10 - Tubular Reabsorption and Secretion PPT (QUIZ 3) Flashcards
How is urine formed?
Via glomerular filtration and tubular reabsorption/secretion
How many times is our entire plasma volume filtered a day?
60 times!
Define reabsorption.
The retention of substances contained in filtrate back into peritubular capillary blood.
What is Filtration Only?
- NO reabsorption
- Metabolism products like urea and creatinine get filtered out
- Foreign substances like drugs (crack) get filtered out
What is Filtration with Partial Reabsorption?
- Electrolytes like sodium and bicarbonate get reabsorbed easily
- Some partial reabsorption and some secretion (I love that the ppt says “maybe”)
What is Filtration with Complete Reabsorption?
- Nutritional substances like glucose and AAs get completely reabsorbed
What is Secretion?
- NO reabsorption
- Stuff like organic acids gets secreted into tubular acid to become urine
What is the filtration rate of glucose through the kidneys dependent on?
Plasma glucose concentration
Where does glucose reabsorption mainly occur?
Proximal convoluted tubule (PCT)
What are the two steps of glucose reabsorption?
- Glucose moves across the apical membrane into the brush border cells
- Glucose diffuses across the basolateral membrane into the peritubular capillaries
How is glucose moved across the apical membrane?
Sodium/glucose transporters use energy from the existing sodium conc. gradient to move glucose against its conc. gradient
What type of diffusion does glucose utilize to enter the peritubular capillaries?
FACILITATED diffusion with GLUT1 and GLUT2
What happens during normal plasma glucose levels (less than 200mg/dl)?
Glucose reabsorption matches with filtration
What happens during high plasma glucose levels (more than 200mg/dl)?
The limited number of glucose transporter proteins prevents reabsorption from keeping up filtration
What happens during higher (highest) plasma glucose levels (more than 350mg/dl)?
Glucose transport proteins are fully saturated and reabsorption cannot go any faster, thus reaching the TRANSPORT MAXIMUM!
Where is excess glucose excreted?
Da urine
What is the threshold concerning the glucose titration curve?
Threshold: the plasma glucose level at which glucose excretion starts
What is splay concerning the glucose titration curve?
Splay is the initial, nonlinear increase in urine excretion
What’s glycosuria?
Glucose excreted in urine due to:
- Diabetes (decreased insulin, increased plasma glucose)
- Pregnancy (hormonal changes resulting in increased renal blood flow and filtration
What’s PAH?
Para-aminohippuric acid
PAH is an organic acid (destined for urine). How much of PAH gets cleared from the plasma?
90%
(TRUE/FALSE): PAH can be used for diagnostics due to its high clearance rate.
(TRUE)
(TRUE/FALSE): There’s always renal absorption of PAH.
(FALSE): There is NO renal absorption of PAH
Where does PAH secretion occur?
PCT
