Microcirculation

Question 1

What is the overall aim of the cardiovascular system?

Answer 1

Adequate blood flow through the capillaries

Question 2

What is the definition of the blood flow rate?

Answer 2

The volume of blood passing through a vessel per unit of time

Question 3

What is the equation which describes the change in pressure in a fluid circuit?

Answer 3

Change in pressure (between A and B) =
Flow rate (Q) x Resistance (R)

Question 4

What is the pressure gradient?

Answer 4

The difference in pressure between Point A and Point B
(P when blood enters the 1st order arteriole - P when blood enters capillaries)

Question 5

What affect will increases in flow rate have on the pressure gradient?

Answer 5

It will increase the pressure gradient

Question 6

Flow rate is proportional to…

Answer 6

Pressure gradient

Question 7

Flow rate is inversely proportional to…

Answer 7

Resistance

Question 8

What is the definition of resistance?

Answer 8

Hindrance to blood flow due to friction between moving fluid and stationary vascular walls

Question 9

What is the equation for the resistance experienced in a vessel?

Answer 9

Question 10

What part of the resistance equation is the most variable and can change from minute to minute?

Answer 10

The radius of the vessel

Question 11

Why is having a pressure difference in the organs essential?

Answer 11

Otherwise blood would not reach tissue capillary beds

Question 12

During vasoconstriction, what happens to the pressure gradient, radius, resistance and flow across the vessel?

Answer 12

No change to pressure gradient
Radius decreases
Resistance increases
Flow to capillaries decreases

Question 13

During vasodilation, what happens to the radius, resistance and flow across the vessel?

Answer 13

No change to pressure gradient
Radius increases
Resistance decreases
Flow to capillaries increases

Question 14

What does increasing BP do to pressure gradient, resistance of the vessel and flow to capillaries?

Answer 14

Increases pressure gradient
No change to resistance
Increases flow to capillaries

Question 15

What is meant by vascular tone?

Answer 15

The arteriolar smooth muscle normally displays a state of partial constriction

Question 16

Why is vascular tone important?

Answer 16

If the smooth muscle is in a contracted state, then the arteriole wall can contract or dilate - if it was fully dilated at rest, it could only constrict, not dilate further

Question 17

What does vascular tone affect?

Answer 17

Radius of the vessel

Question 18

What is meant by active hyperaemia?

Answer 18

When the blood flow to a specific tissue is matched to its needs and is regulated by chemical changes

Question 19

What chemical changes can drive active hyperaemia?

Answer 19

Increased oxygen usage and increased metabolites

Question 20

What affect does active hyperaemia have on the arteries?

Answer 20

Causes them to vasodilate

Question 21

What is myogenic autoregulation?

Answer 21

When the blood flow to a particular organ is matched by its needs, and is dependent on physical stimuli

Question 22

What physical stimuli could trigger myogenic autoregulation?

Answer 22

• A drop in blood temperature
• High blood pressure stretching artery wall

Question 23

What effect does myogenic autoregulation have on the arteries?

Answer 23

causes the arteries to constrict

Question 24

Through what mechanism are the radii of arteries adjusted after a big meal?

Answer 24

Through active hyperaemia in the gut

Question 25

What is the mean arteriole pressure for 120/80 mmHg?

Answer 25

MAP = DBP + 1/3(PP) MAP = 80 + 1/3(40) 93 mmHg

Question 26

What happens to the flow of blood through an arteriole following a rapid increase?

Answer 26

* When the flow increases, so does the stretch on the arterioles * Therefore, this physical stimuli is detected by the arterioles, which then response through myogenic auto-regulation to bring the flow back to normal

Question 27

What is laminar blood flow like?

Answer 27

* Velocity of blood is constant at any one point and blood flows in layers * Blood flows fastest at the centre of the lumen

Question 28

What is turbulent blood flow like?

Answer 28

* Blood flows eratically, forming eddys, and is prone to pooling * Associated with pathophysiological changes to blood vessel endothelium

Question 29

What is turbulent blood flow more likely to cause?

Answer 29

Activate clotting factors and produce a thrombus

Question 30

How is turbulent flow used to measure blood pressure?

Answer 30

Slow deflation of the cuff causes turbulent flow which can be heard with a stethoscope

Question 31

What is the skeletal muscle arteriolar response to exercise?

Answer 31

Active hyperaemia

Question 32

What is the small intestine arteriolar response to exercise?

Answer 32

Myogenic vasoconstriction

Question 33

The radii of the arterioles are adjusted independently to accomplish which two functions?

Answer 33

1. Match blood flow to the metabolic needs of the tissue 2. Regulate systemic arterial blood pressure

Question 34

Through what two mechanisms do the aterioles help regulate arterial blood pressure?

Answer 34

Hormonal and Neural

Question 35

How does the neural control of blood vessel radii occur?

Answer 35

The cardiovascular control center in the medulla sends signals to vasocontrict to increase blood pressure

Question 36

Which hormones are involved in vasoconstriction?

Answer 36

Vasopressin/ADH Angiotensin II Adrenaline/noradrenaline

Question 37

Where can the greatest pressure drop in the CVS be observed?

Answer 37

From one end of the arteriole to the other

Question 38

What is the equation linking mean arterial pressure, cardiac output and total peripheral resistance?

Answer 38

MAP = CO x TPR

Question 39

What is the purpose of capillary exchange?

Answer 39

The delivery of metabolic substrates to the cells of the organisms

Question 40

What is the lumen diameter of a capillary?

Answer 40

7 micrometers

Question 41

What is the cell width of a capillary?

Answer 41

1 micrometer

Question 42

What are capillaries specially designed to do?

Answer 42

Minimise the diffusion distance Maximise surface area and time for diffusion

Question 43

Which tissues have highly dense capillary networks?

Answer 43

More metabolically active tissues

Question 44

Which tissue has a large capacity but limited flow at rest?

Answer 44

Skeletal muscle

Question 45

Why does the lung have such a dense capillary network?

Answer 45

Because of gas exchange which occurs in the lungs

Question 46

What percentage of arterioles are active at rest in skeletal muscle?

Answer 46

10%

Question 47

What happens to the arterioles during exercise in sketeal muscle?

Answer 47

They vasodilate due to active hyperaemia

Question 48

What is the definition of bulk flow?

Answer 48

A volume of protein-free plasma filters out of the capillary, mixes with the surrounding interstitial fluid and is then reabsorbed

Question 49

What is the difference in CO of skeletal muscle when at rest and during exercise?

Answer 49

It increases by 5x

Question 50

What are the very small gaps between endothelial cells in continuous capillaries called?

Answer 50

H2O filled gap junctions

Question 51

What substances can move across the H2O filled gap junctions?

Answer 51

Very small molecules like sodium ions

Question 52

What are fenestrated capillaries?

Answer 52

Where you have little gaps/holes in the capillaries

Question 53

Where are fenestrated capillaries found?

Answer 53

In the glomerulus, intestinal villi and endocrine glands

Question 54

What are some tissues in which continuous capillaries are found?

Answer 54

Fat Muscle Nervous System

Question 55

In which capillary can glucose pass through the wall without the need for glucose transporters?

Answer 55

Fenestrated capillaries

Question 56

What are discontinuous capillaries?

Answer 56

Where there are large caps in the endothelial cells to allow large molecules to pass through

Question 57

Where might you find discontinuous capillaries?

Answer 57

In the liver, bone marrow and spleen

Question 58

What type of capillary structure forms the blood brain barrier?

Answer 58

Continuous, without water filled gap junction

Question 59

What force pushes plasma out the capillary?

Answer 59

Hydrostatic pushing force

Question 60

What force causes plasma to be reabsorbed?

Answer 60

Oncotic pulling force

Question 61

What acts as an oncotic force to pull plasma back into the capillaries?

Answer 61

Plasma proteins in blood vessels

Question 62

What determines transudation of fluids?

Answer 62

Capillary pressure

Question 63

What occurs if pressure inside the capillaries was greater than in the interstitial fluid?

Answer 63

Ultrafiltration

Question 64

What occurs if inward driving pressures are greater than outward pressures across the capillaries?

Answer 64

Reabsorption

Question 65

What is the significance of the fact that ultra-filtration is more effective than reabsorption?

Answer 65

More fluid is lost into the surrounding tissue than is gained - therefore the excess fluid which is lost is picked up by lymphatic vessels and returned to circulation to maintain blood pressure

Question 66

What drives the lymphatic system given there is no central pump?

Answer 66

Pressure differences (results in flow)

Question 67

Where do the lymphatics drain into?

Answer 67

Into the right lymphatic duct and thoracic duct

Question 68

How much Lymph is drained a day?

Answer 68

3L

Question 69

What occurs if the rate of lymph production is greater than the rate of lymph drainage?

Answer 69

Oedema – swelling due to interstitial fluid buildup

Question 70

What is elephantiasis?

Answer 70

* A parasitic disease which arises due to the blockage of lymph nodes * Thus rate of production exceeds rate of drainage, resulting in oedema

Question 71

What is systemic arterial blood pressure regulated by?

Answer 71

Extrinsic controls which travel via nerves or blood

Question 72

How does renin regulate blood pressure?

Answer 72

* Renin from adrenal gland converts angiotensiogen to angiotensin I * ACE in the vasculature of lungs and kidneys converts angiotensin I to II * Angiotensin II increases blood volume and vasoconstriction, increasing BP

Question 73

How do ADH and adrenaline regulate blood pressure?

Answer 73

* Both increase water reabsorption in the kidney * ADH binds to vascular smooth muscle to stimulate vasoconstriction