BIOL 373 midterm #2 Flashcards
Roles of the kidney
1) regulation of extracellular fluid volume and blood pressure
2) regulate plasma osmolarity (Na, Cl)
3) regulates ion balance
4) excretion of waste
5) regulates plasma pH
6) endocrine
Why not only filter the 1% of filtrate that needs to be excreted?
filtering all the liquid then excreting selected solutes is easier because there isn’t a need for specific transport mechanisms
What does the cortex contain
All Bowman’s capsules, proximal and distal tubes
What does the medulla contain
loops of Henle and collecting ducts
What are the tubular elements of the nephron in order?
1) Bowman’s capsule + glomerus (renal corpuscle)
2) proximal tubule
3) descending limb
4) loop of henle
5) ascending limb
6) distal tubule
7) collecting duct to bladder
Conventional circulation
artery -> arteriole -> capillary -> venule -> vein -> heart (nephron: two capillary beds glomerulus capillaries and pertitubular capillaries)
Venous portal system
artery -> arteriole -> capillary -> venule -> capillary -> venule -> vein -> heart
What is cortical nephron in renal circulation
abdominal aorta -> renal artery -> branches of smaller arteries -> … afferent arteriole -> glomerular capillaries -> efferent arteriole -> peritubular capillaries -> venules - > veins
What is the juxtamedullary nephron in renal circulation
afferent arteriole -> glomerular capillaries -> efferent arteriole -> peritubular capillaries / vasa recta -> venules -> veins
Overview of kidney function
kidneys process 180L plasma/ day
urine output is only 1.5 l/day
99% of fluid that passes through kidneys is reabsorbed
1) filtration
2) reabsorption
3) secretion
What is filtration?
movement of water/ solutes from blood into tubules
-only occurs in renal corpuscles
-once in tubules, filtrate will be excreted unless reabsorbed
What is reabsorption?
movement of water/ solutes from filtrate back into blood (peritubular capillaries)
What is secretion?
removing molecules from blood, adding them to filtrate
much more selective than filtration
Where does filtration occur?
Only in the glomerulus
-blood to lumen
Where does reabsorption occur?
Proximal tube, loop of Henle
Where does secretion occur?
proximal tubule, distal tube
Where does excretion occur?
To bladder and external environment from distal tubule
What does urinary excretion depend on?
Filtration, reabsoprtion, and secretion
amount filtered - amount reabsorbed + amount secreted = amount of solute excreted
Nephron 1 - Filtration at renal corpuscle
1) afferent arteriole
2) glomerulus
3) efferent arteriole
4) peritubular capillaries
filtrate is almost identical to plasma in composition (minus blood cells and most of the protein)
Nephron 2 - Reabsorption and secretion
~70% fluid and solute reabsorbed in proximal tubule (iso-osmotic reabsoprtion)
fluid leaving ascending loop of Henle is hypo-osmotic relative to plasma (at this point, 90% of original filtrate has been reabsorbed)
distal tubule and collecting duct are fine tuning of water/ salt balance it is in endocrine control
What is in the liquid after filtration?
100% volume
300 mOsM
180L/day
What is liquid at start of loop of Henle?
54L/ day
30% volume
300 mOsM
What is liquid at end of loop of Henle?
18L/ day
10% volume
100 mOsM
What is in liquid leaving collecting duct?
1.5L/ day
1% volume
50-1200 mOsM
aim for this because this is what we pee a day
Filtration at the renal corpuscle
20% of the plasma moves out of glomerular capillaries into tubules (the rest exits in the efferent arteriole
What is filtration fraction?
% of total plasma volume that filters into tubule
What is the function of the macula densa?
modifies tubular epithelium
-macula densa cells release paracrine factors that act on smooth muscle of afferent arteriole
Monitors tubular salt concentrations and can release paracrine factors that affect afferent arteriole diameter
What are barriers to filtration?
glomerular capillary endothelium
basement membrane
specialized epithelium around glomerulus
What part of the nephron tubule is part of the juxtaglomerular apparatus?
It is part of ascending limb of the loop of Henle where it connects to the distal tubule
