13: Renal Function Flashcards
Three layers of the glomerular filtration barrier
- Cap endothelium
- Glomerular BM
- Podocytes epithelium
Molecules that are 1. Freely filtered, 2. Maybe filtered, and 3. Not filtered in the glomerular apparatus
- Freely filtered: <20 Angstroms
- Maybe filtered: 20-42 A
- Not filtered: 42+ A
Three layers of the glomerular BM
- Lamina rara externa
- Lamina densa
- Lamina rara interna
Composition of the lamina rara interna and externa vs lamina densa
Lamina rara interna/externa: made of proteoglycans, mainly heparin sulfate
Lamina densa: made of type IV collagen and laminins
Purpose of proteoglycans in the lamina rara exerna and interna
Provide electronegative charges to GBM to repel proteins
Glycocalyx of glomerular endothelium
Forms a sticky layer that helps filter what can get through
What charge of particles is more likely to be filtered through the glomerular apparatus
Positive charge (bc of negative glycocalyx)
Things that are freely filtered vs not freely filtered through the filtration barrier
Freely: water, small solutes (glucose, AAs, electrolytes)
Not freely: large molecules (most proteins), cells
What does it mean if excretion exceeds filtration?
Tubular secretion must have occurred
What two volumes are equal to arterial input to the kidney?
Venous output + urine output
Quick conversion: what is 1mL/min in L/day?
1 mL/min -> 1.44 L/day
How does glomerular filtrate compare to plasma?
Isosmotic to plasma, just without proteins and cells
Filtered load vs filtration fraction
Filtered load: rate of filtration of a specific molecule
Filtration fraction: ratio of GFR to RBF
Four conditions that must be present to assume that GFR = Clearance
- Substance freely filterable
- Substance neither absorbed nor secreted
- Substance not synthesized or broken down by kidney
- Substance must be physiologically inert (non-toxic, without renal effects)
Two substances often used when using renal clearance to estimate GFR and WHY
Inulin, creatinine - they are not really reabsorbed or secreted, and are freely filtered
What marker is used in clinical settings to determine GFR? Why is this not ideal?
Creatinine - is it actually secreted in a small amount, but is easier bc it doesn’t require an infusion like inulin does
Adrenergic receptors present on arterial vessels, JG cells, and Na-K ATPases
Arterial vessels: a1
JG cells: B1
Na-K-ATPase: a1
Starling forces that favor vs oppose filtration
Favor: PGC, pi BC
Oppose: PBC, pi GC
Where does pressure drop steeply in renal vasculature
Across afferent and efferent arterioles
Constricting/dilating the efferent/afferent arterioles: two ways to increase and two ways to decrease GFR
Increasing GFR: dilate afferent + constrict efferent
Decreasing GFR: constrict afferent + dilate efferent
Examples of vasoconstrictor moleucles vs vasodilator molecules
Vasoconstrictors: catecholamines, endothelin, ATP, angiotensin II
Vasodilator: prostaglandins, bradykinin, NO, dopamine, ANP, ACE-inhibitors
What happens in PTC with increased GFR?
Increased GFR -> increased PTC oncotic pressure -> increased reabsorption in tubules
Two intrinsic and three extrinsic control mechanisms of hemodynamics
Intrinsic: autoregulation, tubuloglomerular feedback
Extrinsic: symps, hormones, composition of blood
