Lecture 13: Renal Physiology 1 Flashcards
Draw the body composition model
Include solids, water, ICF, ECF, Interstitial, plasma compositions
Ok
What is the 60-40-20 rule?
60% of body weight = water
40% of body weight (2/3 of body water) = ICF
20% of body weight (1/3 of body water) = ECF
Why is plasma regulation important?
It can be directly influenced and its effects cross over to ECF, which affects the environment of the ICF
What is an important rule about fluid intake and loss?
Body wants to match how much it lost to maintain fluid homeostasis
What is third spacing and how does this affect fluid homeostasis?
- Fluid leaks into non-functional area of cells and are trapped there because cells cannot transport them properly (e.g. liver dz, burn)
- body is losing and wasting intravascular fluids (fluid just builds up with no use)
What is the significance of semipermeable cell membranes in fluid homeostasis?
Balance achieved by solutes moving, (or if not, water through osmosis) from high to low concentration gradient through the semipermeable membrane
Why is the maintenance of ECF volume important?
Why is the maintenance of ECF osmolarity important?
- BP regulation
- cell maintenance so they don’t burst or shrink
What are the important characteristics of ICF and ECF?
ICF: more K+, PO4 3-, cell proteins cannot get through membrane
ECF: more Na+, Cl- and HCO3-
*this balance is maintained by the Na/K ATPase
What is the difference between electrolytes and non-electrolytes?
NE: do not dissociate in solution, chargeless
E: ionize in solution, charged, have higher osmotic pressure and ability to drive fluid shift
Very simply, what does osmolality/osmolarity mean (interchangeable in this class)?
How concentrated the fluid is
Polyuria vs Oliguria vs Anuria
> 1.2 L of urine
<1.2 L of urine
No urine production
In polydipsia and Diabetes insipidus, what causes polyuria?
Increased water diuresis but no corresponding salt excretion (losing water, leaving salt) = blood more concentrated = thirst
What is another cause of polyuria?
Increased water diuresis and salt excretion due to excessive salt intakes (losing both water and salt in urine)
What does free water clearance mean and how would you calculate it?
What does a positive free water clearance mean?
how much free water excreted (is urine too diluted or concentrated)
CH20 = V - Cosm = V - (Uosm x V/Posm)
Excess water excreted (negative is vice versa)
How can you measure fluid compartments (ICF and ECF)?
What does an indicator mean?
- Use volume of indicator to estimate the volume of the compartment
- if its an indicator for a compartment, it will go to that compartment and not into others
What are plasma volume indicators?
What are ECF indicators?
-albumin, evans blue dye (use volumes of these to estimate plasma volume)
Iothalamate, thiosulfate, inulin (use volumes of these to estimate ECF volumes)
How do you calculate plasma osmolarity?
2[Na]
What is the Gibbs-Donnan Effect and how does the cell overcome this?
-Negative charges in the ICF creates a gradient that allows ions into the cell
Causes water to follow the ions to try and dilute it leading to cell swelling
-Na/K ATPase keeps the ion balance (3Na out/2 K in)»_space;> Na keeps ECF balance while K maintains ICF balance
Why does fluid flow in and out of the capillary ?
- Pressure gradient that encourages flow from high pressure to low pressure (maintained by Starling forces)
- Also water much more permeable to capillaries than blood, so it flows out easier
Describe the starling forces at the arteriole side vs the venule side
Arteriole side: hydrostatic pressure predominates = fluid pushed out of capillary (filtration)
Venule side: osmotic pressure predominates = fluid pushed into capillary (absorption)
What is the plasma colloid osmotic pressure?
Albumin cannot pass through capillary, but negative charge has a pulling force on fluid that keeps it inside the capillary
What are the major causes of edema?
How is this treated?
- Starling force alteration leading to fluid loss (e.g. low albumin = no PC osmotic pressure or lymphatics unable to collect fluid lost)
- Kidney retaining too much Na+ and water, resulting in increased BP and hypervolemia
Treated with diuretics (excrete all the extra water!)
What does an isotonic cell mean?
What does a hypertonic cell mean?
What does a hypotonic cell mean?
ECF [NaCl] = 0.85% of ICF/300 mOsm > remains same size
ECF [NaCl] > 0.85% of ICF/400 mOsm > cell shrinks
ECF [NaCl] <0.85% of ICF/200 mOsm > cell swells
What happens to plasma osmolarity during ECF volume loss and ECF volume gain?
What happens to hematocrit osmolarity during ECF volume loss and ECF volume gain?
What happens to hematocrit osmolarity during ICF volume loss and ICF volume gain?
Plasma:
ECF volume loss = concentrated plasma
ECF volume gain = diluted plasma
Hematocrit:
ECF volume loss = hematocrit increase (concentrated blood)
ECF volume gain = hematocrit decrease (concentrated blood)
ICF volume loss = fluid flows into ECF = diluted blood/RBCs shrink
ICF volume gain = fluid flows into ICF = concentrated blood/RBCs swell
Crystalloid fluid replacement therapy vs. Colloid fluid replacement therapy
- salts that do not cross the cell membrane thus acts on the ECF (e.g. glucose, lactated ringers and saline)
- large molecules (albumin) that don’t cross the cell membrane. Generate osmotic pressures that pulls fluid from the cell into the blood to compensate for systemic fluid loss
H2O regulates ______ balance which in turn regulates ______ balance
Na+ ; ECF volume/blood serum
(change in H2O balance > change in Na+ balance > leads to change in ECF/body fluid volume balance
Hypotonic/Hyponatremic dehydration
Hypertonic/Hypernatremic dehydration:
Losing more Na+ in the ECF than H2O causing water to flow into more concentrated ICF = blood losing water
Losing more H2O in the ECF than Na+ causing water to flow from ICF to ECF = cells losing water
Measuring fluid shift:
In simplest terms what does volume contraction and volume expansion mean?
Contraction = volume depletion (concentrated blood) Expansion = volume expansion (diluted blood)
When something is iso/hyper/hyposmotic, what does It refer to?
Body fluid osmolarity (ECF)
Using slide table, predict the changes in ECF volume, ICF volume, Hct, osmolarity and plasma protein in various conditions of volume contraction and expansion
The x axis of the Darrow Yannet diagram represents while the y axis of the diagram represents?
Ok
-volume; osmolarity
Conditions where isosmotic volume contraction happens
Conditions where hyperosmotic volume contraction happens
Conditions where hyposmotic volume contraction happens?
- hemorrhage, diarrhea and vomiting
- dehydration, DI and alcoholism
- adrenal insufficiency (no aldosterone or Na+/water resorption)
What happens to heart and kidneys during CHF?
- Heart fails > low CO > low BV, low BP
- Kidney freaks out > stimulate SNS, RAAS, ADH > increase BV, BP by reabsorbing salt and water > fluid overload (edema)
SNS, RAAS and ADH favors volume ______ and water ______
ANP/BNP/Urodilatin favors volume ______ and water ______
Expansion, retention
Contraction, excretion
Draw renin action pathway
Ok
effects of Renin
effects of ADH
effects of ANP
- NaCl resportion via aldosterone
- water retention at tubules
- arteriole dilation, increased fluid loss and decreased renin (decreases preload and TPR)
