Lecture 13: Renal Physiology (Pierce) Flashcards
What is the role of glomerular endothelial glycocalyx?
Forms a sticky substance that plays a role in filtration
-prevents more anions from being filtrated
What happens if the glomerular barrier is damaged?
Proteins can be filtered and be found in the urine
-proteinuria
What passes the filtration barrier?
Water
Small solutes: glucose, amino acids, electrolytes
How is urinary excretion measured?
Urinary excretion = Amount filtered - Amount reabsorbed + Amount secreted
How is tubular reabsorption measured?
Tubular reabsorption = Glomerular filtration - urinary excretion + amount secreted
How is arterial input calculated?
Arterial input = venous output + urine output
What is the formula for urine excretion rate?
Urine excretion rate = [Urinary concentration] x [Urinary flow rate]
x = Ux x V
What is renal clearance?
Flow rate at which substances are removed from plasma by the kidneys per unit of time
How is renal clearance/GFR calculated?
Clearance = {[Urinary concentration] x [Urinary flow rate]} / [Plasma concentration]
How is filtration rate calculated?
FF = GFR/RPF
What is the normal filtration fraction of RPF?
20%
What is average GFR?
125 mL/min
As filtration fraction increases, why does oncotic pressure increase?
As more ions and substances are being filtered, the concentration of proteins in capillaries is increased
What substances have the same filtration and excretion rate?
Inulin (better choice)
Creatinine phosphate
*Both do not have tubular reabsorption
How does the sympathetic nervous system affect the arterial resistance vessels?
Target: α-1 adrenoceptors
-powerful vasoconstriction (more on afferent arteriole)
How does the sympathetic nervous system affect the juxtaglomerular granular cells?
Target: β-1 adrenoceptors
- renin release
- RAAS system
How does the sympathetic nervous system affect the tubular epithelial cells?
Target: α-1 adrenoceptors
- activates Na+/K+ ATPase
- increases sodium reabsorption
What are the three physical factors that contribute to GFR?
1) Hydraulic conductivity: permeability of fenestrated endothelium (Lp)
2) Surface area for filtration (Sf)
3) Capillary ultrafiltration pressure (Puf)
GFR = Ultrafiltration coefficient x Capillary ultrafiltration pressure
How is ultrafiltration pressure calculated?
Puf = Pgc - Pbc - πgf
What affects ultrafiltration coefficient?
Hydraulic conductivity
Surface area - glomerular mesangial cells have contractile properties that can change SA
Kf = Hydraulic conductivity x Surface Area
How does constriction affect the afferent arteriole?
Reduces capillary ultrafiltration pressure
GFR decreases
How does dilation affect the afferent arteriole?
Increases capillary ultrafiltration pressure
GFR increases
How does constriction affect the efferent arteriole?
Pressure increases within capillary –> GFR increases
How does dilation affect the efferent arteriole?
Blood can escape glomerulus –> GFR decreases
What are some substances that can promote vasoconstriction?
Sympathetics: catecholamines
Endothelin
ATP/adenosine
Angiotensin II
What are some substances that can promote vasodilation?
Prostaglandins Bradykinin Nitric Oxide Dopamine ANP ACE-inhibitor
What happens to glomerular tubular balance when GFR rises?
1) Increase in PTC oncotic pressure
2) Increased sodium reabsorption (and other substances)
Describe the myogenic feedback reflex.
Response to changes in blood pressure
-Increased blood pressure will cause afferent arteriolar constriction and efferent arteriolar dilation
Describe the tubuloglomerular feedback.
Links the rate of glomerular filtration to the concentration of salt in the tubule fluid at the macula densa.
- high NaCl concentration rate and reabsorption rate –> contraction of the afferent arteriole
- maintains constant sodium delivery in DCT and constant GFR
Describe macula densa signaling.
Increased delivery of NaCl will increase ATP production and promote vasoconstriction, lowering GFR
How does angiotensin affect kidneys?
Efferent arteriolar vasoconstriction
- Renal blood flow decreases
- GFR increases
- Increased peritubular oncotic pressure
