Lecture 31: Urine composition, functions of the kidney, and basic nephron processes Flashcards
How much normal urine is produced a day?
1.5 L/day
What % of urine is water?
95% - 98%
What is excreted in normal urine?
5
- Urea/uric acid
- H+/NH3 (hydronium ions/ammonia)
- Potassium/sodium
- Drugs
- Toxins
What is found in pathological urine?
6
- Glucose
- Protein
- Blood
- Haemoglobin
- Leucocytes
- Bacteria
How should normal urine look?
Clear, light or dark amber
How should normal urine taste?
Acidic (pH 5-6)
How should normal urine not taste?
Sweet
What is the pH of our urine dependent on?
Diet
What can the pH of vegetarians urine be up to?
7.2
What is the pH of meat eaters (high protein)?
4.8
what is the smell of normal urine?
Unremarkable
What does pathological urine look like?
golden, red, brown or blue
What does pathological urine taste like?
Sweet
What does pathological urine smell like?
Fruits or rotten
What are low oxygen levels detected by?
The kidneys
What does the kidney release?
Erythropoietin (EPO)
What does EPO do?
Stimulates the bone marrow to produce more red blood cells
What can chronic renal failure lead to?
Anaemia
What does anaemia lead to?
Low levels of red blood cells/haemoglobin
What does low levels of red blood cells/haemoglobin lead to?
Low blood oxygen levels
What can happen to substances in the kidneys?
They can be metabolised
What is meant by the kidneys being able to preform gluconeogenesis?
They can produce glucose in a fasted state
What is potassium ion concentration important for?
Many processes
What is the resting membrane potential of all cells based on?
The potassium gradient (inside/outside) of cells
How much potassium is in a banana?
0.5g
How much potassium is needed dietarily daily?
5g
How much potassium is needed to kill a 165lb person?
190g
What do the kidneys do to potassium?
They secrete it
What does kidney disease/failure lead to?
Hyperkalemia (death)
What is lidocaine?
A commonly used local anaesthetic
When is lidocaine excreted by the kidneys?
After metabolism in the liver
Why is lidocaine excreted by the kidneys, after metabolism in the liver?
Due to its fat soluble (lipophilic) nature
How is aspirin excreted?
Directly by the kidneys
Why is aspirin excreted directly from the kidneys?
Because it is highly water soluble (hydrophilic)
What is pH?
-log[H+]
What does pH indicate?
Degree of acidity or alkalinity
What is the range of pH?
0-14
What does a pH of 7 mean?
Neutral
What does a pH of <7 mean?
Acid (excess H+)
What does a pH of >7 mean?
alkaline/basic (excess base)
What is a blood pH of > 7.4 called?
Alkalosis
What is a blood pH of < 7.4 called?
Acidosis
What is the main buffer of the blood stream?
Bicarbonate
How does bicarbonate act as a buffer?
By neutralising so called non-volatile acids coming from metabolism, food and drinks, maintaining a pH of 7.4
What is bicarbonate concentration in the blood controlled by?
The lungs and kidneys
How is bicarbonate concentration in the blood controlled by the lungs and kidneys?
By exhalation of carbon dioxide from the lungs or reabsorption of bicarbonate by the kidneys/secretion of hydrogen ions
What are the 3 basic functions of a nephron?
- Filtration
- Secretion
- Reabsorption
What does filtration in the nephron do?
Creates a plasma-like filtrate of the blood
What does reabsorption in the nephron do?
Removes useful solutes from the filtrate and returns them to the blood
What does secretion in the nephron do?
Adds additional wastes from the blood to the filtrate
What does the balance of filtration/reabsorption/secretion determine?
The way a particular substance is handled in the kidneys
Many substances are filtered with a constant what? at the renal corpuscle
Rate
What is the exception to substances being filtered at a constant rate?
Substances bound to proteins
What are examples of substances that need to be partly/entirely re-absorbed respectively?
(2)
- Na,K
- Glucose
What process occur at the glomerulus?
Filtration
What process occurs at the proximal tubule?
2
- Bulk reabsorption of electrolytes (sodium, potassium)
- Secretion of metabolites, drugs and toxins
What process occurs at the distal tubule?
Fine tuning of electrolytes/water reabsorption
What process occurs at the collecting duct?
Fine tuning of electrolytes/water reabsorption
What only happens to glucose and where does this only happen?
It is only reabsorbed and it only occurs in the proximal tubule
What does potassium reabsorption/secretion depend on?
Diet
Where is water reabsorbed?
In most parts of the nephron
How are drugs/toxins e.g. penicillin mostly excreted?
By active secretion or non-filtration
What happens to big molecules such as albumin?
It is not filtered
What disease(s) are indicated by blood being present in the urine? (3)
- Haematuria
- Urinary tract infection
- Damage to filtration barrier
What disease(s) does a urine sample with a specific gravity not between 50-1335 mOsmol/L indicate? (3)
- Polyuria
- Diabetes mellitus
- Diabetes insipidus
What disease(s) are indicated by glucose being present in the urine? (2)
- Glucosuria
- Diabetes mellitus
What disease(s) are indicated by protein being present in the urine? (3)
- Proteinuria
- Glomerulonephritis
- damage to filtration barrier