Exam 6 - Fluid Compartments & Urine Formation Flashcards
Why kidneys are important
- maintaining constant and appropriate volumes and composition of body compartments
Normal fluid intake
2300 mls / day
- ingested fluids: 2100 mls
- oxidation of carbs: 200 mls
Fluid output
2300 mls/day
- urine: 1400 mls
- Insensible loss via respiratory/skin: 700 mls
- sweat: 100 mls
- feces: 100 mls
Total body fluid
Male: 60% of body weight
Female: 50% of body weight (more fat)
- decreases with age
ECF
- 20% of weight
- 1/3 of total water volume
- Interstitial = 75%
- Plasma = 25%
- Transcellular fluid = 1-2 L
ICF
- 40% of weight
- 2/3 of water volume
- cell composition very consistent
- 100 trillion cells
Gibbs-Donnan Equilibrium
- how ions are distributed on either side of semi-permeable membrane….with non-permeable ions on one side
At equilibrium:
- product of diffusible ions EQUAL
- sum of all cations = sum of anions…on each side
Produces:
- different [ ] of ions on each side w/o need for pump mech
[Na]
In: 10 mEq/L
Out: 142
[K]
In: 140 mEq/L
Out: 4
[Ca]
In: 0.0001 mEq/L
Out: 2.4 mEq/L
[Mg]
In: 58 mEq/L
Out: 1.2
[Cl]
In: 4 mEq/L
Out: 103
[PO4]
In: 75 mEq/L
Out: 4
[HCO3]
In: 10 mEq/L
Out: 28
[Protein]
In: 40 mEq/L
Out: 5
[Glucose]
In: 0-20 mEq/L
Out: 90
pH
In: 7.0
Out: 7.4
[phospholipids in plasma]
280 mg/dl
[cholesterol in plasma]
150 mg/dl
[fat in plasma]
125 mg/dl
[glucose in plasma]
100 mg/dl
[urea in plasma]
15 mg/dl
[lactic acid in plasma]
10 mg/dl
[uric acid in plasma]
3 mg/dl
[creatinine in plasma]
1.5 mg/dl
[bilirubin in plasma]
0.5 mg/dl
[bile salts in plasma]
Trace amounts
Plasma-interstitial water distribution forces
- forces that move fluid in/out of caps
- cap/interstitial hydrostatic
- cap/interstitial oncotic
Intracellular-extracellular water distribution
- controlled by osmotic effect of Na and Cl across membrane
- water moves across membrane in or out to keep ICF isotonic with ECF
1 osmole
1 mole of particles (6.02x10^23) in solution
Plasma mOsm
301.8
Interstitial mOsm
300.8
Intracellular mOsm
301.2
- higher than interstitial due to Donnan effect
- more protein inside of cell
Osmotic pressure of 1 mOsm
- 3 mmHg
- small change in [solute] will shift large volume of H2O creating large fluid shifts
Isotonic solution
- won’t upset osmotic balance
- 0.9% NaCl
Crenate / Crenation
- Cell shrivels up
Osmolarity difference - Intracellular vs extracellular
- quickly corrected….within seconds
- but takes time for equilibrium to be reached throughout entire body
Causes:
- water ingestion
- dehydration
- diarrhea
- massive sweating or fluid loss via kidneys
- CPB
Adding NS to patient
- No change in ECF osmolarity
- Expand ECF volume by amount added
- within 15 min…75% of volume will end up in interstitial….causes edema
Adding hypertonic solution to patient
- ECF osmolarity will increase
- [ECF] > [ICF]….water from ICF to ECF
- Overall increase in osmolarity
- ECF volume increases (more than volume added)
- water added + water shift - ICF volume decreases
- do practice problems*
Assumed normal mOsm/L
280
Adding hypotonic solution to patient
- ECF osmolarity < ICF osmolarity…water moves from ECF to ICF
- Overall decrease in osmolarity
- ECF volume increases
- ICF volume increases
- Do practice problems*
Nutrient solutions for patient
- glucose most common….but…patients normally high glucose on CPB
- isotonic or nearly to (or given slow to keep equilibrium)
- as nutrients metabolized, water left over….
- removed via kidneys
Plasma [Na]
- Na and Cl make up 90% of solute in ECF
- big controllers of osmolarity
- 142 mEq/L
- [Na] and osmolarity go hand in hand
Hypernatremia
High plasma Na
Hyponatremia via Na loss from ECF
- Low plasma Na
- decrease in ECFV
- Increase in ICFV
Causes
- diarrhea/vomiting
- diuretic overdose
- renal disease
- Addison’s disease
Hyponatremia via excess water to ECF
- decrease plasma [Na]
- Increase ECFV
- Increase ICFV
Causes:
- excess water retention
- excess ADH
Consequences of Hyponatremia
- Cell swelling (bad in brain)
- Headache, nausea, lethargic, disoriented
- if [ ] falls to 115-120
- seizures
- coma
- brain damage
- death
- Brain tries to move ions from cells to ECF
- don’t treat too quick…10-12 mmol/L over 24 hrs
- most common electrolyte disorder (25%)
Hypernatremia via water loss from ECF
- increased plasma [Na]
- decrease ECFV
- decrease ICFV
Causes:
- No ADH…very dilute urine
- excess sweating
Hypernatremia via excess Na to ECF
- increased plasma [Na]
- increased ECFV
- decreased ICFV
Causes:
- excess aldosterone (reabsorb H2O and Na…but more Na)
Consequences of Hypernatremia
- cells shrink
- not as common as hypo
- need 158-160 mEq/L
- slow correction best
Intracellular edema
Causes:
- hyponatremia
- decreased cell metabolism
- less Na/K pump activity…Na into cell…less Na out
- no nutrition to cells
- inflammation
- cell membrane permeability goes up…Na into cell
Extracellular edema
Causes:
- leakage of fluid from plasma to interstitial
- failure of lymphatics to return fluid from interstitial to vascular system
look at causes on page 297
Big picture renal function
- control volume/composition of body spaces
- keep homeostatic environment
- by controlling [Na]
- Rid body of wastes produced by body or ingested
- FILTER plasma into tubules
- REABSORB much of the filtrate back to blood
- SECRETE substances from blood into tubules
- usually active process
- substances secreted or NOT reabsorbed are excreted in urine
3 types of gradients
- osmotic
- electrical
- solute
More specific renal functions
- water and electrolyte balance
- Osmolality and electrolyte [ ]
- regulation of BP
- regulation of acid-base balance
- prevent acidosis/alkalosis
- on CPB…acidosis more common…we control respiratory
amino acid metabolism waste
Urea
Muscle creative waste
Creatinine
Nucleic acid waste
Uric acid
Hemoglobin break down waste
Bilirubin
Renal response to Na intake
- able to respond to huge differences in Na intake with small changes to ECFV or [Na]
- also true for most other electrolytes
Kidney / lung and body buffer systems
- Lungs remove CO2
- Kidneys control [bicarb] and [H]
- Kidneys only way to remove sulfuric/phosphoric acid
- byproducts of protein metabolism
RBC production
- kidneys secrete erythropoietin (almost all)
- stimulate RBC production when hypoxic
- Severe renal disease leads to severe anemia due to lack of erythropoietin
Glucose and kidneys
- when fasting…glucose from amino acids
- can make large amounts
Structure of kidneys
look at two diagrams in slides
What % of CO is RBF
- 22% (1100 mls/min based on 5L/min)
Glomerular capillaries
- High pressure - 60 mmHg
- inside Bowman’s capsule
- high rate of fluid filtration
Peritubular capillaries
- Low pressure - 13 mmHg
- high rate of reabsorption
- surrounds nephron tubules
- controller of afferent/efferent arteriole resistance
How many nephrons do we have
- 1,000,000
- > 40 YO….lose 10% per year
- older more prone to hypertension
Structure of nephron
look at diagram in slides
Cortical nephrons
- mostly in cortex
- not much thin loop…mostly thick
- 70-80% of all nephrons
- look up basic functions in book
Juxtamedullary Nephrons
- mostly in medulla
- long segments of thin loop
- 20-30% of nephrons
- look up basic functions in book 325-326
Filling/emptying of bladder
- micturation (nervous) reflex empties it
- ANS spinal cord reflex w/ brain stem input
Detrusor muscle
- smooth muscle of bladder
- surrounds bladder
Trigone area of bladder
- very smooth area inside bladder
- contains openings from ureters
Internal sphincter of bladder
- tone hold urine in (smooth muscle)
External sphincter of bladder
- skeletal muscle
- voluntary control
- conscious prevention of urination
Pelvic nerve
- primary innervation of bladder
- sensory and motor
- sensory: from posterior urethra / initiate reflex
- motor: are parasympathetic
Pudendal nerve
- innervate skeletal muscle fibers of external sphincter
- voluntary control
Pain nerves of bladder
- supply ureters
- can hold in urine up to a point….then ANS overrides voluntary control
Transport of urine into bladder
- Renal calyces are pacemaker for peristalsis of urine down into bladder
- more stretch of calyces = more peristalsis
- parasympathetic enhance peristalsis
- sympathetic inhibit peristalsis
- Detrusor muscle prevents back-flow by constricting down on ureters
Micturition reflex
- volume/bladder pressure directly prop.
- positive feedback…more stretch….stronger contractions
- stronger and stronger over time…can only prevent emptying for so long…eventually inhibitor signals to external sphincter
- urination happens when inhibitory signals > voluntary signals sent to external sphincter
