The Structure of The Mammalian HeartA muscular pumpDivided into two sidesRight side - deoxygenatedLeft side oxygenatedBoth sides of the heart squeeze putting blood under pressurePressure forces blood along the arteries

TipsIf you are asked how the pressure in the arteries is produced, you need to explain that it is due to the contraction of the left ventricle wallsWhen memorising the parts of the heart, remember veins take blood towards the heart, arteries take blood from the heart- pulmonary means lung and vena cava means main veinSo pulmonary artery takes blood away from the heart to the lung. Easy!

External Features of the HeartSits slightly off centre to left of chest cavityLies at an angle with the atria in the middleConsists of dark red muscle that feels firmThe muscle surrounds the two ventriclesAtria are much smaller than the ventricles

External Features of the HeartCoronary arteries lie over the hearts surfaceThey carry oxygenated blood to the heart itselfThese arteries are important and if constricted at all can have serious consequencesRestricted blood flow to the heart can cause angina (pain) or a heart attack (myocardial infarction)

At the top of the heart are tubes- veins carrying blood to the heart and arteries carrying blood away from the heart

Internal Structure of the HeartDivided into 4 chambersTwo atria, receiving blood from the major veinsVena Cava: deoxygenated blood from the body into the right atriumPulmonary Vein: oxygenated blood from the lungs to the left atrium

Internal Structure of the HeartFrom the atria, blood flows through the atrioventricular valves into the ventricles.The valves are thin flaps of tissue arranged in a cup shapeWhen the ventricles contract, the valves fill with blood and remain closedThis ensures blood flows upwards into the major arteries leading away from the heart, and not back into the atriaTendinous cords inside the ventricles attach the valves to the walls of the ventricle and prevent flimsy valves from turning inside out and allowing backflow of bloodCheck out the next 2 slides for diagrams that go with this description

A damaged valve and healthy valve showing tendinous cords

The SeptumA wall of muscle separating the ventricles from each otherEnsures that oxygenated blood does not mix with deoxygenated bloodThe diagram shows a defect in the septum often referred to as a hole in the heart

Leaving the HeartDeoxygenated blood leaving the right ventricle flows into the pulmonary artery leading to the lungsOxygenated blood leaving the right ventricle flows into the aortaThe aorta carries blood to a number of arteries supplying all parts of the body.Semi-lunar (half-moon) valves at the base of the arteries leading from the heart prevent blood flowing back into the heart as the ventricles relax

Blood PressureThe muscles of each chamber contract to create increased pressure in the bloodThe higher the pressure, the further the blood can go

Blood PressureAtria: the muscle is thin, as not much pressure is needed to make blood flow into the ventriclesRight ventricle: thicker walls than the atria, but as the blood is only pumped to the lungs, the pressure is not as great as that created by the left ventricle. Also, the lungs have fine capillaries and the alveoli are thin. The pressure cannot be too high or damage to the capillaries around the alveoli could resultLeft ventricle: 2-3 times thicker than the right ventricle- sufficient pressure is needed to pump blood through the aorta and overcome the resistance of systemic circulation

Units of PressureThe SI unit of pressure is the Pascal, but because blood pressure used to be measured with a tube of mercury whose chemical symbol is Hg, we still use mmHg (millimetres of mercury) as a pressure measurement