Renal Function Tests: Anatomy and GFR

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Questions and Answers

What hormone promotes sodium reabsorption in the kidneys?

Aldosterone (correct)

Vasopressin

Creatinine

Erythropoietin

Glomerular filtration rate (GFR) is a less sensitive indicator of potential renal damage compared to plasma creatinine.

False

What is the primary function of erythropoietin produced by the kidneys?

Stimulate red blood cell production

Aldosterone is secreted from the ______.

adrenal cortex Signup and view all the answers

Match the following kidney functions with their respective descriptions:

Erythropoietin production = Stimulates red blood cell formation Vitamin D metabolism = Regulates calcium and phosphate balance Excretion of urea = Removes waste products from protein metabolism H+ homeostasis = Maintains acid-base balance in the body Signup and view all the answers

Which of the following is true regarding plasma creatinine concentration?

It is easier to measure than GFR. Signup and view all the answers

A decrease in muscle mass can lead to an increase in plasma creatinine levels.

False Signup and view all the answers

What is the unit of measurement for Glomerular Filtration Rate (GFR)?

ml/min Signup and view all the answers

What condition is indicated by glucosuria with normal blood glucose levels?

Malabsorption of glucose Signup and view all the answers

Osmolality in urine should increase after injecting synthetic vasopressin.

True Signup and view all the answers

What is the normal range for microalbuminuria in mg/24h?

30-300 mg/24h Signup and view all the answers

The specific gravity of urine should be greater than ______ to indicate normal distal tubular function.

1.02 Signup and view all the answers

Match the types of albuminuria with their corresponding values:

Normal albumin = < 30 mg/24h Microalbuminuria = 30-300 mg/24h Macroalbuminuria = > 300 mg/24h High proteinuria = > 150 mg/24h Signup and view all the answers

Which of the following correctly describes specific gravity?

Ratio of mass of 1ml of urine to 1ml of water Signup and view all the answers

Normal osmolality in serum is around 285 mmol/kg.

True Signup and view all the answers

What is the primary substance found in macroalbuminuria?

Albumin Signup and view all the answers

Study Notes

Renal Function Tests (I)

Learning outcomes include familiarizing with kidney structure and function, and understanding the importance of glomerular filtration rate (GFR) and plasma creatinine as markers of kidney dysfunction.

Anatomy of Kidneys

Kidneys contain a vascular component: afferent arterioles (blood to glomerulus), glomerulus (capillary tuft filtering blood), and efferent arterioles (blood away). Peritubular capillaries supply renal tissue.
The tubular component begins with Bowman's capsule collecting filtrate. Proximal tubules reabsorb/secrete substances. Loops of Henle, in juxtamedullary nephrons, establish osmotic gradients. Distal tubules and collecting ducts have controlled reabsorption/secretion of sodium, water, potassium, and hydrogen ions, ultimately forming urine.
The juxtaglomerular apparatus regulates kidney functions.
Approximately 20% of plasma entering the glomerulus is filtered.

Structure of the Glomerulus

Kidney functions include extracellular fluid volume regulation, H+ homeostasis, urea excretion, erythropoietin production, and vitamin D metabolism.
Glomerulus components are the basement membrane, capillary lumen, and urinary space. They contain podocytes and endothelial cells. Mesangial cells are contractile and phagocytic.

Aldosterone

Aldosterone, secreted from the adrenal cortex, acts on principal (P) cells in the distal tubule and collecting duct.
It increases sodium reabsorption, modifies sodium channels, and promotes new channel and ATPase expression.

Vasopressin (ADH)

Vasopressin (ADH), released from the posterior pituitary, acts on collecting duct cells.
It promotes insertion of aquaporin-2 water channels into the luminal membrane.
This increases water permeability and subsequent water reabsorption.

Glomerular Filtration Rate (GFR)

GFR assesses glomerular function. Creatinine, a muscle metabolism byproduct, is used in GFR measurements.
Plasma creatinine concentration is dependent on muscle mass. Lower values are seen in wasted individuals or children; pregnancy and vigorous exercise can slightly elevate levels.
Units for GFR measurements are ml/min. Calculating GFR involves multiplying urine creatinine concentration by urine flow rate, then dividing by plasma creatinine concentration. Collection of urine, timed correctly, is essential for accurate GFR results. Incorrect urine collection is a major source of error.

GFR or Plasma Creatinine

GFR changes significantly before detectable plasma creatinine change. GFR is more sensitive to early renal damage.
Plasma creatinine measurements are more precise and easier than GFR measurements.
Plasma creatinine measurements are adequate for monitoring the progression of renal disease and transplantation rejection.

Causes of Elevated Plasma Creatinine

Impaired renal perfusion (due to decreased blood pressure, blood volume reduction, or narrowed renal artery).
Loss of functioning nephrons (e.g., glomerulonephritis with antibody-mediated damage, deposition of immune complexes, increased pressure on the tubule, kidney stones, and prostatic enlargement).

Interpretation of Plasma Urea Measurements

Normal plasma urea range is 2.5-6.6mmol/L.
High protein intake or increased protein breakdown after trauma will increase plasma urea.
Low protein intake, liver failure, and water retention will decrease plasma urea.
Decreased renal perfusion, renal disease, and urinary outflow obstruction can elevate plasma urea.

Summary

Kidneys are crucial for pH balance and toxin removal.
Renal function is important for fluid balance.
GFR and plasma creatinine are used to assess kidney function, but have limitations. Urine dipsticks can be part of initial/routine diagnostics.

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Description

This quiz focuses on the anatomy of the kidneys and the function of renal tests, including the significance of glomerular filtration rate (GFR) and plasma creatinine. It covers kidney structure, including its vascular and tubular components, as well as urine formation processes. Test your understanding of these crucial concepts in renal physiology.