Tubular function Flashcards
What are the main problems the kidney is trying to solve?
Maintain homeostasis-we need to replace used up ions, but get rid of excess, and get rid of urea/toxins
Does it by just shoving into urinary duct all what you don’t want. But we don’t have Urea and H2O pumps-therefore use glomerular filtration which passively makes products pass through
How much water passes into the tubular system a day?
Around 180L-need to reabsorb 99%, while maintaining ion concentrations
What is osmolality? What does it depend on?
Measure of the osmotic pressure exerted by a solution across a semi-permeable membrane
Dependent on number of particles, not their nature
What is the normal range for plasma osmolarity? And Urine Osmolarity?
Plasma: 285-295mosmol (mostly sodium). Urine-50-1200mosmol (mostly sodium)
How is the renal tubular wall organised?
For absorptionTubular fluid is separated from peritubular capillary by epithelium- apical side facing tubule. TJ between the cells, but both absorption and secretion can be paracellular and transcellular. This happens mostly in proximal convoluted tubules
How can we differentiate between different transport modes?
Passive movement-protein idenpendent (lipophilic)-has a straight rate-non limited
Protein dependent-will be limited-curve will be logarithmic
Active movement-couple to ATP or coupled with another port (antiport, coport)-also logarithmic rate
How does water pass through cells?
Can be paracellular and use aquaporins in cells for transcellular-and that’s how the body regulates inktake of water-makes more “openings” for water to come in
How are proteins absorbed?
Epithelium have high affinity binding-to try and grab any proteins left. Endocytosis into endosome, then separation with pH and recycling of the transporter
What is transport maxima?
The rate changes for absorption/reabsorption aren’t just for cells-for the whole system-that’s transport maxima. You can absorb at increasing rates, to a point-and when you reach that transport maxima, it just goes to the urine
What is a good exemple of the use of transport maxima?
As glucose concentration in blood reaches 15/20 mmol, the transport maxima is surpassed, and glucose ends in the urine. This is diabetes mellitus.
Where is sodium reabsorbed?
proximal convoluted tubule (60%), 25% in loop of henle (how we absorb water), 8% in distal convoluted tubule. The last part is the one regulated, because always need 99%. Vary if we need 99% or 99.9%
How are cells lining the tubule organised?
Proximal tubule-many mitochondria to absorb, villi for more surface area
Thin loop of henle-basic cells, not much mito but very tight junction
Ascneding loop of henle and distal tubule also has mitochondria
What is the basic mechanism used to absorb most things in kindey?
Low Na+ intracellularly-constantly being pumped out
What is the use of Na+ in reabsorption?
Use Na as a cotransporter for glucose and AA (provide the energy)-and then the conc in the cells of glucose and AA increase, they exit the cell to blood by themselves
Na can also be antiporter in exchange for H+, reducing in the cell
This H+ can become a factor in making H2CO3 back to H20 and CO2, that then move back easily
What are the only two items that are passively secreted/absorbed?
Water and urea. All the rest is active transport to has a workable rate
What is reabsorbed in the loop of Henle?
Squamous epithelium, where water is passively absorbed, draws in potassium adnd sodium
What is reabsorbed in the ascending limp of the loop of henle?
Cuboidal epithelium. Chloride actively reabsorbed, sodium is passively reabsorbed, bicarbonate reabsorbed bUT impermeable to water
Na is taken in with 2CL and 1K (which then exits)-by then,
