52 Reabsorption and secretion

Question 1

Myogenic mechanism and macula densa feedback

Answer 1

Renal artery pressure autoregulatory mechanisms

Question 2

Increase in arterial BP leads to increased stretching of blood vessels. This leads to increased intracellular Ca++ levels in the cells of the blood vessels. Ca++ promotes vascular resistance, which inhibits blood flow and GFR

Answer 2

Myogenic feedback

Question 3

Depending on how much sodium is filtered in the glomerulus, the macula densa regulates renin (hormone) release. Renin increases the levels of angiotensin II, which increases the resistance of the efferent arterioles, increasing pressure in the glomerular capillaries and increasing GFR.

Answer 3

Tuboglomerular feedback (macula densa feedback)

Question 4

o In the case of increase in BP, the macula densa decreases the afferent arteriolar resistance, decreasing BP in the glomerulus and decreasing GFR

Answer 4

Tuboglomerular feedback (macula densa feedback)

Question 5

T/F. Both secretion and reabsorption can occur by either of two pathways: paracellular and transcellular

Answer 5

True

Question 6

T/F. Tubular secretion occurs if the filtered load is higher than the excreted load

Answer 6

False. Tubular reabsorption occurs if the filtered load is higher than the excreted load

Question 7

GFRPx - UxV = filtered load (mg/min) - excretion rate (mg/min) = ?

Answer 7

Reabsorption rate (mg/min)

Question 8

Transport maximum (Tm) and gradient time mechanisms

Answer 8

Mechanisms of active reabsorption in the proximal tubule

Question 9

Mainly for Na+ reabsorption. It is always 67% (in a normal person) of the filtered load.  Characteristics of carriers: Low affinity, Not easily saturated, High back leak

Answer 9

Gradient-time mechanisms (active reabsorption)

Question 10

Used for all other reabsorbed solutes (i.e. glucose, amino acids, ketone bodies, calcium, phosphate). Characteristics of carriers: High affinity, Easily saturated, Low back leak

Answer 10

Transport maximum (Tm) mechanism (active reabsorption)

Question 11

All reabsorptive processes have a limit on how fast they can occur, either b/c the substance leaks back into the lumen (___) or b/c the transporters are saturated (___)

Answer 11

gradient-time systems, transport maximum systems

Question 12

The difference in plasma glucose concentration b/t the beginning of excretion and the point of maximum filtration. This difference exists b/c the nephrons are not homogeneous, and some become saturated before others. Therefore, excretion will occur before the known saturation point of the transporters

Answer 12

The splay

Question 13

What happens to the Tm as you lose nephrons?

Answer 13

It decreases b/c you have less ability to reabsorb glucose (or other solutes)

Question 14

T/F. Na+ is always reabsorbed with glucose and amino acids (co-transporter mechanism), as well as with other electrolytes. Na+ travels passively along its concentration gradient.

Answer 14

True. The sodium-potassium ATPase establishes the Na+ concentration gradient responsible for this diffusion

Question 15

We always reabsorb equal amounts of Na+ and water in the PT of the kidneys

Answer 15

Isosmotic reabsorption

Question 16

T/F. Sodium reabsorption leads to passive Cl- reabsorption and water reabsorption in the collecting ducts

Answer 16

Fasle. Sodium reabsorption leads to passive Cl-, urea, and water reabsorption in the PT

Question 17

___ occurs if the filtered load is lower than the excreted load

Answer 17

Tubular secretion

Question 18

Clearance of ___ is the marker for eRPF (b/c it is freely filtered and secreted)

Answer 18

PAH

Question 19

Excretion rate (mg/min) – Filtered rate (mg/min) = UXV – GFRPx = ?

Answer 19

Secretion rate (mg/min)

Question 20

ClearancePAH = Urine PAH concentration * flow/(plasma PAH concentration) = UPAH*((V)/(Ppah)) = ?

Answer 20

eRPF (effective renal plasma flow)

Question 21

1) Glomerulotubular balance (Peritubular physical forces)
2) Hormones
3) Sympathetic NS
4) Arterial pressure (pressure natriuresis)
5) Osmotic factors

Answer 21

Mechanisms of regulation of tubular reabsorption

Question 22

Simply means that as filter load increases, reabsorption increases. Regulated by peritubular physical forces (Kf, oncotic pressure of the capillaries, hydrostatic pressure of capillaries)

Answer 22

Glomerotubular balance

Question 23

T/F. In the sympathetic response, the GFR/RPF ratio increases b/c RPF decreases much more than GFR

Answer 23

True

Question 24

T/F. Increased oncotic pressure of peritubular capillaries decreases reabsorption in peritubular capillaries

Answer 24

False. Decreased oncotic pressure (as well as Kf) leads to decreased reabsorption

Question 25

T/F. Increased hydrostatic pressure of the peritubular capillaries decreases reabsorption

Answer 25

True. This is the same as increasing arterial pressure

Question 26

Preferentially constricts the afferent arteriole, decreasing RPF more than GFR, thus increasing the FF, which increases π in the peritubular capillaries and increases reabsorption.
It also directly and indirectly promotes reabsorption of Na+

Answer 26

Sympathetic NS

Question 27

increase in arterial pressure leads to decrease in Na+ reabsorption

Answer 27

Arterial pressure (pressure natiuresis)

Question 28

T/F. Water is reabsorbed only by osmosis. Thus, decreasing the amount of unreabsorbed solutes in the tubules decreases water reabsorption (and increases excretion)

Answer 28

False. Water is reabsorbed only by osmosis. Thus, increasing the amount of unreabsorbed solutes in the tubules decreases water reabsorption (and increases excretion)

Question 29

In this case, plasma glucose concentration is very high. Therefore filtration increases past the saturation point of the reabsorption transporters. At this point, glucose is being excreted, increasing the osmolarity of the urine; which promotes secretion of water and inhibits reabsorption of water

Answer 29

Diabetes mellitus

Question 30

T/F. The major factor controlling what is being reabsorbed is Na+. We always have about the same amount of Na+ being reabsorbed ~67%. Na+ has glucose and amino acid co-transporters. Cl-, bicarbonate, potassium, and water are also reabsorbed w/ Na+

Answer 30

True

Question 31

T/F. H+, organic acids, and bases are all secreted into the proximal tubule (mostly occurs via channels and transporters)

Answer 31

True

Question 32

T/F. Creatinine and urea decrease in TF/P concentration b/c they are being reabsorbed into the proximal tubule

Answer 32

False. Creatinine and urea increase in TF/P concentration b/c they are being secreted into the proximal tubule

Question 33

This portion of the nephron is very permeable to water. The only transport that occurs here is water reabsorption, which leads to increased osmolarity of the filtrate

Answer 33

Descending loop of henle

Question 34

This portion of the nephron is NOT permable to water. Here, reabsorption of Na+, Cl-, K+, Ca++, HCO3-, and Mg++ occurs. Secretion of H+ occurs.

Answer 34

Thick ascending loop of henle

Question 35

T/F. B/c of reabsorption of electrolytes and not water, the filtrate in the thick ascending loop of henle is hypo-osmotic

Answer 35

True

Question 36

T/F. Transport of solutes in the thick ascending loop of Henle is electroneutral

Answer 36

False. Transport of solutes in the thick ascending loop of Henle is electrogenic (generates electrical gradient) b/c of the K+ leak channels

Question 37

This portion of the nephron (electroneutral) Transports Na+ and Cl- into the tubular cells via a co-transporter (Cl- leaks into the renal interstitial fluid). Not permeable to water (aka diluting segment). Contains the macula densa

Answer 37

Early distal tubule. Functionally similar to thick ascending loop. Active reabsorption of Na+, Cl-, Mg++ (and K+, dependent of K+)

Question 38

Permeability to water in these portions of the nephron depends on ADH (if ADH is present, aquaporins are inserted into the tubular cells, rendering them permeable to water)

Answer 38

Early and late distal tubules and collecting tubules

Question 39

These cells reabsorb Na+ and Cl-, and secrete K+ (activated by aldosterone)

Answer 39

Principal cells (of collecting tubules and DT)

Question 40

These cells secrete H+ and reabsorb K+ (via antiporter) depending on the needs of the body

Answer 40

Intercalated cells (of collecting tubules and DT)

Question 41

T/F. Na+ channel (in epithelium) is the major sodium transporter (for reabsorption)

Answer 41

True

Question 42

This portion of the nephron is capable of Na+, Cl- reabsorption. Reabsorbs water (if ADH is present), this concentrates urine. Urea is reabsorbed. Bicarbonate is reabsorbed. H+ is secreted (increasingly in the case of acidosis)

Answer 42

Transport characteristics of medullary collecting ducts

Question 43

What are the only physiological methods of altering GFR?

Answer 43

Constricting or dilating the afferent and/or efferent arterioles

Question 44

The efferent arterioles become the ___ capillaries. These capillaries then become the interlobular veins

Answer 44

Peritubular capillaries