Some interesting facts The heart beats between 80,000 to 100,000 times and pumps approximately 23,000 liters of blood a day! That means it will have beat 2-3 billion times and pumped 50-65 million gallons of blood over a 70-90 year lifespan.
The heart Surrounded by a tough sac:Pericardium Outer part: inelastic white fibrous tissue (prevents heart from overstretching) Inner part: 2 membranes -inner attached to the heart -outer attached to the fibrous tissue Pericardial fluid: between the two inner membranes for friction reduction
The heart Between the two lungs Behind the sternum in the thorax
The heart contains four hollow chambers The top two chambers are called Atria……..(Above) The bottom two chambers are called Ventricles RIGHT LEFT ATRIUM ATRIUM LEFT RIGHT VENTRICLE VENTRICLE MUSCLE
AORTA PULMONARY ARTERY PULMONARY VEIN VENA CAVA SEPTUMThe function of the labelled parts:SEPTUM – Divides the two sides of the heart preventing oxygenated blood mixing with deoxygenated blood.THE PULMONARY VEIN – Transports oxygenated blood to the heart.THE AORTA – Transports oxygenated blood away from the heart to the body.THE VENA CAVA – Transports deoxygenated blood from the body back to the heart.THE PULMONARY ARTERY – Transports deoxygenated blood to the lungs.
Cardiac muscle Cardiac muscle Intercalated discs: cell Muscle fibres surface membranes separating individual muscle cells Interconnecting muscle cells Structure can change to allow ions to diffuse Allowing a fast spread of impulses When one cell is excitedThe action potentialspreadsQuickly to all the others
The cardiac cycle Series of events which takes place during the completion of one heartbeat. Involves repeated contraction and relaxation of the heart muscle, Note that: Contraction = Systole Relaxation = Diastole
Atrial diastole Atria and ventricles both relaxed Blood returning to the heart under low pressure Oxygenated Blood entering the left atrium Deoxygenated blood right atrium Valves closed at the beginning
Atrial diastole When the pressure rises the bicuspid and tricuspid valves open allowing the blood to enter in the ventricles
Atrial systole When atrial diastole ends, the two atria contract simultaneously to pump the blood into the ventricles
Ventricular systole 0.1/0.2 sec. later Contraction Pressure rises in the ventricles making the semi lunar valves to open Blood enter the vessels The closing of the atrioventricular valves during this stage produces the first heart sound (lub)
Ventricular diastole High pressure developed in the aorta and pulmonary artery tends to force some blood back towards the ventricles and this closes the semi-lunar valves of the aorta and pulmonary artery Closing the valves cause the second heart sound (dub).
How the heart acts as a pumpClick me…. (the heart says)
Task Write and explain the process that happens in the heart as blood travels through it. Include all the names of the main parts of the heart covered in the lesson. E.g. 1)Deoxygenated blood enters from the body through the Vena Cava into the right atrium ……………..
Quick Quiz1) What type of muscle is the heart made up of?2) The top two chambers of the heart are called………….?3) The bottom two are called………?4) What divides the left side of the heart from the right side?5) Blood entering the right atrium comes through what?6) Blood leaving the left ventricle travels through what?7) What is the purpose of the valves?
The heart beat The heart is made up of cardiac muscle. Cardiac muscle is myogenic, which means it naturally contracts and relaxes. Therefore, it receives no impulse from a nerve to make it contract.
The heart beat If you remove a heart and place it in well-oxygenated place salt solution at 37 ̊C, the heart will continue to beat for some time Myogenic nature of the stimulation of the heart
The heart beat The cardiac cycle is initiated by a small patch of muscle called the Sino atrial node (SAN) or pacemaker. This node sets the rhythm for all the other cardiac muscle. Pacemaker cells have an inbuilt rhythm that is faster than the other cells in the heart.
The heart beat Stimulus for contraction: SAN (Sino-atrial node) Near the opening of the Vena cava Small numbers of cardiac muscle fibres and a few nerves endings from autonomic nervous system
The heart beat The SA node sends out an excitation wave of electrical activity over the atrial walls. The cardiac muscle responds to this wave by contracting at the same speed as the SAN. Speed rate: 1 m s -1 This results in both right and left atria contracting simultaneously.
The heart beat There is a delay between atrial contraction and ventricular contraction. Fibres between the two chambers that do not conduct the excitation phase cause this delay. Collagen fibres prevent the electrical signals to from passing through the heart wall from atria to ventricles What cause the ventricles to contract then?
The heart beat A second node The AVN (atrio-ventricular node), which picks ups the impulses that have passed through the atrial muscle and respond generating its own electrical impulses After about a delay of 0.15 seconds the AV node passes the wave into His bundle (fibres from the right and left that meet together in the septum) They branch to form the right and left bundle The wave is sent to another set of conducting fibres that run down the centre of the septum between the ventricles called the Purkyne (Purkinje) fibres
The heart beat The wave is then transmitted (very rapidly) down to the bottom of the septum, where it spreads through the ventricles’ walls in an upward direction. This movement causes the muscle to contract and the ventricles squeeze the blood out of the heart.
Task Describe the series of events that lead to the heartbeat Use a diagram to support your explanation
ECG Detects electrical activity during cardiac cycle.PQRSTU
Absolute refractory period Period in which the heart cannot respond to a second stimulus – enables full recover without being fatigued Relative refractory period
Regulation of heart rate Demands of the blood system is always changing Heart rate needs to be adjusted Homeostatic response (nervous and chemical)
Regulation of heart rate Cardiac Output: amount of blood flowing from the heart over a period of time and depends on upon the volume of blood pumped out of the heart at each beat, the stroke volume, and the heart rate (number of beats per minute) CO= SV x HR CO is important variable supplying blood to the blood
Nervous control of Heart Rate Medulla Controls heart rate Nerves connecting medulla and the heart Nervous system divided in voluntary nervous system and an autonomic nervous system (acts automatically)
Nervous control of the heart rate ANS: Sympathetic Nervous System (SNS) excitation and preparation of the body for action Parasympathetic Nervous System (PNS) relaxing influence Both involved in the heart rate
Medulla Cardiac inhibitor centre (CIC) Reduces HR Cardiac accelerator centre (CAC) Stimulates HR
Nervous control of the heart rate PN (vagus nerves) leaves CIC to the heart ( SAN, AVN and bundle of His) Impulses reduce HR Nerves on the CAC run on the SNS To the heart (SAN) Impulses increase HR
Nervous control of the heart rate Coordinated activity of the inhibitor and accelerator centres in the medulla that controls the heart rate
Nervous control of the heart rate Sensory nerve fibres from stretch receptors within the walls of the aortic arch, The carotid sinuses and the vena cava Run to the cardiac inhibitor and accelerator in the medulla Impulses fro the aorta and carotids decrease the heart rate Impulses from the vena cava stimulated the accelerator centre which increases the heart rate This stimulates the stretch receptors and increases the number of nerve impulses transmitted to the centres in the medulla
Nervous control of the heart rate Intense activity Body muscles contract strongly More venous blood return to the heart Walls of vena cava stretch by large quantities of bloodand heart rate increases
Nervous control of the heart rate Increased blood flow to the heart Increases the pressure of the cardiac muscle Cardiac muscle responds automatically contracting more strongly (systole), pumping more blood Stoke volume is increased Starling’s Law
Increased stroke volume stretches the aorta and carotids which in turn, via stretch reflexes, signal the cardiac inhibitor centre to slow the heart rate. This prevents heart from working to fast
Hormonal control Adrenaline secreted by the medulla of the adrenal glands (also produces noradrenaline) Both Stimulate the heart Cardiac output and blood pressure are increased by increased heart rate
Hormonal control Thyroxine: produced by thyroid glands Raises basal metabolic rate Leads to greater metabolic activity, with greater demand for oxygen and production of more heat Result: vasodilation followed by increased blood flow Increased cardiac output