Urinary System Flashcards
Is the blood flow to the kidneys just enough to oxygenate the kidneys, or more?
no, they receive much more blood than they need because they condition the blood
What is a nephron?
smallest unit of the kidney that performs all of the kidneys functions
What are the two regions of the kidney?
renal cortex and renal medulla
Could you name and describe the components of a nephron?
glomerulus: ball like tuft of capillaries where some water and solutes are filtered from the blood
afferent arterioles
efferent arterioles
peritubular capillaries: supply renal tissue and aid in reabsorption and secretion to form urine
bowman’s capsule: hollow tube surrounding glomerulus, filtered plasma flows into
What is the difference between cortical nephrons and juxtomedullary nephrons?
the difference between the two is the length…
cortical (80% nephrons, short loop) and juxtomedullary (20% nephrons, long loop)
What is the path of filtrate from its formation to the renal pelvis?
bowman’s capsule -> proximal tubule -> loop of Henle -> juxtaglomerular apparatus -> distal tubule -> collecting duct -> renal pelvis
What are the three layers of the glomerular membrane and what do they do?
1.) glomerular capillary wall: 100 x more permeable to H2O and solutes than other capillaries in the body
2.) basement membrane: layer of collagen (strength) and glycoprotein ( negative charge repels small plasma proteins)
3.) inner layer of bowman’s capsule: consists of podocytes (epithelial cell that encircles glomerulus, form filtration slits)
What the three basic renal processes?
1.) glomerular filtration
2.) tubular reabsorption
3.) tubular secretion
Which glomerular force pull plasma into the capillaries?
plasma colloid osmotic pressure: plasma proteins are stuck in the capillaries, displacing H2O
Bowman’s capsule hydrostatic pressure: pressure exerted by the fluid in the capsule push fluid back into capillaries
Which glomerular force push plasma out of the capillaries?
glomerular capillary pressure: blood pressure remains high in afferent arterioles
What forces cause plasma to leave the glomerular capillaries and enter Bowman’s capsule?
1.) glomerular capillary pressure
2.) plasma-colloid osmotic pressure
3.) bowman’s capsule hydrostatic pressure
Why is glomerular pressure typically higher than in systemic capillaries?
efferent arteriole is much smaller diameter than the afferent arteriole, creating a higher vascular resistance in the efferent arteriole
What is the glomerular filtration rate (GFR) and what factors does it depend on?
GFR: volume entering Bowman’s capsule per minute
depends on…. net filtration pressure and filtration coefficient
Define filtration coefficient
encompasses surface area available to diffuse thru, and permeability of glomerular membrane
How does arterial blood pressure affect glomerular capillary pressure?
increased arterial blood pressure increases capillary pressure
How does increased arterial blood pressure affect plasma-colloid osmotic pressure? How does it affect the GFR?
does not change the plasma colloid osmotic pressure, but a greater arterial blood pressure means a greater GFR
What are the two intrinsic mechanisms used by the kidneys to counteract changes in GFR?
myogenic and tubuloglomerular feedback
Define myogenic mechanism
stretch of afferent arteriolar smooth muscle (due to increased arterial blood pressure) causes automatic contraction.
tubuloglomerular feedback
in the juxtaglomerular apparatus, tubular cells in the macula densa sense increased or decreased GFR via increased salt concentration
what is the macula densa?
tubular cells in the glomerulus that releases cytokines, which activate granular smooth muscle cells to contract or dilate around afferent arteriole (increase or decrease glomerular capillary blood pressure)
How can GFR be controlled extrinsically?
by the sympathetic nervous system (no parasympathetic innervation)
How does the sympathetic nervous system control glomerular filtrate rate?
arteriolar vasoconstriction, increase cardiac output, mesangial cell contraction
What are mesangial cells, and how are they affected by sympathetic activity?
cells that hold the glomerular capillary bundle together
What are mesangial cells, how are they affected by sympathetic activity?
cells that hold the glomerular capillary bundle together
What is the difference between passive and active reabsorption?
in passive transport no steps require energy to move substance down gradient. In active transport one or more steps of transepithelial transport require energy to be used to move solute against the gradient
What is transepithelial transport?
movement of substances across epithelial cell layers (5 key layers)
What 5 layers must filtrate in the tubules pass thru?
1.) luminal membrane
2.) cytosol of tubular cell
3.) basolateral membrane
4.) interstitial fluid
5.) peritubular capillary wall
Where are the luminal and basolateral membranes?
luminal membrane: plasma membrane of tubular epithelial cell facing lumen
basolateral membrane: plasma membrane of tubular epithelial cell facing interstitial fluid
How is Na+ reabsorption regulated?
1.) Na+/K+ pump in basolateral membrane of tubular cells (dumps Na+ from tubular cell into interstitial fluid of kidney)
2.) Na+ leak channels or passive carriers in luminal membrane (allows Na+ to pass from tubule lumen to tubule cell)
What is the Na+ load? How does the Na+ load affect blood pressure?
Na+ load: total amount of Na+ in the body (not the same as concentration)
How does the Na+ load affect blood pressure?
greater salt load increases osmotic gradient -> leads to water retention (increased ECF volume) -> increased blood plasma -> increased blood pressure
How does Na+ reabsorption occur in distal tubules and collecting ducts?
controlled by hormones based on the Na+ load
ex: large Na+ load -> hormonal action -> more NaCl and H2O excreted
When is renin released? Where is it released from?
in response to reduced salt, ECF volume or blood pressure, granular cells of the juxtaglomerular apparatus (in kidneys) release renin
Where does angiotensin come from?
renin converts angiotensinogen to angiotensin I, which is then converted to angiotensin II (by angiotensin-converting enzyme, from lungs)
Where does aldosterone come from? What does it do?
release is triggered by angiotensin II
promotes insertion of additional Na+ leak channels into luminal membrane and Na+/K+ pumps into basolateral membrane (increases Na+ reabsorption)
What do ANP and BNP do with respect to Na+ reabsorption and arterial blood pressure?
1.) decrease Na+ reabsorption by kidney tubules
2.) decrease RAAS
3.) dilate afferent arterioles
4.) decrease SNS activity (decrease cardiac output, decrease total peripheral resistance)
What is Natriuresis
excretion of large amounts of Na+ in the urine
What is secondary active transport?
glucose and amino acids reabsorbed from filtrate back into peritubular capillaries using energy from Na+ gradient
How is reabsorption of glucose accomplished?
1.)Na/K pump sets up a low gradient in the cell
2.) Sodium and glucose cotransporter (SGLT): moves Na+ down its gradient in order to move glucose against its gradient
3.) glucose transporter (GLUT): facilitated diffusion moves glucose down its concentration gradient
Are both SGLT and GLUT secondary active transporters?
SGLT = secondary active transporter
GLUT = passive facilitated diffusion
What are the forces that drive water from the filtrate into the peritubular capillaries? How is Na+ involved with this?
1.) hydrostatic pressure built up in interstitial fluid from osmotic flow out of tubular cells
2.) plasma-colloid osmotic pressure from greater concentration of plasma proteins leftover in capillary blood (pulls water in)
What are aquaporins?
channels that allow for fast H2O movement
What is urea? Does all of it get reabsorbed?
waste product from the breakdown of protein, becomes increasingly concentrated down proximal tubule as H2O is reabsorbed… half of filtered urea gets reabsorbed (other half excreted in urine)
What is a tubular maximum? Does it occur for both passively and actively reabsorbed solutes?
maximum reabsorption rate that occurs when all carriers for the solute are saturated; occurs for actively reabsorbed substances
What is the filtered load? How is it calculated?
quantity of a substance filtered at the glomerulus per minute
filtered load = plasma concentration x glomerular filtration rate (GFR)
What is the renal threshold?
plasma concentration of a solute at which tubular maximum is reached
What happens if the plasma concentration of a solute is below the renal threshold?
if a plasma concentration is below the renal threshold the kidney will be able to reabsorb all of it.
What happens if the plasma concentration of a solute is above the renal threshold?
some of the solute is not reabsorbed and therefore excreted in the urine
Do the kidneys normally regulate glucose concentration in the blood? Why or why not? How about phosphate and Ca2+ concentration?
Not normally, in normal conditions glucose levels remain well below their renal threshold…. kidneys only regulate glucose in situations like diabetes
phosphate and Ca2+ are regulated by kidneys because their normal plasma concentration are equal to their renal threshold (any additional is immediately excreted)
Besides decreased Na+ load, what is the other way that aldosterone is increased? What does it do regarding this other ion?
increased plasma K+ triggers release of aldosterone from the adrenal cortex. Which then increased tubular K+ secretion and urinary K+ excretion
If a substance is filtered, but NOT reabsorbed OR secreted, how will its plasma clearance rate compare to the GFR? Why?
Recall, average GFR = 125 mL/min of plasma
Plasma clearance rate = GFR
complete volume filtered (GFR) is cleared = 125 mL/min
If a substance is filtered AND reabsorbed, how will its plasma clearance rate compare to the GFR? Why?
Regardless if it is completely or partially filtered and reabsorbed, the PCR is always less than the GFR
If a substance is filtered and secreted, but not reabsorbed, how will its plasma clearance rate compare to the GFR?
always greater than the GFR
Why do some organic ions not get filtered but need to be secreted?
1.) speeds the removal of blood-borne chemical messengers and potentially toxic foreign compounds
2.) removal of organic ions poorly soluble in water, and therefore not excreted by glomerular filtration
What is the plasma clearance rate?
volume of plasma cleared of a particular substance by the kidneys per minute (not the same thing as the volume of urine)
What are the differences between the ascending and descending limbs of the long loop of Henle?
Ascending:
1.) actively transports NaCl out of tubule
2.) is impermeable to H2O
Descending:
1.) does not reabsorb NaCl
2.) highly permeable to H2O via aquaporins
Is the osmolarity of the interstitial fluid the same throughout the medulla of the kidneys? What causes this? How about in the cortex?
The deeper into the medulla the higher the osmolarity gradient. the Na+/K+ pump can create a 200 mOsm/L gradient… countering currents multiply this effect across the vertical gradient (countercurrent multiplication)
is constant in cortex
How does the osmolarity of filtrate change throughout the long loop of Henle? Is it more or less dilute when it comes out?
Filtrate entering the loop of Henle has an osmolarity of 300 mOsm/L, and when it exits the osmolarity decreases to 100 mOsm/L… it is MORE dilute than what came in
What does vasopressin do? How?
Vasopressin increases H2O permeability in the distal and collecting tubes of the loop of Henle… Does this by triggering the insertion of new aquaporins into the luminal membrane
Would water be reabsorbed in the absence or presence of vasopressin?
Water is reabsorbed when vasopressin is present.
Is the blood leaving the kidneys hypertonic or isotonic? Why?
Blood leaving the kidneys is isotonic because blood exits the medulla (entering the vein) at the same osmolarity as when it entered. It maintains the vertical concentration gradient (countercurrent exchange)
What structures prevent urine flow thru the urethra?
1.) internal urethral sphincter
(fold in the bladder wall)
2.) external urethral sphincter (skeletal muscle)
What triggers the micturition reflex? What signal does this reflex send to the external urethral sphincter?
Bladder stretch receptors project to spinal cord, which supplies parasympathetic innervation of bladder smooth muscle.
Which of the urination muscles do we have voluntary control over?
external urethral sphincter
Which branch of the autonomic nervous system controls bladder emptying?
parasympathetic nervous system
