Lecture 31- Urine composition, functions of the kidney and basic nephron processes

Question 1

What is urine used for?

Answer 1

To diagnose diseases

Question 2

What is in normal urine?

Answer 2

• Water
• Creatine
• Urea, Uric acid
• H+, NH3
• Potassium and sodium ions
• Drugs (anti-viral, diuretics)
• Toxins

Question 3

How much of urine is water and why?

Answer 3

• 95-98%
• 1.5L/day
• Because water building up in the extracellular fluid would alter blood pressure

Question 4

Why do we need to get rid of acid H+, NH3 in urine?

Answer 4

To control pH of the blood

Question 5

What is in pathological urine?

Answer 5

• glucose (glucosuria, diabetes)
• protein (proteinuria)
• blood (erythrocytes, haematuria)
• haemoglobin (haemoglobinuria)
• leucocytes
• bacteria (infection)

Question 6

How should normal urine look, taste and smell?

Answer 6

Look:
-clear, light or dark amber look

Taste:
- acidic (pH: 5-6), not sweet!!

Smell:
- unremarkable

Question 7

What is the specific pH of urine dependent on?

Answer 7

• pH dependent on diet!!!
• vegetarians: pH up to 7.2
• meat eaters (high protein): pH 4.8

Question 8

What is the specific colour of urine dependent on?

Answer 8

Darker if dehydrated

Question 9

How does pathological urine look, taste and smell?

Answer 9

Look:
- golden, red, brown, blue

Taste:
- sweet= diabetes mellitus

Smell:

• like fruits: ketosis (fasting), diabetes, chronic alcohol abuse
• rotten: infection (bacteria), tumour

Question 10

What are the functions of the kidney?

Answer 10

-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)

Question 11

What is the important hormone the kidney is invovled in regulating? Explain the response mechanism…

Answer 11

-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

Question 12

What happens in the case of chronic renal failure with regards to EPO?

Answer 12

-Anaemia (low levels of red blood cells/haemoglobin

→ low blood oxygen levels)

Question 13

Specifically how is the kidney invovled in metabolism?

Answer 13

Amino acids

Question 14

What is gluconeogenesis? When is it done by the kidney?

Answer 14

• Is the production of glucose

- Happens when we are fasting or starving

Question 15

Why is regulation of potassium ion levels so important?

Answer 15

• 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.

Question 16

Across the membrane how to potassium levels usually sit? How do sodium levels usually sit?

Answer 16

• Potassium high in the cell, low outside

- Sodium low in the cell, high outside

Question 17

What is the consequence of the kidney not being able to secrete/get rid of potassium?

Answer 17

• Lead to hypercalcemia (high levels of potassium in the blood) which causes death.
• Those on dialysis killed by just eating 3-5 bananas

Question 18

Could you ever kill yourself from excess potassium if you didn’t have kidney failure?

Answer 18

• No
• only 0.5 g K+/banana
• 5 g K+/day dietary need
• 190 g K+ kills a 165lb person

Question 19

How do the kidneys function in drug excretion?

Answer 19

-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)

Question 20

Above what blood pH is considered alkalosis?

Below what blood pH is considered acidosis?

Answer 20

• 7.4

- 7.4

Question 21

How does vomiting change blood pH? How does diarrhoea change blood pH?

Answer 21

• Vomiting gets rid of acid causing alkalosis

- Diarrhoea has the opposite effect, by getting rid of bicarbonate blood pH is made lower (acidosis)

Question 22

What is the main buffer of the blood? How does it do this?

Answer 22

• Bicarbonate (HCO3), maintains a blood pH of 7.4

- By neutralizing so called non-volatile acids coming from metabolism, food and drinks

Question 23

How is the level of bicarbonate in the blood controlled?

Answer 23

• Controlled by the lungs (exhalation of CO2)

- By the kidneys via reabsorption of bicarbonate (HCO3) or secretion of hydrogen ions (H+);

Question 24

What are the three basic nephron processes and how are they done?

Answer 24

• 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

Question 25

How does filtration in the nephron work? Where does it occur?

Answer 25

• Essentially like a sieve only distinguishing what can pass through based on size (small is let through, large will remain)
• Glomerulus

Question 26

What occurs at the proximal tubule of the nephron?

Answer 26

Bulk reabsorption of electrolytes (sodium, potassium),

secretion of metabolites, drugs and toxins

Question 27

What occurs at both the distal tubule and collecting duct of the nephron?

Answer 27

fine-tuning of electrolytes/water reabsorption

Question 28

What is an exception to substances being filtered at a constant rate at the glomerulus?

Answer 28

Substances bound to protein

Question 29

How is glucose handled and in what part of the nephron?

Answer 29

Let through and then fully reabsorbed in the proximal tubule

Question 30

How is potassium handled and in what part of the nephron?

Answer 30

K+ is reabsorbed or secreted in different parts of tubule (depends on diet!!);

Question 31

How is water handled and in what part of the nephron?

Answer 31

water is reabsorbed in most parts of tubule

Question 32

How are drugs and toxins handled and in what part of the nephron?

Answer 32

penicillin (drugs and toxins) is mostly excreted by active secretion, not filtration

Question 33

How are big molecules handled and in what part of the nephron?

Answer 33

big molecules (such as albumin) are not even filtered