PHIS 206 Lecture Notes - Lecture 14: Capillary, Skeletal Muscle, Baroreceptor
2 May 2018
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Lecture 14: The Vasculature
All Together Now
• Branching
o Note relationship between number of branches, cross-sectional area, and velocity
o Low velocity and high surface area of capillaries is key for exchange of nutrients
and wastes
• Vascular system minimize distance between blood and cell
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Capillaries
• Let’s say you were fishing
• Low flow, functionally still “water”
• Enormous area, low velocity
• When lake is big and wide, it looks like water is flowing slower across the lake but it
actually same flow (flow = amount per time) → flow doesn’t change, but it slows down
In and Out
• Interstitial Fluid = Fluid between cells → right outside the capillaries
• Whether water-soluble or lipid-soluble, most things primarily move by diffusion
• Proteins can not leave capillary without substantial help (and serve to hold onto fluid)
• Low to high pressure → diffusion
• Proteins that stay behind (plasma proteins coated in green) gonna hold on to water
• Barrier to get out if water soluble, has some pores that help you get out if your small and
water soluble → if you’re lipid soluble you don’t really have a problem getting out
• Diffusion = cheap (doesn’t cost you anything) but slow (so you have to minimize
distance)
Capillary Beds
• Capillary beds are perfused only when the demand exists
• At any time, no more than ⅓ of all capillary beds are perfused (open)
• Capillaries = exchange takes place
• The ⅓ of capillaries changes so everyone is fed in time
• At rest, there is not enough blood for blood to go everywhere (different when exercising)
• (a) is what you will see during exercise, (b) is what you would see at rest
Exchange
• Nearly all exchange/transport is driven by diffusion (facilitated or simple)
• Cells take glucose and oxygen to produce water, energy, and carbon dioxide
• CO2 goes to blood because CO2 is toxic, needs to get rid of it (CO2 = waste)
•
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