Renal 2 Tubular Function and Micturition Flashcards
what is the function of the nephron?
3 primary functions: filtering, reabsorbing, secreting.
The glomerulus filters blood. Reabsorption occurs along in the convoluted tubules and Loop of Henle. Secretion occurs in the PCT & DCT, and collecting duct. Anything not reabsorbed (urea) becomes the urine + is secreted through the collecting duct.
what materials are completely reabsorbed from the filtrate?
glucose, amino acids and bicarbonate
what materials within the filtrate are regulated and partially reabsorbed?
water, sodium, potassium, chloride
what materials from waste are excreted as waste?
urea, creatinine, drugs, drug metabolites
which section of the Loop of Henle is water-permeable?
the descending limb; lots of water reabsorption and when we reabsorb substances like Na+, K+, or a.a.’s and glucose, water follows it
which section of the Loop of Henle is impermeable to water?
the thicker ascending limb; ions are still pulled out of the filtrate for reabsorption but water cannot follow it
collecting duct
able to modify water reabsorption in the presence of ADH (reabsorb water, w/o ADH water in filtrate ends up in bladder)
interlobular artery
become afferent arterioles feeding the glomerulus
arcuate artery
become efferent arterioles away from the glomerulus, dives down into glomerulus to form peritubular capillaries
recta vasa
straight vessels that collect the stuff we want back
obligatory water reabsorption
occurs when water is “obliged” to follow the solutes being reabsorbed, as aquaporins are always present in the PCT
facultative water reabsorption
aquaporins are inserted in collecting ducts only if ADH is present
where does most obligatory reabsorption occur?
PCT and descending LOH (tubules permeable to water)
where does most facultative reabsorption occur?
in the collecting duct
osmosis and the PCT
movement of water will always be able, linked to passive reabsorption of a number of ions as well as the waste product urea
- by the end of the PCT most organic solutes have been reabsorbed as well as 65% of the water
passive transport
the movement of substances across a cell membrane without the use of energy by the cell, simple diffusion or facilitated diffusion, or leak channels
passive sodium reabsorption
from high [ ] in fluid to low [ ] in tubule cells; sodium may pass through via paracellullar route and pull water with it to end up in the blood
what type of epithelium is the apical border of the tubular cell?
simple cuboidal epithelium
paracellular route
between epithelial cells of PCT
transcellular route
substances pass through the cytoplasm of the PCT epithelial cells and out their base
primary active transport
active transport that relies directly on the hydrolysis of ATP
secondary active transport
uses energy of the movement of ions down their concentration gradient to transport other solutes (like ions and larger uncharged molecules like glucose or a.a.’s)
symporter
when the secondary active transport protein moves both the ion and the solute in the same direction
antiporter
when the secondary active transport protein moves the ion in one direction and the solute in the opposite direction
what do both active transport mechanisms require?
a carrier protein to assist the movement of ions + other solutes
active sodium reabsorption
across apical membrane:
- leakage channels present allowing sodium to come in due to [ ] gradient
when sodium gets inside we do not want [ ] to continually build up (can’t let it continually come in)
- pumped out with sodium-potassium pump
- keeps [Na+] low in cell which allow use of symporters and leak channels for sodium to bring it back
active glucose reabsorption
- occurs in PCT
- gluc. symporter allows Na+ to go down [ ] gradient and has binding sites for 2 Na+ and 1 glucose
- binding changes conformation and allows Na+ to drag 1 glucose in and goes inside tubular cell
- Na+ needs to be pumped out to prev. build up (and K+ in)
transport is couple w/ Na+/K+ pump and facilitated diffusion
why can’t glucose build up inside the cell?
glucose attracts water, therefore it uses a facilitated diffusion transporter on the basolateral membrane allowing glucose to go down [ ] gradient
- moves from cell to bloodstream, followed by water
Na+/H+ antiporter in the PCT
- Na+ into absorptive cell and H+ out
- movement powered by Na+ [ ] gradient (high in filtrate, low in cell)
- H+ came from dissociation of H2CO3 (metabolically active process)
- antiporter uses sodium to kick out H+ to slowly help correct acidosis
- sodium then kicked out of cell using ATP pump to prev. buildup
- HCO3- being generated inside the apical cell has facilitated diffusion transporter that moves it across its [ ] gradient (low in blood)
- HCO3- disappears w/ Na+ into bloodstream
symport system at thick limb of LOH
- water-impermeable
- Na+-K+-2Cl- symporter is a protein allowing Na+ to walk down [ ] gradient which pulls in the other two solutes
- sodium [ ] fixed w/ ATP pump
- chloride leakage diffusion channel: as Cl- build up in cell, channel allows it to leak back into blood (water does not follow)
- potassium: can leak out from high to low [] back into filtrate and keep symporter running
- K+ leak channels may be present
- more Cl- than Na+ on side, helps drive cation movement across paracellular route (attractive forces)
sodium reabsorption in the collecting duct
- there are Na+ leak channels in the collecting duct
- Na+ [ ] regulated w/ ATP pump
- potassium may sometimes build up in blood (can be allowed to leak out of cell across apical membrane, leakage channels inserted there)
- if potassium needs to be conserved, leakage channels will be inserted on basolateral membrane (ensures return to blood)
what can happen from kidney failure?
salts and waste products like urea build up and the blood pH goes down
how does massive edema occur?
due to salt retention
acidemia
results from inability to secrete acids
what can occur with elevated potassium levels?
cardiac arrest b/c the heart depends on K to stabilize
- too much k on the outside of cell results in the heart having a hard time to maintain and reset RMP
structures of the bladder
detrusor muscle, ureteral openings, trigone, internal and external urethral sphincter, deep transverse perineus muscle, levator ani m
where is the bladder situated?
just behind the pubic symphisis/pubic bone
layers of the bladder
epthelium, smooth muscle, and adventitia or serosa on outside
detrusor muscle
Contracts a lot to push Urine out
- smooth muscle inside wall of bladder
ureteral openings
pass through bladder wall at oblique angle; wall pushes on openings of ureters and acts like a vale to close it to prevent urine backflow into ureters
trigone
exists b/w the 2 ureteral openings and the urethra; very smooth section that does not contract and maintains distance b/w the 3 openings to prevent collapse
urethral opening
males: internal urethral sphincter at base of bladder (just above prostate); there to separate urine from seminal fluids
females: no internal urethral sphincter; bladder tilts over and kinks urethra to act like a valve
external urethral sphincter
skeletal muscle part of pelvic control that helps maintain continence by closing off urethra
deep transverse perineus muscle
wraps around opening of urethra
levator ani muscle
wraps around opening of urethra
- helps keep intestines in and helps elevate anal opening (clenching)
- also wrapped around opening for anus to help close it off
- in females, helps to close off anus + vaginal opening + urethral opening
micturition reflex
relaxation of the urethral sphincter in response to increased pressure in the bladder
steps to micturition
- stretch receptors detect bladder distension (200-400mL)
- message sent to sacal spinal cord
- sensory input triggers autonomic reflex
- sends parasympathetic motor signals to detrusor m. (contract) and internal urethral sphincter (relax)
- external urethral sphincter which is striated has voluntary control
How much glucose is in filtrate but not in urine?
162g of glucose in filtrate but none in amino acids
How much protein in the filtrate and how much excreted?
2.0g of protein in the filtrate and 0.1g excreted
How much sodium in the filtrate and how much excreted?
570g of na in filtrate and 4g excreted
How much Uric acid is in filtrate and how much in urine?
8.5 in filtrate and 0.8 in urine
How much creatine in filtrate and urine
1.6g in both
Things that should not be in urine except very tiny amounts are
Blood, glucose, protein and amino acids
What substance is never reabsorbed?
Creative
What sorting does the corpuscle do?
Protein and blood
What sorting do the tubules do?
All the rest besides protein and blood
Where are the collecting ducts and loop of henle located?
Renal medulla
Where to the acuate arteries run along?
Border of medulla and cortex’s
What do interlonular arteries do?
Send individual afferent arterioles to each nephron
Where does the capillary bed spread out?
All over the distal and proximal convoluted tubule and the loop of henle
How much water reabsorption is obligatory?
90%
How much water loss is facilitative?
10%
Active transport
Requires energy
Passive transport
Solutes want to go down in concentration gradient so they follow them
Osmosis
Passive mechanism by which water follows its concentration gradient through a semipermeable membrane
What drives osmosis?
Movement of the solutes from the tubules to the interstitial fluid which often requires energy
Where does most of obligatory water reabsorption occur?
In the proximal convoluted tubule and descending loop of henle b/c they contain tubules which are permeable to water
What is the most active area for reabsorption?
Proximal convoluted tubule
What elements drive osmosis of water?
Cl, K, and Na
What is the apical border of tubular cell composed of?
Simple layer of cuboidal epithelium
What increases surface area for absorption?
Brush border
What is in between tubular cells?
Tight junctions so they don’t leak.. little proteins that link each junction together
- they are not super tight so ions can still move through
Sodium glucose transporter is an example of
Symporter
Sodium hydrogen is
Anti porter
How do the kidneys excrete acids to help maintain pH?
Sodium hydrogen anti porter
What do both primary and secondary transports require?
A carrier protein to assist movement of the ions and solutes
Transporters
Proteins which can only bind and then move solutes at a fixed rate that they have a maximum rate at which they can function
What does glycosuria indicate?
Diabetes is present and Tm has been reached for Na glucose symporter
Are the kidneys highly metabolically active?
Yes
Parafellular
Easy and just moves down concentration gradient
Trans cellular means
Na will go down in conc gradient into the cell and it cannot be left there so water would follow ions causing the cell to break
What reestablishes RMP?
The Na/K pump takes atp to push Na out and into interstitial fluid and takes K into the cell
What drives Na/H anti porter in the proximal c tubule?
Sodium’s high concentration in the filtrate to low inside the cell
Kidney dialysis
Take blood out of veins to dialysis the nasty stuff
Peritoneal dialysis
Stick a port into the peritoneal cavity
And flush in a bunch of fluid which allows salts to enter fluid and then be brought out of body
Bladder is
Smooth muscle, epithelium and adventitia on outside
Urethral opening
Where ureter will come in and out
What is between the urethral opening
Trigone
What sphincter do we have control over?
External urethral sphincter
Do females contain internal urethral sphincter?
No
What holds the sphincter closed?
the somatic nerves holding this sphincter closed are inhibited by micturition reflex (pressure build up usually not enough to open it)
- in adults, there usually has to be a conscious effort to relax it before passing urine
What causes us to pee ourselves?
The detrusor muscle can overcome external urethral sphincter
What is the internal sphincter made of and controlled by?
Made of smooth muscle and controlled but ANS so it’s not under conscious control
