Renal Physiology COPY Flashcards
What are the sources of insensible fluid loss and its approximate rate in dogs?
Respiratory tract
Skin (independent of sweating)
1ml/kg/d in the dog
What are the main water in’s and outs in animals?
In:
- Ingestion
- Carbohydrate oxidation
OUT:
- Insensible losses
- Faecal
- Urinary
What is the fluid composition of a typical animal?
TBW = 60%
- ICF = 40%
- ECF = 20%
- Interstitial = 15%
- Plasma = 5%
Alternative memory aid = 60:40:20 rule
What is the trans cellular fluid compartment?
Specialised ECF e.g. pericardium, synovial fluid etc.
What is the main difference between fluid composition of the plasma and interstitial fluid?
Protein content of the plasma => otherwise the substance make up is pretty much the same so can be considered as the ECF.
What is the Donnan effect and what is its relevance to bodily fluid composition?
= uneven distribution of ionic compounds across a semi-permeable membrane
The plasma has a slight positive charge compared to the IF. This is due to plasma proteins having a slightly negative charge and therefore they retain cations more readily than the IF.
n.b. this effect is usually ignored when considering bodily fluid compartments
What is the difference in membranes between plasma + intestitial fluid vs. ECF + ICF?
Which fluid compartment does the kidney control?
ECF
Name the main:
1) ECF cations
2) ICF cations
3) ECF anions
3) ICF anions
1) Sodium
2) Potassium, magnesium, calcium
3) HCO3, Chloride
4) Phosphates, proteins
What is the main extracellular cation?
Sodium
What is the main extracellular anion?
What is the main intracellular cation?
What is the main intracellular anion?
Protein, closely followed by phosphates
What is osmolality?
What is osmolarity?
The number of osmoles per volume of a solution e.g. mOsm/L
(n.b. osmolarity and osmolality are often equivalent in bodily fluids)
Effective vs. ineffective osmoles
Effective = do not cross the membrane and therefore retain water in a particular compartment Ineffective = cross the membrane and therefore do not retain water in a particular compartment (as they just equilibirate)
Tonicity
The effective osmolality of a solution
Osmolol gap
The difference between calculated and measured osmoles
Serum osmolality calculation
Serum tonicity calculation
What is the approximate canine osmolality?
300mOsm/kg
What is the real meaning of a isotonic/hypotonic/hypertonic fluid?
Refers to what the fluid will do to the intracellular fluid.
Explain what would happen to ECF and ICF volume and osmolarity with the addition of the following fluids:
1) Isotonic fluid
2) Hypertonic fluid
3) Hypotonic fluid
4) Pure water
What is the overally safety factor against oedema in the interstitium expressed as a pressure?
17mmHg
How do changes in pressure in the efferent arteriole of the kidney impact GFR and tubular reabsorption?
Increased efferent pressure –> increased glomerular pressure (thus increased GFR)
Decreased peritubular capillary pressure (thus increased resorption as there is less hydrostatic pressure in these capillaries)
Which section of the LoH is thick vs. thin?
Thin is the first part and is descending. The TAL is the second part.
What are the main differences between cortical and juxtamedullary nephrons?
Cortical - only penetrate a small section of the medulla.
Juxtamedullary - deep into the medulla. Also surrounded by the vasa recta
n.b. the collecting duct penetrates deep into the medulla.
What are the three basic process by which urine forms?
- Glomerular filtration
- Reabsoprtion
- Secretion
What are the main anatomical components of the glomerular filtration barrier and how does this affect molecule movement?
- Capillary endothelium - fenestrations to allow easy movement.
- Basement membrane consisting of negatively charged collagenous proteins
- Podocyte epithelium with slit pores. Sialoglycoprotein coating is also negatively charged.
Summary = protein filtration is prevented by the size of the membrane but also the presence of lots of negative charges that will prevent movement of protiens (size selectivity and charge selectivity).
What is the equation that determines GFR?
What are the forces (and approximate values if you know them) that favour and oppose GFR?
Forces Favouring Filtration
- Glomerular capillary hydrostatic pressure (60mmHg)
- Bowman’s space oncotic pressure (0mmHg)
Forces Opposing Filtration
- Glomerular capillary oncotic pressure (32mmHg)
- Bowmans space hydrostatic pressure (18mmHg)
By what pathologic mechanims might the glomerular filtration coefficient (Kf) be affected?
- Change in the surface area avaible for filtration
- Change in the thickness of the capillary membrane
These are, in turn, the two components of the Kf
Why does urinary tract obstruction reduce GFR?
It increased Bowman’s capsule hydrostatic pressure.
What is the effect of constriction of the afferent or efferent arteriole on renal blood flow?
Both will decrease renal blood flow.
Change in the diameter of which blood vessel will likely have the biggest impact on GFR?
a) afferent arteriole
b) efferent arteriole
Constriction of the afferent arteriole as this reduces both renal blood flow and the glomerular capillary pressure
What is meant by the biphasic effect of efferent arteriolar pressure on GFR?
Small constrictions will increase GFR due to increased glomerular capillary pressure.
Large constrictions will also restrict renal blood flow and therefore decrease GFR.
What are the main deteriminants of renal blood flow (at a basic level)?