Chapter 19 – Vascular System BIOL 2304 Fall 2008 Chapter 19

A. categories and general functions: 1. arteries - carry blood away from heart 2. capillaries - allow exchange of materials between blood and tissue fluid 3. veins - return blood to heart BIOL 2304 Fall 2008 Chapter 19

BIOL 2304 Fall 2008 Chapter 19

most vessel walls have 3 layers B. wall structure most vessel walls have 3 layers lumen = space inside vessel 1. tunica intima / tunica interna endothelium – simple squamous e. subendothelial layer – loose c.t. (collagen) BIOL 2304 Fall 2008 Chapter 19

a. smooth muscle - cells circularly arranged 2. tunica media a. smooth muscle - cells circularly arranged controlled by ANS and chemical factors constriction decreases blood flow and increases systemic blood pressure dilation increases blood flow and decreases systemic blood pressure b. elastic c.t. BIOL 2304 Fall 2008 Chapter 19

3. tunica adventitia / tunica externa c.t. attaches vessel to surrounding structures vasa vasorum nourish outer part of vessel wall BIOL 2304 Fall 2008 Chapter 19

C. arteries 1. elastic (conducting) - large arteries near heart (aorta and major branches) * conduct blood to muscular arteries * low resistance * tunica media = circular elastin sheets with few smooth m. cells * recoil maintains blood pressure during diastole BIOL 2304 Fall 2008 Chapter 19

2. muscular - middle-sized arteries, distal to elastic arteries * tunica media very thick; much smooth m. and some elastin * regulate blood flow to organs * have an internal and an external elastic lamina BIOL 2304 Fall 2008 Chapter 19

3. arterioles - smallest arteries * tunica media contains smooth m. only * diameter controlled by ANS and chemical messengers * diameter determines blood flow and blood pressure BIOL 2304 Fall 2008 Chapter 19

D. capillaries * wall consists of endothelium and basal lamina (no tunica media or externa) * 8 to 10 mm in diameter * join and branch to form capillary beds * cells are joined at spots around perimeter by tight junctions and desmosomes * intercellular clefts are spaces between cells BIOL 2304 Fall 2008 Chapter 19

a. fenestrated capillaries (high permeability) 1. types a. fenestrated capillaries (high permeability) * have fenestra (openings) in endothelial cells * some fenestra are covered by a membrane, others are not * also have intercellular clefts * found in small intestine, synovial joints, kidney BIOL 2304 Fall 2008 Chapter 19

b. continuous capillaries * intercellular clefts but no fenestra * most common type c. sinusoids * wide, leaky capillaries, usually fenestrated * fewer cell junctions * allow passage of large particles * found in bone marrow, spleen, liver BIOL 2304 Fall 2008 Chapter 19

d. low-permeability capillaries * complete tight junctions * no fenestra, no clefts * restricted transport vesicles * can transport specific molecules in or out * found in brain (blood-brain barrier) BIOL 2304 Fall 2008 Chapter 19

* controls blood flow through capillaries 2. capillary beds precapillary sphincter - smooth m. cell wrapped around origin of capillary * controls blood flow through capillaries * sphincter controlled by autoregulation * when sphincter is closed, blood is diverted to thoroughfare channel BIOL 2304 Fall 2008 Chapter 19

E. veins have thinner walls than arteries for the same diameter (larger lumen) act as capacitance vessels - store extra blood (65%) low pressure tunica adventitia thicker than tunica media venous valves prevent backflow BIOL 2304 Fall 2008 Chapter 19

F. vascular anastomosis occurs when vessels join midstream anastomoses provide alternate pathways (collateral channels) BIOL 2304 Fall 2008 Chapter 19

G. circulatory routes 1. pulmonary circuit: right ventricle to lungs to left atrium * pressure supplied by right ventricle * low pressure system * takes low oxygen blood (75% saturated) to lungs and brings high oxygen (98% saturated) blood back to heart BIOL 2304 Fall 2008 Chapter 19

pulmonary semilunar valve pulmonary trunk right ventricle pulmonary semilunar valve pulmonary trunk left and right pulmonary arteries lobar arteries (3 R, 2 L) take blood to lung lobes pulmonary capillaries pulmonary veins (superior and inferior, L and R) left atrium BIOL 2304 Fall 2008 Chapter 19

2. systemic circuit: left ventricle to body to right atrium * pressure supplied by left ventricle * high pressure system * takes O2 to tissues and removes CO2 * distributes nutrients from digestive tract to body * collects wastes and takes them to kidney for excretion BIOL 2304 Fall 2008 Chapter 19

a. circulatory pathways of the brain (cerebral arterial circle, circle of Willis) BIOL 2304 Fall 2008 Chapter 19

anterior communicating a. anterior cerebral a. internal carotid a. posterior communicating a. posterior cerebral a. basilar a. vertebral a. BIOL 2304 Fall 2008 Chapter 19

cross section of neck: BIOL 2304 Fall 2008 Chapter 19

b. hepatic portal circulation portal system = two capillary beds in series, joined by veins or arteries BIOL 2304 Fall 2008 Chapter 19

BIOL 2304 Fall 2008 Chapter 19

capillaries of small intestine, part of large intestine and stomach superior mesenteric vein capillaries of spleen, stomach and pancreas splenic vein capillaries of distal large intestine and rectum inferior mesenteric vein BIOL 2304 Fall 2008 Chapter 19

hepatic portal vein liver liver sinusoids hepatic veins inferior vena cava BIOL 2304 Fall 2008 Chapter 19

c. fetal circulation placenta = organ formed from extra-embryonic membranes and endometrium to exchange materials between fetal and maternal blood the umbilical veins take high-oxygen and high-nutrient blood from the placenta to the fetus the umbilical arteries take low-oxygen, high-waste blood back to the placenta BIOL 2304 Fall 2008 Chapter 19

umbilical vein from placenta   fetal liver hepatic portal vein ductus venosus   inferior vena cava right atrium foramen ovale left atrium right ventricle left ventricle pulmonary trunk ductus arteriosus aorta lungs   internal iliac a. umbilical a. to placenta BIOL 2304 Fall 2008 Chapter 19

1) to bypass the fetal liver adaptations: 1) to bypass the fetal liver ductus venosus - allows some umbilical vein blood to go through the fetal liver but diverts most of it directly into the inferior vena cava 2) to bypass the non-functional fetal lungs foramen ovale – opening in interatrial septum that allows blood to go from the right atrium directly into the left atrium ductus arteriosus – vessel that connects pulmonary trunk and aorta BIOL 2304 Fall 2008 Chapter 19

BIOL 2304 Fall 2008 Chapter 19