Lecture 31: URINE COMPOSITION, FUNCTIONS OF KIDNEY, BASIC NEPHRON PROCESSES Flashcards
What is found in normal urine?
Water, creatinine, urea, uric acid, H+, NH3, Na+, K+, drugs, toxins
How much water is in urine?
1.5L/day
What percentage of urine is water?
95-98%
How does normal urine look?
Clear, light or dark amber
what does normal urine taste like?
Acidic (pH 5-6), not sweet
What does the pH of urine depend on?
Diet
What is the pH of the urine of vegetarians?
Up to 7.2
What is the pH of the urine of meat eaters?
4.8
What is the smell of normal urine?
There is no smell
What may be found in pathological urine?
Glucose, protein, blood (erythrocytes), haemoglobin, leukocytes and bacteria
What is it called when there is haemoglobin in urine?
Haemoglobinuria
What is it a sign of when there is bacteria in urine?
Infection
What does pathological urine look like?
golden, red, brown, blue
What does pathological urine taste like?
Sweet = diabetes mellitus
What may pathological urine smell like?
Fruits or rotten
What may it mean when urine smells like fruit?
ketosis (fasting), diabetes, chronic alcohol abuse
What may it mean when urine smells rotten?
Infection (bacteria), tumor
What is measured in urinalysis?
Blood, specific gravity, glucose, pH and protein
Where is blood found?
Not urine or plasma
What may blood in the urine indicate?
Haematuria, urinary tract infection, damage to filtration barrier
What does specific gravity measure?
Osmolarity
What is the specific gravity of plasma?
285-300 mOsmol/L
What is the specific gravity of urine?
50-1335 mOsmol/L
What may it mean when specific gravity isn’t within the range?
Polyuria, diabetes mellitus, diabetes inspires (concussion)
Where is glucose found?
In plasma but not urine
What may it mean when there is glucose in the urine?
Glucosuria, diabetes mellitus
Where is protein found?
In plasma but not urine
What may it mean when there is protein in the urine?
Proteinuria, glomerulonephritis, damage to filtration barrier
What is the pH of plasma?
7.4
What is the pH of urine?
4.5-8
What may it mean when the pH of urine has changed?
Acidosis, alkalosis, asthma, anxiety disorder
What are the functions of the kidney?
- filters blood
- hormone production (erythropoietin)
- metabolism
- gluconeogenesis (when fasting)
- pH regulation
- excretion of drugs, endogenous metabolites and toxins
- reabsorption ofnutrients
- salt/ion homeostasis
- water homeostasis
What does the kidney detect?
Low oxygen levels
What does the kidney release?
Erythropoietin
What does EPO do?
Stimulates the bone marrow to produce more red blood cells
What may chronic renal failure lead to (EPO)?
Anaemia (low levels of red blood cells/haemoglobin > low oxygen levels)
Why is potassium important in cells?
Resting membrane potential is based on potassium gradient (inside/outside) of cells
Why is potassium important in neurons and cardiomyocytes?
Action potentials, rhythm generation in pace maker cells, contractility, signalling
What does the kidneys do with potassium?
Secrete it as too much can kill
What can kidney disease/failure lead to (potassium)?
Hyperkalemia (death)
What is lidocaine?
A commonly used local anaesthetic in a practice or hospital
What happens with lidocaine?
It is excreted by the kidneys after metabolisation in the liver due to its fat soluble (lipophilic) nature
What happens with aspirin?
It is already highly water soluble (hydrophilic) and excreted directly by the kidneys
What happens with lipophilic things?
Metabolised in liver (some excreted in bile) and excreted directly by the kidneys
What happens with hydrophilic things?
Excreted by the kidneys
What is the formula for pH?
-log[H+]
What does it mean when blood pH is above 7.4?
Alkalosis
What does it mean when blood pH is below 7.4?
Acidosis
What can vomiting cause?
Loss of acid so blood is more basic (alkalosis)
What can diarrhoea cause?
Loss of bicarbonate so blood is more acidic (acidosis)
What is bicarbonate?
The main buffer of the blood neutralising non-volatile acids coming from metabolism, food and drinks, maintaining a blood pH of 7.4
What is bicarbonate concentration in the blood controlled by?
The lungs (exhalation of carbon dioxide) and kidneys by reabsorption of bicarbonate or secretion of hydrogen ions
What does filtration do?
Creates a plasma like filtrate of the blood
What does reabsorption do?
Removes useful solutes from the filtrate and returns them to the blood
What does secretion do?
Adds additional wastes from the blood to the filtrate
What determines the way a substance is handled in the kidneys?
The balance between filtering, reabsorption and secretion
How are many substances filtered?
With a constant rate at the renal corpuscle (glomerulus) with the exception of substances bound to protein
What needs to happen to some substances?
They need to be partly reabsorbed (Na+/K+) or entirely reabsorbed(glucose) or entirely secreted (many drugs)
what is the role of the glomerulus?
Filtration
What is the role of the proximal tubule?
Bulk reabsorption of electrolytes (sodium, potassium), secretion of metabolites, drugs and toxins
What is the role of the distal tubule?
Fine tuning electrolyte/water reabsorption
What is the role of the collecting duct?
Fine tuning electrolyte/water reabsorption
What happens with glucose?
It is reabsorbed only in the proximal tubule
What happens with potassium?
It is reabsorbed (PCT) or secreted (DCT/ collecting duct) in different parts of the tubule (depends on diet)
What happens with water?
It is reabsorbed in most parts of the tubule
What happens with drugs and toxins such as penicillin?
Mostly excreted by active secretion, not filtration
What happens with big molecules such as albumins?
They are not even filtered
