Flashcards in Vascular / Microcirculation Physiology / Cardiac Patho / Test 2/2 Deck (119):
What dictates the rate of blood flow through most tissues?
Tissue need for nutrients
Blood Volume Distribution SYSTEMIC - 84%
Veins = 64%
Arterial = 13%
Capillaries/Arterioles = 7%
Blood Volume Distribution
Pulmonary / Cardiac ?
Cross-Sectional Area (cm2)
Small arteries 20
Small veins 80
Venae cavae 8
What cross sectional area is larger, veins or arteries?
Veins at 80 cm2 vs. 20cm2
This explains the large storage of blood in the venous system in comparison with the arterial system.
Under resting conditions, the velocity of blood averages about ?
33 cm/sec in the aorta but only 1/1000 as rapidly in the capillaries, about 0.3 mm/sec
Blood remains in the capillaries for only ?
This short time is surprising because all diffusion of nutrient food substances and electrolytes that occurs through the capillary walls must do so in this exceedingly short time.
1 - 3 seconds
The blood flow to each tissue of the body is almost always
precisely controlled in relation to the ?
When tissues are active, they need greatly increased supply of nutrients and therefore much more blood flow than when at rest-occasionally as much as ?
20 to 30 times the resting level.
Yet the heart normally cannot increase its cardiac output more than four to seven times greater than resting levels.
The cardiac output is controlled mainly by the ?
sum of all local tissue flows
Arterial pressure is controlled independently of either ?
local blood flow control or cardiac output.
Blood flow through a blood vessel is determined by two factors ?
(1) pressure difference
(2) vascular resistance
Resistance occurs as a result of friction between the
flowing blood and the ?
Intravascular Endothelium wall
The flow through the vessel can be calculated by
the following formula, which is called Ohm's law:
Q = ∆P/R
Q x R
In regards to Laminar Flow of Blood in the Vessels, what flow is higher; center flow or edges flow?
This is described as Parabolic Velocity
When the rate of blood flow becomes too great, when it passes by an obstruction in a vessel, when it makes a sharp turn, or when it passes over a rough surface, the flow may then become ?
Turbulent flow means that the blood flows crosswise in the vessel as well as along the vessel, usually forming whorls in the blood called what?
a measure of blood flow through a vessel
For any given pressure difference (ml/sec/mmHg)
Conductance = 1/Resistance
conductance of the vessel increases in proportion to ?
that the rate of blood flow is directly proportional to the fourth power of the radius of the vessel, which demonstrates once again that the diameter of a blood vessel (which is equal to twice the radius) plays by far the greatest role of all factors in determining the rate of blood flow through a vessel.
4th power of the diameter
d=4 > 4X4X4X4 = 256mL/min
Poiseuille’s Law (“Fourth Power Law”)
F = π∆Pr4/ 8nl
F is the rate of blood flow,
ΔP is the pressure difference between the ends of the vessel,
r is the radius of the vessel,
l is length of the vessel, and
η is viscosity of the blood.
Vessels in Series:
Rtotal = R1 + R2 + R3 + R4 …
Vessels in Parallel:
1/ Rtotal =1/ R1 + 1/R2 + 1/R3 + 1/R4
Viscosity increases as Hct increases, Viscosity is affected by ?
Pulse pressure definition ?
Difference between Systolic and Diastolic.
Two major factors affect the pulse pressure:
(1) the stroke volume output of the heart and
(2) the compliance (total distensibility) of the arterial tree.
(3), less important factor is the character of ejection from the heart during systole.
In patent ductus arteriosus, one half or more of the blood pumped into the aorta by the left ventricle flows immediately backward through the wide-open ductus into the pulmonary artery and lung blood vessels, thus allowing?
The diastolic pressure to fall very low before the next heartbeat.
In aortic stenosis, the diameter of the aortic valve opening is reduced significantly, and the aortic pressure pulse is ?
Decreased significantly because of diminished blood flow outward through the stenotic valve.
S 100 - D 80 = 20 pulse pressure
In aortic regurgitation, the aortic valve is absent or will not close completely. Therefore, after each heartbeat, the blood that has just been pumped into the aorta flows immediately backward into the left ventricle. As a result ?
the aortic pressure can fall all the way to zero between heartbeats.
S 160 - D 0 = 160 pulse pressure
Also, there is no incisura (Dicrotic notch) in the aortic pulse contour because there is no aortic valve to close.
When the heart ejects blood into the aorta during systole, at first only the proximal portion of the aorta becomes distended because the inertia of the blood prevents sudden blood movement all the way to the periphery. However, the rising pressure in the proximal aorta rapidly overcomes this inertia, and the wave front of distention spreads farther and farther along the aorta. This is called what?
transmission of the pressure pulse in the arteries
The velocity of pressure pulse transmission in the following vessels?
Large arterial branches =
Small arteries =
Aorta = 3 - 5 m/sec
Large arterial branches= 7-10 m/sec
Small arteries = 15 - 35 m/sec
In general, the greater the compliance of each vascular segment, the ?
slower the velocity, which explains the slow transmission in the aorta and the much faster transmission in the much less compliant small distal arteries.
In the aorta, the velocity of transmission of the pressure pulse is ?
15 or more times the velocity of blood flow because the pressure pulse is simply a moving wave of pressure that involves little forward total movement of blood volume.
Note the three lower curves that the intensity of pulsation becomes progressively ?
Less in the smaller arteries, the arterioles, and, especially, the capillaries.
Progressive diminution of the pulsations in the periphery is called ?
damping of the pressure pulses
The degree of damping is almost directly proportional to what 2 items ?
1.) Resistance to blood movement in the vessels
2.) Compliance of the vessels
The pulse pressure in old age sometimes rises to as much as
twice normal, because the arteries have become hardened with arteriosclerosis and therefore are relatively noncompliant.
S160 - D80 = 80
In the circulatory system starting with the ascending aorta, the velocity continues to decrease. What happens to the pressure ?
Starting with the ascending aorta, the pressure begins to increase through each circulatory segment until we reach the arterioles; then it just drops.
Aortic regurgitation has a ?
Wide pulse pressure
Veins have the capability to ?
Constrict & Enlarge
The peripheral veins can also propel blood forward by means of a so-called ___ ___, and they even help to regulate cardiac output, an exceedingly important function
Pressure in the R.A. is the
Venous valves are Arranged so that blood can only move toward the heart.Contraction of leg muscles will squeeze bloodtoward the heart known as?
The most purposeful function of the circulation occurs in the ?
What is the capillary count in the human body?
total surface area of 500 to 700 square meters.
(about one-eighth the surface area of a football field).
any single functional cell of the body is more than
20 -30 microns away from a capillary.
Nutrient artery branches 6 - 8 times before it becomes small enough to be called an ?
Arterioles have an internal diameter of ?
< 20 microns
Arterioles branch 2-5x where their ends are
5 - 9 microns in diameter
Highly muscular and their diameters can change manifold describes what vessel?
(the terminal arterioles) ,smooth muscle fibers encircle the vessel at intermittent points. This describes what vessel?
This can open/close the entrance to the capillary ?
Larger than the arterioles and have a much weaker
muscular coat. However, the pressure inside is much less
than that in the arterioles, so that they can still can contract considerably despite the weak muscle.
Structure of Capillary Wall is comprised of unicellular layer of endothelial cells surrounded by a basement membrane with a
thickness of =
I.D. of capillary is ?
5 - 9 micrometers
Name the 2 pores on the capillary wall?
Intercellular Clefts cleft normally has a uniform spacing with a width of about ?
6 to 7 nanometers slightly smaller than the diameter of an albumin protein molecule.
It is believed that most water-soluble substances diffuse through the capillary membrane along the ?
Blood usually does not flow continuously through the capillaries. Instead, it flows intermittently, turning on and off every few seconds or minutes. The cause of this intermittency is the phenomenon called what?
which means intermittent contraction of the metarterioles and precapillary sphincters.
The most important factor found thus far to affect the degree of opening and closing of the metarterioles and precapillary sphincters is the concentration of oxygen in the tissues. When the rate of oxygen usage by the tissue is great so that tissue oxygen concentration decreases below normal, the intermittent periods of capillary blood flow occur more often, and the duration of each period of flow lasts longer, thereby allowing the capillary blood to carry increased quantities of oxygen (as well as other nutrients) to the tissues.
Regulation of Vasomotion
Flow through each capillary is ?
Because there are so many capillaries in tissue the
overall function becomes ?
- average blood flow rate
- average capillary pressure
- average rate of transfer
By far the most important means by which substances are transferred between the plasma and the interstitial fluid is ?
During exchange of substances between blood and tissue, blood flows along the lumen of the capillary, tremendous numbers of water molecules and dissolved particles diffuse back and forth through the capillary wall, providing continual mixing between the interstitial fluid and the plasma. Diffusion results from
Thermal motion of the water molecules and dissolved substances in the fluid bouncing randomly in every direction.
Diffusion - the most important mechanism by which net movement of nutrients and wastes occur across capillary walls.
1. Lipid soluble substances diffuse easily such as O2, CO2
2. Lipid insoluble subbstances such as?
Must diffuse through what?
H2O, Na, Cl, glucose
collective of spaces located between all cells in the body and makes up about 1/6 of total body vol.
Contains 2 solid structures:
1.) collagen fiber bundles:
2.) Proteoglycan filaments
Extend long distances, strong, provide tensional strength.
Collagen fiber bundles
Very fine thin coiled molecules, form a mat of filaments “brush pile” that add structure to the cell body and prevent occurrence of free fluid in this space.
Fluid is entrapped mainly in the minute spaces among the proteoglycan filaments forming a gel-like slurry.
Fluid in interstitium is in gel form and bound by proteoglycan network. This fluid is known as what?
"Brush pile" of proteoglycan filaments - add structure to the cell body and prevent occurence of free fluid in this space. If the pressure here becomes positive, the filaments are pushed apart and free fluid occurs generating what?
Rivulets of free fluid
1/6 of the body is spaces between cells! Called what ?
4 Primary Forces that determine fluid movement across the capillary?
1.) Capillary pressure (Pc)
2.) Interstitial fluid pressure (Pif)3.) Plasma colloid osmotic
4.) Interstitial colloid osmotic
NDP = (Pc - Pif) - (∏p - ∏if)
Interstitial fluid pressure
Plasma colloid osmotic pressure
Interstitial colloid osmotic pressure
Capillary Pressure Tends to force fluid in what direction ?
outward through the capillary.
Estimation of “functional” capillary pressure =
When Interstitial Fluid Pressure is (+), it tends to force fluid ?
inward into the capillary membrane.
When Interstitial Fluid Pressure is (-), it tends to ?
Pull outward from capillary, favoring filtration.
Pressures can vary greatly from tissue to tissue… However, for loose subcutaneous tissue a value of ____ is generally accepted.
“scavenger” system that removes excess fluid, proteins, debris from interstitium.
Plasma Colloid Osmotic Pressure Tend to cause what?
osmosis of fluid back into the capillary.
Plasma Colloid Osmotic Pressure normal values?
28 mm Hg
19 mmHg molecular effects of dissolved protein,
9 mmHg by the cations held in the plasma by the proteins
Name for the behavior of charged particles near a semi-permeable membrane that sometimes fail to distribute evenly across the two sides of the membrane
is exerted by most dissolved substances. Not at the capillary level however because of the clefts.
Colloid osmotic pressure
(oncotic pressure): pressure caused by dissolved proteins in fluid
Plasma Proteins normal levels?
Albumin 69,000 Daltons
Globulins 140,000 Daltons
Fibrinogen 400,000 Daltons
One gram of which protein will raise the COP most?
Its the # of molecules that counts, not the mass.
g/dl = 4.5
∏p = 21.8
g/dl = 2.5
∏p = 6.0
g/dl = 0.3
∏p = 0.2
80% of COP of plasma results from what?
Interstitial Fluid Colloid Osmotic Pressure Tends to cause osmosis of fluid in what direction ?
Outward through the capillary membrane.
While the capillaries are generally impermeable to proteins, some pores are large enough to pass protein from?
capillaries to interstitium.
COP of interstitium =
Starling forces of the Idealized Capillary:
Pif = -1 mmHg
∏if = 8 mmHg
Pc = 30 mmHg
P∏p = 25 mmHg
Pc = 12 mmHg
P∏p = 25 mmHg
(a proportionality constant)
(is the net fluid movement between compartments)
What dominates Net Colloid Osmotic Pressure (COP) ?
Hydrostatic Pressure Dominates at ?
The Arteriolar End
Net Filtration Dominates at ?
Hydrostatic Pressure Drops in ?
At what point does Net Filtration Cease ?
As the Arteriolar pressure continues to drop below the Plasma COP down towards the capillary / venular end.
What else is taking place as Filtration is happening ?
NDP of0.3 mm Hg, causes slightly more filtration of fluid into the interstitial spaces than reabsorption. This slight excess of filtration is called net filtration, and it is the fluid that must be returned to the circulation through the lymphatics. About 2 ml/min … where does this fluid go?
The normal rate of net filtration in the entire body is only about ?
2 milliliters per minute.
An accessory route by which fluid can flow from the interstitial spaces into the blood?
can carry proteins and large particulate matter away from the tissue spaces, neither of which can be removed by absorption directly into the blood capillaries.
Most important, the lymphatics can carry proteins and large particulate matter away from the tissue spaces, neither of which can be removed by absorption directly into the blood capillaries. This return of proteins to the blood from the interstitial spaces is an essential function without which we would die within about 24 hours.
Lymph from the lower body empties through the ?
thoracic duct into the venous system (junction of left IJV and sub clavian vein).
Most of the fluid filtering from the arterial ends of blood capillaries flows among the cells and finally is reabsorbed back into the venous ends of the blood capillaries; but on the average, about ___ of the fluid instead enters the lymphatic capillaries and returns to the blood through the lymphatic system rather than through the venous capillaries. The total quantity of all this lymph is normally only ?
2 to 3 liters each day.
The fluid that returns to the circulation by way of the lymphatics is extremely important because ?
substances of high molecular weight, such as proteins, cannot be absorbed from the tissues in any other way, although they can enter the lymphatic capillaries almost unimpeded.
the endothelial cells of the lymphatic capillary attached by ?
anchoring filaments to the surrounding connective tissue.
At the junctions of adjacent endothelial cells, the edge of one endothelial cell overlaps the edge of the adjacent cell in such a way that the overlapping edge is free to flap inward, thus ?
forming a minute valve that opens to the interior of the lymphatic capillary.
. Interstitial fluid, along with its suspended particles, can push the valve open and flow directly into the lymphatic capillary. But this fluid has difficulty leaving the capillary once it has entered because any backflow closes the flap valve. Thus, the lymphatics have ?
valves at the very tips of the terminal lymphatic capillaries as well as valves along their larger vessels up to the point where they empty into the blood circulation.
Rate of Lymph Flow through the thoracic duct ?
Other ducts ?
Thoracic = 100 ml/hr
Other = 20 mL/hr
A venous block would result in what ?
- Increased Venous Capillary Pressure (vPc).
- Increase in (if) > Increase in Interstitial fluid pressure (Pif)
- Reversal of the Filtration coefficient back into the vessel.