The Structure and Functioning’s of the Human Heart

By Shil Patel and Daivik Gandhi

Contents

• Basic facts• Layers• Vessels• Chambers• Cardiac Cycle• Cardiac Muscle Cells• Electrical Impulses• Calcium ions for contraction

Basic Facts

• Size of a fist.• Roughly between 250 to 350 grams.• Slightly left of the middle of the Chest.• Anterior to the Vertebral Column.• Posterior to the Sternum.• Enclosed in the Pericardium.• The Pericardium is a double walled sac which

protects the Heart.

Layers

• 3 main layers of the Heart.• Epicardium – the inner wall of the Pericardium, made

up of connective tissues and produces Pericardium Fluid for lubrication.

• Myocardium – which is the layer of cardiac muscle, which causes the contractions. Muscle cells contain filaments of proteins, mainly actin and myosin.

• Endocardium – it is the inside layer and it is biologically and embryologic ally very similar to endothelial cells.

Vessels

Chambers

• 4 Chambers of the Heart. • Two Superior Atria. • Two Inferior Ventricles.• The right hand side of the Heart has a thicker

Myocardium because it needs to pump blood at a higher pressure.

The Cardiac Cycle

Cardiac Cycle

• Atrial Systole – Atria contract and the blood flows into the Ventricles. The Semi-Lunar valves are closed.

• Ventricular Systole – Ventricles contract and the blood is forced into the Pulmonary Artery and Aorta. The Atrioventricular Valves are forced shut.

• Diastole – resting phase, all chambers are relaxed and the blood is filling in the Atria.

Cardiac Cycle

Cardiac Muscle Cells

• Found on the walls of the heart.• It is resistant to fatigue.• Coronary arteries refresh and supply oxygen

to the cells.

Electrical Impulses

Electrical Impulse (II)

• The Cardiac muscles need to be able to depolarise without using the nervous system as a source.

• The depolarisation must be very quick!

Calcium ions for Contraction

• During a contraction, many cross-bridges are continuously made and broken causing them to slide past thick filaments and so shorten the sarcomere.

• Tropomyosin (a rod shaped protein) subunits cover myosin head groups on actin fibres.