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1. The Cardiovascular System

Blood Vessels There are 5 types: 1. Arteries 2. Arterioles 3. Capillaries 4. Venules 5. Veins Arteries and veins have 3 layers: 1. Tunica intima – lines the lumen to reduce friction 2. Tunica media – consists of smooth muscle, collagen and elastic fibres 3. Tunica externa – outer layer of collagen and some elastic fibres

Arteries • Carry blood away from the heart • Thicker tunica media => allows wall to stretch and recoil under the pressure of each heartbeat • Smaller lumen • Can feel the ‘pulse’ of arteries stretching and recoiling

Capillaries • Allow exchange of material between blood and cells • Walls are only 1 cell thick • Walls are permeable • Blood in capillaries is at a lower pressure which reduces fluid loss through the walls

Veins • Carry blood to the heart • Blood is at a very low pressure • Thinner tunica media • Valves are present to prevent backflow of blood • Muscle contraction helps move blood through veins

The Heart Heart muscle is called the myocardium. Chordae tendinae connect the valves to the myocardium.

Circulation Pulmonary circulation – deoxygenated blood leaves the right ventricle and is carried to the lungs in the pulmonary artery, oxygenated blood returns to the left atrium in the pulmonary vein Systemic circulation – oxygenated blood leaves left ventricle in aorta, deoxygenated blood returns to the right atrium through the venae cavae Closed system – as our blood stays in blood vessels

Cardiac Cycle

• The pattern of contraction (systole) and relaxation (diastole) of the heart. • Atrial systole – atria are full of blood and contract pushing open the AV valves, when pressure in ventricles exceed atria, AV valves close (‘lubb’ sound) • Ventricular systole – ventricles are full of blood, they contract forcing open the SL valves, when pressure in arteries exceed ventricles, SL valves close (‘dupp’ sound) • When chambers are not in systole – diastole – filling with blood

Blood Pressure • Measured using a sphygmomanometer • A measure of the pressure in aorta • 2 measurements – systolic and diastolic pressures • Written as systolic / diastolic • Normal adult reading – 120 / 80 • Varies with age, level of activity and fitness

Cardiac Output (CO) CO – volume of blood pumped out of the heart in a minute (~5 l/min is normal) Heart rate (HR) – measured by recording pulse, it is the number of times the heart beats in a minute (normal 60-100 bpm) Stroke volume (SV) – volume of blood pumped out of the heart in one beat (normal ~70ml) CO = HR x SV Varies with level of activity and fitness level

1 Cardiovascular system  
1 Cardiovascular system