The Cardiovascular System: Blood Vessels and Circulation Chapter 16

5 Types of Vessels Arteries Arterioles Capillaries Venules Veins Carry blood away from the heart to body tissues Aorta and pulmonary trunk Arterioles Within a tissue or organ branch into numerous microscopic vessels called capillaries Capillaries Groups of capillaries reunite to form small veins: Venules Merge to form larger vessels: Veins Blood vessels that carry blood from the tissues back to the heart Blood reservoirs Certain veins function as reservoirs b/c contain so much of blood

Arteries and Arterioles Arteries have 3 tissue layers surrounding lumen (hollow space) Endothelium Inner layer composed of simple squamous epithelium, a basement membrane, and elastic tissue (internal elastic lamina) Middle layer: smooth muscle and elastic tissue Outer layer: mainly of elastic and collagen fibers Vasoconstriction Decrease in diameter of the lumen of a blood vessel Increase in sympathetic stimulation

Arteries and Arterioles Vasodilation Decrease in sympathetic stimulation Increase in lumen diameter Elastic arteries High proportion of elastic fibers Help propel blood while ventricles are relaxing b/c relax Stretch when blood ejected from heart Ex. Aorta and braciocephaliic, common carotid, subclavian, vertebral, pulmonary, and common iliac arteries Muscular arteries Great vasoconstriction and vasodilation Ex. Brachial artery (arm) and radial artery (forearm)

Arteries and Arterioles A very small, microscopic artery that delivers blood to capillaries Big role in blood flow from arteries  capillaries

Capillaries Are microscopic vessels that connect arterioles to venules Exchange vessels b/c exchange of nutrients and wastes b/w the body’s cells and blood Body tissues w/high metabolic requirements (muscles, liver, kidneys, NS) have many capillary networks

Capillaries Very thin walls, allows many substances to pass through Precapillary sphincters: rings of smooth muscle at the point where capillaries branch from arterioles Numerous, so blood flows slowly through them Capillary exchange: the movm’t of substances into/out of capillaries

Capillary Exchange 1. Diffusion O2, CO2, glucose, amino acids, and hormones by simple diffusion Plasma solutes Sinusoids: gaps b/w endothelial cells in smallest blood vessels in the liver But too large to allow proteins like fibrinogen and albumin to enter bloodstream

Capillary Exchange 2. Bulk flow: filtration and reabsorption Bulk flow: is a passive process by which large numbers of ions, molecules, or particles move together in same direction From area of high pressure  low pressure Continues if pressure difference exists Two opposing pressure drive bulk flow: 1. capillary blood pressure 2. colloid osmotic pressure

Capillary Exchange: Bulk Flow 1. Capillary blood pressure Pressure of blood against the walls of capillaries pushes fluid out of capillaries into interstitial fluid 2. Colloid osmotic pressure Opposing pressure Pulls fluid into capillaries Presence of proteins in plasma and their virtual absence in interstitial fluid gives blood the higher osmotic pressure

Capillaries: Bulk Flow Filtration: water and solute flow out of the blood capillary into the surrounding interstitial fluid via bulk flo Capillary blood pressure higher than blood osmotic pressure for first half of capillary Midway through capillary, pressure drops  reabsorption Reabsorption Water and solutes move via bulk flow from interestitial fluid into the blood capillary

Capillaries: Bulk Flow Autoregulation: the ability of a tissue to automatically adjust its blood flow to match its metabolic demands Regulation of vasodilation and vasoconstriction

Venules and Veins When several capillaries unite  venules Venules: receive blood from capillaries and empty blood into veins return blood to heart

Venules and Veins: Structure Venules = little veins Similar to arterioles Walls thinner near capillary end and thicker towars the heart Veins Structure similar to arteries Outer layer is thickets, and lumen wider than artery In some veins, inner layer folds in = valves (prevent backflow of blood) Varicose veins: due to weak venous valves Blood backflows, causing increase in blood pressure, pushes vein wall outwards Loss of elasticity and stretch

Venous Return The volume of blood flowing back to the heart through systemic veins 1. Contractions of the heart 2. the skeletal muscle pump: (p.395 in leg) 1. while standing, venous valves closer and farther from heart closed, blood flow to heart 2. contraction of leg muscles, compress veins Pushes blood through valve closer to heart  milking At same time, valve farther from heart is uncompressed and closes as blood pushed against it 3. muscle relaxation: pressure falls in compressed section of veins, causes valve closer to heart to close Valve farther from heart opens b/c blood pressure of foot is higher than in leg

Venous Return 3. Respiratory Pump: based on alternating compression an decompression of veins During inhalation the diaphragm moves downward  decrease pressure in thoracic cavity and increase pressure in abdominal cavity abdominal veins compressed greater volume of blood moves from compressed abdominal veins to decompressed thoracic veins and then into right atrium Exhalation: valves in veins prevent backflow of blood from thoracic veins to abdominal veins

Cardiovascular System Circulatory I

Blood Pressure Blood flows from high pressure  low pressure Blood pressure (BP): the pressure exerted by blood on the walls of a blood vessel Highest in aorta and large systemic arteries Falls as distance from left ventricle increases

Resistance Vascular Resistance: opposition to blood flow due to friction b/w blood and the walls of blood vessels Depends on: 1. size of lumen 2. Blood viscosity 3. Total blood vessel length

Vascular Resistance 1. Size of lumen Smaller the lumen, greater is resistance to blood flow Increase in BP

Vascular Resistance 2. Blood viscosity Viscosity (thickness) Higher blood viscosity, higher resistance Increases if dehydration or polycythemia (high number of red blood cells) Decreases if depletion of plasma proteins or RBCs b/c of anemia or hemorrhage decrease BP

Vascular Resistance 3. Total blood vessel length Resistance increases when total length of all blood vessels increases Longer the length  greater contact of blood and vessel wall  causes friction higher BP

Measurement of Blood Pressure: Brachial artery in left arm Device: sphygmomanometer Pressure cuff inflated, artery compressed and blood flow stops Stethoscope below cuff, then cuff deflated

Blood Pressure Systolic Blood Pressure (SBP) First sound as cuff is deflated as artery is opening Force with which blood is pushing against arterial walls during ventricular contraction Diastolic Blood Pressure (DBP) Sounds become faint Represents force exerted by blood remaining in arteries during ventricular relaxation