Phys 2 Flashcards
(28 cards)
GFR
- definition
- how to measure
- Glomerular filtration rate
- amount of plasma filtrate formed per minute
- can be measured by known plasma level of a freely filtered substance and the amt secreted in urine
GFR equation
(urine concentration)(urine flow) / (plasma concentration)
What is normal GFR
125 mL/min
- women 10% less than men
- 7.5 L/h
- 180 L/d
- normal urine volume 1 L/d
- 99% filtrate normally reabsorbed
- indicator of kidney function
Chronic Kidney Disease Stages
1: kidney damage, normal GFR (>90)
2: kidney damage, mild decrease GFR (60-89)
3: moderate decrease GFR (30-59)
4: severe decrease GFR (15-29)
5: kidney failure (<15) or dialysis
Creatinine Clearance
- definition
- volume of plasma that is cleared of creatinine per unit of time
- creatinine is a metabolic byproduct eliminated by the kidney
- even though small amount of creatinine is lost through tubular secretion, CrCl is used as a measurement of GFR
What is normal CrCl
85-135
where is creatine produced? How is it related to creatinine
- produced by the liver
- phosphorylated by ATP to form phosphocreatine
- stored in brain & muscle
- serves as anaerobic phosphorylation source to create ATP (when ADP is plentiful and need ATP)
- creatinine is a breakdown product of phosphocreatine
Filtration membrane
- permeability
- layers
- highly permeable to water and solutes in kidney
- function of membrane’s anatomy
- 3 layers:
1. Fenestrated capillary endothelium
- Visceral membrane of glomerular capsule composed of podocytes
- basement membrane fused between 1 & 2
Filtration Membrane
- capillary pores
- basement membrane
- pore: prevent passage of RBCs
- BM: restricts proteins > 4nm
Filtration Membrane
- what easily passes through
water glucose amino acids electrolytes nitrogenous wastes
What are the three pressures that affect glomerular filtration
- Glomerular hydrostatic pressure (BP): chief force pushing water across filtration membrane (55 mmHg)
- glomerular osmotic pressure: pressure of protein in blood (30 mmHg)
- capsular hydrostatic pressure (15 mmHg)
What is the net filtration pressure through the glomerular capsule
glom. hydrostatic pressure - glom. osmotic pressure + cap. hydrostatic pressure
55 - (30 + 15) = 10 mmHg
How similar are plasma and filtrate?
very similar except for protein content in plasma
how similar are urine and filtrate
very different
Reabsorption and secretion
Reabsorption
- reclaim needed nutrients (glucose, amino acids, etc.)
Secretion
- elimination and pH regulation
where is glucose normal, where is it abnormal
- normal: filtrate
- abnormal: urine
Active transport carriers
- specific for their solute
- most ATP dependent carriers utilize a co-transporter (often Na+)
Tm
- transport maximum
- most quantity of a substance that can be absorbed
- once saturated, no more solutes can be resorbed
- excess substance is eliminated in urine
Tm example
Glucose Tm is 375 mg/min
- hyperglycemia levels >400 mg/ 100 mL
- glucose spills into urine (glucosuria)
Glucose transport
- transporter
- SGLT-2: sodium dependent glucose transporter
- apical membrane of PCT cells
- Na+ and glucose bind to carrier
- Na+ moves down concentration gradient along with glucose into cell
- both solutes are pumped from peritubular lumen to peritubular capillaries (reabsorbed)
Sodium reabsorption
- Na+ single most abundant cation in filtrate
- 80% of active transport energy moves Na+
- cotransport usually sodium-potassium pump
Location of sodium absorption
- 65% in PCT
- 25% in thick ascending limb of Henle
- 5% in DCT
- 4-5% in CD
approx 1% lost in urine
What is the primary force that moves water out of the tubules?
osmotic pressure of medullary gradient
- moves water into peritubular capillaries
Location of water absorption
- 65% in PCT
- 15% in descending loop of Henle
- 19% DCT and CD (more volume as drop down CD)
** can’t have water follow Na+ because it is being reabsorbed, instead, use concentration of medulla to pull the water out instead
