VASCULAR: CAPILLARIES, LYMPH, AND VEINS

Question 1

Function of capillaries

Answer 1

Exchange site for gases, nutrients, water, and waste

Question 2

Where is capillary density greatest and lowest?

Answer 2

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

Low density: cartilage and subcutaneous

Question 3

At rest, how many capillaries are open?

Answer 3

20%

Question 4

What regulates capillary opening?

Answer 4

Capillary opening is regulated by small arteries, arterioles, metarterioles

Question 5

Describe this type of capillary: continuous capillary

Answer 5

• Most common
• Junctions 10-15 nm wide
• Blood brain barrier has tight junctions

Question 6

Describe this type of capillary: fenestrated capillary

Answer 6

• Fenestrations: membrane lined holes through cell
• 20-100 nm wide
• Can be closed by diaphragm
• Exist in the intestine, glomerulus, and exocrine glands

Question 7

Describe this type of capillary: sinusoidal (discontinuous) capillary

Answer 7

• Large gaps between cells
• 100-1000 um
• Facilitate exchange
• Exist in the liver, bone marrow, and spleen

Question 8

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

Answer 8

• Tight junctions
• macromolecules
• fused

Question 9

List the mechanisms of transcapillary exchange?

Answer 9

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)

Question 10

State diffusion equation

Answer 10

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

J: flux : quantity moved per unit time

P: permeability coefficient

A: capillary surface area

Question 11

What can diffuse during capillary exchange?

Answer 11

• 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)

Question 12

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

Answer 12

1. Hydrostatic pressure - blood pressure
2. Oncotic or plasmoid osmotic pressure - blood proteins

Question 13

What is the net filtration pressure?

Answer 13

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

Question 14

Name where capillaries mainly filter and mainly absorb

Answer 14

renal glomerulus

intestinal mucosa

Question 15

precapillary sphincters

Answer 15

regulate flow of blood to capillaries depending on demand.

Question 16

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

Answer 16

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

Question 17

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?

Answer 17

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

Question 18

How can pregnancy disturb the net filtration balance

Answer 18

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

Question 19

How can hypertension disturb the net filtration balance

Answer 19

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

Question 20

How can standing disturb the net filtration balance

Answer 20

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

Question 21

How can dehydration disturb the net filtration balance

Answer 21

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

Question 22

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

Answer 22

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

Question 23

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

Answer 23

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

Question 24

Describe the closed ends of the lymphatic system

Answer 24

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

Question 25

What anchors lymph capillaries to surrounding tissue?

Answer 25

Fine filaments anchor lymph capillaries to surrounding tissue

Question 26

Describe the expansion phase of lymphatic flow

Answer 26

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

Question 27

Describe the compression phase of lymphatic flow

Answer 27

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

Question 28

What regulates lymphatic flow?

Answer 28

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

Question 29

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

Answer 29

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

Question 30

What can removal of lymph nodes cause?

Answer 30

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

Question 31

Describe elephantiasis

Answer 31

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

Question 32

List the 3 layers of veins

Answer 32

tunica intima, tunica media, tunica adventitia

Question 33

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

Answer 33

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

Question 34

What helps to ensure unidirectional flow in the veins?

Answer 34

Valves

Question 35

Compare the compliance of veins and arteries

Answer 35

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

Question 36

define: passive capcitance

Answer 36

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

Question 37

define: active capacitance

Answer 37

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

Question 38

How can sympathetic stimulation affect the vascular capacitance and cardiovascular control

Answer 38

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

Question 39

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

Answer 39

passive
passively

Question 40

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

Answer 40

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

Question 41

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

Answer 41

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

Question 42

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

Answer 42

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. )