Cardiovascular System - Vascular System

Blood & blood vessels What are the components of blood? Plasma – Pale yellow, 90% Water, 8% Protein, 2% Salts Red Blood Cells – Iron rich Haemoglobin combines with oxygen & transported in blood White Blood Cells – Fight infection and disease Platelets – Assist in clotting blood

Functions of blood What are the functions of blood? Transport nutrients such as Glucose and Oxygen whilst removing waste such as Carbon dioxide & Lactic Acid Protect and fight disease through lymphatic system Maintain Homeostasis including temperature regulation, and acid base pH balance

Blood Viscosity A term used to describe the relative thickness of the blood. If the blood is very viscous, it has a high amount of blood cells to plasma and consequently does not flow very quickly Training brings about an increase in total blood volume but the increase in plasma levels is proportionally higher therefore blood viscosity decreases, so faster oxygen delivery to working muscles

The Circulatory System This system is referred as a double circulatory system: Pulmonary system – blood between heart and lungs Systemic system – blood between heart and rest of the body

Blood Vessels The vascular network through which blood flows to all parts of the body comprises of arteries, arterioles, capillaries, venules and veins. Arteries and Arterioles Arteries are high pressure vessels which carry blood from the heart to the tissues. The largest artery in the body is the aorta which is the main artery leaving the heart. The aorta constantly subdivides and gets smaller. The constant subdivision decreases the diameter of the vessel arteries, which now become arterioles. http://www.youtube.com/watch?v=qcgcACrNLIk&feature=related

Arteries Arteries are composed of three layers of tissue: 1 an outer fibrous layer — the tunica adventitia or tunica externa 2 a thick middle layer — the tunica media 3 a thin lining of cells to the inside — the endothelium or tunica interna. The tunica media is comprised of smooth muscle and elastic tissue, which enables the arteries and arterioles to alter their diameter.

Arteries Arteries tend to have more elastic tissue, while arterioles have greater amounts of smooth muscle; this allows the vessels to increase the diameter through vasodilation or decrease the diameter through vasoconstriction. It is through vasoconstriction and vasodilation that the vessels can regulate blood pressure and ensure the tissues are receiving sufficient blood — particularly during exercise.

Arteries and arterioles have three basic functions: • to act as conduits carrying and controlling blood flow to the tissues • to cushion and smooth out the pulsate flow of blood from the heart • to help control blood pressure.

Veins and venules Veins are low pressure vessels which return blood to the heart. The structure is similar to arteries, although they possess less smooth muscle and elastic tissue. Venules are the smallest veins and transport blood away from the capillary bed into the veins. Veins gradually increase in thickness the nearer to the heart they get, until they reach the largest vein in the body, the venae cavae, which enters the right atrium of the heart.

Veins and Venules The thinner walls of the veins often distend and allow blood to pool in them. This is also allowed to happen as the veins contain pocket valves which close intermittently to prevent back flow of blood. This explains why up to 70% of total blood volume is found in the venous system at any one time.

Capillaries Capillaries are the functional units or the vascular system. Composed of a single layer of endothelial cells, they are just thin enough to allow red blood cells to squeeze through their wall. The capillary network is very well developed as they are so small; large quantities are able to cover the muscle, which ensures efficient exchange of gases.

Capillaries If the cross-sectional area of all the capillaries in a muscle cell were to be added together, the total area would be much greater than that of the aorta. Distribution of blood through the capillary network is regulated by special structures known as pre-capillary sphincters, the structure of which will be dealt with later in this chapter.

Veins Before looking at venous return it is important to look at the structure of veins. Veins have thinner walls than arteries. Veins also have valves.

Venous return mechanism’s The pressure of blood in the veins is too low to push blood back to the heart. This problem is overcome in a number of ways. Hydrostatic Pressure Gravity Action of the Heart Inspiration Pocket Valves Adjacent Arteries Skeletal Pump

Skeletal Pump The muscles surrounding the veins expand and contract, pressing on veins and causing a pumping effect. This muscle action is particularly important in maintaining venous return during exercise. It is referred to as the skeletal pump. Contracting skeletal muscles press against veins Blood is forced through one-way venous valves

Adjacent Arteries The surges of pressure in the adjacent arteries cause them to push against the veins, creating a regular pumping effect.

Pocket Valves The blood in the veins can only move towards the heart; It cannot fall back to where it came from. This is because at regular intervals there are semi lunar pocket valves situated in large veins.

Pocket Valves These allow the free flow of blood towards the heart, but they close to prevent blood towards the heart, but they close to prevent blood flowing away from the heart. Affect of gravity – This causes a ballooning of the veins, and is called venous pooling. If this is repeated over long periods of time, the result is a breakdown of the valves and changes in the vein walls commonly called varicose veins.

Inspiration Increases thoracic volume, and so decreases thoracic pressure. The vein in this region expand, causing blood to be ‘sucked’ through them. During inspiration – Pressure decreases in thoracic cavity Pressure increases in abdominal cavity, squeezing abdominal veins Result – unequal pressure creates an upward “sucking” effect that pulls blood towards the heart.

Gravity Gravity assists the flow of venous blood from body parts above the heart. However, it also hinders the flow from parts below the heart.

Action of the Heart The pumping action of the heart causes blood to flow in to replace the blood pumped out. This creates a sucking action in the veins close to the heart.

Hydrostatic Pressure There is an attraction between the molecules in any fluid moving in a particular direction, and this attraction helps maintain the constant flow. This is called hydrostatic pressure. This is important in blood, particularly as the fluid column moves back, against gravity, to the heart.

Summary The pressure of blood in the veins is too low push blood back to the heart. This problem is overcome in a number of ways. Hydrostatic Pressure Gravity Action of the Heart Inspiration Pocket Valves Adjacent Arteries Skeletal Pump

Blood Pressure

Learning Objective To understand how you take blood pressure To identify what an average pressure reading is and the units its displayed in To understand how blood pressure is controlled and how exercise effects it

Success Criteria You can define blood pressure giving an average reading with the correct units You can take someone's blood pressure accurately You can explain how the body controls blood pressure and how exercise effects it

Home Learning What is a sphygmomanometer used for? What is the average reading of a Sphygmomanometer? What part of the body controls this reading? What two factors influence the reading? TAKING BLOOD PRESSURE 120MMHG/80MMHG VASOMOTOR CONTROL CENTRE – MEDULLA OBLONGATTA IN THE BRAIN Cardiac output & Blood viscosity

Blood Pressure Controlled by the Vasomotor Centre (medulla oblongata in brain) Blood pressure is the force exerted by the blood against the walls of the blood vessels. It is necessary to maintain blood flow though the circulatory system It is determined by two main factors – Cardiac Output – the volume of blood flowing into the system from the left ventricle. Resistance to flow – the impedance offered by the blood vessels to the blood flow.

Blood Pressure Blood pressure = cardiac output x resistance Therefore, blood pressure increases when either cardiac output or resistance increases. Blood pressure in the arteries also increases and decrease in a pattern which corresponds to the cardiac cycle during ventricular systole, when blood is pumped into the aorta and lowest during ventricular diastole.

Blood Pressure Measurement BP is usually measured a the brachial artery using a sphygmomanometer, and is recorded as mmHg of systolic pressure over diastolic pressure: SYSTOLE pressure is experienced when the heart pumps blood into the system DIASTOLIC pressure is recorded when the heart is relaxing and filling with blood. Typical Reading = 120mmHg 80mmHg http://www.youtube.com/watch?v=u6saTO8_o2g

Blood Pressure and Exercise BP Changes during exercise. During Aerobic exercise, the systolic pressure increases as a result of increased cardiac output, while diastolic pressure remains constant, or in well trained athletes may even drop as blood feeds into the working muscles. During isometric or anaerobic exercise both systolic and diastolic pressure rise significantly due to increased resistance of the blood vessels.

PRACTICAL DEMO In pairs you are going to take each others blood pressure using a more current Sphygmomanometer. These are digital and are almost as accurate as the original but are easier to use as you do not have to listen for the pulse. http://www.youtube.com/watch?v=4TkWagnP8pg