Lecture 7: Renal Blood Flow Flashcards
What are the normal and dysfunction levels for BUN?
10:1 = Normal = Normal filtering GFR
>20:1 = Decreased GFR = Pre-Kidney failure
<10:1 = Full kidney failure
If you are not given the glucose or BUN concentrations how do you calculate Osmolality?
Osmolality = (2 x sodium)
Total renal blood flow is approximately what percentage of resting cardiac output?
20%
How many liters of filtrate are produced per day?
180 L
Substances leaving the plasma must pass through filtration barriers before entering the tubule lumen, what are they?
1) Glomerular capillary endothelium (pores)
2) Basal lamine (acellular basement membrane)
3) Filtration slits between the pedicles of the podocytes in the inner layer of Bowman’s capsule
What is found on the glomerular capillary wall epithelium; how does this affect permability compared to other capillaries?
- Many large pores between enodthelial cells
- Many large holes (fenestrations) in the endothelial cells
* 100x more permeable to H2O and solutes than other capillaries
What is the largest protein we want filtering throught the Bowman’s capsule and approximately what percent gets through?
- Albumin (smallest plasma protein)
- <1%
What 2 factors constitue the selectivity of the basment membrane to particle movement?
- Size of particle
- Charge of particle
What causes the negatively charged molecules to be repelled from filtration barrier; found in which layers?
Glycoproteins in basement membrane and podocytes
Basment membrane prevents molecules larger than what from passing through?
7 nm or no greater than 40,000 daltons
Discuss the filtraton differences of postive, neutral, and negatively charged molecule?
Positive: More filtered
Neutral: In the middle
Negative: Less filtered
*Notice the filtration rate as size changes for each
What is Hematuria and what is it indicative of?
- RBC’s in the urine
- Indicative of renal or kidney diseases/presence of kidney stones
How much protein is normally excreted in the urine daily, what is it called when more than this value is excreted?
- 150 mg
- Proteinuria = >150 mg excreted
What causes albuminuria?
Due to disruption of the negative charges (glycoproteins) within the basement membrane.
What are Tamm-Horsfall proteins; derived from?
Low-molecular weight proteins (LMWP) derived from the cells of Thick-ascending limb, accounts for 25 mg of daily protein excretion
Function of Podocytes?
- Structural support for basement membrane
- Repel negatively charged plasma proteins
Podocyte damage is commonly referred to as what syndrome; does this cause renal failure?
- Nephrosis
- Usually does not cause renal failure initially. Damage disrupts the relationship between podocytes and basement membrane = loss of strucutral support
The juxtaglomerular apparatus is made up of what 2 cells types?
1) Macula Densa (sensor cells)
2) Juxtaglomerular cells (aka granular cells) - renin
What do the Macula densa cells sense?
- Salt content
- Fluid volume
What 2 things do the Macula densa cells do if they sense LOW salt and LOW fluid volume?
1) Tell the granular cells (juxtaglomerular) to release renin
2) Dilate the afferent arterioles of the glomerulus = increased glomerular hydrostatic pressure
The juxtaglomerular cells secrete renin in response to what 3 things?
1) Beta-adrenergic stimulation
2) Decreased renal perfusion pressure
3) Signals from the Macula densa
What causes juxtaglomerular cells to release renin?
Decreased renal arterial pressure = Decreases stretch = decreased intracellular calcium concentration.
What are the 3 major mechanisms for the regulation of renin release?
1) Perfusion pressure (low = renin release)
2) Sympathetic nerve activity (activation = renin release)
3) NaCl delvivery to macula densa (low = renin release)
What is Tubuloglomerular feedback?
When NaCl is decreased (sensed by Macula densa), Renin secretion is stimulated and vice versa.
