Venous Physiology Flashcards
What is known as the pressure on the walls of a vessel? AKA difference in pressure between the vein and tissue
Transmural pressure
What type of pressure is determined by the difference between the pressure within a vein and in the tissue?
Transmural pressure
What is known as the pressure within the vascular system because of the weight of a column of blood?
Hydrostatic pressure
What describes fluid movement across the capillary?
Starling equilibrium
What is capacitance?
Volume of blood that a vessel can hold at a given pressure
What are the capacitance vessels of the body?
VEINS
The venous side holds about how much of the total blood volume within the body?
2/3rds
What happens to the resistance as the cross-sectional area of a vessel increases?
Resistance to flow decreases
What ability do veins have to accommodate increases in blood flow without increased the pressure gradient?
Their ability to change shape
Where is hydrostatic pressure greatest?
Lower in the body
What is the formula for hydrostatic pressure?
density of blood x gravity x height of column of blood
What does total pressure within a blood vessel include?
dynamic pressure (supplied by heart contraction) + hydrostatic pressure
What plays a greater role in determining overall venous pressure?
Hydrostatic pressure
When is the pressure within the vascular system about equal to dynamic pressure?
When lying down
When lifting a hand above your head, what will happen to the hydrostatic pressure?
Decreases
Will exercising increase or decrease the pressure gradient in the venous system?
The pressure will decrease which causes the pressure gradient to INCREASE by vasodilation
With a LOW transmural pressure, where is pressure highest and lowest?
Lower pressure INSIDE the vein compared to outside at the tissue
Function of compression stockings to decrease blood pooling?
It increases tissue pressure (outside vein) which then decreases transmural pressure (inside vein)
What describes movement of fluid across the capillary?
Starling equilibrium
What forces act to move fluid OUT of the capillary in relation to starling equilibrium?
- High intra-capillary pressure (pressure in capillary > tissue) or low interstitial pressure
- Interstitial osmotic pressure (solutes in tissue > capillary)
What forces act to move fluid INTO the capillary in relation to starling equilibrium?
- Low intra-capillary pressure (pressure in capillary < tissue) or high interstitial pressure
- Capillary osmotic pressure (solutes in capillary > tissue)
Does standing increase or decrease capillary pressure?
Increases - forcing fluid out of capillaries and into tissues
What is the fluid that moves out of the capillary and into the tissues picked up by?
Lymphatics system
What is known as the pressure exerted by fluid when there is a difference in the concentrations of solutes across the capillary endothelium?
Osmotic pressure
What will a DVT do to venous pressures?
Cause an increase due to blood not being able to return to heart as quickly
What will a DVT do to capillary pressures?
With increased venous pressures, there will also be increased capillary pressures leading to edema
During inspiration, what happens to the pressure in the chest vs. abdomen?
Chest pressure - decreases
Abdominal pressure - increases which partially collapses the IVC
Does inspiration or expiration aid in venous blood flow coming up from the legs towards the heart?
Expiration - less pressure within the abdominal cavity
What is the minimum pressure inside a vein needed to prevent collapse?
5 mmHg
In a 6-foot-tall individual in a standing position, hydrostatic pressure will add approximately how much to the measured pressure at the ankle?
100 mmHg
What is the pressure gradient across the capillary bed in an uplifted arm owing to the change in hydrostatic pressure?
40 mmHg
When an individual moves from a supine to a standing position, which of the following pressures specific to the venous system increases?
a. osmotic pressure
b. hydrostatic pressure
c. transmural pressure
d. gravitational force
Transmural pressure
How does the action of the calf muscle pump, under normal circumstances, offset fluid loss in interstitial tissue?
It helps to DECREASE venous pressure
What is the difference between the pressure gradient across the capillary bed in a supine and standing position?
Nothing, it is the same
What is the reference point for dynamic pressure?
LV
What is the reference point for hydrostatic pressure?
RA (2-6 mmHg)
How does standing influence capillary pressure? (hint: will it increase or decrease)
Increases - forcing fluid OUT of the capillaries and into the tissues
