Renal Flashcards
Apical membrane
Faces the lumen
Basolateral membrane
Side facing the capillary
Top two causes of kidney failure
DM (due to glycosylation of the glomerulus) and HTN
Functions of the kidney
Activate vitamin D, secrete EPO, remove wastes, maintain fluid/electrolyte/pH balance
The kidney can produce glucose from
amino acids
Do we generate nephrons?
Nah, fool.
Serious renal impairment doesn’t occur until ____-____% of nephrons have been damaged
75-90%
This means that clinical findings may not be evident until late in the disease course
What is contained in the cortex?
The glomerulus and portions of the tubules
What is contained in the medulla?
Loop of Henle and collecting ducts.
The kidneys receive __% of the CO
25%
What is a basement membrane?
A sheet of fibers beneath any epithelium
Blood and protein in the urine are signs of
glomerular injury
What are mesangial cells?
Specialized SM cells in the glomerulus. Their function is to provide structural support to the glomerular capillaries, regulate blood flow of the glomerular capillaries by their contractile activity (regulate GFR), and are involved in phagocytosis .
Remember that SM cells can change their phenotype when they are injured, causing them to multiple and begin secreting extracellular matrix (collagen). Secretion can start clogging up our filtration system.
When we have glomerular injury, either the glomerulus will clog up and not filter enough, or it will open up and allow too much stuff to pass through (RBCs and protein).
Normal GFR is about
125
These things are totally reabsorbed from the proximal tubule
Glucose, amino acids, and proteins.
Most of the bicarb is reabsorbed in the proximal tubule as well.
What does the macula densa do?
It senses the concentration of filtrate in the thick ascending limb. Based on the concentration, it will constrict or dilate the afferent arteriole and increase or decrease the release of renin.
Low concentration causes afferent vasodilation and increased renin release.
High concentration causes afferent constriction and decreased renin release.
What do the JG cells do?
These are specialized SM cells in the afferent arteriole. They secrete renin in response to a drop in pressure.
Angiotensin II causes constriction mostly in this vessel
Efferent arteriole.
Symporter responsible for reabsorbing filtered glucose
SGLT2
Glucose travels with a sodium
Symporter can be saturated at a BG of 180, resulting in glucosuria.
How do we reabsorb bicarb?
Remember we don’t have a transporter for bicarb, so it combines with H+ in the lumen to form H2CO3, and then dissociates into H20 and CO2 in the presence of CA. This gets absorbed across the membrane.
Once inside the cell, the same process happens in reverse in the presence of CA. At the end, bicarb is reabsorbed, and another H+ is kicked into the lumen to combine with another bicarb.
Where do we get the ammonia used to buffer acid?
The amino acid glutamine. This is good for buffering acid because it provides an ammonia group to bind with H+ in the lumen, and also creates a new bicarb that enters the bloodstream, further treating the acidosis.
Kidney response to alkalosis
Excreting some of the filtered bicarb
How does aldosterone result in potassium excretion?
It increases the activity of the basolateral Na/K pump. More sodium ends up being reabsorbed, and potassium ends up getting excreted.
Effect of ADH
ADH (vasopressin) binds to the V2 receptor on the basolateral side, causing the placement of aquaporins in the lumen of the collecting tubule.
Two potential problems with ADH
1) Diabetes insipidus
- Damage to pituitary causes insufficient ADH release
2) Nephrogenic diabetes insipidus
- The collecting tubules are unresponsive to ADH
Renin is released in response to
1) Decreased BP (low blood flow to kidneys)
2) Low sodium levels (sensed by the macula densa)
3) SNS activation of the JG cells via B1
Atrial Natriuretic Peptide (ANP) is released in response to _____ and causes _____
Overstretch of atrial cells due to excess fluid volume
ANP inhibits the secretion of renin, and thereby the actions of angiotensin II. Results in afferent dilation and efferent constriction as well as loss of sodium and water.
Urodilantin is released in response to
Released by the distal and collecting tubules in response to high circulating volume.
Acts by inhibiting salt and water reabsorption. I can’t really find anywhere how it does this, so it’s probably not important.
Urodilantin is similar to _____ in structure and function
ANP
How do osmotic diuretics work?
By increasing the osmolality of the filtrate, causing water to remain in the tubule, resulting in increased urine volume.
How do ACE inhibitors work?
They block the formation of angiotensin II (and thusly, aldosterone as well).
How do loop diuretics work and what patient population do they work well for?
Inhibit the Na/K/2Cl channels in the thick ascending loop and are good for those with impaired renal function.
How do thiazide-like diuretics work and what patient population do they work well for?
They block the Na/Cl symporter in the distal tubule. This increases the concentration of the filtrate, and water follows. These are good for those with normal kidney function.
Examples of potassium wasting diuretics
Osmotic, loop, and thiazide-like
Example of a potassium sparing diuretic
Aldosterone blocking agents
Renal considerations in infancy
Kidneys are immature
1) Low GFR
2) Reduced ability to concentrate urine (subject to volume depletion)
Renal considerations in the elderly
The kidneys begin to diminish in size and functions due to the loss of nephrons. Starts after the 4th decade, and significantly by the middle of the 6th decade.
This means
- Low RBF
- Low GFR
- Decreased ability to concentrate urine
- More susceptible to fluid loss and electrolyte imbalances
(sort of similar to infancy)
This synthetic molecule can be used to measure GFR
Inulin
When would you want to do a 24 hour urine collection?
To evaluate substances that are excreted in varying concentrations throughout the day (like protein)
The normal color of urine is due to
Urochrome pigments (urobilin)
Is normal urine slightly acidic or basic?
Slightly acidic
WBC casts are associated with
Renal infections (pyelonephritis)
RBC casts are associated with
Inflammation of the glomerulus (glomerulonephritis)
Epithelial casts are associated with
ATN, because they indicate the sloughing of tubular cells
Does urine osmolality and spec grav stay the same of fluctuate throughout the day?
It should normally fluctuate. If it does not fluctuate, it could indicate renal impairment.
How does creatinine enter the circulation?
It is the end result of muscle metabolism and is excreted ONLY by the kidney.
What affects creatinine levels in the body?
1) Rate of creatinine produced by the muscle (should be about constant)
2) Rate of creatinine excreted by the kidney (which is determined mostly by the GFR)
Plasma creatinine levels will rise proportionately to a fall in
GFR
Normal creatinine level
.7 - 1.5
Normal BUN level
10-20
Normal BUN:Creat ratio
10-20
Urea is the end product of
Protein metabolism. An increase in BUN may indicate a decrease in renal function.
Why is urea a poor measure of renal function?
Because it is influenced by hydration status, dietary protein intake, and rate of protein catabolism.
Why isn’t creatinine completely accurate in assessing GFR?
Because some is secreted into the lumen.