THE BLOOD VESSELS (vascular system). CONTENT 1)Overview of Vascular System 2)Arterial Pressures and Flow 3)Capillary Exchange 4)Venous Blood Flow 5)Regulation

THE BLOOD VESSELS

(vascular system)

CONTENT

1) Overview of Vascular System

2) Arterial Pressures and Flow

3) Capillary Exchange

4) Venous Blood Flow

5) Regulation of the Vascular System

6) Special Circulations

H2OGlucoseLipidsAmino acidsVitaminesMineralsO2

Blood vessel

External Environment

Permeability of Blood Vessels ?

Tissue cells

permeable to

H2OGlucoseLipidsAmino acidsVitaminesMineralsO2,

ArteriesVeins

Capillaries

veins54%

capillaries 5%

arteries 11%12%

18%Distribution of Blood

(at rest)Distribution of Blood

(at rest)

1) Simplest pathway

Circulatory pathwaysCirculatory pathways

artery

100 mmHg0

vein capillary

2) Portal systemLiver intestines

coronary

4) Arterial anastomoses

3) Arteriovenous anastomosis

skin

Skeletal muscles

Skin

Brain

Liver-Intestine

Coronary

The blood flows along pressure gradient.

100 mmHg

40

40

40

40

40

20

20

20

20

20

0

Can blood vessel volume change quickly ?

Can blood vessel volume change quickly ?

Skeletal muscles

Skin

Brain

Liver-Intestine

Coronary

hemorrhagehemorrhage afterbefore

Skin

Liver-Intestine

Skeletal muscles

Coronary

Brain

100 mmHg

Total BVV Individual BVV Total BVV Individual BVV

Skin

Liver-Intestine

Skeletal muscles

Coronary

Brain

98 mmHg

20%

Functions of blood vessels? Functions of blood vessels?

#1: help maintain blood pressure #1: help maintain blood pressure

before Vascular ShockVascular Shock after

Skin

Liver-Intestine

Skeletal muscles

Coronary

Brain

Total BVV Total BVV

Skin

Liver-Intestine

Skeletal muscles

Coronary

Brain

100 mmHg 50 mmHg

before Exercise Exercise after

Skin

Liver-Intestine

Skeletal muscles

Coronary

Brain


Skin

Liver-Intestine

Skeletal muscles

Coronary

Brain

100 mmHg 100 mmHg

before Dinner Dinner after

Skin

Liver-Intestine

Skeletal muscles

Coronary

Brain


Skin

Liver-Intestine

Skeletal muscles

Coronary

Brain

100 mmHg 100 mmHg

before Hypothermia Hypothermia after

Skin

Liver-Intestine

Skeletal muscles

Coronary

Brain


Skin

Liver-Intestine

Skeletal muscles

Coronary

Brain

100 mmHg 100 mmHg

Functions of blood vessels? Functions of blood vessels? #2: help redistribute blood #2: help redistribute blood

autonomic nerves

muscle

hormonesautoregulation

precapillary sphincters

1) Overview Of Vascular

System

2) Arterial Pressures

and Flow



5) Regulation of the

Vascular System


100 mmHg

40

40

40

40

40

0

20

20

20

20

20

Is the blood flow

continuous or intermittent ?

both

systole

120 mm Hg40 mm Hg

Intermittent flow continuous flow

heart aorta

earlydiastole

100 mm Hg40 mm Hg

heart aorta

75 mm Hg 40 mm Hgend ofdiastole(refilled)

heart aorta

systole

120 mm Hg40 mm Hg

heart aorta

Function of large arteries?

Function of large arteries?

change intermittent flow into continuous flow

change intermittent flow into continuous flow

hose

systole

120 mm Hg

75 mm Hg

40 mm Hg

40 mm Hgend ofdiastole(refilled)

heart

heart

aorta

aorta

systolic pressure (Ps)

diastolic Pressure (Pd)

pulse pressure (Pp)

Predict the change in Ps and Pp in atherosclerosisPredict the change in Ps and Pp in atherosclerosis

- is the average pressure over the cardiac cycle

- MAP = Pd + 1/3 (Ps – Pd)

Mean arterial pressure (MAP)

systolic pressure (Ps)

diastolic Pressure (Pd)

110 mmHg

80 mmHg

- MAP = 80 + 1/3 (110 – 80) = 90 (mmHg)

The pressure pulse disappears in capillaries.The pressure pulse disappears in capillaries.

Pulse Points

Measure arterial pressures using sphygmomanometerMeasure arterial pressures using sphygmomanometer

BLOOD FLOW Definition: volume of blood moving through a blood vessel in a given time (ml/min)

F = P

R

P1 P2

P = P1 - P2F

Peripheral Resistance

- opposition to blood flow due to friction between the blood and the blood vessel wall and among components of the blood

heart

120 mm Hg40 mm Hg

Total vascular bed

Factors on Peripheral Resistance

1) blood viscosity ()

- A measure of thickness of the blood

RBCs Plasma lipids

- resistance

- stable (short-term)


1) blood viscosity ()

2) blood vessel length

- length resistance

- stable


1) blood viscosity () - stable (short-term)

2) blood vessel length

- stable

3) blood vessel radius

- radius resistance

- change quickly under physiological control

Poiseuile’s law

r4

8LF =

2x

16x

Poiseuile’s law

r4

8LF =

2x

16x

1) Overview Of Vascular

System

2) Arterial Pressures

and Flow

3) Capillary Blood Flow

and Exchange


5) Regulation of the

Vascular System


Capillary Blood Flow

is gated by precapillary sphincters

- blood shunt

- open alternatively

Permeable to:

O2, CO2

ions H2O

glucose amino acids fatty acids vitamins hormones Impermeable to:

proteins

blood cells

Capillary Wall

Routes of the cross-wall movement

1) intercellular cleft

2) fenestration

more important in specific regions like liver, bone marrow, and

lymphoid organs

3) endothelial cells

driving force for the movement?

Basementmembrane

Mechanisms of Capillary Exchange

1) simple diffusion:

regulated by:

- concentration gradient

- permeability of capillary

walls

Particles move along their own concentration gradient.

O2O2

CO2CO2


1) simple diffusion

2) filtration/reabsorption (difficult stuff!)

filtrationfiltration

reabsorptionreabsorption

-- fluid movement from plasma to interstitium (outward)

Filtration

Reabsorption

-- fluid movement from interstitium back to plasma (inward)

determined by: - hydrostatic pressures- colloid osmotic pressures

CapillaryBPCapillaryBP

capillary hydrostatic pressure (BP)

- favor filtration

- decreases from arterial end to venous end

CapillaryBPCapillaryBP

Interstitial hydrostatic pressure


Interstitial fluid hydrostatic pressure

- favor filtration in loose connective tissues

- favor reabsorption in encapsulated organs (brain, kidneys)

Plasma colloid osmotic (oncotic) pressure (p)

- favor reabsorption

Capillary BPCapillary BPInterstitial hydrostatic pressure


Plasma colloid osmotic pressurePlasma colloid osmotic pressure

What does colloid mean ?

solution colloid suspension

particle size < 1 nm 1-100 nm > 100 nm

stand still

Aftercentrifugation

Whole blood

Plasma

NaCl

Whole bloodPlasmaNaCl


Plasma colloid osmotic pressure

- is generated by large molecules like proteins that are impermeable to capillary wall.

Plasma protein

gm/dL p (mmHg)

Albumin 4.5 21.8

globulins 2.5 6.0

fibrinogen 0.3 0.2

Total 7.3 28.0

How do plasma proteins generate

colloid osmotic pressure ?

Review of Osmosis and Osmotic Pressure

A B

100% H2O 100% H2O

A B

100% H2O < 100% H2O

100% H2O < 100% H2O

A B

Osmosis

100% H2O < 100% H2O

A B

hydrostatic pressure

osmotic pressure

Balance between hydrostatic pressure and osmotic pressure is reached.

100% H2O < 100% H2O

A B

osmotic pressure

Principle-1

differential membrane permeability

A B

Principle-1


% H2O % H2O

% H2O % H2O

A B

Principle-1


100% H2O < 100% H2O

A B

osmotic pressure

Principle-2

determined by the number of particles

100% H2O < 100% H2O

A Bcapillary wall

plasmaproteins

plasmaInterstitialfluid

Question 1 Can electrolytes generate osmotic pressure across capillary wall?

100% H2O < 100% H2O

A Bcapillary wall

plasmaproteins


Question 2 Can blood cells generate osmotic pressure across capillary wall?

100% H2O < 100% H2O

A Bcapillary wall

plasmaproteins


Question 3 Does plasma osmotic pressure favor filtration or reabsorption?

salts

proteinsWater Concentration = 70%

Water Concentration = 90%

interstitial fluid

Blood

salts

proteins

cell

Capillary BPCapillary BPInterstitial hydrostatic pressure



Interstitial oncotic pressureInterstitial oncotic pressure

4) Interstitial oncotic pressure

- favor filtration,- generated by proteins leaked out of capillary .

SUMMARY

What is the difference between diffusion and filtration/reabsorption ?

plasma

Filtration

interstitium

diffusion


1) simple diffusion

2) filtration/reabsorption (difficult stuff!)

3) transcytosis

transcytosistranscytosis

Large molecules such as peptide hormones and other proteins, have to be transported across endothelial cells via endocytosis/exocytosis.

transcytosis

1) Overview Of Vascular System

2) Arterial Pressures And Flow





BLOOD VESSELS

VEINS

- thinner walls but larger lumens, - able to constrict,- act as blood reservoirs,

contain ~60% of body’s blood, thus, called capacitance vessels.

- travel in parallel with arteries,- located more superficially.

- Venous valves prevent backflow of venous blood.

- assisted by respiration and skeletal muscle contraction.

Characteristics of Venous Blood Flow

Incompetent venous valves cause hemorrhoids & varicose veins.Incompetent venous valves cause hemorrhoids & varicose veins.







BLOOD VESSELS

Maintaining Blood Pressure

100 mmHg

40

40

40

40

40

0

20

20

20

20

20

The regulated targets:

1) The heart

2) Blood vessel wall

3) Precapillary sphincters

Essential !

Mechanisms of Vascular Control

1) Neural Control

2) Hormonal Control

3) Autoregulation (Local Control)

a. Control by sympathetic nervous system

- innervates arteries and arterioles in almost all organs,

- releases norepinephrine (NE) as neurotransmitter,

- causes vasoconstriction (except in the heart and brain).

b. Control by parasympathetic nervous system

- innervates some arteries and arterioles,

- releases acetylcholine (Ach) as neurotransmitter,

- causes dilation of arteries and arterioles.

Neural Reflexes

1) Baroreceptor-Initiated Reflexes

2) Chemoreceptor-Initiated Reflexes

1) Baroreceptor-Initiated Reflexes The reflexes sense variation of MAP, and try to bring MAP back to normal immediately.

When MAP increases

Stretch of baroreceptors to a greater extend

Cardiovascular centers

Autonomic nerves

heart rate and cardiac contractility, and peripheral vasodilatation

Drop of MAP

When MAP drops

Stretch of baroreceptors to a lesser extend

Cardiovascular centers

Autonomic nerves

Increase in heart rate and cardiac contractility, and peripheral vasoconstriction

Elevation of MAP

chemoreceptor

2) Chemoreceptor-Initiated Reflexes - The reflexes sense variation of O2, CO2, and pH of the blood, and try to bring them back to normal immediately.

- The reflexes serve the primary purpose of regulating respiration, with side effects on blood vessels.

Hormonal Control of Blood Vessels 1) Epinephrine and Norepinephrine

2) Angiotensin II

3) Vasopressin = antidiuretic hormone (ADH)

4) Atrial Natriuretic peptide

Hormonal Control of Blood Vessels 1) Epinephrine and Norepinephrine

- secreted from adrenal gland,

- cause peripheral vasoconstriction via alpha adrenergic receptors.

(Note: low dose epinephrine can cause vasodilation in a few organs via beta-2 adrenergic receptors)

2) Angiotensin II

- is converted from blood borne angiotensinogen under the regulation of renin which is produced in kidney.

- is released from posterior pituitary when blood volume decreases or osmolarity increases,

- causes vasoconstriction via V1 receptor.

3) Vasopressin (antidiuretic hormone)

Vasopressin

posterior pituitary

anterior pituitary

- is released from atria when blood volume increases,

- caused vasodilation and natriuresis/diuresis.

4) Atrial Natriuretic peptide (factor)

Local Control of Blood Flow – Autoregulation

100 mmHg- Autoregulation is the

automatic adjustment of

blood flow to each tissue

in proportion to its

requirements at any given

instant.

- Changes in blood flow through individual organs are controlled intrinsically by modifying the diameter of local arterioles feeding the capillaries.

- two mechanisms: metabolic and myogenic

METABOLIC (chemical) CONTROLS - Declining levels of oxygen and accumulation of metabolic waste products (CO2, low pH, and inflammatory chemicals) cause increased blood flow to the local area by vasodilation of arterioles and relaxation of precapillary sphincters.

Local chemicals involved in autoregulation

hypoxia,

adenosine,

H+, lactic acid,

CO2 ,

K+.

All of the above causes vasodilation.

Myogenic Controls

Smooth muscles in the walls of arterioles respond to STRETCH due to changes in blood pressure and blood low to prevent large fluctuations in local blood flow.

a. Increased stretch causes vasoconstriction.

b. Decreased stretch causes vasodilation.

c. The overall result is constant perfusion.

d. possibly via stretch-regulated Ca channels.

Constant flow

Mechanisms of Vascular Control

1) Neural Control

2) Hormonal Control

3) Autoregulation (Local Control)

SUMMARY







BLOOD VESSELS

Cerebral Circulation

1)

2)

Sources of arterial blood flow to the brain

1)

2)

Drain to jugular vein and vertebral vein

Susceptibility to ischemia

- seconds: loss of consciousness

- minutes: irreversible injury

Regulation

- constant (60 -160 mmHg),

- due to strong autoregulation

- proportional to local neuronal activities.

(CO2, pH, adenosine, and K+),

Coronary Circulation

Can cardiac muscles get nutrients from the blood in heart chambers?

The cardiac muscles get nutrients from coronary circulation.

Anterior view Posterior view

Features of Coronary Circulation

• ~ 225 ml/min (4-5% CO) at resting state,

RV

LVepicardium

endocardium

• decreased blood flow in systole,

• pressure gradient from endocardium to epicardium,

• highly efficient uptake of oxygen (70/100).

Features of Coronary Circulation

• rich in arterial anastomosis to secure blood supply.

RV

LVepicardium

endocardium

Features of Coronary Circulation (continued)

• regulated primarily by local metabolic products such as adenosine, K+, H+, and CO2.

ATPADPAMP

adenosine adenosine

Coronary arterioles

Blockade of coronary artery causes myocardial infarction, or heart attack.

RV

LVepicardium

endocardium

Pulmonary Circulation

Two vascular beds:

1) pulmonary vasculature from pulmonary A

to alveoli

2) bronchial vasculature from aorta

to bronchial tree

Pulmonary Vasculature

- Distribution: to alveoli

- Function :

Characteristics

- low resistance/pressure,

- 500-700 SF,

- affected by gravity.

systemic vasculaturepulmonary vasculatureConstriction of Dilation of

O2

Ventilation-Perfusion Ratio

Bronchial vasculature

Function:

Distribution

Provide oxygenated blood to bronchial tree.

from bronchial arteries

Cutaneous Circulation

Skin

warm hot

SSkin vessels under emotional control

HeadNeckShouldersupper chest

SKELETAL MUSCLE CIRCULATION

• Local factors dominate

during exercise.

• low flow at rest,

Blood Distribution at Rest

Blood Distribution during Exercise

Regulation during Exercise

1. The neural control

2. Control by local factors

1) from motor cortex 2) from proprioceptors

- initiates the following changes:

The neural control

cardiac output,

unstressed volume (venous blood),

venous return.

Venous return is assisted by muscular activity and respiration.

Vasoconstriction in

Skin,

Intestines,

kidneys, and

inactive muscles.

2) Control by local factors

- lactate, K+, and adenosine,

- vasodilation only in the active skeletal muscle,

- The number of perfused capillaries is increased.

1) Overview of Vascular System

2) Arterial Pressures and Flow





SUMMARY OF BLOOD VESSELS

Documents

THE BLOOD VESSELS (vascular system). CONTENT 1)Overview of Vascular System 2)Arterial Pressures and Flow 3)Capillary Exchange 4)Venous Blood Flow 5)Regulation