Renal System Physiology 3 - Teel

Question 1

Isosmotic urine:

Hypoosmotic urine:

Hyperosmotic urine:

Answer 1

U/P osmolarity of 1

U/P osmolarity < 1 (less solutes in urine) (lighter) (positive free water clearance)

U/P osmolarity > 1 (more solutes in urine) (darker) (negative free water clearance)

U/P = Urine / Plasma osmolarity

Question 2

Countercurrent multiplication concept

Answer 2

Conditions in descending limb affect conditions in ascending limb

Question 3

Why does osmolarity not change during secretion in proximal tubule?

Answer 3

Equal amount of solute and water secrete, so osmolarity does not change.

Question 4

Thin descending limb

Answer 4

Permeable to water but not solute

Question 5

Thin ascending limb

Answer 5

Permeable to solute. Salt leaves

Question 6

Thick ascending limb

Answer 6

Salt leaves. becomes hypoosmotic

Question 7

Distal tubule

Answer 7

Water and salt reabsorbed

Question 8

Cortical / medullary collecting ducts

Answer 8

water nacl urea can be reabsorbed into medullary interstitium

Question 9

Maximum medullary concentration gradient

Answer 9

1200 mosm/L. This is about 4x osmolarity of plasma (300)

Question 10

Vasa recta definition

Answer 10

Peritubular capillaries that follow loop of henle

countercurrent exchange

Question 11

Vasa Recta facts

Answer 11

Freely permeable, unlike ascending/descending limb
Osmolarity of blood in vasa recta = medullary interstitium
Vasa recta stabilizes medullary concentration gradient.

Question 12

AVP (Arginine vasopressin) mechanism

Answer 12

Stimulates insertion of AQP2 (aquaporins) water channels into apical membranes of tubular principal cells in cortical / medullary collecting ducts

Also stimulates transport of urea from medullary collecting ducts into medullary interstitium.

Question 13

Might be on Quiz:
Where’s most of our body water?

Answer 13

Intracellular fluid: 28 L
Extracellular Fluid: 14 L -> Interstitial fluid 10.5 L (between cells), Plasma 3.5 L

Answer: Intra

Question 14

How to maintain osmolarity of extracellular fluid if its too high?

Answer 14

AVP.

1.) high plasma osmolarity (too much solute in plasma)-> shrinkage of osmoreceptors -> hypothalamus secretes AVP.

Question 15

ADH vs. AVP

Answer 15

ADH is a characteristic of AVP. AVP has an antidiuretic effect.
ADH is just an effective AVP.

Point is its going to affect permeability of nephron / collecting duct which will influence urine output.

Question 16

Factors that stimulate hypothalamic neurons and secretion of AVP:

Answer 16

increased plasma osmolarity
decreased blood volume
decreased blood pressure
nausea
morphine/nicotine/cyclophosphamide

Question 17

What happens when you increase your excretion load of salt?

Answer 17

This can decrease ECF volume (increase osmolarity of ECF)

Question 18

What monitors salt in filtrate

Important quiz question

Answer 18

Macula Densa Cells in distal convoluted tubules monitor salt in tubular fluid.

Granular Cells (juxtaglomerular cells) in afferent arterioles sense osmolarity of blood.

Question 19

JG cells secrete ____ in response to ____.

Answer 19

JG cells secrete renin in response to lower renal perfusion pressure or lower salt load delivered to the macula densa.

Question 20

Renin-angiotensin-aldosterone system

Answer 20

lower MAP -> lower renal perfusion pressure -> renin (from kidney)

Renin makes angiotensinogen (from liver) to angiotensin I

ACE (from lung) converts angiotensin I -> 2

Angiotensin II signals release of Aldosterone (from adrenal gland) and vasoconstriction

Aldosterone -> increase Na+ reabsorption, increase blood volume -> increase MAP
Vasoconstriction -> increase TPR -> increase MAP

All of this is a whole negative feedback loop.

Question 21

Volume contraction

Isosmotic contraction:
Hypoosmotic contraction:
Hyperosmotic contraction:

Answer 21

Isosmotic contraction: water and solutes are lost equally. Maintain normal ECF
Hypoosmotic contraction: solutes are lost and not replaced in ECF-> hyponatremia
Hyperosmotic contraction: loss of more water than solutes -> hypernatremia

Question 22

Volume Expansion

Isosmotic expansion:
Hypoosmotic expansion:
Hyperosmotic expansion:

Answer 22

Isosmotic expansion: occurs with excess intake of 0.85% saline (same conc. as plasma)
Hypoosmotic expansion: occurs with intake/retention of pure water.
Hyperosmotic expansion: occurs with drinking / IV infusion of hypertonic solutions. Water moves into ECF

Question 23

extra: Difference between osmolarity and tonicity

Answer 23

tonicity: effect of concentration on osmolarity

Question 24

When does edema occur?

Answer 24

When filtration forces exceed reabsorption (increase CHP, increase TOP, decrease POP)
increased permeability of systemic capillaries too.

Review: Hydrostatic pressure makes it go away from start point. Oncotic pressure makes it bring towards it.
Capillary hydrostatic pressure = goes out of capillaries
tissue oncotic pressure = goes out of capillaries
plasma oncotic pressure = goes out of tissue
tissue hydrostatic pressure = goes out of tissue

Question 25

Congestive heart failure (CHF)

Answer 25

Hearts not pumping efficiently. Tend to retain fluids, leading to increase of blood volume in capacitance vessels (veins). body misinterprets this thinking its hypovolemia, so it increases AVP and RAA.

Question 26

Nephrotic syndrome

Answer 26

Results in more plasma proteins being filtered out than it should be, thus decreasing POP, increases RAA activity -> retention of salt/water

Question 27

Cirrhosis

Answer 27

Renal retention of NaCl and water -> increased intravascular volume -> increased CHP. Decrease synthesis of albumin -> decrease POP.

Question 28

What diseases cause edema?

Answer 28

caused b y altered starling forces.
CHF
Nephrotic syndrome
Cirrhosis of the liver
Cyclic Edema (female menstrual cycle)
NSAIDS

Question 29

Hypernatremia
Hyponatremia
Hyperkalemia
Hypokalemia

Answer 29

Hypernatremia: excess intake of salt
Hyponatremia: Not enough salt
Hyperkalemia: excess potassium
Hypokalemia: not enough potassium

Question 30

Volatile problem for ventilation:

How to handle it?

Answer 30

Retain CO2, you’re going to create acid condition in blood. get rid of too much, you create alkaline problem.

Handle by breathing

Question 31

Non volatile problem in kidneys:

How to manage this?

Answer 31

metabolic reactions can create nonvolatile acids like h2so4, h3po4, urea, etc.

Handle by reclaiming filtered bicarbonate.

In bowman’s capsule: we filter tons of things like bicarbonate. Bicarbonate has an alkaline effect, so if you lose it, it impacts pH of blood, so u don’t normally want to lose it. So you reabsorb it.

Question 32

Mechanism of reabsorption of HCO3-

Answer 32

80% in proximal tubules, 10% distal tubular a-intercalated cells.

In Tubule lumen, bicarbonate is broken into CO2 and Water, where it can pass through basolateral membrane. It converts back to bicarbonate in the tubule cell, then exits through apical membrane to interstitial space. It is thus reabsorbed.

Tubular cell MUST secrete a H+ ion to convert OH- to H2O in lumen so H2O can thus go into tubular cell.

Question 33

Titratable acid

Answer 33

H+ that is secreted into lumen can acidify HPO4 2- to H2PO4 -. Makes it less basic and more acidic in lumen.

Question 34

Ammonium excretion

Answer 34

Tubule cells can metabolize glutamine. When they do this, they can generate 2NH4+., 2 H+, 2 NH3.

NH3 secreted into tubular fluid, combines with secreted H+ and makes NH4+ in lumen. When this happens, a new HCO3- is formed.

Question 35

How is NH4+ recycled / reabsorbed?

Answer 35

NH4+ in tubular fluid is reabsorbed into medullary interstitium from TAL. It recycles by reentering thin regions of ascending/descending limbs and medullary collecting ducts.

Question 36

Purpose of upregulating glutamine metabolism?

Answer 36

Helps get rid of acid. Helps reclaiming filtered bicarbonate, and generating hydrogen ions in exchange for bicarbonate.