P: capillaries + veins

Question 1

Arterioles function

Answer 1

regulate blood flow to capillary beds

Question 2

Venules function

Answer 2

collecting channels and storage vessels

Question 3

Internal diameters of capillaries?

Answer 3

4-9µm

Question 4

Continuous capillary structure

Answer 4

• Adjacent endothelial cells tightly joined together
• Intercellular clefts permit passage of ions & small molecules
• Not permeable to proteins
• Muscle, lungs and adipose tissue

Question 5

Fenestrated capillary structure:

Answer 5

• Wider intercellular pores provide greater permeability
• Permeable to small proteins
• Kidney, endocrine gland & intestinal capillaries have numerous fenestrations

Question 6

Discontinuous capillary structure

Answer 6

• Large, leaky capillaries with pores
• Allow red and white blood cells and various serum proteins to pass
• Liver, spleen and bone marrow.

Question 7

What are true capillaries?

Answer 7

smooth muscle at origin of capillary (called precapillary sphincter). Regulates entry of blood to capillary. Also participate in delivery of. Nutrients + removal of wastes from cells and deliver blood into venules - nutritional flow.

Question 8

What do arteriovenous shunts do?

Answer 8

bypass capillaries - nonnutritional flow

Question 9

Capillary blood pressure (hydrostatic pressure) increases from:

Answer 9

• Dilation of arterioles –> increased inflow
• Increased venous pressure –> reduced outflow

Question 10

Transmural pressure:

Answer 10

intravascular pressure - extravascular pressure.

Question 11

Effect of an increase in transmural pressure:

Answer 11

triggers contraction of terminal arterioles

Question 12

Effect of a decrease in transmural pressure:

Answer 12

triggers relaxation of terminal arterioles

Question 13

Ways of transcapillary exchange:

Answer 13

• Diffusion
• Filtration
• pinocytosis

Question 14

Capillary flow-limited transport:

Answer 14

• Small molecules pass rapidly through pores and accumulate at arterial end of capillary if blood flow is slow
• If flow is rapid, diffusion happens further down capillary, increasing supply to tissues
• Larger molecules diffuse at slower rate + diffuse further down capillary
• Increase in blood flow/ increase in capillary density increases supply of diffusible solutes.

Question 15

How do lipid-soluble molecules (O2, CO2) diffuse in capillaries?

Answer 15

Through endothelial walls, not limited to pores.

Question 16

Filtration at capillaries:

Answer 16

• Bulk movement of fluid through pores in capillaries into interstitial area forms tissue gel due to proteoglycan content of extracellular environment
• Rivulets of free-moving flid adjacent to cells and collagen fibres
• Direction and magnitude of movement of fluid between capillaries and interstitium is determined by relative strength of hydrostatic and osmotic forces.

Question 17

Hydrostatic forces:

Answer 17

• Hydrostatic pressure moves fluid out of capillaries into interstitial fluid, driving capillary filtration
• Dependent on capillary bp, which is dependent on arterial and venous pressures
• Increase in arterial or venous pressure elevates capillary hydrostatic pressure
• Increases in arteriolar resistance reduces capillary hydrostatic pressure
• Vasodilation of arterioles and constriction of venules raises hydrostatic pressure

Question 18

Hydrostatic forces when moving to standing position:

Answer 18

• Initial movement of blood to lower extremities raises arterial and venous pressure, increasing capillary hydrostatic pressure
  Increased filtration and oedema results if not corrected by myogenic regulation.

Question 19

Average capillary hydrostatic pressure:

Answer 19

32mmHg at arterial end, 15mmHg at venous end.

Question 20

Oncotic pressure/ colloid osmotic pressure:

Answer 20

Plasma has a higher [solute] –> this creates an osmotic pressure called colloid osmotic pressure or oncotic pressure. This promotes movement of water out of tissue fluid into capillaries (absorption). Stays at abot 25mmHg

Question 21

Starling forces:

Answer 21

opposing hydrostatic and oncotic pressures

Question 22

Determining factors if capillaries filter or absorb?

Answer 22

• Magnitude of capillary hydrostatic pressure
• If capillary hydrostatic pressure is very high: 100% filtration. If it is very low: 100% absorption.

Question 23

What is pinocytosis?

Answer 23

Movement of fluid across endothelial cells by vesicles

Question 24

How does pinocytosis work?

Answer 24

• Section of cell membrane engulfs plasma
  
  • Membrane buds off (endocytosis) to form intracellular vesicle
  • Vesicle is transported across cell + fuses with cell membrane (exocytosis), releasing contents into interstitial fluid
    Responsible for exchange of large molecules.

Question 25

Total lymph production rate:

Answer 25

120ml/hr

Question 26

[Protein] of lymph from most tissues:

Answer 26

around 2g/dl

Question 27

[Protein] of lymph from liver:

Answer 27

around 6g/dl

Question 28

[Protein] of lymph from intestines:

Answer 28

3-4g/dl

Question 29

What is oedema?

Answer 29

Excess fluid accumulation in extracellular spaces caused by excessive capillary filtration and/or poor lymphatic drainage

Question 30

Causes of oedema?

Answer 30

• Increases capillary filtration coefficient
  
  • Increased capillary hydrostatic pressure
  • Decreased plasma colloid osmotic pressure

Question 31

How does increased blood pressure/ venous obstruction cause oedema?:

Answer 31

increases capillary filtration pressure –> more tissue fluid formed at arteriolar ends of capillaries

Question 32

How does increased tissue protein concentration cause oedema?:

Answer 32

Decreased osmosis of water into venular ends of capillaries –> localized tissue edema due to leakage of plasma proteins through capillaries through inflammation + allergic reactions.

Question 33

Pressure of blood in the right atrium. How does decreased plasma protein concentration cause oedema?

Answer 33

Decreases osmosis of water into venular ends of capillaries.

Question 34

What is central venous return?

Answer 34

Pressure of blood in the right atrium.

Question 35

Effect of increased pressure in smaller veins (venous pressure):

Answer 35

increased venous return to right atrium when CVP is unchanged.
Increase in blood volume and reduction in compliance of veins increases overall venous pressure.

Question 36

Effect of reduced CVP?

Answer 36

Reduction in CVP increases venous return to right atrium

Question 37

Effect of gravity on venous pressure:

Answer 37

• Pooling of blood in lower extremities of arterial and venous systems
  
  • Higher compliance of veins –> greater pooling + distension
    Reduces venous return and cardiac output

Question 38

Orthostatic hypotension:

Answer 38

when moving from lying to standing, blood pooled in thoracic cavity shifts towards lower extremities, causing an immediate drop in venous return + cardiac output. Resultant drop in arterial pressure.