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chpt 19

blood vessels

What carries oxygenated blood away from the heart; except for pulmonary circulation and umbilical vessels of a fetus? Arteries
What contact tissue cells and directly serve cellular needs Capillaries
What carry deoxygenated blood toward the heart ? Veins
In Tunica intima, Endothelium lines the lumen of all vessels
In Tunica media,Smooth muscle and sheets of elastin. Sympathetic vasomotor nerve fibers control vasoconstriction and vasodilation of vessels
In Tunica externa ,Collagen fibers protect and reinforce Larger vessels contain vasa vasorum to nourish the external layer
These are large thick-walled arteries with elastin in all three tunics Eg: Aorta and its major branches Large lumen offers low-resistance Act as pressure reservoirs—expand and recoil as blood is ejected from the heart Elastic (Conducting) Arteries
Distal to elastic arteries; deliver blood to body organs Have thick tunica media with more smooth muscle Active in vasoconstriction Muscular (Distributing) Arteries and Arterioles
Smallest arteries Lead to capillary beds Control flow into capillary beds via vasodilation and vasoconstriction Arterioles
Microscopic blood vessels Walls of thin tunica intima, one cell thick Pericytes help stabilize their walls and control permeability Capillaries
Abundant in the skin and muscles Tight junctions connect endothelial cells Intercellular clefts allow the passage of fluids and small solutes Continuous Capillaries
The least permeable capilllary ? Continuous capillaries of the brain
More permeable than continuous capillaries Function in absorption or filtrate formation (small intestines, endocrine glands, and kidneys) Fenestrated Capillaries
Fewer tight junctions, larger intercellular clefts, large lumens Usually fenestrated Allow large molecules and blood cells to pass between the blood and surrounding tissues Found in the liver, bone marrow, spleen Sinusoidal Capillaries
Interwoven networks of capillaries form the microcirculation between arterioles and venules
What directly connects the terminal arteriole and a postcapillary venule Vascular shunt
10 to 100 exchange vessels per capillary bed Branch off the metarteriole or terminal arteriole True capillaries
Regulated by local chemical conditions and vasomotor nerves
Precapillary sphincters regulate blood flow into true capillaries
Formed when capillary beds unite Very porous; allow fluids and WBCs into tissues Venules
Formed when venules converge Have thinner walls, larger lumens compared with corresponding arteries veins
veins Blood pressure is lower than in arteries
veins have a _____________ ___________ which consist of collagen fibers and elastic networks Thin tunica media and a thick tunica externa
veins contain 65% of blood supply
Adaptations that ensure return of blood to the heart Large-diameter lumens offer little resistance Valves prevent backflow of blood Most abundant in veins of the limbs veins
Venous sinuses flattened veins with extremely thin walls
Force per unit area exerted on the wall of a blood vessel by the blood Blood pressure (BP)
Resistance (peripheral resistance) Opposition to flow Measure of the amount of friction blood encounters
Three important sources of resistance Blood viscosity Total blood vessel length. Blood vessel diameter
The “thickness” of the blood due to formed elements and plasma proteins Blood viscosity
The longer the vessel, the greater the resistance encountered Blood vessel length
Small-diameter arterioles are the major determinants of peripheral resistance
Abrupt changes in diameter or fatty plaques from atherosclerosis dramatically increase resistance Disrupt laminar flow and cause turbulence Resulting in a bruit
Blood flow (F) is directly proportional to the blood (hydrostatic) pressure gradient (P) If P increases, blood flow speeds up
Blood flow is inversely proportional to peripheral resistance (R) If R increases, blood flow decreases
Is highest in the aorta Declines throughout the pathway Is 0 mm Hg in the right atrium Systemic pressure
pressure exerted during ventricular contraction Systolic pressure
lowest level of arterial pressure Diastolic pressure
difference between systolic and diastolic pressure Pulse pressure
pressure changes created during breathing move blood toward the heart by squeezing abdominal veins as thoracic veins expand Respiratory “pump”:
contraction of skeletal muscles “milk” blood toward the heart and valves prevent backflow Muscular “pump”
The main factors influencing blood pressure: Cardiac output (CO) Peripheral resistance (PR) Blood volume
cardiac output isDetermined by venous return and neural and hormonal controls
Resting heart rate is maintained by the cardioinhibitory center via the parasympathetic vagus nerves
neural and hormonal controls Counteract fluctuations in blood pressure by altering peripheral resistance short term blood pressure
renal regulation Counteracts fluctuations in blood pressure by altering blood volume Long-term blood pressure
A cluster of sympathetic neurons in the medulla that oversee changes in blood vessel diameter Maintains vasomotor tone (moderate constriction of arterioles) Receives inputs from baroreceptors, chemoreceptors, and higher brain centers Vasomotor center
Baroreceptors taking part in the carotid sinus reflex protect the blood supply to the brain
Baroreceptors taking part in the aortic reflex help maintain adequate blood pressure in the systemic circuit
Chemoreceptors respond to rise in CO2, drop in pH or O2
Adrenal medulla hormones norepinephrine (NE) and epinephrine cause generalized vasoconstriction and increase cardiac output
generated by kidney release of renin, causes vasoconstriction Angiotensin II
what causes blood volume and blood pressure to decline, causes generalized vasodilation. Lower BP ANP + BNP
A  in arterial bp release of renin
Renin produces the production of angiotensin II
Angiotensin II is a potent vasoconstrictor
Created by: jennysevere24