Capillary Function

Question 1

What is the distribution of blood circulating in different regions determined by?

Answer 1

The output of the left ventricle

Contractile state of the resistance vessels (arterioles)

Question 2

What is the circulatory system composed of?

Answer 2

Conduits (channels) arranged in series and in parallel

Question 3

What is low pressure in the cardiovascular circuit?

Answer 3

25/10mmHg

Question 4

What is high pressure in the cardiovascular circuit?

Answer 4

120/80 mmHg

Question 5

What causes decreased pressures in CV?

Answer 5

Energy being consumed to overcome frictional resistance

Question 6

Where is pressure highest and lowest in blood vessels?

Answer 6

Beginning of small arteries, pressure decreases until it most significantly drops in arterioles

Question 7

What is the increase in number of vessels from the aorta and capillaries?

Answer 7

3-billion fold

Question 8

Where is blood volume greatest in the systemic circulation?

Answer 8

Veins

Question 9

Where is blood volume greatest in the pulmonary circulation?

Answer 9

Equally divided

Question 10

Where does blood flow velocity become very slow? And why is this useful?

Answer 10

In the capillaries. Useful for exchange of diffusable substances

Question 11

What does resistance to flow depend on?

Answer 11

Dimensions of the tube and characteristics of the fluid

Question 12

What is the caliber of the vessel?

Answer 12

Principle determinant of resistance to blood flow through any vessel

Question 13

What is the organ supplied by? And what is it drained by?

Answer 13

Supplied by artery

Drained by vein

Question 14

What is series resistance?

Answer 14

The total resistance of the system is arranged in series is equal to the sum of the individual resistances

Question 15

What structure is the aorta?

Answer 15

Predominantly elastic structure, peripheral arteries become more muscular until at arterioles where musuclar layer predominates

Question 16

What is microcirculation?

Answer 16

Circulation of blood through arterioles, capillaries and venules and neighbouring lymphatic vessels

Question 17

What are capillaries?

Answer 17

Smallest of the body’s blood vessels

Question 18

How many cells thick are capillaries?

Answer 18

One cell thick (endothelium)

Question 19

What is the capillaries used for?

Answer 19

Transfer of oxygen and other nutrients from the bloodstream to the other tissues in the body

Question 20

How far away are tissue cells from capillaries?

Answer 20

60-80 micrometers

Question 21

How much blood do capillaries contain at any one time?

Answer 21

Roughly 250ml

Question 22

What are the different types of capillaries?

Answer 22

Continuous, Fenestrated, Dicontinuous

Question 23

Describe continuous capillaries

Answer 23

Adjacent endothelial cells closely joined together
Muscle, lungs, adipose and CNS
Often have pericytes associated with them

Question 24

Describe fenestrated capillaries

Answer 24

Wide intercellular pores allow rapid fluid movement

Kidney, endocrine glands and intestines

Question 25

Describe discontinuous capillaries

Answer 25

Distance between endothelial cells so great they appear as sinusoids (little cavities) in the organ Liver, bone marrow and spleen

Question 26

Where is capillary density high?

Answer 26

Metabolically active organs

Question 27

What does blood flow in capillaries depend on?

Answer 27

Contractile state of arterioles

Question 28

What is the average velocity of blood flow in capillaries?

Answer 28

Roughly 1mm/sec

Question 29

How is fluid in extracellular environment of body distributed between blood and tissue compartments?

Answer 29

By filtration and osmotic forces acting across capillary walls

Question 30

How much of the blood volume is made up by the intracellular compartment?

Answer 30

Two-thirds

Question 31

How much of the blood volume is made up by the extracellular compartment?

Answer 31

One third | 80% in tissues and 20% in plasma

Question 32

How is the distribution of water in a capillary determined?

Answer 32

By balance between opposing forces acting on capillaries

Question 33

In what three ways does transcapillary exchange occur?

Answer 33

Diffusion Filtration Pinocytosis

Question 34

What is transcapillary exchange?

Answer 34

Solvent and solute moving across the capillary endothelial wall

Question 35

Describe diffusion in transcapillary exchange

Answer 35

300mL water/ min moves across capillary wall by diffusion | Diffusion of water, 40x greater than rate at which brought to capillaries by blood flow

Question 36

Describe filtration in transcapillary exchange

Answer 36

0.06mL water per minute moves across capillary wall as a result of filtration and absorption 2% plasma passing capillaries is filtered

Question 37

How does the exchange of solutes/gases across the capillary wall?

Answer 37

Simple diffusion

Question 38

What gases are highly lipid soluble?

Answer 38

O2 and CO2

Question 39

What are water soluble substances?

Answer 39

Water, ions, glucose and amino acids

Question 40

What does it mean if substances are water-soluble?

Answer 40

Cannot cross the endothelial cell membranes. Diffusion is limited to the aqueous clefts between endothelial cells

Question 41

What does concentration of the molecule in blood reach equilbrium with?

Answer 41

Concentration in interstitial fluid near origin of capillary from parent arteriole

Question 42

When does the concentration fall to negligible?

Answer 42

Near the arterial end of the capillary

Question 43

What are the problems with flow-limited transport?

Answer 43

Large molecules can't pass through, diffusion is rate limiting

Question 44

What is diffusion limited transport?

Answer 44

Diffusion of small lipid-insoluble molecules is so rapid that diffusion limits blood-tissue exchange only when distances between capillaries and parenchymal cells are great

Question 45

What is the direction/magnitude of water movement across capillary wall?

Answer 45

Sum of hydrostatic and osmotic pressure that exists across a membrane

Question 46

What does an increased concentration of osmotically active particles within vessels favour?

Answer 46

Movement of fluid into vessels from interstital space

Question 47

Is hydrostatic pressure in capillaries constant?

Answer 47

No

Question 48

What does increased arterial/venous pressure cause?

Answer 48

Elevated capillary hydrostatic pressure

Question 49

What does a closure of arteries cause?

Answer 49

Reduce in capillary pressure

Question 50

What is the principle force in capillary filtration?

Answer 50

Hydrostatic forces

Question 51

What is the capillary hydrostatic pressure in the arterial and venous end?

Answer 51

Arterial end- roughly 32 mmHg | Venous end- roughly 15mmHg

Question 52

What is a key factor in restraining fluid loss?

Answer 52

Osmotic pressure of plasma proteins

Question 53

What is osmotic pressure also referred to?

Answer 53

Colloid osmotic pressure or oncotic pressure

Question 54

What is the total osmotic and oncotic pressure of plasma?

Answer 54

Total osmotic pressure- roughly 6000mmHg | Oncotic pressure- roughly 25mmHg

Question 55

What does the oncotic pressure do as a result of osmosis?

Answer 55

Favours movement of water into capillaries

Question 56

How much of the capillary filtrate is returned?

Answer 56

Roughly 85%

Question 57

What happens to the remaining 15% of capillary filtrate?

Answer 57

Returns to lymphatic system

Question 58

What are the three layers that make up blood vessels?

Answer 58

The tunica intima, tunica media, and tunica externa

Question 59

What does the tunica intima do?

Answer 59

Reduces friction between the vessel walls and the blood

Question 60

What is the role of the tunica media?

Answer 60

Controls vasoconstriction an vasodilation of the blood vessels

Question 61

What is the role of the tunica externa?

Answer 61

Protects, reinforces, and anchors the vessel to surrounding structures.