2. SESSION OUTCOME
At the end of the lecture, the group should be able to:
1. describe the basic principles of solute transport in a renal tubule
and;
2. understand the concepts on reabsorption and secretion along
different parts of the nephrons.
15. Tubular reabsorption
Both requires passive and active
transport mechanism
Solute can be transported through
paracellular pathway or transcellular
Water moves through osmosis
16. Primary Active Transport of Na+
Sodium diffuses across the luminal
membrane into the cell down an
electrochemical gradient
Sodium is transported across the
basolateral membrane against an
electrochemical gradient by the
sodium-potassium ATPase pump.
Sodium, water, and other substances
are reabsorbed from the interstitial
fluid into the peritubular capillaries
by ultrafiltration
17.
18. Secondary Active Transport mechanism
No energy required
Includes Sodium glucose
transporter(SGLT2 and SGLT1)
Sodium-hydrogen exchanger(NHE)
Carrier molecule is needed
19. “PUNONG PUNO NA
AKO SA INYONG
LAHAT!, DI KO NA
KAYA ah!!!”
PETMALU KA
BATO!!!!
GLUCOSE
20. TUBULAR TRANSPORT
MAXIMUM
It is the maximal amount of a substance (in mg) which
can be transported (reabsorbed or secreted) by tubular
cells/min.
Carrier proteins have a maximum transport
capacity (Tm) which is due to saturation of the
carriers.
29. Cellular Ultrastructure and Primary Transport
Characteristics of Proximal Convoluted Tubule
65-67% filtered load is reabsorb
Contains extensive brush border
structure
Site for the secretion of toxin, organic
acids and bases
Reabsorption is highly passive
30. TRANSPORT IN EARLY PCT
Na ion uptake primarily coupled by
hydrogen ion(antiporter) ,glucose(co-
transport),amino acid and lactate
Transtubular osmotic gradient drive
water movement across cell
membrane
31. TRANSPORT IN LATE PCT
Na and Cl is transported through
parallel operation of Na/H exchanger
and Cl/base
Cl is passively reabsorb in the
basolateral membrane
32. Cellular Ultrastructure and Transport Characteristics of
Thin and Thick Loop of Henle
not permeable to H2O
very permeable to H2O)
No brush border structure (few
mitochondria) and minimal level of
metabolic activity.
No brush border structure (few
mitochondria) and minimal level of
metabolic activity.
20% of filtered load of Na, Cl and K are
reabsorbed
33. TRANSPORT IN THICK
ASCENDING LIMB
Movement of sodium across the
luminal membrane is mediated primarily
by a 1-sodium, 2-chloride, 1-potassium co-
transporter
Tubular fluid is very diluted
Site of action of some diuretics
35. Countercurrent Multiplier System
in the Loop of Henle
Active transport of sodium ions and co-
transport of potassium, chloride, and other
ions.
Active transport of ions from the
collecting ducts into the medullary
interstitium.
Facilitated diffusion of large amounts
of urea from the inner medullary collecting
ducts into the medullary interstitium.
36.
37.
38. Animal Max. Urine Conc. (mOsm /L)
Beaver 500
Pig 1,100
Human 1,400
Dog 2,400
White Rat 3,000
Kangaroo Mouse 6,000
Australian Hopping Mouse 10,000
39. • The vasa recta
serve as
countercurrent
exchangers
• Vasa recta blood
flow is low
(only 1-2 % of
total renal
blood flow)
41. • not permeable to H2O
• not very permeable to urea
• permeability to H2O depends on ADH
• not very permeable to urea
42. Figure 27-12;
Guyton and Hall
Sodium Chloride Reabsorption and Potassium
Secretion in Collecting Tubule Principal Cells
43.
44. Cellular Ultrastructure and Transport Characteristics of
Medullary Collecting Tubules
The permeability of the medullary collecting
duct to water is controlled by the level of
ADH
Unlike the cortical collecting tubule, the
medullary collecting duct is permeable to
urea,
49. Summary of Water Reabsorption and
Osmolarity in Different Parts of the Tubule
• Proximal Tubule: 65% reabsorption, isosmotic
• Desc. loop: 15-20% reabsorption, osmolarity increases
• Asc. loop: 0% reabsorption, osmolarity decreases
• Early distal: 0% reabsorption, osmolarity decreases
• Late distal and coll. tubules: ADH dependent
water reabsorption and tubular osmolarity
• Medullary coll. ducts: ADH dependent water
reabsorption and tubular osmolarity
Editor's Notes
Paracellular transport refers to the transfer of substances across an epithelium by passing through the intercellular space between the cells. It is in contrast to transcellular transport, where the substances travel through the cell, passing through both the apical membrane and basolateral membrane.
An electrochemical gradient is a gradient of electrochemical potential, usually for an ion that can move across a membrane. The gradient consists of two parts, the chemical gradient, or difference in solute concentration across a membrane, and the electrical gradient, or difference in charge across a membrane. When there are unequal concentrations of an ion across a permeable membrane, the ion will move across the membrane from the area of higher concentration to the area of lower concentration through simple diffusion. Ions also carry an electric charge that forms an electric potential across a membrane. If there is an unequal distribution of charges across the membrane, then the difference in electric potential generates a force that drives ion diffusion until the charges are balanced on both sides of the membrane.
In secondary active transport, two or more substances interact with a specific membrane protein (a carrier molecule) and are transported together across the membrane. As one of the substances (for instance, sodium) diffuses down its electrochemical gradient, the energy released is used to drive another substance (for instance, glucose) against its electrochemical gradient.
If Tm is exceeded, then the excess substrate enters the urine. Many substances are reabsorbed by carrier mediated transport systems e.g. glucose, amino acids, organic acids, sulphate and phosphate ions.
The technical definition of an equivalent is the amount of substance it takes to combine with 1 mole of hydrogen ions.
The threshold for glucose refers to the filtered load of glucose at which glucose first begins to be excreted in the urine.
The technical definition of an equivalent is the amount of substance it takes to combine with 1 mole of hydrogen ions.