Microcirculation & Oedema

Question 1

how do u describe tunica intima?

Answer 1

single layer of endothelial cells: simple squamous epithelial cells.

Question 2

describe structure of capillary

site for what?

capillaries are know as what?

Answer 2

• single layer of endothelial cells
• no smooth muscle
• held together by tight junctions
• surroundered by basement membrane (what the endothlial cells rest on)
• site for: exchange of nutrients and waste products between circulation and intersitiual fluid that surrounds cells
• capillaries are known as exchange vessles

Question 3

Answer 3

Question 4

what is anatomy of capillary bed?

Answer 4

Question 5

what are precapillary sphincters made from?
what is role of ^?

Answer 5

precapillary sphincters:

• bands of smooth muscle
• can adjust bloodflow through capillary bed - e.g. when they close, they can make arteriovenouse anastamoses

Question 6

what are arteriovenous malformations?

Answer 6

• when feeding arteries are connected dircetly to venous system (i.e. abscence of capillary bed)
• can cause bleeding / haemorrhage due to high pressure

Question 7

what distinguishes capillaries from arterioles?

Answer 7

arterioles have smooth muscle, capillaries do not

Question 8

what are the three types of capillaries?

Answer 8

1. continous capillary
2. fenestrated capillary
3. discontinous / sinusoidal capillary

Question 9

Answer 9

Question 10

Answer 10

Question 11

describe structure of continous capillaries (2)
what can diffuse through em?
what are the two subdivisions and where found?

Answer 11

• sealed endothelium
• tight junctions
• pinocytic vesicles
• allow movement of water and ions

subdivisions:

1. those with numerous transport vesicles (caveolae): skeletal muscles, lungs, gonads and skin
2. those with few vesicles: CNS / bbb

Question 12

describe structure of fenestrated capillary? (3)

what do they allow transport of?

where found?

Answer 12

• continous / closed basal lamina
• small pores in endothelial cells
• tight junctions
• pinocytic vesicles
• transport: free passage of salts and water. plasma –> tissues
• location: tissues specialised for bulk fluid exchange - exocrine glands, intestines, pancrease & glom. of kidneys

Question 13

sinusoidal / discontinous capillaries: i) structure, ii) locations & iii) allow transport of what?

Answer 13

structure:

• special fenestrated endothelial cells
• **discontinous basal lamina
• **lack pinocytic vesicles

allow transport of:

• **red & white blood cells
• serum proteins**

locations:

• **spleen
• liver
• bone marrow**

Question 14

where do u find each of the different types of capillaries?

Answer 14

• *discontinous**:
• spleen
• liver
• bone marrow
• *fenestrated:**
• exocrine glands
• intestines
• pancreas
• glom. of kidneys
• *continous:**
  1. those with numerous transport vesicles (caveolae): skeletal muscles, lungs, gonads and skin
  2. those with few vesicles: CNS / bbb

Question 15

Answer 15

Question 16

what are the 4 methods of movement through capillary endothelial cells?

Answer 16

Question 17

what does diffusion through capillaries depend on? (3)

what is the diffusion coeffcient like for:

a) small, lipid soluble molecules
b) lipid insoluble & larger molecules

Answer 17

1. diffusion:
   - depends on density of capillaries (high: large SA for exchange & short distance between each cap)
   - concentration gradient
   - diffusion coefficient

small, lipid soluble molecules
molecules that can diffuse across capillaries:
1.o2
2 co2
3. anaesthetics

lipid insoluble & larger molecules:
depends on the characteridtic of the capillary wall:
i) continous capillaires = limited passage
ii) fenestrated / discontinous = faciliate movement of large molecules

Question 18

(diffusion is detemined by which law?)

Answer 18

(flicks law: amount moved = area x conc gradient x diffusion coefficient)

Question 19

what is paracellular diffusion?

e.g. of where occurs?

Answer 19

Paracellular transport refers to the transfer of substances across an epithelium by passing through the intercellular space between the cells.

e.g. kidneys

Question 20

what are caveolae?

Answer 20

caveolae: specialised pits that undergo endocytosis

Question 21

which two factors determine the movement of water across capillary endothelium (4)

what can u calculate using these^?

Answer 21

• *1. hydrostatic pressure**
  i) HPc: hydrostatic pressure in capillary (changes depending where - arteriol end (33 mmHG) > venous end (17mmHg))
  ii) HPif: Hydrostatic pressure in intersitial fluid (usually 0)
• 2. oncotic pressure: (**Oncotic pressure, or colloid osmotic-pressure, is a form of osmotic pressure induced by the proteins, notably albumin, in a blood vessel’s plasma (blood/liquid) that causes a pull on fluid back into the capillary)*
  i) OPc: capillary colloid osmotic pressure - normally: 26 mm Hg (higher conc of protein (esp albumin in blood - fluid is reabsorbed back into blood, which causes pressure )
  ii) OPif: intersititial colloid osmotic pressure - 1mmHg

can calculate: Net filtration pressure

youtube.com/watch?v=rPWf43lYcBU

Question 22

how do u calculate net filtration pressure?

Answer 22

NFP = (HPc - HPif) - (OPc - OPif)

Question 23

Net filtration pressure at arterial end / venous end? what does it mean occurs here?

Answer 23

Question 24

within capillary bed: what is happening at a) arterial end b) venou end?

Answer 24

a) arterial end: filtration
b) venous end: absorbtion

= starling hypothesis

Question 25

structure of lymphathic capillaries? (5)

Answer 25

- endothelial lining - large intercellular gaps - permeabmle basement membrane - end as blind sacs within tissues - one way valves

Question 26

why do have lymph fluid?

Answer 26

bc not all fluid is reabsorbed in capillary beds - so need drainage back ## Footnote *Functionally, the lymphatic vascular system runs in parallel to the blood venous system, in that both return fluids centrally (see Figure 2). Lymphatic vessels carry lymph, which is largely water gathered from interstitial tissue spaces. Fluid appears in the interstitial spaces because blood capillary walls are somewhat leaky, admitting part of the aqueous component of blood, along with some proteins.*

Question 27

where are lymphatic capillaries in relation to blood capillaires?

Answer 27

in close association / proximity

Question 28

describe water movement in body in lymph system

Answer 28

**water movement is in continual flux**

Question 29

how much lymph is returned to circulation a day? what happens if this is maintained correctly?

Answer 29

**2/4L lymph returned to circulation a day**: if wrong = **oedema**

Question 30

what is oedema? what are symptoms?

Answer 30

**oedema**: increased volume in the interstitial compartment leading to tissue swelling (aka fluid retention) * *symptoms**: - swollen / puffy ankles , feet or legs - shiny, stretched or red skin

Question 31

how can u distinguish oedema vs other forms of swelling?

Answer 31

if pitting oedema produced: = oedema -\> apply firm pressure and it **doesnt** bounce back

Question 32

explain the 4 main factos that cause oedema

Answer 32

1. **increased capillary hyrdostatic pressure** - venous pressures become elevated (e.g. through gravitational forces / heart failure) - this reduces the hydrostatic pressure gradient - reduces reabsorbtion from interstitial fluid back into capillary * *2. decrease in plasma oncotic pressure** - decreases the pressure driving fluid back into capillary - reduces reabsorbtion * *3. increased capillary permeability** - allows more water to leave cap - also reduces the oncotic pressure different by allowing protein to leave the vessel more easily **4. lymphatic obstruction**

Question 33

what are the two types of lymph obstruction / lymphoedema?

Answer 33

**primary:** genetic cause **secondary:** damage to lymphatic system (e.g. surgery, elephantiasis - worm infection, tissue injury)

Question 34

what can cause: 1. increased capillary hydrostatic pressure? 2. decrease in plasma oncotic pressure:? 3. increased capillary permeability: **?** **4.** secondary lymphoedema:

Answer 34

1. increased capillary hydrostatic pressure: **heart failure** 2. decrease in plasma oncotic pressure: **hypoproteinemia (**less proteins in blood). **e.g. malnutririon (Kwashiorkor) or liver disease** 3. increased capillary permeability: **vascular damage (burns / trauma / inflammation)** **4.** secondary lymphoedema: **surgery, elephantiasis - worm infection, tissue injury**

Question 35

how can u treat oedema?

Answer 35

1. treat underlying disease that causes oedema 2. treat oedema itself: **diuretics** (loop or osmotic)