Microcirculation

Question 1

What are the parts of the microcirculation?

Answer 1

1st order arteriole
terminal arteriole
pericytic venule
venule
capillaries
precapillary sphincter
smooth muscle

Question 2

What is the overall aim of the cardiovascular system?

Answer 2

adequate blood flow through the capillaries

Question 3

What is blood flow rate?

Answer 3

volume of blood passing through a vessel per unit time

Question 4

How do you calculate flow rate?

Answer 4

Q= deltaP/ resistance

flow rate= pressure gradient/ resistance

Question 5

What is the pressure gradient?

Answer 5

Question 6

What is resistance?

Answer 6

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

Question 7

How do you calculate resistance?

Answer 7

R= 8L/ r^4

l= vessel length
r= vessel radius

it can also be R= (8 x n x L)/ r^4
n= blood viscosity

Question 8

What happens when you halve the radius?

Answer 8

flow decreases x16

Question 9

What happens to pressure, resistance and flow when blood pressure increases?

Answer 9

pressure increases
flow increases

Question 10

What happens to pressure, resistance and flow when there is arteriolar vasoconstriction?

Answer 10

resistance increases
flow decreases

Question 11

Where does the biggest pressure drop occur?

Answer 11

between arterioles

Question 12

What regulates the pressure within the system?

Answer 12

arterioles

Question 13

How do you calculate flow in an organ?

Answer 13

Question 14

What is special about the pressure gradient in tissues?

Answer 14

They are all the same
- only resistance varies
- it determines flow

Question 15

What happens if there is no pressure difference?

Answer 15

Blood would not reach tissue capillary beds

Question 16

Why is vascular tone important?

Answer 16

It allows the arteriole to constrict further or dilate

Question 17

What happens during relaxation/ vasodilation to radius, resistance and flow?

Answer 17

radius increases
resistance decreases
flow increases

Question 18

What happens during contraction/ vasoconstriction to radius, resistance and flow?

Answer 18

radius decreases
resistance increases
flow decreases

Question 19

What is vascular tone?

Answer 19

arteriolar smooth muscle normally displays a state of partial constriction- aka the vascular tone

Question 20

Radii of arterioles are adjusted independently to accomplish two functions, what are these 2 functions?

Answer 20

Function 1: Match blood flow to the metabolic needs of specific tissues (depending on body’s momentary needs)

Function 2: Help regulate systemic arterial blood pressure

Question 21

How is the “Match blood flow to the metabolic needs of specific tissues (depending on body’s momentary needs)” regulated?

Answer 21

Regulated by local (intrinsic) controls and independent of nervous or endocrine stimulation

Question 22

How is the “Help regulate systemic arterial blood pressure” regulated?

Answer 22

Regulated by extrinsic controls which travel via nerves or blood and are usually centrally coordinated

Question 23

Explain in more detail the function “Match blood flow to the metabolic needs of specific tissues (depending on body’s momentary needs)”.

Answer 23

This function may be chemically driven.
Increases metabolites and O2 usage.
Vasodilation of arterioles.
- skeletal muscles dilate to allow more nutrients etc. to a particular tissue

This is called active hyperaemia (chemically driven change)

Question 24

Explain in more detail the function “Help regulate systemic arterial blood pressure”.

Answer 24

This function may be physically driven.
Decrease blood temperature.
Increase stretch (distension) due to increased BP.
Vasoconstriction of arterioles
- divert blood away

This is called myogenic autoregulation (physically driven change e.g., using an ice pack)

Question 25

What happens to resistance, flow, perfusion with autoregulation and no autoregulation?

Answer 25

Question 26

How do you calculate cardiac output?

Answer 26

blood pressure (MAP)/ Total peripheral resistance (TPR) Q= MAP/ TPR

Question 27

How does the neural aspect of the arteriole function "help regulate arterial blood pressure" work?

Answer 27

Neural Cardiovascular control centre in the medulla Leads to vasoconstriction Leading to decreased blood flow in specific organs (you want this acutely as this can become dangerous)

Question 28

How does the hormonal aspect of the arteriole function "help regulate arterial blood pressure" work?

Answer 28

vasopressin/ ADH Angiotensin II Adrenaline/ noradrenaline they all lead to vasoconstriction

Question 29

What is the purpose of capillary exchange?

Answer 29

The purpose of capillary exchange is the delivery of metabolic substrates to the cells of the organism [which is the ultimate function of the CVS]

Question 30

What is the diameter of a capillary?

Answer 30

7 micrometers lumen diameter

Question 31

What is the width of capillary wall?

Answer 31

1 micrometer width

Question 32

How are capillaries designed to promote?

Answer 32

Ideally suited to enhance Fick's law Minimise the diffusion distance Maximise the surface area and time for diffusion

Question 33

Why is capillary density important?

Answer 33

highly metabolically active tissues have denser capillary networks skeletal muscle= 100cm2/g myocardium/ brain= 500cm2/g lung= 3500cm2/g

Question 34

What is a special feature of skeletal muscle?

Answer 34

skeletal muscle has a huge capacity, but limited flow at rest - at rest most arterioles are closed off, doesn't function normally

Question 35

How does cardiac output from rest and exercise differ considering the different organs involved?

Answer 35

Question 36

What do continuous capillaries have?

Answer 36

H2O filled gap junction

Question 37

Where can you find fenestrated capillaries?

Answer 37

e.g., in the kidney

Question 38

What are fenestrated capillaries?

Answer 38

larger gaps between endothelial cells

Question 39

Where can you find discontinuous capillaries?

Answer 39

bone marrow - exit route for WBC liver - large metabolic capacity spleen, lymph nodes, and endocrine glands

Question 40

What are discontinuous capillaries?

Answer 40

even larger gaps and pores

Question 41

What are the 3 types of capillaries?

Answer 41

Question 42

What type of capillary is the blood brain barrier?

Answer 42

Continuous Really small junctions tight control of what leaves the BBB and enters the brain

Question 43

What is bulk flow?

Answer 43

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

Question 44

What are the 2 forces acting on capillaries?

Answer 44

Hydrostatic "pushing" force Oncotic "pulling" force

Question 45

What is starling's hypothesis about fluid movement?

Answer 45

"...there must be a balance between the hydrostatic pressure of the blood in the capillaries and the osmotic attraction of the blood for the surrounding fluids. " " ...and whereas capillary pressure determines transudation, the osmotic pressure of the proteins of the serum determines absorption."

Question 46

What is the fluid movement for ultrafiltration?

Answer 46

pressure inside the capillary> pressure in the IF

Question 47

What is the fluid movement during reabsorption?

Answer 47

inward driving pressures> outward pressures across the capillary

Question 48

Does hydrostatic pressure change across the capillary?

Answer 48

Yes, it decreases

Question 49

what happens to oncotic pressure across the capillary?

Answer 49

It stays the same

Question 50

What is oncotic pressure?

Answer 50

form of osmotic pressure induced by the proteins, notably albumin, in a blood vessel's plasma that causes a pull on fluid back into the capillary.

Question 51

What is the significance of the fact that ultrafiltration is more effective than reabsorption?

Answer 51

There is a net loss THE ROLE OF THE LYMPHATIC SYSTEM

Question 52

What are the parts of the lymphatic system?

Answer 52

Blood capillary Arteriole Lymphatic endothelium Anchoring filament Interstitial fluid Openings Tissue cells Lymphatic capillary

Question 53

What is the lymphatic system specialised to do relating to direction of flow?

Answer 53

designed to ensure fluid can only enter the lymphatic system and not leave

Question 54

What are the different lymph nodes and ducts you need to know?

Answer 54

Right lymphatic duct Entrance of thoracic duct into subclavian vein Thoracic duct

Question 55

Describe the lymphatic system.

Answer 55

There is no pump to induce flow Drainage-right lymphatic duct- thoracic duct Right and left subclavian veins

Question 56

How many litres of lymph a day?

Answer 56

3L

Question 57

How does lymph move around the body?

Answer 57

Negative pressure of lungs and contraction of skeletal muscle

Question 58

How does an oedema form with lymph?

Answer 58

rate of production> rate of drainage (too much fluid leaving capillaries staying in the space)

Question 59

What causes elephantiasis?

Answer 59

parasitic blockage of lymph nodes or sometimes rate of production> rate of drainage

Question 60

What is the pressure entering and leaving arterioles?

Answer 60

93 mmHg entering 37 mmHg leaving

Question 61

Why are capillaries so important?

Answer 61

critical exchange vessels for nutrients, signals and waste

Question 62

How would you describe capillaries?

Answer 62

narrow, thin, highly branched

Question 63

What is density in capillaries proportional to?

Answer 63

metabolic activity

Question 64

How would you describe lymph vessels?

Answer 64

blind ended, single layered, contains large permeable water-filled one way channels

Question 65

When is excess interstitial fluid drained?

Answer 65

constantly

Question 66

What directs lymph flow?

Answer 66

skeletal and respiratory pumps (vessels coalesce to lower neck

Question 67

What are lymph nodes for?

Answer 67

defence mechanism

Question 68

What does lymphatic failure lead to?

Answer 68

oedema