Lecture 31- Urine composition, functions of the kidney and basic nephron processes Flashcards
What is urine used for?
To diagnose diseases
What is in normal urine?
- Water
- Creatine
- Urea, Uric acid
- H+, NH3
- Potassium and sodium ions
- Drugs (anti-viral, diuretics)
- Toxins
How much of urine is water and why?
- 95-98%
- 1.5L/day
- Because water building up in the extracellular fluid would alter blood pressure
Why do we need to get rid of acid H+, NH3 in urine?
To control pH of the blood
What is in pathological urine?
- glucose (glucosuria, diabetes)
- protein (proteinuria)
- blood (erythrocytes, haematuria)
- haemoglobin (haemoglobinuria)
- leucocytes
- bacteria (infection)
How should normal urine look, taste and smell?
Look:
-clear, light or dark amber look
Taste:
- acidic (pH: 5-6), not sweet!!
Smell:
- unremarkable
What is the specific pH of urine dependent on?
- pH dependent on diet!!!
- vegetarians: pH up to 7.2
- meat eaters (high protein): pH 4.8
What is the specific colour of urine dependent on?
Darker if dehydrated
How does pathological urine look, taste and smell?
Look:
- golden, red, brown, blue
Taste:
- sweet= diabetes mellitus
Smell:
- like fruits: ketosis (fasting), diabetes, chronic alcohol abuse
- rotten: infection (bacteria), tumour
What are the functions of the kidney?
-Filters blood
-Hormone production (erythropoietin)
-Metabolism
-Gluconeogenesis
-pH regulation
-Excretion of drugs, endogenous metabolites and toxins
(aspirin, anti-viral drugs, urea, uric acid, herbal toxins)
-Re-absorption of nutrients (amino acids, glucose)
-Salt/ion homeostasis (Na+, K+, Ca2+ ,blood pressure)
-Water homeostasis (hydration, blood pressure)
What is the important hormone the kidney is invovled in regulating? Explain the response mechanism…
-Erythropoietin (EPO)
-Low oxygen levels in the blood are detected by kidneys causing release of erythropoietin
-EPO then stimulates the bone marrow to produce
more red blood cells
What happens in the case of chronic renal failure with regards to EPO?
-Anaemia (low levels of red blood cells/haemoglobin
→ low blood oxygen levels)
Specifically how is the kidney invovled in metabolism?
Amino acids
What is gluconeogenesis? When is it done by the kidney?
- Is the production of glucose
- Happens when we are fasting or starving
Why is regulation of potassium ion levels so important?
- Because potassium ions are vital for many functions
- Resting membrane potential is based on K+ gradient (inside/outside) of cell
- Manipulating this membrane potential via movement of ion is vital in the generation of action potentials, rhythm generation in pacemaker cells, contractility and signaling. Potassium helps to bring membrane potential back to baseline.
Across the membrane how to potassium levels usually sit? How do sodium levels usually sit?
- Potassium high in the cell, low outside
- Sodium low in the cell, high outside
What is the consequence of the kidney not being able to secrete/get rid of potassium?
- Lead to hypercalcemia (high levels of potassium in the blood) which causes death.
- Those on dialysis killed by just eating 3-5 bananas
Could you ever kill yourself from excess potassium if you didn’t have kidney failure?
- No
- only 0.5 g K+/banana
- 5 g K+/day dietary need
- 190 g K+ kills a 165lb person
How do the kidneys function in drug excretion?
-lidocaine is excreted by the kidneys after metabolisation in the liver due to its fat soluble (lipophilic) nature
-aspirin, a common pain killer, is already highly water
soluble (hydrophilic) and excreted directly by the
kidneys (doesn’t need to go through liver)
Above what blood pH is considered alkalosis?
Below what blood pH is considered acidosis?
- 7.4
- 7.4
How does vomiting change blood pH? How does diarrhoea change blood pH?
- Vomiting gets rid of acid causing alkalosis
- Diarrhoea has the opposite effect, by getting rid of bicarbonate blood pH is made lower (acidosis)
What is the main buffer of the blood? How does it do this?
- Bicarbonate (HCO3), maintains a blood pH of 7.4
- By neutralizing so called non-volatile acids coming from metabolism, food and drinks
How is the level of bicarbonate in the blood controlled?
- Controlled by the lungs (exhalation of CO2)
- By the kidneys via reabsorption of bicarbonate (HCO3) or secretion of hydrogen ions (H+);
What are the three basic nephron processes and how are they done?
- Filtration= creates a plasma-like filtrate of the blood
- Reabsorption= removes useful solutes from the filtrate and returns them to the blood
- Secretion= adds additional wastes from the blood to the filtrate
How does filtration in the nephron work? Where does it occur?
- Essentially like a sieve only distinguishing what can pass through based on size (small is let through, large will remain)
- Glomerulus
What occurs at the proximal tubule of the nephron?
Bulk reabsorption of electrolytes (sodium, potassium),
secretion of metabolites, drugs and toxins
What occurs at both the distal tubule and collecting duct of the nephron?
fine-tuning of electrolytes/water reabsorption
What is an exception to substances being filtered at a constant rate at the glomerulus?
Substances bound to protein
How is glucose handled and in what part of the nephron?
Let through and then fully reabsorbed in the proximal tubule
How is potassium handled and in what part of the nephron?
K+ is reabsorbed or secreted in different parts of tubule (depends on diet!!);
How is water handled and in what part of the nephron?
water is reabsorbed in most parts of tubule
How are drugs and toxins handled and in what part of the nephron?
penicillin (drugs and toxins) is mostly excreted by active secretion, not filtration
How are big molecules handled and in what part of the nephron?
big molecules (such as albumin) are not even filtered
