1. Chapter 31: The human circulatory system
Leaving Certificate Biology
Higher Level

2. The Circulatory System
Organisational complexity of the human involves having multiple organs and tissues each with their own individual functions and an extensive network of tubes carrying oxygen and nutrients to every living cell of the human body and the efficient disposal of wastes produced by all the living cells of the human

3. The Circulatory System
The circulatory system of the human is a closed system whereby blood continually flows around the body inside a network of blood vessels and oxygen, carbon dioxide, nutrients, and wastes diffuses into and out of these vessels
The closed system involves blood flowing through structures in the following order: strong muscular heart, arteries, arterioles, capillaries, venules, veins and finally back to the heart

4. The Circulatory System
Advantages of the closed circulatory system are:
Blood can be pumped around the body fast for fast and efficient delivery of oxygen and nutrients and fast and efficient removal of wastes
Blood can be directed to different areas of the body through constriction and dilation of the blood vessels where needed

5. Blood Vessels Arteries: carry blood away from heart
Arterioles (small arteries): carry blood from the arteries to the capillaries
Capillaries: carry a single-file of red blood cells through their lumens delivering oxygen and nutrients and removing wastes from local cells and tissues
Venules (small veins): carry blood from the capillaries to the veins
Veins: carry blood towards the heart

6. Arteries and Veins Large ARTERY VEIN lumen, with Small valves lumen,No
valves
Endothelial
cells
VALVE
Elastic
tissue
Smooth
Muscle
(involuntary)
Collagen
Thick wall
Thin wall

7. Differences between arteries and veins
Artery
Vein
Carries blood away from heart
Carries blood toward heart
Blood under high pressure
Blood under low pressure
Thick walls
Thin walls
Pulse flow
Smooth flow
Narrow lumen
Large lumen
No valves
Valves present
Blood rich in oxygen (except pulmonary artery)
Blood poor in oxygen (except pulmonary veins)

8. Smooth Muscle, Skeletal Muscle and Valves
Smooth muscle is involuntary (not under conscious control): surrounds arteries and veins and help to push blood along
Skeletal muscles in the legs and arms help to push blood along veins back to the heart
Valves present in veins help to prevent blood flowing backwards thus preventing pooling of blood in the extremities

9. The Heart
Located slightly to the left of the sternum between the lungs above the diaphragm
Composed of cardiac muscle (doesn’t fatigue as easily as skeletal or smooth muscle)
Size of clenched fist

10. INTERNAL STRUCTURE OF THE HUMAN HEART
(Fig. 27.9
p 261)

11. Double Circulation
In the heart there is two separate pumps – one on the right and one on the left – separated by the septum
Double circulation in the human is necessary in order to keep deoxygenated (right-side) blood separate from oxygenated blood (left-side)
The two circuits are called:
Pulmonary circuit
Systemic circuit

12. Blood Flow Through the Pulmonary Circuit
Deoxygenated blood enters right atrium from the superior and inferior vena cavae which have carried blood from the upper and lower bodies, respectively
Right atrium contracts and blood flows through the tricuspid valve
Blood then enters right ventricle which in turn contracts
Right ventricular contraction causes the tricuspid valve to close and the semi-lunar valve to open and blood flows in the pulmonary artery
The pulmonary artery carries blood to the lungs to become re-oxygenated as the blood flows through the capillaries that surround the alveoli

13. Blood Flow Through the Systemic Circuit
Oxygenated blood is carried from the lungs via the pulmonary veins to the left atrium
Blood enters the left atrium and the left atrium contracts forcing blood through the bicuspid valve
Blood then enters left ventricle which in turn contracts more strongly than the right ventricle but at the same time
Left ventricular contraction causes the bicuspid valve to close and the semi-lunar valve to open and blood flows into the aorta
The aorta carries the blood to the head, upper body, and lower body to deliver oxygen and nutrients

14. Coronary Artery
Cardiac muscle itself needs oxygen and nutrients in order to continue pumping
Therefore, the heart itself is supplied with blood via a small branch from the aorta
The coronary arteries splits up into many arterioles and capillaries that perfuse through the heart muscle
These capillaries then drain into venules and into the coronary veins which eventually drain back directly into the right atrium

15. The Hepatic Portal System
The hepatic portal system begins in the capillaries of the digestive system and ends in the portal vein – it does not connect directly to the heart
Consequently, portal blood contains substances absorbed by the stomach and intestines
Portal blood is passed through the hepatic lobules where nutrients are absorbed and toxins are excreted or detoxified

16. Detailed Study of the Heart Beat
The heart beat is controlled entirely by the pacemaker – which is a bundle of specialised nervous tissue located in the top of the right atrium
The pacemaker is also called the sino-atrial (SA) node
Pacemaker sends out regular nervous impulses which travel along the axons of the nerve cells out through the walls of the atria – this causes the atria to contract
Atrial contraction is also called atrial systole

17. Detailed Study of the Heart Beat (cont.)
The impulse from the SA node travels via axons to the atrio-ventricular (AV) node – located further down in the right atrium
This sets up an impulse that travels from the AV node down nerve fibres through the ventricular muscle causing the ventricles to contract – also called ventricular systole

18. Detailed Study of the Heart Beat (cont.)
The rate at which the SA node fires can be controlled by various factors:
Exercise
Temperature
Emotion
Shock

19. Heart Sounds
Sound of the heart beat is caused by the opening and closing of the valves of the heart
The “lub” sound is caused by the closing of the tricuspid and bicuspid valves closing and the semi-lunar valves opening as the ventricles contract
The “dub” sound is caused by the semi-lunar valves closing as the ventricles relax

20. Pulse
A pulse is the pressure the flowing blood exerts on the walls of an artery causing the walls of the artery to expand
Pulse can be felt most easily on the wrist or on the neck
Pulse rate (pulses/min) is an indicator of heart rate (heart beats/min)
Average heart rate is 72 bpm in an adult

21. Blood Pressure
Blood pressure is given as a large number over a usually smaller number, e.g. 120/80 mmHg would be a normal blood pressure reading for a healthy adult
The larger number is the systolic pressure – which is the pressure the blood exerts on the walls of an artery the moment the blood passes through
The smaller number is the diastolic pressure – which is the pressure the blood exerts on the walls of the artery the moment there is no movement of blood
Blood pressure is measured using a sphygmomanometer

22. Blood Pressure (continued)
Drugs that reduce blood pressure and hence heart rate are:
Anti-hypertensives: stimulate vasodilation where the smooth muscle surrounding all the blood vessels relax and the blood vessels widen thereby reducing blood pressure
Diuretics: stimulate loss of water from the blood by closing the pores present in the collecting duct of nephrons – therefore water is NOT reabsorbed into the blood – if there is reduced blood volume this reduces blood pressure and also heart rate
Beta-blockers: act on the pacemaker of the heart directly reducing its rate

23. Effects of Smoking, Diet, and Exercise on the Circulatory System
Nicotine, present in all cigarettes, is an extremely addictive chemical that causes increased heart rate and blood pressure by causing arteries and arterioles to narrow (vasoconstriction)
Diet:
Diet high in saturated fat and cholesterol causes increased risk of blockages in the arteries and arterioles (caused by atherosclerosis [fatty deposits in blood vessels]) – the main cause of heart attacks and strokes

24. Effects of Smoking, Diet, and Exercise on the Circulatory System (cont
Causes the heart to beat faster and stronger thereby causing the heart muscle to increase in size
Improves circulation by stimulating formation of more capillaries – thereby indirectly reducing blood pressure
Increases the body’s ability to use oxygen – therefore the heart does not have to work as hard at rest
Reduces body weight – thereby reducing blood pressure as the heart does not have to work as hard to pump blood