Section 6 Flashcards
Why do venules respond to arteriolar chemical signals?
Venules respond to arteriolar chemical signals to ensure matched inflow and outflow of blood through the capillaries.
What is the role of venules in the venous system?
Venules, despite having minimal tone and generating little resistance to blood flow, play a role in responding to arteriolar chemical signals to maintain matched inflow and outflow through the capillaries.
What distinguishes veins from arteries in terms of their function as vessels?
Unlike arteries, veins are not considered conductance vessels but are instead considered capacitance vessels.
Why are veins considered capacitance vessels?
Veins are considered capacitance vessels because they have a large diameter, offer little resistance to flow, and serve as a blood reservoir, accommodating more blood due to their ability to easily distend.
What is the role of smooth muscle in the walls of veins?
The smooth muscle in the walls of veins has little myogenic tone, allowing veins to easily distend and accommodate more blood, serving as a blood reservoir.
What percentage of blood is typically found in the veins at any given time?
At any given time, around 60% of the blood in the body is in the veins.
What is venous return, and how is it expressed?
Venous return is the volume of blood returning to the atria per minute. It is expressed in units similar to cardiac output, measured in Litres per minute.
How does increasing venous capacity impact circulating blood?
Increasing venous capacity means more blood is being stored, potentially reducing the amount of available circulating blood. Conversely, decreasing venous capacity results in more blood circulating.
Why is regulating venous capacity important?
Regulating venous capacity is crucial for controlling venous return, ensuring that the volume of blood returning to the heart is balanced. Under steady-state conditions, venous return must be equal to cardiac output.
True or false:
Under steady-state conditions, venous return must be equal to cardiac output.
True
Despite being a low-pressure system, venous capacity affects venous return and hence cardiac output. Why does this phenomenon occur?
You should be thinking of the Frank-Starling Relationship! If venous return increases, by decreasing venous capacity, then this will lead to an increase in ventricular end diastolic volume, which will increase cardiac output. If venous return decreases, by increasing venous capacity, then there will be a decrease in ventricular end diastolic volume, which will decrease cardiac output.
How does sympathetic activity influence venous return?
Increasing sympathetic activity decreases venous capacity, leading to increased venous return and subsequently higher cardiac output.
What is the role of the skeletal muscle pump in venous return?
When skeletal muscles contract, they compress nearby veins, reducing venous capacity and increasing venous pressure, contributing to enhanced venous return.
: Explain the impact of gravity on venous return.
Gravity increases hydrostatic pressure in veins below the heart, expanding venous capacity and potentially decreasing venous return. However, mechanisms like increased sympathetic activity and the muscle pump counteract these effects.
What is the function of venous valves?
Venous valves prevent backward flow of blood, ensuring the effectiveness of mechanisms like venous vasoconstriction and the muscle pump in moving blood towards the heart.
