AUBF 311: Renal Function

Nephron

Functional unit of kidney

1. Cortical: 85%; filtration and reabsorption

2. Juxtamedullary: 15%; concentration

1 - 1.5 million

Amount of nephrons per kidney

25%

Approximately how much blood (pumped by the heart) does the kidney receive?

Renal Blood Flow + Urinary Filtrate Flow

1. Renal artery (blood enters)

2. Afferent arteriole

3. Glomerulus (bowman’s capsule)

4. Efferent arteriole

5. Proximal convoluted tubule + Peritubular capillaries (reabsorption)

6. Loop of Henle (descending then ascending) + Vasa recta (maintains osmotic/salt gradient)

7. Distal convoluted tubule + Peritubular capillaries (final adjustment of urine)

8. Renal vein (clean blood leaves kidney) + collecting duct (concentration of urine)

9. Renal pelvis

10. Renal calyces

11. Ureter

12. Bladder (temporary storage of urine)

13. Urethra

14. UGHHHHH

1200 mL / min

Average renal blood flow

600 - 700 mL / min

Average renal plasma flow

Glomerular Filtration Barrier

Consists of a coil of approximately 8 capillary lobes

Bowman’s Capsule

Where the glomerulus is located

<70, 000 MW

Glomerulus acts as a nonselective filter, allowing plasma substances with molecular weights of _____ to pass into the nephron

Renin-Angiotensin-Aldosterone System (RAAS)

System that responds to changes in blood pressure and plasma sodium content

Aldosterone

Sodium-retaining hormone that is released by adrenal cortex

Antidiuretic Hormone (ADH)

Water-retaining hormone that is release by the posterior pituitary gland

Vasopressin

Other name of ADH

Ascending Loop of Henle

Passive reabsorption of water takes place in all parts of the nephron except the ____, the walls of which are impermeable to water

• “Countercurrent mechanism”

160 - 180 mg/dL

Plasma renal threshold of glucose

Inversely Proportional

Relationship of body hydration to ADH in terms of urine volume

Urea Clearance

Earliest glomerular filtration test

Creatinine Clearance

Measures the waste product of muscle metabolism

• Unreliable for Px with muscle-wasting diseases or athletes taking specific supplements

• False positive in heavy meat diet

Cystatin C Clearance

Measures a small protein (13, 359 MW)

• Screening + monitoring of glomerular filtration rate (GFR)

• Recommended for:

  • Pediatrics

  • Diabetics

  • Geriatrics

  • Critically ill Px

β2-Microglobulin Clearance

Measures a small protein (11, 800 MW)

• Distinguish kidney disorders as glomerular/tubular

• Identify end-stage renal disease and early rejection of kidney transplant

• Increased amount = Tubular damage

Concentration Test

Test to determine tubular reabsorbability

Fishberg Concentration Test

Concentration test where Px is deprived of fluids for 24 hrs before measuring SG

Mosenthal Concentration Test

Concentration test that compares day and night urine spx in terms of volume and SG

3:1

Urine to serum ratio that indicates normal tubular reabsorption

p-aminohippuric acid (PAH) Test

Most common test associated with tubular secretion and renal blood flow

• Measures exact amount of plasma flowing through the kidney

Night

Lowest pH / Most acidic urine is found at what time of the day?

Renal Tubular Acidosis

Inability to produce acid urine in presence of metabolic acidosis

• Caused by impaired tubular secretion of Hydrogen ions

Phenolsulfonphthalein (PSP) Test

A tubular secretion test that uses a dye

• may produce anaphylactic shock