filtration, reabsorption, and secretion (midterm 3) Flashcards
what is GFR
glomerular filtration rate, the rate of fluid extraction from the glomerular capillaries into Bowman’ capsule (~180 L/day - ~ 2 mL/min into Bowman’s)
what are the 3 major layers of the glomerular capillary membranes (most cap membranes only have 2!)
- the endothelium of the capillary
- a basement membrane
- a layer of epithelial cells (podocytes) surrounding the outer surface of the capillary basement membrane
what is filtered in glomerular filtration and at what rate compared to water
- Sodium, glucose, and inulin are filtered as freely as water
- Myoglobin is filtered 75% as rapidly as water; albumin 0.5% as water
what is the equation for GFR
Kf (filtration coefficient) x (PG - PB - πG + πB)
PG = glomerular hydrostatic pressure
PB = Bowman’s capsule hydrostatic pressure
πG = glomerular capillary colloid osmotic pressure
πB = Bowman’s capsule colloid osmotic pressure
what is net filtration favored by
glomerular hydrostatic pressure (PG) and Bowman’s capsule colloid osmotic pressure ( πB)
- typically, πB ~ 0 because there is no protein transport into Bowman’s capsule
what is the major determinant of GFR
PG - increased PG = increased GFR
what is PB usually and what does it do to GFR
18 mmHg - reduces GFR
what happens to GFR with πG
increased πG = decreased GFR
what are the three things glomerular hydrostatic pressure is determined by
- Arterial pressure (increased arterial pressure increases glomerular hydrostatic pressure and GFR)
- Afferent arteriolar resistance (increased resistance reduces glomerular hydrostatic pressure and decreases GFR)
- Efferent arteriolar resistance (increased resistance (up to a point!) reduces glomerular capillary outflow, increases glomerular hydrostatic pressure and increases GFR)
what is the total renal blood flow of a 70 kg person
1200 mL/min (21% of cardiac output)
in normal vs renal tissue, what is the correlation between BF and metabolic demand
normal: BF = metabolic demand
renal: BF > renal metabolic demand
what do vasoconstrictors do to GFR
they decrease blood flow and therefore decrease GFR
norepinephrine, epinephrine
what do vasodilators do to GFR
they decrease renal vasculature resistance, increase BF, and increase GFR
what does increased sympathetic stimulation do to GFR
decreases renal arterial diameter, decreases BF, decreases GFR
what is tubuloglomerular feedback
changes in sodium chloride concentration causes changes in the macula densa, that then control renal arteriolar resistance (graph on pg 13 of notes/ desktop)
what is urinary excretion rate equal to
filtration rate minus reabsorption rate plus secretion rate
how do glomerular filtration and tubular reabsorption compare to urinary excretion
they are very large relative to it
are glomerular filtration and tubular reabsorption selective
glomerular filtration is non-selective
tubular reabsorption and secretion is highly selective
what does filtration lead to
reabsorption
what are the transport mechanisms during reabsorption
tubular epithelium -> interstitial space -> peritubular capillary endothelium
what is primary active transport through the tubular membrane linked to
the hydrolysis of ATP via
- Sodium-potassium ATPase
- Hydrogen ATPase
- Hydrogen-potassium ATPase
- Calcium ATPase
what does secondary active transport through the tubular membrane involve
Na+/glucose co-transport
Na+/amino acid co-transport
Na+/H+ counter-transport
do active transport and passive transport have limits
active transport has a maximum limit
passive transport has no limit
what is passive transport determined by
electrochemical gradient
membrane permeability
fluid retention time within the tubule
what does sodium transport do
drives water reabsorption by osmosis
what is the concentration of molecules along the nephron a result of
the individual molecules’ transport and the transport of water
what is the concentration of sodium, glucose, and creatine/urea along the nephron + how they are transported
- Sodium is highly transported, but its concentration does not change as water is also highly removed
- Glucose concentration falls dramatically, as it is transported much more quickly than water
- Creatinine and urea increase in
concentration and urea is not reabsorbed
what are the three segments of the loop of Henle
- descending thin segment (highly permeable to water)
- ascending thin segment
- thick ascending segment (thick epithelial cells capable of active reabsorption of sodium, chloride, and potassium - ~ 25% of these filtered molecules are reabsorbed here)
how is the distal tubule of a nephron similar to the loop of Henle
they both reabsorb most ions including sodium, potassium and chloride, but are impermeable to water and urea
what two cell types do the late distal tubule and cortical collecting tubule contain
- principal cells, which reabsorb sodium and water and as secrete potassium
- intercalated cells, which reabsorb potassium and secrete hydrogen
what is glomerulotubular balance
increased GFR => increased tubular resistance (proximal tubular reabsorption is 65% of GFR)
what is the equation for tubular reabsorption and what does everything stand for
Kf x (-Pc + Pif + πc - πif)
- Peritubular hydrostatic pressure (Pc)
- Renal interstitium hydrostatic pressure (Pif)
- Peritubular colloid osmotic pressure (πc)
- Renal interstitium colloid osmotic pressure (πif)
what are Pc and πc functions of and what do they do to absorption
Pc = f(Pa) (increased Pa, increased Pc => decreased reabsorption
and Pc = f(Ra, E) (decreased Ra, E (resistance of afferent and efferent arterioles), increased Pc => decreased reabsorption)
πc = f(πA) (increased πA, increased πc => increased reabsorption)
and πc = f(FF) (increased filtration fraction, increased plasma F, increased plasma (protein), increased πc => increased reabsorption
what is the effect of arterial pressure regulation between 75 and 160 mmHg
only a slight effect on renal BF and GFR
what happens when GFR auto regulation is impaired
arterial pressure can cause large increases in GFR and a greater effect on sodium and water excretion
