Option D: Human Physiology D.4 The heart http://i.livescience.com/images/i/000/057/264/original/human-body-heart-130925.jpg?1380117166

D.4 Essential idea: Internal and external factors influence heart function.

D.4.U1 Structure of cardiac muscle cells allows propagation of stimuli through the heart wall. Cardiac muscle cells are y-shaped and join end to end in a complex network. They are striated (due to the arrangement of the contractile proteins actin and myosin), they may have one or two nuclei, and they are not under voluntary control. They also have many mitochondria and are highly vascular which prevent them from becoming fatigued.

These adaptations allow for synchronization of muscle contraction. D.4.U1 Structure of cardiac muscle cells allows propagation of stimuli through the heart wall. Cardiac muscle cells have special structures that allow the propagation of stimuli through the heart wall: Intercalated discs – Specialized junction consisting of a double membrane containing gap junctions. Gap junctions have channels that allow cytoplasm sharing between adjacent cells. This allows the electrical signal (ion movement) to pass quickly from one cell to the next. Branching – The y-shape allows the cells to be interconnected and also allows the wave of depolarization to pass easily form one cell to the network of cells. These adaptations allow for synchronization of muscle contraction.

12 6 1 7 2 11 5 8 3 9 10 4 Heart valve Synonym(s) Right atrioventricular valve Tricuspid valve Left atrioventricular valve Bicuspid valve; Mitral valve Right semilunar valve Pulmonary valve; Pulmonary semilunar valve Left semilunar valve Aortic valve; Aortic semilunar valve

The signal sent from the SA node cannot pass from atria to ventricles. D.4.U2 Signals from the sinoatrial node that cause contraction cannot pass directly from atria to ventricles. SL valves AV valves The cardiac cycle includes the sequence of events when the heart beats. The heart contracts without nerve stimulation. This is achieved by a group of specialized cells called the sinoatrial (SA) node aka pacemaker. Gap junctions allow the contraction to spread rapidly across the entire atrium causing the atria to undergo systole (contract). The signal sent from the SA node cannot pass from atria to ventricles.

D.4.U3 There is a delay between the passing on of a stimulus at the AV node. AND D.4.U4 This delay allows time for atrial systole before the atrioventricular valves close. SL valves AV valves To stimulate the ventricle to contract, the signal reaches another specialized group of cells called the atrioventricular (AV) node. There is approximately a 0.1 second delay before the AV node sends out its own action potential. Why do you think there needs to be a delay before the ventricle contracts??? It allows the atria time to send the blood to the ventricles before the ventricles contract and the AV valves close

D.4.U5 Conducting fibers ensure coordinated contraction of the entire ventricle wall. The signal from the AV node spreads through fibers to specialized tissue call Purkinje fibers. This signal causes the ventricle to undergo systole. Remember, the ventricle walls are much thicker than the atria and therefore require this system of conducting fibers and Purkinje fibers.

Atria and ventricles relaxed Blood flows into atria from veins REVIEW 6.2.A2 Pressure changes in the left atrium, left ventricle and aorta during the cardiac cycle. AND D.4.U6 Normal heart sounds are caused by the atrioventricular valves and semilunar valves closing causing changes in blood flow. SL valves AV valves Atria and ventricles relaxed Blood flows into atria from veins Atrial pressure higher than ventricular but lower than artery pressure AV valves open SL valves closed “DUB” Atria contract Ventricles relaxed Blood pushed into ventricles Atrial pressure increases slightly higher (no big increase needed as much of the blood already moved passively to ventricles) AV valves open SL valves closed Atria relaxed Ventricles contract Blood pushed into arteries Early: Ventricular pressure increases above atrial pressure AV valves close “LUB” SL valves closed Late: Ventricular pressure increases above artery pressure SL valves open AV = atrioventricular  tricuspid & bicuspid (mitral) valves SL = semilunar  pulmonary & aortic valves AV valves close “LUB” SL valves closed “DUB”

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D.4.S3 Mapping of the cardiac cycle to a normal ECG trace. An electrocardiogram (ECG) is a test that measures the electrical activity of the heartbeat It can be used to determine if electrical activity is normal and it may be used to determine if parts of the heart are too large or overworked. http://www.heart.org/HEARTORG/Conditions/HeartAttack/SymptomsDiagnosisofHeartAttack/Electrocardiogram-ECG-or-EKG_UCM_309050_Article.jsp#.VsXyKtLwudK

P wave: shows voltage given off by SA node; marks atrial systole D.4.S3 Mapping of the cardiac cycle to a normal ECG trace. P wave: shows voltage given off by SA node; marks atrial systole Note: SA node also repolarizes but the electrical activity is hidden by QRS complex Point Q: point when AV node sends its impulse QRS complex: impulse from AV node spreads down conducting fibers to Purkinje fibers; marks ventricular systole T wave: AV node is repolarizing (ions returning to resting potential)

Voltage/mV Time/s U wave: origin for this wave is not clear - but probably represents "afterdepolarizations" in the ventricles http://4.bp.blogspot.com/_5Nslwo9F6bI/S_EU-Kcs4DI/AAAAAAAAAg4/5f0VSazrcN4/s1600/ECG+trace+%26+basics.jpg

D.4.S1 Measurement and interpretation of the heart rate under different conditions. We addressed this skill in the labs we performed for the Blood System unit. Heart rate can be detected in a number of ways: pulse in wrist using fingers not thumb, side of neck below jaw, or use of hand-grip heart monitors like we used. Different conditions could include types of exercise, intensity of exercise, recovery from exercise, relaxation, body position including lying down, breathing and breath holding. http://www.pcrush.com/images/300/827631.jpg http://cdn1.medicalnewstoday.com/content/images/articles/258/258118/two-left-fingers-feeling-a-pulse-on-right-wrist.jpg http://images.agoramedia.com/everydayhealth/gcms/pg-sixty-second-health-checks-05-full.jpg

Blood Pressure and Rate of Flow D.4.S2 Interpretation of systolic and diastolic blood pressure measurements. Blood Pressure and Rate of Flow During ventricular systole, heart contracts and blood is forced into arteries under high pressure During ventricular diastole, heart relaxes and blood pressure falls in arteries Blood pressure is measured to record the regular cycle of pressure in the arteries as the heart contracts Usually measured in upper arm (brachial artery) with a sphygmomanometer and stethoscope Average pressure for young adult male is 120 (systolic)/80 (diastolic)

Common heart problems - Pacemakers D.4.A1 Use of artificial pacemakers to regulate the heart rate. Common heart problems - Pacemakers In some individuals the sinoatrial node (aka pacemaker) malfunctions or they may have a block in the signal conduction pathway. “Bradycardia is a heartbeat that is slower than normal. Heart block is a disorder that occurs if an electrical signal is slowed or disrupted as it moves through the heart. Heart block can happen as a result of aging, damage to the heart from a heart attack, or other conditions that disrupt the heart's electrical activity. Some nerve and muscle disorders also can cause heart block, including muscular dystrophy.” https://www.nhlbi.nih.gov/health/health-topics/topics/pace/whoneeds

Common heart problems - Pacemakers D.4.A1 Use of artificial pacemakers to regulate the heart rate. Common heart problems - Pacemakers To regulate the heartbeat, patients may be fitted with an artificial pacemaker. The device is placed under the skin in the chest area. It has wires (leads) that are threaded through a blood vessel that leads into the interior of the heart. The leads supply regular electrical impulses to the heart. Placement of the leads will depend upon the patient’s particular heart problem. https://www.nhlbi.nih.gov/health/health-topics/topics/pace/howdoes

Common heart problems – Heart attack & Defibrillators D.4.A2 Use of defibrillation to treat life-threatening cardiac conditions. Common heart problems – Heart attack & Defibrillators Heart attacks (cardiac arrest) happens when the blood supply to the heart is reduced and the heart is deprived of oxygen. Abnormalities, such as ventricular fibrillation, in the cardiac cycle can occur. When this happens the ventricles begin twitching due to rapid and chaotic contraction of individual cardiac cells. To restore a normal heart rhythm, first responders use a defibrillator to first detect if fibrillation is occurring and if it is, an electrical discharge is given off. *An AED is a portable defibrillator. http://www.nhlbi.nih.gov/health/health-topics/topics/aed/howtouse

Common heart problems – Hypertension D.4.A3 Causes and consequences of hypertension and thrombosis. Common heart problems – Hypertension Hypertension is higher than “normal” blood pressure. This cannot be determined by one blood pressure measure as many factors can increase blood pressure, such as stress. It is best to regularly monitor your blood pressure. Causes: Loss of elasticity and a build up of plaque. Recall that plaque formation often is the result of high levels of lipids and cholesterol in blood. Consequences: Damage to artery cells can lead to them becoming narrower and stiff Weakening of artery causing an aneurysm (bulge in artery wall) that can burst and cause internal bleeding Stroke due to blood vessels in the brain becoming weak and narrow, leak or rupture or clots in arteries Kidney failure due to damage to arteries leading to kidneys and capillaries in the glomerulus http://blogs.furman.edu/wellness/files/2014/11/1-heart-e.jpg

One form of thrombosis is deep vein thrombosis (DVT) D.4.A3 Causes and consequences of hypertension and thrombosis. Thrombosis is the condition when a clot (thrombus) forms in a blood vessel. Common heart problems – Thrombosis One form of thrombosis is deep vein thrombosis (DVT) Causes: Sitting for a long period of time can cause a clot to form in one of the larger veins, usually the leg. (Slow-flowing blood is more likely to clot) Consequences: All or a portion of the clot can break loose and travel to a smaller vein, blocking blood flow (especially dangerous if the clot becomes lodged in a vein in the lung) Anticoagulation is often called thinning the blood. Medicines which work in this way are called anticoagulants. However, they do not actually thin the blood. They alter certain chemicals in the blood to stop clots forming so easily. Anticoagulants do not dissolve the clot. Anticoagulation prevents a DVT from getting larger and prevents any new clots from forming. The body's own healing mechanisms can then get to work to break up the clot. http://patient.info/health/deep-vein-thrombosis-leaflet http://www.stjohnprovidence.org/upload/images/Hospital%20and%20Centers/SJ%20Macomb-Oakland%20Hospital%20Macomb%20Center/Interventional%20Radiology/DVT_normal_and_embolus.gif

Another form of thrombosis is coronary thrombosis D.4.A3 Causes and consequences of hypertension and thrombosis. Thrombosis is the condition when a clot (thrombus) forms in a blood vessel. Common heart problems – Thrombosis Another form of thrombosis is coronary thrombosis Causes: Build up of plaque in a coronary artery causing substantial narrowing of the lumen resulting in slow blood flow and clot formation. Consequences: Heart attack

D.4.S4 Analysis of epidemiological data relating to the incidence of coronary heart disease. Epidemiology is the branch of medicine that deals with the incidence, distribution, and possible control of diseases and other factors relating to health. Coronary heart disease (CHD) refers to damage to the heart caused by a reduction in blood supply to the heart. Read pages 526-527 in your textbook to see who is at risk of CHD and how it can be prevented. http://www.world-heart-federation.org/fileadmin/user_upload/images/CVD_Health/worldmapOverview.jpg