2/25/08 Blood Vessels Chapter 19 – Day 1

2/25/08 Blood Vessel Structure Fig. 19.1

2/25/08 Blood Vessels - Intro  Blood vessels are essentially a “pipeline” to: ♦Carry blood TO parts of the body = arteries ♦Carry blood BACK FROM parts of the body = veins  Subdivisions ♦Pulmonary blood vessels: blood to the lungs and back ♦Systemic blood vessels: blood to and from the rest of the body

2/25/08 Blood Vessels - Intro  Veins = mostly deoxygenated – except pulmonary vein & umbilical vein  Arteries = mostly oxygenated – except pulmonary artery & umbilical artery  Capillaries = interconnecting vessels ♦Enable gas exchange, etc.  Blood vessel structure and comparison activity in lab

2/25/08 Blood Vessel Structure Fig. 19.1

2/25/08 Arteries vs. Veins - Similarities 3 Layers  Tunica Externa ♦Connective Tissue  Tunica Media ♦Smooth muscle cells ♦Elastic fibers (arteries) ♦Collagen fibers  Tunica Interna ♦Elastic layer ♦Endothelial cells & connective tissue with elastic fibers (arteries)

2/25/08 Arteries vs. Veins  Arteries are thick walled  Larger arteries have more elastic fibers ♦Tunica media – thicker, concentric & longitudinal ♦Tunica interna – internal elastic membrane  ARTERIES ♦Elasticity Ability to stretch when full = high pressure Return to their original state when relaxed ♦Contractability More smooth muscle (than veins) Vasodilation, Vasoconstriction  Both veins & large arteries need O2 – supplied by vaso vasorum

2/25/08 Arteries vs. Veins  Hierarchy of organization ♦(learn examples from text)  Largest vessels coming out of heart or to heart  These carry the most volume ♦If arteries – they have the highest pressure  Diagram on board and Fig  Be able to work though these – know order and characteristics

2/25/08 Blood Vessel Hierarchy Fig. 19.2

2/25/08 Capillaries Fig. 19.5

2/25/08 Arteries vs. Veins  Different jobs and different driving forces  Arteries ♦Force of contraction pushes blood forward ♦Blood pressure = driving force ♦Moves downhill to lower extremities - gravity  Veins ♦Lower extremities to heart = against gravity ♦Low pressure ♦Relies on other driving forces

2/25/08 Veins  Two features help to push blood forward: ♦Valves – keep blood from flowing backward (flow is possible in 1 direction only) ♦Skeletal muscle contraction Helps to push blood forward ♦Breathing action Pressure in chest helps venous flow ♦All contribute to venous return Fig. 19.6

2/25/08 Blood vessel function  Ultimately blood delivers O 2 & nutrients to tissues as well as removing wastes  How does this happen?  Any organ: ♦Blood vessels (in & out): arteries – smallest branch = capillary ♦The organ is infused with capillaries ♦Nutrient exchange occurs at this level  In the capillaries – only the endothelial layer is present  Substances in the capillaries move to the Interstitial Fluid → then into cells

2/25/08 O 2, Nutrient, and Waste Exchange  Waste products are released into the interstitial fluid  Waste products are then taken up by fenestrated capillaries because they are typically large molecules (recall differences between fenestrated & continuous capillaries) Fig. 19.4

2/25/08 O 2, Nutrient, and Waste Exchange  Exchange between blood and interstitial fluid 1.Simple (& Facilitated) Diffusion: ♦In response to a concentration gradient 2.Filtration ♦Force pushes out substances – based on pressure 3.Osmosis ♦Reabsorption of water

2/25/08 Diffusion  Ions and small organic molecules (glucose, amino acids, urea – move through pores in fenestrated capillaries or move via diffusion between endothelial cells of adjacent capillaries  Ions (Na+, K, etc.) diffuse across endothelial cells by passing through channels in cell membranes  Large water-soluble compounds can only work enter or leave blood stream via fenestrated capillaries  Lipids (FAs, steroids) and lipid-soluble compounds (esp. CO2, O2) cross capillary walls by diffusion through endothelial cell membranes  Plasma proteins can only diffuse through in sinusoids (such as those in the liver)

2/25/08 Filtration  Driving force = PRESSURE in capillary = Capillary Hydrostatic Pressure (CHP)  Water is forced across a capillary wall and small solutes travel with the water ♦Through endothelial cells or pores of fenestrated capillaries Fig

2/25/08 Reabsorption  Occurs as a result of osmosis ♦Diffusion of water across selectively permeable membrane Remember, water molecules move toward soln with higher solute concentration  Process by which dissolved solutes is moved  Osmotic pressure = amount of pressure that must be applied to prevent osmotic movement across a membrane ♦BCOP = blood colloid osmotic pressure = osmotic pressure of blood  Remember…hydrostatic pressure forces water OUT of solution, whereas osmotic pressure draws water INTO a solution

2/25/08  Pressures have to be balanced so that fluid in and out can be coordinated Fig

2/25/08 Filtration & Reabsorption  If BHP > BOP in the blood vessel, fluid is pushed out  If BHP < BOP fluid enters in  IFHP & IOP – low & stable because there are fewer proteins in interstitial fluid  Net Filtration Pressure is the difference between the net hydrostatic pressure and the net osmotic pressure: ♦Net filtration = net hydrostatic – net colloid pressurepressure osmotic pressure  If positive fluid moves OUT of capillary  If negative fluid moves INTO capillary

2/25/08 Equilibrium  Analogy to filtration experiment ♦Charcoal = cells & proteins ♦CuSO 4 = nutrients & O 2  Cells & Proteins remain in blood vessel  H 2 O, hormones, other chemicals, nutrients, O2, glucose, ions = pushed out  Equilibrium between arterial & venus ends maintains proper pressure differences  Excess fluid expelled into tissues causes an increase in interstitial fluid – if in excess, causes EDEMA ♦Excess fluid buildup, swollen ankles, etc Read in book and follow handout

2/25/08 Equilibrium  Equilibrium between arterial & venus ends maintains proper pressure differences  Excess fluid expelled into tissues causes an increase in interstitial fluid – if in excess, causes EDEMA ♦Excess fluid buildup, swollen ankles, etc Read in book and follow handout  Different demands for gas and nutrient exchange  For proper delivery – the cardiovascular system depends on: 1. Cardiac Output 2. Peripheral Resistance 3. Blood Pressure

2/25/08 Equilibrium  Different demands for gas and nutrient exchange  For proper delivery – the cardiovascular system depends on: 1. Cardiac Output 2. Peripheral Resistance 3. Blood Pressure

2/25/08 Equilibrium  Need constant control of these factors to maintain homeostasis = CARDIOVASCULAR REGULATION  Controlled by ♦Autoregulation Mechanisms Local factors change pattern of blood flow w/in capillary beds Response to chemical changes in interstitial fluids ♦Neural Mechanisms Respond to changes in arterial pressure or blood gas a specific site stimulates cardiovascular centers of ANS ♦Endocrine Mechanisms Releases hormones that enhance short-term adjustments and direct long-term changes in cardiovascular performance

2/25/08 Equilibrium

2/25/08 Auto Regulation  Local changes ♦Sphincters near capillaries are adjusted ♦Depend on local VASODILATION & VASOCONSTRICTION chemicals (nitrous oxide) – know examples from text (p 547) Vasodilator: factor(s) that promote the dilation of precapillary sphincters Local vasodilators act at the tissue level & accelerate blood flow through the tissue of origin

2/25/08 Neural Mechanisms  Neural Mechanisms ♦Sympathetic division controls… Smooth muscle tone (vasomotor tone) Increased sympathetic impulses (  vasoconstriction) Decreased sympathetic impulses (  vasodilation) ♦Receptors

2/25/08 Capillaries Fig. 19.5