BIOL 244 Lecture 13 (October 7)Chapter 19 Blood Vessels Circulatory route Simplest and most common route Heart arteriesarteriolescapillariesvenulesveins Passes through only one network of capillaries from the time it leaves the heart until the time it returns Portal system Blood flows through 2 consecutive capillary networks before returning to heart- Between hypothalamus and anterior pituitary- In kidneys- Between intestines to liver Anastomoses Anastomosis- point where 2 blood vessels merge Arteriovenous anastomosis (shunt)- artery flows directly into vein bypassing capillaries Venous anastomosis Most common One vein empties directly into another Reason vein blockage less serious than an arterial blockage Arterial anastomosis 2 arteries merge Provides collateral (alternative) routes of blood supply to a tissue Coronary circulation and around joints Principles of blood flow Blood supply to a tissue can be expressed in terms of flow & perfusion Blood flow- the amount of blood flowing through an organ, tissue, or blood vessel in a given time (ml/min) At rest, total flow is quite constant, & is equal to the cardiac output (5.25L/min) Important for delivery of nutrients & oxygen, and removal of metabolic wastes Hemodynamics Physical principles of blood flow based on pressure & resistance- F is proportion to difference in pressure/resistance to flow- The greater the pressure difference between 2 points, the greater the flow; the greater the resistance the less the flow Blood pressure- the force that blood exerts against a vessel wall Measured at brachial artery of arm using sphygmomanometer.  Normal value 120/75 mm Hg Determined by cardiac output, blood volume, & peripheral resistance Systolic pressure: peak arterial BP taking during ventricular contraction Diastolic pressure: minimum arterial BP taken during ventricular relaxation Pulse pressure: difference between systolic & diastolic pressure Mean Arterial Pressure (MAP): diastolic pressure + 1/3 of pulse pressure Vasomotion is a quick & powerful way of altering blood pressure & flow Local control Neural control Hormonal control Capillary exchange The most important blood in the body is in the capillaries Only through capillary walls are exchanges made between the blood and surrounding tissues Capillary exchange- two way movement of fluid across capillary walls Water, oxygen, glucose, amino acids, lipids, minerals, antibodies, hormones, wastes, carbon dioxide, ammonia Mechanisms involved Diffusion, osmosis, transcytosis, filtration, & reabsorption Mechanisms of venous return Venous return- the flow of blood back to the heart Pressure gradient- blood pressure is the most important force in venous return Gravity drains blood from head & neck Skeletal muscle pump in the limbs Contracting muscle squeezed out of the compressed part of the vein Thoracic (respiratory) pump Inhalation- thoracic cavity expands & thoracic pressure decreases, abdominal pressure increases forcing blood upward- Central venous pressure fluctuates 2 mm Hg inhalation, 6 mm Hg exhalation Blood flows faster with