Urea + Electroylte Tests Flashcards
1
Q
Which components are typically filtered by the kidneys?
A
- Low molecular weight (LMW) components are filtered by the kidneys.
2
Q
What is the normal glomerular filtration rate (GFR) in humans?
A
- The normal GFR is approximately 120 mL/min.
3
Q
What is the typical range of urine production in a 24-hour period?
A
- Normal urine production is between 1–2 liters per day
4
Q
Why is glomerular filtration rate (GFR) important?
A
- GFR is a key indicator of overall health and is particularly important for assessing kidney function and drug excretion.
5
Q
Which substance is commonly used as a proxy marker for GFR?
A
- Creatinine is used as a proxy marker for GFR because it is completely filtered by the kidneys and not reabsorbed.
6
Q
What is creatinine?
A
- Creatinine is a waste product formed from the normal breakdown of creatine, a compound essential for muscle energy metabolism
7
Q
How is creatinine eliminated from the body?
A
- Creatinine is filtered out of the blood by the kidneys and excreted in urine.
8
Q
Why does muscle mass affect creatinine levels?
A
- Muscle mass affects creatinine levels because creatinine production is proportional to muscle metabolism, meaning individuals with more muscle mass produce more creatinine
9
Q
What happens to the majority of creatinine in the kidneys?
A
- About 90–95% of creatinine is filtered through the glomerulus.
10
Q
What happens to the remaining 5–10% of creatinine in the kidneys?
A
- the remaining 5–10% of creatinine is secreted into the urine by the cells of the distal tubule.
11
Q
What is the Cockcroft-Gault equation used for?
A
- The Cockcroft-Gault equation is used to estimate creatinine clearance (CrCl), which reflects kidney function.
12
Q
What is the Cockcroft-Gault equation ?
A
- CrCl (mL/min) = (140-age) x weight x (1.23 male/1.04 female) / SrCr (μmol/L)
13
Q
What creatinine clearance (CrCl) ranges correspond to kidney impairment?
A
• 50–20 mL/min: Mild impairment
• 20–10 mL/min: Moderate impairment
• <10 mL/min: Severe impairment
14
Q
Why is creatinine clearance (CrCl) inherently inaccurate?
A
- CrCl slightly overestimates GFR because a small amount of creatinine is secreted by the renal tubules
- its accuracy is influenced by various patient factors.
15
Q
In which patients is CrCl particularly inaccurate?
A
• Patients with significant muscle wastage.
• Patients with low muscle mass.
• Cachexic (severely malnourished) patients.
• Patients with rapidly changing serum creatinine levels.
16
Q
What is acute kidney injury (AKI)?
A
- AKI is a sudden decline in kidney function, characterized by reduced glomerular filtration rate (GFR)
- impaired fluid and electrolyte balance, and accumulation of waste products in the blood.
17
Q
What are the primary causes of AKI?
A
- Pre-renal: Reduced blood flow to the kidneys (e.g., dehydration, hypotension).
- Intrinsic: Direct damage to kidney tissues (e.g., acute tubular necrosis, glomerulonephritis).
- Post-renal: Obstruction of urine outflow (e.g., kidney stones, enlarged prostate).
18
Q
How is urea produced ?
A
- in the liver
- after the delaminating of amino acids
19
Q
How is urea cleared form the body ?
A
- by the golmerular filtration
- it is a major source of N loss from the body
20
Q
Is urea reabsorbed in the body ?
A
- some urea is reabsorbed by passive tubular reabsorption
21
Q
What does high level of urea indicate ?
A
- dehydration
- gastric blood loss
- infection
22
Q
What does low level of urea indicate ?
A
- oedema
- pregnancy
- low protein diet
23
Q
Where is potassium primarily found in the body?
A
- Potassium is primarily an intracellular cation, meaning most of it is found inside cells.
24
Q
Why are serum potassium (K+) levels important?
A
- Serum K+ levels are crucial because they influence membrane potential and can cause rapid changes in cell function, particularly in nerve and muscle cells.
25
What percentage of potassium is available for exchange in the body?
- About 90% of the total body potassium is available for exchange.
26
Where is the remaining 10% of potassium in the body found?
- the remaining 10% of potassium is bound in red blood cells (RBCs) and other tissues.
27
How are potassium and sodium movements related in the kidneys?
- K and Na movements are closely related because as Na is actively reabsorbed, K moves into the filtrate to maintain membrane potential balance.
28
How do hydrogen ions (H+) move in relation to potassium in the kidneys?
- H+ ions tend to move with potassium in the renal tubules
- but this depends on the ability of the tubular cells to secrete H+.
29
What happens to potassium levels in acidosis?
- hyperkalemia (high potassium)
- because hydrogen ions shift into cells, and potassium shifts out to maintain charge balance.
30
What happens to potassium levels in alkalosis?
- hypokalemia (low potassium)
- hydrogen ions shift out of cells, and potassium moves into cells to maintain balance
- less in bloodstream
31
What is the normal range for potassium in the body
?
3.6 - 5.2 mmol/L
32
What happens when the water content of the blood is low?
- blood water content is low (due to too much salt or sweating)
- brain produces more ADH, causing the kidneys to reabsorb more water
- resulting in low urine output / less water in urine (small volume of concentrated urine).
33
What happens when the water content of the blood is high?
- blood water content is high (due to drinking too much water)
- the brain produces less ADH
- leading to low reabsorption of water by the kidneys and high urine output (large volume of dilute urine).
34
What is the definition of hyponatremia?
- serum sodium concentration of less than 135 mmol/L.
- Treatment is typically required when serum sodium is below 120 mmol/L.
35
What is the most common cause of hyponatremia?
- rarely due to low sodium intake but is usually caused by defective homeostatic mechanisms
- such as the inability to properly regulate water and sodium balance.
36
What is the underlying issue in most cases of hyponatremia?
- often an excess of water relative to sodium, meaning there is more water than sodium in extracellular fluid
37
What is required to develop hyponatraemia ?
- Source of free water
• Impaired ability of the urine to excrete dilute urine.
• Reduced solute intake
• Poor renal function
38
What are symptoms of people with hyponatraemia ?
- Cerebral edema
• Confusion
• Seizures
• Coma
• Brain herniation (in severe cases)
39
What is hypernatraemia ?
- marked decrease in water relative to sodium.
• Does not occur unless there is impaired thirst
mechanisms or lack of access to water
• Can be cause by drugs or (usually) by drinking sea
water
40
What is the role of glomerular filtration in protein loss?
- the glomerular filtration system is designed to filter out large molecules, such as proteins, and prevent them from crossing into the filtrate.
41
What is the normal range for protein loss in the urine?
- A protein loss of <150 mg/day is considered normal.
42
What is microalbuminuria?
- Microalbuminuria refers to the loss of albumin in the urine at levels of >30 mg/L.
