Page 38 - Color_Atlas_of_Physiology_5th_Ed._-_A._Despopoulos_2003

A. Osmosis (water diffusion)
∆π
a b Example Lumen Interstice
C osm C osm b
a C H 2 O
C H 2 O
H 2 O
b
a
C osm > C osm , Aqua-
porins
i.e.,
a b
H 2 O C H 2 O > C H 2 O
a b Water diffusion Filtration and Convection
from a to b
Epithelium
of renal
collecting duct
b
a
Water flux J V = K f · ∆π ( C osm – C osm )
~
Osmosis,
B. Filtration
∆P Example
P a P b Glomerular
Plate 1.12
capillary
a
P > P b
and
∆P > ∆π x
x
a b Blood
Water filtration
from a to b
∆π x
∆P ∆π
Water flux J V = K f · (∆P– ∆π x ) Primary Filtrate (= oncotic pressure
urine of plasma proteins)
C. Plasma protein binding
Prevents excretion
(e.g., binding of heme by hemopexin)
Protein Blood
side Transports substances in blood
3+
(e.g., binding of Fe ions by apotransferrin)
Provides rapid access ion stores
2+
(e.g., of Ca or Mg )
2+
Helps to dissolve lipophilic substances in blood
(e.g., unconjugated bilirubin)
a b Affects certain medications (e.g., many sulfonamides):
H 2 O Protein-bound fraction
– not pharmacologically active
– not filtratable (delays renal excretion) 25
25
– functions as an allergen (hapten)
Despopoulos, Color Atlas of Physiology © 2003 Thieme
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