The Mammalian Circulatory System

Transcription

1 The Mammalian Heart

2 The Mammalian Circulatory System Recall: What are the 3 cycles of the mammalian circulatory system? What are their functions? What are the three main vessel types in the mammalian circulatory system? What are their functions? What are the main components of blood? What are their functions?

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4 jugular vein carotid artery pulmonary artery superior vena cava inferior vena cava pulmonary vein aorta hepatic vein mesenteric arteries hepatic portal vein renal vein iliac vein renal artery iliac artery

5 Cardiac Circulation superior vena cava semilunar valve right atrium atrioventricular valve (tricuspid valve) right ventricle inferior vena cava aorta pulmonary artery pulmonary veins left atrium atrioventricular valve (bicuspid valve) semilunar valve left ventricle septum

6 From the upper body To the upper body To the lungs To the lungs From the lungs From the lungs From the lower body To the lower body

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8 Directional Blood Flow The heart itself is divided into 4 chambers and 2 sides separated by a septum. Blood only flows in one direction in the circulatory system. Blood returns to the heart through veins and exits the heart through arteries. Veins bring blood to the atria. Blood then flows to the ventricles. The blood then exits the heart through arteries. To keep blood flowing in one direction in the heart, there are valves that prevent backflow of the blood when the close. These valves only open in one direction.

9 Control of Heartbeat A heartbeat is divided into periods of relaxations (diastole) and contractions (systole). During diastole, the heart muscles are relaxed. Blood flows into the atriums through the veins. The heart has two nodes which are responsible for controlling contraction of the chambers which results in a heartbeat.

10 Control of Heartbeat The sinoatrial node (the pacemaker of the heart) then sends out a signal that contracts the atriums (atrial systole). This causes blood to flow past the atrioventricular valves into the ventricles. The atrioventricular node then sends out a signal that contracts the ventricles (ventricular systole). This causes the atrioventricular valves to close, and the semilunar valves open. The lub-dub sound of a heart beat is the sound of first the atrioventricular valves closing and then the semi-lunar valves closing.

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12 Blood Pressure Upon contraction of the ventricles (systole), blood rushes out into the arteries. This produces high pressure in the arteries. When the heart muscles relax and blood is returning to the heart, there is lower pressure in the arteries. When blood pressure readings are given as two numbers, they represent the pressure at systole and at diastole. E.g mm Hg

13 Electrocardiogram When the SA node and the AV node send out signals, they are electrical impulses that travel along the walls of the atria and ventricals, causing them to contract. An electrocardiogram (ECG) can measure the change in voltage for these impulses which produces an electrocardiograph which displays a regular pattern for a heartbeat. An irregular pattern indicates fibrillation, which is a random contracting of muscles which can sometimes be reset by a strong electrical current to the heart.

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15 Cardiac Output Cardiac output is a measure of the volume of blood pumped from each ventricle per unit of time. Cardiac output is affected by two factors: stroke volume and heart rate. Cardiac output = stroke volume x heart rate Stroke volume is the amount of blood pumped out of the heart in a heartbeat. Heart rate is the number of beats per period of time. Average stroke volume is around 70 ml and average resting heart rate is around 70 beats per minute. What is the cardiac output? If an average person has 5L of blood, how long would it take to pump their total blood volume?

16 Heart Rate and Fitness Maximum heart rate is the highest heart rate that can be attained during high physical activity. This rate is reduced with age. However, maximum heart rate does not seem to correlate with fitness. The time to return to a resting heart rate seems to be a better indicator of physical fitness. A low resting heart rate is also associated with general physical fitness as a lower number of beats is needed to delivery blood to the body. This indicate efficiency per pump.

17 Stroke Volume and Fitness There are two factors that affect stroke volume: 1. How easily the heart fills with blood. i. This is affected by distensibility (stretchiness) of the ventricles. 2. How easily the heart empties the blood. i. This is affected by the strength of ventricular contractions. Regular cardiovascular exercise can increase stroke volume by enlarging and strengthening the chambers. Cardiovascular exercise can also increase distensibility of the ventricles.

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19 Atherosclerosis Build-up of fatty material forms a plaque through a chain of reactions that blocks blood flow in the artery. Medication, an angioplasty or a coronary bypass may be necessary to treat the problems of high blood pressure and blood clots that are associated with arteriosclerosis.