solute transport: reabsorption and secretion Flashcards
SIMPLE DIFFUSION
- net movement represents molecules or ions moving down their electrochemical gradient
- from higher concentration to lower concentration
- e.g respiratory diseases
FACILITATED DIFFUSION (passive process)
molecule or ion moving ACROSS a membrane down its electrochemical gradient ATTACHES TO A SPECIFIC MEMBRANE BOUND PROTEIN
ACTIVE TRANSPORT
- PROTEIN MEDIATED TRANSPORT THAT USES ATP AS A SOURCE OF ENERGY to move a molecule or ion agains its electrochemical gradient
- movement from LOWER concentration to HIGHER concentration
PROTEIN MEDIATED TRANSPORT
- uniport
- symport
FACILITATED TRANSPORT
- uniport
- moves a SINGLE MOLECULE or ions IN ONE DIRECTION
- e.g. uptake of glucose into skeletal muscle or adipose tissue
- calcium into skeletal muscle
- ATPase provides energy
symport (cotransport)
- coupled protein transport of 2+ solutes in the same direction
- e.g. Na-glucose, Na-amino acid transporters
- occurs in the kidney or small intestine
transport maximum (TM) is directly proportional to
- carried saturated
- number of functioning transporters (e.g. insulin)
facilitated diffusion
concentration of substance is directly proportional to
- transport rate
chemical specificity occurring in simple diffusion
- the substance must have a certain chemical structure
- ONLY NATURAL ISOMER will be transported
- e.g. D-glucose not L-glucose
competition for carriers for protein mediated transport
SIMPLE DIFFUSION
- glucose and galactose will generally compete for the same transport protein
- glucose on the membrane add galactose to the medium decrease the rate
PRIMARY ACTIVE TRANSPORT
- ATP is CONSUMED DIRECTLY by transporting protein
- e.g. Na/K-ATPase pump, calcium-dependent ATPase pump of the SR (uniport)
- HAS ATPase activity
SECONDARY ACTIVE TRANSPORT
- DEPENDS INDIRECTLY on ATP as a source of energy
e. g. Na-glucose (COTRANSPORT) in proximal tubule, that depends on ATP utilized by Na/KATPase pump - NO ATPase activity
- high concentration outside low concentration inside
co- transport
- substance moved on the same direction
counter-transport
- substance moved on different direction
from lower concentration to higher concentration
- active transport secondary to the pumping of Na in the basal membrane
increase luminal concentration is proportional to
- gradient, and uptake
H+ moved up a concentration gradient
- secondary active tranport
reabsorption of Na
- in the proximal tubule
Transport Maximum System (TM)
- carriers are saturated
- carriers have a high affinity for substrate
- there is low back leak
concept: the entire filtered load is reabsorbed until the carriers are saturates then the excess is excreted - number of functioning carriers
low back leak
- is the back diffusion of the substance into the tubule after it is reabsorbed into the interstitium
minimal back leak
- back leak of glucose occurs because the proximal tubule is not permeable to glucose
glucose concentration is plasma is directly proportional to AKA renal threshold or plasma threshold
- glucose rate being filtered
- is a passive process (FACILITATED DIFFUSION) into bowman’s capsule
- plasma glucose are saturated
removing one KIDNEY
- loss 50% of functioning nephrons
- loss 50% of carriers pumping glucose
- TM 50%
TM is the index of
- number of functioning nephrons
SPLAY
- curved in the plateau
- due to unsaturated nephrons at the same time
- there is saturated at the same time unsaturated nephrons
glucosuria (excretion)
- filtered is > reabsorbing glucose
- at the beginning of splay
- at the renal or plasma threshold
the higher the plasma concentration of glucose
- the higher the glucose filtration rate
lowest level of plasma glucose where reabsorbing at TM
- after splay
lowest level of plasma glucose where glucose is appearing in the urine
- at the splay
- reabsorbing at a rate below TM
increase GFR
- increase load delivered to all nephrons
- renal threshold decrease
pregnancy
- increase GFR
- decrease renal threshold
GFR is inverse to
- renal threshold
UREA
- freely filtered
- partially reabsorbed
- passive diffusion
diuresis
- urea excretion
proximal reabsorption of sodium
- gradient time system
- low affinity to substrate
- 2/3 or 66% are reabsorbed in the proximal tubule
proximal tubules
- Na pumping (most O2 and ATP consumed by the kidney goes into this pump)
- K
- Cl
- water
GFR determines the
- metabolic load of the kidney
- the filtered load of sodium
PAH
- is freely filtered
- impossible to be reabsorbed
PAH infusion 1000x (over infusion) to a patient to calculate the clearance for renal plasma flow
- GFR
PAH clearance at low plasma concentration is called
- effective renal plasma flow (ERPF)
compounds compete with PAH as an additive to lessen the effect of a drug
organic anion
- penicillin
- furosemide
- acetazolamide
- salicylate
compounds compete with PAH as an additive to lessen the effect of a drug
organic cations
- atrophine
- morphine
- procainamide
- cimetidine
- amiloride
filter load
= GFR x Px amt /volume mg/ml
excretion
= Ux urine concentration of substance x V urine flow
freely filtered but no transport
- sucrose
- mannitol
the secretion rate of INULIN
- always equals the filtration rate of INULIN
uncontrolled diabetic excretion of glucose
- is always to be less than the filtered load
diabetic but no glucose in the urine
- all of the filtered glucose is reabsorbed
- the filtration rate must equal the reabsorption rate
creatinine
- index of GFR clinically
- tiny amount is secreted
secretion of PAH is always > than
- the filter load
20% OF filtered in the kidney is
- completely reabsorbed
protein
- non is filtered nor reabsorbed
- 100 % will be excreted
sodium always appears
- in the urine
waters follows
- sodium
urea follows
- water
western diet forming (high meat)
- acid urine
