Principles of Tubular Transport Flashcards
What are the 3 processes in urine formation?
Ultrafiltration
Reabsorption
Secretion
What is usually never found in urine?
Proteins
How does water move throughout the nephron?
Passive transport. There are no active transport processes for water.
What processes use facilitated diffusion?
Glucose transport into RBCs
What processes use active transport?
Active Na resorption and endocytosis for protein transport and requires the use of ATP.
What processes use secondary active transport?
Requires an indirect energy source in an ion gradient and it can be saturated as it is limited by carriers (Tm)
Examples are Na+-H+ exchangers
What is the transcellular pathway?
Uses a specific pump such as an Na/K-ATPase pump
What is the paracellular pathway?
Movement of ions via solvent drag and it occurs with ions like Ca2+, Mg2+ and K+
What is CaO2 - CvO2?
It is the O2 extraction from the blood
How does the (CaO2 - CvO2) change as O2 demand and O2 supply both increase in the heart?
No change in CaO2 - CvO2
How does the (CaO2 - CvO2) change as O2 supply decreases and O2 demand remains constant in the skeletal muscle?
The CaO2 - CvO2 will increase, indicating increased extraction of O2 from the blood
How does decreased O2 supply affect the kidney?
In the kidney, it will decrease the O2 demand with no change in CaO2 - CvO2. This means as blood flow decreases to the kidney, it requires less O2.
What is the normal handling of glucose in the kidney?
Normally 100% of the glucose is reabsorbed
What is the reabsorption of glucose equal to in an equation?
R = F - E
S = 0
When can the tubular transport maximum (Tm) be calculated?
Only when the Tm is exceeded
What is the Tm for glucose equal to?
Tm (glucose) = (Pa GFR) - (UV)
What is the renal plasma threshold (RPT) of glucose?
The RPT is the point where glucose first appears in urine.
Describe the normal handling of PAH.
Normally over 90% of PAH is secreted
What is the equation for the secretion of PAH?
S = E - F
R = 0
What is the Tm for PAH equal to?
Tm (PAH) = (UV) - (PaGFR)
What is the RPT of PAH defined as?
The RPT of PAH is the point where the secretion slope of PAH first decreases
What is diuresis?
It is a urine flow greater than 1 mL per minute
What is the function of mannitol?
It acts as an osmotic diuretic
What is the fate of mannitol in the nephron?
It is filtered but not reabsorbed
How does mannitol function as an osmotic diuretic?
It holds excess water in the tubule by osmotic forces which leads to increased urine flow.
How can glucose function as an osmotic diuretic?
Normally glucose is 100% reabsorbed but if some is left in the tubule, it will hold excess water by osmotic forces and leads to increased urine flow. It will also cause dehydration and thirst.
