Flow through tubes

Question 1

Ohm’s Law

Answer 1

ΔP = F x R

Question 2

Pouiselle’s Law

Answer 2

Question 3

In laminar flow, pressure gradient is proportional to flow by the relationship ___.

In turbulent flow, pressure gradient is proportional to flow by the relationship ___.

Answer 3

In laminar flow, pressure gradient is proportional to flow by the relationship:

ΔP ∝ ΔF

In turbulent flow, pressure gradient is proportional to flow by the relationship:

ΔP ∝ ΔF²

Question 4

Resistance of tubes in series vs in parallel

Answer 4

In series: Sum of resistances

In parallel: R_T = ( 1 / R₁ + 1 / R₂ + 1 / R₃ . . . 1 / R_i )^-1

Question 5

The higher Reynold’s number, . . .

Answer 5

. . . the more likely you are to have turbulent flow

Question 6

As chronic bronchitis progresses. . .

Answer 6

. . . patients must utilize their accessory breathing muscles more and more to overcome the increasing resistance of their airways and support laminar air flow.

Question 7

As a fluid moves along a tube, . . .

Answer 7

. . . the pressure of the fluid will drop due to the work it is doing to overcome the resistance of the tube.

Question 8

In respiratory physiology, flow is represented by __.

In cardiovascular physiology, flow is represented by __.

Answer 8

In respiratory physiology, flow is represented by V.

In cardiovascular physiology, flow is represented by Q.

Question 9

Characteristics of laminar flow

Answer 9

• All flow in the tube is parallel to the long axis of the tube (radial flow)
• Fluid traveling at the center of the tube moves more rapidly than fluid near the wall of the tube
• Pressure difference between two points is directly proportional to the flow (double the pressure difference → double the flow).

Question 10

Characteristics of marginally laminar / disturbed flow / transitional flow

Answer 10

• Characteristics of both laminar and turbulent flow
• Flow is generally laminar but there are eddies generated at angles to the long axis of the tube, usually at branch points, changes in direction of the tube or regions of irregularity in the wall.

Question 11

Turbulent flow

Answer 11

• Flow occurs both parallel to the long axis of the tube and perpendicular to the axis (axial flow).
• Often results in the creation of noise when the fluid hits the wall of the tube (wheezing, murmurs, bruits)
• With turbulent flow, the pressure difference between two points is proportional to the square of the flow

Question 12

Reynold’s Number

Answer 12

Question 13

Bernoulli’s Equation

Answer 13

Question 14

Continuity Equation

Answer 14

Question 15

viscosity

Answer 15

force per unit area resisting flow

Question 16

Wheeze vs Murmur vs Bruit

Answer 16

Wheeze : respiratory

Murmur : cardiac

Bruit : vascular

Question 17

The resistance of the small airways of the lung does not inhibit our ability to breathe because. . .

Answer 17

. . . these airways are in parallel, not in series.

Question 18

Under normal circumstances the greatest resistance to airflow resides in. . .

Answer 18

. . . the medium sized bronchi.

Question 19

Why is it good that the velocity of air in the lungs is minimized in the smallest vessels?

Answer 19

1. This is where gas exchange takes place
2. It reduces Reynold’s number, preventing turbulent flow in these tubes with narrow diameters

Question 20

The lowest total cross-sectional area in the vascular system is in the ___.

The highest total is in the ___.

Answer 20

The lowest total cross-sectional area in the vascular system is in the aorta.

The highest total is in the capillaries.

Question 21

Vacsular pressures

Answer 21

Question 22

mean arterial pressure

Answer 22

the mean pressure in the aorta just after the blood exits the left ventricle

Question 23

central venous pressure

Answer 23

pressure at the right atrium

Question 24

ΔP for circulatory system

Answer 24

Mean arterial pressure - Central venous pressure

Question 25

ΔP = flow x resistance in the circulatory system

Answer 25

MAP – CVP = Q x SVR SVR = systemic vascular resistance

Question 26

pulmonary vascular resistance

Answer 26

resistance of the pulmonary system

Question 27

Bernoulli's principle applied to pressure at different points in a continuous tube of varying diameter

Answer 27

Question 28

Major determinants of pulmonary flow resistance

Answer 28

* Smooth muscle tone * Elastic recoil of lung * Tethering of alveolar connective tissue to pleura

Question 29

Resistance to fast vs slow breathing

Answer 29

Question 30

Hysteresis

Answer 30

The phenomenon in which the value of a physical property lags behind changes in the effect causing it.

Question 31

Airway smooth muscle tension exhibits ___ during the inhalation/exhalation cycle for any given level of autonomic nervous system tone.

Answer 31

Airway smooth muscle tension exhibits **hysteresis** during the inhalation/exhalation cycle for any given level of autonomic nervous system tone. That is, the airways are wider at a given lung volume when that lung volume is reached via deflation as opposed to via inflation. This is explained by **stress relaxation**. If you stretch tissue and hold it in that stretched position momentarily, the elastic forces will relax a bit.

Question 32

Transmural airway pressure

Answer 32

P_airway - P_pleura Always positive at rest due to the resting negative pressure of the pleura.

Question 33

Distending pressure

Answer 33

Any positive transmural pressure. Called distending because it keeps the lung in its distended position. Distending pressure is lost in pneumothorax or with other forms of lung collapse.

Question 34

During exercise when expiratory muscles are recruited to evacuate air, the pleural pressure during expiration. . .

Answer 34

. . . **is often positive. If it is higher than the airway pressure, then the transmural pressure is positive, and the airways may collapse. In healthy individuals, it is the smooth muscle and cartilage surrounding the airways that prevents this.**

Question 35

Why is pressure in the alveoli during inspiration lower than atmospheric pressure?

Answer 35

1. The velocity of particles in the alveoli is increased by the continuity equation, since they are being forced through a smaller tube. By Bernoulli's equation, this corresponds to a decrease in mural pressure. 2. The particles are doing work on the walls of the airway to overcome resistance as they travel through the airways. 3. The terminal airways are more likely to have turbulent flow due to their smaller diameter, and this means that to sustain flow pressure must decrease. You can also think about this one in terms of the work done on the walls of the vessel by a turbulent fluid (ex, the energy of the sound waves we hear as wheezing)

Question 36

Equal pressure point

Answer 36

The point in a tube containing a moving fluid where the transmural pressure is zero.

Question 37

Alveolar pressure equation

Answer 37

P_alveolus = P_{elastic recoil} + P_pleura

Question 38

TLC

Answer 38

Total lung capacity - the maximal volume someone can breathe in before they cannot breathe in anymore

Question 39

Residual volume

Answer 39

The volume left after someone fills their lungs to the TLC and then breathes out as hard and fast as possible until they cannot anymore

Question 40

Vital capacity

Answer 40

TLC - RV

Question 41

Volume-Flow diagram

Answer 41

Question 42

Conduit vessels

Answer 42

Transport quickly to and from regions of the body (aorta, vena cavae)

Question 43

Distribution vessels

Answer 43

Distribute blood specifically to and from particular organs

Question 44

Resistance vessels

Answer 44

Account for the bulk of the resistance in circulation (the arterioles)

Question 45

Exchange vessels

Answer 45

Allow for the movement of gases, fluids, and nutrients into and out of the blood (capillaries)

Question 46

Capacitance vessels

Answer 46

Vessels that serve as a reservoire of blood. Capable of holding large amounts of volume at low pressure, characteristic of structures with high compliance (C = ΔV/ΔP)

Question 47

\_\_\_ is an important regulator of venous return

Answer 47

**venoconstriction** is an important regulator of venous return

Question 48

Vaso vasorum

Answer 48

Tiny blood vessels that penetrate into the walls of muscular blood vessels to supply their tunica media.

Question 49

\_\_\_ bolsters blood pressure between ventricular contractions.

Answer 49

**Elastic recoil of the aorta** bolsters blood pressure between ventricular contractions.

Question 50

Continuous capillaries

Answer 50

Capillaries that allow little to no exchange across tight junctions of the endothelial cells. In these cells the basement membrane is intact.

Question 51

Fenestrated capillaries

Answer 51

Have small pores in-between endothelial cells to allow for the exchange of nutrients.

Question 52

Discontinuous capillaries

Answer 52

aka sinusoids Have many large gaps in between the endothelium and basement membrane. These are the leakiest capillaries, found in the spleen, liver, and bone marrow.

Question 53

Skeletal muscular pump

Answer 53

Question 54

Starling forces

Answer 54

Physical forces that govern the movement of fluids (and proteins) into and out of capillaries. Consist of two **filtration forces** (the direction of which is from **capillary to interstitium**) and two **reabsorption forces** (the direction of which is from **interstitium to capillary**). The filtration forces are **capillary hydrostatic pressure** and **interstitial oncotic pressure.** The reabsorption forces are **capillary oncotic pressure** and **interstitial hydrostatic pressure**.

Question 55

The principal Starling force of filtration is \_\_\_. The principal Starling force of reabsorption is \_\_\_.

Answer 55

The principal Starling force of filtration is **capillary hydrostatic pressure**. The principal Starling force of reabsorption is **capillary oncotic pressure**. (most of which comes from albumin)

Question 56

Groups of vasoactive factors

Answer 56

Question 57

Autoregulation

Answer 57

A result of **myogenic and metabolic regulation of vasodilation**. If perfusion pressure either falls or rises acutely over a range of perfusion pressures in a given organ's vascular supply, these factors will control vessel diameter and **buffer** the change to keep flow relatively constant for a period of time. The range of autoregulation is between approximately **60 to 170 mmHg.**

Question 58

Myogenic regulation

Answer 58

Intrinsic property of vascular smooth muscle. In response to stretch pressure, they contract, vasoconstricting the vessel and increasing resistance. This prevents a surge of bloodflow from damaging the delicate capillaries behind the arterioles.

Question 59

Metabolic regulation

Answer 59

Vasodilation caused by release of metabolites by local tissue (adenosine, lactic acid, potassium, etc.) Metabolites of excercising muscle have similar effects.

Question 60

Endothelial regulation

Answer 60

Endothelial factors may act on smooth muscle to regulate tone, such as endothelin (a vasoconstrictor), NO and prostacyclin (vasodilators), etc.

Question 61

Coronary bloodflow

Answer 61

Heavily autoregulated, so perfusion stays roughly constant independent of heart activity. This is in part through **shear stress activating iNOS** in endothelium and NO-mediated vasodilation, and also through myogenic and metabolic pathways. Unique to coronary flow, it is linked to the cardiac cycle: **During systolic contraction flow is decreased and outflow is increased**, and the opposite during diastole.

Question 62

The ___ cells in the heart are the poorest perfused, and most affected by the systolic/diastolic tide of the coronary arteries.

Answer 62

The **subendocardial** cells in the heart are the poorest perfused, and most affected by the systolic/diastolic tide of the coronary arteries.

Question 63

The arteriovenous pressure drop in the pulmonary circulation is ~\_\_\_, while it is ~\_\_\_ in the systemic circulation.

Answer 63

The arteriovenous pressure drop in the pulmonary circulation is ~**10 mmHg**, while it is ~**90 mmHg** in the systemic circulation.

Question 64

The greatest location of resistance in the circulatory system (greatest contributor to the drop in pressure from left ventricle to the right atrium) is found in:

Answer 64

The medium size arteries likely a combination of their branching patters (transitional turbulence) and size, as well as the fact that some are in series rather than in parallel.

Question 65

Marginal turbulence is most common at. . .

Answer 65

. . . vessel bifurcations.

Question 66

The highest airway resistance is at approximately . . .

Answer 66

. . . the 6th branching point of the main bronchi.

Question 67

Air coming out of the lung on exhalation is naturally more turbulent than going in on inspiration because. . .

Answer 67

. . . the compression by the diaphragm also affects the volume of the airways. This effect is reduced the more slowly you breathe out.

Question 68

A plaque or stenosis in the renal arteries will result in . . .

Answer 68

. . . **a large blood pressure barrier to glomerular filtration.**