Circulatory System of a Mammal

2. Circulatory System of a Mammal

3. Components of circulatory systems Multi-cellular animals overcome the limitations of diffusion by having a specialized circulatorysystem. This comprises: • a heart • a fluid in which substances are transported • vessels through which the fluid can flow. The two types of circulatory system are open (e.g. molluscs, arthropods) and closed (e.g. vertebrates, a few invertebrates).

4. Closed circulatory systems In a closed circulatory system, blood is fully enclosed within blood vessels at all times. From the heart, blood is pumped through a series of progressively smaller vessels. In the smallest vessels, capillaries, substances diffuse in and out of the blood and into cells. heart capillaries Blood then returns to the heart via a series of progressively larger vessels.

5. Closed circulatory systems

7. The human heart The heart is a muscular organ located between the lungs in the centre of the chest (thorax), and is about the size of a fist. It pumps blood continuously around the body. An organism can lose consciousness within just a few seconds if the brain is deprived of blood. In foetuses, the heart begins beating about 5–6 weeks after conception.

8. Cardiac muscle The heart mainly consists of cardiac muscle tissue, which like smooth muscle (but not skeletal muscle), contracts involuntarily. Cardiac muscle is made up of cells that are connected by cytoplasmic bridges. This enables electrical impulses to pass through the tissue. It contains large numbers of mitochondria and myoglobin molecules.

9. Structure of the heart

10. What structure?

13. Name the blood vessel in each of the following descriptions: Joins the right ventricle to the capillaries of the lungs pulmonary artery Carries oxygenated blood away from the heart aorta Carries deoxygenated blood away from the liver hepatic vein The first main blood vessel that an oxygen molecule reaches after being absorbed from an alveolus pulmonary vein Has the highest blood pressure aorta Questions:

14. Blood flow through the heart

15. Preventing backflow Blood always flows in the same direction as it moves through the heart during each circulation of the body. Why is it important that blood does not flow backwards?

16. Heart valves Semilunar valve Semilunar valve Atrioventricular valve Atrioventricular valve The chambers of the heart are separated by valves which prevent blood from flowing in the wrong direction. There are valves between the atria and the ventricles… …and there are valves leading out of the ventricles.

17. How are valves held in place? The valves between the atria and ventricles are connected to the inner walls of the heart by tough tendons. valve open

18. How are valves held in place? The tendons allow the valves to close and hold the valve flaps in place. They prevent the valves from flipping up and turning inside out. Why is this important? valve closed valve open

21. The cardiac cycle

22. Interactive heart

23. Cardiac output The amount of blood pumped around the body is called the cardiac output, and depends on two factors: • the stroke volume – the volume of blood pumped by the left ventricle in each heart beat. A typical value for an adult at rest is 75ml. • the heart rate – the number of times the heart beats per minute. A typical value for an adult at rest is 70bpm. cardiac output = stroke volume × heart rate A typical resting cardiac output is 4–6 litres per minute. This can rise to as much as 40 litres per minute in highly trained endurance athletes.

25. Now try the exam style questions.

26. The table shows the pressures in the left atrium, left ventricle and aorta during a cardiac cycle. • Give the number of one stage where: • blood flows into the aorta • The valve between the atrium and the ventricle is open

27. Give the number of one stage • where blood flows into the aorta. • Aorta • For blood to flow from the left ventricle to the aorta, the pressure in the ventricle must be higher than the pressure in the aorta. • Left semilunar valve • Left • ventricle

29. Give the number of one stage where the valve between the atrium and the ventricle is open. • If the valve is open, the pressure in the left atrium must be higher than the pressure in the ventricle. • Left atrium • Left atrioventricular valve • Left ventricle

31. Applying your knowledge • AO2 Candidates should be able to • (b) apply scientific knowledge and processes to unfamiliar • situations. Remember: you may not have seen the wrapping before but you will be familiar with what is inside. The context may be new but the biology will be familiar.

32. A hole in the heart is caused when the wall between the right atrium and the left atrium does not close properly when the heart is developing. This leaves a hole through which blood can pass between the two atria. • 3a Use your knowledge of pressure to explain why blood flows from the left atrium to the right atrium. • 3b The blood in the right atrium of a person with a hole in the heart is different in its oxygen concentration from the blood in the right atrium of a healthy person. • In what way is it different? • Explain what causes this difference. • 3c The blood pressure in the pulmonary arteries of a person with a hole in the heart is different from that in the pulmonary arteries of a healthy person. • In what way is it different? • Explain what causes this difference.

33. The material used in this question is not on your specification. • The question will contain all the information you need so read it carefully. • A hole in the heart is caused when the wall between the right atrium and the left atrium does not close properly when the heart is developing. This leaves a hole through which blood can pass between the two atria. • The situation may be new but the biology will be familiar. It is about the heart and blood flow. • So, don’t panic

34. Hole in the heart • Left atrium • Right atrium

35. 3a Use your knowledge of pressure to explain why blood flows from the left atrium to the right atrium. (2 marks) • Blood flows from high pressure to low pressure; • Blood pressure higher in left atrium; • R • L

36. 3b The blood in the right atrium of a person with a hole in the heart is different in its oxygen concentration from the blood in the right atrium of a healthy person. • In what way is it different? • (1 mark) • Explain what causes this difference. (2 marks) • R • L • Has a higher oxygen concentration; • Mixed with blood from left atrium • Which is coming from • lungs;

37. 3c The blood pressure in the pulmonary arteries of a person with a hole in the heart is different from that in the pulmonary arteries of a healthy • person. • In what way is it different? • (1 mark) • Explain what causes this difference. (1 mark) • R • L • Has a higher pressure; • Contains additional blood from left atrium;

38. Heart disease – use pages 94-96 to fill in the gaps on the sheet. Homework: Complete ‘The heart and heart disease’ section of Unit 1 booklet to hand in on Wednesday 4th March.

39. Heart disease – why worry? • Heart disease kills more people in the UK than any other disease. • Almost half of heart disease deaths are from coronary heart disease (CHD). • CHD affects the pair of blood vessels – the coronary arteries, which supply the heart muscle with the glucose and oxygen that it requires for respiration.

40. Atheroma • Atheroma is the name for a fatty deposit which forms within the wall of an artery.

41. Atheroma • It begins as fatty streaks that are accumulations of white blood cells that have taken up low-density lipoproteins (LDLs). • LDLs are the “bad” form of cholesterol.

42. Atheroma • Fatty streak laid down by LDL-laden white blood cells. • Streaks start to enlarge to form an atheromatous plaque (these most commonly occur in larger arteries). • These plaques bulge into the lumen of arteries and restrict the flow of blood.

43. Thrombosis • As the blood flow is restricted, blood pressure increases. • This causes some damage to the lining (endothelium) of the artery. • Platelets start to aggregate and lay down a blood clot. • This is now called a thrombus.

44. Thrombosis • Sometimes a thrombus may become dislodged and move around the body. • This mobile thrombus can settled elsewhere and block other arteries and veins. • This is particularly problematic if the thrombus moves to the lungs.

45. Aneurysm • Atheromas that lead to the formation of a thrombus also weaken the artery walls. • These weakened points swell to form a balloon-like blood-filled structure called an aneurysm. • Aneurysms frequently burst, leading to haemorrhage. • This then leads to a loss of blood in that region of the body. • A brain aneurysm is known as a cerebrovascular aneurysm (CVA), or stroke.

46. Myocardial infarction • Also known as a heart attack. • The term literally means a reduced supply of oxygen to the muscle of the heart. • MI is a symptom of CHD. • MI results from a blockage in one of the coronary arteries.

47. Myocardial infarction • If the blockage is close to the junction of the coronary artery and the aorta, then the heart will stop beating because the blood supply is completely cut off.

48. Write definitions for the following terms • Atheroma • Thrombosis • Aneurysm • Myocardial infarction

49. What are the risk factors for CHD?

50. What are the risk factors for CHD? • Smoking • High blood pressure • Blood cholesterol • Diet