Mammalian Transport System Ch. 8 Part 4 Heart Function

Structures to Know Atria (Atrium) or auricle Upper chambers Receive blood from veins Ventricles Lower chambers Blood flows into from the atria and out through arteries Aorta Pulmonary artery Venae cavae (vena cava) Pulmonary veins Coronary arteries Bring oxygenated blood back to the heart Septum Wall of muscle that separates chambers on the right side of the heart from the chambers on the left side of the heart Blood cannot pass through

Valves and Nodes to know Atrioventricular valves (between the atrium and the ventricle) Mitral/bicuspid valve (LEFT SIDE OF HEART) Tricuspid valve (RIGHT SIDE OF HEART) Semilunar valves Pulmonary Valve Aortic Valve Sinoatrial node (SAN) Patch of specialized muscle fibers in RIGHT ATRIUM Pacemaker Atrioventricular node (AVN) Patch of conducting muscle fiber located in upper septum Purkyne tissue Conducting muscle fibers running down septum, along the right and left ventricles

Valves Atrioventricular valves (between the atrium and the ventricle) Mitral/bicuspid valve (LEFT SIDE OF HEART) Tricuspid valve (RIGHT SIDE OF HEART) Semilunar valves Pulmonary Valve Aortic Valve

Important!!!! Heart is myogenic  does NOT need outside nerve impulses to initiate heart beat Valves in heart do NOT actively open and close Valves open and close due to PRESSURE changes in chambers Closing of valves create thump-thump of heartbeat

Structure of Heart Atrium walls  thin, muscular walls Low pressure exerted Ventricle walls  thick and muscular Right ventricle  small force needed to push blood to lungs Left ventricle  large force needed to push blood all over body VERY MUSCULAR Greater pressure developed in left ventricle than left atria

The Cardiac Cycle Sequence of events that make up 1 heart beat Heart beats about 70x a minute 3 stages of the cycle 1.Atrial systole 2.Ventricular Systole 3.Ventricular Diastole Systole  Contraction Diastole  Relaxation

Atrial Systole Heart filled with blood Muscle in atrial walls (very thin) contract Not a lot of pressure from this contraction Enough pressure to force blood in atria through ATRIOVENTRICULAR VALVES (AV) into ventricles No back flow of blood into pulmonary veins or vena cava b/c of semilunar valves

Ventricular Systole Ventricles contract 0.1 s after atria contracts Thick, muscular ventricle walls push blood out (exert high pressure) AV valve shut when pressure in ventricles exceeds pressure in atria Semilunar valves open Blood rushes up into aorta & pulmonary artery Lasts for 0.3 seconds

Ventricular Diastole After 0.3 seconds, ventricular muscle relaxes Ventricle pressure decreases Semilunar valves shut, preventing backflow of blood Blood only fills in cusps of valves Blood from veins flow into the 2 atria Blood is at low pressure Walls of atria expand to accommodate blood (very little resistance) Some blood trickles into ventricles through AV valve Atria contracts and cardiac cycle begins again

Control of the Heart Beat Myogenic muscles Naturally contracts and relaxes No nerve impulses required Sinoatrial Node (SAN) Set out rhythm for all other muscle cells to contract SAN contraction rhythm slightly faster than the rest of the heart SAN contracts  wave of excitation (depolarization) sent across all of the atria & muscles of atria contract

Things NOT to say when describing nodes: “Signal” “Wave” alone “Pulse” “Message” “Nerve impulse” You SHOULD describe the function of SAN using: “Wave of excitation” “depolarization” “impulse”

Ventricle contraction SAN causes contraction of all atria muscles Ventricle muscles delayed due to band of fibers between the atria and ventricles that does NOT conduct electric impulses Only path for impulses to reach ventricles is through path of conducting fibers in septum called ATRIOVENTRICULAR NODE (AVN) AVN receive excitation from atria, delays it 0.1s and then passes it to another bunch of conducting fibers called the PURKINJE FIBERS or PURKYNE TISSUE Wave of excitation is sent up ventricle walls— bottom-up

Fibrillation When muscular walls of heart flutter rather than contract and relax as a whole Rapid, irregular, unsynchronized contraction of muscle cells Atrial fibrillation (non fatal) Afib Can lead to stroke Ventrical fibrillation (fatal) Vfib Faint, cardiac arrest Caused by: Electric shock or damage to large areas of muscle in walls of heart Miss firing of electric impulse from atria Instead of electrical impulse going from atria to AVN to Purkinje tissue in the ventricle, all muscle cells in ventricle get excited in all directions

Electrocardiograms (ECGs) Graph plotting voltage vs. time Records electrical potentials of heart over time Place electrodes over opposite sides of heart P = wave of excitation over atrial walls Q, R, S = wave of excitation over ventricle walls T = recovery of ventricle walls Contraction time = time b/t Q and T Filling time = time b/t T and Q

How To Read an ECG EKG paper is a grid where time is measured along the horizontal axis. Each small square is 1 mm in length and represents 0.04 seconds. Each larger square is 5 mm in length and represents 0.2 seconds. Voltage is measured along the vertical axis. 10 mm is equal to 1mV in voltage.

Calculating Heart from ECG 1.Determine rate of strip Time of strip is given; measure strip with ruler and divide length by sec of strip or… May be given 20mm * s -1 2.Measure distance of one cardiac cycle Beginning of one P to the beginning of the next P