Kidneys and Dialysis Flashcards
Nephron
functional unit of the kidneys
- Glomerulus: Filtration Membrane –> 1 000 000 per kidney
!!! Pressure in Glomerulus is kept constant! - local pressure regulation by changing the diameter
- 2 arteriole systems connected serially
Tasks of the kidney
- clearing blood from urea, watersoluble toxins and medicaments
actuator in:
- body fluid regulation
- regulation of pH
- blood pressure regulation
- blood formation
Autoregulation
- Perfusion stays constant –> independent of blood pressure changes
- keep pressure in Glomerulus constant
- renal blood perfusion constant for a wide range of arterial blood pressure values (80-200 mmHg)
Exchanger
- passive process –> they don’t consume energy
- countercurrent exchangers are more efficient than parallel flow exchange
- heat and matter exchange in body
Does the kidney operate as a countercurrent exchanger?
partly, it is doing more: Countercurrent exchange and Countercurrent Multiplication
Countercurrent Multiplication: builds up own concentration gradient against spatial gradient using active energy –> different to countercurrent exchange!!
–> automatic build-up of osmotic gradient
Chronic Kidney Failure
4 Stages:
1) visible hypertension
2) creatinine value: 2 - 8 mg/dl
3) maximal creatinine values: 8 mg/dl up to renal decompensation
4) creatinine values: 10 - 13 mg/dl
- -> need for dialysis or transplant
Therapy Option: Transplantation
pros & cons
- not in position of the healthy kidney
Advantages:
- continuous treatment
- fewer secondary diseases
- mobility
- freedom from time management
Disadvantages:
- rejection of organ
- immunosuppression
- lack of organ donations
Therapy Option: Peritoneal Dialysis
- peritoneum as a semipermeable membrane
- sac with fresh solution & sac with consumed solution
Therapy Option: Hemodialysis
- blood purification
- dialyzer: Countercurrent exchanger
- additional Ultrafiltration
- vascular access through arm
- 3x per week, 4-6 hours each –> great life restriction
- clearance, specifically for high molecular weight proteins is worse than in kidneys –> higher mortality
Ultrafiltration - Formula
UFR = L * A * (Pnet - Posm) L = hydraulic permeability of the membrane A = membrane area Pnet = transmembrane pressure Posm = osmotic pressure
Membrane Therapy - Hemodialysis
- classic procedure for chronic blood purification
- ultrafiltration: 1-2 l/h
- lower TMP
Membrane Therapy - Hemofiltration
compare to Hemodialysis
- when it needs to be faster
- UFR 3 l/h
- higher transmembrane pressure, lower flow rates –> protective for circulatory system
- hemofilters –> different pores: you can suck larger molecules out of blood
Membrane Therapy - Hemodiafiltration
- mixed concept –> common for chronic patients
- transmembrane pressure between Hemodialysis and Hemofiltration
- still works with dialysis
Hypotension
What may be an influencing factor?
life-threatining condition
- due to unadjusted ultrafiltration rate
- -> sudden, unpredictable drop of blood pressure
Body Compartments
Intracellular volume: 23l
Intestitial volume: 15l
Blood volume: 5l
goal: keep all compartments equally regulated (not reality!)
Future: Closed-Loop Control
What are the effects of Body Core Temperature on
- Cardiac Output
- Blood pressure compensation
- total peripheral resistance
- use active control over selected parameters
e. g. body core temperature
increasing body temperature:
- -> total peripheral resistance decreases
- -> cardiac output increases
- -> insufficient blood pressure compensation
What kind of pressure is required for ultrafiltration?
phyiscal negative pressure
By which differential equation can the static behavior of an exchanger be described?
1st order ordinary differential equation
Anti Diuretic Hormone (ADH)
- recovers water from the collecting tube
–> regulates level of water and electrolytes in the body
How does NaCl reach the ascending region of the loop of Henle?
NaCl is actively pumped
Ultrafiltration
- important variables
- what does solvent drag mean?
important variables:
- hydrostatic pressure gradient
- osmotic pressure gradient
- Solvent drag: extraction of fluid and particles simultaneously due to a pressure gradient
Lowflux vs. Highflux Dialyzers
low flux –> smaller diameter of pores
high flux –> higher diameter of pores
UFR = 3000 ml/h
–> high flux membranes need lower TMP to reach the same rate of UFR!
Does a Dialyzer exchange heat?
Yes, very efficient heat exchanger
- idea: moderate cooling of patient to stabilize heat blood pressure