3F - Reabsorption and Secretion

Reabsorption uses what kind of transport?

luminal to the basolateral

Secretion uses what kind of transport

basolateral to the luminal

Transport Maximum (Tm)

rate that we can have reabsorption/secretion based on the available transport proteins (type and number), in tubule

ex) more doors and bigger doors allows more people to exit

Majority of the PCT is

• Reabsorption of 100% glucose

• change osmolarity: reabsorption of 65% Na2+

• change osmolarity: reabsorption of H2O

• reabsorb 80-90% bicarbonate

Reabsorption of glucose

cross luminal membrane, basolateral, interstitial fluid, blood (peritubular capillary)

• luminal: Na/Glucose transport, using Na gradients to pull both materials into the cell

• glucose now how concentration and can move by facilitated diffusion through glucose uniporter into the blood

• aka: move Na/Gluc In and Gluc out into blood

Facilitated diffusion is

passive

Glucose Secondary Transport

depends on sodium potassium pump that established the sodium gradient

Sodium Potassium Pump

primary transport because directly using ATP

Sodium Reabsorption

• Na transport protein/uniporter diffuses from high to low (facilitated diffusion)

• Na from low to high thru Na/K pump into pump (primary active transport)

• K is being moved in the cell

• so far 35% Na that was initially filtered is remaining, PCT does the majority

As sodium moves out

• effects osmolarity

• want to move H2O out

Obligatory H2O Reabsorption

H2O follows the Na

• ex) reabsorb Na, change osmolarity to reabsorb more water

H2O movement can be

paracellular or transcellular

H2O Transcellular Movement

• In PCT theres a constant number of transport proteins (aquaporins)

• facilitated diffusion by aquaporins

• 65%

Bicarbonate Reabsorption

• HCO3- + H+ = Carbonic Acid H2Co3

• dissociates into CO2 and H2O

• H2O stay in tubular fluid and CO2 diffuse out of cell

• …….

Thin Segment

hairpin turn on nephron limb between the ascending and descending limb and is in the medulla region

• picks up urea

As we move down into the medulla

• more concentrated

• higher osmolarity

Collecting Ducts

where urea exits into the medulla

Counter Current Exchange

tubular fluid flows move in the opposite direction of the blood

• enhances reabsorption

Vaso Recta

nephron loop region + juxtamedullary nephrons

Nepheron Loop Descending Limb is

• permeable to water (reabsorb 10% more)

• impermeable to salt

Nepheron Loop Ascending Limb is

• permeable to salt (reabsorb 25% more)

• impermeable to water

Are the DCT and Collecting duct still modifying the tubular fluid?

yes

Intercalated Cells

• constantly reabsorbing K

• regulate blood pH with Type A and Type B

• in DCT + Collecting Ducts

Type A intercalated Cells

respond to acidic blood

• secrete H+ to increase pH and make more basic

• reabsorb more bicarbonate HCO-

Type B Intercalated Cells

respond to basic blood

• reabsorb more H+ ions

• lower pH to be more acidic

Principle Cells

• respond to hormones: ADH, Aldosterone, Parathyroid

• reabsorb Na, H2O, Ca

• secrete K if need

• in DCT + Collecting Ducts

ADH

anti-diuretic hormone targets principal cells

• stimulate aquaporin products and gets added to lumen and basolateral membrane

• facilitates H2O reabsorption

• dec urine vol

• inc blood vol

Aldosterone

regulated by the Renin-Angiotensin Mechanisms

• get aldosterone in response to release of renin

• inc Na reabsorption

• inc H2O reabsorption: inc aquaporins on both membranes

• inc K secretion: to move Na in cell to move into blood

Parathyroid Hormone

• secreted in response to low blood calcium

• want to inc Ca reabsorption

• impact DCT + collecting ducts

• inhibit phosphate reabsorption in PCT

Renal Papilla

where the collecting ducts meet and drain urine at the center of the renal pyramid

Minor Calyx

drains into indvidual renal pyramid

Major Calyx

multiple minor calyx drain here

Renal Pelvis

major calyx join a large open area

Urine Order

1. renal papilla

2. minor calyx

3. major calyx

4. renal pelvis

5. ureter

6. bladder

Bladder

• distensible: hold up to 1L

• detrusor muscle: thick wall

Nutritarian

• controlled release of urine from the bladder to the urethra

• control internal and external urethral sphincter

• controlled by nervous system

Internal Urethral Sphincter

involuntary

External Urethral Sphincter

voluntary

Barcorecptors

• in the bladder wall that detects pressure

• detects signal

• signal to peripheral and central nervous system via afferent pathway

• send signal back to bladder

• involuntary relaxes internal urethral sphincter

• you decide the relaxation of external urethral sphincter after