Introduction to Cardiovascular System PDF

Introduction to Cardiovascular system DR.MOHAMMED ALI ALKAABI Components of the cardiovascular system Distribution system – vessels & blood Pump – the heart Exchange mechanism - capillaries  Blood Transports O2 , metabolic substrates, CO2 and waste products around the body...

Introduction to Cardiovascular system DR.MOHAMMED ALI ALKAABI Components of the cardiovascular system Distribution system – vessels & blood Pump – the heart Exchange mechanism - capillaries  Blood Transports O2 , metabolic substrates, CO2 and waste products around the body There is exchange of these substances between the blood and cells of the body Exchange occurs by diffusion (98%) Substances diffuse between the blood and the surrounding tissue The function of the cardiovascular system is to provide adequate conditions for diffusion to each tissue of the body Where does diffusion take place? Capillaries are the site for diffusion between blood and the tissues Capillaries are composed of a single layer of endothelial cells surrounded by basal lamina  Diffusion Some substances e.g. O 2 and CO 2 are lipophilic and diffuse through the lipid bilayer Other molecules such as glucose, amino acids, and lactate are hydrophilic and diffuse through small pores in the capillaries but prevent movement of mat. with MW. more than 60000. All molecules will move down their concentration gradient Diffusion through capillaries small hydrophilic (lipid insoluble) substance such as glucose diffuse through aqueous pores between endothelial cells  What factors affect diffusion Rate of diffusion depends on: – area – diffusion ‘resistance’ – concentration gradient  Area Rate of diffusion depends on the area available for exchange The area for exchange between capillaries and tissues is generally very large – it depends on capillary density A tissue that is more metabolically active will have more capillaries  Diffusion resistance Resistance to diffusion depends on: – Nature of the molecule e.g. lipophilic or hydrophilic, size – Nature of the barrier e.g. pore size and number of pores for hydrophilic substances – Path length depends on: ✓ capillary density ✓ path is shortest in the most active tissues Diffusion resistance is mostly low  Concentration Gradient rate of diffusion is dependent on the concentration gradient – the greater the concentration gradient the greater the rate of diffusion – the concentration that matters is between capillary blood and tissues for exchange to continue the concentration gradient between the capillary blood and tissues must be maintained  Concentration Gradient a substance which is used by the tissues will have a lower concentration in capillary blood than arterial blood how much lower depends on: ✓ rate tissues use the substance ✓ rate of blood flow through the capillary bed  Maintaining the concentration gradient At any rate of use, the lower the blood flow the lower the capillary concentration The rate of blood flow must be high enough to maintain a sufficient concentration gradient for diffusion i.e. rate of blood flow determines the concentration gradient driving O 2 diffusion into the cells  Supply and Demand blood flow must match the tissues’ metabolic needs – the higher the rate of metabolism the greater the demand for O2 and nutrients – increases in metabolism must be met by increases in blood flow – the rate of blood flow is known as the perfusion rate  Blood flow to different tissues Brain needs a high, constant flow – 0.5 ml.min-1.g-1 Heart muscle needs high flow which increases during exercise – 0.9 to 3.6 ml.min-1.g-1 Kidneys need a high, constant flow – 1.0 ml.min-1.g-1 Blood flow to skeletal muscle can be very high during exercise and gut blood flow is high after a meal Blood flow to different tissues Tissue Min. flow l.min Max. flow l.min Brain 0.75 0.75 Heart 0.3 1.2 Kidneys 1.2 1.2 Gut 1.4 2.4 Muscle 1 16 Skin 0.2 2.5 Others 0.2 0.2 Total 5 24.5  Blood flow must adjust to meet requirements At rest total blood flow is about 5 l.min-1 In exercise this can rise to 25 l.min-1  Regulating blood flow If a pump is just connected to a network of vessels blood will only flow to the parts that are easiest to perfuse The brain is harder to perfuse due to gravity To regulate blood flow you need to add resistance to the system – Reduce the ease with which some regions are perfused to direct blood flow to the more difficult to perfuse regions Arterioles are the resistance vessels  Regulating blood flow If a pump is just connected to a network of vessels blood will only flow to the parts that are easiest to perfuse The brain is harder to perfuse due to gravity To regulate blood flow you need to add resistance to the system – Reduce the ease with which some regions are perfused to direct blood flow to the more difficult to perfuse regions Arterioles are the resistance vessels  Pump Heart is two pumps in a series The left heart pumps blood around the systemic circulation The right heart pumps blood around the pulmonary circulation  The Circulation Heart pumps blood to arteries Arteries supply arterioles Arterioles supply capillaries Capillaries drain into venules Venules drain into veins Veins return blood to the heart  Need for flexibility The total flow in the system has to be able to change. This requires a temporary store of blood which can be returned to the heart at a different rate. Veins have thin walls which can easily distend or collapse enabling them to act as a variable reservoir for blood. The capacitance of the veins provides the temporary store Basics of the circulation Distribution of blood in the CVS 5% 11% 17% 67% veins heart and lungs arteries and arterioles capillaries