Lecture 26: Microcirculation I and II

Question 1

Microcirculation

Answer 1

Refers to the functions of the smallest blood vessels, capillaries, and neighboring lymphatic vessels

Question 2

Two functions of microcirculation

Answer 2

1. Exchange of nutrients and waste products in the tissue

2. Site of fluid exchange between vascular and interstitial compartments

Question 3

Blood is delivered to the capillary bed via

Answer 3

arterioles

Question 4

The degree of constriction or relaxation of the smooth muscle of the arterioles markedly affects

Answer 4

blood flow to the capillaries

Question 5

Pre-capillary sphincters

Answer 5

Precede some capillaries and help to regulate blood flow

Question 6

Structure of capillaries

Answer 6

Thin walled and are composed of a single layer of endothelial cells

Question 7

Capillary pores

Answer 7

• Present between cell junctions

- Permit passage of water soluble substances

Question 8

What can pass through the lipid bilayer

Answer 8

Lipid soluble substances like O2 and CO2

Question 9

What must be transported by vesicular transport?

Answer 9

Large molecules such as protein hormones

Question 10

Three types of capillaries

Answer 10

1. Continuous
2. Fenestrated
3. Sinusoid

Question 11

Where are continuous capillaries found

Answer 11

Most regions of the body

Question 12

Fenestrated capillary structure

Answer 12

Contain pores that permit small molecules to filter through without having to pass between clefts

Question 13

Fenestrated capillaries are found where

Answer 13

In endocrine organs, the glomerulus of the kidneys, and the absorptive areas of intestinal tract

Question 14

Sinusoid capillary structure

Answer 14

Gaps between adjacent endothelial cells which permit the free exchange of water and solutes as large as plasma proteins

Question 15

Sinusoid capillaries are found where?

Answer 15

Liver and bone marrow

Question 16

Are precapillary sphincters innervated?

Answer 16

Nope

Question 17

What are precapillary sphincters sensitive to?

Answer 17

Local metabolic changes

Question 18

Do capillaries actively participate in the regulation of blood flow?

Answer 18

Nope, they have no smooth muscle

Question 19

When a muscle becomes more active,

Answer 19

a greater percentage of pre-capillary sphincters relax simultaneously, which opens up more capillary beds

Question 20

Concurrent arteriolar vasodilation increases

Answer 20

Blood flow to organs

Question 21

As a result of more blood flowing through more open capillaries,

Answer 21

The total volume and sa available for exchange increases and the diffusion distance between the cells and an open capillary decreases

Question 22

Two things that regulate the blood flow through a particular tissue

Answer 22

1. Degree of resistance offered by the arterioles in the organ which is controlled by sympathetic activity and local factors
2. Number of open capillaries controlled by the action of the same local metabolites on smooth muscle of terminal arterioles and precapillary sphincters

Question 23

Capillary exchange is accomplished two ways

Answer 23

1. Passive diffusion

2. Bulk flow

Question 24

Passive diffusion

Answer 24

• Down concentration gradient

- Primary mechanism for exchange of individual solutes

Question 25

Bulk flow

Answer 25

• Movement in bulk of protein-free plasma across capillary walls between blood and surrounding interstitial fluid
• Encompasses ultrafiltration and reabsorption

Question 26

Starling pressures

Answer 26

• differences in the hydrostatic and osmotic pressures between the plasma and interstitial fluid
• Fluid movement across a capillary wall is driven by this

Question 27

Hydraulic conductance (Kf)

Answer 27

• Filtration rate of fluid per mmHg

- Influenced by the size of the water filled pores

Question 28

Hydraulic conductance determines

Answer 28

How much fluid movement will be produced for a given pressure difference

Question 29

Capillary hydrostatic pressure (Pc)

Answer 29

• Hydrostatic pressure extered on the inside of the capillary walls by the blood
• Tends to force fluid out of the capillaries into the interstitial fluid (filtration)

Question 30

Capillary hydrostatic pressure is more affected by changes in

Answer 30

venous pressure than changes in arterial pressure

Question 31

Capillary hydrostatic pressure is highest and lowest where?

Answer 31

Highest at the arteriolar end of the capillary and lowest at the venous end

Question 32

Interstitial hydrostatic pressure (Pi)

Answer 32

• Fluid pressure exterted on the outside of the capillary wall by the interstitial fluid
• Pressure tends to force fluid into the capillaries

Question 33

Normal interstitial hydrostatic pressure

Answer 33

Very low, nearly zero

Question 34

Capillary osmotic pressure (3.14c)

Answer 34

• Forces opposing filtration
• Effective osmotic pressure of capillary blood due to the presence of plasma proteins
• Determined by the protein concentration of capillary blood

Question 35

Interstitial osmotic pressure (3.14i)

Answer 35

• Force favoring filtration
• Determined by the interstitial fluid protein
• Normally there is little loss of protein in the capillaries, meaning this value is close to 0

Question 36

A positive net exchange pressure

Answer 36

• Outward pressure exceeds inward pressure

- Filtration pressure

Question 37

Negative net exchange pressure

Answer 37

• Inward pressure exceeds outward pressure

- Reabsorption pressure

Question 38

Two pressures that tends to move fluid out of the capillaries

Answer 38

1. Capillary pressure

2. Interstitial pressure

Question 39

Two opposing pressures that tend to move fluid into the capillaries

Answer 39

1. Capillary osmotic pressure

2. Interstitial hydrostatic pressure

Question 40

Once interstitial fluid enters a lymphatic vessel, it is called

Answer 40

lymph

Question 41

Are lymphatic openings bigger or smaller than pores in blood capillaries?

Answer 41

Bigger

Question 42

The lymphatic system is responsible for

Answer 42

returning interstitial fluid and proteins to the vascular compartment

Question 43

What directs the flow of lymph towards its venous outlet in the chest?

Answer 43

Smooth muscle and one way valves