Kidney physiology Flashcards
what are some examples of problems thatmess with homeostasis of water and electrolytes?
-haemorrage
-unusual eating or drinking behaviour
-severe dehydration, rapid fluid loss from the gut or after burns
-unintended consequences of drug actions
what is the water and electrolyte homeostasis?
-intake/loss must be in balance
what is the typical input of water?
2.5L day
1200ml water
1000ml food
300ml metabolic
what is the typical output of water?
2.5L per day
1500ml urine
100ml swear
200ml faeces
700ml insensible loss
what can affect the output of water?
temperature
humidity
activity
what happens during periods of heavy exercise or in hot/humid conditions?
sweat loss can >2L/hour, >10L/day
urine output reduced in these conditions
what are the daily recommendations of salt?
6g/day
3.75g/day if 51 or older or have high BP, diabetes or chronic kidney disease
how much CO goes to kidneys?
25% supplies the 200g of tissue
625ml/100g/min
what is the blood pressure in glomerular capillaries?
50-60mmHg
how do we achieve high BP in glomerular capillaries?
renal artery is short and has a relatively large radius
what are the sequence of blood vessels in the glomerular capillaries?
afferent arteriole
glomerular capillaries
efferent arteriole
tubular capillaries
venule
what are the 2 types of nephrons?
superficial and juxtamedullary
which type of nephron is water reabsorption more effective?
longer jjuxta-medullary nephrons
what are the 4 sections of the nephron?
PCT
loop
DCT
collecting duct
what is reabsorption?
active pumping from filtrate in tubules
(substances that are retained are water, glucose, amino acids and electrolytes)
what is secretion?
active pumping into tubules
for substances to be eliminated faster than filtration alone allows (H+, ammonia, uric acid and some drugs)
what else can affect pumping rates?
hormones
eg aldosterone can adjust the rates of Na and K excretion
where does filtration of small molecules and water occur?
between podocytes
cut off is 67KD
what are some small molecules that can filter through podocytes?
ions, urea, glucose, amino acids and small proteins
what is the normal glomerular filtration rate?
90-140ml/min
what is the brush border?
-active resporption of glucose, amino acids, NA and K ions
-co transporters, aqueous channels, membrane pumps
-substantial water reabsorption
what has happened by the end of the PCT?
-complete reabsorption of glucose and amino acids
-substantial reabsorption of Na and water
volume of filtrate reduced by 2/3rds
which wall of the loop of henle is thicker?
thinner wall descending into the medulla
thicker wall ascending from the medulla
why is the wall ascending thicker?
so it can pump the solute up
what occurs at the loop of henle?
Solute diffuses into descending tubule: Counter-current mechanism ‘recycles’ solutes.
Ion pumping develops high osmotic pressure at the tip of the loop.
No net re-absorption here.
what happens in the Distal Convoluted Tubule?
Similar structure and function to Proximal Tubule. Compare A and C. No need for glucose transporters
Less intense electrolytes and water re-absorption
DCT ion pumping can be controlled by hormones like aldosterone to ‘fine tune’ Na + and K + exchange
what happens in the collecting duct?
concentration of urine
CDs pass close to tips of Loop
If CDs are permeable to water, then moves out of the duct to concentrate filtrate.
Duct permeability set by ADH/AVP.
When ADH/AVP is present Aquaporins are inserted into the luminal membrane to allow water movement.
Rapid insertion/removalallows quick responses
what is the normal plasma osmolarity?
300mOsm
what happens when water intake is restricted?
When water intake is restricted, plasma osmolarity ↑.
More ADH/AVP is secreted by the hypothalamus.
ADH ↑ the water permeability of Collecting Ducts.
More water is reabsorbed.
Concentrated urine is produced.
what is the max conc of urine?
1200 mOsm.
what is the minimum urine output?
1ml/min
what happens when excess water is consumed?
If excess water is consumed, plasma osmolarity falls
Hypothalamus secretes less ADH/AVP.
Collecting Duct walls loose permeability to water.
Dilute urine is produced.
what is the max urine output?
20ml/min
how is filtration pressure controlled?
Hypo-filtration initiates secretion of Renin by the Juxtaglomerular apparatus.
Renin splits Angiotensinogen to makeAngiotensin I which is converted to Angiotensin II a powerful vasoconstrictor.
This system regulates renal blood flowand glomerular filtration rate (low BP, low renal flow, hypofiltration, etc)
what enhances the system that increases BP?
sympathetic NS
where is renin released from?
juxtaglomerular cells
what is angiotensin II a?
a powerful vasoconstrictor
what triggers the RAAS system?
hypofiltration
what happens when electrolyte concentrations fall?
aldosterone levels increase
where is aldosterone released from?
secreted by golmerulosa cells of the adrenal cortex
what is reabsorbed in the proximal tubule?
water
NaCl
amino acids
glucose
potassium
bicarb
what moves into the proximal tubule?
H+
ammonium
which part of the nephron is rich in aquaproins?
descending loop
water reabsorbed
what is reabsorbed in the distal tubule?
NaCl, water and bicarb
what is absorbed into the tubule in the distal tubule?
H+
ammonium
potassium
what is the structure of transitional epithelium?
lower cells - cuboidal/ columnar
apical cells - cuboidal when not stretched
