Enabling Objectives
  1. Outline the principles of the circulation. Name the major arteries and veins of the trunk and limbs, and discuss the structure of blood vessels.
  2. Describe the landmarks for finding the sites where the arterial pulse can be felt and blood pressure measured in an emergency.
  3. Describe the form, and name the chambers and valves of the heart. Define the pericardium. Name and describe briefly the venae cavae, pulmonary veins, pulmonary trunk and aorta.
  4. Define the mediastinum and describe the cardiac shadow on XRay. Discuss the significance of mediastinal widening.
  5. Describe the right ventricle, interventricular septum and the tricuspid and pulmonary valves.
  6. Outline the histological features of cardiac muscle and the parts of the conducting system of the heart.





Principles of Circulation

The function of the circulatory system is to supply nutrients and oxygen towards, but waste away from the tissue. The role of the arteries is to supply high pressure oxygenated blood towards the tissue and the role of the veins is to carry carbondioxide away from the tissue as well as waste products. Overall there are two kind of circulation the systemic and the pulmonary.
The pulmonary is the

What are the major arteries & veins and their structures?

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Type
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Arteries
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Veins
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Function
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Structure
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Superior Vena Cava
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Inferior vena Cava
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Posterior superior portion of the right atrium takes blood to the right atrium from head, neck, upper limbs and chest.


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Supplies blood to right atrium from the trunk, viscera and the lower limbs. The cardiac veins of the heart return blood to the coronary sinus, a large, thin walled vein that opens into the right atrium inferior to the connection with the superior vena cava.
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What are the landmarks for finding pulses?

Basic Anatomy, Physiology and Histology of the heart (e.g. Anatomy of the valves, heart walls and movement).

The heart is located near the anterior chest wall, directly posterior to the sternum. The great veins and arteries are located, It’s base sits posterior to the sternum at the third costal cartilage, the apex is the inferior tip of the heart. A adult heart measures about 12.5 cm from the apex to the top, it reaches the fifth intercostal space to the left of the midline. The heart is surrounded by pericardial sac and that is in the mediastinum which is surrounded by the pleural cavities of both of the lungs. The mediastinum also contains the great vessels, oesaophagus, thymus and trachea.
The membrane that sourrounds the heart is the pericardium and the space in between is called the pericardial cavity. The Pericadial cavity is filled with air and the serous membrane is the lining of the pericardium and they can be divided into the visceral and parietal pericardium, the visceral pericardium or epicardium surrounds the lining of the heart and the parietal pericardium lines the inner surface of the pericardial sac (this sac is mostly made of collagen fibers, and stabilises the positioning of the heart).
The pericardial cavity contains pericardial fluid which helps for lubrication and reduction of friction of the heart against the surfaces of the heart and its surroundings. Pericarditis can be produced if an infection of the pericardium is caused due to parthogens. The sound made by the scratching of the surfaces can be heard through a stethoscope. And overproduction of pericardial fluid in case of inflammation can cause cardiac tamponade which restricts the movements of the heart.

The four cardiac chambers are easily identifiable, the atria have thin walls for expansion and the if no blood is present then the outer portion of each atrium deflates and becomes a lumpy, wrinkled flap also knowns a atrial appendage or auricle. The coronary sulcus is the groove between the atria and the ventricles, these grooves contain fat and there is the anterior interventricular sulcus and the posterior interventricular sulcus.

The heart wall is made of three different layers: an outer epicardium, a middle myocardium and an inner endocardium.

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Epicardium
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Myocardium
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Endocardium
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This is the visceral pericardium that covers the surface of the heart, exposed mesothelium and loose areolar connective tissue that connects to the myocardium makes up this serous membrane.

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The myocardium (muscular wall of the heart), forms the atria and ventricles. This layer contains cardiac muscle tissue, blood vessels and nerves. The myocardium consists of concentric layers of cardiac muscle tissue. The atrial myocardium contains muscle bundles that wrap around the atria and form figure eights that encircle the great vessels. Superficial ventricular muscles wrap around both ventricles; deeper muscle layers spiral around and between the ventricles toward the apex.
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The inner surfaces of the heart, including those of the heart valves, are covered by the endocardium, as sinple squamous epithelium that is continuous with the endothelium of the attached great vessels.
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The cardiac muscles are connected to each other by intercalated discs. At an intercalated disc, the interlocking membranes of adjacent cells are held two discs are held together by either desmosomes or linked by gap junctions. Differences between cardiac muscles and skeletal muscle fibers are as follows: they are smaller in size, a single, centrally located nucleus, branched connections between cells and presence of intercalated discs.

The right atrium corresponds with the right ventricle and the left atrium with the left ventricle. The atria are separated by the interatrial septum; the ventricles are separated by the much thicker interventricular septum. Atrioventricular valves fold of fibrous tissue, extend into the openings between the atria and ventricles. This makes flow of the blood in one way direction only.

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Right Atrium
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· Receives blood from systemic circuit from superior/inferior vena cava
· In fifth month of fetal development foramen ovale forms, an oval opening lets the blood flow from the right to the left atrium, in adults this is sealed off and the fossa ovalis forms.
· The posterior walls and the interatrial septum have smooth surfaces, however the walls inside the auricle contain prominent ridges called the pectinate muscles or musculi pectinati.

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Right Ventricle
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The Blood enters the right ventricle through flaps or cusps and they are part of the atrioventricular valve, also known as tricuspid valve, the end of the cusps is attacked to the chordae tendineae tendinous connective tissue fibers. These fibers connect the cusps with the papillary muscles. These valves prevent backflow of the blood into the atrium when the ventricle contracts. Without chordae tendineae the flaps would be both ways and the flood could flow backwards, the internal surfaces are made of trabeculae carneae and moderator bands for the control of contraction of the cardiac muscle. The moderator muscle delivers the stimulus for contraction. The blood then enters the conus arteriosus a conical puch that ends at the pulmonary valve, these valves are half moon shaped or semilunar valve. The blood then enters the pulmonary trunk, the cusps again prevent the backflow of blood, once the
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Left Atrium
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Left Ventricle
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What components of the mediastinal widening show on X-Ray?