Lecture 12: VENOUS BLOOD FLOW AND THE HEART

Question 1

Where is the most blood found in humans?

Answer 1

In the systemic veins

Question 2

What do humans have in their circulatory system?

Answer 2

More blood than they need

Question 3

How much blood is stored in the systemic veins?

Answer 3

Approximately 2/3

Question 4

Why can’t the excess blood be in other areas of the circulatory system?

Answer 4

Cant be in the heart, pulmonary circuit (too short), arteries (maintaining MAP) or capillaries (too small)

Question 5

What is the total blood volume in a 70kg human?

Answer 5

Approximately 5L

Question 6

What is CO at rest?

Answer 6

Approximately 5L/min

Question 7

What is arterial pressure at rest?

Answer 7

Approximately 100mmHg

Question 8

What is arterial volume at rest?

Answer 8

Approximately 0.7L (13%)

Question 9

What is venous pressure at rest?

Answer 9

Approximately 5mmHg

Question 10

What is venous volume at rest?

Answer 10

Approximately 3.2L (64%)

Question 11

What is the structure of arteries?

Answer 11

Thick and rigid tunica media so no way of allowing extra volume

Question 12

What is the compliance of arteries?

Answer 12

Low

Question 13

What is the structure of veins?

Answer 13

Thin and compliant tunica media so is able to allow extra volume

Question 14

What is the compliance of veins?

Answer 14

high

Question 15

What is compliance?

Answer 15

The extent to which a vessel allows deformation in response to an applied force

Question 16

What is the formula for compliance?

Answer 16

change in volume/change in pressure

Question 17

What happens in arteries?

Answer 17

Large change in pressure results in a small change in volume

Question 18

What happens in veins?

Answer 18

Small change in pressure results in a large change in volume

Question 19

What do veins have?

Answer 19

Survival value

Question 20

What can veins do in an emergency situation?

Answer 20

Move blood across to arteries

Question 21

What would happen after an arterial puncture?

Answer 21

Loss of arterial blood

Question 22

What would happen after loss of arterial blood?

Answer 22

Life threatening fall in arterial pressure

Question 23

What would happen after a life threatening fall in arterial pressure?

Answer 23

It will be sensed by the nervous system and venoconstriction will occur

Question 24

What control is venoconstriction under?

Answer 24

Neural

Question 25

What happens due to venoconstriction?

Answer 25

Veins constrict and push blood froward into the heart and arteries

Question 26

What does high vascular compliance in veins mean?

Answer 26

That blood tends to accumulate (pool)

Question 27

What volume is larger?

Answer 27

venous volume is larger than arterial volume

Question 28

How is venous volume while supine (lying down)?

Answer 28

Uniform from head to toe

Question 29

How is venous volume in the upright position?

Answer 29

Below the heart it increases and above the heart it decreases (due to gravity)

Question 30

Where is there extreme venous pooling?

Answer 30

In the legs and feet

Question 31

What counteracts venous pooling?

Answer 31

Valves and tone of surrounding tissue

Question 32

What does a continuous column have?

Answer 32

No valves

Question 33

What happens in a continuous column?

Answer 33

Heavy at bottom

Question 34

What does a discontinuous column have?

Answer 34

Valves

Question 35

What happens in a discontinuous column?

Answer 35

More even distribution of weight

Question 36

What tissue particularly counteracts venous pooling?

Answer 36

Skeletal muscle because it can alter its tensile state

Question 37

What varies among individuals?

Answer 37

Resting muscle tone

Question 38

What does muscle tone act to do?

Answer 38

Stiffen the veins - makes them less compliant and prone to pooling

Question 39

What do some people prone to fainting have?

Answer 39

Low muscle tone and excessive venous pooling

Question 40

What does skeletal muscle contractions increase?

Answer 40

Venous return to the heart

Question 41

What happens when a muscle contracts?

Answer 41

It pushes blood up and down

Question 42

What do valves superior to the contracting muscle do?

Answer 42

Open, allowing blood to move to the heart

Question 43

What do valves inferior to the contracting muscle do?

Answer 43

Are forced close, preventing back flow of blood to the capillaries

Question 44

What is contracting muscle causing blood to flow to the heart called?

Answer 44

The skeletal muscle pump

Question 45

What does increased venous return mean?

Answer 45

Increased stroke volume

Question 46

What is starlings law of the heart?

Answer 46

The more stretch muscle fibres are before a contraction, the stronger the contraction will be

Question 47

How does a stronger contraction occur (starlings law)?

Answer 47

When ventricles fill with more blood because of increased venous return, the thick and thin filaments are pulled further apart so can generate a greater maximum force of contraction