3. The upper border of the third right costal cartilage 1 cm from the right sternal line
4.
5. Heart muscle cells build to form involuntary striated muscles strands, which form the walls of the heart, called the myocardium. Under a microscope, the striated muscle strands look like long chain links.
7. Unlike other muscle cells, heart cells are highly resistant to fatigue because they have more mitochondria organelles than any other cell in the body. Mitochondria are a cell's "digestive system," which breaks down nutrients into cell energy. This continuous supply of energy helps stop muscle fatigue.
9. Intercalated disks synchronize the contractions of all cardiomyocytes. Under a microscope they appear white and act as a double membrane to separate heart cells. These disks regulate the passage of positive and negative electrons. As electric currents repel and attract, it causes electron depolarization, which regulates heartbeat contractions.
11. T-tubules, or transverse tubules, are plasma membranes that surround each cell and organize them into pairs to create the striated muscles strands used to build the myocardium. Other muscle strands in the body are grouped using four cells.
14. The fibrous layer - composed of tough, white fibrous tissue covering the heart and anchoring it to the diaphragm, sternum and large blood vessels.
15. The serous layer - a thin inner membrane composed of a thin fibrous layer on top of a simple squamous epithelium. This layer folds back over and adheres to the heart forming the visceral pericardium.
16.
17. (B). The Myocardium - the muscular wall of the heart composed of cardiac muscle and a reinforcing internal network of fibrous connective tissue called the "skeleton of the heart". This connective tissue serves two primary functions:
18. It provides anchorage for the cardiac muscle and the atrioventricular valves. The portion of the skeleton anchoring the A-V valves is called the coronary trigone.
19. The elastic component of the skeleton provides the recoil that assists in filling the chambers following systole.
20. (C). The Endocardium - lines the chambers of the heart. In the chambers it consists of a simple squamous epithelium
21.
22. pulmonary valve: located between the right ventricle and the pulmonary artery
23. mitral valve: located between the left atrium and the left ventricle
24.
25. As the left atrium contracts, more blood flows into the left ventricle.
26.
27.
28. The atrioventricular node is located in the right atrium medial to the tricuspid valve. The A-V node receives the wave of depolarization about 50msec after it leaves the S-A node. However, the passage of the wave through the A-V node slows down and takes about three times longer to pass through the node (150 msec). This delay is crucial for the normal functioning of the heart. It permits the atrial myocardium to finish its contraction before the ventricular contractions begin.
41. The ventricles finish their systole. This creates a high enough pressure on the blood in the ventricles to overcome the downward force of blood in the pulmonary trunk and aorta. This open the semilunars and allow about 70 ml of blood to be ejected from each ventricle.
42.
43. The ventricles enter diastole and begin to fill. This produces a decrease in ventricular blood pressure. As a result, the blood in the pulmonary trunk and aorta begins to flow back down towards the ventricles. The cusps of the similunars fill with this blood and close the valve. This action produces the second heart sound "dup". The recoil of the descending blood against the cusps of the semilunars produces the slight, transient rise in aortic blood pressure called the "dicrotic notch".REFFERENCES<br />http://www.mamashealth.com/heart.asp<br />http://www.answers.com/topic/heart<br />http://www.wisc-online.com/objects/ViewObject.aspx?ID=AP12504<br />http://www.buzzle.com/articles/human-heart.html<br />http://www.theodora.com/anatomy/the_heart.html<br />http://www.tki.org.nz/r/science/science_is/activities/resources/heart_chest_cavity.pdf<br />http://stanfordhospital.org/healthLib/greystone/heartCenter/heartIllustrations/anatomyandFunctionoftheHeartValves.html<br />http://www.med.umich.edu/histology/fieldtrip/fieldtripheart.html#heartWall<br />http://en.wikipedia.org/wiki/Heart_(anatomy)<br />http://emedicine.medscape.com/article/905502-overview<br />http://www.gopetsamerica.com/anatomy/heart.aspx<br />http://faculty.ucc.edu/biology-potter/heart.htm<br />http://www.cardioconsult.com/Anatomy/<br />http://www.ehow.com/facts_5827452_structure-heart-cell.html<br />
![Human heart<br />The heart is a hollow muscular organ of a somewhat conical form; it lies between the lungs in the middle mediastinum and is enclosed in the pericardium (Fig. 490). It is placed obliquely in the chest behind the body of the sternum and adjoining parts of the rib cartilages, and projects farther into the left than into the right half of the thoracic cavity, so that about one-third of it is situated on the right and two-thirds on the left of the median plane. Every day, the heart pumps about 2,000 gallons (7,600 liters) of blood, beating about 100,000 times<br />Size of human heart<br />The heart, in the adult, measures about 12 cm. in length, 8 to 9 cm. in breadth at the broadest part, and 6 cm. in thickness. Its weight, in the male, varies from 280 to 340 grams; in the female, from 230 to 280 grams. The heart continues to increase in weight and size up to an advanced period of life; this increase is more marked in men than in women.<br />Position of heart<br />The heart is a hollow muscular organ of a somewhat conical form; it lies between the lungs in the middle mediastinum and is enclosed in the pericardium It is placed obliquely in the chest behind the body of the sternum and adjoining parts of the rib cartilages, and projects farther into the left than into the right half of the thoracic cavity, so that about one-third of it is situated on the right and two-thirds on the left of the median plane.<br />Front view of heart and lungs<br />The heart is demarcated by:<br />,[object Object]](https://image.slidesharecdn.com/humanheart-110209090416-phpapp01/85/human-heart-1-320.jpg)
