Kidney + Dialysis Flashcards
Define ‘homeostasis’.
Maintenance of nearly constant conditions in the internal environment.
What is the difference between extracellular and intracellular fluid, providing examples?
Extracellular: Fluid existing outside of cells - sodium, chloride, bicarbonate ions + nutrients e.g. O2, glucose amino acids, CO2.
Intracellular: Within cells. Large amounts of potassium, magnesium & phosphate ions.
Explain the production and handling of ammonia in the body.
- Amino acids used for energy production.
- When extracting amino groups from amino acids by liver, ammonia generated.
- Ammonia highly toxic. Liver removes ammonia by forming urea.
- Urea non-toxic. Diffuses from liver into body fluids.
What are the main functions of the kidney?
- Excretion of metabolic waste produces such as urea + foreign chemicals.
- Regulation of water/electrolyte balances.
- Regulation of osmolality and electrolyte concentrations.
- Regulation of arterial pressure.
- Secretion, metabolism and excretion of hormones.
- Stimulate RBC production.
- Maintain calcium levels.
What is the functional unity within the kidney?
The nephron.
What are the main stages of nephron function?
- Fluid filtered from blood in glomerular capillaries, flowing into Bowman’s capsule.
- Passes into proximal tubule. Filtered fluid converted to urine.
- Passes into loop of Henle. Ascending and descending limb.
- Plaque and macula densa at end of ascending limb control nephron function.
What are two types of nephron and their characteristic features?
Cortical - Short loop of Henle.
Juxtamedullary - Long loop of Henle. Reaches deep into medulla.
What three processes effect the rate at which substances are excreted in urine? How are they related?
- Glomerular filtration from blood into Bowman’s capsule.
- Reabsorption from tubules into blood.
- Secretion from blood back into tubules.
Excretion = Filtration - Reabsorption + Secretion
What are the four ways of handling substances in the formation of urine?
- Substance freely filtered. Not reabsorbed.
- Freely filtered. Part of filtered load reabsorbed back into blood.
- Freely filtered but not excreted. Fully reabsorbed.
- Freely filtered. Not reabsorbed. Secreted from capillary blood into renal tubules.
Why are large amounts of water & solutes filtered in the kidney only to be reabsorbed?
High glomerular filtration rates (GFR) allows rapid removal of waste, filtering blood many times per day.
Allows rapid control of volume and composition of body fluids.
What are the three distinct segments of the loop of Henle?
- Thin descending segment - high permeability to water.
- Thin ascending segment - virtually impermeable to water.
- Thick ascending segment - epithelial cells capable of active reabsorption of sodium, chloride & potassium.
What is the role of antidiuretic hormone (ADH)?
- Medullary collection ducts reabsorb sodium. Permeable to urea which is reabsorbed.
- Reabsorption of water in medullary ducts controlled by concentration of ADH. High levels increase permeability - more reabsorption.
- Water levels monitored by nerve cells in brain. Signals pituitary gland to control release of ADH.
What is dialysis?
The clinical purification of blood by dialysis as a substitute for normal kidney function.
Dialysis involves separation of particles in a liquid on bases if differences in their ability to pass through a membrane.
What is haemodialysis?
Most common form of dialysis.
Insert needle attached to dialysis machine into blood vessel. Blood transferred into machine which filters waste and excess fluids. Filtered blood then passed back into patients’ body.
What is the difference between using a semi-permeable membrane and ultra-filtration.
Semi-permeable - Concentration gradient drives diffusive flow.
Ultra-filtration - Pressure difference drives convective flow across membrane.
What is the equation for solute leaving the blood?
Qb,i * (Cb,i - Cb,o) + QvCb,o
What is the equation for solute appearing in the dialysate?
Qd,i(Cd,o - Cd,i) + QvCd,o
What is dialyzer clearance.
Dialyzer clearance, K, describes the efficiency of membrane devices i.e. solute removal rate from blood related to solute concentration at inlet.
What is the effect of ultrafiltration rate Qv on dialyzer clearance?
Increases diffusive solute transport and therefore clearance increases.
What are the assumptions made in a one compartment model?
- High permeability of cells to solute being modelled.
2. Rapid blood flow that transports solute throughout a totally perfused body.
When is a one compartment model valid?
If solute flux in/out of cells faster than flux of solute from extracellular space accessible to dialysate.
What is the problem associated with one compartment models for modern dialyzers?
Urea removed more efficiently from extracellular space than intracellular compartment.
Urea concentration in plasma falls faster than predicted - urea inbound.
After dialysis, flow from intracellular to extracellular compartment cases increase in post dialysis urea in plasma - urea rebound.
What are some of the patient complications associated with diaysis?
- Hypotension
- Muscle cramps
- Nausea and vomiting
- Headache
- Chest pain
- Itching
- Fever and chills
- Hypertension
What are some of the technical complications of dialysis?
- Clotting
- Haemolysis (RBC damage)
- Blood lead
- Power failure
- Air embolism
