Water and Electrolytes Flashcards
what gains water in the body
water ingested and water formed in metabolism
what loses water
urine, faeces
sweat and expired air
do we gain or lose more water every day
even
what part of water balance is under homeostatic control
urination
what are the features of the kidney
glomerulus
proximal convoluted tubule
loop of henle
distal convoluted tubule
collecting ducts
label this
what does the glomerulus do
involved in renal blood flow and filtration of plasma
what is the renal blood flow rate
1200ml per minute
what is ithe glomerular filtration rate
120ml per minute
what are the filtration pressures
pressures that vary along the length of glomerular capillary form afferent arterioles
what is the capillary hydrostatic pressure
45-50mmHg
what is the plasma protein oncotic pressure
25-35mmHg
what is the capsular pressure
10mmHg
what is the net filtration pressure
10-15mmHg
what does the proximal convoluted tubule absorb
60-70% of the glomerular filtrate
what is absorbed in the proximal convoluted tubular
ions and small organic molecules
what is secreted in the proximal convoluted tubule
hydrogen ions
how are things absorbed in the proximal convoluted tubule
active transport and facilitated diffusion
is there any control of reabsorption in the proximal convoluted tubular
very little
what occurs in the loop of henle
this is important for concentration of urine
length of the loop correlates with the ability to concentrate urine
what is the countercurrent exchange mechanism
this is how urine is concentrated in the loop of henle, and the concentration depends on active transport pumps in the thick ascending limb of the loop of henle
what is the net reabsorption of liquid in the loop of henle
10%
what is absorbed in the distal convoluted tubule
sodium
chloride
calcium
what is secreted in the distal convoluted tubule
hydrogen
potassium
what hormones control the activity of the distal convoluted tubular
aldosterone
atrial natriuretic hormone
ADH
parathyroid hormone
what happens in the collecting ducts of the kidney
water reabsorpiton, under the influence of ADH, and there are membrane channels for water reabsorption
how does water move along the collecting ducts
along osmotic gradients created by the counter current exchange mechanism
which hormones regulate water and electrolytes
antidiuretic hormone
renin angiotension aldosterone system
atrial natriuretic hormone
what is vasopressin
ADH, produced in the hypothalamus and released from the posterior pituitary gland
what does vasopressin act on
the distal convoluted tubule and collecting ducts to increase water and permeability by insertion of aquaporin channels
water moves passively between the tubule lumen and the interstitial fluid
what leads to an increase in ADH release in the posterior pituitary
decreased plasma volume
decreased baroreceptor
increased plasma osmorality
increased osmoreceptor activation
what is ADH secretion increased by
decreased extracellular fluid
increased extraecllular fluid osmorality
ADH also causes constriction of blood vessels
how is a decreased in extracellular fluid detected
low pressure receptors in the atria and great veins
how is an increase in extracellular fluid osmorality detected
osmoreceptors in the hypothalamus
what are electrolytes
ions present in intracellualr and extracellular fluid
what are electrolytes subject to the control of
homeostasis
what are some important electrolytes
sodium
potassium
hydrogen
calcium
what does much of the homeostatic control of electrolytes involve
determining how much is excreted through the kidneys
how is sodium controlled
RAAS and ANH
describe how RAAS controls sodium levels
promotes reabsorption of sodium and water in distal convoluted tubule in exchange for potassium and hydrogen ions
angiotensin is a potent vasoconstrictor
describe how the atrial natriuretic hormone controls sodium
increases excretion of sodium and water, and has the opposite effects of aldosterone
what stimulates atrial natriuretic hormone release
an increase in plasma volume which causes an increase in atrial distension
why do cell membrane potentials rely on extracellular fluid
due to the presence of potassium
what can small changes in potassium ions lead to
nerve and muscle function
what regulates potassium levels
aldosterone
what are the two disorders of ADH secretion
hyposecretion and hypersecretion
describe hyposecretion of ADH
happens in diabetes inspidus, where there are large volumes of inspid, tasteless urine
describe hypersecretion of ADH
syndrome of inappropriate ADH, which leads to excess ADH and water retention
what are the effects of potassium electrolytes on nerve function
increasing extracellular fluid leads to depolarisation
depolarisation causes axons to fire action potential
membrane potential does not return to resting levels, the result is that the axon is in refractory period
why are there potassium salts in toothpaste
to desensitise hypersensitive dentine
what is the manufacturers claim in regard to potassium salts in toothpaste
potassium ions will diffuse from paste along the dentinal tubules and raise the potassium ion concentration at the end of the tubules. this leads to depolarised nerves, and inactivated sodium channels, causing a prolonged refractory period
the issue is that potassium ion build up does not persist
what causes an increase in renin secretion
- decreased plasma volume
- increased sympathetic nerve activity
- decreased renal blood flow, leading to a decrease in glomerular blood flow, leading to stretch of J-G baroreceptors and decreased sodium concentrations in tubular fluid
- this affects the juxta glomerulosa apparatus, increasing renin secretion
what are the two factors that increase renin secretion
increased sympathetic nervous activity and the macula densa
what is the macula densa
lining of specialised cells in the kidney
is there much control over the glomerular filtration rate
no because of the flow
are there any hormonal impacts in the proximal convoluted tubule
no it happens despite any hormonal action
describe the counter current exchange
flow is generated into the loop of henle, which works to concentrate the urine.
the concentration depends on the active transport in the thick limb of the loop of henle, so there are working pumps
what is the sodium ion involved in
depolarisation of nerves
what are calcium ions involved in
cardiac conducting system, or as second messenger
what are the chlorine ions involved in
saliva secretion, as they produce a concentration gadient with chloride in the lumen, to allow water flow into the lumen
why do we excrete hydrogen ions
to prevent metabolic acidosis
what does ADH do to allow water absorption
provides channels
which hormone is involved in water absorption
ADH
which hormone is involved in electrolyte reabsorption
RAAS and ANH
what is octopressin
vasoconstrictor used in local anaesthetic
how long after dirnking does fluid get lost through urine
half an hour
which ions are exchanged when absorbing water and sodium
potassium and hydrogen
what does sensitive toothpaste cause the production of
tertiary dentine by odontoblasts