Higher Human Biology Unit 2 Physiology & Health KEY AREA 6: Structure and Function of the heart

Higher Human Biology We are going to build on the knowledge and skills that you developed during N5 and will learn about the following Physiology & Health key areas : - Key Area 1 – Reproductive Organs Key Area 2 –Hormonal Control of Reproduction Key Area 3 – Biology of Controlling Fertility Key Area 4 – Ante- and Postnatal Screening Key Area 5 – Structure and Function of Arteries, Capillaries and Veins Key Area 6 – Structure and Function of the heart Key Area 7 – Pathology of Cardiovascular Disease (CVD) Key Area 8 – Blood Glucose Levels and Obesity

N5 Revision - Circulatory System Blood is transported in the Circulatory System. The heart is made up of cardiac muscle tissue. The 4 chambers of the heart are:- Right Atrium Right Ventricle Left Atrium Left Ventricle The right ventricle pumps blood to the lungs. The left ventricle pumps blood to the WHOLE BODY! Therefore the muscle of the left ventricle is much thicker than the right ventricle muscle

N5 Revision - Pathway of Blood 1. Blood from the Body 2. Vena cava vein 3. Right Atrium 4. Right Ventricle 5. Pulmonary Artery 6. LUNGS 7. Pulmonary Vein 8. Left Atrium 9. Left Ventricle 10. Aorta artery 11. Blood to the Body 12. Arteries 13. Capillaries 14. Veins Vena Cava Vein

N5 Revision - Heart Structure Tricuspid Valve Bicuspid Valve Semi-lunar Valves Valves STOP the blood from flowing backwards Bitesize Heart Function (0:40) Bitesize animation of heart

N5 Revision - Coronary Arteries Coronary Arteries supply the heart muscle with blood containing oxygen and nutrients (e.g. glucose) Coronary Veins take carbon dioxide and wastes away from the heart

Physiology & Health Learning Intentions KEY AREA 6 – Structure & Function of the Heart a)Cardiac function and cardiac output b)Cardiac Cycle c)Structure and function of the Cardiac Conducting System d)Blood pressure

6a) Structure and function of the heart Atrio-ventricular (AV) valves prevent black flow of blood from ventricles to atria Semi-lunar (SL) valves prevent backflow of blood at the entrance of the pulmonary and aorta arteries. These valves open during ventricular contraction allowing blood into the arteries, and close when arterial pressure exceeds ventricular pressure

6b) Cardiac function and Cardiac Output At each contraction of the heart, the right ventricle pumps the same volume of blood through the pulmonary artery (and round to the lungs) as the left ventricle pumps through the aorta (and round the body) Heart Rate (Pulse) is the number of heartbeats that occurs per minute Stroke Volume is the volume of blood expelled by each ventricle on contraction. The stronger the contraction, the greater the stroke volume. Cardiac output is the volume of blood pumped out of a ventricle per minute. Thus:- CARDIAC OUTPUT (CO) = HEART RATE (HR) X STROKE VOLUME (SV)

6c) Cardiac Cycle The cardiac cycle refers to the pattern of contraction (systole) and relaxation (diastole) shown by the heart during one complete heartbeat The average cardiac cycle is 0.8seconds, which is based on a heart rate of 75 beats per minute

6d) Atrial and Ventricular Diastole (relaxing) The blood returning from the vena cava and pulmonary veins going into the atria causes the volume of blood in the atria to increase and some of the blood flows into the ventricles AV valves open SL valves closed

6e) Atrial systole (atria contracting) & ventricular diastole (ventricles relaxing) Atrial systole causes the remainder of the blood to go through the AV valve to the ventricle. This is due to the fact that atrial pressure exceeds ventricle pressure, so the AV valves are pushed open and blood then enters the ventricles. During atria systole(contraction) and ventricular diastole (relaxing), the two atria contract simultaneously and send the remainder of the blood down into the ventricles through the open AV valves. The ventricles fill up with blood and the SL valves remain closed AV valves open SL valves closed

6f) Ventricular systole (ventricles contracting) & atrial diastole (atria relaxing) Closes the AV valves and pumps the blood out through the SL valves to the aorta and pulmonary artery

6g) Cardiac Conducting System The sequence of events that occurs during each heartbeat is brought about by the activities of the pacemaker and the conducting system of the heart The auto-rhythmic cells of the sino-atrial node(SAN)(pacemaker) is located in the wall of the right atrium and sets the rate at which the cardiac muscle cells contract

6h) Cardiac Conducting System 1.Impulses from the SAN spreads through the muscle cells in the wall of the two atria making them contract simultaneously (atrial systole). 2.The impulses are then picked up by the Atrio-Ventricular node (AVN) which located is centrally near the base of the atria 3.The impulses pass from the AVN into a bundle of conducting fibres which divide into left and right branches into each ventricular wall, causing contraction of the two ventricles (ventricular systole). **This ensures that ventricle systole occurs slightly later than atrial systole – which allows for the ventricles to fill completely before they contract** 4.The timing of cardiac cells contracting is controlled by the impulse from the SAN spreading through the ventricles – these impulses generate currents that can be detected by an electrocardiogram (ECG) The heart beat originates in the heart itself but is regulated by both nervous and hormonal control

6i) Autonomic Nervous Control of the Heart Control centres in the medulla of the brain regulate the rate of the SAN through the antagonistic action of the autonomic nervous system (ANS)

6j) Autonomic Nervous Control of the Heart 1.The cardio-accelerator centre sends its nerve impulses via sympathetic nerves to the heart 2.The cardio-inhibitor centre sends its information via a parasympathetic nerve to the heart 3. The two pathways are antagonistic to one another in that they have opposite effects on heart rate:- a)An increase in the number of nerve impulses arriving at the SAN (pacemaker) via the sympathetic nerve results in an increase in heart rate due to the sympathetic accelerator nerves releasing the neurotransmitter noradrenaline b)An increase in the number of nerve impulses arriving at the SAN (pacemaker) via the parasympathetic nerve results in a decrease in heart rate due to the slowing parasympathetic nerves releasing the neurotransmitter acetylcholine

6k) Hormonal Control of the Heart During exercise or stress, the sympathetic nervous system acts on the adrenal glands in the kidneys, making them release the hormone epinephrine (adrenaline) into the bloodstream. On reaching the SAN (pacemaker), this hormone causes the pacemaker to generate cardiac impulses at a higher rate, and brings about an increase in heart rate

6l) Interpretations of Electrocardiograms The electrical activity of the heart generates tiny currents that can be picked up by electrodes placed on the skin surface Normal ECG patterns consist of 3 distinct waves:- (1)P wave – is the electrical impulses spread over the atria from the SAN (2)QRS wave complex – is the electrical impulses passing through the ventricles (3)T wave – is the electrical recovery of the ventricles near the end of the ventricular systole

6m) Blood Pressure Changes Blood pressure is the force exerted by blood against the walls of the blood vessels BP is measured using a BP sphygmomanometer in units of millimetres of mercury (mmHg) BP is generated by the contraction of the ventricles and is highest in the aorta and pulmonary artery As the heart goes through systole and diastole during each cardiac cycle, the arterial pressure rises and falls During ventricular systole, the pressure of blood in the aorta rises to a maximum e.g. 120mmHg During ventricular diastole, the pressure of blood in the aorta drops to a minimum e.g. 70mmHg Normal BP is written as 120/70 mmHg

6n) Measurement of blood pressure Using a sphygmomanometer 1.The cuff is inflated until it stops blood flow 2. The cuff is allowed to deflate gradually until the pressure in the artery is greater than the pressure in the cuff. The blood starts to flow( detected by a pulse) at systolic pressure 3. More air is released from the cuff until no pulse detected – this is at diastolic pressure

6o) Measurement of blood pressure Hypertension (high blood pressure) is the prolonged elevation of blood pressure when at rest e.g. above 140/90mmHg Hypertension is a major risk factor for many diseases that have a relatively high incidence later in life e.g. coronary heart disease and strokes Hypertension is commonly found in people that are: - overweight - not taking enough exercise - eating high fat diet - eating too much salt - under continuous stress - smokers

Physiology & Health Questions KEY AREA 6 – Structure and function of the heart 1.Testing Your Knowledge 1Page 172Q’s What you should knowPage172Q Quick Quiz