Tubular Processing Flashcards
Does the majority of reabsorption occur in proximal or distal parts of the nephron?
Proximal, specifically proximal convoluted tubule.
Does the majority of fine tuning of water and solute excretion occur in proximal or distal parts of the nephron? What is this fine tuning under the control of?
Distal parts, under hormonal control.
Describe the tubule fluid leaving the PCT in terms of osmotic pressure. Why is this?
The fluid is isosmotic because the PCT epithelium is freely permeable to water.
In the nephron, where are essentially all the glucose and amino acids reabsorbed?
PCT.
How does glucose enter the tubular cells from the luminal side of the nephron tubule? What is the concentration gradient like?
Sodium glucose co-transporters (SGLT2 mainly).
Against the concentration gradient.
How does glucose leave the tubular cells of the nephron to enter the interstitial fluid?
Facilitated diffusion via glucose transporters.
Describe the glucose transport maximum (Tm). What does this lead to?
There are a finite number of SGLT transporters on the PCT cells. If the amount of glucose in the filtrate increases, it eventually reaches a transport maximum where reabsorption cannot go any faster.
This leads to loss of glucose in urine. Water is also retained in the tubule lumen and excreted along with the glucose. This is called osmotic diuresis.
Sodium reabsorption is linked to the secondary active transport of what into the tubular lumen of the nephron?
Hydrogen (H+) ions.
Reabsorption from the tubule lumen of the thick ascending limb is mediated primarily by what?
Sodium, potassium 2-chloride co-transporter (Na+K+2CL-).
What is the charge of the lumen of the thick ascending limb? What does this encourage?
The charge of the lumen is positive.
It encourages paracellular reabsorption of cations, e.g. Ca2+ and Mg2+.
What is the key transporter on the luminal side of the early DCT?
Sodium-chloride co-transporter (moving Na+ and Cl- into cell).
Which hormone is sometimes present in the late DCT? What does its presence and absence affect?
Antidiuretic hormone (ADH).
Water permeable when ADH is present.
Water impermeable when ADH is absent.
What are the 2 main cell types in the late DCT and what are their main roles?
- Principal cells - involved in sodium reabsorption and potassium secretion.
- Intercalated cells - involved in potassium reabsorption and hydrogen ion secretion.
On the principal cells of the late DCT, how does sodium enter the cells from the luminal side?
Epithelial sodium channels.
The number of epithelial sodium channels on the luminal side of the principal cells of the late DCT are under the control of what?
Aldosterone.
