Exam - The Tubular Function Flashcards
what are events occurring in the tubules
glomerular filtration
what occurs in glomerular filtration
bulk movements (water + dissolved substances) –> tubular fluid composition close to a protein free plasma
what happens to the fluid in the tubule
it gets transformed into urine
reabsorption of fluid
water and dissolved substance from tubular lumen to peritubular capillaries
secretion of fluid
substances transported from the peritubular capillaries to the tubular lumen
in passive reabsorption, what determines what is passively absorbed
molecular size and liposolubility
how much urea is passively reabsorbed
50-60%
examples of substances in passive reabsorption
negative ions
drugs
environmental toxins
what is tubular secretion for
only selected substances
where does tubular secretion occur
from peritubular capillaries –> across tubular cells –> into lumen
how does tubular secretion occur
some by primary active transport, some by secondary active transport, some by passive diffusion
what would be secreted by primary active transport
one system for organic acids
one system for organic bases
what would be secreted by secondary active transport
H+
what would be secreted by passive diffusion
several steroid hormones
drugs
what does glucose filter as easily as
water –>glucose concentration in glomerular filtrate = plasma concentration
where is glucose reabsorbed
only in proximal tubule
how does glucose get reabsorbed
secondary active transport
do kidneys participate in regulating glucose levelds
no, just prevent its loss
will glucose appear in urine
not normally unless glucose concentration in plasma is extreme
renal threshold for glucose
the lowest plasma concentration at which glucose can be detected in urine
splay
deviation from an ideal curve
what happens if there is glucose in urine
diabetes mellitus
what are the the first main causes of diabetes mellitus
insulin regulation of blood glucose does not work –>glucose levels in plasma increase dramatically passed the Tmax —> kidney cannot handle it all –> excretes glucose
what is the second main cause of diabetes mellitus
genetic defect affecting the transport mechanism of glucose in the proximal tubule –> reduced Tmax –> glucose excreted even when plasma levels are low
do proteins pass through the glomerular membrane
no - not usually present in glomerular filtrate except small peptides and small proteins
what are proteins reabsorbed by
epithelial cells of the proximal tubules by endocytosis
what happens to proteins once reabsorbed
they are broken down into amino acids in epithelial cells
where can residual amounts of proteins in urine be sometimes observed
in dogs
is it normal for there to be proteins in the urin
no - glomerulus should not let them pass
what is the main reason for protein leakage
imbalance of charge in glomerular membrane
why are proteins repulsed by basal lamina
proteins are negatively charged and so is the basal lamina
when can some proteins pass through the membrane
if the membrane loses its polarit
why is there a low ion concentration in urine
the reabsorption of many ions equals the amount filtered
how are ions regulated
most of the reabsorption of ions is hormonally controlled
what affects plasma levels and thus filtration for most ions
intestinal absorpotion
what is the most important organ for Na+ control
kidney
what is the most important factor regulating extracellular and blood volumes
Na+
what is the additional importance of Na+
transport of other substances are coupled to Na+ in secondary active transport
examples of things that are transported coupled to Na+
the reabsorption of glucose, amino acid, bicarbonate, Cl-, and PO4-
secretion of H+ and K+
how much of the metabolism of the kidney is energy spent in Na+ transport
80%
where is th site of most Na+ and filtered water reabsorption
proximal tubule
characteristic of proximal tubule
porous
is the loop of Henle less of more permeable than the proximal tubule
less
are the distal tube and collecting duct permeable to Na+ and water
barely - tight junctions between epithelial cells
what is permeability and reabsorption in the last part of the distal tubule and collecting duct controlled by
hormonal control
what is the most important factor stimulating Na+ reabsorption int he distal tubule and collecting duct
aldosterone
what is a mineralocorticoid
liposuble steroid hormone synthesized and released by the adrenal cortex
what does aldosterone induce
synthesis of Na+ channels and pump in epihtlial cells, therefore increasing Na+ transport
what happens if there is no aldosterone
all the Na+ entering the distal tubule will be excreted in urine = death within a couple of days
were is ECF content relatively low
inside cells - needs to be maintained within a narrow Rangel
where is K+ reabsorbed
actively in proximal tubule
where is K+ secreted
distal tubule and collecting duct
what are changes in K+ mainly due to
secretion since 100% filtered is reabsorbed
what does K+ concentration control
aldosterone release
what percentage of Ca2+ is bound to proteins in plasma
50%
what form of Ca2+ can be filtered in glomerulus
only free form
where is Ca2+ reabsorbed
mostly in proximal tubule
where does the regulated reabsorption of Ca2+ occur
in the ascending limb of the loop of Henle, the distal tubule and the collecting ducts
what stimulates Ca2+ reabsorption
parathyroid hormone (PTH)
what percentage of filtered Ca2+ is generally excreted
1-2%
what is very important to maintain blood volume
tubular reabsor[tion of water
how does tubular reabsorption of water occur
between epithelial cells through a tight junction
through epithelial cells (aquaporins)
what is the tubular reabsorption of water influenced by
movements of Na+ because osmosis is a diffusion process
where does most water reabsorption occur
proximal tubular
what do most structures possess
aquaporins
what structure does not posses aquaporins
the ascending limb of the loop of Henle
what are aquaporins up regulated by in the distal tubule and collecting duct
ADH from pituitary –> increases water reabsorption
