Lecture 13: Renal Physiology (Pierce)

Question 1

What is the role of glomerular endothelial glycocalyx?

Answer 1

Forms a sticky substance that plays a role in filtration

-prevents more anions from being filtrated

Question 2

What happens if the glomerular barrier is damaged?

Answer 2

Proteins can be filtered and be found in the urine

-proteinuria

Question 3

What passes the filtration barrier?

Answer 3

Water

Small solutes: glucose, amino acids, electrolytes

Question 4

How is urinary excretion measured?

Answer 4

Urinary excretion = Amount filtered - Amount reabsorbed + Amount secreted

Question 5

How is tubular reabsorption measured?

Answer 5

Tubular reabsorption = Glomerular filtration - urinary excretion + amount secreted

Question 6

How is arterial input calculated?

Answer 6

Arterial input = venous output + urine output

Question 7

What is the formula for urine excretion rate?

Answer 7

Urine excretion rate = [Urinary concentration] x [Urinary flow rate]

x = Ux x V

Question 8

What is renal clearance?

Answer 8

Flow rate at which substances are removed from plasma by the kidneys per unit of time

Question 9

How is renal clearance/GFR calculated?

Answer 9

Clearance = {[Urinary concentration] x [Urinary flow rate]} / [Plasma concentration]

Question 10

How is filtration rate calculated?

Answer 10

FF = GFR/RPF

Question 11

What is the normal filtration fraction of RPF?

Answer 11

20%

Question 12

What is average GFR?

Answer 12

125 mL/min

Question 13

As filtration fraction increases, why does oncotic pressure increase?

Answer 13

As more ions and substances are being filtered, the concentration of proteins in capillaries is increased

Question 14

What substances have the same filtration and excretion rate?

Answer 14

Inulin (better choice)
Creatinine phosphate

*Both do not have tubular reabsorption

Question 15

How does the sympathetic nervous system affect the arterial resistance vessels?

Answer 15

Target: α-1 adrenoceptors

-powerful vasoconstriction (more on afferent arteriole)

Question 16

How does the sympathetic nervous system affect the juxtaglomerular granular cells?

Answer 16

Target: β-1 adrenoceptors

• renin release
• RAAS system

Question 17

How does the sympathetic nervous system affect the tubular epithelial cells?

Answer 17

Target: α-1 adrenoceptors

• activates Na+/K+ ATPase
• increases sodium reabsorption

Question 18

What are the three physical factors that contribute to GFR?

Answer 18

1) Hydraulic conductivity: permeability of fenestrated endothelium (Lp)
2) Surface area for filtration (Sf)
3) Capillary ultrafiltration pressure (Puf)

GFR = Ultrafiltration coefficient x Capillary ultrafiltration pressure

Question 19

How is ultrafiltration pressure calculated?

Answer 19

Puf = Pgc - Pbc - πgf

Question 20

What affects ultrafiltration coefficient?

Answer 20

Hydraulic conductivity
Surface area - glomerular mesangial cells have contractile properties that can change SA

Kf = Hydraulic conductivity x Surface Area

Question 21

How does constriction affect the afferent arteriole?

Answer 21

Reduces capillary ultrafiltration pressure

GFR decreases

Question 22

How does dilation affect the afferent arteriole?

Answer 22

Increases capillary ultrafiltration pressure

GFR increases

Question 23

How does constriction affect the efferent arteriole?

Answer 23

Pressure increases within capillary –> GFR increases

Question 24

How does dilation affect the efferent arteriole?

Answer 24

Blood can escape glomerulus –> GFR decreases

Question 25

What are some substances that can promote vasoconstriction?

Answer 25

Sympathetics: catecholamines
Endothelin
ATP/adenosine
Angiotensin II

Question 26

What are some substances that can promote vasodilation?

Answer 26

Prostaglandins
Bradykinin
Nitric Oxide
Dopamine
ANP
ACE-inhibitor

Question 27

What happens to glomerular tubular balance when GFR rises?

Answer 27

1) Increase in PTC oncotic pressure

2) Increased sodium reabsorption (and other substances)

Question 28

Describe the myogenic feedback reflex.

Answer 28

Response to changes in blood pressure

-Increased blood pressure will cause afferent arteriolar constriction and efferent arteriolar dilation

Question 29

Describe the tubuloglomerular feedback.

Answer 29

Links the rate of glomerular filtration to the concentration of salt in the tubule fluid at the macula densa.

• high NaCl concentration rate and reabsorption rate –> contraction of the afferent arteriole
• maintains constant sodium delivery in DCT and constant GFR

Question 30

Describe macula densa signaling.

Answer 30

Increased delivery of NaCl will increase ATP production and promote vasoconstriction, lowering GFR

Question 31

How does angiotensin affect kidneys?

Answer 31

Efferent arteriolar vasoconstriction

• Renal blood flow decreases
• GFR increases
• Increased peritubular oncotic pressure