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Lecture 2 The cardiovascular system includes two circuits: 1. Pulmonary circuit Circulates blood through the lungs 2. Systemic circuit Circulates blood to the tissues of the body The heart beats to circulate blood throughout the body Blood Pressure: the pressure of blood against the wall of the blood vessel Blood pressure measured with a SPHYGMOMANOMETER. SYSTOLIC BLOOD PRESSURE: the highest arterial pressure reached during ejection of blood from the heart. DIASTOLIC BLOOD PRESSURE: lowest arterial pressure, occurs while ventricles relax. Normal resting blood pressure is 120 mm Hg over 80 mm Hg in brachial artery of arm (120/80) Because there are many more capillaries than arterioles, blood moves very slowly. This allows for substance exchange between the blood and surrounding tissues. Arteries Arterioles Capillaries Veinules Veins Blood velocity is inverse to the total cross-sectional area of blood vessels! (As area up, vel down) In the capillary beds, fluid is exchanged between the blood and tissue. Three forces control movement of fluid and other substances: a. Osmotic pressure (due to relatively low water concentration of blood) tends to cause water to move from tissue fluid to blood. b. Blood pressure (due to heart) tends to cause water to move from blood to tissue fluid. c. Diffusion (due to concentration gradients) allows materials to cross capillary walls At the arteriole end of the capillary: blood pressure (40 mm Hg) is greater than osmotic pressure (25 mm Hg) filtration occurs: water, small molecules (amino acids, glucose, oxygen) are forced out, while blood cells and plasma proteins remain inside vessels tissue fluid (plasma without plasma proteins) is formed BP and OP are about equal molecules follow their diffusion gradients as diffusion occurs concentration of O2 and nutrients (amino acids, glucose) is always greater in the blood, so they diffuse out into tissue concentration of CO2, H2O and wastes are greater in tissues, so they diffuse into the blood BP (10 mm HG) is less than OP (25 mm HG) water not moves back into blood all water moves into the blood excess fluid is taken up by the LYMPHATIC CAPILLARIES and becomes LYMPH lymph is eventually returned to the blood Waste waste molecules molecules CO CO2 WATER Water amino acids Amino acids WATER Water O O22 GLUCOSE Glucose 2 Blood pressure in veins in minimal Instead of blood pressure, venous return depends on: 1. Skeletal muscle contractions 2. Valves in the veins 3. Respiratory movement When the skeletal muscles contract, they compress the weak walls of the veins and pushes the blood through the valves. Once blood is forced past the valves in the veins, it cannot flow backwards. When a person inhales, the thoracic pressure falls and abdominal pressure rises. This helps blood flow back to the heart because blood flows in the direction of reduced pressure. is a liquid connective tissue which has different types of cells suspended in fluid. Blood 1. 2. 3. 4. Maintaining homeostasis. For transport (of gases, hormones, wastes, nutrients) Clotting (seal injuries) Fight infections. If allowed to sit in a test tube without clotting, blood will divide into TWO MAIN PARTS: A. PLASMA (liquid portion – 55% of blood) B. FORMED ELEMENTS (solid portion – 45%) Yellowish fluid Contains water and dissolved organic and inorganic substances (proteins, gases, salts, nutrients, wastes) The composition of mammalian plasma Plasma 55% Constituent Water Major functions Solvent for carrying other substances Icons (blood electrolytes Sodium Potassium Calcium Magnesium Chloride Bicarbonate Osmotic balance pH buffering, and regulation of membrane permeability Separated blood elements Plasma proteins Albumin Osmotic balance, pH buffering Fibringen Clotting Immunoglobulins (antibodies) Defense Substances transported by blood Nutrients (such as glucose, fatty acids, vitamins) Waste products of metabolism Respiratory gases (O2 and CO2) Hormones Figure 42.15 Consists of: a. RED BLOOD CELLS (ERYTHROCYTES) - over 95% of formed elements - transports O2 - formed in bone marrow b. WHITE BLOOD CELLS (LEUKOCYTES) - fight infection - formed in bone marrow & lymphoid tissue c. PLATELETS (THROMBOCYTES) - function in blood clotting.