Urine Formation Tubular Reabsorption & Secretion (PART 1) Flashcards
Second step in urine formation; occurs due to active and
passive transport mechanisms from all parts of the renal
tubules; most of this process occurs in the ________ ______
proximal tubule
Reabsorption in the proximal tubule – most water and
solutes are recovered by the blood, leaving only a small
volume of tubule fluid to move on to the loop of Henle:
1–______: actively transported out of tubule fluid into blood
2– ________ AND ________: passively transported out of tubule fluid by means of sodium cotransport mechanism
3– Chloride, phosphate, and bicarbonate ions passively move into blood due to an imbalance of _____ ________
4– Water: movement of sodium and chloride into blood causes an _______ imbalance, moving water passively into blood
5– Urea: about ½ of urea passively moves out of ______ with the rest moving on to the loop of Henle
Sodium
Glucose and amino acids
electrical charge
osmotic
tubule
Reabsorption in the LOOP OF HENLE
1– Water is reabsorbed from the tubule fluid, and
urea is picked up from the interstitial fluid in the
__________ limb
2– Sodium and chloride are reabsorbed from the
filtrate in the __________ limb, where the
reabsorption of salt makes the tubule fluid dilute
and creates and maintains a high osmotic pressure
of the medulla’s interstitial fluid
descending
ascending
Reabsorption in the DISTAL tubules and COLLECTING ducts:
1– Distal tubule reabsorbs ______ by active transport but in smaller amounts than in the proximal tubule.
2– ____ is secreted by the posterior pituitary and targets the cells of distal tubules and collecting ducts to make them more permeable to water.
3– With the reabsorption of _______ in the collecting duct, the urea concentration of the tubule fluid increases, causing urea to diffuse out of the collecting duct into the medullary interstitial fluid.
4– _______ participates in a countercurrent multiple mechanism, that along with countercurrent mechanisms of the loop of Henle and vasa recta, maintains the high osmotic pressure needed to form concentrated urine and avoid dehydration
sodium
ADH
water
Urea
Calculation of Tubular Reabsorption
Reabsorption = Filtration - ____________
Excretion
Transport Maximum
Transport Maximum: Is the number of carriers in the renal
tubules available to ferry each particular substance. Once the transport maximum is reached for all _______, further increases in tubular load are not reabsorbed and are excreted.
___________is the tubular load at which transport maximum is exceeded in some nephrons. This is NOT exactly the same as the transport maximum of the WHOLE kidney because some nephrons have lower transport max’s than others.
Examples: glucose, amino acids, phosphate, sulphate
nephrons
Threshold
Reabsorption of Water and Solutes is
Coupled to ______ Reabsorption
Na+
Transport characteristics of thin and thick loop of Henle.
THIN =?? NAME ONE!
THICK?? NAME 3!!
- THIN - very permeable to H2O = ~ 25% of filtered load
- THICK = Reabsorption of Na+, Cl-, K+, HCO3, Ca++, Mg++
BUT…… does SECRETION of H+
AND……NOT permeable to H2O!!
Early Distal Tubule
Functionally similar to _______ ascending loop
1 • NOT permeable to ______ (called diluting segment)
2 • Active reabsorption of Na+, Cl-, K+, Mg++
3 • Contains ________ ________
thick
water
macula densa
EARLY and LATE Distal Tubules and Collecting Tubules.
- EARLY = ~ 5% of filtered load NaCl reabsorbed, NOT permeable to_____ and NOT very permeable to
_______. - LATE = permeability to H2O depends on _____, NOT very permeable to urea.
H2O
urea
ADH
Late Distal and Cortical Collecting
Tubules “Principal Cells” – Secrete _____.
K+
Late Distal and Cortical Collecting
Tubules “Intercalated Cells” – Secrete ______
H+
Concentrations of solutes in different parts of the tubule depend on relative _________ of the solutes compared to water.
- If water is reabsorbed to a _______ extent than the
solute, the solute will become more concentrated in
the tubule (e.g. creatinine, inulin) - If water is reabsorbed to a ________ extent than the
solute, the solute will become less concentrated in
the tubule (e.g. glucose, amino acids)
reabsorption
greater
lesser
Regulation of TUBULAR Reabsorption:
• Glomerulotubular Balance • Peritubular Physical Forces • Hormones X 5 NAME ALL 5!! HINT...AAANP • Sympathetic Nervous System • Arterial Pressure (pressure natriuresis) • Osmotic factors
- aldosterone
- angiotensin II
- antidiuretic hormone (ADH)
- natriuretic hormones (ANF)
- parathyroid hormone
Glomerulotubular Balance
Total rate of reabsorption increases as the filtered load
__________, even though the % of GFR reabsorbed remains relatively constant at about 65%.
increases
