Bell Work 1.What is the heart? 2.Where is it located? 3.What is the difference between an artery and a vein? 4.Can a vein's blood have more oxygen than an artery’s blood? 5.What organ does the word pulmonary refer to? 6.What do the prefixes tri- and bi- mean? 7.What is a wall? 8.What is a chamber? 9.What is a valve?

The Heart How big is the heart? – About the size of your fist and weighs less than a pound – It is hollow and cone-shaped Where is the heart? – The middle cavity of the thorax called the mediastinum flanked by the lungs How is it positioned? – The apex is directed toward the left hip and rests on the diaphragm while the base points toward the right shoulder and lies beneath the second rib.

The Heart Cover The heart is enclosed by a double sac of serous membrane called the pericadium Epicardium or visceral pericardium – thin layer that tightly hugs the external surface of the heart and is considered to be a part of the heart wall Parietal pericardium – loosely applied layer that helps protect the heart while anchoring it to surrounding structures.

The Heart Wall The heart wall is composed of three layers – Epicardium – outer layer describe previously – Myocardium – The layer that actually contracts. It is composed of thick bundles of twisted cardiac muscle – Endocardium – layer of endothelium that lines the inner chambers of the heart

The Chambers of the heart The heart has four chambers or cavities. Two superior atria (singular atrium) and two inferior ventricles Atria – receiving chambers. Blood returns to the heart through veins and fills the atria under low pressure Ventricles – thick walled, discharging chambers. When they contract, blood is propelled out of the heart

Verses The right ventricle forms most of the anterior heart and is used in the pulmonary circuit which involve the lungs The left ventricle forms the apex and is used in the systemic circuit involve the body Arteries carry blood away from the heart Veins carry blood toward the heart Systolic pressure – the pressure in the arteries at the peak of ventricle contraction Diastolic pressure – the pressure when the ventricles are relaxing

Values The heart contains four valves to keep the blood flowing in one direction. There are two artioventricular (AV) valves that are located between the atria and ventricles. These prevent a backflow from the ventricles back into the atria. Left AV is called the bicuspid valve (has two flaps) and the right AV is called the tricuspid (has three flaps). They are anchored to the heart walls by chordae tendineae and this prevents the valves from flipping into the atria

The other two valves – the semilunar valves Pulmonary – prevents blood heading toward the lungs to flow back into the heart Aortic – prevents blood heading toward the body to flow back into the heart The semilunar valves are closed when the heart is relaxed and are forced open when the heart contracts, while the AV valves are open when the heart is relaxed but are forced closed when the heart contracts.

Cardiac Circulation Let us follow the blood as it returns from the body and enters the heart Oxygen deprived blood approaches the heart through the venae cavae (inferior and superior) and enters into the right atrium Blood then fills the right ventricle as it passes by the tricuspid valve. The right ventricle contracts, forcing the tricuspid valve to close, the pulmonary semilunar valve to be forced open, and the blood to travel the lungs through the pulmonary arteries.

The lungs recharge the blood with oxygen and the blood returns to the heart. Oxygen rich blood returns to the heart using the pulmonary veins and enter the left atrium. The blood flows past the open bicuspid valve into the left ventricle. The left ventricle contracts forcing closed the bicuspid valve, forces the aortic semilunar valve open, and forces the blood out to the body via the aorta. The blood uses various arteries to reach all parts of the body. Capillary beds are used for gas exchanges, and the blood is brought back to the heart via veins and the process repeats.

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