Renal Function

What percentage of blood pumped through the heart do the kidneys recieve?

25%

What are the kidneys a natural monitor of?

blood pressure and volume

Macroscopic Structure of the kidney

• cortex

• medulla

• pelvis

What is the functional unit of the kidney?

nephron

What are the main functions of the renal system?

• excretory

• regulatory

• synthetic

What do cortical nephrons do?

removal of waste products and reabsorption of nutrients

Juxtamedullary nephrons

• located in medulla

• 15% of nephrons

• loops of henle (concentration of urine)

What are the causes of glomerular filtration?

• hydrostatic pressure (diff sizes of arterioles)

• oncotic pressure caused by protein

• shield of negativity

Glomerulus

located in the Bowman capsule and filters the blood

RAAS

responds to changes in blood pressure and sodium content

Where is renin produced?

juxtaglomerular cells

RAAS triggers the release of what hormones?

aldosterone (adrenal) and ADH (hypothalamus)

How much water loss is too much water loss?

120 mL/min

Tubular reabsorption via active transport

• carrier protein required

• PCT: glucose, AAs, and salts

• Loop of Henle: chloride

• PCT and DCT: sodium

Tubular reabsorption via passive transport

• based on concentration gradient or electrical potential

• PCT and loop of Henle: Urea

• ascending loop of Henle: Sodium

Water is passively reabsorbed in all parts of the nephron, EXCEPT?

in the ascending loop of Henle (impermeable to H2O)

Maximal Reabsorptive Capacity (Tm)

max reabsorption ability for a solute by renal tubules

What is the plasma renal threshold for glucose?

160 - 180 mg/dL (higher will go into urine causes tubular damage or diabetes)

Renal Threshold

plasma concentration at which active transport stops

ADH (antidiuretic hormone)

• regulates reabsorption of water

• vasopressin

• made in hypothalamus

• controls DCT and collecting duct walls

What would the urine sample of a patient with LOW ADH look like?

• low specific gravity

• dilute urine

• high volume

Urine sample with HIGH ADH?

• high specific gravity

• concentrated urine

• low volume

Increased body hydration leads to?

dec ADH and inc urine volume

Decreased body hydration leads to?

inc ADH and dec urine volume

What are the 2 purposes of tubular secretion?

• eliminate waste not filtered by the glomerulus

• maintain acid/base balance

A patient in renal tubular acidosis would have urine with a pH of what?

8.0 or more (alkaline)

GFR

measures the filtering capacity of the glomeruli (24 hour urine samples)

Creatinine Clearance

• most common GFR test

• not changed by diet or urine flow

• not reabsorbed

What are some disadvantages of using Creating as a clearance substance?

• some is secreted by tubules (inc in blood)

• medications inhibit tubular secretion

• heavy meat diet can raise plasma levels

• not reliable in pts w/ muscle wasting or athletes

• not accurate for kids

Creatinine clearance formula

(urine creatinine X urine volume) / plasma creatinine

What is the formula for urine volume > mL/min ?

V= total volume / (60 × 24)

eGFR (estimated)

estimation screening as part of the metabolic profile and used to monitor pts already diagnosed with renal disease/inc risk (no 24 hour collection needed)

What tests assess the renal tubular function?

reabsorption tests (osmolarity and specific gravity)

what is the normal ratio for osmolarity (urine to serum)?

1:1

P-aminohippuric acid (PAH)

• given via IV (completely removed from blood)

• normal would be 600-700 mL/min per kidney