lecture 7: microcirculation

Question 1

what is the arterial flow of blood ?

Answer 1

first order arterioles
terminal arterioles
capillaries

Question 2

what is the venous flow of blood?

Answer 2

post capillary venues
venues
veins

Question 3

hat is the blood flow rate?

Answer 3

how much blood is passing through a vessel at any given time?

Question 4

what is the equation of flow?

Answer 4

flow = change in pressure / resistance

Question 5

what is change in pressure?

Answer 5

Mean Arterial Pressure

Question 6

what is resistance of blood dependent on?

Answer 6

• blood viscosity
• vessel length
• vessel radius - MOST IMPORTANT

Question 7

what is the major determinant of the blood flow?

Answer 7

• resistance of the arterioles in the organ

Question 8

how is blood flow affected diagram ?

Answer 8

INSERT DIAGRAM

Question 9

what is the mean arterial pressure entering the arteries?

Answer 9

93 mmHg

Question 10

what is the mean arterial pressure of the blood leaving arterioles?

Answer 10

37 mmHg

Question 11

what is vascular tone?

Answer 11

– the state of partial vasoconstriction that arteriolar

smooth muscle displays to allow constriction AND dilation if needs be.

Question 12

what is a pressure gradient ?

Answer 12

pressure A (blood entering ) - pressure B (blood leaving)

without the pressure difference the blood would not reach tissue capillary beds

Question 13

what is poiseulles law?

Answer 13

R is proportional to 1/r^4

r radius
R resistance

Question 14

what are the functions of the adjusting of the radius of arterioles?

Answer 14

• matching the blood flow to the metabolic needs of the tissue (regulated intrinsically by the tissue)
• to help regulate the arterial blood pressure

Question 15

how is the blood flow matched to the metabolic needs of the tissue?

Answer 15

a. chemical responses
- >the muscle becomes more metabolically active
- > the o2 usage increases
- > vasodilation happens
- > this is active hyperaemia

b. physical environment - > the tissue responds to local changes in temp
- > vasoconstriction happens so less heat is lost in the blood flow \
- > this is auto regulation

Question 16

what is active hyperaemia?

Answer 16

an increase in organ blood flow that is associated with increased metabolic
activity of an organ or tissue.

Question 17

what is auto regulation?

Answer 17

raised BP increases stretch on cells which stimulates myogenic vasoconstriction.

Question 18

what is an equation linking cardiac output, blood pressure and total resistance

Answer 18

cardiac output = blood pressure / total resistance

Question 19

what are the two ways that arterial blood pressure is regulated extrinsically?

Answer 19

neural - regulated by cardiovascular control centre in the medulla
hormonal

Question 20

how does neural regulation work?

Answer 20

• regulated by cardiovascular control centre in the medulla
  1. to increase BP, vasoconstriction happens
  2. the adrenoreceptors facilitate constriction and dilation

Question 21

how does hormonal regulation work?

Answer 21

• the brain mimics Sympathetic nervous system

1. different hormones like vasopressin , angiotensin ii and noradrenaline help regulate arterial BP

Question 22

how wide are capilleries ?

how thick are capillaries ?

Answer 22

7 micrometers

1 micrometer

Question 23

why is capillary density important?

Answer 23

every cell in the body needs to be close to a capillary to deliver O2, glucose ect.

Question 24

what is ficks law

Answer 24

emphasising minimising diffusion distance and time and maximising surface area

Question 25

which tissues have the greatest capillary density?

Answer 25

- skeletal muscle - myocardium muscle - brain - lungs they need a lot of oxygen

Question 26

what does the skeletal muscle do in absence of exercise?

Answer 26

the skeletal muscle shuts off the majority of its capillaries via the pre capillary sphincters in absence of exercise

Question 27

what are the three types of capillaries?

Answer 27

- continous small water filled gap junctions to allow passage of electrolytes - fenestrated have holes called fenestrae - discontinuous - large holes with passage for bigger cells like leukocytes in the bone marrow also in the liver

Question 28

what is the blood brain barrier an example of?

Answer 28

continuous - there are very very tight gap junctions (there are some parts of the brain with a leaky good brain barrier which is just normal continuous capillary walls)

Question 29

what is bulk flow?

Answer 29

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

Question 30

what forces the plasma out?

Answer 30

- hydrostatic pressure (from the heart) - oncotic pressure (from the osmotic pressure)

Question 31

what is ultrafiltration?

Answer 31

- at the arteriolar end the pressure inside the capillary is bigger than the pressure in the interstitial space

Question 32

what is reabsorption?

Answer 32

at the venous end the pressure in the interstitial fluid is more than the hydrostatic pressure in the capillary

Question 33

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

Answer 33

- this means some fluid is NOT reabsorbed so the extra fluid goes to the lymphatic fluid we are always losing fluid

Question 34

what are lymphatic vessels like?

Answer 34

they are blind ended not a closed loop like blood vessels

Question 35

what does the lymphatic system have?

Answer 35

one way valves to prevent back flow

Question 36

what drives the lymphatic system?

Answer 36

- muscle pressures | - thoracic cavity pressures

Question 37

what are key roles of lymphatic system

Answer 37

- to get excess fluid, which was not reabsorbed, back into the blood - immunity

Question 38

what does the lymph drain into?

Answer 38

- thoracic duct - right lymphatic duct - right subclavian vein - left subclavian vein

Question 39

what is oedema?

Answer 39

- if the amount of lymph produced is greater than the rate of removal of the fluid

Question 40

what might cause oedema?

Answer 40

- this is caused by parasitic blockage of the lymph nodes elephantiasis