The Structure of The Mammalian Heart

• A muscular pump• Divided into two sides• Right side - deoxygenated• Left side – oxygenated• Both sides of the heart squeeze putting

blood under pressure• Pressure forces blood along the arteries

Tips

• If 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 walls

• When 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 vein’

• So… pulmonary artery takes blood away from the heart to the lung…. Easy!

External Features of the Heart

• Sits slightly off centre to left of chest cavity

• Lies at an angle with the atria in the middle

• Consists of dark red muscle that feels firm

• The muscle surrounds the two ventricles

• Atria are much smaller than the ventricles

External Features of the Heart• Coronary arteries lie over the

heart’s surface• They carry oxygenated blood to the

heart itself• These arteries are important and if

constricted at all can have serious consequences

• Restricted 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 Heart

• Divided into 4 chambers• Two atria, receiving blood

from the major veins• Vena Cava:

deoxygenated blood from the body into the right atrium

• Pulmonary Vein: oxygenated blood from the lungs to the left atrium

Internal Structure of the Heart

• From the atria, blood flows through the atrioventricular valves into the ventricles.

• The valves are thin flaps of tissue arranged in a cup shape

• When the ventricles contract, the valves fill with blood and remain closed

• This ensures blood flows upwards into the major arteries leading away from the heart, and not back into the atria

• Tendinous 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 blood

Check out the next 2 slides for diagrams that go with this description

A damaged valve and healthy valve showing tendinous cords

The Septum

• A wall of muscle separating the ventricles from each other

• Ensures that oxygenated blood does not mix with deoxygenated blood

The diagram shows a defect in the septum often referred to as a ‘hole in the heart’

Leaving the Heart

• Deoxygenated blood leaving the right ventricle flows into the pulmonary artery leading to the lungs

• Oxygenated blood leaving the right ventricle flows into the aorta

• The 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 Pressure

• The muscles of each chamber contract to create increased pressure in the blood

• The higher the pressure, the further the blood can go

Blood Pressure

• Atria: the muscle is thin, as not much pressure is needed to make blood flow into the ventricles

• Right 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 result

• Left 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 Pressure

• The 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