9.2 Normal Kidney Function

Question 1

Normal urinary voiding frequency

Answer 1

4-6 times per day.

Question 2

Maximum bladder urine capacity. How much urine do the kidneys produce per hour?

Answer 2

300-400mL (can go as high as 500/700 in women/men respectively). Approx 30mL per hour produced by the kidneys

Question 3

How full does the bladder have to be before people feel the need to urinate?

Answer 3

Approx 150-250mL for most people.

Question 4

List the components of normal human urine

Answer 4

• Water
• Salts
• Nitrogenous solutes (urea, creatinine, uric acid)
• Traces of carbs, horrmones, fatty acids, and ions

Question 5

Normal eGFR (including weird units)

Answer 5

> =90mL/min/1.73m^2 body surface

Question 6

Define Glomerular Filtration Rate

Answer 6

The rate at which blood is filtered through the glomerular basement membrane

Question 7

Quantitatively, what happens to GFR as we age (and why is this important)? What happens to creatinine levels in this time, and what happens to bladder function?

Answer 7

• GFR decreases by about 1mL/min per year after age 20 (important for implications on drug clearance)
• Creatinine remains constant, since sarcopenia decreases creatinine production
• Bladder also becomes less elastic, leading to increased frequency of voiding

Question 8

Explain how NSAIDs damage the gastric mucosa (including which type), and - by contrast - how they can damage the kidneys

Answer 8

• NSAIDs inhibit COX enzymes, which produce thromboxane (platelet aggregration) and prostaglandins
• Certain prostaglandins decrease acid secretion in the stomach, increase bicarbonate/mucous secretion from mucous/epithelial cells respectively. When these are inhibited, we see damage (such as ulceration) of the stomach
• Prostaglandins also enable afferent arteriole dilation in the kidney, increasing renal blood flow when required. Therefore, NSAIDs counteract this, potentially worsening renal function

Question 9

What happens to GFR during pregnancy? Why, and what hormones drive this?

Answer 9

• Increased by 40-50%, stays that way throughout most of pregnancy
• Increased plasma volume, increased cardiac output, renal vasodilation
• Oestrogen and progesterone drive these

Question 10

During pregnancy, the renal pelvis/ureter dilates. What pathology does this increase the likelihood of, and what other factors contribute?

Answer 10

Increased UTI risk (easier access/more surface area for pathogens), also due to glycosuria secondary to high GFR and decreased glucose resorption

Question 11

What are the effects of increased GFR during pregnancy on urea, creatinine, sodium, and protein?

Answer 11

• Decreased protein, urea, and creatinine
• Increased sodium (also contributes to increased blood pressure)

Question 12

How does urinary frequency/urgency change during pregnancy? Why?

Answer 12

• Frequency increases (higher GFR)
• Urgency increases and bladder capacity decreases in response to growing uterus

Question 13

What is the link between low birth weight and renal function? Why?

Answer 13

• Increased risk of poor renal function
• Thought to be due to reduced nephron number, and to increased risk of hypertension (which damages renal vasculature)