Kidney Function Flashcards
How many nephrons in the kidneys?
2.5 million
What are the three stages of urine formation and where do they occur?
Filtration (renal corpuscle)
Reabsorption (convoluted tubule)
Secretion (distal convoluted tubule)
What happens in filtration?
Blood pressure forces water and solutes across walls of glomerular capillaries
What happens in reabsorption?
Water and solutes removed from filtrate across tubular epithelium into peritubular fluid (fluid surrounding tubule), via diffusion or carrier proteins
Reabsorbed substances eventually reenter blood
What happens in secretion?
Solutes transported from peritubular fluid across tubular epithelium into tubular fluid
What is the net filtration rate?
Net filtration pressure acting across glomerular membrane, depends on:
- Glomerular hydrostatic pressure
- Capsular hydrostatic pressure (acts against)
- Colloid osmotic pressure (acts against)
What effects the glomerular filtration rate?
Renal blood flow
Arteriolar constriction
What is the glomerular filtration rate (GFR)?
Amount of filtrate produced by kidneys each minute
What is the structure of the glomerular membrane?
- Endothelial layer of capillary
- Basement membrane
- Layer of epithelial cells lining capsule
What is clearance?
The volume of plasma passing through the kidneys per unit time to produce the amount of a solute in urine
When does clearance equal the GFR?
When a substance is not reabsorbed from urine or secreted into the tubules
How can GFR be accurately measured?
Inulin
- An inert polysaccharide not metabolised in the body and neither reabsorbed or secreted by tubules
What is the creatinine clearance test?
Compares creatinine level in blood and urine
A value of 100 means kidneys working 100%
(Creatinine elimination per hour/plasma creatinine conc.)
What is countercurrent multiplication?
Exchange of substances between descending (thin) and ascending (thick) segments of a nephron
What is the purpose of the countercurrent?
- Effectively reabsorbs water and solutes
- Establishes concentration gradient in peritubular fluid that passively reabsorbs water from collecting ducts
How does the countercurrent work?
- Na and Cl ions actively pumped out from ascending loop
- Interstitial fluid ion concentration increases
- Osmotic movement of water out of thin loop
How is concentrated urine produced following dehydration?
- Increase in osmotic pressure detected by osmoreceptors in hypothalamus, so ADH produced by pos. pituitary gland
- ADH increases reabsorption of water in collecting tubules
- Blood is diluted, osmotic pressure decreases, ADH release decreases
What is it called when the body produces a large volume of urine?
Diuresis
What does ADH do?
Increases the permeability of the collecting ducts to water
What controls osmolarity?
Concentration of sodium, which is controlled by ADH, thirst centre and aldosterone
Where is aldosterone produced?
Adrenal glands
What does aldosterone do?
Increases K+ secretion into distal and collecting tubules
What is Addison’s disease?
Destruction of adrenal gland - Hyperkalaemia
- Cardiac arrhythmias
What is the effect of an adrenal gland tumour?
Very low blood potassium
- Failure of nerve transmission due to hyperpolarisation of membranes
- Hypokalaemia
