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