Cardiovascular Physiology 29

Question 1

Which blood vessels are 60% of the blood volume contained?

Answer 1

The venous blood vessels

Question 2

Where is 1/3 of the blood in the venous system found?

Answer 2

In the liver, bone marrow and skin

Question 3

Why are veins considered high capacitance vessels?

Answer 3

Because they are able to store large volumes of blood

Question 4

How does the composition of veins differ from arteries?

Answer 4

Veins have less smooth muscle than arteries and their walls have a higher collagen to elastin ratio than arteries

Question 5

What is meant by the veins are highly distensible?

Answer 5

They expand very easily at low pressures but have little elastic recoil

Question 6

What does constriction of the veins in the liver, skin and lungs do?

Answer 6

Redistributes 20% of the blood volume to delicate organs like the brain and skeletal muscle

Question 7

What induces constriction of the veins in the liver, skin and lungs?

Answer 7

Sympathetic stimulation

Question 8

What is the relative pressure of the venous system?

Answer 8

It is a low pressure system

Question 9

What do flap like valves in veins do?

Answer 9

They close if blood begins to back up in a vein

Question 10

What do Venous valves do?

Answer 10

Prevent the backflow of blood into the capillaries

Question 11

What is meant by venous valves compartmentalize the veins?

Answer 11

They distribute the weight of the blood into compartments

Question 12

What mechanisms help return blood from the veins to the heart?

Answer 12

• Contraction of venous smooth muscle
• The skeletal muscle pump
• The respiratory pump

Question 13

What is the smooth muscle around the veins innervated by?

Answer 13

The sympathetic nervous system

Question 14

What causes contraction of the venous smooth muscle?

Answer 14

The release of norepinephrine from sympathetic nerve endings

Question 15

What happens when arterioles constrict?

Answer 15

The forward flow of blood is reduced

Question 16

What happens when the veins constrict?

Answer 16

It increases venous pressure, driving more blood out of the veins into the heart increasing forward flow

Question 17

How does the Skeletal pump increase Venous Return?

Answer 17

The Skeletal muscles contract which increases venous pressure forcing more blood back to the heart

Question 18

How does the Respiratory pump increase venous return?

Answer 18

Inspiration increases venous return due to pressure changes between the abdomen and thorax which increase the pressure difference between the peripheral veins and the heart

Question 19

What do any changes in venous return cause?

Answer 19

Changes in stroke volume and affects output through the frank starling mechanism

Question 20

Which mechanisms increase venous return?

Answer 20

• Skeletal muscle pump
• Respiratory pump
• Increased sympathetic activity to the venous smooth muscle

Question 21

How do the mechanisms for increasing venous return affect stroke volume through the frank-starling mechanism?

Answer 21

The increase in venous return causing an increase in atrial pressure increasing end-diastolic ventricular volume which increases the cardiac fiber length causing a greater force during contraction and a greater stroke volume