The Arteries Arteries (efferent vessels)

Transcription

1 The Heart Your heart beats about 100,000 times every day. During the course of the day, the heart pumps about 8,000 Liters(or 2,200 gallons) of blood. 13-1

2 It beats day and night every day of our lives, but what does the heart really do for us? Your heart, quite simply, is a pump. But it is one of the most fascinating pumps you'll ever learn about. First you must understand that every cell in our body - from the cells in our hair to the cells in our toes need OXYGEN and NUTRIENTS to survive and keep us alive. Since they can't get these nutrients themselves, blood is used to deliver them right to the cells. (sort of like room service) The basic job of the heart is pump that blood through your body so that the blood can deliver the oxygen and nutrients right to the cells. The heart keeps your blood pumping at all times as it picks up oxygen from your lungs and nutrients from your digestive system and sends them to all cells of your body. Your heart is the power behind the delivery system. Inside the heart is four chambers. Two of those chambers send the blood up to your lungs to get oxygen, then the other two chambers send that oxygen rich blood to the rest of your body. Valves inside of the heart make sure that the blood only moves in one direction. The younger you are, the faster your heart beats. A baby's heart beats about 90 times a minute. A twelve year old heart beats about 78 times a minute and an adult heart beats about 70 times a minute. Of course the more active you are, the more your heart beats, since the cells need oxygen faster to keep you moving. 13-2

3 Blood vessels 13-3

4 The Arteries Arteries (efferent vessels) and arterioles take blood away from the heart. The largest artery is the aorta. The middle layer of an artery wall consists of smooth muscle that can constrict to regulate blood flow and blood pressure. Arterioles can constrict or dilate, changing blood pressure. 13-4

5 The Veins Venules drain blood from capillaries, then join to form veins(afferent vessels) that take blood to the heart. Veins have much less smooth muscle and connective tissue than arteries. Veins often have valves that prevent the backward flow of blood when closed. Veins carry about 70% of the body s blood and act as a reservoir during hemorrhage. 13-5

6 The Capillaries Capillaries have walls only one cell thick to allow exchange of gases, nutrients, and wastes with tissue fluid. Capillary beds are present in all regions of the body but not all capillary beds are open at the same time. Contraction of a sphincter muscle closes off a bed and blood can flow through an arteriovenous shunt that bypasses the capillary bed. 13-6

7 Anatomy of a capillary bed 13-7

8 Capillary exchange 13-8

9 The heart has four chambers: two upper, thin-walled atria, and two lower, thickwalled ventricles. The atria are very small since they are responsible only for pumping blood the the ventricles. The ventricles are much larger and stronger since they are responsible for pumping blood to the lungs and the body. Which ventricle is larger? Why? 13-9

10 The septum is a wall dividing the right and left sides. The interatrial septum divides the two atria and the interventricular septum divides the two ventricles. Atrioventricular valves occur between the atria and ventricles the tricuspid valve on the right and the bicuspid valve on the left; both valves are re-enforced by chordae tendinae attached to muscular projections within the ventricles. These valves block openings between the atria and ventricles to prevent backflow and maintain a one-way flow of blood through the heart

11 External Heart Anatomy A deep groove (called the coronary sulcus) separates the atria and ventricles. It is usually filled with large amounts of fat

12 External Heart Anatomy Reference points on the heart: Base: where the large veins and arteries enter and leave the heart Apex: lower, pointed tip of the heart (hangs free) Borders: Superior border: formed by the bases of the major vessels and the two atria Right border: formed by the right atrium Left border: formed by the left ventricle and small part of the left atrium Inferior border: formed by the wall of the right ventricle 13-12

13 External heart anatomy 13-13

14 Semilunar valves occur between the ventricles and the attached arteries. The aortic semilunar valve lies between the left ventricle and the aorta, while the pulmonary semilunar valve lies between the right ventricle and the pulmonary trunk

15 Body Circuits All of the blood vessels in the body are grouped into two main categories: Pulmonary circuit: includes all of the vessels that carry blood to and from the lungs Systemic circuit: includes all of the blood vessels that carry blood to and from the entire body 13-15

16 Major arteries and veins of the systemic circuit 13-16

17 Blood Flow Through the Heart Blood enters the right atrium of the heart through the systemic circuit through the superior and inferior vena cava. The blood will flow from the right atrium into the right ventricle through the right atrioventricular valve (or tricuspid valve)

18 Blood Flow Through the Heart Blood leaves the right ventricle of the heart through the pulmonary semilunar valve and enters the pulmonary circuit through the left and right pulmonary arteries. In the pulmonary trunk, exchange of gases, nutrients, and wastes occurs. Blood leaves the pulmonary circuit through the left and right pulmonary veins

19 Blood Flow Through the Heart The left and right pulmonary veins deliver blood to the left atrium. Blood flows from the left atrium to the left ventricle through the left atrioventricular valve (bicuspid or mitral valve). Blood leaves the left ventricle through the aortic semilunar valve and re-enters the systemic circuit through the aorta

20 Passage of Blood Through the Heart Blood follows this sequence through the heart: superior and inferior vena cava right atrium tricuspid valve right ventricle pulmonary semilunar valve pulmonary trunk and arteries to the lungs pulmonary veins leaving the lungs left atrium bicuspid valve left ventricle aortic semilunar valve aorta to the body

21 Passage of Blood Through the Heart Vena cava Right atrium Tricuspid valve Pulmonary semilunar Right ventricle valve Pulmonary arteries Pulmonary circuit Systemic Circuit Aorta Aortic semilunar valve Left ventricle Pulmonary veins Left atrium Bicuspid valve 13-21

22 Passage of Blood Through the Heart 13-22

23 Internal view of the heart 13-23

24 Path of blood through the heart 13-24

25 The Heartbeat Is similar to skeletal muscle contraction, but different. 1. (Contraction) Action potential arrives at the cell membrane, sodium ion channels are triggered to open. These channels are called fast channels because they open quickly and remain open for only a few milliseconds

26 The Heartbeat 2. (Plateau) As voltage rises, sodium ion channels close and calcium ion channels open. These channels are called slow channels because they open slowly and remain open for a longer period of time. This produces a plateau in cardiac cell contraction. This is a MAJOR difference between skeletal and cardiac muscle cell contraction- the presence of a plateau between action potentials

27 The Heartbeat 3. (Relaxation) As plateau is maintained, calcium ion channels begin to close and slow potassium ion channels begin to open. These restore the resting potential to the cardiac muscle cell

28 The Heartbeat plateau contraction relaxation 13-28

29 The Heartbeat An absolute refractory period occurs after an action potential begins. During this period, the cardiac muscle cell membrane cannot respond at all to sodium ions. This prevents wave summation and the formation of tetanic contractions in cardiac muscle (allows for complete relaxation before the next contraction occurs). This is another major difference between cardiac and skeletal muscle cell contraction.

30 The Heartbeat Absolute refractory period 13-30

31 The Heartbeat Each heartbeat is called a cardiac cycle. When the heart beats, the two atria contract together, then the two ventricles contract; then the whole heart relaxes. Systole is the contraction of heart chambers; diastole is their relaxation. The heart sounds, lub-dup, are due to the closing of the atrioventricular valves, followed by the closing of the semilunar valves

32 Blood Pressure The pumping of the heart sends out blood under pressure to the arteries. Blood pressure is greatest in the aorta; the wall of the left ventricle is thicker than that of the right ventricle and pumps blood to the entire body. Blood pressure then decreases as the cross-sectional area of arteries and then arterioles increases

33 Blood Pressure The top number of blood pressure (systolic) occurs during ventricular systole (contraction of the ventricles). The bottom number of blood pressure (diastolic) occurs during ventricular doastole (relaxation of the ventricles)

34 Intrinsic Control of Heartbeat The SA (sinoatrial) node, or pacemaker, initiates the heartbeat and causes the atria to contract on average every 0.85 seconds. (The heartbeat is not initiated by the nervous sytem. This is called automaticity or autorhythmiticity.) The AV (atrioventricular) node conveys the stimulus and initiates contraction of the ventricles. The signal for the ventricles to contract travels from the AV node through the atrioventricular bundle to the smaller Purkinje fibers.

35 Conduction system of the heart 13-35

36 Extrinsic Control of Heartbeat A cardiac control center in the medulla oblongata speeds up or slows down the heart rate by way of the autonomic nervous system branches: parasympathetic system (slows heart rate) and the sympathetic system (increases heart rate). Hormones epinephrine and norepinephrine from the adrenal medulla also stimulate faster heart rate

37 The Electrocardiogram An electrocardiogram (ECG) is a recording of the electrical changes that occur in the myocardium during a cardiac cycle. Atrial depolarization (contraction) creates the P wave, ventricle depolarization (contraction) creates the QRS wave, and repolarization (relaxation) of the ventricles produces the T wave

38 Electrocardiogram 13-38

39 Coronary Circulation The coronary arteries supply much needed oxygenated blood containing nutrients to the heart. Blood pressure here is the highest found anywhere in the systemic circuit to ensure a continuous flow of blood to the working heart. The coronary arteries are small, so are easily clogged. The right coronary artery supplies blood to the right atrium, both ventricles, and other portions of the heart. The left coronary artery supplies blood to the left ventricle, left atrium, and interventricular septum

40 Coronary artery circulation 13-40

41 Atherosclerosis Atherosclerosis is due to a build-up of fatty material (plaque), mainly cholesterol, under the inner lining of arteries. The plaque can cause a thrombus (blood clot) to form. The thrombus can dislodge as an embolus and lead to thromboembolism

42 Stroke, Heart Attack, and Aneurysm A cerebrovascular accident, or stroke, results when an embolus lodges in a cerebral blood vessel or a cerebral blood vessel bursts; a portion of the brain dies due to lack of oxygen. A myocardial infarction, or heart attack, occurs when a portion of heart muscle dies due to lack of oxygen

43 Partial blockage of a coronary artery causes angina pectoris, or chest pain. An aneurysm is a ballooning of a blood vessel, usually in the abdominal aorta or arteries leading to the brain. Death results if the aneurysm is in a large vessel and the vessel bursts. Atherosclerosis and hypertension weaken blood vessels over time, increasing the risk of aneurysm

44 Coronary Bypass Operations A coronary bypass operation involves removing a segment of another blood vessel and replacing a clogged coronary artery. It may be possible to replace this surgery with gene therapy that stimulates new blood vessels to grow where the heart needs more blood flow

45 Coronary bypass operation 13-45

46 Clearing Clogged Arteries Angioplasty uses a long tube threaded through an arm or leg vessel to the point where the coronary artery is blocked; inflating the tube forces the vessel open. Small metal stents are expanded inside the artery to keep it open. Stents are coated with heparin to prevent blood clotting and with chemicals to prevent arterial closing

47 Angioplasty 13-47

48 Dissolving Blood Clots Medical treatments for dissolving blood clots include use of t-pa (tissue plasminogen activator) that converts plasminogen into plasmin, an enzyme that dissolves blood clots, but can cause brain bleeding. Aspirin reduces the stickiness of platelets and reduces clot formation and lowers the risk of heart attack

49 Heart Transplants and Artificial Hearts Heart transplants are routinely performed but immunosuppressive drugs must be taken thereafter. There is a shortage of human organ donors. Work is currently underway to improve self-contained artificial hearts, and muscle cell transplants may someday be useful

50 Hypertension About 20% of Americans suffer from hypertension (high blood pressure). Hypertension is present when systolic pressure is 140 or greater or diastolic pressure is 90 or greater; diastolic pressure is emphasized when medical treatment is considered. A genetic predisposition for hypertension occurs in those who have a gene that codes for angiotensinogen, a powerful vasoconstrictor