Lecture 14: The circulatory system

Question 1

Why does the circulatory system require different blood vessels?

Answer 1

To accommodate different pressures

Question 2

What do muscular arteries do?

Answer 2

They control resistance to flow

Question 3

What do elastic arteries do?

Answer 3

They allow for smooth, pulsatile flow

Question 4

What do capillaries act as?

Answer 4

Exchange vessels for nutrients

Question 5

What are veins?

Answer 5

Low pressure capacitance vessels that hold a reservoir of blood

Question 6

What are the common layers of blood vessels?

Answer 6

Lumen

Tunica intima (interna)

Tunica media

Tunica adventitia (externa)

Question 7

Describe the Tunica intima (interna)

Answer 7

Endothelium

Supporting connective tissue

Release of paracrine signals

Question 8

Describe the Tunica media

Answer 8

• Elastic tissue
• Smooth muscle

Question 9

Describe the Tunica adventitia (externa)

Answer 9

• Principally collagen

Question 10

Does the tunica media get inflammed during disease?

Answer 10

Yes

Question 11

What do veins and arteries have in common?

Answer 11

Endothelial layer/ Tunica intima (interna)

Muscular layer/ Tunica media

External layer/ Tunica adventitia (externa)

Question 12

When do the valves in veins shut?

Answer 12

If the pressure comes down in the wrong direction

Question 13

Is it true that blood vessels require specialisations to
cope with different pressures and functions?

Answer 13

Yes

Question 14

How do elastic arteries store energy?

Answer 14

• Due to their thick tunica media
• The energy stored in the wall of elastic arteries during systole is released in diastole, maintaining the blood flow at this time and smoothing it

Question 15

Is it true that in arteries, the tunica media is denser the further away you are from the lumen?

Answer 15

Yes

Question 16

What does the Windkessel Effect describe?

Answer 16

• Describes how elastic arteries dampen the pulsatile nature of blood flow, turning the heart’s “stop-and-go” beats into smoother, more continuous flow.

Question 17

When the heart pumps blood (systole), large arteries like the aorta stretch to hold the extra blood. When the heart relaxes (diastole), the arteries recoil and push the blood forward, helping maintain smooth, continuous blood flow—this is called the Windkessel effect.

Answer 17

When the heart pumps blood (systole), large arteries like the aorta stretch to hold the extra blood. When the heart relaxes (diastole), the arteries recoil and push the blood forward, helping maintain smooth, continuous blood flow—this is called the Windkessel effect.

Question 18

Does aortic pressure ever fall to 0?

Answer 18

No, so blood flow in arteries is always pulsatile and so always moving

Question 19

Is it true that elastic arteries convert intermittent pressure into pulsatile flow/

Answer 19

Yes

Question 20

Is it true that the pulmonary and systemic circulation follow the same pattern but at different pressure?

Answer 20

Yes

Question 21

What does blood flow in blood vessles depend on/

Answer 21

Blood flow depends on blood vessel radius

Question 22

What 3 factors is resistance to blood flow in blood vessels determined by?

Answer 22

Length of blood vessels

Viscosity of blood

Radius of blood vessels

Question 23

is it true that longer blood vessels provide greater resistance to blood flow?

Answer 23

Yes

Question 24

Does the length of each blood vessel remain constant?

Answer 24

Yes

Question 25

Viscosity of blood and how it affects resistance to blood flow...

Answer 25

Blood with a lot of solute would provide more resistance Solutes such as hemocrit, albumin, etc do not change much under normal circumstances

Question 26

Is it true that small arteries and artreioles are the site of controlled resistance to blood flow?

Answer 26

Yes The contraction of the smooth muscle reduces the diameter

Question 27

What law describes how blood flow depends on vessel radius?

Answer 27

Ohms law

Question 28

Give ohms law

Answer 28

Ohms Law: Q = (P1 – P2)/R, where Q=flow, (P1-P2) = pressure difference between the two ends and R is the resistance of the vessel

Question 29

This resistance will rise if the vessel is narrower; the flow will be reduced; and the pressure drop will be increased:

Answer 29

This resistance will rise if the vessel is narrower; the flow will be reduced; and the pressure drop will be increased:

Question 30

What is meant by the phrase: 'blood flow is normally laminar'?

Answer 30

"Blood flow is normally laminar" means that blood usually flows in smooth, straight layers, with little mixing between them. Flow is fastest at the centre and slowest – essentially stationary – at the outside

Question 31

What is blood flow proportional to ?

Answer 31

Resistance

Question 32

Give the equation that shows that blood flow is inversely proportional to resistance

Answer 32

R is resistance; η is viscosity, l is length, and r is radius and π is the mathematical constant (approximately 3.14). Thus a reduction in radius by ½ gives an increase in resistance of 16 fold Only radius changes in this equation

Question 33

Do very small changes in radius result in large changes in flow?

Answer 33

Yes

Question 34

What happens to the blood flow when the velocity is high?

Answer 34

Blood flow becomes turbulent The layers (laminae) of laminar flow break up and flow becomes disordered In these circumstances, the resistance to flow is raised Turbulent flow tends to lead to endothelial damage and hence to arterial disease

Question 35

What controls access to microcirculation?

Answer 35

Sphincters control access to the microcirculation

Question 36

Is it true that Sphincters constrict/dilate arterioles?

Answer 36

Yes

Question 37

How are capillaries designed to optimise diffusion?

Answer 37

- Capillaries are thin walled, essentially a single layer of endothelial cells (on a basement membrane) - Their structure minimises resistance to diffusion into and from the interstitium

Question 38

What determines gas and nutrient exchange in capillary beds?

Answer 38

Blood flow

Question 39

How do metabolites and respiratory gases cross the capillary walls?

Answer 39

Via diffusion

Question 40

What equation shows that blood flow determines gas and nutrient exchange in capillary beds?

Answer 40

J= P.A(Ci - C0) P is the permeability coefficient; A the area of exchange. In most cases, the concentration gradient (Ci-Co) that generates this flux (J) is dissipated by the end of the capillary bed. The flow of blood therefore determines how much is delivered or removed from a particular tissue

Question 41

How easily do lipid soluble molecules cross the capillary walls?

Answer 41

Lipid soluble molecules, which include O2 and CO2, diffuse easily through capillary cell membranes.

Question 42

How easily do hydrpohilic molecules cross the capillary walls?

Answer 42

Hydrophilic molecules travel through pores, via a paracellular route.

Question 43

How easily do molecules >60kd cross capillary walls?

Answer 43

Molecules >60kd are not transferred and many plasma proteins are retained in the circulation – important in the equilibrium between plasma and the e.c.f.

Question 44

What is the site of fluid equilibrium? (between the plasma and the interstitial fluid)

Answer 44

Capillaries

Question 45

What is the interstitial fluid/tissue fluid?

Answer 45

Interstitial fluid is the fluid that surrounds and fills the spaces between cells in your body tissues. 🧫💧

Question 46

Equilibrium in capillary beds are determined by pressures known as...

Answer 46

Starling’s forces

Question 47

Starling’s forces...

Answer 47

Loss of fluid from the plasma, owing to hydrostatic pressure Reabsorption of fluid into plasma, owing to colloid osmotic pressure or oncotic pressure

Question 48

Describe hydrostatic pressure

Answer 48

- This is the blood pressure inside the capillary. - It pushes fluid out of the capillaries into the surrounding tissue. - Happens more at the arterial end of the capillary.

Question 49

Describe osmotic pressure

Answer 49

- This is caused by proteins (like albumin) in the blood. - These proteins pull fluid back in to the capillaries from the tissue. - Happens more at the venous end.

Question 50

What is the equilbrium between the plasma and tissue fluid determined by?

Answer 50

Hydrostatic pressure

Question 51

At the arteriole end what force is greater, hydrostatic pressure or oncotic pressure?

Answer 51

Hydrostatic pressure. This pushes fluid out of the capillaries.

Question 52

Is osmotic pressure caused by plasma proteins?

Answer 52

Yes

Question 53

does osmotic pressure usually remain the same?

Answer 53

Yes — osmotic pressure tends to stay fairly constant across the capillary. That’s because it depends mostly on the concentration of plasma proteins, especially albumin, which doesn't easily leave the capillaries.

Question 54

Does osmotic pressure at the venule end draw fluid back into the capillaries?

Answer 54

yes

Question 55

What is filtration determined by?

Answer 55

Filtration is determined by hydrostatic and oncotic pressure: The Starling hypothesis

Question 56

Is it true that Filtration/reabsorption depends on the difference between hydrostatic and oncotic pressure?

Answer 56

Yes

Question 57

Filtration pressure =

Answer 57

Filtration pressure = hydrostatic pressure – oncotic pressure

Question 58

Balance is not be perfect, but it’s necessary for lymphatic sampling

Answer 58

Any excess of fluid is taken up into lymphatics and returned to the circulation Larger lymphatics have valves and contract rhythmically Samples the blood for foreign particles

Question 59

Do muscle pumps enhance venous return?

Answer 59

Yes

Question 60

When your leg muscles contract during movement, they squeeze the nearby veins, pushing blood back toward the heart. One-way valves in the veins stop the blood from flowing backward. This muscle pump action helps improve venous return, especially from the lower body.

Answer 60

When your leg muscles contract during movement, they squeeze the nearby veins, pushing blood back toward the heart. One-way valves in the veins stop the blood from flowing backward. This muscle pump action helps improve venous return, especially from the lower body.

Question 61

To summarise, this lecture has considered:

Answer 61

The structure and function of blood vessels in the systemic circulation The role of elastic arteries in smoothing pulsatile flow The role of resistance vessels in regulating blood flow The role of capillaries in exchange and in the equilibrium between plasma and interstitial fluid The role of veins as capacitance vessels