Urine Production: Filtration Flashcards
what metabolic waste products are made in the liver?
urea
creatinine
bilirubin
where is urea reabsorbed?
- most reabsorbed in PCT (30-40%)
- small amount in medullary collecting duct
what is creatinine made from?
muscle breakdown
how much creatinine is reabsorbed in the kidney?
none
what is bilirubin made from?
breakdown of RBC
name the steps of urine production
- filtration in glomerulus
- reabsorption in PCT
- counter-current concentration in loop of Henle (& collecting duct)
- secretion in DCT
- excretion in collecting duct
what is the first step of urine production?
filtration
where does filtration occur?
glomerulus
what is the osmolarity in the glomerulus?
300
how much blood is in the kidney at all times?
20%
glomerular filtration is based on ____
size
the glomerulus is composed of…
fenestrated capillaries reinforced by basement membrane, and podocytes (slit pores)
what is the normal glomerular filtration rate (GFR)?
~125 mL/min
how does filtrate compare to plasma?
same but no protein
what is the equation for filtered load?
plasma concentration x GFR
what osmolarity is considered hypotonic?
less than 300 mmol
what osmolarity is considered hypertonic?
more than 300 mmol
what osmolarity is considered isotonic?
300 mmol
what effect would a 50% decrease in efferent arteriolar resistance have on GFR?
substantial decrease
with a chronic decrease in GFR by 50%, what changes in plasma concentration would you find for:
- creatinine
- K+
- glucose
- Na+
- phosphate
- H+
- creatinine increases until renal excretion of creatinine returns to normal
- glucose, K, Na, H stay constant (closely regulated)
- phosphate maintained until GFR below 20-30% of normal
what changes would you expect in renal blood flow, GFR, and peritubular capillary hydrostatic P, from a 50% decrease in afferent arteriolar resistance and no change in arterial pressure?
- increase renal blood flow
- increase GFR
- increase peritubular capillary hydrostatic P
what is the net pressure driving glomerular filtration given the following:
- glomerular capillaries hydrostatic P = 50mmHg
- Bowman’s space hydrostatic P = 12mmHg
- glomerular capillaries colloid osmotic P = 30mmHg
- no protein in glomerular ultrafiltrate
50 - 12 - 30 = 8mmHg
what is the concentration of urea in tubular fluid at the end of the proximal tubule compared to the plasma?
higher than concentration of urea in the plasma
how does urea reabsorption in the proximal tubule compare to in the cortical collecting collecting tubule?
PCT > collecting tubule
(40-50% in PCT; none in collecting tubule)
what is the equation for net glomerular filtration pressure?
glomerular hydrostatic P - bowman’s hydrostatic P - glomerular osmotic P
