Outline (1)

Question 0

For the circulatory system what parts are: distributors, pump and exchange mechanism?

Answer 0

• Distributors: blood and vessels
• Pump: heart
• Exchange: capillaries

Question 1

Why do we have a circulatory system and what’s its role?

Answer 1

• Can’t use diffusion - takes too long.
• Time taken is proportional to distance^2
• System to carry O2 and nutrients to cells and to remove waste products.

Question 2

What are capillaries?

Answer 2

• Single layer of epithelial cells surrounded by basal lamina

Question 3

How do O2, CO2, glucose, amino acids and lactate diffuse through capillaries?

Answer 3

• O2/CO2 can diffuse directly through phospholipid bilayer
• Glucose/AA/lactate are hydrophilic and diffuse through small pores in capillaries
• All move down concentration gradient

Question 4

What is diffusion rate dependant on?

Answer 4

• Surface area
• Concentration gradient
• Diffusion resistance

Question 5

What does surface area depend on?

Answer 5

• Capillary density on tissue

Question 6

What does the concentration gradient depend on?

Answer 6

• Greater the gradient the faster the rate of diffusion
• Substance used in tissues: Conc in capillaries < conc in arterial blood
• High rate of blood flow maintains high concentration gradient

Question 7

What is diffusion resistance dependent on?

Answer 7

• Nature of molecule: lipophilic/hydrophobic/size
• Nature of barrier: no pores/pore size
• Path length: capillary density, shortest in most active tissues.

Question 8

What is blood flow rate also known as?

Answer 8

• Perfusion rate

Question 9

What is the perfusion rate in the following:

• Brain
• Heart
• Kidneys
• Overall at rest
• Overall during exercise

Answer 9

• Brain: 0.5ml/min/g
• Heart: 0.9-3.6ml/min/g
• Kidneys: 3.5ml/min/g
• Overall at rest: 5l/min
• Overall during exercise: 25l/min

Question 10

Why is resistance needed in the circulatory system?

Answer 10

• Allows perfusion to harder to access areas (e.g. brain)

- Arterioles are the resistance vessels.

Question 11

Why is there a need for flexibility in the circulatory system?

Answer 11

• Total flow in system needs to be able to change depending on activity level
• Needs a storage system - veins: thin walls for easy distension/collapse - variable reservoir for blood - returned to heart at different rate.