Heart

• Circulatory systems

  Systems responsible for delivering oxygen and nutrients to tissues and removing waste products
• Cardiovascular system

  Responsible for delivering oxygen extracted from the air around us to the muscle tissues for respiration
• Cardiovascular system

  • Includes the heart, a dual-action pump
  • Includes the blood vessels
  • Includes the blood which actually transports the oxygen
• Oxygen delivery

  1. Oxygenated blood exits the left side of the heart

  2. Transported to muscle tissues via the SYSTEMIC circulatory system

  3. Oxygen is released to the muscles

  4. Deoxygenated blood returns to the right side of the heart

  5. Travels to the lungs via the PULMONARY circulatory system

  6. Takes on more oxygen

  7. Process continues
• The heart is a network of blood vessels, valves and chambers directing blood flow around the circulatory system.

  The top two chambers are known as ATRIA. They receive blood from the circulatory systems.

  The bottom two chambers, the VENTRICLES, receive blood from the atria to pump onwards to the next stage of the cycle.
• Valves prevent backflow of blood through the heart. The tricuspid valve separates the right ventricle from the right atrium. The bicuspid (mitral) valve separates the left ventricle from the left atrium.
• Blood flows into the right atrium from the superior vena cava and inferior vena cava. Blood then passes through the tricuspid valve into the right ventricle. From here it travels out of the pulmonary artery to the lungs where carbon dioxide is removed and oxygen added. This process occurs in the capillaries within the alveoli.
• Blood leaving the lungs enters the left atrium through the pulmonary veins. It then passes through the bicuspid valve into the left ventricle. Blood leaves the left ventricle through the aortic semilunar valve and enters the aorta. This carries the blood to all parts of the body except the lungs.
• Conduction system


  The system that controls the cardiac cycle in the heart
• Heart


  • It is MYOGENIC, meaning it has the capacity to generate its own electrical impulse
  • The impulse is transmitted through the cardiac muscle to stimulate contraction
• conduction system

  1. Sino-atrial (SA) node initiates the impulse

  2. Impulse is transported through both atria

  3. Impulse is received by the atrio-ventricular (AV) node

  4. AV node delays the impulse briefly then releases it onwards to the bundle of His

  5. Bundle of His splits the impulse down the left and right bundle branches

  6. Impulse reaches the Purkinje fibres

  7. Both ventricles will contract causing the blood to be ejected into the circulatory systems

  8. Brief break where no impulse is generated allowing blood to enter the atria
• ATRIAL SYSTOLE – the phase when both atria contract to force blood into the ventricles through the bicuspid and tricuspid valves.

  VENTRICULAR SYSTOLE – the phase when both ventricles contract to eject blood into the pulmonary artery and aorta for transportation around the circulatory systems.

  DIASTOLE – the relaxation phase of the cardiac cycle, no contraction takes place and blood enters the atria from the vena cava and pulmonary vein
• Heart rate - number of beats per minute. At rest = 60/75 beats per min. Maximum HR = 220 - age
• Cardiac output - volume of blood pumped out of the heart per minute. CO = stroke volume x heart rate. Rest - 5L/min. Maximal - 20/30L/min
• Stroke volume - the volume of beats of blood ejected from right ventricle per beat. Rest - 70 ml/beat. Maximal SV - 100-120ml
• Heart rate regulation

  Neural control
• Sympathetic nervous system

  • Stimulates the SA node to increase heart rate
  • Allows body systems to adapt to the environment
  • Increases oxygen supply to muscles during exercise
• Heart rate regulation during exercise

  1. Sympathetic nervous system stimulates SA node

  2. Increases heart rate

  3. Provides greater oxygen supply to muscles
• Heart rate regulation after exercise

  1. Parasympathetic nervous system reduces stimulation of SA node

  2. Reduces heart rate

  3. Returns to resting levels
• SYMPATHETIC NERVOUS SYSTEM

  The sympathetic nervous system is responsible for increasing heart rate. This is controlled by the CARDIAC CONTROL CENTRE situated in the MEDULLA OBLONGATA of the brain.

  The Cardiac Control Centre receives information from receptors concerning various changes in the body as a result of exercise being undertaken.

  The CCC then sends impulses down the ACCELERATOR NERVE to increase the firing rate of the SA Node, thus increasing heart rate meaning more oxygen is delivered to the working muscles.
• Baroreceptors - detect increase in pressure. Found in blood vessels
• Chemoreceptors - detect increase in acidity and decrease in pH. Found in the blood
• Proprioreceptors - detect change in movement. Found in tendons and muscle fibres
• PARASYMPATHETIC NERVOUS SYSTEM

  The parasympathetic nervous system is responsible for reducing heart rate. This is also controlled by the CARDIAC CONTROL CENTRE situated in the MEDULLA OBLONGATA of the brain.

  The Cardiac Control Centre receives information from receptors concerning various changes in the body as a result of exercise ceasing.

  The CCC then sends impulses down the VAGUS NERVE to decrease the firing rate of the SA Node, thus decreasing heart rate meaning less oxygen is delivered to the working muscles
• Heart rate regulation – hormonal control

  In response to exercise the ADRENALIN and NOR-ADRENALIN are released from the ADRENAL GLAND. These hormones have a direct effect on the force of contraction of the heart muscle, thus increasing Stroke Volume and the firing rate of the SA node, thus increasing Heart Rate. The combined effect will increase Cardiac Output and delivery of oxygenated blood to the working muscles.
• The vascular system is a dense network of blood vessels. It includes the blood which travels through the system transporting oxygen, carbon dioxide and essential nutrients throughout the body.
• ARTERIES – transport oxygenated blood from the heart. The largest of these is the AORTA which receives blood from the LEFT VENTRICLE.
• VEINS – larger blood vessels carrying deoxygenated blood back towards the heart. The largest of these is the VENA CAVA which delivers deoxygenated blood back to the RIGHT ATRIA of the heart.
• VENULES – the smaller blood vessels carrying deoxygenated blood back towards the heart.
• ARTERIOLES – smaller arteries which have a large layer of smooth muscle allowing the lumen diameter to be altered
• CAPILLARIES – are vessels of a single layer of cells which penetrate the muscle and organ cells. They allow for gas, nutrient and waste exchange.
• Venous return mechanisms

  • Pocket valves
  • Muscular pump
  • Respiratory pump
  • Smooth muscle
  • Gravity
• Pocket valves


  One way valve located in the veins which prevent the backflow of blood
• Cardiac output at rest


  Approximately 5 litres per minute
• Muscular pump

  • The contraction of skeletal muscle during exercise which compresses the veins forcing blood back towards the heart
• Cardiac output during maximal exercise

  25-40 litres per minute depending on fitness levels
• Respiratory pump


  • During inspiration and expiration a pressure difference between the thoracic and abdominal cavities is created which squeezes blood back towards the heart
• Smooth muscle


  • The layer of smooth muscle in the walls of the veins venoconstricts to create venomotor tone maintaining pressure in the vein and thus helping the transport of blood back to the heart
• Redistribution of cardiac output during exercise

  1. Increased cardiac output is redistributed to areas of the body which need it most, namely the working muscles

  2. This is done by the VASCULAR SHUNT MECHANISM
• Gravity


  • Blood from above the heart returns towards the heart with the help of gravity