THE CARDIOVASCULAR SYSTEM LEARNING OBJECTIVES Understand the interaction

THE CARDIOVASCULAR SYSTEM

LEARNING OBJECTIVES • Understand the interaction between the cardiovascular and respiratory systems • Identify and describe the external and internal structures of the heart. • Describe and explain the events of the cardiac cycle and how it is linked to the conduction system • Know definitions and resting values for stroke volume, heart rate & cardiac output. • Describe and explain changes in heart rate, stroke volume and cardiac output during sub–maximal and maximal work • Explain how changes in heart rate are regulated by neural, hormonal and intrinsic factors. • Be able to represent graphically heart rate response to varying intensities of workload and during recovery. • Describe and explain the distribution of cardiac output at rest and on exercise via the vascular shunt and vasomotor control centre • Describe how carbon dioxide and oxygen are carried in the blood • Describe the mechanisms of venous return • Describe the effects of a warm up and cool down on the vascular system.

Cardiovascular and respiratory systems • Aerobic exercise uses oxygen to supply the energy needed • Three distinct systems work together to ensure oxygen is supplied to the working muscles during exercise • These are the heart, vascular (blood vessels) and respiratory systems.

The Heart • The heart is a double pump – two separate pumps that work side by side • The right side pumps deoxygenated blood to the lungs • The left side pumps oxygenated blood to the rest of the body • The heart consists of four chambers –two upper atria and two lower ventricles • The atrio-ventricular valves separate the atria and ventricles • The semi-lunar valves are found in the pulmonary artery and aorta. Exercise 1 Exercise 2 Exercise 3

The cardiac cycle How blood flows through the heart • Two phases systole – contraction phase (atrial and ventricular) – 0. 3 secs diastole – relaxation phase – 0. 5 secs • • • DIASTOLE atria fill with blood pressure rises atrioventricular valves open blood passes by gravity into ventricles • semi lunar valves closed Exercise 4 • • • SYSTOLE Atrial systole Atria contract Forces remaining blood into ventricles Ventricles remain relaxed Ventricular systole Ventricles contract at same time Blood pressure increases AV valves forced shut (so no backflow) Semi-lunar valves forced open Blood pushed into aorta and pulmonary artery

The conduction system of the heart How the cardiac cycle is controlled • Initial impulse begins in the right atrium – sinoatrial node SAN (pace maker) • Wave of contraction spreads through atria causing them to contract • Impulse passed to atrioventricular node AVN (lies between atria) • AVN sends impulse along muscle fibres between ventricles (Bundle of His) • Impulse conducted down septum to base of ventricles to Purkinje fibres • Causes ventricles to contract Exercise 5 http: //www. quia. com/rd/30225. html? AP_rand=604219036 Click here for a summary sheet (Exercise 7) Exercise 6

Heart definitions • STROKE VOLUME- volume of blood ejected from the heart when the ventricles contract (at rest = 70 cm 3) • HEART RATE – the number of (ventricle) contractions in one minute (at rest = 72 bpm) • STROKE VOLUME – (Q) volume of blood ejected from the heart in one minute (at rest = 5 Litres) • Q = HR X SV Exercise 8

Responding to exercise • As exercise begins the following sequence of events takes place in the heart • 1. Resting heart rate – about 72 for untrained but for trained can be as low as 60. • 2. Anticipatory rise – due to the release of the hormone adrenalin. This acts on the SA node to increase heart rate. • 3. Rapid increase of HR – at start of exercise due to receptors: proprioreceptors detect increased movement; chemoreceptors detect increased CO 2 and lactic acid and decreased O 2. These stimulate the CCC which stimulates SA node to increase HR • 4. Continued but slower increase of HR – due to continued effect of receptors, increase in blood temp and increase in venous return.

• 5 A Slight fall/ steady plateau – (aerobic sub maximal work) – due to oxygen supply meeting demand, baroreceptors slow HR to optimal via stimulation of para sympathetic nerves. • 5 B Continued rise in heart rate – ( maximal aerobic work) – due to anaerobic work where supply is below demand to increasing lactic acid levels. • 6 Rapid fall in heart rate – as exercise stops due to decreased stimulation by receptors. • 7 Slower fall in heart rate towards resting levels- due to elevated HR to help repay oxygen debt and to remove by products of respiration such as lactic acid. • You should be able to show this information graphically • Make sure whether the question asks for maximal or sub maximal exercise – use either 5 A or 5 B • NB maximum heart rate is 220 minus age Exercise 9

Control of heart rate • Heart rate is regulated by the cardiac control centre found in the medulla oblongata of the brain. • The cardiac control centre is controlled by the autonomic nervous system. • This system consists of sensory and motor nerves from either the sympathetic or parasympathetic nervous system. • Sympathetic nerves increase heart rate and parasympathetic nerves decrease heart rate. • The cardiac control centre initiates either sympathetic or parasympathetic nerves to stimulate the sino-atrial node to increase or decrease heart rate.

There are three main factors which affect the activity of the cardiac control centre. They are neural, hormonal and intrinsic. • Neural control During exercise sensory receptors stimulate the cardiac control centre. These receptors include: proprio-receptors which sense that movement has increased. chemoreceptors which sense changes in chemicals in the muscles and blood. These changes include increased levels of carbon dioxide and lactic acid and increased acidity in the blood. baroreceptors which are sensitive to stretch within the blood vessel walls. These detect increased blood pressure. The cardiac control centre responds to this information by stimulating the sino-atrial node via the sympathetic cardiac accelerator nerve to increase heart rate.

• Hormonal control • Before and during exercise adrenalin is released in the blood. • This stimulates the sino-atrial node to increase heart rate. • Intrinsic control • During exercise temperature increases which increases the speed of nerve impulses which in turn increases heart rate. • Venous return increases heart rate which directly increases EDV and therefore stroke volume (Starlings Law). Exercise 10

Blood vessels • There are three main groups of blood vessels. • Arteries and arterioles- transport oxygenated blood away from the heart. • Capillaries – bring blood to the tissues where oxygen and carbon dioxide are exchanged. • Veins and venules – transport deoxygenated blood back towards the heart.

Blood vessel structure • Blood vessels have three layers except capillaries which are single walled. • Arteries and arterioles have middle layer of smooth muscle which allows them to vasodilate (widen) and vasoconstrict (narrow). • Arterioles have precapillary sphincters at the entry to the capillary. These control blood flow. • Capillaries are one cell thick to allow efficient gaseous exchange. • Venules and veins have thinner muscular walls. The can vasodilate and vasoconstrict. They also have valves to prevent the backflow of blood.

Venous return • Starlings Law of the Heart states that stroke volume is dependent on venous return. • At rest the amount of blood returning to the heart (venous return) is enough to supply the demands of the body. • On exercise this is not enough so venous return must be increased. This happens in the following ways.

MECHANISM POCKET VALVES DESCRIPTION One way valves Prevent back flow Direct blood towards the heart MUSCLE PUMP Veins between skeletal muscles When muscles contract on exercise blood squeezed along these veins back to heart RESPIRATORY PUMP On exercise breathing deeper & faster Causes pressure changes in thorax & abdomen Increased pressure squeezes large veins here forcing blood back to heart SMOOTH MUSCLE Middle layer of veins are smooth muscle Contraction & relaxation of this pushes blood back to heart GRAVITY Blood from upper body aided by gravity as it flows back to heart.

Click on the links to complete the exercises • • Exercise 11 summary sheet Exercise 12 matching exercise Exercise 13 crossword Exercise 14 cloze exercise

VASCULAR SHUNT • At rest only a small % of the blood supply is supplied to the muscles (15%). • The rest supplies the bodies organs. • Changes during exercise – • Increased cardiac output is supplied to the muscles (8085%). • Less blood is supplied to the body organs. • Blood supply to the brain is maintained. • During light exercise increased supply to the skin reduces temperature. • The process of redistributing blood supply is called the vascular shunt mechanism. • Skeletal muscle arterioles and pre-capillary sphincters vasodilate increasing blood supply to muscles. • Organ arterioles and pre-capillary sphincters vasoconstrict decreasing blood supply to organs.

VASCULAR SHUNT MECHANISMS ORGANS INCREASED STIMULATION OF SYMPATHETIC NERVES VASOCONSTRICTION OF ARTERIOLES & PRE CAPILLARY SPHINCTERS DECREASED BLOOD FLOW (Q) TO CAPILLARIES OR NON ESSENTIAL ORGANS MUSCLES DECREASED STIMULATION OF SYMPATHETIC NERVES VASODILATION OF PRE CAPILLARY SPHICTERS AND ARTERIOLES INCREASED BLOOD FLOW (Q) TO CAPILLARIES OR WORKING MUSCLES

CONTROL OF THE VASCULAR SHUNT MECHANISM • This is controlled by the vasomotor control centre found in the medulla oblongata of the brain. • Chemoreceptors and baroreceptors stimulate the VCC. • VCC stimulates the sympathetic nervous system which control blood vessel lumen diameter of organs and muscles.

Click on the links to complete the exercises • Exercise 15 Cloze exercise • Exercise 16 work sheet • Exercise 17 Summary sheet

Oxygen and carbon dioxide transport Oxygen is transported in two ways: 1. 97% is carried in the red blood cells bound to haemoglobin as oxyhaemoglobin. 2. 3% is carried dissolved in the plasma. Carbon dioxide is transported in three ways: 1. 70% combined with water within the red blood cells as carbonic acid. 2. 23% combined with haemoglobin as carbaminohaemoglobin. 3. 7% dissolved in the plasma.

Warm up • • Warm up – effects on vascular system Gradual increase in blood flow brings more oxygen to working muscles • An increase in temperature produces 1. An increase in the rate transport of enzymes needed for the energy systems. 2. A decrease in the viscosity of the blood which improves blood flow 3. An increase in oxygen dissociating from oxyhaemoglobin • A warm up delays the onset of blood lactic acid

Cool down • An active cool down keeps respiratory and muscle pumps working which prevents blood pooling in the veins and maintains venous return. • Capillaries remain dilated which means more oxygenated blood reaches the muscles which results in more lactic acid and carbon dioxide being removed. Exercise 18

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