ions Flashcards
what is diffusion
the process where atoms or molecules intermingle because of their random thermal motion
problems with diffusion in multicellular organisms
rapid of microscopic distances
slow over macroscopic
need circulatory systems to bring cells in diffusion range
cell membrane - barrier - allow concentration gradients
what is osmosis
movement of water
across a PPM
from hypotonic soln to hypertonic soln
tight junctions
stop paracellular transport
keep polarity of cell - otherwise membrane proteins would spread out
3D
tighter in stomach than in SI - SI allow water through
what modulates transcellular transport
the membrane proteins
paracellular transport
through TJ and lateral intercellular spaces
transcellular transport
through the epithelial cells
conc grad different on either side of the cell - need different membrane proteins
channel proteins
aqueous pores
allow specific solutes to pass through
carrier proteins
bind to solute - conformational change of protein
transport across membrane
do channel/carrier proteins allow faster transport
channel
just pass - no conformational change
simple diffusion
through the membrane
no membrane proteins involved
gating of ion channels
voltage
extracellular ligand
intracellular ligand
mechanically gated
types of carrier mediated transport
uniport
symport
antiport- try to equilise charge, secondary AT
Active transport
energy
enhances conc grad
primary AT
linked directly to cellular metabolism - use ATP
secondary AT
drives energy form conc grad of another substance that is actively transported
Facilitated diffusion
enhances the rate a substance can flow down conc grad
equilibrate substance across membrane
passive
primary active transporters
Na/K ATPase
H/K ATPase
secondary active transporters
SGLT-1 co-transport
HCO3- /Cl- counter transport
Na/H+ counter transport
facilitated diffusion transporters
GLUT-5
GLUT-2
these move monosaccharides across the enterocytes
absorption of carbohydrate
glucose and galactose taken in by secondary active transport with na- can go uphill
this is done by SGLT-1 on apical membrane
fructose move in by facilitated diffusion via GLUT-5 - low intracellular concentration so can diffuse in
all leave by facilitated diffusion through GLUT-2, high capacity low affinity
the need to absorb water
99% water that goes into GI tract is reabsorbed
powered by absorption of ions
greatest amount water absorbed in SI - jejunum
ions absorbed by passive diffusion
8L water absorbed SI, 1.4L - LI
water comes from secretions into gut
mechanism that water is absorbed by
standing gradient osmosis
driven by Na
becomes more efficient as travel down intestine
what process is iron essential for
ox transport - RBC
ox phhos
in excess is toxic - body cant actively excrete it
therefore need to absorb quickly but also limit absorption
how is iron present in the diet and its absorption
inorganic iron - Fe2+ ferrous or Fe3+ ferric
as part of haem group - Hb, myoglobin and cytochromes if eat meat
can only absorb Fe2+
Fe3+ insoluble salts with hydroxide, phosphate, HCO3-
vit c reduce Fe3+ to 2+
haem smaller part of diet but absorbed more readily
Haem
dietry haem - bioavailable
absorbed into intect enterocyte
what are vitamins
organic compounds cannot be manufactured by the body vital to metabolism fat soluble - A D E K - transported to brush border in micelles K taken up by AT
Vitamin B12
liver contains large store
impaired absorption = retarded maturation of RBC - pernicious anaemia
most B12 is bound to proteins
