in the blood circulation system, and thereby creating a lub-dub sound while pumping the blood in the entire body (Oliveira, Gomes and Jogre 2014).

a) In the above-mentioned reading, the upper and lower part of the reading possess much significance as it provides a clear idea about the status of heart to the clinician. The upper portion of the reading determine the highest pressure in patient’s arteries while contraction of the heart muscle. This pressure is known as systolic pressure. On the other hand, the lower portion of the reading is known as diastolic pressure and determines the lowest blood pressure as soon as the heart is in-between beats. The usual blood pressure is between 120/80 and 90/60 and beyond this range the pressure indicates that the heart is working too much to pump blood to the entire body (Su et al. 2012). The high blood pressure is the result of the sympathetic nervous system that causes the body and mind ready for action and leads to elevate the blood pressure, whereas the parasympathetic nervous system is responsible for the normalization of the low or high blood pressure.

b) The clinician logged the blood pressure of the 46-year-old patient thrice and the average rating is 138/85 mm Hg. This blood pressure is greater than the standard blood pressure range that is 120/80 mm Hg. However, at this age, the range of higher blood pressure starts from 140/90 mm Hg. therefore, the patient need to change his lifestyle and dietary habits to lower the blood pressure or maintain it at normal level. Several factors make the blood pressure to fluctuate throughout the day. The factors are stress, hypertension alcohol, drugs, cessation of exercises leads the blood pressure to fluctuate (Su et al. 2012). Therefore, the patient should avoid alcohol, unhealthy and junk food, and should work out every day to control his blood pressure at normal level. He should avoid cholesterol rich food and should not involve in stressful situation to maintain his blood pressure.

a) During exercise, the body and specifically the muscles that are being used, requires more energy to maintain the resting state of the body. Therefore, the need of oxygen becomes double as the rate of metabolism increases while working out. This indicates the excessive generation of carbon-di-oxide in the body> Further, the ratio of CO2 to O2 also increases as the metabolism converted from fat utilization to carbohydrate utilization (Fletcher et al. 2012). This increases the normal pressure of the body and increases according to the intensity of the workout. The systolic blood pressure increase to normalize the blood pressure ad exceeds beyond 200 mm Hg. however the diastolic pressure did not changes and if the diastolic pressure increases even by 10 mm Hg, it is considered as hypertension (Billinger et al. 2014). On the other hand, the stroke volume also increases while working out and reaches up to 80-90ml/beat where as in resting state the stroke volume is around 50-70ml/beat. Another factor determines and controls the blood gas and concentration while working out. The medulla oblongata receives a nerve impulse as the baroreceptors detects the high blood pressure. Then the impulse is being forwarded to the SAN, which binds the acetylcholine to bring the heart rate back to normal (Kenney, Wilmore and Costill 2015).


Billinger, S.A., Arena, R., Bernhardt, J., Eng, J.J., Franklin, B.A., Johnson, C.M., MacKay-Lyons, M., Macko, R.F., Mead, G.E., Roth, E.J. and Shaughnessy, M., 2014. Physical activity and exercise recommendations for stroke survivors: a statement for healthcare professionals from the American Heart Association/American Stroke Association. Stroke, 45(8), pp.2532-2553.

Boulpaep, E.L., 2012. Arteries and veins. Medical physiology, 2nd Edn, pp.467-81.,+veins+and+capillary&ots=lOnmcDyo7s&sig=eJUiufiKT0vIKVcmfXUNMKFffXI

Fletcher, G.F., Ades, P.A., Kligfield, P., Arena, R., Balady, G.J., Bittner, V.A., Coke, L.A., Fleg, J.L., Forman, D.E., Gerber, T.C. and Gulati, M., 2013. Exercise standards for testing and training: a scientific statement from the American Heart Association. Circulation, 128(8), pp.873-934.

Gaztañaga, L., Marchlinski, F.E. and Betensky, B.P., 2012. Mechanisms of cardiac arrhythmias. Revista Española de Cardiología (English Edition), 65(2), pp.174-185.

Kenney, W.L., Wilmore, J. and Costill, D., 2015. Physiology of sport and exercise 6th edition. pp. 123-145, Human kinetics.

Oliveira, S.C., Gomes, E.F. and Jorge, A.M., 2014, July. Heart sounds classification using motif based segmentation. In Proceedings of the 18th International Database Engineering & Applications Symposium (pp. 370-371). ACM.

Pappano, A.J. and Wier, W.G., 2012. Cardiovascular Physiology E-Book: Mosby Physiology Monograph Series. 10th Edn, pp. 234-245, Elsevier Health Sciences.

Su, H.M., Lin, T.H., Hsu, P.C., Chu, C.Y., Lee, W.H., Chen, S.C., Lee, C.S., Voon, W.C., Lai, W.T. and Sheu, S.H., 2012. Association of interarm systolic blood pressure difference with atherosclerosis and left ventricular hypertrophy. PloS one, 7(8), p.e41173.

Ussher, J.R. and Drucker, D.J., 2012. Cardiovascular biology of the incretin system. Endocrine reviews, 33(2), pp.187-215.

West, J.B., 2012. Respiratory physiology: the essentials. 9th Edn, pp. 234-256, Lippincott Williams & Wilkins.,+veins+and+capillary&ots=RnQQ6sJtC0&sig=C6PHqtkbtWSAJPxtuR-Go5A7Dak

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