Zusammenfassung der Ressource
K+ in the Kidney
- in a normal diet we
consume far to much
potassium
- body has to deal with this in some way = excretion
- the nephron
- low potassium - absorption of K+ into bones
- normal or high potassium - more secretion
of potassium
- conc. ICF = 150mM and ECF = 4mM
- maintained in a very close range -
above 5mM = hyperkalemia and
below 3.5mM = hypokalemia
- body tries to maintain a net balance of 0
- why is the conc of K+ important?
- High ICF conc.
- maintain cell volume - pump action
- regulation of pH
- control of enzyme function
- control DNA and protein synthesis
- control of growth and cell proliferation
- Low ECF conc.
- maintain steep K+ gradient across membrane
- maintain potential of cells
- Low levels of K+ prevents
problems with excitation and
contraction
- Action potential firing
- Muscle contraction
- Cardiac rhythmicity
- Physiological role of K+
- cell volume maintenance
- Low K+ = cell shrinkage
- High K+ = cell swelling
- intracellular pH regulation
- low K+ = cell acidosis
- high K+ = cell alkalosis
- enzyme function
- DNA/ protein synthesis
- lack of K+ results in
reduction of protein synthesis
= stunted growth
- roles of transmembrane K+ ratio
- resting membrane potential
- reduced K+ inside to outside - depolarization
- increased K+ inside to outside - hyperpolarization
- neuromuscular activity
- low plasma K+ - muscle weakness, paralysis, vasodilation and respiratory failure
- high plasma K+ - conduction disturbances, arrhythmia and fibrillation
- cardiac activity
- low K+ - slow conduction of
pacemaker cells, arrhythmia
- High K+ - conduction
disturbances, arrhythmia and
fibrillation
- Vascular resistance
- Low K+ - vaso-constriction
- high K+ - vaso-dilation
- K+ and the heart
- high conc. = heart fibrillation and death
- low conc. = low T wave, high U wave
- overall K+ homeostasis - daily intake = excreted, net = 0
- most K+ excreted via urine
- when intake is greater than excreted amount we have a + balance
- when intake is less than excreted we have a - balance
- how does body respond to changes in K+
- extracellular renal function - increase K+ uptake into cells
- increase pump function and secrete more K+
- intracellular renal function - regulation of reabsorption and
secretion of K+ along nephron - occurs after several hours
- extra renal affects of EPO,insulin, aldosterone
- more sodium out, more potassium in
- EPO released from chromatin cells form the adrenal medulla increases Na+ K+ ATPase activity
- insulin released from beta cells
- aldosterone released
from zone glomerulosa
cells from adrenal cortex
- intra-renal effects - GFR x K+ plasma = daily filtered load
- depends on diet - increase in K+ in diet, increase in K+ filtered load
- low diet of K+ reabsorption
- proximal tubule
- paracellular pathway
- apical K+ channels
- NKCC2
- sets up voltage across membrane
- 67% reabsorbed
- minimal secretion to lumen
- thick ascending limb
- NKCC2
- 20% reabsorbed
- paracellular pathway
- distal tubule
- collecting duct
- reabsorption: intercalated cells (30%)
- K+/H+ exchanger
- pH important
- Na+ reabsorption and K+ section principle cells (70%)
- aldosterone is important
- ENaC
- K+ Cl- co transporter
- low K+ = low flow rate, low/no secretion
- normal or increased K+
- secretion
- distal tubule
- collecting duct
- excreted in urine
- secretion- high plasma K+, action of aldosterone
- when we have high K+ we see different things occurring in all
areas of the body - lungs, liver, adrenal glands, heart and kidney
- if we increase plasma K+ we stimulate the adrenal cortex to release aldosterone
- Aldosterone
- Late distal tubule and collecting duct
- ROMK1 is important
- ENaC activity - cell more positive and lumen more negative
- increase in Na+ K+ ATPase activity on BL membrane
- entry of Na+ makes cell potential more positive
= driving force for K+ exit across apical
membrane (secretion)
- increase pump function and therefore increase K+
- Increase Na+ K+ Activity
- change in electrochemical gradient - aldosterone is secreted
- K+ permeability increases and K+ is secreted
- Activation of Na+ K+ ATPase - increases intracellular K+
- increases K+ secreted across apical membrane - collecting duct and late distal tubule
- reabsorption
- proximal tubule
- thick ascending limb
- secretion is high compared to single flow rate
- Summary
- K+ homeostasis is crucial for
survival - ICF = 150mM and ECF =
4mM
- Hormones effect tubular flow rate in K+ secretion
- various segments of nephron
involved in reabsorption and
secretion
- K+ can be transported into tissues