Lecture 9: Measuring renal function Flashcards
(30 cards)
Define osmolality
Defined as the concentration of all solutes in a given weight of water and is expressed as units of either osmolality (milliosmoles of solute per kilogram of water, mOsm/kg H2O) or osmolarity (milliosmoles of solute per liter of water, mOsm/L H2O).
Describe the renin-angiotensin-aldosterone system
A reduction in afferent arteriole pressure causes the release of renin from the JG cells, whereas increased pressure inhibits renin release.
When renin is released into the blood, it acts upon a circulating substrate, angiotensinogen, that undergoes proteolytic cleavage to form angiotensin I.
Vascular endothelium, particularly in the lungs, has an enzyme, angiotensin converting enzyme (ACE), that cleaves angiotensin 1 to angiotensin II.
Angiotensin II acts on the adrenal cortex to release aldosterone, which in turn acts on the kidneys to increase sodium and fluid retention
What is the effect of aldosterone in the kidney
- Increase sodium and fluid retention
- Acts on the mineralocorticoid receptors in the distal tubules
- Aldosterone increases sodium reabsorption
Why must hydrogen ion concentrations needs to be kept in a tight range?
As hydrogen ions can cause the denaturation of proteins
Name foods in which is acidic?
White bread
Alcohol
Sugar
Name foods in which are alkaline
Veg e.g. kelp, cayenne peppers
Why is serum creatinine a good marker of glomerular filtration rate
Creatinine is produced from skeletal muscle at a relatively steady state.
It is freely filtered at the golermuli and then neither secreted into nor reabsorbed from the tubular filtrate to any significant degree.
Therefore, the amount filtered per unit time will equal the amount exreted in the same time.
Creatinine is produced by ____ muscle
Skeletal
The concentration of serum creatinine doubles with each ____% reduction in GFR
50%
Increased potassium intake ____ the secretion of aldosterone, which ____ cell potassium uptake.
A) increases
B) increases
What is the most important equation regarding acid base
Describe what happens to this equation if a strong acid e.g. hydrogen chloride is added
When a strong acid such as HCl is added to the bicarbonate buffer solution, the increased H+ released from the acid (HCl → H+ + Cl) is buffered by HCO3.
As a result, more H2CO3 is formed, causing increased CO2 and H2O production. From these reactions, one can see that H+ from the strong acid HCl reacts with HCO3 to form the very weak acid H2CO3, which in turn forms CO2 and H2O. The excess CO2 greatly stimulates respiration, which eliminates the CO2 from the extracellular fluid.
the kidneys regulate extracellular fluid H+ concentration through three fundamental mechanisms
(1) secretion of H+
(2) reabsorption of filtered HCO3
(3) production of new HCO3
The kidney excrete acid in 3 principles
- Reabsorbs filtered bicarbonate
- Filters non-volatile acids eg sulphuric acid
- Proximal tubule synthesises ammonium (NH4+)
Describe the pathway of calcium homeostasis
- Low serum calcium levels is detected by the parathyroid glands.
- Parathyroid glands have calcium sensing receptors on them- low calcium causes them to release parathyroid hormone (PTH)
- Action of PTH:
- In bones increases activity of osteoclasts- releases calcium in the blood stream.
- Acts on the tubular cells of the kidneys causing the increase in absorption of calcium.
- Acts on the kidneys to produce activated vitamin D- that acts on the gut to absorp calcium.
- Increases phosphate excretion
- Bone: rapid access to calcium, however when more calcium is absorbed the calcium stores in bone will be resolved.
What toxic molecules are metabolised by the kidney
- Insulin
- Beta 2 microglobulin
- Medicines
•Erythropoietin secreted from where?
Interstitial cells of the kidney
What are the 3 basic processes of the nephron
•Glomerular Filtration: Filtering of blood into tubule forming the primitive urine (glomerular filtrate)
•Tubular Reabsorption: Selective absorption of substances from tubule to blood
•Tubular Secretion: Secretion of substances from blood to tubular fluid
What is the normal glomerular filtration rate (GFR)?
Approx 100mL/min
around 144L per day
What is the unit measure of kidney function
Total Glomerular Filtration Rate (GFR)
Describe the concept of clearance
the volume of plasma from which a substance is completely removed per unit time
Give an equation for the clearance
The clearance of which exogenous substance is the gold standard for measuring GFR
Inulin
If inulin is the gold standard for measuring GFR why is it not used?
too cumbersome and expensive for routine clinical practice
