Calculating Renal Function

Question 1

Describe the macroscopic structure of the kidney

Answer 1

Kidney is located in posterior wall of abdomen

Divided into the outer cortex which receives most blood supply involved in reabsorption of filtered material

Inner medulla that concentrates the urine and removes water and concentrates the solutes to form urine

Question 2

Describe the microstructure structure of the kidney (nephrons)

Answer 2

Starts off with the glomerulus and bowmans capsule that loops into the loop of henle

Loop of henle- vascular and tubular system interlinking

Bowmans capsule- deals with filtration of smaller molecules into the tubular system into the tubular fluid and reabsorption of solutes that move in and out of tubular, blood and fluid

Question 3

Describe the functions of the kidney

Answer 3

Homeostatic regulation of water and inorganic ion balance (Na+, K+, Mg2+, Ca2+)- removal of ions to remain balance

Maintaining internal environment of blood pressure (balances water in body), acid/base, ions

Removal of metabolic waste products and foreign chemicals (includes drugs) from blood

Production and secretion of essential substances

• Erthyroprotein- red blood cell production
• Renin- blood pressure angiotensin system
• Vitamin D3 (calcitriol)- necessary when kidneys are not working properly

Question 4

How do you measure kidney function?

Answer 4

GFR

Question 5

If kidneys are not functioning correctly, describe what this can result in?

Answer 5

1. Loss of nutrients from the body- vitamin D
2. Failure to remove toxins (drugs = accumulation = may have to review dose)
3. Blood pressure effects
4. Rise in electrolytes like potassium can lead to problems in heart

Question 6

Explain what glomerular flirtation rate is

Answer 6

The volume of fluid filtered from renal glomerular capillaries into the bowman’s capsule per unit time

Indication of number of functioning nephrons

The best way to measure kidney function- measure what is exactly filtered in each nephron

Question 7

How can you measure GFR?

Answer 7

Injection of: not practical
Inulin- polysaccharide
EDTA
Iohexol

Measuring amount of urine per unit time with exogenous marker administered- not feasible in clinical setting

ESTIMATE GFR using CREATININE- creatine break down product

Question 8

What is the relationship between GFR and serum creatinine

Answer 8

As creatinine level rises, kidneys are failing

Question 9

How do you workout the cockcroft and gault formulation in males and females

Answer 9

Male=
1.23 x (140-age) x weight (kg)
——————————————-
Creatinine in micromol/L (CrCl)

Female=
1.05 x (140-age) x weight (kg)
——————————————–
Creatinine in micromol/L (CrCl)

Question 10

What do you have to watch out for in serum creatinine

Answer 10

Serum creatinine on its own is not enough to work out kidney function

Question 11

How do you estimate GFR (eGFR) using the MDRD equation

Answer 11

Requires a 4 variable formula of age, gender, ethnicity and serum creatinine

More precise measure of GFR

Good for calculating people of average/normal body weight

Question 12

How do you work out the GFR absolute for extremes of body weight

Answer 12

GFR Absolute= eGFR x (individual’s body surface area/1.73)

Question 13

What does the BNF class as classes of extremes of weight

Answer 13

BMI of less than 18.5kg/m2 or greater than 30kg/m2

Question 14

Give examples of toxic drugs to the kidneys

Answer 14

Aciclovir