Blood Vessels1.pptx

Blood Vessels Objectives • Describe the layers that form the wall of a blood vessel and state function of each. • Compare structure and function of 3 types of arteries. • Describe structure and function of veins. • Explain how veins differ from arteries. • Describe the structure and function of a...

Blood Vessels Objectives • Describe the layers that form the wall of a blood vessel and state function of each. • Compare structure and function of 3 types of arteries. • Describe structure and function of veins. • Explain how veins differ from arteries. • Describe the structure and function of a capillary bed. Objectives • Define blood pressure, blood flow and resistance • Locate major blood vessels of the body Blood vessels • Blood is carried in a closed system of vessels that begins and ends at the heart • The three major types of vessels are arteries, capillaries, and veins • Arteries carry blood away from the heart, veins carry blood toward the heart • Capillaries contact tissue cells and directly serve cellular needs Structure of blood vessels • Arteries and veins are composed of three tunics – tunica interna, tunica media, and tunica externa • Lumen – central blood-containing space surrounded by tunics • Capillaries are composed of endothelium with sparse basal lamina Structure of blood vessels Tunics of blood vessels • Tunica interna (tunica intima) – Endothelial layer that lines the lumen of all vessels – In vessels larger than 1 mm, a subendothelial connective tissue basement membrane is present • Tunica media – Smooth muscle and elastic fiber layer, regulated by sympathetic nervous system – Controls vasoconstriction/vasodilation of vessels • Tunica externa (tunica adventitia) – Collagen fibers that protect and reinforce vessels Elastic (conducting) arteries • Thick-walled arteries near the heart; the aorta and its major branches – Large lumen allow low-resistance conduction of blood – Contain elastin in all three tunics – Withstand and smooth out large blood pressure fluctuations – Allow blood to flow fairly continuously through the body Muscular (distributing) arteries and arterioles • Muscular arteries – distal to elastic arteries; deliver blood to body organs – Have thick tunica media with more smooth muscle and less elastic tissue – Active in vasoconstriction • Arterioles – smallest arteries; lead to capillary beds – Control flow into capillary beds via vasodilation and constriction Capillaries • Capillaries are the smallest blood vessels – Walls consisting of a thin tunica interna, one cell thick – Allow only a single RBC to pass at a time – Pericytes on the outer surface stabilize their walls • There are three structural types of capillaries: continuous, fenestrated, and sinusoids Capillary beds Capillary beds Capillary beds • A microcirculation of interwoven networks of capillaries, consisting of: – Vascular shunts – metarteriole–thoroughfare channel connecting an arteriole directly with a postcapillary venule – True capillaries – 10 to 100 per capillary bed, capillaries branch off the metarteriole and return to the thoroughfare channel at the distal end of the bed Venous (system ) venules • Are formed when capillary beds unite – Allow fluids and WBCs to pass from the bloodstream to tissues • Postcapillary venules – smallest venules, composed of endothelium and a few pericytes • Large venules have one or two layers of smooth muscle (tunica media) Venous system (veins) • Veins are: – Formed when venules converge – Composed of three tunics, with a thin tunica media and a thick tunica externa consisting of collagen fibers and elastic networks – Capacitance vessels (blood reservoirs) that contain 65% of the blood supply Venous system (veins) • Veins have much lower blood pressure and thinner walls than arteries • To return blood to the heart, veins have special adaptations – Large-diameter lumens, which offer little resistance to flow – Valves (resembling semilunar heart valves), which prevent backflow of blood • Venous sinuses – specialized, flattened veins with extremely thin walls (e.g., coronary sinus of the heart and dural sinuses of the brain Blood flow • Actual volume of blood flowing through a vessel, an organ, or the entire circulation in a given period: – Is measured in ml per min. – Is equivalent to cardiac output (CO), considering the entire vascular system – Is relatively constant when at rest – Varies widely through individual organs, according to immediate needs Blood pressure • Force per unit area exerted on the wall of a blood vessel by its contained blood – Expressed in millimeters of mercury (mm Hg) – Measured in reference to systemic arterial BP in large arteries near the heart • The differences in BP within the vascular system provide the driving force that keeps blood moving from higher to lower pressure areas Resistance • Resistance – opposition to flow – Measure of the amount of friction blood encounters as it passes through vessels – Generally encountered in the systemic circulation – Referred to as peripheral resistance (PR) • The three important sources of resistance are blood viscosity, total blood vessel length, and blood vessel diameter Resistance factors—viscosity and vessel length • Resistance factors that remain relatively constant are: – Blood viscosity – thickness or “stickiness” of the blood – Blood vessel length – the longer the vessel, the greater the resistance encountered Resistance factor—vessel diameter • Changes in vessel diameter are frequent and significantly alter peripheral resistance • Resistance varies inversely with the fourth power of vessel radius (one-half the diameter) – For example, if the radius is doubled, the resistance is 1/16 as much Systemic blood pressure • The pumping action of the heart generates blood flow through the vessels along a pressure gradient, always moving from higher- to lowerpressure areas • Pressure results when flow is opposed by resistance • Systemic pressure: – Is highest in the aorta – Declines throughout the length of the pathway – Is 0 mm Hg in the right atrium • The steepest change in blood pressure occurs in the arterioles Factors aiding venous return • Venous BP alone is too low to promote adequate blood return and is aided by the: – Respiratory “pump” – pressure changes created during breathing suck blood toward the heart by squeezing local veins – Muscular “pump” – contraction of skeletal muscles “milk” blood toward the heart • Valves prevent backflow during venous return Factors aiding venous return Maintaining blood pressure • Maintaining blood pressure requires: – Cooperation of the heart, blood vessels, and kidneys – Supervision of the brain Maintaining blood pressure • The main factors influencing blood pressure are: – Cardiac output (CO) – Peripheral resistance (PR) – Blood volume • Blood pressure = CO x PR • Blood pressure varies directly with CO, PR, and blood volume Chemicals that increase blood pressure • Adrenal medulla hormones – norepinephrine and epinephrine increase blood pressure • Antidiuretic hormone (ADH) – causes intense vasoconstriction in cases of extremely low BP • Angiotensin II – kidney release of renin generates angiotensin II, which causes intense vasoconstriction • Endothelium-derived factors – endothelin and prostaglandin-derived growth factor (PDGF) are both vasoconstrictors Chemicals that decrease blood pressure • Atrial natriuretic peptide (ANP) – causes blood volume and pressure to decline • Nitric oxide (NO) – has brief but potent vasodilator effects • Inflammatory chemicals – histamine, prostacyclin, and kinins are potent vasodilators • Alcohol – causes BP to drop by inhibiting ADH Circulatory shock • Three types include: – Hypovolemic shock – results from large-scale blood loss – Vascular shock – poor circulation resulting from extreme vasodilation – Cardiogenic shock – the heart cannot sustain adequate circulation Major arteries Major veins • Name some major veins!!!!!!