Chapter 19

Question 1

List + describe the 6 functions of the kidneys.

Answer 1

1) regulation of extracellular fluid volume + blood pressure
2) regulation of osmolarity
3) maintenance of ion balance
4) homeostatic regulation of pH
5) excretion of wastes
6) production of hormones

Question 2

Know the anatomic relationship between the vascular + tubular elements of the nephron.

Answer 2

look at whiteboard

Question 3

What are the 3 processes of the nephron.

Answer 3

1) filtration
2) reabsorption
3) secretion

Question 4

Describe filtration.

Answer 4

• fluid from blood into lumen of the nephron
• occurs at renal corpuscle
• filtered plasma (=filtrate) is excreted unless reabsorbed

Question 5

Describe reabsorption.

Answer 5

• materials in the filtrate are passed back into the blood
• occurs with peritubular capillaries

Question 6

Describe secretion.

Answer 6

• materials from blood into lumen of tubule
• occurs with peritubular capillaries

Question 7

What is the equation for the amount of solute excreted?

Answer 7

amount filtered - amount reabsorbed + amount secreted

Question 8

Describe the filtration barriers between the blood and the lumen of the nephron, and explain how they can be modified to control filtration.

Answer 8

1) glomerular capillary endothelium –> fenestrated (have pores)
2) basement membrane
3) epithelium of Bowman’s capsule –> foot processes + filtration slits (podocytes)

Question 9

Describe the pressures that promote and oppose glomerular filtration.

Answer 9

1) capillary blood pressure (PH) –> favors
filtration
- hydrostatic pressure
2) capillary colloid osmotic pressure (π) –>
opposes filtration (pulls fluid back to plasma)
- due to proteins in plasma
3) capsule fluid pressure (P fluid) –> opposes
filtration
- hydrostatic pressure inside Bowman’s
capsule

Question 10

Define glomerular filtration rate, and give average values for GFR.

Answer 10

glomerular filtration rate (GFR) –> volume of fluid filtered per unit time

avg value –> 180 L/day

Question 11

what is filtration fraction?

Answer 11

% renal flow that filters into the tubule

Question 12

What is the net pressure equation for Bowman’s capsule?

Answer 12

P(H) - π - P(fluid) = 10 mmHg into Bowman’s
capsule

Question 13

What is GFR influenced by?

Answer 13

1) net filtration pressure –> renal blood flow & blood pressure
2) filtration coefficient –> slit surface area (of capillaries) & filtration barrier permeability

Question 14

Explain how GFR can be influenced by local and reflex control mechanisms.

Answer 14

1) myogenic response –> intrinsic ability of vascular smooth muscle to respond to pressure change (autoregulation)
2) tubuloglomerular feedback (to right) –> paracrine control
- juxtaglomerular apparatus –> macula densa cells detect NaCl in the filtrate + granular cells secrete renin (enzyme)
3) hormones + autonomic neurons –> by changing resistance in arterioles or by altering the filtration coefficient

Question 15

Increased resistance in the afferent arteriole _________ GFR.

Answer 15

decreases

Question 16

Increased resistance in the efferent arteriole _________ GFR.

Answer 16

increases

Question 17

Decreased resistance in the afferent arteriole _________ GFR.

Answer 17

increases

Question 18

Decreased resistance in the efferent arteriole _________ GFR.

Answer 18

decreases

Question 19

Describe the steps of tubuloglomerular feedback.

Answer 19

1) GFR increases
2) flow thru tubule increases
3) flow past macula densa increases
4) paracrine signal from macula densa to afferent arteriole
5) afferent arteriole constricts
6) resistance in afferent arteriole increases
7) hydrostatic pressure in glomerulus decreases
8) GFR decreases

Question 20

Distinguish between transcellular transport and paracellular pathways.

Answer 20

transcellular transport –> (Transepithelial transport) –> Substances cross apical and basolateral membranes of the tubule epithelial cells

Paracellular pathway –> Substances pass through the cell–cell junction between two adjacent cells

Question 21

Describe and give examples of active and passive reabsorption in the proximal tubule.

Answer 21

Active:
- transport of Na+
- secondary active transport –> symport w/Na+

Passive:
- urea
- endocytosis –> plasma proteins

Question 22

Define saturation.

Answer 22

maximum rate of transport that occurs when all carriers are occupied by (are saturated with) substrate

Question 23

Describe the steps in sodium-linked reabsorption.

Answer 23

1) Na+ moves down its electrochemical gradient using the SGLT protein to pull glucose into the cell against its conc. gradient
2) Glucose diffuses out the basolateral side of the cell using the GLUT protein
3) Na+ is pumped out by Na-K-ATPase

Question 24

Define transport maximum.

Answer 24

the transport rate at saturation

Question 25

Define renal threshold.

Answer 25

the plasma concentration at which a substance first appears in the urine

Question 26

Explain and give examples of the importance of tubular secretion in renal function.

Answer 26

• active movement of molecules from extracellular fluid into nephron lumen –> important in homeostatic regulation of K+ and H+
• increasing secretion increases nephron excretion

Question 27

Explain mathematically and in words the relationship between the excretion of a solute and its renal clearance.

Answer 27

Clearance of X = excretion rate of X (mg/min) / [X]plasma (mg/ml plasma)

*Clearance is a noninvasive way to measure GFR

Question 28

Explain how clearance can be used as an indirect indicator of renal handling of a solute.

Answer 28

clearance –> Rate at which a solute disappears from the body by excretion or by metabolism

Question 29

What is the equation for excretion?

Answer 29

Excretion = filtration – reabsorption + secretion

Question 30

What are the downsides of using insulin and creatinine to measure GFR?

Answer 30

Inulin, plant polysaccharide, freely filters, but is neither reabsorbed or secreted