Lecture 39 - Reabsorption and Secretion Flashcards
the three processes involving nephrons, collecting ducts, and their blood supply in urine formation are:
glomerular filtration, tubular absorption, and tubular secretion
ultrafiltrate is formed in the renal ____ and modified during its course through the _____
cortex, medulla
what are the tubules within the medulla responsible for?
reabsorbing, excreting, and concentrating the urinary filtrate
how many gallons of blood do the kidneys filter per day?
45
what percent of blood volume is reabsorbed by the kidneys, and what percent goes on to become urine?
99% is reabsorbed, 1% becomes urine
_____ is the first of three processes by which metabolic wastes are separated from the blood and urine is formed
ultrafiltration
what is ultrafiltration?
it is the non-specific filtration of blood under high pressure that occurs in the renal corpuscle of the nephron
in the glomerulus, which arteriole has a wider diameter: the afferent or the efferent?
the afferent. having a smaller diameter in the efferent arteriole is what makes the renal corpuscle have such a high pressure, favoring filtration
in the glomerulus, which arteriole has a narrower diameter: the afferent of the efferent?
the efferent. this produces a high resistance to outflow, so blood gets backed up in the glomerulus. This raises the pressure in the glomerulus, creating an environment that favours filtration
the renal corpuscle is a term to describe a combination of what two structures?
the glomerulus + bowman’s capsule
how many layers of cells does bowman’s capsule have?
two. podocytes and endothelial cells
what are the cellular extensions of podocytes that wrap around the blood vessels of the glomerulus called?
pedicels
where is the filtrate collected before entering the proximal tubule
the urinary space
what are the three major players of the glomerular filtration barrier?
endothelium, glomerular basement membrane, and podocytes
the glomerular endothelial cells are characterized by numerous _____ that allow water and non-cellular components of the blood to pass through. This acts mainly as a barrier to the cells in the blood.
fenestrations
the inner layer of cells of the bowman’s capsule are called:
podocytes
the glomerular basement membrane is a product of the fusion of the basement membranes produced by:
endothelial cells and podocytes
what two cells secrete the proteins that make up the glomerular basement membrane?
endothelial cells and podocytes
what is the main barrier to proteins in the renal corpuscle?
the glomerular basement membrane
the glomerular basement membrane is made up of a protein mesh in a _____ matrix
gelatinous
The glomerular basement membrane prevents filtrations of what sized compounds?
a) >400 Da
b) >7000 Da
c) >6500 Da
b) >7000 Da
T/F: the glomuerular basement membrane has lower permeability to cations compared to anions
false. it has a lower permeability to anions
which two layers of the glomerular basement membrane have negative charge?
lamina rara externa (LRE) and lamina rara interna (LRI)
T/F: podocytes are epithelial cells that cover the inner part of the glomerular basement membrane
False. They are epithelial cells, but they cover the outer part of the basement membrane
what is the slit diaphragm?
the space between the foot processes of podocytes that act as molecular sieves, providing additional filtration barrier based off size exclusion
why is the glomerular filtrate called ultrafiltrate of plasma?
because the larger components (platelets and blood cells) are not filtered
what is different between ultrafiltrate and plasma/interstitial fluid?
it has a lower protein concentration
Name some things that are easily filtered into the ultrafiltrate
water, Na, Cl, urea, uric acid and phosphate
T/F: no albumin is able to enter the ultrafiltrate
False. small amounts of albumin do make it across the membrane, but it is completely reabsorbed in the proximal tubules
What is glomerular filtration rate (GFR)?
a measure to describe the total amount of filtrate formed by all the renal corpuscles in both kidneys per minute
what is considered a normal GFR?
GFR > or = to 90
Glomerular filtration rate (GFR) is influenced by
both the ____ pressure and the ____ pressure on either side
of the capillary membrane of the glomerulus
hydrostatic and osmotic
glomerular filtration will occur when the _____ hydrostatic pressure exceeds the hydrostatic pressure of ________
glomerular, Bowman’s Capsule
Will dehydrated people have a higher or lower GFR than normal?
lower, because they have lower blood volume, and therefore lower glomerular blood pressure
what are two things that can increase the potential for filtration?
dilation of the afferent arteriole to allow for more blood into the glomerulus (increased P) OR constriction of the efferent arteriole so less blood can leave the glomerulus (also increases P)
Will increased Bowman’s Capsule hydrostatic pressure increase or decrease GFR?
decrease GFR. The bowman’s hydrostatic P acts against the glomerular hydrostatic P
why does a ureter obstruction to the flow of urine result in decreased GFR?
the urine will back up into Bowman’s capsule, increasing the pressure there. This will in turn decrease GFR
what is tubular reabsorption?
the transport of water and solute from tubular fluid to the peritubular capillaries
what is tubular secretion?
transport of solute from the peritubular capillaries to the tubular fluid
what is the second of the three processes by which blood is filtered and urine is formed?
selective reabsorption
if important substances such as Na, glucose, a.as, etc can easily pass through the glomerular membrane, why arent they constantly lost via the urine?
selective reabsorption
where does the majority of selective reabsorption occur?
the proximal convoluted tubule, which extends from the bowmans capsule
where is the proximal tubule located?
the cortex
the proximal tubule is composed of ____ epithelium joined together by ____
simple columnar, tight junctions
What is a distinguishing feature of the proximal tubule?
apical brush border
what is the function of the apical brush border of the proximal tubule?
increase the surface area for reabsorptive function
why are the cytoplasm of the proximal tubule cells densely packed with mitochondria?
needed to supply energy for active transport of Na ions out of the cells to create a concentration gradient
there are ___ pumps on the basal and lateral surfaces of tubular epithelial cells to supply energy for active transport of Na, glucose, and a.as out of the tubular fluid and into the blood
Na/K ATPase
what creates/maintains the strong electrochemical gradient required for Na to move into the tubular cells from the tubular lumen?
Na/K ATPase that pump Na out of the cell to the interstitial fluid
What structure found on the luminal (apical) surface of the tubular cells assists in transporting Na and glucose out of the lumen and into the cells?
Na/Glucose cotransporter
how does glucose move against its concentration gradient from the proximal tubular lumen into the tubular epithelial cells?
Na/glucose cotransporter
Glucose is transported against its concentration gradient from filtrate back into the bloodstream. where does the energy driving this process come from?
The Na/Glucose cotransporter uses the electrochemical gradient created by the Na/K ATPase to power the process
Is water actively or passively transported out of the filtrate and into the blood?
passively. it follows the other ions to maintain an isotonic fluid environment inside the capillaries
How does the body get rid of end products such as urea and uric acid that have been passively reabsorbed?
secretion in the proximal tubules
How do the kidneys aid in pH homeostasis?
the tubular secretion of H+ from the blood into the tubular fluid
what is the typical pH of urine?
6.0
What is the typical pH of blood?
7.35-7.45
the secretion of H+ is mainly the result of a ____ exchanger, which is an antiporter in the apical membrane
Na+/H+ exchanger
what provides the energy needed for the Na/H antiporter to push H against its concentration gradient and into the urine?
Na/K ATPase
what is the third of the three processes that form urine?
secretion
urine leaves the kidney through the ____, is stored in the ____, and then removed through the _____
ureter, bladder, urethra
what are three examples of filtered substances that are secreted as wastes?
urea, creatine, some drugs
what can a buildup of creatine in the blood be a sign of?
impaired kidney function
individuals with kidney diseases will demonstrate higher or lower GFR?
lower GFR
What are two indicators of impaired kidney function in a urinary analysis?
blood cells and proteins
Glucose
high quantities of _____ in urine may indicate disease or hormonal conditions
protein
What type of disease is the leading cause of CKD in dogs (less often in cats)
Glomerular diseases like glomerular nephritis or renal amyloidosis
what are the two major causes of prteinuric renal disease in dogs?
glomerular nephritis and renal amyloidosis
how do they routinely define human glomerular disease?
Human glomerular disease is routinely defined following
(1) examination light microscopic sections with a specific panel of histochemical stains,
(2) immunofluorescence to detect the presence of immunoglobulins and complement components, and
(3) transmission electron microscopy.
what are some clinical signs of urinary protein loss?
mild: weight loss, lethargy
severe: edema, abdominal fluid collection
extensive: renal failure, anorexia, nausea, and vomiting
what is the most important treatment for glomerular diseases?
identification and correction of any underlying disease processes
