Chapter 19 Flashcards
List + describe the 6 functions of the kidneys.
1) regulation of extracellular fluid volume + blood pressure
2) regulation of osmolarity
3) maintenance of ion balance
4) homeostatic regulation of pH
5) excretion of wastes
6) production of hormones
Know the anatomic relationship between the vascular + tubular elements of the nephron.
look at whiteboard
What are the 3 processes of the nephron.
1) filtration
2) reabsorption
3) secretion
Describe filtration.
- fluid from blood into lumen of the nephron
- occurs at renal corpuscle
- filtered plasma (=filtrate) is excreted unless reabsorbed
Describe reabsorption.
- materials in the filtrate are passed back into the blood
- occurs with peritubular capillaries
Describe secretion.
- materials from blood into lumen of tubule
- occurs with peritubular capillaries
What is the equation for the amount of solute excreted?
amount filtered - amount reabsorbed + amount secreted
Describe the filtration barriers between the blood and the lumen of the nephron, and explain how they can be modified to control filtration.
1) glomerular capillary endothelium –> fenestrated (have pores)
2) basement membrane
3) epithelium of Bowman’s capsule –> foot processes + filtration slits (podocytes)
Describe the pressures that promote and oppose glomerular filtration.
1) capillary blood pressure (PH) –> favors
filtration
- hydrostatic pressure
2) capillary colloid osmotic pressure (π) –>
opposes filtration (pulls fluid back to plasma)
- due to proteins in plasma
3) capsule fluid pressure (P fluid) –> opposes
filtration
- hydrostatic pressure inside Bowman’s
capsule
Define glomerular filtration rate, and give average values for GFR.
glomerular filtration rate (GFR) –> volume of fluid filtered per unit time
avg value –> 180 L/day
what is filtration fraction?
% renal flow that filters into the tubule
What is the net pressure equation for Bowman’s capsule?
P(H) - π - P(fluid) = 10 mmHg into Bowman’s
capsule
What is GFR influenced by?
1) net filtration pressure –> renal blood flow & blood pressure
2) filtration coefficient –> slit surface area (of capillaries) & filtration barrier permeability
Explain how GFR can be influenced by local and reflex control mechanisms.
1) myogenic response –> intrinsic ability of vascular smooth muscle to respond to pressure change (autoregulation)
2) tubuloglomerular feedback (to right) –> paracrine control
- juxtaglomerular apparatus –> macula densa cells detect NaCl in the filtrate + granular cells secrete renin (enzyme)
3) hormones + autonomic neurons –> by changing resistance in arterioles or by altering the filtration coefficient
Increased resistance in the afferent arteriole _________ GFR.
decreases
Increased resistance in the efferent arteriole _________ GFR.
increases
Decreased resistance in the afferent arteriole _________ GFR.
increases
Decreased resistance in the efferent arteriole _________ GFR.
decreases
Describe the steps of tubuloglomerular feedback.
1) GFR increases
2) flow thru tubule increases
3) flow past macula densa increases
4) paracrine signal from macula densa to afferent arteriole
5) afferent arteriole constricts
6) resistance in afferent arteriole increases
7) hydrostatic pressure in glomerulus decreases
8) GFR decreases
Distinguish between transcellular transport and paracellular pathways.
transcellular transport –> (Transepithelial transport) –> Substances cross apical and basolateral membranes of the tubule epithelial cells
Paracellular pathway –> Substances pass through the cell–cell junction between two adjacent cells
Describe and give examples of active and passive reabsorption in the proximal tubule.
Active:
- transport of Na+
- secondary active transport –> symport w/Na+
Passive:
- urea
- endocytosis –> plasma proteins
Define saturation.
maximum rate of transport that occurs when all carriers are occupied by (are saturated with) substrate
Describe the steps in sodium-linked reabsorption.
1) Na+ moves down its electrochemical gradient using the SGLT protein to pull glucose into the cell against its conc. gradient
2) Glucose diffuses out the basolateral side of the cell using the GLUT protein
3) Na+ is pumped out by Na-K-ATPase
Define transport maximum.
the transport rate at saturation
Define renal threshold.
the plasma concentration at which a substance first appears in the urine
Explain and give examples of the importance of tubular secretion in renal function.
- active movement of molecules from extracellular fluid into nephron lumen –> important in homeostatic regulation of K+ and H+
- increasing secretion increases nephron excretion
Explain mathematically and in words the relationship between the excretion of a solute and its renal clearance.
Clearance of X = excretion rate of X (mg/min) / [X]plasma (mg/ml plasma)
*Clearance is a noninvasive way to measure GFR
Explain how clearance can be used as an indirect indicator of renal handling of a solute.
clearance –> Rate at which a solute disappears from the body by excretion or by metabolism
What is the equation for excretion?
Excretion = filtration – reabsorption + secretion
What are the downsides of using insulin and creatinine to measure GFR?
Inulin, plant polysaccharide, freely filters, but is neither reabsorbed or secreted
