Lecture 17: Tubular Reabsorption And Secretion Flashcards
Describe paracellular and transcellular routes for reabsorption
Para: movement btw tubular cells
Trans: movement through tubular cells
List the 3 kinds of aquaporins and their specific locations in the renal tubules.
Aquaporin-1: widespread, renal tubules.
Aquaporin-2: present in apical membranes of collecting tubule cells. Controlled by ADH
Aquaporin-3: present in basolateral membranes of collecting tubule cells
List and compare types of transporters:
Symporter: contransport- moves w/ Na+ gradient
Antiport: countertransport . Moves against Na+ gradient
List and describe major types of ATPases and channels found in the renal tubules and indicate their specific locations
ENaC channel: found in apical membrane. Closed by Rx amiloride. Opened by some hormones.
CFTR (Cl-) channels and K+ channels: found in apical membranes of some segments of nephron- driven by [ ] gradient of substance concerned.
Na+K ATPase
H+ ATPase
H+K+ ATPase
Ca++ATPase
Discriminate among facilitated, active, and secondary active transport and know examples of specific transporters
Facilitated transport: transport occurring through channels or uniporters, ex: glucose transport.
Active Transport: transport directly coupled to an energy source-Na+K+ATPase. Ca++ ATPase
Secondary active transport COTRANSPORT: transport coupled indirectly to an energy source. SGLT2: reabsorbs 90% glu. SGLT1 reabsorbs 10% glu
List the substances thatre actively secreted into renal tubules
Creatinine
Para-ampinohippuric acid
Define transport maximum and the limiting factor and explain how the r/t glucose reabsorption
Transport maximum: limit to the rate at which the solute can be transported
Limiting factor: # of transporters available.
Maximum transport is the amt. that will be reabsorbed by the tubule. Anything past that will be excreted.
List reasons as to why some passively reabsorbed substances dont have a transport maximum to
- Rate of diffusion is determined by electrochemical gradient of the substance.
- Permeability of membrane for the substance
- Time that the fluid containing the substance remains w/in the tubule.
How do electrochemical gradients and time the substance is in the tubule affect rate of transport?
More time = more reabsorption
More difference in gradients will cause more reabsorption
Define solvent drag
osmotic movement of water reabsorption can also carry some solutes [mostly Na+]
Describe the transport characteristics of the proximal tubule and the specific kinds of molecules/ions and direction transported.
Highly metabolic=lots of mito.
Reabsorbs 65% of filtered Na+, Cl-, HCO3, and K+
Reabsorbs all filtered glucose and AAs
Secretes H+, organic acids, bases
First 1/2: cotransport w/ glu, AAs, and other solutes
Second 1/2: reabsorption is mainly w/ Cl-
ACID-BASE here -carbonic acid -> HCO3
Describe the transport characteristics of the thin descending loop of henle and the specific kinds of molecules/ ions and direction transported.
Highly permeable to water and moderately permeable to most solutes, including urea and Na+
Reabsorbs 20% of filtered water
Describe the transport characteristics of the ascending [thin and thick] loop of henle and the specific kinds of molecules/ions and direction transported
Thin ascending loop: impermeable to water
Thick ascending segment: Na+K+ATPase pump, Na+, K+, and Cl- co-transporter, slight back leak of K+ into lumen.
IMPERMEABLE TO WATER
Site of action for lop diuretics
Describe the transport characteristics of the early and late distal tubule and the specific kinds of molecules/ions and direction transported
Early distal tubule: IMPERMEABLE to water and urea.
Na+, Cl-, Ca++, and Mg++ reabsorbed
Late distal tubule:
Reabsorbs Na+, Cl-, HCO3,
secrete K+ into lumen
Primary site of K+ sparing diuretics
Describe the specific functions and locations of the principal cells and the intercalated cells
Late distal tubule and collecting duct:
Principal cells:
reabsorb Na+ and secrete K+
Intercalated cells:
Reabsorb K+ and HCO3 ions from lumen and secrete H+ ions
Describe the transport characteristics of the medullary collecting duct and the specific kinds of molecules/ions and direction transported
Epithelial cells are cuboidal. Smooth surfaces. Few mito.
Permeable to water CONTROLLED BY ADH.
Permeable to urea.
Capable of secreting H+ against a [ ] gradient.
Can also reabsorb Na+,Cl-
Review forces [starling forces] that determine fluid reabsorption by peritubular capillaries
Pc=13 ->interstitial
Pif=6 interstitial
38-28= 10
Bulk flow= net reabsorption 10 mm Hg
*pushed to the capillaries more than the lumen for secrection/excretion
For aldosterone, describe the source, function, site of action, and stimulus for secretion.
Aldosterone Source: adrenal cortex
Function: increases Na+ reabsorption and stimulates K+ secretion.
Site of action: major-on the principal cells of the cortical collecting ducts
Stimulus for secretion: increased extracellular K+ and levels of angiotensin II
Relate addison’s disease to lack of aldosterone and conn’s syndrome to aldosterone hyerpsecretion.
Addisons disease is asso. W/ absence of aldosterone= marked loss of Na+ and accumulation of K+
Conn’s syndrome asso. W/ hypersecretion of aldosterone
Describe function and effects of angiotensin II and r/t its effects on the proximal tubule.
Angiotensin II function: increased Na+ and water reabsorption.
Returns BP and extracellular volume toward normal.
Effects angiotensin II:
Stimulates aldosterone secretion.
Constricts efferent arterioles.
Directly stimulates Na+ reabsorption in proximal tubules, loops of henle, distal tubules, and collecting tubules.
Describe source, function, and effects of ADH, ANP, PTH
ADH:
source: posterior pituitary.
Function: increases water reabsorption.
Effects: binds to V2 receptors in late distal tubules, collecting tubules, and collecting ducts. Increases formation of cAMP.
ANP:
Source: atrial cells in response to distension. Function: inhibits reabsorption of Na+ and water
PTH: source parathyroid glands. Function: increases Ca++ reabsorption
Explain mathematically how renal clearance is calc and the role of insulin in calc GFR
Renal clearance=volume of plasma that is completely cleared of the substance by the kidneys per unit time.
Clearance rate = (urine [ ] of substance s X urine flow) x plasma [ ] of substance s
Inulin: polysaccharide (5200) not produced in body. Completely filtered but not reabsorbed or secreted.
GFR= (urine [ ] of substance X urine flow) / plasma [ ] substance = Cs
GFR= (Us x V)/Ps = Cs
