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Heart - Physical features.

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Heart Physical features: The heart consists of: - Muscle tissue (Cardiac muscle) - Coronary blood vessels (Carries blood to/from the heart-actually supplying the heart itself) - Conducting tissue (SAN, AVN, sets the basal rhythm) - Connective tissue (Moderator bands-especially in Left Ventricle, interventricular septum) - Epicardial fat (energy store) The above image is from http://www.biosci.uga.edu/almanac/bio_104/notes/may_7.html. The heart is a muscular organ (rich in myoglobin-an oxygen storage molecule, giving it a deep red colour) enclosed in a fibrous sac, the pericardium, and located in the chest (thorax). The narrow space between the pericardium and the heart is filled with a watery fluid that serves as a lubricant as the heart moves within the sac. The inner surface of the myocardium (cardiac muscle cells) is lined by a thin layer of cells known as endothelial cells or endothelium. The heart is divided into right and left halves, each consisting of an atrium and a ventricle. Located in each half of the heart are the atrioventricular valves (AV valves) which permit one way blood flow from atrium to ventricle but not from the ventricle to atrium. The opening and closing of the AV valves is a passive process resulting from pressure differences across the valves. More about this will be explained later. To prevent AV valves from being pushed up into the atrium the valves are fastened to muscular projections (papillary muscles) ...read more.


The parietal pericardium consists of an outer layer of thick, fibrous connective tissue and an inner serous layer. The serous layer, consisting largely of mesothelium together with a small amount of connective tissue, forms a simple squamous epithelium and secretes a small amount of fluid. Normally the total volume of this fluid is only about 25 to 35 ml. This fluid layer lubricates the surfaces to allow friction free movement of the heart within the pericardium during its muscular contractions. The fibrous layer of the parietal pericardium is attached to the diaphragm and fuses with the outer wall of the great blood vessels entering and leaving the heart. Thus, the parietal pericardium forms a strong protective sac for the heart and serves also to anchor it within the mediastinum. So preventing it from thrashing around when it is contracting. It also protects it from external shocks and over-distension of the heart with blood in extreme conditions The visceral pericardium is also known as the epicardium and as such comprises the outermost layer of the heart proper. The epicardium (or visceral pericardium) forms the outer covering of the heart and has an external layer of flat mesothelial cells. These cells lie on a stroma of fibrocollagenous support tissue, which contains elastic fibres, as well as the large arteries supplying blood to the heart wall, and the larger venous tributaries carrying blood from the heart wall. ...read more.


2. Ventricular diastole The increase in atrial pressure resulting from atrial filling is represented by the v wave and causes atrial pressure (yellow waveform) to exceed ventricular pressure (blue waveform). As a result, the atrioventricular valves open, and blood under pressure begins to enter the ventricles in a period of rapid ventricular filling. Even before the atria enter systole, the ventricles are filled with blood to approximately 70% of their capacity. When the atria do finally contract, additional blood enters the ventricles and elevates the intraventricular pressure. As the ventricles contract, blood is forced backward, closing the AV valves and a sharp rise in ventricular pressure occurs. Blood, now under less pressure, continues to enter the ventricles in a period of reduced ventricular filling called diastasis. Via ventricular suction. As the atria contract, the remaining blood is ejected into the ventricles, accounting for about 20% of cardiac output. Atrial and ventricle pressure increase slightly due to the weak atrial contraction. This increases the stretch of the ventricle, therefore a lot more power for the ventricle systole. Therefore creating a bigger systole, than otherwise possible. This period of increased atrial pressure is represented by the a wave on the atrial (yellow) waveform. The end of atrial systole marks the beginning of ventricular systole, and the cardiac cycle begins again. The volume at the end of ventricle diastole is around 260 cm3. The blood forced intot eh aorta is around 130 cm3, and is called the stroke volume. (the volume of blood ejected in one stroke) http://baraboo-sauk.uwc.edu/Academics/ClassResources/Biology/phs203pg/Lecture%20pictures/cardiac-cycle.jpg ...read more.

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