6.2

Question 1

Describe capillary walls

Answer 1

• rather leaky -> allows the exchange of materials; oxygen and nutrients with cells in tissues, and waste products, such as carbon dioxide and urea, back into the capillaries to be transported by blood
• small diameter (5 µm wide)
• made of only a single layer of cells
• have permeable membranes
• may contain pores to aid in the transport of materials between tissue fluid & blood
• may becontinuousw endothelial cells held together by tight junctions → limits permeability of large molecules

Question 2

What is the purpose of valves in veins

Answer 2

ensure that blood flows in one direction only, that is towards the heart, by preventing backflow

Question 3

When do valves open

Answer 3

when muscles contract

Question 4

when do valves close

Answer 4

when muscles relax

Question 5

where is blood flow slowest

Answer 5

in the capillaries

Question 6

tissue fluid/interstitial fluid

Answer 6

the liquid part of blood that passes through the capillary wall, to bathe tissue cells

• composed of:
  water, sugars, salts, fatty acids, amino acids, coenzymes and hormones, as well as waste products from the cells