Chapter 19
Correctly order vessel tunic layers starting from either supporting connective tissue or lumen space.
(intima) endothelial layer subendothelial layer (internal elastic membrane) (media) smooth muscle layer elastin sheets (externa) loose collagen fibers nerves, elastic fibers lymphatic vessels vasa vasorum
Define the terms and capillary bed and microcirculation.
-Capillary beds - concentration of capillaries supplying blood to body tissues (inside organs) -microcirculation - blood flow through capillary beds, composed of terminal arterioles, capillaries, venules draining capillary blood
Differentiate between continuous capillaries found outside the brain and those making up the blood-brain barrier.
-The difference would be that the continuous capillaries that make up the blood-brain barrier would be that they have no intercellular cleft. - The continuous capillaries found outside the brain would be that they have intercellular cleft.
Define the terms tunic and lumen as they relate to blood vessels.
-Tunic - has three blood vessel layers inner, middle, outer. -Lumen - central opening in all blood vessels, determines a vessel's internal diameter (ID) + perfusion rate -lumens may be defined by a single layer of endothelium or several tissue layers (tunics) extending outward from endothelium
Differentiate between arteries, veins, & capillaries on a functional basis.
-arteries - carry blood away from heart diverge/branch into smaller vessels -capillaries - smallest vessels for gas, nutrients, & waste exchange -substance transfer = blood > interstitial space > tissue cells (nearby) -veins - carry blood towards heart converge/join into larger vessel
Describe structural/functional features of all 3 vessel tunics.
-intima: smooth uninterrupted inner surface, dec friction inc blood flow, support lumen endothelium -media: cause changes in lumen ID affecting BP and flow, allows expansion/recoil -externa: protect vessels, control smooth muscle, expand/recoil, lymph return, vasa vasorum
Define the terms pericyte, intercellular cleft, fenestration, and sinusoid.
-pericytes - mesenchymal-like cells located on outer endothelium surface to help stabilize capillary walls - intercellular clefts - incomplete (unjoined) tight junctions that allow outward passage of fluids/small solutes -fenestrations - small oval pores riddle endothelial surface - sinusoids - large intercellular clefts appearing as window-like pores, makes an irregularly shaped lumen
Describe origins/destinations of plasma fluid, interstitial fluid, and lymph fluid.
-plasma fluid - "forced out" of distal capillaries, becoming interstitial fluid (interface) -interstitial fluid - enters lymphatic capillaries, becomes lymph -lymphatic vessels - returns lymph fluid to blood circulation
Differentiate between true capillaries and a vascular shunt.
-vascular shunt - mechanism to divert blood fluid, consists of a metarteriole & thoroughfare channel -true capillaries - 10-100 capillary branches off a metarteriole delivering blood to local tissues, merge at thoroughfare channel
Describe venous sinuses, venous anastomoses, atrial anastomoses and ateriovenous anastomoses. Identify their common locations.
-venous anastomoses - most common type, seen on back of hands/feet (rarely blocked) -arterial anastomoses* - collateral channels in joints, heart, brain, abdominal organs -arteriovenous anastomoses - vascular shunts seen in digestive/urinary tissues
Recall the relative portions of blood volume in the circulatory system compartments.
Arteries and arterioles- 15% Pulmonary blood vessels- 12% Heart- 8% Capillaries- 5% Veins and Venules- 60%
Describe structure/function of elastic (conducting) arteries, muscular (distributing) arteries, arterioles, and capillaries.
Arterioles- smallest arteries interfacing with tissue capillary beds, deliver blood to tissues located inside body organs Capillaries- microscopic blood vessels present in most body tissues Primary: timely exchange of materials b/w blood plasma and interstitial fluid Elastic (conducting) arteries- large ID w/ thick-walls, includes aorta/major aortic branches, most elastin of any vessel, primary function: conduct blood from heart to medium-size arteries Muscular (distributing) arteries- distal to elastic arteries, proximal to arterioles, more smooth muscle & active in vasoconstriction, primary function: deliver blood to body organs
Define the terms blood flow, cardiac output, blood pressure, and resistance.
Blood flow (F) - blood volume flowing through a vessel, an organ, or entire circulation in a given time (mL/min) BP - pressure (force per unit area) exerted by circulating blood on blood vessel walls Resistance (R) - opposition to blood flow (F) through one or more vessels cardiac output = is equal to blood flow
Explain the relationship between blood flow, difference in blood pressure (P), and peripheral resistance. Recall which factor is more important in controlling local blood flow.
Blood flow (F) is directly proportional to difference in blood pressure ((deta)P) between two points in circulation pressure difference (P) between a proximal point & a distal point creates a hydrostatic pressure gradient (high-to-low) If BP increases, then flow increases If BP decreases, then flow decreases Blood flow is INVERSELY proportional to resistance encountered during systemic circulation. (R is a more important factor than pressure change in influencing local blood pressure) If BP increases, flow decreases If BP decreases, flow increases.
List three factors influencing systemic blood pressure.
Cardiac output peripheral resistance blood volume
Describe the structure, function, and body locations of continuous, fenestrated, and sinusoidal capillaries.
Continuous : Location - skin, muscles, lung, CNS Characteristics: -least permeable (leaky), most common -components = tight junctions, intercellular clefts, complete basement membrane pericytes (support cells) -continuous or unbroken since adjacent endothelial cells are held together mostly by tight junctions -involved in perfusion of capillary beds (Blood-brain barrier - modified continuous capillaries found in majority of brain tissue, tight junctions are seen between all endothelium = no intercellular cleft) Fenestrated Location - sm. intestine, endocrine glands kidneys Characteristics: -more permeable than continuous capillaries -components = tight junctions, intercellular clefts, complete basement membrane, fenestrations -fenestrations - small oval pores riddle endothelial surface -involved primarily in active nutrient absorption or filtrate formation Sinusoid Capillaries (Sinusoids): Location - liver, bone marrow, lymphoid tissue, some endocrine organs Characteristics: -most permeable type (fewest tight junctions), limited distribution -components = tight junctions, intercellular clefts, incomplete basement membrane, sinusoids -sinusoids - large intercellular clefts appearing as window-like pores, makes an irregularly shaped lumen -involved in large molecule passage between blood & surrounding tissues -sluggish blood flow allows for great solute exchange
Discuss the effects of decreased blood pressure on heart activity (ESV, EDV).
Decreased BP aroreceptors in carotid sinuses and aortic arch are inhibited. Impulses from baroreceptors stimulate cardioacceleratory center (and inhibit cardioinhibitory center) and stimulate vasomotor center. Increased sympathetic impulses to heart cause increased HR, increased contractility, and increased cardiac output. Vasomotor fibers stimulate vasoconstriction causing increased resistance. Increased cardiac output and increased resistance return blood pressure to homeostatic range.
Explain why a blood pressure gradient is necessary for blood circulation.
Heart pumping action generates initial blood flow (F) through blood vessels along a pressure gradient
Describe blood pressure differences in aorta, arteries, arterioles, capillaries, venules, veins, and venae cavae.
Highest BP is seen in Aorta near the heart and declines throughout the length of circulation. Steepest BP change occurs in arterioles (small ID offers most resistance to blood flow) Aorta: ~120-80 mmHg Arteries: >120-80 Arterioles: > 100-80 Capillaries: ~40 Venules: ~20 Veins: >20 Venae Cavae: ~0
Discuss the effects of arterial atherosclerosis on affected arteries and normal blood flow.
Interrupts laminar flow dramatically increasing resistance. (Turbulence)
Explain why low capillary pressure is desirable.
It does not rupture fragile, thin-walled continuous capillaries (leaky)
Explain why the aorta is called a pressure reservoir.
It is the largest elastic (conducting) artery and elastic arteries serve as auxiliary pumps (aka- pressure reservoirs) in between contractions. This means they move blood while ventricles are filling.
Define the terms perfusion & closed circulation.
Perfusion - pumping of a fluid through an organ or tissue through a closed system of vessels includes both blood & lymphatic fluid Closed circulation - blood circulation via the pumping to the heart pushing through closed vessels
Describe both short-term and long-term blood pressure regulations mechanisms.
Short-term neural control involves actions by blood vessel baroreceptors, chemoreceptors, brain centers -Epinephrine and Norepinephrine: (Increases BP) -Increase cardiac output (CO) [affects HR and contractility] -Occurs at Heart (Beta 1 receptors) -Increases Peripheral resistance [PR] (vasoconstriction) -Occurs in arterioles (alpha receptors) -Angiotensin II: (Increases BP) -Increases PR (vasoconstriction) -Occurs in arterioles -Atrial Natriuretic Peptide (ANP): (Decreases BP) -Decreases PR (vasodilation) -Occurs in arterioles -Antidiuretic Hormone (ADH): (Increases BP) -Increases PR (vasoconstriction) -Occurs in arterioles -Increases blood volume (decreases water loss) -Occurs in kidney tubule cells -Aldosterone: (Increases BP) -Increases blood volume (decreases water and salt loss) -Occurs in kidney tubule cells Long-term: involves changes in blood volume that are renal-mediated. -Direct: alters water volume INDEPENDENT of hormones -Indirect: Renin, ADH, aldosterone effect sodium/water reabsorption
Trace normal blood flow through a capillary bed during parasympathetic control.
Terminal arteriole > metarteriole + true capillaries + thoroughfare channel > postcapillary venule
Trace altered blood flow through a capillary bed during sympathetic activation.
Terminal arteriole > metarteriole > thoroughfare channel > postcapillary venule
Define the term anastomoses.
Vascular anastomoses - union or joining together of blood vessels in certain body areas
Describe how vasodilation and vasoconstriction affect blood flow (F)
Vasoconstriction: NARROWS blood vessel lumen ID. Vasoconstriction of a renal artery/arteriole causes decreases flow into the kidneys w/o affecting blood flow to other organs. Vasodilation: widens blood vessel lumen ID.
Describe special adaptations that help veins return blood to the heart.
Veins have greatly ↓ blood pressure & thinner walls than corresponding arteries at same body level special adaptations needed to help return blood to heart: -large-diameter lumens - offer little resistance to blood flow -valves - prevent blood backflow especially in lower limbs, composition resemble heart semilunar valves
Compare/contrast venous blood pressure to arterial blood pressure.
Venous: -Steady, changes little during cardiac cycle (driving pressure is only ~15mm Hg) -Pressure difference best demonstrated during blood loss: -Cut vein- slow, even blood flow (oozing) -Lacerated artery- fast, spurting blood flow (pulsatile) -Low venous pressure DIRECTLY reflects cumulative effect of all encountered peripheral resistance during systemic circulation. -Only 1 mm Hg pressure is needed to move blood from vena cavae into right atrium. Arterial: Reflects two factors of arteries close to heart: -Elasticity- conducting artery's ability to stretch (compliance) -Blood volume: amount of blood forced into elastic arteries at any one time. -Highest BP is seen in aorta near heart, declines through length of circulation. -steepest BP change occurs in arterioles where small ID causes most resistance (R) to blood flow (F)
Describe structure and functions of venules, veins, and venous sinuses. Explain why veins are called capacitance vessels.
Venules - formed where several capillaries unite (merge), avg. lumen ID = 20 m -postcapillary venules - smallest venules only composed of endothelium + a few associated pericytes - extremely porous vessels, allow fluids/inflammatory WBCs to pass from bloodstream into tissues -larger venules have one or two layers of smooth muscle in tunica media -also display a thin tunica externa Veins - formed where several venules converge (merge) -has a greater diameter than an artery at same body level -capacitance vessels (blood reservoirs) since they cancontain 60-65% of blood supply* at any one time -see all three tunics: -tunica interna - single endothelial layer -tunica media - thin, vena cavae expressing greatest amount of smooth muscle -tunica externa - thick, consists of collagen fibers + elastic networks Venous sinuses - specialized, wide/flattened veins w/ extremely thin walls -heart coronary sinus -brain venous sinuses The veins are called capacitance vessels (blood reservoirs because they have 60%-65% of blood supply.
Describe what is meant by ateriovenous shunting.
creates an arteriovenous shunt, blood moves from metarteriole directly into thoroughfare channel bypassing true capillaries
Explain how blood is propelled through arteries while the heart is in diastole.
elastic arteries serve as auxiliary pumps (pressure reservoirs), the recoil after expansion provides pressure needed
Describe arterial elasticity and its relationship to blood volume.
elasticity - conducting artery's ability to stretch (compliance) blood volume - amount of blood forced into elastic arteries at any one time
Recall which 4 organs cooperate to ensure adequate blood pressure.
heart blood vessels kidneys brain (CNS) control
Correctly order the route of different types of blood vessels starting at the heart and returning blood to the heart.
heart elastic arteries (largest) muscular arteries (large) arterioles (small) capillaries (smallest) venules (small) veins (larger) vena cavae (largest) heart
Discuss pressure differences in systemic circulation starting at the aorta and ending at the right atrium.
highest BP is seen in aorta near heart & declines throughout circulation Pressure is 0 mmHg in the right atrium
Describe laminar flowing of blood and how turbulence affects it.
laminar flow (streamlining) - relative speed/position of blood in different areas of a blood vessel cross section remains constant turbulence from vessel lesions interrupt laminar flow dramatically increasing resistance
Describe how muscular arteries reduce pulsations.
muscular arteries eliminate more pulsing as blood flows to target organ
List the 3 sources of peripheral resistance and know how each affects blood flow.
peripheral resistance - type of resistance (R) most encountered in peripheral systemic circulation away from heart Blood viscosity - internal resistance to blood flow that is related to its "thickness" or "stickiness" -polycythemia - increase red blood cell mass causes increase viscosity -anemia - decrease red blood cell mass results in decrease viscosity -see increase F but less RBCs means decrease O2 delivery to tissues
Define pulsatile, systolic pressure, diastolic pressure, pulse pressure, and mean arterial pressure.
pulse pressure - difference between systolic/diastolic pressures mean arterial pressure (MAP) - average arterial pressure propelling blood to tissues/organs Systolic pressure = peak aortic pressure during ventricular contraction Diastolic pressure = lowest aortic pressure during ventricular relaxation Pulsatile: rise/fall of aortic BP (pulsatile = throbbing)
List three factors aiding venous blood return.
respiratory pump - inspiration decreases thoracic pressure, aspirates (sucks) blood towards right atrium from thoracic vein muscular pump - local skeletal muscle contractions "milk" blood in thin-walled deep veins back towards heart smooth muscle - sympathetic activation promotes tunica media muscle vasoconstriction
Explain the effects of smooth muscle contraction and relaxation on blood vessel diameter.
smooth muscle relaxation increases lumen ID, contraction decreases lumen ID
Recall the type of blood vessel where the steepest blood pressure change occurs.
steepest BP change occurs in arterioles where small ID causes most resistance (R) to blood flow (F)
Explain the function of precapillary sphincters as it relates to regulating blood flow through a capillary bed.
sympathetic stimulation causes precapillary sphincter (smooth muscle "cuff") surrounding of each true capillary to contract
Describe the function of the vasa vasorum.
vasa vasorum (vessel-of-vessels) - tiny system of external blood vessels found in larger veins/arteries -"feeds" external vessel layers while -lumen blood nourishes internal layers originates from a branch off of an artery
