19 - Renal: Urine Formation Flashcards
Dilute urine
(why we’d want it, what it signafies, how it’s created)
Why we’d want it:
- too much water in the body or too few ions
- avoid fatal water intoxication (blood is too dilute)
- concentrate the blood
What it signifies:
- dilute urine is high in water content and more dilute in ions than the blood (< 300mOsm/L)
How it’s created:
- using a short-loop/cortical nephron
- increase osmolarity DOWN nephron (up to 900)
- decrease osmolarity UP nephron (down to 100)
- IMPERMEABLE collecting duct decreases osmolarity further (down to 65)
- lack of ADH
Concentrated Urine
(why we’d want it, what it signafies, how it’s created)
Why we’d want it:
- to remove ions (particularly sodium)
What it signifies:
- urine is more concentrated than the blood (> 300 mOsm/L)
How it’s created:
- using long-loop/juxtamedullary nephrons
- increase osmolarity DOWN nephron (up to 1200)
- decrease osmolarity UP nephron (down to 200)
- PERMEABLE collecting duct increases osmolarity (up to 1200)
- presence of ADH makes it permeable
what is osmolarity measured in and what is the average osmolarity of the blood?
300mOSm/L
(milliosmoles)
Diuretics
(common medication, function)
furosemide (LASIX) is a common diuretic used to treat hypertension
inhibits Na-K-2Cl pumps in ascending LOH to decrease water reuptake and increase urination (therfore decreases blood volume –> decrease blood pressure)
Hormonal regulation of tubular reabsorption
- Antidiuretic hormone (ADH) edition
- ADH (also called vasopressin) production in hypothalamus
- release to posterior pituitary triggered by high osmolarity in the blood
- synthesizes water pores in the collecting duct
- increases activity of Na-K-2Cl symporter
- promotes creation of concentrated urine
Hormonal regulation of tubular reabsorption
- Renin-Angiotensin II-Aldosterone-System (RAAS) edition
- renin production by granular cells in juxtaglomerular apparatus
- triggered by low blood pressure
- renin promotes conversion of angiotensinogen into angiotensin I
- ACE converts angiotensin I into angiotensin II
- decreases glomerular filration rate (less filtrate)
- increase activity of Na/H antiporters (increased Na reabsorption)
-
increases aldosterone release
- increase Na and Cl reabsorption in collecting duct
- increase K excretion
- concentrated urine: reduce urination - urine has less sodium, more potassium, more H+
evaluate kidney function
(main methods)
urinalysis analyzes the volume, physical, chemical and microscopic properties of urine
blood analysis will evaluate the waste product levels in the blood
urinalysis
(normal vs abnormal indicators)
Physical
- volume: 1-2 L/day | highly variable, outside this range
- color: apple juice | highly variable, dark, milky…
- turbidity: transparent | cloudy
- odor: mild | fruity or foul
- pH: 6 | under 4.5 or above 8.0
normal | abnormal
blood analysis (from a renal perspective)
blood urea nitrogen (BUN)
- high BUN levels means kidneys are not excreting it properly - not functioning properly
- likely signals very low GFR too
blood plasma creatinine
- levels should be very low and consistent (no buildup)
- levels above 110µmol/L can indicate poor kidney function
renal function tests
renal clearance = UV/P
- testing how much of a substance is cleared from the blood plasma by the kidney per unit of time
- assess the concentration in urine (U), in blood plasma (P) and volumetric rate of urine output (V)
glomerular filtration rate = UV/P
- rate of blood filtration by the kidneys (flow of plasma into the glomerular space)
- tested using substance that is not reabsorbed or secreted by tubules like Inulin
- measure inulin concentrations in blood and urine, and urine output
