Lecture 30: Functions of the kidney and nephron process

Question 1

What are the seven major functions of the kidneys?

Answer 1

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Endocrine functions

Metabolic functions:

pH-regulation

Water homeostasis

Salt/ion homeostasis

Re-absorption of nutrients:

Excretion of medications, toxins and metabolites:

Question 2

What is the endocrine function of the kidneys?

Answer 2

Erythropoietin (EPO)

➤ low blood oxygen levels are detected by the kidneys
➤ the kidneys release EPO
➤ EPO stimulates the bone marrow to produce more red blood cells

Chronic kidney/renal failure
➤ the kidneys cannot make enough EPO
➤ reduced red blood cell production
➤ ANAEMIA: low blood oxygen levels

Question 3

What is the main metabolic feature of the kidneys?

Answer 3

Gluconeogenesis

During fasting, or when our body is under stress, The kidneys make glucose (from lactate)

Question 4

What is a the standard blood pH range?

Answer 4

The blood is tightly maintained between pH 7.35-7.45

Question 5

What are the sources of acid in the body?

Answer 5

▪ Acids coming from metabolism, food and drink - direct sources of H+ (Non-volatile acids)

▪ Carbon dioxide from metabolism

Question 6

How do the kidneys help regulate blood pH?

Answer 6

by reabsorption and secretion of bicarbonate (HCO3-) and hydrogen ions (H+)

Question 7

How do the kidneys maintain K+ ion levels and what can happen if K+ builds up in the blood?

Answer 7

Kidneys secrete K+ (potassium), to maintain potassium
balance

Kidney disease/failure can lead to hyperkalemia (death)

▪ Kidneys cannot secrete enough potassium. Potassium builds up in the blood and can cause arrhythmias (irregular heart beat/signaling)

Question 8

How is aspirin (a common pain killer) processed in the body?

Answer 8

can be excreted directly by the kidneys due to its high water solubility (hydrophilic)

Question 9

How is lidocaine (a commonly used local anaesthetic) processed in the body?

Answer 9

excreted by the kidneys after metabolism in the liver due to its fat soluble (lipophilic) nature

Question 10

How are medications in general processed in the body?

Answer 10

Medications are filtered and secreted by the kidneys to
be excreted from the body in the urine

Question 11

How does the kidney maintain total water balance?

Answer 11

▪ Total body water remains relatively constant
▪ Intake and loss of water must balance
▪ Urine output is adjusted to maintain balance

Question 12

What percentage of extracellular fluid (ECF) is plasma and what makes up the remaining ECF?

Answer 12

20% of the ECF is plasma

80% of the ECF is interstitial fluid

Question 13

How can the volume of water in the different compartments of the body change?

Answer 13

▪ how much water there is in the body
▪ the osmolarity of the body water compartments (water moves to where the osmolarity is highest)

Question 14

What would an increase in plasma do to blood pressure?

Answer 14

It would also increase blood pressure

Question 15

What would a decrease in plasma do to blood pressure?

Answer 15

It would decrease blood pressure

Question 16

What would an increase in intracellular fluid do to cells?

Answer 16

Cause the cells to swell

Question 17

What would an decrease in intracellular fluid do to cells?

Answer 17

cause the cells to shrink

Question 18

What does osmolarity mean?

Answer 18

The total number of solute molecules in a solution

Question 19

What is normal osmolarity in the ECF and ICF?

Answer 19

Extracellular fluid (including plasma):
- 275-300 mosmol/L

Intracellular fluid:
- 275-300 mosmol/L

Question 20

What osmolarity would a Concentration of 145 mmol/L NaCl have?

Answer 20

Osmolarity:

= 145 mmol/L Na+ + 145 mmol/L Cl-

= 290 mosmol/L

Question 21

What does isosmotic osmolarity mean?

Answer 21

▪ same amount of solute molecules per litre
▪ same osmolarity

Question 22

What does hyposmotic osmolarity mean?

Answer 22

Increase in water (hyper-hydration)
▪ less solute molecules per litre
▪ decrease in ECF/plasma osmolarity

Question 23

What does hyperosmotic osmolarity mean?

Answer 23

Decrease in water (dehydration)
▪ more solute molecules per litre
▪ increase in ECF/plasma osmolarity

Question 24

What would happen if we lost water from the ECF (Hypotonic)

Answer 24

• ECF osmolarity increases
• Water moves from ICF → ECF until the osmolarity of each is balanced
• Loss of water from BOTH ECF and ICF
• Cells shrink

Question 25

What would happen if we gained water to the ECF (Hypotonic)

Answer 25

• Water gain into the ECF
• ECF osmolarity decreases
• Water moves from ECF → ICF until the osmolarity of each is balanced
• Gain of water to BOTH ECF and ICF
• Cells swell

Question 26

What would happen if we lost isosmotic fluid from the ECF? (Water AND salt)

Answer 26

• The osmolarity of the ECF and ICF are the still same
• No NET water movement
• Decrease in ECF volume ONLY

Question 27

What would happen if we gained isosmotic fluid to the ECF? (Water AND salt)

Answer 27

• The osmolarity of the ECF and ICF are still the same
• No NET water movement
• Increase in ECF volume ONLY

Question 28

If you drink 1 L of isosmotic fluid the volume of your
extracellular fluid (ECF) will increase by:
1. 0 L
2. 0.33 L
3. 0.66 L
4. 1 L

Answer 28

4

Question 29

Can plasma be freely filtered in the nephron?

Answer 29

Most substances in plasma are freely-filtered

▪ Exception: large proteins (e.g. albumin)and substances bound to proteins

▪ Water and solutes are filtered at a constant rate at the renal corpuscle (glomerulus)

▪ Creates a plasma-like filtrate of the blood (a lot needs to be reabsorbed

Question 30

Where does the kidney secrete substances and why is this important?

Answer 30

Secretion = Movement of solutes from the peritubular
capillaries (blood) into the tubular fluid (nephron)

Occurs in the Proximal convoluted tubules

Removes additional substances that weren’t originally filtered (waste products) from the blood by secreting them into the tubular fluid so they are excreted in the urine
▪ E.g. metabolites, medications and toxins

Question 31

Why is reabsorption important in the kidneys?

Answer 31

Reabsorption = Movement of solutes from the tubular fluid (nephron) into the peritubular capillaries (blood)

Returns useful substances to the blood so they are NOT excreted in the urine

Question 32

What is absorbed in the PCT’s and how much?

Answer 32

▪ Bulk reabsorption of ions (sodium), water
and nutrients (glucose)

Question 33

What is absorbed in the nephron loop and how much?

Answer 33

▪ Bulk reabsorption of ions (sodium), water

Question 34

What is absorbed in the distal tubule and collecting duct?

Answer 34

▪ Fine-tuning reabsorption of ions (sodium) and water

Question 35

What is the kidneys process for Na+?

Answer 35

▪ Freely filtered

▪ Not secreted

▪ Almost fully reabsorbed: in most parts of the nephron

▪ Small amount excreted in urine

Question 36

What is the kidneys process for Glucose?

Answer 36

▪ Freely filtered

▪ Not secreted

▪ Fully reabsorbed: in the proximal tubule

▪ None excreted in urine

Question 37

What is the kidneys process for medications and toxins eg. PAH (p-aminohippurate)?

Answer 37

▪ Freely filtered

▪ Entirely secreted

▪ Not reabsorbed

▪ ALL in blood is excreted in urine

Question 38

What is the kidneys process for Creatinine and
inulin?

Answer 38

▪ Freely filtered

▪ Not secreted

▪ Not reabsorbed

▪ ALL filtered is excreted in urine

Question 39

Which of the following processes is NOT a function
of the kidney?
1. Gluconeogenesis
2. Secretion of glucose
3. Filtration of blood
4. Secretion of medications

Answer 39

2