Blood Vessels

arteries carry blood ____ (toward or away from) the heart

away from

in the systemic circulation, arteries carry _____ (oxygen-rich or oxygen-poor) blood ; in the pulmonary circulation, arteries carry _____ (oxygen-rich or oxygen-poor) blood

• oxygen rich

• oxygen poor

veins carry blood _____ (toward or away from) the heart

toward

in the systemic circulation, veins carry _______ (oxygen-rich or oxygen-poor) blood ; in the pulmonary circulation, veins carry _______ (oxygen-rich or oxygen-poor) blood

• oxygen poor

• oxygen rich

artery characteristics

• have thicker tunica media

• have thicker wall overall

• has elastic membranes

vein characteristics

• may contain valves

• has an irregularly shaped lumen in prepared tissue

• has a thicker tunica externa

tunica intima characteristics

• contains the endothelium that lines the lumen

• the innermost layer of a blood vessel wall

• the only layer of a capillary wall

• provides a smooth surface for blood flow

tunica media characteristics

• bulkiest layer in an artery

• regulates blood vessel lumen diameter

• the middle layer of a blood vessel wall

• mostly contains smooth muscle and elastin

tunica externa characteristics

• the outermost layer of a blood vessel wall

• composed largely of collagen fibres

• in larger vessels, contains the vasa vasorum

what is vasoconstriction

lumen diameter decreases as the smooth muscle contracts

what is vasodilation

lumen diameter increases as the smooth muscle relaxes

are capillaries capable of vasoconstriction/dilation

no because they do not have muscular walls (their walls are much thinner)

elastic artery characteristics

• the aorta

• called conducting arteries

• largest diameter

• convey blood to medium-sized arteries

• act as pressure reservoirs

• contain more elastin than other artery types

• expand and recoil as the heart ejects blood

muscular artery characteristics

• called distributing arteries

• carry blood to specific body organs

• the brachial artery

• thickest tunica media of all vessels

why are capillaries called exchange vessels

because their exceedingly thin walls allow them to transfer oxygen/nutrients from blood → body tissues

how do the structure and location of capillaries make them ideally suited for their function

• their thin walls, composed of a single layer of endothelial cells, allow for efficient diffusion of substances

• their widespread network throughout tissues ensures close proximity to cells, minimizing the distance for diffusion

continuous capillary characteristics

• the most common type of capillaries

• the least permeable type of capillaries

• often have associated pericytes

• abundant in skin, muscles, lungs, and CNS

fenestrated capillary characteristics

• feature fenestrations that increase permeability

• found in areas of active filtration or absorption

sinusoid capillary characteristics

• the most permeable type of capillaries

• found in the liver, bone marrow, spleen, and adrenal medulla

• have large intercellular clefts and fenestrations but fewer tight junctions

the ___________ is the flow of blood through a capillary bed from an arteriole to a venule

microcirculation

in most body regions a _______ arteriole branches into 10-20 _______ that form the capillary bed ; these branches then drain into a _________ venule

• terminal

• capillaries

• postcapillary

blood flows through the capillary bed when arterioles are _______ and no blood flows through the capillary bed when arterioles are ________

• dilated

• constricted

two structural features of veins that help compensate for low venous pressure

1. large lumens/thin walls: offer relatively little resistance to blood flow

2. venous valves: prevent blood from flowing backward in veins just as valves do in the heart

which component of the cardiovascular system contains the most blood

systemic veins

why are anastomoses important

they provide alternate pathways (collateral channels) for blood to reach a given body region

where are arterial anastomoses common

brain and heart

blood flow

the volume of blood flowing through a vessel, organ, or the entire circulation in a given period (mL/min)

blood pressure

the force per unit area exerted on a vessel wall by the contained blood, expressed by mm of mercury (mm Hg) ; systemic arterial blood pressure in the largest arteries near the heart

resistance

• opposition to flow

• measure of the amount of friction blood encounters as it passes through the vessels

• because most friction is encountered in the peripheral (systemic) circulation, the term total peripheral resistance (TPR) is generally used

blood always moves from an area of ______ (higher or lower) pressure to an area of _______ (higher or lower) pressure

• higher

• lower

three important sources of resistance in a blood vessel

1. blood viscosity: the internal resistance to flow

2. total blood vessel length: longer vessel = greater resistance

3. blood vessel diameter: smaller diameter = greater resistance

   • changes frequently/greatly alters TPR due to vasoconstriction/dilation

what does directly proportional mean in terms of blood flow and difference in blood pressure

when difference in blood pressure increases, blood flow increases and vice versa

what does inversely proportional mean in terms of blood flow and TPR

when the change in TPR increases, blood flow decreases and vice versa

does pressure or resistance influence blood flow more

resistance is more important for influencing blood flow

1. the pumping action of the heart generates blood _____

2. blood _____ results when blood flow is opposed by ______

3. blood pressure is the highest in the ______ and declines throughout the pathway until it reaches 0 mm Hg in the right atrium

1. flow

2. pressure / resistance

3. aorta / right atrium

systolic pressure

the pressure peak generated by ventricular contraction

diastolic pressure

the lowest level of pressure generated by the aortic valve closing

pulse pressure

the difference between systolic/diastolic pressures

mean arterial pressure (MAP)

the pressure that propels blood to the tissues ; not halfway between, rather

MAP = diastolic pressure + (pulse pressure/3)

in the systemic circulation, the steepest drop in blood pressure occurs in the _____ which offer the greatest resistance to blood flow

arterioles

at what point in the systemic circulation does the pulse pressure disappear

muscular arteries

list four main vital signs that are monitored by medical professionals

1. pulse

2. blood pressure

3. respiratory rate

4. body temp.

which pressure point could be compressed to help stop the bleeding from a laceration to the thigh

femoral artery

why is it desirable to have low capillary blood pressure

• capillaries are fragile and high pressures would rupture them

• most are extremely permeable; even the low capillary pressure can force solute-containing fluids (filtrate) out of the blood/into the interstitial space

three functional adaptations that are critical to venous return

1. the muscular pump: skeletal muscle activity squeezing “milk” blood toward the heart

2. the respiratory pump: moves blood up toward the heart as pressure changes in the ventral body cavity during breathing

3. sympathetic venoconstriction: reduces the blood volume in the veins → pushed toward the heart

equation for cardiac output (CO) or flow and total peripheral resistance (TPR) relate to mean arterial pressure (MAP)

MAP = CO x TPR

factors that increase MAP

• increased blood vessel length

• dehydration

• release of epinephrine from the adrenal medulla

• increased total peripheral resistance

• increased stroke volume

• increased blood volume

factors that decrease MAP

• decreased blood viscosity

• decreased venous return

• decreased cardiac output

• increased diameter of blood vessels

• decreased heart rate

• stimulation of arterial baroreceptors

short term regulation of blood pressure

• alters cardiac output

• may involve the cardiovascular centre

• alters total peripheral resistance

• involves neural and hormonal controls

• may involve the baroreceptor reflex

long term regulation of blood pressure

• alters blood volume

• includes direct and indirect renal mechanisms

• may involve the renin-angiotensin-aldosterone system

• involves the kidneys

in response to ____ blood pressure the baroreceptor complex increases cardiac output and total peripheral resistance

falling

rising arterial blood pressure _______ baroreceptors

activates

decreased input from baroreceptors _______ the cardio-inhibitory centre

inhibits

increased __________ input causes an increase in cardiac output

sympathetic

decreased ______ input leads to vasodilation

sympathetic

the baroreceptor reflex protects against ____ term changes in blood pressure

short

failure of the baroreceptor reflex results in orthostatic _____

hypotension

_____ output from the vasomotor centre leads to vasodilation

decreased

what is tissue perfusion

the flow of blood through body tissues or organs

examples of extrinsic control of blood flow through tissues

• control is from outside the tissue or organ

• use nerves or hormones to maintain mean arterial pressure (MAP)

causes of vasodilation

• atrial natriuretic peptide

• nitric oxide

• low oxygen levels

• decreased intravascular pressure

causes of vasoconstriction

• increased sympathetic input

• antidiuretic hormone (vasopressin)

• stretch of vascular smooth muscle

• endothelins

• angiotensin II

blood flow through skeletal muscle

blood flow can increase tenfold or more during physical activity

blood flow through lung

low oxygen levels cause local vasoconstriction and high levels promote vasodilation

blood flow through skin

blood flow increases significantly when body temp. rises

blood flow through brain (cerebral blood flow)

maintained at a relatively constant level at all times

blood flow through heart (coronary blood flow)

under resting conditions uses far more of the oxygen supplied to it than other organs ; the only way to increase available oxygen is to increase blood flow

the total cross-sectional area _____ (increases or decreases) from arteries to capillaries, so blood flow _______ (slows or speeds up)

• increases

• slows

the total cross sectional area _______ (increases or decreases) from capillaries to veins so blood flow ______ (slows or speeds up)

• decreases

• speeds up

the total cross-sectional area is greatest in ____ (arteries, capillaries, or veins).

capillaries

blood flows fastest in ____ (arteries, capillaries, or veins) and slowest in ______ (arteries, capillaries, or veins).

• arteries

• capillaries

capillary exchange of respiratory gasses, most nutrients, and metabolic wastes occurs between the blood and interstitial fluid by ____ (diffusion or bulk flow)

diffusion

_____ (diffusion or bulk flow) across capillary walls causes continuous mixing of fluid between the plasma and the interstitial fluid compartments

bulk flow

net filtration occurs at the ______ (arteriolar or venous) end of a capillary ; net filtration “pushes” fluid _____ (out of or into) a capillary

• arteriolar

• out of

net reabsorption occurs at the _____ (arteriolar or venous) end of a capillary ; net reabsorption “pulls” fluid ____ (into or out of) a capillary

• venous

• into

______ (hydrostatic or osmotic) pressure is due to nondiffusable solutes that cannot cross a boundary between two fluid compartments ; in blood vessels this pressure is due to plasma proteins (mainly albumin)

osmotic

______ (hydrostatic or osmotic) pressure is due to fluid pressing against a boundary between two fluid compartments ; in blood vessels this pressure is due to blood pressure

hydrostatic

fluid moves from the capillary into the interstitial space when the pressures driving fluid out of the capillary are ____ (greater or less) than the pressures pulling fluid back into the capillary ; this occurs when the value for the net filtration pressure (NFP) is ______

• greater

• positive

fluid moves from the interstitial space into the capillary when the pressures driving fluid out of the capillary are ____ (greater or less) than the pressures pulling back into the capillary ; this occurs when the value for the net filtration pressure (NFP) is ______ (positive or negative)

• less

• negative

unusually low levels of plasma proteins (mainly albumin) can result in tissue _____, a condition in which the interstitial spaces become congested with fluid

edema