Topic 15: Urinary System Flashcards
How do we test for the presence of starch in urine?
The IKI test
If digestion of starch has occurred:
- starch WILL NOT BE present in test tube
- test will be NEGATIVE (yellow)
If digestion has NOT occurred:
- starch WILL be present in test tube
- test will be POSITIVE (blue-black)
How do we test for the presence of sugar in urine?
Benedict’s test
If digestion of starch has occurred to produce sugars:
- sugar WILL BE present in test tube
- test will be POSITIVE (yellow-orange-red)
If digestion has NOT occurred:
- sugar WILL NOT BE present in test tube
- test will be NEGATIVE (clear light blue)
What do the kidneys contribute to the endocrine system?
They produce renin (BP), and erythropoietin (RBC production)
What are 3 processes in the nephron that lead to urine formation?
- Glomerular Filtration - water and small solutes are forced out of blood in the glomerulus into Bowman’s capsule due to pressure differences across filtration membrane
- Tubular Reabsorption - valuable substances like water, glucose, and ions are transported from the filtrate in nephron back into bloodstream
- Tubular Secretion - additional waste products and excess ions are actively transported from peritubular capillaries into the lumen of the nephron tubules to be excreted in urine
20% of plasma in glomerulus is filtered into Bowman’s capsule via bulk flow (ΔP) across the filtration membrane. The filtrate is identical to plasma EXCEPT large proteins. What does the filtration membrane consist of?
a) fenestrated endothelium (part of glomerulus)
b) podocytes (a layer of Bowman’s capsule) with filtration slits between
c) fused basement membranes
What is the glomerular filtration rate (GFR)?
~180 L/day filtrate (both kidneys) = 125 mL/min (so the entire plasma volume is filtered ~65 times per day)
What are the different regions of Tubular Reabsorption in the nephron?
a) Proximal Convoluted Tubule (PCT) ~> unregulated
b) Loop of Henle ~> reabsorbs into vasa recta
c) Distal Convoluted Tubule (DCT)
d) Collecting Duct
What is reabsorbed in the PCT of the nephron?
i. glucose, AAs (active transport)
ii. Na+
iii. small proteins
iv. vitamins
v. obligatory (unregulated) reabsorption of H2O (osmosis follows solutes)
RESULT: large amount of solute removed and volume of the filtrate is reduced ~> filtrate is now isotonic to plasma
What is reabsorbed in the Loop of Henle?
i. descending limb (DL): unregulated (obligatory) reabsorption of H2O only
ii. ascending limb (AL): impermeable to water, but get active transport of Na+, Cl-
What is reabsorbed in the DCT of the nephron?
i. reabsorbs Na+, Cl-, Ca++
ii. impermeable to H2O
What is reabsorbed in the late DCT and Collecting Duct of the nephron?
i. reabsorb Na+
~> aldosterone ⇑ Na+ reabsorption
~> ANP ⇓ Na+ reabsorption
ii. facultative (regulated) reabsorption of H2O
~> ADH ⇑ (ANP inhibits ADH)
Tubular Secretion is the movement of substances from peritubular blood INTO filtrate in nephron lumen. What are the main substances secreted?
a) wastes e.g. urea, uric acid, some hormones
b) K+ (⇑ by aldosterone)
c) H+ or NH4+ ⇒ maintains blood plasma pH
Urine may be concentrated or dilute. What are the differentiating traits of these 2 types?
- Concentrated
• dehydrated, low BP
• in late DCT & CD:
- a) aldosterone ⇑ Na+ reabsorb
- b) ADH ⇑ facultative (regulated) H2O reabsorb (responds to need)
• urine can be up to 1200 mOsm/L - Dilute
• excess plasma H2O, high BP
• in late DCT & CD:
- a) ANP inhibits ADH, aldosterone - impermeable to H2O, NaCl
What is mOsm?
A unit of osmotic pressure
What are the different hormonal methods of urine regulation?
Renin-angiotensin system
ADH
Aldosterone
ANP
Describe how the body uses ADH in the regulation of urine
→ ⬆️ facultative reabsorption of H2O (late DCT & CD)
→ ADH⬆️ if:
a) low BP or vol.
b) ⇑ plasma concentration
c) ⇑ angiotensin II
d) nicotine, nausea
→ ADH⬇️ if:
a) reverse of a, b, c
b) ⇑ ANP
c) alcohol
What is diabetes insipidus?
The body does not produce ADH or kidneys do not respond to ADH
→ Result = large amounts of dilute urine & increased thirst
Describe how the body uses ANP in the regulation of urine
⬆️BP causes the release of ANP. Effects of ANP include:
⬇️renin (∴ angiotensin II),
⬇️ADH
⬇️aldosterone
⬇️vasoconstriction
All of the above lead to ⬆️urine volume (more WATER OUT, reduces BP)
What are normal constituents found in urine?
a) H2O
b) nitrogenous wastes
c) regulated substances e.g. ions
d) pH 4.5 - 8.0 (Ave = 6.0)
What do the nitrogenous wastes of urine consist of?
- UREA from AA metabolism
- URIC ACID from nucleic acid breakdown
→ poorly water soluble: accumulation = gout (in joints) or kidney stones - CREATININE from breakdown of creatine
→ production/excretion constant, no reabsorption
→ used to estimate GFR - can indicate kidney disease before symptoms occur
What are 2 abnormal constituents found in urine?
- PROTEIN – proteinuria (aka albuminuria): due to ⇑ permeability of glomerulus
- due to e.g. heavy metals, glomerulonephritis - GLUCOSE – glycosuria
- temporary e.g. IV glucose
- pathological e.g. diabetes mellitus: high blood glucose
How do the kidneys autoregulate their glomerular filtration rate (GFR)?
- myogenic:
• ⬆️MAP: stretch ⇒ afferent arteriole smooth muscle contracts ⇒ prevents ⬆️BP in glomerular caps (& vice versa) - juxtaglomerular apparatus:
• ⬇️BP: ⬇️GFR ⇒ flow of filtrate past macula densa ⬇️ - causes release of local factors ⇒ afferent arteriole DILATES ⇒ ⬆️GFR to resting
How can the SNS regulate the glomerular filtration rate (GFR)?
It uses arteriole vasoconstriction:
> constricting:
AFFERENT arteriole: ⬇️GFR
EFFERENT arteriole: ⬆️GFR
True or false: during extreme physical stress, the GFR is decreased
True. This helps the body conserve fluid
