1. Arteries - Carry Blood Away from Heart
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Anatomy Lecture Objectives Chapter 19 Chapter 19 - Vascular System 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 B. wall structure - most blood vessel walls have 3 layers lumen = space inside vessel 1. tunica intima / tunica interna endothelium - simple squamous e. subendothelial layer - loose c.t. (collagen) 2. tunica media a. smooth muscle - cells circularly arranged controlled by ANS and chemical factors constriction (smooth muscle contracts) decreases blood flow and increases systemic blood pressure dilation (smooth muscle relaxes) increases blood flow and decreases systemic blood pressure b. elastic c.t. 3. tunica adventitia / tunica externa c.t. attaches vessel to surrounding structures vasa vasorum nourish outer part of vessel wall Strong/Fall 2008 page 1 Anatomy Lecture Objectives 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 2. muscular - middle-sized arteries, distal to elastic 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 3. arterioles - smallest arteries tunica media contains smooth m. only diameter controlled by ANS and chemical messengers diameter determines blood flow and blood pressure 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 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 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 Strong/Fall 2008 page 2 Anatomy Lecture Objectives Chapter 19 d. low-permeability capillaries 2. capillary beds metaarteriole thoroughfare channel venule capillaries precapillary sphincter - smooth m. cell wrapped around origin of capillary controls blood flow through capillaries when sphincter is closed, blood is diverted to thoroughfare channel sphincter controlled by autoregulation (local control, not nervous system) 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 F. a vascular anastomosis occurs when vessels join midstream anastomoses provide alternate pathways (collateral channels) Strong/Fall 2008 page 3 Anatomy Lecture Objectives 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 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 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 Strong/Fall 2008 page 4 Anatomy Lecture Objectives Chapter 19 a. circulatory pathways of the brain (cerebral arterial circle, circle of Willis) anterior communicating a. anterior cerebral a. internal carotid a. posterior communicating a. posterior cerebral a. basilar a. vertebral a. cross section of neck: Strong/Fall 2008 page 5 Anatomy Lecture Objectives Chapter 19 b. hepatic portal circulation portal system = two capillary beds in series, joined by veins or arteries 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 hepatic portal vein liver liver sinusoids hepatic veins inferior vena cava Strong/Fall 2008 page 6 Anatomy Lecture Objectives Chapter 19 c. fetal circulation placenta = organ formed from extra-embryonic membranes and endometrium to exchange materials between fetal and maternal blood 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 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 a. foramen ovale – opening in interatrial septum that allows blood to go from the right atrium directly into the left atrium b. ductus arteriosus – vessel that connects pulmonary trunk and aorta Strong/Fall 2008 page 7 .