LIU Chuan Yong

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LIU Chuan Yong ??? Institute of
Physiology Medical School of SDU Tel [phone]
(lab) 88382098 (office) Email
liucy_at_sdu.edu.cn Website www.physiology.sdu.edu.c
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Section 3

• Physiology of the Blood Vessels

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I. Physiological Classification of Blood Vessels
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Windkessel Vessel --- Aorta and big arteries.

• Contain a large amount of elastic tissue besides
  the smooth muscle.
• Transiently store blood during systole, and then
  shrink to produce onward blood flow during
  diastole.

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• Convert the sharp pressure fluctuations in the
  left ventricle (0 to 120 mmHg) into much smaller
  pressure fluctuations in the arteries (80 to 120
  mmHg).
• Convert the intermittent ventricular ejection
  into continuous blood blood in the vessels
• This function of large arteries is known as
  Windkessel effect.

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2. Distribution Vessel Middle arteries

• Rich in smooth, systole or diastole under some
  physical and chemical factors.
• Together with resistance vessels, they match the
  blood flow to different organs with their
  requirements.

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Distribution of Cardiac Output
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3. Precapillary Resistance Vessels
Small arteries and arterioles

• Less elastic than the larger arteries
• Hhave a thicker layer of smooth muscle.
• Provide the greatest resistance to blood flow
  through the arterial system
• since they have narrow lumina.

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4. Precapillary Sphincter muscle-

• Partially determines the amount of blood flowing
  through a particular capillary bed
• Allow only 5 - 10 of the capillary in bed
  skeletal muscles, for example, to be open at
  rest.

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5. Exchange Vessel Capillary

• the walls are composed of only one cell layer
• a simple squamous epithelium, or endothelium.
• permits a more rapid transport of materials
  between the blood and the tissues.

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Make Up of Blood Vessels Capillaries
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6. Capacitance Vessel Systemic veins

• Have a large diameter but a thin wall, which
  includes a thin muscle coat.
• The number is about twice as much as the number
  of arteries,
• The large number and cross sectional area gives
  them an enormous capacity to hold blood.

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Capacitance Vessel Systemic veins

• Most of the time, veins hold more than half the
  blood volume .
• are known as capacitance vessels.
• the great distensibility of veins makes their
  capacity adjustable.
• In times of need, a considerable amount of blood
  can be squeezed from the veins to areas where it
  may be needed.

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II Basic Concept of Hemodynamics

• Blood Flow,
• Resistance of Blood Flow
• and Blood Pressure

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1. Blood Flow (Q)

• Concept The quantity of blood that passes a
  given point in the circulation in a given period
  of time.
• The overall blood flow in the systemic
  circulation is identical to the cardiac output

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(2) Factors determining blood flow
(interrelationships among blood flow, pressure
and resistance.)

• ?P the pressure difference between the two ends
  of the vessels
• R frictional force produced when blood fIows
  through blood vessels.
• Q ?P / R

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(3) Laminar flow and turbulent flow

• Laminar flow blood flows in streamlines with
  each layer of blood remaining the same distance
  from the wall

Laminar flow
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(3) Laminar flow and turbulent flow

• Turbulent flow blood flow in all directions in
  the vessel and continually mixes within the
  vessel.
• because of
• the velocity of blood flow is too great,
• is passing by an obstruction,
• making a sharp turn,
• passing over a rough surface)

C, constriction A, anterograde R, retrograde
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2. Resistance of Blood Flow

• From Q ?P / R (1)
• we get R ?P / Q (2)
• According to Poiseuilles law, Q p?P r4/8?l (3)
• From (3) and (2), we get R 8 ?l/ p r4 p
  is constant
• Note that the resistance (R) of a vessel is
  directly proportional to the blood viscosity (?)
  and length (l) of the vessel,
• but inversely proportional to the fourth power of
  the radius ( r ).
• Normally, L and ? have no change or almost no
  change.
• Therefore, the diameter of a blood vessel plays
  by far the greatest role of all factors in
  determining the resistance ( R ) of blood flow.

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3. Blood pressure

• Blood pressure means the force exerted by the
  blood against the vessel wall
• ( or the force exerted by the blood against any
  unit area of the vessel wall)
• Blood Pressure is stored energy (potential energy)

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Formation of the blood pressure

• (1) Mean circulatory filing pressure (MCFP)
• when heart beat is stopped, the pressure in any
  point of cardiovascular system is equal. This
  pressure is called MCFP
• systemic circulation, 7 mmHg
• pulmonary circulation, 10 mmHg.
• (2) Total peripheral resistance.

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Formation of the blood pressure

• (3) Cardiac pumping
• Energy released from heart contraction is
  transferred into parts,
• 1) kinetic energy (1 of the total),
• 2) potential energy (pressure) (99 of the
  total).
• That means most part of energy used to create the
  blood pressure

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Blood Pressure Generated by Ventricular
Contraction
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Formation of the blood pressure

• (4)Elasticity of Windkessel vessel
• ? diastolic blood pressure
• ? continuous blood flow in diastole
• ? buffering blood pressure

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4. Physical Characteristics of the Systemic
Circulation

• (1)The velocity of blood flow in each segment of
  the circulation is inversely proportional to its
  cross-sectional area.

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4. Physical Characteristics of the Systemic
Circulation

• (2) Pressure and resistance in the various
  portion of the systemic circulations.
• The decrease in pressure in each part of the
  systemic circulation is directly proportional to
  the vascular resistance.

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III. Arterial Pressure
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1. Concept of Arterial Pressure

• Blood pressure in the aorta and other big
  arterials.

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2. Normal Range of Arterial Pressure

• Systolic pressure (Ps) the maximum of the
  pressure during systole
• Diastole pressure (Pd) the minimum pressure
  during diastole
• Pulse pressure the difference between Ps and Pd
  
• Mean arterial pressure the average pressure
  throughout each cardiac cycle.
• Mean arterial pressure (Pm) Pd Pulse pressure
  / 3

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Mean arterial pressure
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Normal range of arterial pressure

• At rest, the arterial pressure of Chinese adult
  young people should be
• Ps 100 120 mmHg
• Pd 60 80 mmHg
• Pulse pressure 30 40 mmHg

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Measurement of the arterial pressure

• Direct (inserting a cannula into the artery)

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Measurement of the arterial pressure

• Indirect (auscultatory) method
• Stethoscope

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Blood Pressure (BP)
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3. Factors Determining Arterial Pressure

• Stroke volume ---- Ps
• Heart rate ---- Pd
• Total peripheral resistance (Ps)
• Action of Windkessel vessel (aorta and other
  large arteries) Pulse pressure
• Mean circulatory filling pressure

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IV. Venous Pressure and Venous Return
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Venous Pressure

• Central venous pressure
• Peripheral venous pressure

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Central venous pressure

• The pressure in the right atrium.
• Normally about 0 mmHg.
• Regulated by a balance between
• the ability of the right ventricle to pump blood
  out
• the tendency of blood to flow from the peripheral
  back into the right atrium.
• Clinical importance
• the hemorrhage
• right heart failure

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Peripheral venous pressure

• Venous pressure in the organs
• Properties
• Low pressure
• Affected by the hydrostatic pressure
• Usually veins are collapsed. (Why?)

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Transmural pressure

• Blood pressure - The pressure adjacent tissues
  exerted on the blood vessel.
• If the transmural pressure is negative (smaller
  than 0), the vein is collapsed

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Venous Return

• Concept The quality of blood flowing from veins
  into the right atrium per minute
• Factors affecting venous return
• Mean system filling pressure
• Cardiac contractility
• Position of the body
• Action of muscular pump
• Respiration movement

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Factors affecting venous return

• 1) Mean systemic filling pressure
• 2) Cardiac contractility
• Cardiac contractility stroke volume
  ventricular pressure in diastole period blood
  from atria and large veins to ventricle venous
  return
• 3) Position of the body
• From lying to standing increase of the
  blood in veins dilation of veins in the lower
  part of the body decrease of venous return

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Factors affecting venous return

• 4) Action of muscular pump (or venous pump)

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Factors affecting venous return

• (5) respiration movement.
• Negative pressure in the thoracic cavity that
  changes with respiratory movement dilation of
  venae cave increase of venous return

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V Microcirculation
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1.Functional anatomy of the microcirculation
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2. pores in the capillary membrane
A
B
A, Continuous Capillaries B, Fenestrated
Capillary
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2. pores in the capillary membrane

• Structurally, capillaries have no smooth muscle
  in their walls.
• They are lined by only a single layer of
  endothelial cells.
• There are gaps between endothelial cells to allow
  for exchange of nutrients and metabolites.

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3. Capillary pressure.

• Arterial end 30 40 mmHg
• Venous end, 10 15 mmHg
• Middle part 25 mmHg

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4. Exchange of nutrients and other substances
between the blood and interstitial fluid

• (1) Diffusion through the capillary membrane.
• Lipid-solute substance can diffuse directly
  through the cell membranes of the capillary
• Water-soluble, liquid-insoluble substance, such
  as Na , Cl, glucose and so forth, diffuse only
  through the capillary pores.

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4. Exchange of nutrients and other substances
between the blood and interstitial fluid

• (2) Transport through the capillary membrane by
  pinocytosis.
• Proteins and many much large substance in the
  plasma (such as lipoprotein) are transported
  through the capillary membrane by means of
  pinocytosis.
• (3) Filtration.
• When the hydrostatic pressure is different on
  the two sides of membrane, the greater pressure
  on one side causes slightly increased diffusion
  of water and dissolved substances toward the
  opposite side.

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VI The Interstitial Fluid

• Water within the body accounts for 60 of the
  total body weight (body fluid)
• 2/3 intracellular compartment
• 1/3 extracellular compartment
• 80, interstitial fluid
• 20, blood plasma

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The distribution of extracellular fluid between
the plasma and interstitial compartments is in a
state of dynamic equilibrium. Tissue fluid is
not normally a stagnant pond but is rather a
continuously circulating medium, formed from and
returning to the vascular system.
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In this way, the tissue cells receive a
continuously fresh supply of glucose and other
plasma solutes that are filtered through tiny
endothelial channels in the capillary walls
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The daily intake and excretion of body water and
its distribution between different intracellular
and extracellular compartment
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1. Formation of the interstitial fluid

• Effective Filtration Pressure (Capillary
  Pressure Interstitial Colloid Osmotic Pressure)
  (Plasma Colloid Osmotic Pressure Interstitial
  Hydrostatic Pressure) (crystal
  pressure?)

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2. Factors Determining Formation of the
Interstitial Fluid (Mechanism of Edema)

• Edema is an abnormally large collection of fluid
  in the interstitial space.
• From the physiology of capillaries and
  lymphatics,
• edema may be due to one or more of the following
  causes

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Mechanism of Edema

• (1) Capillary pressure
• Right heart failure systemic edema
• Left heart failure pulmonary edema
• Late pregnancy edema in legs and foot (pressure
  of uterus on inferior vena cava)

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Mechanism of Edema

• (2) Plasma colloid osmotic pressure
• Protein malnutrition, liver disease (inadequate
  albumin synthesis ) or renal disease (protein
  loss in urine) hypoproteinemia low plasma
  colloid osmotic pressure
• (3) Permeability of capillary wall
• Inflammation or allergy leakage of abnormally
  large quantities of proteins from capillaries

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Mechanism of Edema

• (4) Lymphatic drainage
• Lymphatics are the second circulatory system.
• Structurally, lymphatics are a network of
  blind-ended thin endothelial tubes.
• Although the endothelial lining is not
  fenestrated,
• the intercellular junctions are permeable to
  large molecules.

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Mechanism of Edema

• (4) Lymphatic drainage (continued)
• Lymphatics collect proteins, lipids and other
  large molecules which leak out of capillaries
  into the interstitial space,
• to prevent the osmotic pressure of interstitial
  space from rising,
• and thereby prevent abnormal accumulation of
  fluid in the interstitial space.
• Reduced lymphatic drainage, e.g. in filariasis,
  or involvement of lymph nodes in malignancy
• local or systemic edema.

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3. The function of lymph

• Removing protein from interstitial fluid.
• Regulating balance between plasma and
  interstitial fluid (reabsorption l0 of
  filtration fluid).
• Absorption nutrients (8090 of fat) from
  gastrointestinal tract.
• Removing the particles such as RBC, bacteria,
  lymphatic cell, tissue cell in the interstitium.
• Defense function (to ingest bacteria and to
  produce antibodies)