Renal Systems Flashcards
Effective osmolality equation (calculate in renal patients like you would do AG or winters. Don’t skip on this equation). Normal range:
2 (Na+ plasma) + (plasma Glucose/18)
Normal range: 285-295 mOsm/kg serum H2O
Body’s default physiologic state
Conservation (antidiuresis)
AVP (ADH, Vasopressin)
Arginine vasopressin: Works to increase bp. Secreted from posterior pituitary. Triggers Aquaporins
Where is most fluid stored?
In the cells (intracellularly). Note that the least amount of fluid is stored in blood. Also note Oxidation of carbs, protein, and fats produces water. (eating food, and drinking it gives us water)
How do we lose water?
Urine, FECES, sweat, respiratory. Note that we MAY or MAY NOT know we are losing it.
Why is intracellular and interstitial (1st and 2nd place respectively) water important?
They act as reserves in cases of low bp and blood volume
What is special about effective circulating volume (ECV)?
Effective circulating pressure is approximately equal to perfusion pressure. ECV is the pressure sensed by baroreceptors and afferent arterioles (kidneys) in the carotid sinus. We can’t sense volume, so we sense pressure instead.
What 3 things contribute to venous return? Difference between stressed and stressed volume.
Mean systemic filling pressure (Pmcf), RA pressure, and vascular resistance Stressed becomes stressed volume. Used to generate perfusion pressure.
Pathway of congestive heart failure in euvolemic patient. 1. Heart fails. Note: ECF = plasma + interstitium. Cost and benefit analysis of this compensatory pathway
- Decreased CO.
- Reduece effective circulating volume due to low pressure at baroreceptors
4.Compensation by fluid retention at kidneys (note sns did not kick in to increase hr and inotropy for an increase in perfusion) - Expansion of extracellular fluid volume depletion in face of increased extracellular volumes
End result: EFFECTIVE volume takes the L (less blood is in circulation). However, there is an increase in plasma and extracellular volume (edema).
Benefit: increased intracardiac filling pressure (RAP).
Cost: Volume overload and pulmonary/peripheral edema
Osmole
Total particle in solution. Effective osmoles creates osmotic pressure, used o drive fluid direction
Main (MOST) effective osmole
Na+. NEEDS an active transport (which is why it’s so effective). Effects body water distribution.
What is an effective osmole?
Osmole which stays in compartment unless transported by active transport into another compartment. Tends to hold onto H2O in the compartment that the osmole lives.
Describe glucose as an osmole
Effective osmole. Needs primary or secondary active transport. Does not create large osmotic gradient like Na+ (most of glucose is in muscle or brain, so it doesn’t have a deep enough squad to do so). If you screw up Glucose re-uptake (insulin deficiency or resistance) in blood, it stays there
Describe BUN (blood urea nitrogen) as an osmole
Ineffective. Lipid soluble, so it readily equilibriates between plasma membranes,
Plasma: Na+ K+ Cl- Glucose (F) BUN Osmolality Specific gravity
Plasma: Na+ 136-145 meq/L (140) K+ 3.5-5.0 meq/L (4) Cl- 98-106 meq/L (100) Glucose (F) 75-115 mg/dl (<110) BUN 10-20 mg/dl (10) Osmolality 285-295 mOsm/kg (290) Specific Gravity (1.005 - 1. 030)
Why do you need Na, K, Cl, and Ca? How does water fit into this?
All of these ions ore osmoles used to keep H2O in the body. Separately, they deal with electrophysiology (Na and K), Acid Base (Cl-), and Contractility (Ca)
Na flows (in/out) K flows (in/out)
Na flows into cell, K flows out
Describe the blood path from the renal artery, bypassing proximal tubule. Job of peritubular capularies
Renal artery –> Afferent arteriole –> glomerulus –> efferent arteriole –> vasa recta –> renal vein
Peritubular caps. are ion destination during reabsorption/ ion source during secretion. They also keep kidneys alive.
Job of glomerulus
Filtration. 100%. Nothing else. Filtration occurs no where else either.
What gets filtered in glomeruli?
Everything, including small proteins (albumin). 100% of albumin is reabsorbed in a normal glomeruli. Same as RBCs.
Job of secretion
Osmoles from the efferent arteriole, peritubular caps., or just interstitium are transported INTO the lumen of the proximal tubule to become a part of forming urine.
Job of reabsorption
Opposite of secretion. Moving stuff from forming urine in proximal tubule into the interstitium (efferent arteriole) to eventually, likely, become of the the blood circulation
What creates filtration barrier of glomerulus?
Podocytes and their foot processes, as well as filtration slits.
Describe filtering fate of the following osmoles:
- Most proteins
- Inulin (NOT INSULIN!)….note that this is no longer used to measure kidney function
- Urea
- Glucose
- Creatinine (kidney function measuring standard)
- Most proteins - NOT filtered. Clearance through gfr = 0 (as in, you will NORMALLY not find this in urine)
- Inulin (NOT INSULIN!) - Filtered. Not reabsorbed, Not secreted. Clearance therefore = GFR (100% of the cleared inulin will be found in the urine)
- Urea - Filttered, partially reabsorbed. Clearence is therefore less than GFR
- Glucose - Filtered, completely reabsorbed. Clearance = 0 (will NOT find in urine, NORMALLY)
- Creatinine - Filtered and secreted. Clearence is about the same as GFR