Anatomy 2 Test 2: Ch 19 Blood Vessels Part 1

Arteries, capillaries and veins

-Arteries: take blood (usually oxygenated, except in the pulmonary artery) away from the heart -Veins: returns blood (usually deoxygenated) to the heart -Capillaries: exchange points from the arteries and the veins. + the walls of the arteries and veins are too thick that diffusion doesn't work well. In the capillaries, their walls are 1 cell thick aka thin enough so diffusion works better here

Blood flow is directly proportional to blood pressure gradient

-Blood pressure gradient: change of blood pressure from 1 area to another, typically from the arteries to the veins -if the pressure gradient increases, blood flow will speed up aka if we increase the amt of blood coming out of the heart, it causes pressure to increase on one end causing more blood to move across the system

Relationship between flow, pressure and resistance (he wants us to know the relationship between them, he won't make us do calculations)

-Equation: Blood Flow (F) = delta P/ Resistance (R). + it demonstrates the 2 relationships below and the equation can be rearranged 1. Blood flow (F) is directly proportional to blood pressure gradient (^P) 2. Blood flow is inversely proportional to peripheral resistance

Example questions of relationships

-If you increase/decrease resistance what will happen to blood flow? -If you decrease/increase pressure gradient what will happen to blood flow

Graph showing the pressure changes and pulsatile nature

-Near the aorta and arteries the pressure is highest and pulstile nature is present bc the pressure rises and falls alot -Along the arterial transition (the line between the arterioles and capillaries) the pulsatile nature starts to smooth out and you have a more uniform flow to where the pulsatile pattern is lost -Picture also demonstrates mean pressure: the average pressure. Is calculated by taking the avg pressure at the end of systole and bottom of diastole

Two types of pressure

-Systolic pressure: pressure exterted in the aorta during ventricular contraction + avg is 120 -Diastolic pressure: level of aortic pressure when the heart is relaxed +avg is 80 in a normal adult -Highest pressure occurs at the peak of contraction and lowest occurs at the bottom of relaxtion within the heart

Even though pressures are low in the capillaries, this is desirable bc

1. High BP would rupture fragile, thin-walled capillaries (they are one cell thick) 2. Most capillaries are very permeable, so low pressure forces some filtrate into interstitial spaces + a little bit of pressure is still present for the exchange of nutrient and fluids

Blood vessels

3 major types: arteries, veins, capillaries -they form a closed delivery system that begins and ends at the heart

Question: Knowing that energy is conserved, and pressure is a form of energy imparted to the blood by the heart, what is happening as the pressure is dropping? aka what happens to the energy of blood pressure as it moves from arteries to veins

As pressure drops from arteries to veins, the energy is being converted to heat -heat is being generated as the cells and blood vessels are rubbing against each other -this is a reason why our blood is 1c higher in temp than the rest of the body -if blood pressure increases, more heat will be generated bc more rubbing and friction will occur

Capillary blood pressure

By the time blood flows to the capillaries, alot of the pressure has already been lost by heat -Pressure ranges from 35 mm Hg at beginning of capillary bed to ∼17 mm Hg at the end of the bed + When blood comes out of the arteries, the pressure is 93mmhg + When blood comes out of arterioles pressure and into the capillaries is 35mmhg + When blood comes into the venules its 75mmhg

Relative proportion of blood volume throughout cardiovascular system

He's he doesn't want us to memorize the percentages but just know that veins have more blood than the arteries -Veins and venules: 60% -Systemic arteries and arterioles: 45% -Pulmonary blood vessels: 8% -Heart: 8% -Capillaries: 5%

Factors aiding in venous return

Low pressure of venous side requires adaptations to help with venous return... -Muscular pump. respiratory pump, sympathetic venoconstriction

Systemic blood pressure

Pumping action of heart generates blood flow. Pressure results when flow is opposed by resistance -Systemic pressure is highest when blood is coming out of the aorta bc its directly connected to the hear -Systemic Pressure is lowest when in the veins -Systemic Pressure drop is steepest in the arterioles bc thats where the greatest change in resistance will happen. This occurs as a result of the changes in diameters and cross sections that occurs in the arteriole branches -Blood pressure near heart is pulsatile (pressure rises and falls with each heartbeat) and becomes smoother as it gets away from the heart

Capillaries

The smallest blood vessels, and the site of exchange of chemicals and waterbetween the blood and the tissues -diameter is so small that only 1 rbc can pass through at a time -consists of thin tunica media and epethilal cells. Is the innermost tunica intima. -Pericytes: stem cells that help stabilize capillary beds and controls permeability and vessel repairs. + since they are stem cells they have the ability to differentiate into other epithelial cells + permeability: allowing things to come in and out. The more pericytes, the thicker the walls, the less the permeability bc its harder for things to come in -Function 2: delivers hormones to target cites bc diffusion can cary hormones to their target receptors -allows for waste and gas exchange to occur effectively

The relationship of blood vessels to each other and the lymphatic vessels

There is a connection between the lymphatic vessels and the cardiovascular vessels via veins -we start with arteries, arterioles (the smallest type of artery), capillary beds, and then venules which will converge to form veins

Adaptations of veins

Venous valves and venous sinuses -blood pressure in the veins are lower than in the arteries so these adaptations ensure the one way flow of blood back to the heart -they are similar to the AV and SL valves of the atria and ventricles -Venous valves: prevents back flow of blood. Only promotes blood back to the heart -Venous sinuses: are flattened veins with extremely thin walls. Serves as a reserve for blood + ex: coronary sinus of the heart, dural sinus of the brain

Muscular arteries

are called distibuting arteries bc they deliver blood to specific body organs -they have the thickest tunica media aka the thickest walls with more smooth muscles but less elastic tissue -Bc of this thickness they don't expand easily and are just passage ways for blood to travel to different organs -active in vasoconstriction: the narrowing of the diameter of the blood vessel which is important for blood vessel regulation -they also branch out into smaller arterioles which will branch into capillary beds -When you constrict and narrow the diameter of the vessels you increase the afterload and increase the blood pressure time

1. Diameter can be changed in real time:

blood vessel diameter can be changed within secs to mins depending on local agents that cause dialation or constriction. -This can occur faster than agents that increase RBC's or shorten vessel length (losing weight). Viscosity and vessel length are constant -diameter can quickly change via the nervous system or the endocrine system

3 sources of resistance

blood viscosity, total blood vessel length, blood vessel diameter

fenestrate capillary

capillaries that have large fenestrations (pores) that increase permeability -present in areas of active filitration (kidneys) or absorption (intestines) and areas of endocrine hormone secretion -fenestrations are covered by a thin layer of condensed extracellular glycoproteins. This layer has little effect on solute and fluid movement -the number of fenestrations incapillaries increases during active absorption of nutrients.

Tunica media

consists of smooth muscle, elastic fibers and an external elastic membrane -smooth muscle: allows the blood vessel to relax or contract in order to change the diameter of the vessel

Different types of capillaries

continuous, fenestrated, sinusoids

Muscular pump

contraction of skeletal muscles "milks" blood back toward heart; valves prevent backflow -helps squeeze blood from one chamber to the next -as muscles press against the wall which narrows the diameter, that will help increase pressure which increase blood flow -they are able to move in a one way direction bc of the valves -Ex: walking around helps move muscles which further constrict veins causing inc in pressure and flow of blood back to heart

Types of arteries

elastic, muscular, arterioles -types are based on size and function

interstitial fluid

fluid in the spaces between cells. -In capillaries, there is an exchange between your blood plasma and the interstitial fluid across the capillary walls

Blood vessel diameter

has greatest influence on resistance -The smaller aka more narrow the diameter, the higher the resistance. The larger the diameter, the smaller the resistance -analogy: water hose normally and putting thumb over the end -Why is blood vessel diameter the greatest influence on resistance: diameter can be changed in real time, diameter is the most sensitive parameter

capillary beds

interwoven networks of capillaries between arterioles and venules -consists of 2 types of vessels: vascular shunt and true capillaries 1.Vascular shunt aka : channel that connects arteriole directly with venule. Is present in the middle of the capillary bed which is why its aka (metarteriole- thoroughfare channel) 2. True capillaries: actual vessels involved in exchange

Calculation of MAP (not gonna ask us about the equation or to calculate so disregard)

is calculated by adding diastolic pressure + 1/3 (SBP-DBP) -Example: BP = 120/80; - so MAP = 80 + (1/3)*(120-80) -MAP declines w increasing distance from the heart bc the difference between sys and diast. will be lower

mean arterial pressure (MAP)

is the pressure that propels blood to tissues -considered to b more useful bc its the avg pressure thoughout the entire system of the body and when measuring systolic and diastiolic seperately, on the graph they both eventually converge to this value + With a steady MAP pressure, flow is nonpulsatile (think after the arterioles) -Heart spends more time in diastole, so not just a simple average of diastole and systole

Resistance aka peripheral resistance

oppositon to flow, its the measurement of the amount of friction blood encounters with the vessels and the movement/rubbing of blood cells against themselves -similar to afterload (aka blood pressure) in cardiac output -the higher the amount of friction the more resistance there will be -resistance is more specific and can refer to body regions and organs -peripheral resistance refers to the enter body aka systemic circuit. This allows it to be most similar to the afterload that occurs in the heart -afterload only refers to the heart

Tunica externa

outer layer of blood vessel -composed of collagen fibers and vaso vorsum making it more rigid than the other layers. -Collagen: a very thick fillament that is found in connective tissue and give it tensile strength. It functions similarly in blood vessels to give the blood vessels structural integrity -Vasa vasorum: blood vessels that feed nutrition to the larger vessel. Aids in allowing larger vessels within them to give them their own blood flow. + vasa vasorum is present bc vessels are thick enough where diffusion isn't effective so thats why you need circulation within the vessels themselves to supply nutrients and pick up wastes and deliver gases

Anastomoses

points where 2 blood vessels merge. There are vascular, arterial, arteriovenous and venous anastomes -Vascular anastomoses: interconnections of blood vessels -Arterial anastomoses aka collateral channels: connections between arteries. Provides alternate pathways to ensure continous flow of blood even if an artery is blocked -Arteriovenous anastomes: connection between arteriole and venule, example of this is the metarteriole-thouroughfare channel -Venous anastomes: connects veins to veins. Are so abundant that blocked veins rarely stop blood flow

Respiratory pump

pressure changes during breathing move blood toward heart by squeezing abdominal veins and expanding thoracic veins -as you breath, thoracic cavity and veins expand which drops the pressure in this area -this drop in pressure moves blood to the abdominal cavity to help return blood back to the heart -occurs when we are standing up

Sinusodal capillaries

rarest type of capillary. Is the most permeable and is found in limited locations -found only in the liver, red bone marrow, spleen and adrenal medulla -has fewer tight junctions; usually fenestrated with larger intercellular clefts; incomplete basement membranes -Contains macrophages in lining to capture and destroy foreign invaders -are irregular shaped and have large lumen that allows large molecules and whole cells to pass across their cells

Venous blood pressure

remains steady, changes very little during the cardiac cycle -frictional forces aren't present bc most of the pressure has already been lost as heat -has a small pressure gradient of only 15mmhg and remain at this value throughout the venous system -Pressure remains low bc with low pressure if a vein is cut, low pressure of venous system causes blood to flow out smoothly. With high pressure like if an artery is cut, blood spurts out because pressure is higher

2. Diameter is the most sensitive parameter

resistance varies inversely with fourth power vessel radius -4th power: refers to an exponential change. Any small change in the radius will have a big effect on resistance -If radius increases, resistance decreases and vice versa -Ex: if radius is doubled, resistance drops to 1/16. -you don't have to make large changes in the radius or diameter for it to change the resistance

Veins

responsible for carrying blood to the heart which increase cardiac output. Are similar to elastic arteries -After the arterioles enter the capillary beds, the capillary beds will reconnect and converge into venules and then the venules will connect into veins -Formation of veins begins once venules converge -contain all 3 tunics but have thinner walls than arteries -they have large lumens which make veins good storage vessels -Capacitance vessels: veins are reffered to as blood reserves bc they contain up to 65% of blood supply. They are distensible meaning they can expand in order to increase volume of blood -Venules: Are very similar to capillaries bc they consist of endothelium and few pericytes. Is very porous which allows fluids and WBC's to flow into tissues + larger venules will have 1 or 2 layers of smooth muscle cells

Small diameter arterioles are major determinants of peripheral resistance

since these vessels are already at such a small diameter, any further changes will have a larger effect on the resistance -the smaller the diameter of arterioles, the larger the cross sectional area of the vessels. A bigger impact is made across the body in the smaller vessels than in larger vessels

Arterioles

smallest arteries with multiple levels -known as resistance arteries bc they are small enough that even tiny changes in their diameter will have big changes and contributes to blood flow. Has a bigger impact on bp regulation -Function: controls flow of blood into capillary beds by allowing vessels to dialate or constrict + ex: constricition can occur when exercising by having the arterioles cut off blood supply to other organs that don't need it at the time like digestive and resistive organs -Larger arterioles: have all three tunics, but their tunica media is chiefly smooth muscle with a few scattered elastic fibers -Smaller arterioles: are mostly single layer of smooth muscle surrounding endothelial cells

Blood pressure

the force/hydrostatic pressure exerted by blood on the walls of blood vessels -expressed in mmHG aka mm of mercury -hydrostatic: fluid pressure aka pressure of water bc a large component of the blood is water (large amt of blood plasma is made out of water) -Pressure gradient: provides driving force that keeps blood moving from higher- to lower-pressure areas + blood moves from the heart to the large arteries, arterioles, capillary beds, venules and veins + highest pressure is in the arteries, lowest pressure is in the veins

Blood flow is inversely proportional to peripheral resistance

the higher the resistance, the lower the blood flow -if resistance increases, blood flow decreases -Similar to how increase in afterload decreases the cardiac output -Resistance is more important in influencing local blood flow bc it is easily changed by altering blood vessel diameter + resistance is the majority of what contributes to the afterload that the heart has to work against bc the more you have to work, the less blood that will come out per beat + resistance is more easily changed and change occurs faster

tunica intima

the innermost layer of a blood vessel -consists of the endothelium, subendothelial layer and internal elastic membrane + endothelium: layer of endothelial cells that regulate vascular tone aka the diameter that vessels can stretch causing it to dialate or constrict. Most things concerning the endothelium lead to dialation.

Continous capilaries

the least permeable and most common types of capillary -is abundant in skin muscle, lungs and the CNS -pinocytic vessels are responsible for moving fluid across the endothelial cell -Continous capililarries of the brain: Form blood brain barrier, totally enclosed with tight junctions and no intercellular clefts

Length of blood vessels

the longer the blood vessel, the higher the resistance bc there is a greater amt of blood vessels than can encounter resistance and friction -is similar to friction in the pulmonary and system circuits. Pulmonary circuit has less friction bc blood has a shorter length to travel than the systemic circuit which travels throughout the whole body

Blood viscosity

the thickness or stickness of blood due to increased formed elements and plasma proteins -the higher the amount of RBC, the thicker the blood allowing it to become more viscous -increase in blood viscosity increases resistance bc its hard for thicker blood to flow than thinner blood -occurs when going up in high altitude bc your body will start to make more RBC bc it needs more oxygen -Main ways the viscosity is changed: + changing the amt of RBC's : the more RBC's the more viscous that blood will be + Dehydration: the less water in the blood, the more viscous aka thickness of blood

Anatomy of a capillary bed (pic is on slide 14)

the true capillaries branch of of the throughfare channel -True capillaries have a ring of smooth muscles (sphincter) that can be opened or closed + open sphincter: blood will flow from the middle channel into the capillaries which provides nutrients to the surrounding tissues + closed sphincter: restrict most blood flow into the true capillaires. Blood will flow thru the metaarteriole and throughfare channel but not the capillaries

Elastic arteries

thick walled arteries that are closer to the heart with low resistance lumen -since they are elastic, they are able to expand and compress back to its original size -elastin is found mainly in the tunica media -they are known as reservoirs bc they can accomodate a larger volume of blood as needed -Acts as pressure reserves aka volume reserves that expand and recoil as blood is ejected from the heart. Allowing for continuous blood flow downstream between heartbeats -has smooth muscle but doesn't contribute as much to the distribution of blood due to blood pressure regulation -elastic arteries give rise to muscular arteries -ex: aorta and its branches

3 layers of blood vessels

tunica intima, tunica media, tunica externa -layers are also referred to as tunics that surround the vessel lumen which is what contains blood

sympathetic venoconstriction

under sympathetic control, smooth muscles constrict, pushing blood back toward heart bc of the pressure the exert in the veins -ex: exercising stimulates your sympathetic nervous system to send more blood to the right side of the heart which increases cardiac outpt

Blood flow

volume of blood flowing through vessel, organ, or entire circulation in given period -measured in ml/minute and is the same as cardiac output for the entire vascular system + cardiac output: amt of blood flowing through the heart -Difference between cardiac output and blood flow: blood flow can be defined for different regions (blood flow of the kidneys, liver) but cardiac output can only be assigned to the heart