Component of plasma, glomerular filtrate and urine: between the plasma + glomerular filtrate and the urine where is there the most of chloride? glucose? urea? uric acid?
-more in the urine than the plasma+glomerular filtrate
-no glucose in urine
-lots of urea in urine
-lots of uric acid in urine
Component of plasma, glomerular filtrate and urine: What are the four basic steps in urine formation?
1) filtration
2) reabsorption (solutes, water)
3) secretion (additional wastes)
4) excretion
Functions of proximal convoluted tubule (PCT): what are the five functions of the PCT?
1. reabsorption of organic nutrients
2. active reabsorption of ions
3. reabsorption of water
4. passive reabsorption of ions
5. secretion
Tubular absorption or reabsorption in PCT: What type of cells are in the PCT? Where? and and what does this mean?
-polarized epithelial cells
-apical and basolateral membrane -have two membranes that are different
Tubular absorption or reabsorption in PCT: what is the apical membrane looking at? where is the basolateral membrane and closer to what??
-looking at lumen, inside of the cell
-is on the outside of the cell, closer to the capillaries
Tubular absorption or reabsorption in PCT: what does tubular reabsorption do?
-removes useful solutes form the filtrate, returns them to the blood
Tubular reabsorption: what are the two types of transport?
-paracellular reabsorption
-transcellular reabsorption
Tubular reabsorption: what kind of process is paracellular reabsorption? and where does it occur and through what?
-a passive process that occurs between adjacent tubule cells through tight junctions
Tubular reabsorption: what is transcellular reabsorption? what is it mediated by? what type of process is it?
-movement through an individual cell
-it is mediated by channels transporters, or pumps
-it can be active, passive or facilitated
PCT reabsorption: what is a characteristic of the PCT section of the tubule? How are most solutes transported?
-PCT is the most active section of the tubule for reabsorption
-transport of most solutes is facilitated by the Na+ concentration gradient established by the sodium pump
where does secretion of H+ also occur?
-in the PCT
PCT reabsorption: What happens when glucose is filtered?
-all of it goes back to the blood (none in the pee)
PCT reabsorption: what is in the interstitial tissue that goes back to the blood when filtered?
-H2O
-amino acids
-glucose
-Na+
-Cl-
-potassium
-calcium
-bicarbonate
-phosphate
-urea
PCT reabsorption: what is in the PCT lumen that does not go back to the blood when filtered?
H+ and some drugs
Active transport in the PCT: what does active transport need?
-it needs ATP and carrier proteins
Active transport in the PCT: explain the process from the PCT lumen to the blood
-PCT lumen (amino acids, glucose, Na+)
-transport
-PCT cell
-ATP
-interstitial tissue (amino acids, glucose, Na+)
-reabsorption
-blood
Diffusion in the PCT: explain the process from the PCT lumen to the blood
-PCT lumen: filtrate (compounds in high concentration)
-PCT cell
-diffusion
-interstitial tissue
-blood (compounds in low concentration)
Diffusion in the PCT: what will happen to chloride? and why does this happen?
-chloride will follow sodium (accumulation of positive charges draws Cl- out)
Diffusion in the PCT: how does diffusion progress (concentration)?
-high to low concentration
Water reabsorption in PCT: what are two processes?
-osmosis (passive absorption)
-passive diffusion
Water reabsorption in PCT: where will water go in osmosis and when? what does this result in?
-water will move into the peritubular capillaries following reabsorption of solutes
-obligatory water reabsorption
Water reabsorption in PCT: where does water go in passive diffusion and how?
-into peritubular capillaries by cellular or paracellular diffusion
PCT basolateral membrane: in Na+, what is expressed here?
-expression of the Na+ pump
PCT basolateral membrane: what is the most abundant cation in the filtrate in expression of the Na+ pump? what does the pump use and for what? what happens to intracellular Na+? what does this pump ensure?
-Na+ is the most abundant cation in the filtrate
-pump uses ATP (energy)
-decreases intracellular Na+
-ensures one-way process form apical to basolateral membrane
-
-
PCT basolateral membrane: what does the Na+/K+ ATPase create? and what does that do?
-creates the gradient and creating one way process
PCT apical membrane: what happens to transport of solute in expression of Na_ transporters? and what is involved?
-transport of solute is coupled to Na+ transport
-symporter
-antiporter
PCT apical membrane: What happens to transport of solute in expression of channels?
-transport of solute is not coupled to Na+ transport
PCT apical membrane: what does obligatory water reabsorption follow?
-obligatory water reabsorption following osmotic gradient
What is needed for glucose reabsorption in PCT: what percent of glucose is reabsorbed in PCT?
100%
What is needed for glucose reabsorption in PCT: what do we need for reabsorption?
-Na+ glucose symporter
-Na+/K+ ATPase
What is needed for glucose reabsorption in PCT: where is the Na+ glucose symporter? where is the Na+/K+ ATPase?
-in apical membrane
-in basolateral membrane
Glucose reabsorption in PCT: what does the symporter do?
-transport of Na+ and glucose into the cell
Glucose reabsorption in PCT: how is Na+ transported? and where and by what?
-Na+ is actively transported out of PCT cells by Na+/K+ ATPase
Glucose reabsorption in PCT: where does glucose diffuse? what kind of diffusion? where? and how?
-glucose diffuses into the interstitium via facilitated diffusion using the glucose transporter
Glucosuria: what is glycosuria? and what is this a result of?
-when some glucose remains in the urine
-diabetes mellitus
-mutations in symporter
Glucosuria: what is diabetes mellitus? what happens tot eh symporter?
-high blood glucose
-symporter cannot work fast enough to reabsorb all the glucose
Glucosuria: when do we see mutations in symporter? name an example. what happens in this?
-rare genetic mutations
-familial renal glucosuria
-glucose in urine is high even though blood glucose level is normal
Glucosuria: what happens in familial renal glucosuria?
-glucose in urine is high even though blood glucose level is normal
Glucosuria: What is an example of a disorder when there are mutations in the symporter?
-familial renal glucosuria
Bicarbonate reabsorption in PCT: what is bicarbonate important for? how is bicarbonate reabsorbed? what does reabsorption depend on?
-is important to maintain acid base balance
-bicarbonate is not directly reabsorbed (in two steps)
-reabsorption depends on the enzyme carbonic anhydrase
Bicarbonate reabsorption in PCT: what happens in step 1?
-formation of carbonic acid (H2CO3) in the tubule
-formation of CO2
Bicarbonate reabsorption in PCT: what happens in step 2?
-formation of bicarbonate (HCO3-) in PTC cells
-diffusion of bicarbonate into blood vessels
What is needed for bicarbonate reabsorption: what will you have in the basolateral membrane? what will you have in the apical membrane?
-bicarbonate transporter and Na+/K+ ATPase pump
-Na+/H+ exchanger or antiporter
What is needed for bicarbonate reabsorption: what are the three things you need for bicarbonate reabsorption?
-bicarbonate transporter
-Na+/K+ ATPase pump
-Na+/H+ exchanger or antiporter
What is needed for bicarbonate reabsorption: what is not in the apical membrane?
-there is not a transporter for bicarbonate in the apical membrane
Step 1: Bicarbonate reabsorption: what happens in step 1?
-formation of carbonic acid
-formation of carbon dioxide (CO2)
Step 1: Bicarbonate reabsorption: how is carbonic acid formed?
-H+ secretion into the tubule lumen by Na+/H+ antiporter
-HCO3- in the filtrate reacts with H+ to form H2CO3
-luminal carbonic acid anhydrase (CA)
Step 1: Bicarbonate reabsorption: how is CO2 formed? where does it diffuse?
-dissociation of H2CO3
-CO2 diffuses into the PCT
Step 1: Bicarbonate reabsorption: in cells, where does CO2 also come from?
metabolism
Step 2: Bicarbonate reabsorption: what happens in step 2?
-formation of HCO3- in PTC cells
-bicarbonate diffusion
Step 2: Bicarbonate reabsorption: in formation of HCO3- in PTC cells, what happens to CO2? what happens to H2CO3?
-hydration of CO2 --> carbonic anhydrase (enzyme)
-hydrolysis of H2CO3 forms HCO3- --> H+ production
Step 2: Bicarbonate reabsorption: in bicarbonate diffusion, what happens to HCO3-? where does it go? what happens to Na+ and how?
-HCO3- leaves the cells by facilitated transport
-diffuses into the capillaries
-Na+ is transported out of the cells by the Na+/K+ ATPse
Step 2: Bicarbonate reabsorption: how many HCO3- are absorbed for every secreted H+? and what kind of process is it?
-one HCO3- is absorbed for every secreted H+
-it is an active process
Passive reabsorption of Ions, cations, and urea in PCT: when does this happen? and the process?
-happens in the second half of the PCT
- aa --> NH3+ --> urea in liver
Passive reabsorption of Ions, cations, and urea in PCT: where is Cl- in high concentration? so where happens to Cl- and what does this cause? what does this promote?
-Cl- is in high concentration sin filtrate
-Cl- diffuses: interstitial fluid becomes more negative
-promotes diffusion of cations
Passive reabsorption of Ions, cations, and urea in PCT: what is formed and for what? what does this result in?
-formation of electrochemical and osmotic gradients for Cl-, K+, Ca2+, Mg2+ and urea
-passive diffusion in to capillaires
Passive reabsorption of Ions, cations, and urea in PCT: what does creation of osmotic gradient promote?
-promotes reabsorption of water