BIOL 1412 Urinary system

What organs form urine + regulate the composition of blood plasma?

Kidneys

What is the functional unit of the kidney?

Nephron

What 4 structures transport urine?

Renal pelvis, ureters, urinary bladder, urethra

As one of its many functions, what do the kidneys maintain?

Plasma volume (∴ maintain bp [MAP])

What 3 things do the kidneys regulate?

[Ions] + [H₂O], acid-base balance

What 3 things do the kidneys eliminate?

Wastes, drugs, hormones

The kidneys produce + secrete what 2 hormones as per its endocrine function?

Renin + erythropoietin

What is renin secreted to maintain?

Blood pressure

What is erythropoietin secreted for?

RBC production

What are the 2 broad parts of a nephron unit?

Renal corpuscle + tubules

What 2 things is the renal corpuscle made up of?

Glomerulus + renal capsule

What are the 5 tubules of a nephron?

Proximal convoluted tubule (PCT), descending loop (DL), ascending loop (AL), distal convoluted tubule (DCT), collecting duct (CD)

What 3 processes in the nephron lead to urine filtration?

Glomerular filtration → tubular reabsorption → tubular secretion

What is the premise of glomerular filtration?

H₂O + small solutes forced out of blood → glomerulus → Bowman’s capsule

Why does glomerular filtration happen?

Due to pressure differences across the filtration membrane

What is the premise of tubular reabsorption?

Valuable substances are transported from filtrate in nephron → back to bloodstream

What is the premise of tubular secretion?

Additional waste/excess products are actively transported from peritubular capillaries → lumen of nephron (to be excreted as urine)

What are peritubular capillaries?

Tiny blood vessels that wrap around the renal tubules in the kidney

During the process of glomerular filtration, how much plasma in the glomerulus is filtered into Bowman’s capsule?

20%

By what transportation method is plasma filtered into Bowman’s capsule from the glomerulus?

Bulk flow (pressure difference/ΔP across filtration membrane)

What 3 parts make up the filtration membrane?

Glomerulus (fenestrated endothelium), fused basement membranes, podocytes w/ filtration slits between (layer of Bowman’s capsule)

Filtrate is almost identical to plasma, but differs in that it does not contain what?

Large proteins

What 5 things are contained in filtrate, besides ions + vitamins?

H₂O, glucose, aa, urea, some small proteins

What is the approximate pH of filtrate?

~7.45

What are the 4 pressures relating the urinary physiology?

_{HP = Hydrostatic Pressure ~~~ OP = Osmotic Pressure}

Glomerular HP, blood HP, capsular HP, capsular OP

Which pressure represents blood pressure inside glomerular capillaries?

Glomerular HP

What is the pressure of glomerular HP, + does it favour/oppose filtration?

55 mmHg, favours filtration

What is the pressure of blood OP, + does it favour/oppose filtration?

30 mmHg, opposes filtration

What is the pressure of capsular HP, + does it favour/oppose filtration?

15 mmHg, opposes filtration

What is the pressure of capsular OP, + does it favour/oppose filtration?

0 mmHg, favours filtration

Adding up pressures that favour + oppose filtration separately, then calculating the difference leaves us with what Net Filtration Pressure (NFP)?

NFP = (55 + 0) - (30 + 15) = 10mmHg

What is glomerular filtration rate (GFR)?

Amount of filtrate the kidneys filter from the blood into Bowman’s capsules per a chosen unit of time

At an NFP of 10mmHg, there is about ~___L/day of filtrate (both kidneys)

“180”

With both kidneys collectively making ~180L of filtrate a day, how many mL are made per minute?

125mL/min

Normally, one’s entire plasma volume is filtered how many times per day?

~65 times per day

Though one’s plasma volume is continuously being filtered, how much of filtered volume remain at the end of the collecting duct?

< 1%

Why does GFR need to be regulated?

So it doesn’t change when systemic blood pressure changes

If GFR wasn’t kept from changing along with systemic blood pressure, what would happen?

⬆MAP = ⬆GFR

(vise versa)

What can happen if GFR is too high?

Valuable nutrients and H₂O may be lost in the urine (filtrate passes through too quickly for proper reabsorption)

What can happen if GFR is too low?

Blood is not being filtered fast enough, wastes may accumulate in the blood

What 2 regulatory processes are there for GFR?

Intrinsic + extrinsic

Which type of regulation is autoregulation?

Intrinsic regulation

Intrinsic regulation of GFR monitors blood pressure within what range?

Resting to moderate exercise

What are the 2 types of intrinsic regulation for GFR?

Myogenic + juxtaglomerular complex (apparatus)

If ⬆MAP, how does myogenic regulation work (works vise versa)?

Causes a stretch → afferent arteriole sm. musc. contracts → prevents ⬆BP in glomerular capillaries

What monitors [NaCl] in filtrate flowing past it?

Macula densa (specialized cells in the DCT)

As for juxtaglomerular complex (apparatus), what does it mean for [NaCl] if filtrate flow/GFR is high (works vise versa)?

Reabsorption may be inadequate, leaving more NaCl in the filtrate to be excreted as urine

As for juxtaglomerular complex (apparatus), how does GFR return to resting after increasing due to ⬆BP in glomerular capillaries (works vise versa)?

⬆[NaCl] in filtrate at macula dense → afferent arteriole constricts → GFR ⬇ to resting

What is extrinsic regulation primarily controlled by?

SNS

How does the SNS affect both arterioles (afferent + efferent) in a nephron?

Vasoconstricts them

What is the effect of the afferent arteriole constricting?

⬇Flow into glomerulus

What is the effect of the efferent arteriole constricting?

Blood backs up in glomerulus

How would GFR be affected with a moderate SNS activation?

Both arterioles balance → GFR doesn’t change much

How would GFR be decreased by extrinsic regulation under extreme stress?

Constricting afferent arteriole

For what 2 reasons would the afferent arteriole constrict under extreme stress?

Conserve fluid + redirect blood to critical organs

NFP can change from what 2 pressures?

Blood OP + capsular HP

In the case of dehydration, how would blood OP + GFR change (⬆/⬇)?

⬆BOP, ⬇GFR

Why would a higher blood OP = lower GFR?

Because it opposes filtration at the glomerulus

What is nephrotic syndrome?

When proteins leak into the urine (abnormal)

In the case of burns or nephrotic syndrome, how would blood OP + GFR change (⬆/⬇)?

⬇BOP, ⬆GFR

What are 3 given examples of a urinary tract obstruction?

Kidney stones, inflammation, prostate enlargement

How does a urinary tract obstruction affect capsular HP + GFR?

⬆CHP, ⬇GFR

Approximately, how may litres of urine are produced per day?

1-1.5 L/day

Approximately, how many litres of fluid are filtered per day?

180L/day

99% of filtrate is reabsorbed from the tubules into what 2 capillaries?

Peritubular + vasa recta

Tubular reabsorption may be what 2 types?

Active or passive

What 4 things are actively reabsorbed?

Na⁺, some other ions, glucose, amino acids

What 3 things are passively reabsorbed?

Cl^-, H₂O, urea

Proximal Convoluted Tubule (PCT) is un/regulated?

Unregulated

What 2 things are 100% reabsorbed in the PCT via active transport?

Glucose + amino acids

What ion is 65% reabsorbed in the PCT via active transport?

Na⁺

How are small proteins reabsorbed in the PCT?

Endocytosis into tubule cell → amino acids → blood

What 2 additional things are reabsorbed in the PCT?

Vitamins + H₂O (via osmosis - follows solutes)

After the PCT, a large amount of solute has been removed, meaning what for the volume of the filtrate?

It is now reduced

After the PCT, what is the tonicity of filtrate to plasma?

Isotonic

What is the unit of measurement for osmotic pressure?

mOsmoles/L

What is the osmolarity of filtrate after the PCT?

300 mOsm/L

Loop of Henle reabsorbs into what capillary bed?

Vasa recta

What is the only thing that the descending limb (DL) is permeable to?

H₂O (via osmosis)

What is the only thing that the ascending limb (DL) is permeable to?

NaCl (via active transport)

The initial part of the Distal Convoluted Tubule (DCT) reabsorbs what 3 ions?

Na⁺, Cl^-, Ca⁺²

The initial part of the Distal Convoluted Tubule (DCT) is impermeable to what?

H₂O

The later part of the Distal Convoluted Tubule (DCT) + Collecting Duct (CD) reabsorb what 2 things?

Na⁺ + H₂O

What hormone increases Na⁺ reabsorption?

Aldosterone

What hormone decrease Na⁺ reabsorption by inhibiting aldosterone?

ANP (Atrial Natriuretic Peptide)

What hormone increases H₂O reabsorption in the late DCT → CD, which further concentrates the urine?

ADH (antidiuretic hormone)

Nephrons normally reabsorb what percentage of filtered H₂O, NaCl, glucose, + urea, respectively?

H₂O (99%), NaCl (99.5%), glucose (100%), urea (50%)

Filtrate may contain trace amino acids + small proteins, but abnormal underlying causes may cause someone to contain what 2 things in their urine?

Glucose + blood

Tubular secretion involves movement of substances from __________ blood into filtrate of nephron lumen

“peritubular”

What are the 4 main substances that are secreted into filtrate to be eliminated from the body as urine?

Wastes (urea, uric acid, some hormones), K⁺, H⁺ or NH₄⁺

⬆K⁺ by what hormone?

Aldosterone

Why would the body want to eliminate H⁺ or NH₄⁺?

To maintain blood plasma pH

What does the countercurrent multiplier mechanism permit excretion of?

Urine on a spectrum from dilute to concentrated (100-1200mOsm/L)

What does the countercurrent multiplier mechanism produce + maintain?

A vertical osmotic gradient

Does vertical osmotic gradient mean there is more or less [solute] in the ISF as you move deeper into the medulla (i.e. lower down the descending limb)

⬆[solute]

What is the vertical osmotic gradient specifically produced by?

Juxtamedullary nephrons

Within the Loop of Henle, considering the countercurrent multiplier mechanism, fluid flows in parallel tubes (DL, AL) in _________ directions

“opposite”

The ascending limb actively filters the salt/NaCl from filtrate → ISF via what mechanism?

NaCl pump

As filtrate moves down the DL, ___ enters the ISF

“H₂O”

Does concentrated or dilute filtrate enter the AL?

Concentrated with solute (because H₂O was just reabsorbed)