SP&RS 14

Question 1

Describe the circulatory system.

Answer 1

Dual circulation system in series.

Question 2

Why does the circulatory system require different vessels.

Answer 2

To accommodate different pressures and functions. Veins, arteries and capillaries.

Question 3

Describe veins.

Answer 3

-low venous pressure (0-8mm Hg)
-capacitance vessels holding a reservoir of blood.
-can dramatically increase the amount of blood in the heart.

Same structure as artery but also has valve.

Question 4

Describe capillaries.

Answer 4

-exchange vessels
-nutrient exchange, allow diffusion

1 cell thick, least amount of distance for fastest exchange of diffusion.

Question 5

Describe arteries.

Answer 5

-high arterial pressure (~100mm Hg)

elastic arteries:
-smooth muscle pulsatile flow

muscular arteries:
-control resistance to flow
-further away from the heart

External eleastic membrane, smooth muscle, internal elastic membrane, lumen, endothelium.

Question 6

What is the common structure of blood vessels?

Answer 6

Tunica adventitia (externa)- principally collagen

Tunica media- elastic tissue and smooth muscle

Tunica intima (interna)- endothelium, supporting connective tissue and release of paracrine signals

Lumen

Question 7

What do elastic arteries do?

Answer 7

They absorb high pressure and store energy.

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.

More sense, further away from lumen- can withstand more pressure.

Question 8

What would happen if arteries were completely rigid?

Answer 8

-Ventricular pressure rises to a maxim during systole- the systolic pressure. It falls to a low level during diastole- to accept more blood.
-If arteries were rigid, arterial pressure would also fall during diastole.
-If flow follows pressure, it would be intermittent.

Question 9

How does the volume of arteries and pressure work together?

Answer 9

Arteries are sufficiently compliant that their volume increases with pressure.

-As blood is pumped into the aorta and major arteries, they stretch, this increases the volume inside the tube.
-Thus in systole, more blood flows in than out.
-The walls of the aorta and elastic arteries recoil in diastole, maintaining blood flow.

Question 10

What is the Windkessel effect?

Answer 10

Expansion during high pressure and recoil at low pressure.

Therefore, aortic pressure never reaches 0.

Question 11

What do elastic arteries convert?

Answer 11

They convert intermittent pressure into pulsatile flow.

-Aortic pressure rises to a maximum during systole (systolic pressure).
-It falls to a minimum during diastole (diastolic pressure).
-Flow follows the pressure, but it never reaches 0. It s pulsatile rather than intermittent.

Question 12

Do pulmonary and systemic circulation follow the same pattern?

Answer 12

Yes, they follow the same pattern at different pressures.

Question 13

What does blood flow depend on?

Answer 13

Blood vessel radius.

Question 14

What is resistance determined by?

Answer 14

Length of blood vessels
Viscosity of blood
Radius of blood vessels

Question 15

How does the length of blood vessels affect blood flow?

Answer 15

-Longer blood vessels would provide greater resistance.
-The length of each vessel remains constant.

Question 16

How does the viscosity of blood affect blood flow?

Answer 16

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

Question 17

Can the length of blood vessels, viscosity of blood and radius of blood vessels change over time?

Answer 17

Length of blood vessels: relatively constant day-to-day, but over time changes (e.g. growth of child).

Viscosity of blood: relatively constant, but changes as a response (e.g. mestrual cycle or cut on skin).

Radius blood vessels: can change over time.

Question 18

Where is the site of controlled resistance to flow?

Answer 18

Small arteries and arterioles.

Question 19

What is the relationship between resistance and pressure?

Answer 19

Resistance will rise if the vessel is narrower, the flow will be reduced and the pressure will drop if increased.

Question 20

What is Ohms Law?

Answer 20

Q = (P1-P2)/R

Q = flow
(P1-P2) = pressure difference between the two ends
R = resistance of the vessel

Question 21

How can blood flow be described? Why

Answer 21

Blood flow is normally laminar.

-Friction on wall causes edges to slow down.
-Flow is considered essentially as layers of fluid that move over each other.
-Flow is fastest at the centre and slowest at the outside.

Question 22

What is Poiseuille equation (laminar flow)? What does it tell us about flow?

Answer 22

R = 8nl/pir4

R = resistance, n = viscosity, l = length, r = radius
8nl = constant, it doesn’t change inside a single individual
pi = constant

Reduction in radius by 1/2 gives an increase in resistance by 16-fold.

Flow is proportional to resistance.

Question 23

What happens when the layers of laminar flow break up?

Answer 23

Flow becomes disordered.

-If velocity is high, flow becomes turbulent.
-Rebounds and causes damage to epithelial cells.
-Can lead to arterial disease.

Question 24

What do sphincters do?

Answer 24

Control access to the microcirculation (capillaries).

Question 25

What type of arteries control how blood moves into capillaries?

Answer 25

Muscular arteries. E.g. restrict the size of artery and increase the size of the diameter of capillary.

Question 26

What is the role of capillaries?

Answer 26

-Exchange of blood gases and metabolites. -Generation of an equilibrium between plasma and interstitial fluid. -Designed to optimise diffusion and resistance.

Question 27

What determines the gas and nutrient exchange in capillary beds? What equation describes this?

Answer 27

Blood flow (and conc). J = P.A(Ci-C0) P = permeability coefficient, A = area of exchange, (Ci-C0) = concentration gradient, J = flux which is generated by concentration gradient J is usually dissipated by the end of the capillary bed.

Question 28

What is the permeability coefficient determined by?

Answer 28

The thickness of tissue.

Question 29

How do molecules determine permeability (lipid soluble molecules, hydrophilic molecules and molecules >60kd)?

Answer 29

Lipid soluble molecules (including O2 and CO2): diffuse easily through capillary cell membranes). Hydrophilic molecules: travel through pores, via a paracellular route. 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 30

What are the two components of extracellular fluid volume?

Answer 30

-3l of plasma -10.5l of interstitial fluid There is an equilibrium between these two compartments. Capillaries are the site at which this equilibrium is determined.

Question 31

What is Starling's forces?

Answer 31

Capillary beds are the site at which equilibrium between plasma and interstitial fluid is established, this is governed by 'Starling forces'. -Loss of fluid from the plasma, due to hydrostatic pressure. -Reabsorption of fluid into plasma, due to colloid osmotic pressure / oncotic pressure.

Question 32

How does hydrostatic pressure affect the equilibrium between plasma and interstitial fluid?

Answer 32

-Arteriolar end has a higher hydrostatic pressure than the venular end. -There is no oncotic pressure, so water is pushed out and does not go back in. -Fluid is forced out of the bloodstream.

Question 33

How does oncotic pressure affect the equilibrium between plasma and interstitial fluid?

Answer 33

-Oncotic pressure in the capillaries cannot change. -This is counteracted by osmotic pressure of plasma proteins. -Large molecules (>60kd) do not cross capillary walls. -Their osmotic pressure draws back fluid into capillaries.

Question 34

What is the Starling hypothesis?

Answer 34

Filtration/reabsorption is determined by difference between hydrostatic pressure and oncotic pressure. Filtration pressure = hydrostatic pressure - oncotic pressure

Question 35

Where does filtration and reabsorption take place in the capillaries?

Answer 35

Filtration- arterial end (higher hydrostatic pressure) Reabsorption- venular end (lower hydrostatic pressure)

Question 36

What is lymphatic sampling?

Answer 36

-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 37

What is the relationship between capillary beds and the lymphatic system?

Answer 37

Capillary beds are associated with the lymphatic system. Lymphatic capillaries have a valve system due to low pressure.

Question 38

What type vessels are veins?

Answer 38

Capacitance vessels, providing a reservoir of blood.

Question 39

Does the pulmonary circuit hold any excess blood volume?

Answer 39

No, it does not hold any fluid reserve. Blood volume is approximately 5l and ~3.3l reservoir that can be recruited in time of need.

Question 40

How is the venous return enhanced?

Answer 40

By the muscle pump. -No reservoir inside lungs, but muscle has one. -Tense leg muscles, lots of blood goes to he heart, therefore more air to the muscles.

Question 41

How does the respiratory pump enhance venous return.

Answer 41

To breath you have to constantly change pressure in lungs and entire chest.

Question 42

How does the muscle pump effect orthostatic intolerance and exercise?

Answer 42

Orthostatic intolerance- postural hypotension Exercise- venous return, stroke volume and cardiac output.