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 describe 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 (Pressure when blood enters the 1st order arteriole - Pressure 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

R = 8Ln / Pi r^4

Where L = vessel length
n = blood viscosity
r = radius

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 radius, resistance and flow across the vessel?

Answer 12

Radius decreases
Resistance Increases
Flow decreases

Question 13

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

Answer 13

Radius Increases
Resistance Decreases
Flow Increases

Question 14

What is meant by vascular tone?

Answer 14

The arteriolar smooth muscle normally displays a state of partial constriction

Question 15

Why is vascular tone important?

Answer 15

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 16

What does vascular tone affect?

Answer 16

Radius of the vessel

Question 17

What is meant by active hyperaemia?

Answer 17

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

Question 18

What chemical changes can drive active hyperaemia?

Answer 18

Increased oxygen useage
Increase metabolites

Question 19

What affect does active hyperaemia have on the arteries?

Answer 19

causes them to vasodilate

Question 20

What is myogenic autoregulation?

Answer 20

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

Question 21

What physical stimuli could trigger myogenic autoregulation?

Answer 21

A drop in blood temperature
Stretch in the artery wall due to higher blood pressure

Question 22

What effect does myogenic autoregulation have on the arteries?

Answer 22

causes the arteries to constrict

Question 23

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

Answer 23

Through active hyperaemia in the gut

Question 24

What is the mean arteriole pressure?

Answer 24

93 mmHg

Question 25

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

Answer 25

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

Question 26

What is the skeletal muscle arteriolar response to exercise?

Answer 26

Active hyperaemia

Question 27

What is the small intestine arteriolar response to exercise?

Answer 27

Myogenic vasoconstriction

Question 28

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

Answer 28

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

Question 29

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

Answer 29

Hormonal and Neural

Question 30

How does the neural control of blood vessel radii occur?

Answer 30

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

Question 31

Which hormones are involved in vasoconstriction?

Answer 31

Vasopressin/ADH Angiotensin II Adrenaline/noradrenaline

Question 32

What happens to the pressure gradient when there is vasoconstriction?

Answer 32

It decreases

Question 33

Where can the greatest pressure drop in the CVS be observed

Answer 33

From one end of the arteriole to the other

Question 34

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

Answer 34

MAP = CO x TPR

Question 35

What is the purpose of capillary exchange?

Answer 35

The delivery of metabolic substrates to the cells of the organisms

Question 36

What is the lumen diameter of a capillary?

Answer 36

7 micrometers

Question 37

What is the cell width of a capillary?

Answer 37

1 micrometer

Question 38

What are capillaries specially designed to do?

Answer 38

Minimise the diffusion distance Maximise the surface area and time for diffusion

Question 39

Which tissues have highly dense capillary networks?

Answer 39

More metabolically active tissues

Question 40

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

Answer 40

Skeletal muscle

Question 41

Why does the lung have such a dense capillary network?

Answer 41

Because of gas exchange which occurs in the lungs

Question 42

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

Answer 42

10%

Question 43

What happens to the arterioles during exercise in skeletal muscle?

Answer 43

They vasodilate due to active hyperaemia

Question 44

What is the definition of bulk flow?

Answer 44

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

Question 45

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

Answer 45

It increases by 5x

Question 46

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

Answer 46

H2O filled gap junctions

Question 47

What substances can move across the H2O filled gap junctions?

Answer 47

Very small molecules like sodium ions

Question 48

What are fenestrated capillaries?

Answer 48

Where you have little gaps/holes in the capillaries

Question 49

Where are fenestrated capillaries found?

Answer 49

In the glomerulus, intestinal villi and endocrine glands

Question 50

What are some tissues in which continuous capillaries are found?

Answer 50

Fat Muscle Nervous System

Question 51

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

Answer 51

Fenestrated capillaries

Question 52

What are discontinuous capillaries?

Answer 52

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

Question 53

Where might you find discontinuous capillaries?

Answer 53

In the liver, bone marrow and spleen

Question 54

What type of capillary structure forms the blood brain barrier?

Answer 54

Continuous, without water filled gap junction

Question 55

What force pushes plasma out the capillary?

Answer 55

Hydrostatic pushing force

Question 56

What force causes plasma to be reabsorbed?

Answer 56

Oncotic pulling force - causes plasma to be reabsorbed

Question 57

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

Answer 57

Proteins in the blood

Question 58

What determines transudation of fluids?

Answer 58

Capillary pressure

Question 59

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

Answer 59

Ultrafiltration

Question 60

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

Answer 60

reabsorption

Question 61

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

Answer 61

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 62

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

Answer 62

Pressure differences (results in flow)

Question 63

Where do the lymphatics drain into?

Answer 63

Into the right lymphatic duct and thoracic duct

Question 64

How much Lymph is drained a day?

Answer 64

3L

Question 65

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

Answer 65

Oedema - swelling due to interstitial fluid buildup

Question 66

What is elephantiasis?

Answer 66

A parasitic disease which arises due to the blockage of lymph nodes, meaning there is no flow of fluid, gets trapped in the blood vessels