Chapter 26: The human circulatory system Leaving Certificate Biology Higher Level

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

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

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

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

Differences between arteries and veins ArteryVein Carries blood away from heart Carries blood toward heart Blood under high pressureBlood under low pressure Thick wallsThin walls Pulse flowSmooth flow Narrow lumenLarge lumen No valvesValves present Blood rich in oxygen (except pulmonary artery) Blood poor in oxygen (except pulmonary veins)

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

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

INTERNAL STRUCTURE OF THE HUMAN HEART (Fig p 261)

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

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

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

Coronary Arteries

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 The portal blood contains substances absorbed by the stomach and intestines

Detailed Study of the Heart Beat

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

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

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

Blood Pressure

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

Effects of Smoking, Diet, and Exercise on the Circulatory System