PHYSIOLOGY : Venous and Capillary Pressure and Flow

DISCLAIMER: phases of cardiac venous pulse are not included; this is also very much summarized (crammed at the last hour)

venous system

venous system

a low resistance, low pressure, high distensible part of the vascular system

venous system

When blood or plasma is infused into the vascular system, about 25 to 30 times more blood migrates to what system?

about 25 to 30 times more

When blood or plasma is infused into the vascular system, __________ blood migrates to venous system rather than the arterial system.

20

At normal pressures, the veins are approximately __ times more distensible than the arteries.

veins

relatively thin walled structures

venous valves

they prevent back flow of venous blood

venous valves

They support the column of blood so that increase in capillary pressure in the dependent parts of the body are minimized

varicose veins

marked dilation or insufficiency of the venous valves leads to

central venous pressure

it is the pressure in the right atrium, at the entrance of the great vein

central venous pressure

it is regulated by a balance between the ability of the heart to pump out blood from the right atrium and the tendency for blood to flow from the peripheral vessels back into the right atrium

decreases

If the cardiac pumping is strong, central venous pressure ____

increases

If cardiac pumping is weak, central venous pressure ____

increases

Central venous pressure ____ with an increase in flow of blood into the right atrium from the veins

increase in blood volume, increase on large vessel tone throughout the body; with resultant increase in peripheral venous pressure, dilation of the systemic small vessels with decrease in peripheral resistance

what conditions can cause an increase in venous return?

Peripheral venous pressure

the pressure in the peripheral veins, and is dependent to a certain extent on the central venous pressure.

central venous pressure

to a certain extent, the peripheral venous pressure is dependent on ____

intravascular catherization

Venous pressures, either central or peripheral, are ordinarily determined by _____

centimeters of water in a vertical manometer

venous pressure is usually expressed as ___

10-15 mm Hg

Mean pressure values on the venous side normally range from ____ in small venule

4-8 mm Hg

Mean pressure values on the venous side normally range from ___ in peripheral veins

0-2 mm Hg

Mean pressure values on the venous side normally range from ____ in the vena cava

respiratory venous pulse and cardiac venous pulse

what are the two patterns of venous pressure pulse?

cardiac venous pulse

This pattern of venous pressure pulse represents a retrograde reflection of a somewhat distorted version of the right atrial pulse pattern

Respiratory venous pulse

With inspiration, external veins tend to collapse while thoracic veins distend, with expiration, the above changes are reversed, and the peripheral veins distend with blood. What is this pattern of venous pressure pulse?

a wave, c wave, x descent, v wave, y descent

the cardiac venous pulse consists of:

vis a tergo, vis a fronte, vis a latere

enumerate the determinants of venous pressure

Vis a tergo

This refers to the pressure transmitted into any vessel by a ventricular systole, acting in the direction of blood flow.

Vis a fronte

This refers to any pressure that affects flow of blood into the right atrium.

resistance to flow from capillaries, resistance to flow from the arterial side

Vis a tergo may be influenced by:

resistance from the veins, resistance from the heart

Vis a fronte may be influenced by:

Vis a letere

It is the force from the sides

muscle pump, increased venomotor tone secondary to autonomic nerve stimulation

Vis a latere may be influenced by:

mean circulatory pressure and auxiliary factors

The factors influencing the return of blood from the left ventricle through the venous system and back to the heart are classified into:

skeletal muscle pump, venous valves, venomotor tone, respiratory pump, suction effect of cardiac contration and relaxation

Enumerate the auxiliary factors

Mean circulatory pressure

This is a static pressure expressing the degree of fullness of the systemic circulation.

systemic filling pressure

it is another term for mean circulatory pressure

systemic filling pressure

it represents the hemodynamic gradient for the entire systemic circulation from the root of the aorta to the right atrium.

7 mm Hg

what is the mean value of systemic filling pressure

rhythmic cycles of reflex contraction and relaxation

they are responsible for the unconscious swaying motion of the body when an individual stand still

skeletal muscle pump

When an individual stand, there is rapid migration of blood from the thorax to the lower parts of the body, resulting in decreased venous return and a 20-25% fall in resulting in cardiac output. As a result muscles contraction and blood within the veins is squeezed centrally, and during relaxation the veins refill. What auxiliary factor is this?

skeletal muscle pump

it plays a key role in maintaining venous return during walking and running

skeletal muscle pump

it serves to lower venous pressure in the dependent parts of the leg, facilitate venous return, and relieve venous congestion in the area

venous valves

they are very thin, transparent, cusp-like structure in the veins of the extremities, which insure unidirectional flow

Venomotor tone

Constriction of splanchnic veins in certain stresses, as in hemorrhage and shock, shifts stored blood in the splanchnic circulation to the general circulation, and thus substantially increases venous return and cardiac output. What auxiliary factor is this?

Respiratory pump

This refers to the assistance given to venous return by the mechanical movements of respiration

-2 to -4 mm Hg

The intra-thoracic pressure is usually slightly sub-atmospheric and varies during quiet breathing from about _____ during expiration

-5 to -7 mm Hg

The intra-thoracic pressure is usually slightly sub-atmospheric and varies during quiet breathing from about _____ during inspiration

systemic filling pressure

it is the main force driving blood toward the heart

Suction effect of cardiac contraction and relaxation

During ventricular systole, when the AV valves are closed, the AV ring is drawn downward by the ventricles. Thus, enlarging the atria, and lowering the relative internal pressures within the atria. These tend to increase flow from the vena cava and pulmonary veins. What auxiliary factor does this refer to?

microcirculation

it is considered as a closed system, however, its walls are much more permeable than those of any other part of the circulation

least

The vessels that make up the microcirculation have an irregular course and configuration; because of their great total cross-sectional area, the flow velocity is ____ at this point.

True capillaries

they are the most important functional units of the microcirculation

True capillaries

They are short, narrow tubes, about 7-10 um in diameter, with a wall consisting of a single layer of endothelial cells and a basement membrane.

single layer of endothelial cells and a basement membrane

the wall of true capillaries consist of:

actin and myosin

at least 5% of endothelial cell protein consists of ____

hydraulic conductivity

Across venules, the contractile proteins regulate ____

sympathetic vasoconstrictor fibers

Flow through the arterioles and metarterioles is controlled mainly by ____

FALSE

Flow through the capillaries is under neural control. TRUE or FALSE?

arteries, arterioles, and precapillary sphincters

What regulates the flow through capillaries?

autoregulation

What is the process that involves the regulation of arteries, arterioles, and precapillary sphincters, influenced by the local metabolic state of the tissue or organ?

metabolic and myogenic autoregulation

microcirculation is capable of controlling its own circulation through ____