VASCULAR: CAPILLARIES, LYMPH, AND VEINS Flashcards

1
Q

Function of capillaries

A

Exchange site for gases, nutrients, water, and waste

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

Where is capillary density greatest and lowest?

A

In tissues with high O2 consumption such as cardiac muscle, skeletal, glands, brain

Low density: cartilage and subcutaneous

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

At rest, how many capillaries are open?

A

20%

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

What regulates capillary opening?

A

Capillary opening is regulated by small arteries, arterioles, metarterioles

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

Describe this type of capillary: continuous capillary

A
  • Most common
  • Junctions 10-15 nm wide
  • Blood brain barrier has tight junctions
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

Describe this type of capillary: fenestrated capillary

A
  • Fenestrations: membrane lined holes through cell
  • 20-100 nm wide
  • Can be closed by diaphragm
  • Exist in the intestine, glomerulus, and exocrine glands
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

Describe this type of capillary: sinusoidal (discontinuous) capillary

A
  • Large gaps between cells
  • 100-1000 um
  • Facilitate exchange
  • Exist in the liver, bone marrow, and spleen
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

_________ form at the ends of endothelial cells which prevents the leakage of _________ from capillary. This makes it appear as if their membranes are _____

A
  • Tight junctions
  • macromolecules
  • fused
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

List the mechanisms of transcapillary exchange?

A
  1. Diffusion (gases, small solutes)
  2. Filtration
  3. Bi-directional vesicular transport
    a. transcytosis of macromolecules
    b. transendothelial channels (stack of fused endocytotic vesicles across cell)
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

State diffusion equation

A

J = ([solute]out - [solute]in)PA

J: flux : quantity moved per unit time

P: permeability coefficient

A: capillary surface area

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

What can diffuse during capillary exchange?

A
  • Gases - direct diffusion across endothelial membrane
  • Small solutes - diffusion through small pores and clefts
  • Polar molecules have decreased permeability due to poor lipid solubility
  • Large molecules have no diffusion above 60 kDa (ex: albumin can’t diffuse)
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

What are the two forces that govern filtration at the capillary?

A
  1. Hydrostatic pressure - blood pressure
  2. Oncotic or plasmoid osmotic pressure - blood proteins
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

What is the net filtration pressure?

A

The net filtration pressure is 0.3 mmHg or 2-3 litres a day

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

Name where capillaries mainly filter and mainly absorb

A

renal glomerulus

intestinal mucosa

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

precapillary sphincters

A

regulate flow of blood to capillaries depending on demand.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

Describe how injury to the capillaries, severe burns, or inflammation will disturb the net filtration balance

A

If you injure capillaries, severe burns, or inflammation, this will all result in damage or increased leakiness of the capillaries → we lose plasma protein concentration in the blood → oncotic pressure decreases → increased filtration → increased interstitial fluid → edema

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
17
Q

Generally the lymphatic tissues can come with increase in interstitial fluid but if it can’t, it leads to edema. What are some of the causes of capacity exceeding?

A
  • Motionless (lymph doesn’t circulate)
  • Lymph glands are removed
  • Lymph is blocked by tumors
18
Q

How can pregnancy disturb the net filtration balance

A

With pregnancy, there is an increase in blood volume but the same amount of blood proteins which result in dilute blood protein concentration → oncotic pressure decreases → increased filtration → increased interstitial fluid → edema

19
Q

How can hypertension disturb the net filtration balance

A

Hypertension → increase in hydrostatic pressure → increase in filtration → increase in interstitial fluid → edema

20
Q

How can standing disturb the net filtration balance

A

Standing → increase in venous pressure and pooling of blood in legs → increase in filtration → increase in interstitial fluid → edema

21
Q

How can dehydration disturb the net filtration balance

A

Dehydration lowers plasma volume → plasma protein concentration increases → increase in oncotic pressure → decrease in filtration

22
Q

Where does lymph on the left side of the head and neck drain into?

A

thoracic duct which drains into left subclavian vein at the junction with left internal jugular

23
Q

Where does lymph on the right side of the head and neck drain into?

A

Right head and neck drain into the right subclavian vein at junction with right internal jugular

24
Q

Describe the closed ends of the lymphatic system

A

Differs from capillary beds as it has closed ends. The ends can open when interstitial pressure increases. These ends are valve-like inter-endothelial junctions

25
Q

What anchors lymph capillaries to surrounding tissue?

A

Fine filaments anchor lymph capillaries to surrounding tissue

26
Q

Describe the expansion phase of lymphatic flow

A
  • Pinterstitial > Lymphatic
  • Interendothelial “valves” allow interstitial fluid to enter initial lymphatic
27
Q

Describe the compression phase of lymphatic flow

A
  • Movement of tissue e.g. skeletal muscle pump
  • Lymphatic compression
  • Plymphatic > P interstitial
  • Interendothelial valves close
  • Lymph forced downstream past secondary valve
28
Q

What regulates lymphatic flow?

A
  1. Interstitial pressure: increase net efflux from capillaries → increase in interstitial pressure and increase in lymphatic flow
  2. Compression forces: skeletal muscle contraction propels lymph towards central areas
  3. Myogenic tone: stretch causes smooth muscle contraction and lymphatic constriction; moves lymph towards central areas
29
Q

What is the average flow of lymph and why is it important?

A

There is a flow of 2-3 liters of lymph which is slow, unidirectional, and required to prevent edema.

30
Q

What can removal of lymph nodes cause?

A

Removal of lymph nodes can cause lymphedema of hand, arm, back, breast, and trunk (e.g. breast cancer)

31
Q

Describe elephantiasis

A

Elephantiasis: extensive swelling of lower half of body due to obstruction of lymph flow by parasitic roundworms

32
Q

List the 3 layers of veins

A

tunica intima, tunica media, tunica adventitia

33
Q

Why is it important the veins are highly compliant and very distensible

A

High capacitance
Allows for venous pooling
At rest, 70% of blood is on the venous side of circulation

34
Q

What helps to ensure unidirectional flow in the veins?

A

Valves

35
Q

Compare the compliance of veins and arteries

A

Arteries are highly compliant and distensible
- Important for their role in receiving high pressure blood flow
- Allows arteries to reduce pulsatility and act as pressure reservoirs

Compliance of veins varies with blood pressure
- compliance is very high at low blood pressure
- high capacitance: large ∆V with small ∆P
- capacitance allows veins to act as volume reservoirs
- compliance decreases at high blood pressures

36
Q

define: passive capcitance

A

Passive capacitance: passive changes in venous volumes (e.g. flow change)

37
Q

define: active capacitance

A

Active capacitance: active changes in venous volume (e.g. sympathetic vasoconstriction)

38
Q

How can sympathetic stimulation affect the vascular capacitance and cardiovascular control

A

Sympathetic stimulation (e.g. hemorrhage) → active constriction of venous VSM → decreased venous volume → increased venous return → increased cardiac output

Sympathetic stimulation → vasoconstriction of arteriole VSM → decreased flow into vascular bed → decreased venous flow → passive recoil of veins → decreased venous volume → increased venous return → increased cardiac output

39
Q

Fill in the blank: capacitance changes in the peripheral veins are ______ . The veins are responding to what is flowing into them ______

A

passive
passively

40
Q

How did the splanchnic circulation experiment prove that splanchnic circulation shows active capcitance

A

If we keep inflow rate constant, there are changes in capacitance in the venous bed of splanchnic circulation with sympathetic circulation. Thus splanchnic circulation shows active capacitance

41
Q

Describe the symptoms, complications, and treatment associated with varicose veins

A

Symptoms:
- Heavy/aching legs
- Ankle swelling
- Skin discolouration (build up of metabolites)
Complications
- Predisposition to syncope (fainting)
- Intolerance to standing
- Eczema, dermatitis
- Thrombophlebitis (PE, DVT, stroke, MI)
Treatment
- Compression stockings
- Elevation of legs
- Anti-inflammatory/anti-coagulant drugs
- Removal of the vein

42
Q

Describe how the peripheral vascular system and the splanchnic vascular system differ in terms of capacitance response with sympathetic stimulation

A

peripheral vascular system has only a passive capacitance response when there is sympathetic stimulation. Splanchnic vascular system also has an active capacitance response that accounts for 10% of the capacitance response (other 90 is passive. )