Renal Hemodynamics Flashcards
Osmolarity =?
Osm = concentration * # of dissociable particles
mOsm/L =?
mOsm/L = mmol/L * (#of particles/mol)
Oncotic pressure
osmotic pressure generated by large molecules such as proteins (π)
What happens to the intracellular and extracellular fluid volume as well as osmolarity when you drink water?
Decreased osmolarity
Increased ECF and ICF

What happens to the intracellular and extracellular fluid volumes as well as osmolarity if you drink a hyperosmotic solution?
*pulls water from cells*
Increased osmolarity
Increased ECF
Decreased ICF

What happens to the intracellular and extracellular fluid volumes as well as osmolarity during sweating or dehydration (hypoosmotic)?
Increased osmolarity
Decreased ICF
Decreased ECF

What is an isoosmotic solution?
No change in osmotic pressure, so no water flows into the cell when ECF increases
Ex: Gatorade
Describe the flow of fluid through a nephron
Cortex
- Glomerulus
- Bowman’s capsule
- Proximal convoluted tubule
- *Medulla**
4. Thin descending loop of Henle
- Thin ascending loop of Henle
- Thick ascending loop of Henle
Cortex
- Distal convoluted tubule
- Cortical collecting tubule
Medulla
- Medullary collecting tubule

What is the juxtaglomerular (JG) apparatus and what are its two main cell types?
Portion of the tubule where the late thick ascending limb of Henle’s loop courses between the arterioles.
Granular cells
Macula densa cells

What is the function of granular cells (juxtaglomerular cells) in the JG apparatus?
Differentiated smooth muscle cells in the walls of arterioles; responsible for the secretion of renin (increases BP)
What is the function of macula densa cells in the juxtaglomerular apparatus?
Contributes to the control of glomerular filtration rate and to the secretion of renin
What is filtered load?
Mass of material filtered through glomeruli
What is reabsorption?
Process by which material is transported from the tubules to the peritubular capillaries
What is secretion?
Process by which material is transported from peritubular capillaries to the tubules
What is excretion?
Filtered load + reabsorption + secretion
Process by which material moves through the length of the nephron
What is the glomerular filtration rate (GFR)?
Rate at which material/substances are filtered through the glomerular capillaries
Main index of kidney function
What is glomerular filtration?
Bulk flow of fluid from glomerular capillaries into Bowman’s capsule
What is glomerular filtrate?
Fluid within Bowman’s capsule; normally doesn’t contain cells; essentially protein-free; contains most inorganic ions and low molecular weight organic solutes
Describe the flow of filtered substances into Bowman’s capsule

- Fenestrae in the glomerular capillary endothelial layer
- Basement membrane
- Slit in diaphragms between podocyte foot processes
What is the primary function of slit diaphragms of podocyte processes?

Size-selective filter
What are the physical aspects of filtrate that regulate filtration of substances? (2)
- Substance size: > 70 kDa mwt not filtered
- Electrical charge: negatively charged molecules are less filtered (surfaces of filtration barrier coated with polyanions)
Does glucose get completely reabsorbed or secreted in the kidney?
Reabsorbed; no glucose should be present in the urine
What are the physical aspects of the glomerulus-endothelial cell barrier that regulate the filtration of substances?
Permeability: size of spaces/fenestra between endothelial cells; size of spaces between epithelial podocytes of Bowman’s capsule
Volume of filtrate formed per unit time (GFR)
What is a normal GFR for an adult human? (total for two kidneys)
~180 L/day
60 - 125 mL/min
What GFR would indicate renal failure?
< 40 mL/min
What is Kf?
Ultrafiltration coefficient (permeability * surface area of glomerular capillaries)
GFR =?
GFR = Kf * net filtration pressure (NFP)
How is permeability determined in regard to Kf? (2)
- size of space/fenestra between capillary endothelial cells
- Size of pores between epithelial podocytes of Bowman’s capsule
How is surface area determined in regard to Kf?
mesangial (in glomerulus) cell status and number of viable nephrons
What are the components of the Net Filtration Pressure equation?
NFP = (PGC + πBC) - (PBC + πGC)
NFP = (PGC + πBC) - (PBC + πGC)
PGC: glomerular-capillary hydrostatic pressure
πBC: oncotic pressure of fluid in Bowman’s capsule (typically 0 bc no protein in Bowman’s capsule)
PBC: hydrostatic pressure in Bowman’s capsule
πGC: oncotic pressure in glomerular-capillary plasma
What is a normal NFP in humans?
+16 mm Hg
What would be the result of an increased glomerular surface area due to relaxation of glomerular mesangial cells? (Kf)
Hint: GFR = Kf (PGC - PBC - πGC)
Increased GFR
What would be the result of an increase in renal arterial pressure, decrease in afferent-arteriolar resistance, and increase in efferent-arteriolar constriction? (PGC)
Hint: GFR = Kf (PGC - PBC - πGC)
Increased GFR
What would be the result of an increase in intratubular pressure due to an obstruction of tubule or extrarenal urinary system? (PBC)
Hint: GFR = Kf (PGC - PBC - πGC)
Decreased GFR; does not happen often
What would be the result of an increase in systemic-plasma oncotic pressure and decrease in renal plasma flow? (πGC)
Hint: GFR = Kf (PGC - PBC - πGC)
Decreased GFR; increased protein in the blood
What is a normal renal blood flow?
~1.1 L/min
What factors determine RBF? (2)
- mean arterial pressure
- contractile state of renal arterioles
Flow =?
F = (Paorta - Pvenous) / Resistance
F = ∆P/R
What are the functions of renal blood flow? (5)
- Indirectly determines GFR
- Modifies rate of solute and water reabsorption by the proximal tubule
- Participates in the concentration (and dilution) of urine
- Delivers oxygen, nutrients, and hormones to nephron cells; returns CO2 and reabsorbed fluid and solutes to circulation
- Delivers substrates for excretion in urine
What factors influence afferent and arteriolar caliber? (4)
- Renal sympathetic nerves (secrete norepinephrine); renal vasoconstriction
- Renin-angiotensin system
- Autoregulation
- Prostaglandins
How are RBF and PGC affected during renal vasoconstriction? What does this ultimately lead to?
Decreased RBF and Small initial increase in PGC
Ultimately leads to a net decrease in NFP and a small decrease in GFR
What is Angiotensin II and how is it made in the body?
A powerful vasoconstrictor that decreases RBF; part of the renin-angiotensin system
Angiotensinogen is converted to Angiotensin I by action of renin, which is then converted to Angiotensin II by action of angiotensin-converting enzyme (ACE)
What effect does AngII have on the kidneys? PGC? RBF? Kf? GFR?
Constricts both afferent and efferent arterioles (more so efferent)
increasing PGC
decreases RBF
decreases Kf by acting on mesangial cells
decreases GFR
What are the four major inputs that control the production of renin by granular cells of the JG apparatus?
- Intrarenal baroreceptors
- Macula densa
- Renal sympathetic nerves
- Angiotension II (negative feedback inhibition)

How does autoregulation of RBF and GFR occur? (2)
- Myogenic response
- Tubuloglomerular feedback
What is a myogenic response?
Intrinsic property of vascular smooth muscle; tendency to contract when stretched
What is the function of tubuloglomerular feedback (TGF)?
Maintain relatively constant GFR during changes in MAP
How does TGF function? (5 steps)
*Must be within “autoregulatory range”*
- Increased MAP causes increased GFR
- Increased GFR raises flow through tubules
- Increased flow increases delivery to macula densa
- Macula densa triggers release of adenosine by the JGA
- Adenosine constricts afferent arteriole, which increases resistance and decreases PGC which decreases GFR back to normal

What is the autoregulatory range for MAP that allows for TGF to occur?
60-180 mm Hg

What are prostaglandins and what effect do they have on blood vessels?
Metabolites of arachidonic acid produced by renal sympathetic stimulation and angiotensin II; vasodilators
Ex: PGI2 (prostacyclin) and PGE2
How does nitric oxide (NO) affect renal blood flow?
Vasodilator; counteracts angiotensin II and catecholamines; produced by increased shear force on endothelial cells when blood flow increases
How does dopamine affect renal blood flow?
Vasodilator produced by the proximal tubule; increases RBF and inhibits secretion of renin