Renal System Physiology 2 - Teel

Question 1

Renal Blood flow (RBF) ratios in cortex and medulla
RBF = __% cardiac output

Answer 1

90% to cortex, 10% to medulla
20% cardiac output
Changes in renal blood flow and renal plasma flow affect GFR

Question 2

When Ra increases (resistance of afferent arterioles), what happens to renal blood flow?

When Re increases (resistance of efferent arterioles), what happens to renal blood flow?

Answer 2

Ra increasing = afferent arterioles are constricting, causing a decrease in renal blood flow.
GFR then decreases due to decreased PG (pressure from glomerulus)

Re increasing = efferent arterioles constricting, causing buildup of pressure before, which is where glomerulus is. GFR and PG both increase. Renal blood flow still decreases.

Question 3

How to measure Renal Plasma Flow?

Answer 3

PAH is in the blood, gets filtered, it is not reabsorbed, gets secreted, 100% clearance. If this happens then we have an indicator of Renal Plasma Flow.
The clearance PAH is an estimate of renal plasma flow. (responsible for GFR)

Question 4

Tubuloglomerular feedback (TGF)

Answer 4

increase renal arterial pressure = increase RBF = increase GFR = increase of NaCl to macula densa cells

Response: vasoconstriction of afferent arterioles = decrease RBF = decrease GFR = decrease delivery of NaCl to macula densa cells

Question 5

Factors affecting RBF and GFR:
Angiotensin II
Catecholamines
Arginine vasopressin (AVP)
Atrial natriuretic peptide (ANP)

Answer 5

Angiotensin II : decrease RBF and decrease GFR
Catecholamines : decrease RBF and decrease GFR
Arginine vasopressin (AVP) : decrease urine output
Atrial natriuretic peptide (ANP) : increase RBF and increase GFR

Question 6

What is the Glomerulotubular balance concept, and what are some things that stimulate reabsorption?

Answer 6

Glomerulotubular balance concept: reabsorbing a relatively constant fraction of some sort of filtered sodium load.

Aldosterone stimulates reabsorption of Na+ by upregulating ENACs and Na/K exchange
Adrenergic stimulation increases reabsorption of Na+ by upregulating Na/H & Na/K exchange
AVP stimulates reabsorption of Na+ in TAL and principal cells of cortical collecting ducts
ANP increases excretion of Na+ by increasing RPF / GFR which increases Na load delivered to distal tubules.

Question 7

Paracellular Transport
Transcellular Transport

Answer 7

Paracellular: between adjacent tubular cells. Most of reabsorption of Cl here in proximal tubules & cortical collecting ducts
Transcellular: Cl by : Across apical membrane / basolateral membrane.

Question 8

In thick ascending limb (TAL) of hindley’s loop, 1 specific transporter that transports 3 different ions.

Answer 8

Na/K/2Cl all go in same direction. Cotransport, not exchange

Question 9

Renal Handling of Urea and Water

Where is Urea filtered/ reabsorbed and how?

Answer 9

Urea freely filtered at glomerulus. Reabsorbed from inner medullary collecting ducts into medullary interstitium and loops of Henle.

Urea is a solute and water tends to follow it.

Question 10

Renal Handling of Solutes

How is phosphate reabsorbed?

Answer 10

Filtered phosphate is 80% reabsorbed in proximal tubules via cotransport with Na+

Question 11

Difference between cotransport and exchange

Answer 11

Cotransport: same direction
Exchange: opposite direction

Question 12

Renal Handling of Solutes

How is calcium reabsorbed?

Answer 12

more than 1/2 of filtered Ca2+ reabsorbed paracellularly in proximal convoluted tubules.

Reabsorption stimulated by PTH and Vit. D3

Question 13

Renal Handling of Solutes

How is Mg2+ reabsorbed?

Answer 13

About 70% of filtered Mg2+ reabsorbed in TAL. (NOT PROX CONV TUBULE)

Reabsorption is largely unaffected by Vit. D3

Question 14

Which cells reabsorb / secrete K+

Answer 14

a-intercalated cells reabsorb K+.
Principal cells secrete K+

Question 15

Renal Handling of Solutes

How is K+ reabsorbed/filtered?

Answer 15

Reabsorption of filtered K+ is paracellular in proximal tubules.
Cotransport is via Na/K/2Cl in TAL (reabsorption). a-intercalated cells reabsorb K+. Principal cells secrete K+
Freely filtered

Question 16

Hormones that help potassium levels in blood

Answer 16

Insulin, Aldosterone, Epinephrine allow Dietary K+ absorbed from gut into blood.

Question 17

Hypokalemia vs Hyperkalemia

Answer 17

Hypokalemia: not enough potassium in blood
Hyperkalemia: high potassium levels

Question 18

What happens when you increase potassium intake?

Answer 18

Increased K+ intake -> increased plasma K concentration -> increased aldosterone -> increased k secretion cortical collecting tubules -> increased k excretion

Question 19

Renal Handling of Glucose

How is it reabsorbed?
How is it filtered?

Answer 19

Reabsorbed in proximal tubule via apical SGLT1 & 2 and basolaterally via GLUT1 and GLUT2.
Glucose normally 100% reabsorbed.

Freely filtered

Question 20

Filtered load:

Answer 20

Plasma concentration x GFR

Question 21

Renal Handling of Glucose

Relationship between filtered load, reabsorption, excretion

Answer 21

Filtered load = linear. As plasma concentration increases, so does filtered load of glucose.

Reabsorption of glucose: stabilizes due to transporters overloading. Originally increases as plasma conc. and filtered load increases, but will start to stay in blood glucose.

Excretion: Nothing in beginning, but if you have too much glucose, will start to excrete. Glucose in urine now. Normal until around 280 mg/dl

Theres only so much glucose u can reabsorb. Once transporters in proximal tubule become saturated, it starts to appear in your urine.

Question 22

Renal handling of protein, oligopeptides, and AAs

Answer 22

Proximal tubular cells remove filtered protein by endocytosis

Apical membrane H+ oligopeptide cotransporters remove oligopeptides

Proximal tubular cells reabsorb filtered AAs by Na+ dependent / Na+ independent mechanisms.