Lecture 13: Renal Physiology 1

Question 1

Draw the body composition model

Include solids, water, ICF, ECF, Interstitial, plasma compositions

Answer 1

Ok

Question 2

What is the 60-40-20 rule?

Answer 2

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

Question 3

Why is plasma regulation important?

Answer 3

It can be directly influenced and its effects cross over to ECF, which affects the environment of the ICF

Question 4

What is an important rule about fluid intake and loss?

Answer 4

Body wants to match how much it lost to maintain fluid homeostasis

Question 5

What is third spacing and how does this affect fluid homeostasis?

Answer 5

• 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)

Question 6

What is the significance of semipermeable cell membranes in fluid homeostasis?

Answer 6

Balance achieved by solutes moving, (or if not, water through osmosis) from high to low concentration gradient through the semipermeable membrane

Question 7

Why is the maintenance of ECF volume important?

Why is the maintenance of ECF osmolarity important?

Answer 7

• BP regulation

- cell maintenance so they don’t burst or shrink

Question 8

What are the important characteristics of ICF and ECF?

Answer 8

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

Question 9

What is the difference between electrolytes and non-electrolytes?

Answer 9

NE: do not dissociate in solution, chargeless
E: ionize in solution, charged, have higher osmotic pressure and ability to drive fluid shift

Question 10

Very simply, what does osmolality/osmolarity mean (interchangeable in this class)?

Answer 10

How concentrated the fluid is

Question 11

Polyuria vs Oliguria vs Anuria

Answer 11

> 1.2 L of urine
<1.2 L of urine
No urine production

Question 12

In polydipsia and Diabetes insipidus, what causes polyuria?

Answer 12

Increased water diuresis but no corresponding salt excretion (losing water, leaving salt) = blood more concentrated = thirst

Question 13

What is another cause of polyuria?

Answer 13

Increased water diuresis and salt excretion due to excessive salt intakes (losing both water and salt in urine)

Question 14

What does free water clearance mean and how would you calculate it?
What does a positive free water clearance mean?

Answer 14

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)

Question 15

How can you measure fluid compartments (ICF and ECF)?

What does an indicator mean?

Answer 15

• 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

Question 16

What are plasma volume indicators?

What are ECF indicators?

Answer 16

-albumin, evans blue dye (use volumes of these to estimate plasma volume)
Iothalamate, thiosulfate, inulin (use volumes of these to estimate ECF volumes)

Question 17

How do you calculate plasma osmolarity?

Answer 17

2[Na]

Question 18

What is the Gibbs-Donnan Effect and how does the cell overcome this?

Answer 18

-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)&raquo_space;> Na keeps ECF balance while K maintains ICF balance

Question 19

Why does fluid flow in and out of the capillary ?

Answer 19

• 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

Question 20

Describe the starling forces at the arteriole side vs the venule side

Answer 20

Arteriole side: hydrostatic pressure predominates = fluid pushed out of capillary (filtration)
Venule side: osmotic pressure predominates = fluid pushed into capillary (absorption)

Question 21

What is the plasma colloid osmotic pressure?

Answer 21

Albumin cannot pass through capillary, but negative charge has a pulling force on fluid that keeps it inside the capillary

Question 22

What are the major causes of edema?

How is this treated?

Answer 22

1. Starling force alteration leading to fluid loss (e.g. low albumin = no PC osmotic pressure or lymphatics unable to collect fluid lost)
2. Kidney retaining too much Na+ and water, resulting in increased BP and hypervolemia

Treated with diuretics (excrete all the extra water!)

Question 23

What does an isotonic cell mean?
What does a hypertonic cell mean?
What does a hypotonic cell mean?

Answer 23

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

Question 24

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?

Answer 24

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

Question 25

Crystalloid fluid replacement therapy vs. Colloid fluid replacement therapy

Answer 25

• 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

Question 26

H2O regulates ______ balance which in turn regulates ______ balance

Answer 26

Na+ ; ECF volume/blood serum

(change in H2O balance > change in Na+ balance > leads to change in ECF/body fluid volume balance

Question 27

Hypotonic/Hyponatremic dehydration

Hypertonic/Hypernatremic dehydration:

Answer 27

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

Question 28

Measuring fluid shift:

In simplest terms what does volume contraction and volume expansion mean?

Answer 28

Contraction = volume depletion (concentrated blood)
Expansion = volume expansion (diluted blood)

Question 29

When something is iso/hyper/hyposmotic, what does It refer to?

Answer 29

Body fluid osmolarity (ECF)

Question 30

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?

Answer 30

Ok

-volume; osmolarity

Question 31

Conditions where isosmotic volume contraction happens
Conditions where hyperosmotic volume contraction happens
Conditions where hyposmotic volume contraction happens?

Answer 31

• hemorrhage, diarrhea and vomiting
• dehydration, DI and alcoholism
• adrenal insufficiency (no aldosterone or Na+/water resorption)

Question 32

What happens to heart and kidneys during CHF?

Answer 32

• 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)

Question 33

SNS, RAAS and ADH favors volume ______ and water ______

ANP/BNP/Urodilatin favors volume ______ and water ______

Answer 33

Expansion, retention

Contraction, excretion

Question 34

Draw renin action pathway

Answer 34

Ok

Question 35

effects of Renin
effects of ADH
effects of ANP

Answer 35

• NaCl resportion via aldosterone
• water retention at tubules
• arteriole dilation, increased fluid loss and decreased renin (decreases preload and TPR)