Renal L2: from blood plasma to urine (Reabsorption and secretion)

Question 1

_____% of plasma entering kidneys is filtered

Answer 1

20%

Question 2

_____ml of filtrate/min; ____ L/day; Average plasma volume = _____ L

Answer 2

125; 180; 2.75

Question 3

Plasma is filtered __ times per day!

Answer 3

65

Question 4

Without reabsorption total plasma volume lost in ____min!!!!

Answer 4

30

Question 5

What is reabsorption? Why is it important?

Answer 5

selective movement of substances from tubules back into blood

Filtrate (same contents as plasma without protein) contains substances we want to keep (eg. Water, electrolytes & nutrients)

Question 6

Reabsorbed substances travel back into the ____system via _____ capillaries

Answer 6

venous; peritubular

Question 7

Out of the 180 L/day plasma filtered, ____ L/day is reabsorbed! Why produce excessive filtrate and then reabsorb most of it?!

Answer 7

178.5 allows control; can get various toxics, drugs into filtrate–> doesn’t always have a specific receptor

Question 8

Which tubule is where most of the filtrate is reabsorbed? What is specifically reabsorbed in this tubule?

Answer 8

Proximal tubule (60-70%)

Approx. all organic nutrients (glucose & amino acids) –60-70% Na+& Cl-+ other ions –60-70% water

Question 9

What is reabsorbed in the Loop of Henle?

Answer 9

25% water and Na+reabsorption very specific role (abililty to be [urine]- dilute or concentrated)

Question 10

What is reabsorbed in the distal tubule and collecting duct?

Answer 10

Hormonally controlled reabsorption of water and Na+ important for maintaining blood volume

Question 11

How does reabsorption occur?

Answer 11

Molecules must move from the tubule lumen to the interstitial fluid & capillaries

1. Transepithelial transport (1)
2. Paracellular pathway (2)

Question 12

What is the Transepithelial transport?

Answer 12

More common; through cell

Question 13

What is the Paracellular pathway?

Answer 13

between the cells (2)

Question 14

Movement can be _____ and ______.

Answer 14

Passive; Active

Question 15

What does passive movement mean?

Answer 15

No steps require ATP

Question 16

What does active movement mean?

Answer 16

at least one step requires ATP`

Question 17

What are the 5 barriers that must be crossed during transepithelial transport?

Answer 17

1. Na+is reabsorbed by active transport to produce concentration & electrical gradients
2. Movement of Na+produces an electrical gradient that favours the movement of anions into the ECF (eg. Cl-) (-ve ions pass passively into ECF)
3. Movement of Na+and anions increasesthe solute concentration in the ECF and water follows via osmosis
4. Movement of water into the ECF concentratesthe remaining solutes in the lumen allowing passive diffusion of solutes into the ECF (eg. Urea) (NA+ re-absorption is important for initiating the process)

Question 18

Filtrate entering the tubular system has the same solute concentration as the extra-cellular fluid. A _____ must be produced to allow reabsorption

Answer 18

gradient

Question 19

Nearly all _______ is reabsorbed from the filtrate. It is reabsorbed along the length of the tubule and plays different roles at each site

Answer 19

Na+

Question 20

What is the role of the proximal tubule?

Answer 20

Aids reabsorption of glucose, amino acids, water, Cl-and urea

Question 21

What is the % reabsorbed in the proximal tubule?

Answer 21

67%

Question 22

What is the role of the Loop of Henle?

Answer 22

Allows productionof urine of varying concentrations

Question 23

What is the % reabsorbed in the Loop of Henle?

Answer 23

25%

Question 24

What is the role of the distal tubule?

Answer 24

Regulates ECF volume; blood volume hormonally controlled

Question 25

What is the % reabsorbed in the distal tubule?

Answer 25

8%

Question 26

What is the process of reabsorption in terms of Na+?

Answer 26

* Na+transport across the basolateral membrane is active (Na+-K+pump) and produces a Na+concentration gradient(low in cell, high in the interstitial fluid) 2) * Transport across the luminal membrane is passive and down the concentration gradient

Question 27

How does Na+ concentration gradient aid the reabsorption of other essential molecules (eg. glucose)? What does each of the steps require in terms of active or passive diffusion?

Answer 27

1. Secondary active transport 2. Facilitated diffusion 3. Primary active transport

Question 28

Actively reabsorbed molecules have a transport \_\_\_\_\_

Answer 28

maximum

Question 29

Membrane carriers have specificity. What does that mean?

Answer 29

only carry designated molecules

Question 30

There are a limited number of carriers in the tubular cell membranes. What does that mean if there is an excess of molecules?

Answer 30

If the number of molecules in the filtrate exceeds the available carriers, some molecules will not be reabsorbed….

Question 31

What is the transport maximum (Tm)? What does this mean?

Answer 31

Transport maximum (Tm) = transport rate when carriers are saturated no longer transportation is available

Question 32

What is the renal threshold?

Answer 32

Renal threshold = plasma concentration at which Tm is reached and molecule (eg. Glucose) first appears in the urine

Question 33

Why are some substances secreted form the plasma into the filtrate?

Answer 33

use for substances that that are too high in conc. Reduce their concentration in the blood

Question 34

What are 3 commonly secreted substances?

Answer 34

1. K+ –Organic ions 2. H+(hydrogen ion) 3. HCO3-(bicarbonate)

Question 35

Why is K+ secreted?

Answer 35

maintain ECF concentration (use for neurons and muscles )

Question 36

Normally, K+concentration is ____ (high/low) in the ECF. Why?

Answer 36

low membrane excitability (as it usually "inhibits" repolarises)

Question 37

Normally, quite a ___ (hight/low) [Na+] in ICF ____ (high/low) [Cl] in ICF

Answer 37

high; low

Question 38

K+secretion comes from the _____ and \_\_\_\_\_\_. They are _____ controlled (eg. Aldosterone)

Answer 38

distal tubule; collecting duct; Hormonally

Question 39

How is K+ secreted?

Answer 39

Na+/K+ pump

Question 40

Where is the Na+/K+ pump found?

Answer 40

basolateral membrane- to regulate Na+ and K+

Question 41

What are 4 characteristics of organic ions?

Answer 41

1. Bodily derived ions * Prostaglandins and epinephrine 2. Xenobiotics= molecules foreign to the body * Eg. Drugs 3. Secretion occurs in the proximal tubule * Organic anion transporters * Organic cationtransporters 4. Transporters are non-selective * Transport many substances based on chemical structure * Different drugs competitively bind same transporter * slower rate of excretion from body