Tubular Reabsorption and Secretion Flashcards Preview

Physiology Renal ABS 2018 > Tubular Reabsorption and Secretion > Flashcards

Flashcards in Tubular Reabsorption and Secretion Deck (75):

What are the 2 options for substances entering the nephron?

1. Reabsorption- MAJORITY of the time (~178 L/day)
2. Secreted


Does Filtration have regulation? Reabsorption?

1. Filtration= NO
2. Reabsorption= Yes


What 3 parts of the nephron function to do reabsorption? How much?

1.Proximal tubule-60 %
2. Loop of Henle - a small amount
3. Distal tubule- everything else- also where we have most of our regulation of reabsorption


What 11 substances are reabsorbed by the proximal tubule?

1. Na+
2. Cl-
6. HCO3-
7. Glucose
8. Amino Acids
9. Vitamins
10. Urea
11. Choline


What 6 things are reabsorbed from the Loop of Henle? What does this contribute to?

1. Na+
2. Cl-
3. K+
4. Mg 2+
5. Ca2+
6. NH4+
b. Helps establish the concentration gradient


Why is reabsorption in the distal tubule so significant? What 6 substances are regulated?

1. This is where we have our highly regulated substances
a. H2O
b. Ca2+
c. Na+
d. Cl-
e. H+
f. K+


How many ways can reabsorption happen?Names?

2 ways
1. Transcellular pathway- 2ary active transport) goes through the cell and also crosses 2 membranes (Apical + Basolateral membranes)
2. Paracellular pathway- substances can go between tight junctions without going through cells.


Process/ Passageway for reabsoption.

1. Substance must cross 2 membranes and one cell.
2. They require transporters and a long process


What is facilitated diffusion?

1.Use of an integrated membrane protein
2.No energy is used- diffusion goes from high concentration to low concentration.
3. Protein can be a channel or a carrier


What does secondary active transport rely on?

1. A sodium gradient
2. Active transporter that uses ATP to being a substance out of a cell.


What 2 types of transporters do Na use?

1. Cotransporters
2. Countertransporters


Explain the process of secondary active transport.

Na will always move down its concentration gradient by going from ECF to ICT. The Na will help another substance move against its concentration gradient either as a co transporter or a countertransporter


What transporters are located on the apical membrane? Its role?

1.Na/Glucuse transporter (co transporter)
2. Allows Na and G from the tubular fluid to enter the cell...


Explain the process to reabsorb Na from tubular lumen to the bloodstream.

1.First, we have secondary active transport - Na/K ATPase at the Basolateral membrane. This will pump Na out of the cell-- into the peritubular fluid, and K will enter the cell. 2. This will create a concentration gradient
3. Then we go to the apical membrane where we have Na/Glucose co transporters. These will allow Na to be absorbed from the tubular lumen and into the cell... glucose is pulled along with it.
4. Once Na is in the cell, it goes to the basolateral membrane-- gets pumped out into the peritubular fluid and eventually through the capillary endothelial cell to enter the blood.
5. Glucose will leave the cell also on the basolateral side via GLUT2 transporters-- and will pull glucose DOWN its concentration gradient into the ISF and finally can enter the blood stream.


Why can't the NA/K ATPase pump be on the apical membrane vs only on the basolateral membrane?

Na from the tubular fluid will be pumped in and back out of the apical end--


What is important to note about transporters and electrolytes

Where we place our transporters can determine where out electrolytes end up.


What is the relationship for glucose pertaining to amount of glucose and filtration ?

The more glucose, the more filtration we have.


How much glucose is usually reabsorbed when filtered?

100 %


What is Tmax?

The highest rate at which our transporters can transport molecules - they reach saturation at this point.


What happens to whatever is filtered and not reabsorbed when transporters reach Tmax?

It gets excreted in the urine.


When do we see glucose in urine?

1. Diabetes
People with high glucose levels
They filter all the glucose they can and when they reach as much glucose as possible, the portions not reabsorbed are EXCRETED.


What is the Tmax of glucose?

320 mg/min


For glucose, what happens between Filtration vs. Tmax when:
a. Filtration is BELOW Tmax
b. Filtration = Tmax
c. Filtration is ABOVE Tmax

a. Reabsorption, no glucose excretion
b. Reabsorption, no glucose excretion
c. Reabsorption, glucose excretion


What is Splay?

Refers to the idea that there is variability in the body(heterogeneity of our nephrons
We have 2 types
1. Cortical- shorter nephrons- shorter proximal tubules- less transporters- hit Tmax earlier- will see glucose in the urine earlier than 320 mg/min
2. Juxtamedullary- longer nephrons - longer proximal tubules- more transporters-


What kinds of substances do we secrete?

OPPOSITE DIRECTION of Reabsorption- essentially the same process
Metabolic waster products (urea, uric acid,)
Bioactive products (hormones)


What helps reabsorption in the proximal and distal tubules of a nephron?How?

1. microvilli-- important for increased surface area for reabsorption


What are 8 organic substances we reabsorb?


2. amino acids
3. acetate
4.krebs cycle intermediates
5.water soluble vitamins
8.many others


What are the 4 main proceseses for transporters?

1. Secondary active transport
2. have a Tmax- usually way over what is normally filtered
3. SPECIFICITY- only substances with transporters can be freely filtered (stereospecifity)
4. can be INHIBITED by drugs and disease


How much is reabsorbed at the proximal tubule?

100 %-- anything else will be excreted because there are no more transporters outside the proximal tubule


What is a filtered load?

FL= GFR x Plasma concentration


What percent of Na filtered is reabsorbed? where? how much is excreted?

95 % of Na that is filtered is reabsorbed
65-75% - in the P.T
15-20% - in LoH
5% - in DT
only 5% on Na will be in the urine


What transporters are located at the Proximal convoluted tubule of the apical membrane?

1. Na/Glucose
2. Na-/ Amino Acids
3. Na/ Other Solutes (Lactate, PO4-)
4. Na/H (only counter-transporter /anti-porter- important for HCO3- reabsorprtion)


In order to reabsorb Na, what substances also need to be moved? Why?

Negative ions must be moved as well. Because you cannot separate charge- will create a electrical gradient- which is not what we want. So we must move an negative charge when moving positively charged Na.


What is the major anion on our plasma?

Chloride (Cl-)


How does Cl- get into the blood?

It will be dragged along with Na and other substances because of the electrical gradient.
It will pass through TIGHT JUNCTIONS- using the PARACELLULAR pathway.
Therefore, does have transporters to travel through.

*Cl follows Na!


Why don't Na levels in Tubular Fluid /Plasma decrease?

We reabsorb a lot of Na-- but we have to remember that water follows Na. This only DECREASES the MASS of Na, but the CONCENTRATION remains the SAME!


Why do we see an increase in TF/P ration for Chloride?

It mirrors Na because it takes the electrical gradient. It will enter the cell via tight junctions-- using the paracellular pathway.


What do you know about Inulin? Why are Inulin TF/P ratio levels high?

1. Inulin comes from sugar. It is NOT ENDOGENOUS (not made in the body). -- no transporters for it...
2. Inulin is freely filtered.
3. Does not have transporters in the body-- so when it gets to the proximal convoluted tubule, it does NOTHING-- it REMAINS in the tubular fluid! -
4. The mass of inulin doesn't change- but the concentration increases because H2O leaves every time Na is reabsorbed in the Proximal tubule.


Explain the difference in substances for Mass vs. Concentration.

1. Na - mass decreases in the TF because it gets reabsorbed- BUT concentration remains the same because H2O moves with Na.
2. Inulin- the mass of inulin in the TF does not change, but the concentration increases because H2O leaves with Na during reabsorption in the Proximal Tubule.


What are the 2 segments of the loop of Henle? Permeabiliy?

1. Descending limb: permeable to H2O, impermeable to solutes- NO Reablsorption here
2. Ascending limb: permeable to solutes- REABSORPTION here, impermeable to H2O

Think about concentration levels in different areas of the loop of Henle-- if in Descending limb- as you go down, the concentration increases because this makes sense because you have water being able to leave---
On the other hand, in the ascending limb-- H2O is imperemable-- which allows the tube to be less concentrated as you go up the loop of Henle. Only solutes can leave.


What transporter do we have on the apical membrane of the Ascending Loop of Henle? What ions does it move? Up or down gradient?

It moves 4 ions
1. 1 Na, 2 Cl, 1 K
Na goes down its gradient
2 Cl move down its gradient
K moves up its gradient
-they all move into the cell


Explain the EASY process for Reabsorption in the DCT for principal cells?

1. Na/K ATPase pump- moves 3 Na out/2 K in to establish a concentration gradient on the B.L.M
2. on A.M- Na/Cl symporter pulls Na (DOWN concentration gradient) and Cl into the cell.
3. Cl is pulled across from B.LM. to the blood via a Cl channel.


Explain the HARD process for Reabsorption in the DCT for principal cells?



3 aldosterone functions

1. Increases the number of Na/K ATPases on the Basolateral membrane- for a stronger gradient
2. Na channel that the aldosterone opens on the Apical membrane
3. Opens a K channel on the Apical membrane- K flows OUT OF CELL- AKA will get secreted from cell since there is a high concentration inside cell -- and finally it will be excreted in the urine.


What are diuretics? How do they work?

1. A drug that causes you to urinate.
2. This helps lower your blood volume
3. Used in patients with high blood pressure/ hypertension
4. Block/ turn off Na/ Cl transporter. - so you won't rabsorb


What are diuretics? How do they work?

1. A drug that causes you to urinate.
2. This helps lower your blood volume
3. Used in patients with high blood pressure/ hypertension
4. Block/ turn off Na/ Cl transporter at the Apical membrane. - so you won't reabsorb it - it will stay in the urine
5. Blocks Na channel that aldosterone opens on Apical membrane- block Na and H2O reabsorption.


Descending limb and Ascending limb loop of Henles are also known as what type of segments, respectively?

1. Descending Lime: Concentrated Segment
2. Ascending Limb: Diluting segment


What effects K levels inside the cell?

K concentrations are high inside the cell.
1. Insulin- brings K into cells
2. Epinephrine
3. Aldosterone
Has a role in acid base balance.


What happens when you have a normal-high K diet?

1. REABSORPTION in the Proximal Tubule
2. REABSORPTION in the Thick Ascending Limn
3. SECRETION in Distal Tubule + Collecting Duct


What happens when you have a low K diet? (really hard to do)

1. REABSORPTION in the Proximal Tubule
2. REABSORPTION in the Thick Ascending Limn
3. REABSORPTION in Distal Tubule + Collecting Duct


How does K enter the blood in Proximal tubule? in the Thick ascending limb? Distl tubule?

1. Doesn't use the transcellular pathway.
2. Passes through tight junctions- Paracellular pathway
3. In Proximal Tubule: Reabsorbed by Bulk flow - which is when we reabsorb so much stuff in the proximal tubule that K just gets swept away and reabsorbed in P.T. to go back into blood.
4. Apical membrane has Na/Cl/ K pump- K goes against gradient to enter cell - and gets either secreted or reabosrbed
5. When ALDOSTERONE mediated- Aldosterone opens Na channels to allow Na to enter cell and then it will also open K channels so that it allows K to be secreted-- and then excrete K.


How do we control K secretion?

1. Homeostatic control - negative feedback regulation.
2. Aldosterone- K levels will change aldosterone levels


What substances can change aldosterone levels?

1. K levels
2. Blood volume


How does aldosterone affect contractility?

Increased aldosterone levels means you have increased K excretion.
K is important for contractility- for nerve cells, muscle cells, increase or decrease arrhythmias


Explain the mechanism from K intake to K excretion.

1. Increased K intake
2. Increased Plasma concentration
3. Increased aldosterone secretion
4. Increased plasma aldosterone
5. Increased K secretion
6. Increased K excretion


What role does Ca play in our bodies?

1. Muscle contractility (cardiac, smooth and skeletal muscle)
2. Secondary messenger


What 3 organ systems require the use of Ca?

1. GI Tract
2. Kidney
3. Bone


What happens when we lose Ca?

1. Low Calcium levels
2. Parathyroid releases PTH
A. Increase Ca levels - by going to bone and cause reabsorption - by breaking down Ca matrix of bone and taking Ca from there to bring Ca levels up
B. goes to kidney - to increase reabsorption of Ca in the kidneys
C. Increase Ca in GI Tract when Vitamin D is active (done by the kidney)
D. All lead to increased Ca levels in the blood


What happens when we have too much Ca?

1. High Calcium levels
2. Parathyroid releases Calcitonin
A. DECREASE Ca levels - by going to bone and stimulating deposition of Ca into bone -
B. goes to kidney - to REDUCE reabsorption of Ca in the kidneys
C. Stop resorption of Vitamin D from kidney to DECREASE Ca reabsoption in the GI Tract
D. All lead toDECREASED Ca levels in the blood


How much Ca is reabsorbed and in which places? How much is excreted in the urine?

1. 60% -in proximal tubule
2. 10% in Distal tubule
3. 5 % - Collecting duct
4. 5% - excreted in the urine.


Explain the relationship between Calcium and Phosphate in the blood?

Calcium is no longer active in the blood when bound to phosphate


If we want blood Ca levels to rise, what do we want blood Phosphate levels to do ?



How does PTH work? 3 actions.

1. Increase Ca levels by
a. Increasing Ca channels of Apical membrane
b. Increasing Ca ATPases on BLM
2. Decrease PO43- levels
3. This means we will try to reabsorb Ca and secrete PO43-


How much Phosphate is usually secreted, why?

5-20 % - this is important because we do not want Calcium Phosphate to be formed in the blood because this means that Calcium will no longer be active and cannot perform certain functions.


Where are the majority of PTH receptors located?

Distal Convoluted Tubule


Do we know how Ca is reabsorbed in the Proximal Convoluted tubule?

NO - we don't know the transporters


Do we know how Ca is reabsorbed in THICK Ascending limb (LoHenle) ?

1. Yes
2. in the THICK ascending loop of Henle
3. It begins on the APICAL membrane - Calcium channels
Ca levels are usually LOW INSIDE cell.
allows Ca to enter cell when channel opens
Leads to Ca on the BLM where there is a Ca ATPase.
Primary active transport of Ca from inside of cell at BLM into the blood (against concentration gradient)


How is Ca reabsorbed in the Distal Tubule?

*Same exact way as in the Thick ascending limb loop of Henle!!

1. Ca Channel on Apical Membrane
2. BLM has Ca ATPase- useing primary active transport and gets Ca into ISF--> blood


Name 3 actions of ADH.

1. H2O reabsorption
2. Na reabsorption
3. H+ secretion (role in acide base balance)


What 2 places is ADH active in the kidney? Specific actions?

1. Proximal Tubule
a. H2O reabsorption
b. Na reabsorption
c. H+ secretion

2. Distal Tubule/ Collecting Duct
a. H2O reabsorption


Name 3 actions of Aldosterone.

a. H2O reabsorption
b. Na reabsorption
c. K+ secretion


Name the action of ANP. What is ANP? How does it function?

1. Decrease blood pressure/blood volume
2. DECREASE Na/ NaCl Reabsorption
3. Atrial natriuretic peptide/Factor- it comes from the Atrium- secreted in response to stretch. (AKA- high blood volume/BP)
4. It is the only hormone we have that acts in response to increased BP/BV.


What are the actions of PTH?

1. Phosphate secretion
2. Ca reabsoprtion


Where is PTH active?

1. Proximal Tubule
2. Thick Ascending Loop of Henle
3. Distal Tubule


Where is Aldosterone active?

1. Distal Tubule
2. Collecting duct