Blood Vessels-Chps. 14-19 Transporting nutrients and oxygen to the tissues Transporting waste...
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Transcript of Blood Vessels-Chps. 14-19 Transporting nutrients and oxygen to the tissues Transporting waste...
Blood Vessels-Chps. 14-19
• Transporting nutrients and oxygen to the tissues• Transporting waste products away from the tissues• Transporting hormones
Powered by the pumping action of the heartHeartArteries-
Elasticmuscular
ArteriolesCapillariesVenulesveins
2
Lecture outlineI. Review anatomy of vessels
A. ArteriesB. ElasticC. MuscularD. Arterioles- resistance vesselsE. Capillaries- exchange vesselsF. Veins- capacitance vessels
II. Ohm’s law is flow = change in pressure/ resistanceA. Blood Flow
i. Laminar vs. turbulent B. Pressure- blood pressure
i. Mean arterial pressure (MAP)
ii. Central venous pressureiii. Pulse pressure
C. Resistancei. Factors of resistance-
Poiseuille’s law
III. Getting to know “Flow” betterA. VelocityB. Control of flow
i. Autoregulationii. Nervous systemiii. Endocrine-kidney (unit 4)
IV. Exchange of extracellular fluid- the microcirculationA. Starling Forces
i. Capillary hydrostatic pressureii. Interstitial hydrostatic pressureiii. Capillary colloid osmotic pressureiv. Interstitial colloid osmotic pressure
B. Lymphatic drainageC. Causes of edema
3
Arteries• Branch and diverge• Blood away from heart • Walls have 3 tunics
– Tunica intima-simple squamous endothelium
– Tunica media-circular sheets of smooth muscle (vasodilation and vasoconstriction- diameter controlled by local factors and sympathetic NS)
– Tunica adventitia- connective tissue with collagen and elastin in longitudinal arrangement
4
Arteries• Elastic- largest arteries near
heart– Low resistance– More elastin interspersed with
the tunica media– Can distend and recoil back
to pump blood (maintain blood pressure)
• Muscular-– Supply organs– Can regulate diameter of
artery to control blood supply to organ
– Thick tunica media with more smooth muscle
– External and internal elastic lamina.
5
Arterioles
• Smallest arteries- “resistance arteries”
• THICK tunica media- little compliance
• Diameter controlled by local factors (intrinsic) and sympathetic division (extrinsic) and long-term factors (hormones)
• Metarterioles- just upstream of capillary beds.
• Precapillary sphincters-controls blood reaching capillary bed.
6
Capillaries
• Smallest blood vessels• Single layer of endothelial
cells and basal lamina• Renew interstitial fluid- pick
up wastes, drop off nutrients, etc.
• Most cells only 20-30 µm away
• Over 10 billion of them.
7
Types of Capillaries• Continuous
– Most common and least permeable
– Intercellular clefts and transcellular cytosis allows for exchange of molecules
– Abundant in skin and muscle • Fenestrated
– “Holes” in the endothelial membrane
– Found in kidney• Sinusoidal/ discontinuous
– Most permeable and least common
– Big ‘holes” in endothelial membranes
– Big clefts between cells– Liver, spleen, and bone marrow
especially
9
Veins
• Volume reservoir- “capacitance vessels” (60-70%) of blood• Have vasomotor control.• Valves in abdominal veins prevent backflow• Skeletal muscle “pump” and respiratory pump
10
Vascular Distensibility= is the fractional increase in volume for each mmHg rise in pressure times original volume- veins are 8x more distensible
0 mmHg 100 mmHg
Artery
Vein 800 ml
100 ml
In hemodynamics, it’s more valuable to know the total quantity of blood that can be stored in a given portion of the circulation for each mmHg pressure rise. Capacitance = increase in volume/increase in pressureThe capacitance of veins is 24 times that of arteries.
11
Ohm’s Law
• Q=P/R• Flow (Q) through a blood
vessel is determined by: • 1) The pressure difference
(P) between the two ends of the vessel– Directly related to flow
• 2) Resistance (R) of the vessel– Inversely related to flow
• Can you rearrange the equation above and solve for P? Solve for R?
12
Blood Flow (L/min)
• Blood flow is the quantity of blood that passes a given point in the circulation in a given period of time.
• Unit of blood flow is usually expressed as milliliters (ml) or Liters (L) per minute.
• Overall flow in the circulation of an adult is 5 liters/min which is the cardiac output.
• CO= HR X SV
• 70 b/min x 70 ml/beat =4900ml/min
13
Characteristics of Blood Flow
• Blood usually flows in streamlines with each layer of blood remaining the same distance from the wall, this type of flow is called laminar flow.
– When laminar flow occurs, the velocity of blood in the center of the vessel is greater than that toward the outer edge creating a parabolic profile.
Blood Vessel
Laminar flow
14
Laminar Vs. Turbulent Blood Flow
Turbulent flow
Causes of turbulent blood flow:• high velocities• sharp turns in the circulation• rough surfaces in the circulation• rapid narrowing of blood vessels
• Laminar flow is silent, whereas turbulent flow tend to cause murmurs.
• Murmurs or bruits are important in diagnosing vessels stenosis, vessel shunts, and cardiac valvular lesions.
15Aortic Aneurysm Atherosclerosis
Effect of Wall Stress on Blood Vessels
Turbulent flow increases resistance and wall stressNitric oxide released by endothelial cells to reduce the stress
16
Blood Pressure—The driving force Stephen Hales
1733• Blood pressure (hydrostatic pressure) is the force exerted by the blood against any unit area of vessel wall.
• Measured in millimeters of mercury (mmHg). A pressure of 100 mmHg means the force of blood was sufficient to push a column of mercury 100mm high.
• All vessels have it – but we’re usually addressing arteries when we refer to it.
17
contracted
Ejected Blood
When the LV contracts more blood enters the arterial system than gets pushed onward. This causes the arteries to stretch and pressure within them to rise. The highest pressure achieved is known as the systolic pressure.
18
relaxedRecoil of the elastic artery
As the LV relaxes, the stretched arterial walls recoil and push the contained blood onward through the system. As they recoil, the amount of blood contained decreases as does pressure. The lowest pressure achieved just before the next contraction is the diastolic pressure.
19
Mean Arterial Pressure (MAP)
• Is an average, but not a simple arithmetic average
• Heart spends longer in diastole than systole
• Value is significant- why?• The difference between the mean
arterial pressure and the pressure in the venous system drives the blood through the capillary beds.
• MAP= .4 (systolic) + .6 (diastolic)= 96mmHg
• Venous pressure is about 2mmHg
FLOW = arterial - venous pressure (P)resistance (R)
100 mmHg
R = .1mmHg/ml/min
A
20 mmHg
100 mmHg
R = .1mmHg/ml/min
B
0 mmHg
FLOW = 1000 ml/min
FLOW = 800 ml/min
20
Central Venous Pressure• Pressure in the right atrium is called
central venous pressure.
• determined by the balance of the heart pumping blood out of the right atrium and flow of blood from the large veins into the right atrium.
• normally 0 mmHg, but can be as high as 20-30 mmHg.
• More vigorous heart contraction (lower CVP).
• Less heart contraction (higher CVP)• Factors that increase CVP:
- increased blood volume- increased venous tone (peripheral pressure)- dilation of arterioles- decreased right ventricular function- Skeletal and respiratory pumps
Figure 15-9; Guyton and Hall
21
Arterial Pulsations and Pulse Pressure• The height of the pressure pulse is the systolic
pressure (120mmHg), while the lowest point is the diastolic pressure (80mmHg).
• The difference between systolic and diastolic pressure is called the pulse pressure (40mmHg).
Systolic Pressure
Diastolic Pressure
Pulse Pressure}
22
Factors Affecting Pulse Pressure
• Stroke volume —increases in
stroke volume increase pulse
pressure, conversely decreases
in stroke volume decrease
pulse pressure.
• Arterial compliance —decreases in compliance increases pulse pressure; increases in compliance decrease pulse pressure.
Figure 15-5; Guyton and Hall
23
DiastolicPressure
Systolic PressureCardiac output
Total Peripheral resistance
Mean Pressure
Time
Stroke volume
Arterial compliance
}Pulse Pressure
HR x SV = CO = MAP/ TPRHR x SV = CO = MAP/ TPRMAP= (0.4 SP) + (0.6 DP)MAP= (0.4 SP) + (0.6 DP)PP= SP- DPPP= SP- DP
Stroke volume
Heart
rate
24
Damping of Pulse Pressures in the Peripheral Arteries
• The intensity of pulsations becomes progressively less in the smaller arteries.• The degree of damping is proportional to the resistance of small vessels and arterioles and the compliance of the larger vessels.•Elastic arteries:
• large radii, low resistance, some pressure reservoir
•Muscular arteries•Smaller radii•Little more resistance•More pressure reservoir
•Arterioles•Thick tunica media vs. radius•major pressure reservoir
Figure 15-6; Guyton and Hall
What’s an anatomical reason for why the pressure fluctuation disappears here?
25
Blood Pressure Profile in the Circulatory System
Systemic Pulmonary
Aor
ta
Lar
ge a
rter
ies
Smal
l art
erie
s
Art
erio
les
Cap
illa
ries
Pre
ssu
re(m
mH
g)
0
20
40
60
80
100
120
Ven
ule
s
Smal
l vei
ns
Lar
ge v
ein
s
Ven
ae c
avae
Pu
lmon
ary
arte
ries
Art
erio
les
Cap
illa
ries
Ven
ule
s
Pu
lmon
ary
vein
s
Circulatory pressure- averages 100mmHg Arterial blood pressure-100-35mmHgCapillary pressure- 35mmHg at beginning and 10-15mmHg at endVenous pressure-15-0mmHg
•Large pressure drop across the arteriolar-capillary junction
26
How Would a Decrease in Vascular Resistance Affect Blood Flow?
FLOW = P RESISTANCE
FLOW = P RESISTANCE
Conversely,
Therefore, flow and resistance are inversely related!
• Resistance is the impediment to blood flow in a vessel.
• Can not be measured directly
Resistance R = ΔP = mmHg Q ml/min
27
Resistance makes a difference for the two sides of the heart!
• Let’s say the CO (flow) is roughly 100ml/sec (easier math).
• To calculate systemic resistance vs. pulmonary resistance we need to know pressure differences.
• Pulmonary resistance is 16-2/100• Systemic resistance is 100/100• So, CO is same on each side of
heart (has to be!), but right side generates less pressure due to lower resistance (1/7th than systemic).
16mmHg
2mmHg
100 mmHg
0mmHg
R = ΔP = mmHg Q ml/min
28
Factors of Resistance
Poiseuille’s Law = Q =_Pr4
8l• Blood viscosity• Total vessel length• Vessel diameter
• Resistance (length)(viscosity)
(radius)4
29
Viscosity
• What are the major contributors to blood viscosity?
• As viscosity increases, resistance will…
• An increase in plasma EPO will cause resistance to…
Figure 14-11; Guyton and Hall
Figure 14-12; Guyton and Hall
30
Total Vessel Length
• Longer the vessel.....more opportunity for resistance.
Radius
31
So, lets review:Blood Flow is volume flowing/time
• Ohm’s Law• Blood Flow (Q) = Δ P/ R
• Increase pressure- increase blood flow
• Decrease resistance- increase blood flow
• Increase resistance- decrease blood flow
– Vessel diameter– Viscosity– length– Turbulence (usually
result of an occlusion reducing vessel diameter unevenly)
P1 P2
ΔP= P1-P2
Blood flow in center is fastest- because that is the area of least resistance
• As resistance decreases, flow will…
• As the pressure gradient increases, flow will…
• Which does the heart influence more: pressure gradient or resistance?
32
Flow (amount of blood/time) MUST be the same through vessels in
series!If a pipe’s diameter changes over its length, a fluid will flow through narrower segments faster than it flows through wider segments because the volume of flow per second must be constant throughout the entire pipe.
Flow (volume/time) vs. velocity (distance/time) are NOT synonyms!
33
If capillaries have such a small diameter, why is the velocity of blood flow so slow?
We need slow blood flow in the capillaries—the exchange vessels
Aorta >Arterioles> Small veins >Capillaries
34
Control of blood flow through vessels- Why is this important?
• Perfusion vs. ischemia vs. hypoxia vs. anoxia vs. infarction
• Tissue Perfusion Dependent on:– Cardiac output– Peripheral resistance– Blood pressure
• Regulation of perfusion dependent on:– Autoregulation (Acute, local,
intrinsic)– Neural mechanisms (acute)– Endocrine mechanisms (long-
term)
http://www.flometrics.com/services/artery/
35
Autoregulation the automatic adjustment of blood flow to each tissue in proportion to the tissue’s requirements at any
instant even over a wide range of arterial pressures
Working Muscle Tissue
active hyperemia: when tissues
become active, blood flow increases.
Aka: intrinsic metabolic vasodilation
Tissue CO2 levels rise
Tissue O2 levels fall
Tissue temp. rises
Lactic acid levels rise
CO2 removed
Arterioles serving tissue vasodilate and precapillary
sphincters relax
Increased blood flow to tissue
Lactic acid removed
Heat removed O2 delivered
Now arterioles will vasoconstrict and precapillary sphincters contract
36
Autoregulation of Blood Flow to specific tissues
• Vasodilator agentsHistamineNitric oxideElevated temperaturesPotassium/hydrogen ionsLactic acidCarbon dioxideAdenosine/ ADP
• VasoconstrictorsNorepinephrine and
epinephrineAngiotensinVasopressin (ADH)Thromboxane
37
Arterial Pressure = Cardiac Output x Total Peripheral Resistance
Long Term BP control- hormonal
Short term BP control- nervous
Other ways to ultimately change blood flow throughout the body is to change Pressure and Resistance
38
Brain Centers involved in Short Term BP Control
• Vasomotor – Adjusts peripheral
resistance by adjusting sympathetic output to the arterioles
• Cardioinhibitory- transmits signals via vagus nerve to heart to decrease heart rate. (parasympathetic)
• Cardioacceleratory/ contractility-sympathetic output
39
Vasomotor control: Sympathetic Innervationof Blood Vessels
• Sympathetic nerve fibers innervate all vessels except capillaries and precapillary sphincters (precapillary sphincters
follow local control)
• Innervation of small arteries and arterioles allow sympathetic nerves to increase vascular resistance.
• Large veins and the heart are also sympathetically innervated.
Figure 18-2; Guyton and Hall
40
Anatomy of the Baroreceptors• spray type nerve endings located in
the walls of the carotid bifurcation called the carotid sinus and in the walls of the aortic arch-pressoreceptors that respond to stretch.
• Signals from the carotid sinus are transmitted by the glossopharyngeal nerves .
• Signals from the arch of the aorta are transmitted through the vagus into the NTS.
• Important in short term regulation of arterial pressure.– They are unimportant in long term
control of arterial pressure because the baroreceptors adapt.
Figure 18-5; Guyton and Hall
41
Response of the Baroreceptors to Arterial Pressure
• Baroreceptors respond to changes in arterial pressure.
• As pressure increases the number of impulses from carotid sinus increases which results in:
1) inhibition of the vasoconstrictor 2) activation of the vagal center
Constrict
Common Carotids
Constrictors
Pressure at
Carotid Sinuses
Arterial Pressure
Figure 18-5; Guyton and Hall
Figure 18-7; Guyton and Hall
42
Functions of the Baroreceptors• Maintains relatively constant pressure despite
changes in body posture.
DecreaseCardiac Output
Sensed ByBaroreceptors
Supine StandingDecrease
Venous return
VasomotorCenter
SympatheticNervous Activity
DecreaseArterial Pressure
BP rises
Detected by baroreceptors in aortic arch & carotid sinus
Info sent to cardiac and vasomotor centers
Decreased vasomotor activity
Decreased PR
Increased cardioinhibitory activity
Decreased cardioacceleratory activity
Decreased CO
Decreased BP
Decreased NE release on arterioles
Vasodilation
Increased vagus activity
Increased ACh release on heart
Decreased SV and HR
Decreased NE release on heart
44
Carotid and Aortic Chemoreceptors
• Chemoreceptors are chemosensitive cells sensitive to oxygen lack, CO2 excess, or H ion excess.
• Chemoreceptors are located in carotid bodies near the carotid bifurcation and on the arch of the aorta.
• Activation of chemosensitive receptors results in excitation of the vasomotor center.
Sympatheticactivity
Chemoreceptors VMCO2CO2pH
BP
Figure 18-5; Guyton and Hall
45
Nervous control also found in the heart- Bainbridge Reflex
• Prevents damming of blood in veins, atria and pulmonary circulation.
• Increase in atrial pressure increases heart rate.
• Stretch of atria sends signals to VMC via vagal afferents to increase heart rate and contractility.
VasomotorCenter
Heart rate Contractility
Atrial Stretch
Vagal
afferents
46
The Microcirculation-chapter 16
• Important in the transport of nutrients to tissues.
• Site of waste product removal.• Over 10 billion capillaries with surface
area of 500-700 square meters perform function of solute and fluid exchange.
Figure 16-1; Guyton and Hall
47
Most substances are exchanged via diffusion
Concentration differences across capillary enhances diffusion.
48
• Capillary hydrostatic pressure (Pc)-tends to force fluid outward through the capillary membrane.
(30 mmHg arterial; 10mmHg venous- average 17.3mmHg)
• Interstitial fluid hydrostatic pressure (Pif)- opposes filtration when value is positive (but it’s not positive-- due to lymphatic drainage! – 3mmHg).
Figure 16-5; Guyton and Hall
Determinants of Net Fluid Movement across Capillaries-Starling forces
49
Determinants of Net Fluid Movement across Capillaries-Starling forces
• Plasma colloid osmotic pressure ( c)- opposes filtration causing osmosis of water inward through the membrane – Colloid osmotic pressure of the blood plasma. (28mmHg)– 75% from albumin; 25% from globulins
• Interstitial fluid colloid pressure ( if) promotes filtration by causing osmosis of fluid outward through the membrane – Colloid osmotic pressure of the interstitial fluid. (8mmHg)– 3gm%
Figure 16-5; Guyton and Hall
50
Net Forces in Capillaries
Mean forces tending to move fluid outward:Mean Capillary pressure 17.3
Negative interstitial free fluid pressure 3.0 Interstitial fluid colloid osmotic pressure 8.0TOTAL OUTWARD FORCE 28.3
Mean force tending to move fluid inward: Plasma colloid osmotic pressure 28.0TOTAL INWARD FORCE 28.0
Summation of mean forces:Outward 28.3Inward 28.0
NET OUTWARD FORCE 0.3
mmHg
Net filtration pressure of .3 mmHg which causes a net filtration rate of 2ml/min for entire body (2-4 liters/day!)
Filtration= Kf X (Pc- Pif - c + if)
Capillary BP
Capillary OP
Pre
ssur
e
Distance along the capillaryArterial end Venous end
Filtration
Reabsorption
If capillary BP is greater than capillary OP, there will be net movement of fluid out of the capillary.
If capillary BP is less than capillary OP, there will be net movement of fluid into the capillary.
Filtration= Kf X (Pc- Pif - c + if)
52
2ml/min Excess tissue fluid is returned to the blood vessels via the lymphatic system!
• Lymphatic vessels collect lymph from loose connective tissue – Fluid flows only toward the
heart– Collect excess tissue fluid
and blood proteins and carry to great veins in the neck
– All three tunics– NO pump!– Valves!
• contains plasma, water, ions, sugars, proteins, gases, amino acids- is colorless, but low in protein compared to blood
• Lymph can contain hormones, bacteria, viruses, cellular debris, traveling cancer cells, macrophages
53
Causes of Edema• Excessive accumulation of tissue
fluid.• Edema may result from:
– High arterial blood pressure.– Venous obstruction.– Leakage of plasma proteins
into interstitial fluid.– Valve problems– Cardiac failure– Decreased plasma protein.– Obstruction of lymphatic
drainage. Elephantiasis- Wuchereria bancrofli
I would see your homework packet and study page 303 of Guyton and Hall!
54
Unbalanced Ventricular Output
55
Unbalanced Ventricular Output
56
Hypertension capillary BP ISF formation
Starvation
Lack of dietary
protein
in plasma albumin
capillary OP
Histamine
ISF formation
capillary permeability
Vasodilation capillary BP
ISF formation
57
Burn/crush injury
capillary permeability Cap OP ISF
formation
L. Ventricle failure
Backup of blood in pulmonary circuit
pulmonary capillary BP
ISF formation
Decreased blood flow in systemic
circuit
systemic capillary BP
ISF formation