Module 3: Renal I

Question 1

What is the primary function of the kidneys?

Answer 1

Homeostatic regulation of water and ion content in the blood.

Question 2

What are the 6 secondary kidney functions?

Answer 2

1. Regulation of ECF and blood pressure
2. Regulation of osmolarity
3. Maintanence of ion balance
4. Regulation of pH
5. Excretion of wastes
6. Production of hormones

Question 3

What is the functional unit of the kidney? What is their distribution in the kidney?

Answer 3

The nephron. 80% are cortical, 20% are juxtamedullary.

Question 4

Starting at the renal artery and finishing in the renal vein, what path would blood flow through the vasculature of the kidney (6)?

Answer 4

1. Renal artery
2. Afferent arterioles
3. Glomerulus (capillaries)
4. Efferent arterioles
5. Peritubular capillaries
6. Renal vein

Question 5

What are the 4 processes of the nephron? Describe the movement.

Answer 5

1. Filtration: blood to lumen
2. Reabsorption: lumen to blood
3. Secretion: blood to lumen
4. Excretion: lumen to outside the body

Question 6

Where does the majority of reabsorption occur?

Answer 6

Proximal tubule.

Question 7

What part of the nephron is responsible for creating dilute urine?

Answer 7

Loop of Henle.

Question 8

The peritubular capillaries reabsorb a large quantity of _____ but not much _____, causing the osmolarity to _____.

Answer 8

Solute, water, drop (become hypoosmotic).

Question 9

What is the formula to determine amount excreted?

Answer 9

Excreted = filtered + secreted - reabsorbed

Question 10

Of the plasma that enters the Bowman’s capsule, how much is actually filtered? What is this amount called? What is its final breakdown?

Answer 10

20%. This is the filtration fraction, and 19% will be reabsorbed while less than 1% will be excreted.

Question 11

What acts as a filtration barrier in the kidney? What three features help it to filter? What additional cell helps influence?

Answer 11

The renal corpuscle.

1. Capillary endothelial cells: fenestrated (allow large amounts of fluid to move through).
2. Basal lamina: ECM.
3. Podocyte end feet: wrap around capillaries forming a barrier.

Mesangial cells can also influence filtration by contracting, changing the surface area.

Question 12

Three pressures govern filtration from the glomerular capillaries to the renal tubules, what are they and how do they influence filtration?

Answer 12

1. Hydrostatic pressure (P_H): favours filtration
2. Colloid osmotic (oncotic) pressure (π): opposes filtration
3. Bowman’s capsule hydrostatic pressure (P_fluid): opposes filtration

Question 13

Glomular filtration rate (GFR)

1. What is it?
2. What is the normal value in L/day?
3. Influenced by what two factors?
4. Regulated by what vessels?

Answer 13

1. The volume of fluid that filters from the glomerular capillaries into the Bowman’s capsules per unit time
2. 180 L/day
3. Influenced by:
   
   1. Filtration pressure
   2. Filtration coefficient
4. Regulated primarily by renal arterioles

Question 14

Renal blood flow depends on _____ which is determined by _____ in both _____ and _____ _____.

Answer 14

Overall resistance, resistance, afferent, efferent arterioles

Question 15

If RBF goes from an arteriole of larger to smaller diameter, what will happen to GFR?

Example: normal AA to constricted EA.

Answer 15

GFR will increase (P_GC increases)

Question 16

If RBF goes from an arteriole of smaller to larger diameter, what will happen to GFR?

Example: normal AA to dilated EA.

Answer 16

GFR will decrease (P_GC decreases)

Question 17

What are the two ways that GFR is autoregulated?

Answer 17

1. Myogenic response of the afferent arterioles (myogenic autoregulation)
   
   • Contraction in response to stretch of the vessel
   • Carried out by stretch activated channels
2. Tubuloglomerular feedback: fluid flow through the tubule portion of the nephron influences GFR
   
   • Macula densa cells: epithelial cells that come into close contact with afferent and efferent arterioles
     
     • Possibly send paracrine signals
     • Increased cilia movement may signal them
   • Granular cells: secrete renin

Question 18

Besides autoregulation, what other two factors influence GFR? Describe them.

Answer 18

1. Sympathetic neurons
   
   • Release NE that acts on a1-adrenergic receptors on AA’s and EA’s, leading to vasoconstriction
   • Only alters when there is a sharp rapid drop.
2. Hormones: believed to act on podocytes (size of slits) or mesangial cells (contraction [SA])
   
   • Angiotensin II: vasoconstrictor
   • Prostaglandins: vasodilators

Question 19

Why do we filter 180 L/day when we only excrete 1% of it? (2)

Answer 19

1. Removes unwanted materials
2. Simplifies regulation and allows it to occur rapidly

Question 20

What are the two types of transport in reabsorption? What are two other reabsorption mechanisms?

Answer 20

1. Transcellular: substances cross the apical and basolateral membranes of the tubule cells to enter into the ECF
2. Paracellular: between cell-to-cell junctions

Other:

1. Passive reabsorption through tight junctions
2. Endocytosis

Question 21

Filtrate in the lumen and ECF is considered _____ when looking at osmolarity.

Answer 21

Isosmotic.

Question 22

What two methods actively transport Na+?

Answer 22

1. Na-K ATPase
2. Secondary active transport (symport) using an organic molecule or ion

Question 23

Define saturation.

Answer 23

The maximum rate of transport that occurs when all available membrane carriers in the nephron are occupied.

Question 24

Define transport maximum.

Answer 24

The transport rate at saturation.

Question 25

Define renal threshold. When does it occur?

Answer 25

The plasma concentration of a solute when it first begins to appear in the urine. It occurs at the transport maximum.

Question 26

Peritubular capillaries favor (secretion/reabsorption).

Answer 26

Reabsorption.

Question 27

Secretion

1. Movement from:
2. Depends mainly on:
3. Passive/active
4. Why do we need secretion?

Answer 27

1. ECF into lumen of nephron
2. Membrane transport proteins
3. Active
4. We need secretion for:
   
   1. Homeostatic regulation
   2. Removal of organic compounds

Question 28

During secretion, how do we remove organic compounds? What is this mechanism?

Answer 28

We use organic anion transporters. This is an tertiary active transport process where the OAT uses energy from transporting dicarboxylates down its concentration gradient while moving organic anions against its concentration gradient.

Question 29

What does secretion do to the excretion of a substance?

Answer 29

It enhances it.

Question 30

What can excretion tell us? What can it not tell us?

Answer 30

It can tell us what the body is eliminating. It cannot tell us the details of renal function.

Question 31

What do we use as a noninvasive way to measure GFR?

Answer 31

Renal clearance.

Question 32

Define clearance. What is its formula?

Answer 32

The rate at which a solute dissapears from the body by excretion or metabolism.

Clearance = excretion rate of X / [X} in plasma

Question 33

Why is inulin good for laboratory testing of GFR? Why is it not good in a clinical setting.

Answer 33

It is the most accurate non-invasive method. It is completely filtered and not absorbed.

It is impractical clinically because inulin would need to be introduced via IV for 24 hours to give results.

Question 34

Why is creatinine a good measure of GFR? What problem does it pose?

Answer 34

Fairly accurate method. Freely filtered, but secreted in small amounts. This causes the GFR to be slightly overestimated.

Question 35

If GFR = clearance, what happens to:

1. Filtered vs excreted
2. Renal handling

Answer 35

1. Filtered = excreted
2. Filtered, not reabsorbed, not secreted

Question 36

If GFR > clearance, what happens to:

1. Filtered vs excreted
2. Renal handling

Answer 36

1. Filtered > excreted
2. Filtration, net reabsorption

Question 37

If GFR < clearance, what happens to:

1. Filtered vs excreted
2. Renal handling

Answer 37

1. Filtered < excreted
2. Filtration, net secretion