Chapter 27 -The Heart & Blood Vessels

Transcription

1 Chapter 27 -The Heart & Blood Vessels 3.2 Learning Objectives Organisational Complexity of the human 1. Describe the structures and organisation of tissues in the closed circulatory system. 2. Discuss the role of muscle tissues and valves. 3. Draw the structure of the heart. 4. Explain the two-circuit circulatory system and describe the main pathways of blood circulation. 5. Dissect, display and identify an ox s or a sheep s heart. 6. Describe cardiac supply through the cardiac artery and vein. 7. Demonstrate a simple understanding of: heartbeat and its control pulse blood pressure. 8. Discuss the effect of smoking, diet and exercise on the circulatory system. 9. Investigate the effect of exercise on the breathing rate or pulse of a human. 10. *Show an awareness of specialised heart muscle tissue and the existence and location of pacemaker nodes (SA and AV). 11. *Describe the heart cycle, systole and diastole periods. Two types of circulatory system: 1. Open circulatory system - involves a heart pumping blood through open ended vessels. The blood moves around all of the body s cells and returns to the heart through holes in the heart wall. Examples: Slugs, Spiders, Crabs. 2. Closed circulatory system blood remains enclosed in bloods vessels e.g. humans. Advantages of a closed system: Blood can circulate faster Blood flow is easier to regulate e.g. more blood can flow to the legs if necessary Human circulatory system consists of: 1. Blood, 2. Heart & 3. Blood vessels.

2 Blood vessels: Arteries carry blood away from the heart Veins carry blood to the heart Capillaries connect arteries to veins Arteries Veins Carry blood away from the heart Carry blood to the heart Blood is under high pressure Blood is under low pressure Thick, strong walls Thin, weaker walls Small lumen Large lumen No valves Valves present Structures of arteries and veins: Arteries and veins have similar structures The walls of a vein are thinner than the walls of an artery The outer layer of collagen (protein) is a tough layer that prevents the vessel from expanding too much The middle layer of muscle & elastic fibres can alter the size of the vessel The inner layer of living cells is called the endothelium lines the lumen valves open valves close blood Valves: Blood pressure in veins is lower than that of arteries There is an increased chance of blood flowing backwards To prevent this happening, veins have valves. Capillaries: Capillaries are tiny blood vessels. They have very thin porous walls this allows exchange of materials between the blood and body tissues

3 The Heart: The heart is located between the two lungs, slightly to the left hand side of the chest/thorax It is made of cardiac muscle and is surrounded by a double membrane called the pericardium. Cardiac muscle is slow to fatigue. The heart is divided into two sides by a wall called the septum The two upper chambers atria (atrium) The two lower chambers ventricles Ventricles pump blood out of the heart (left ventricle is thicker pumps blood all around the heart) The atria and ventricles are separated by valves The left atrium and left ventricle are separated by the bicuspid valve. The right atrium and right ventricle are separated by the tricuspid valve. The semi lunar (half moon shaped) valves allow blood to flow out of the heart into the main arteries Blood flow in the heart: - Oxygenated blood contains high levels of oxygen and comes from the lungs, and goes around the body supplying the cells. - Deoxygenated blood contains low levels of oxygen and comes from the body, and goes to the lungs.

4 Deoxygenated blood enters the heart through the venae cavae (inferior lower part of the body, superior upper part of the body) The right atrium contracts forcing blood through the tricuspid valve. The tricuspid valve closes. Blood is forced out of the heart through the semilunar valves in the pulmonary artery. This blood then travels to the lungs. Oxygenated blood returns to the heart from the lungs. Oxygenated blood enters the left atrium through the pulmonary veins. Blood is pumped through the bicuspid valve into the left ventricle The bicuspid valve closes. The blood is pumped out to the body through the semilunar valve in the aorta. Double Circulation: The heart is a double pump. One side pumps blood to the lungs (pulmonary circuit). While the other side pumps blood around the rest of the body (systemic circuit) Advantages of double circulation: Oxygen rich and oxygen poor blood are separated. Blood pressure is high enough to reach all parts of the body Portal system: A portal system is one in which the blood starts and ends in capillaries The vessel/s in a portal system do not connect directly to the heart e.g. hepatic portal vein connects stomach & intestines to the liver Blood supply to the heart: The muscle of the heart is supplied with blood by the coronary arteries.

5 The coronary arteries branch from the aorta at the point where it leaves the heart. Blockage of the coronary arteries is a common cause of heart attack. Control of heartbeat: The heartbeat is controlled by a small bundle of specialised tissue called the pacemaker (right atrium). The pacemaker sends out regular electrical impulses. The brain can cause the pacemaker to speed up or slow down. 1. The pacemaker (sino-atrial node) pulses. This causes the atria to contract (atrial systole) 2. This stimulates the AV node (atrio ventricular) (found further down the right atrium) 3. The AV node sends an impulse down the muscle fibres in the septum. 4. The impulses from these fibres cause the ventricles to contract (ventricular systole) Stages of heartbeat: Diastole refers to when the heart chambers are relaxed; systole is when they contract. *3 stages HL 1. Blood enters the heart Atria and ventricles are relaxed Blood enters the atria All valves are closed 2. Blood is pumped to the ventricles Electrical impulses from the pacemaker cause the atria to contract (atrial systole) The tricuspid and bicuspid valves open Blood is pumped to the ventricles 3. Blood is pumped from the heart The atria relax and impulses from the AV node cause the ventricles to contract (ventricular systole) The tricuspid and bicuspid valves are forced shut The semilunar valves are forced open Blood is pumped out of the heart The ventricles relax and the semilunar valves close The venae cavae & pulmonary veins open & the cycle starts again

6 Sounds of the heartbeat: Sound of the heartbeat is called the lub-dub sound. The lub sound is due to the bicuspid and tricuspid valves being forced shut when the ventricles contract The shorter dub sound is due to the semi-lunar valves snapping shut. Pulse: A Pulse is the alternate expansion and contraction of the arteries. The pulse can be felt most easily in the wrist or neck. The average adult pulse is 72 beats per minute Blood pressure: Blood pressure is the force exerted by the blood against the walls of the blood vessels (mainly arteries). Blood pressure is recorded using a Sphygmomanometer by measuring the pressure needed to stop the flow of blood in the arteries of the upper arm. Blood pressure is given as two readings. The top value records the systolic pressure (when ventricles contract). The lower value records the diastolic pressure when there is no pulse (when ventricles relax). Average BP for a young adult is 120/80 mm of mercury. High blood pressure occurs when the lower value is over 95mm of Hg. High blood pressure (often caused by blockage in arteries) indicates the heart has to pump harder. This may lead to stroke/heart attack. Lifestyle & the heart: Smoking: Nicotine is addictive, it increases the heart rate and raises blood pressure Carbon monoxide reduces the ability of the blood to carry oxygen Chemicals also increase the risk of blood clots and cancer Diet: A fat rich diet increases the chance of arteries becoming blocked High salt intake raises the blood pressure. Obesity can contribute to high blood pressure and heart attacks. Exercise: Enlarges and strengthens the heart. Improves circulation & helps reduce body weight.