Tubular Reabsorption + Tubular Secretion

Question 1

tubular reabsorption

Answer 1

• process of fluid and substances going from filtrate back into blood
• reabsorbed substances move through tubule’s membrane barriers (mainly in PCT) to reach peritubular capillaries
• hormonally regulated, occurs via active & passive transport

Question 2

what would happen without tubular reabsorption?

Answer 2

entire blood plasma would drain away as urine within 1 hour

Question 3

materials reabsorbed in PCT (10)

Answer 3

• all glucose + amino acids (via active transport)
• sodium ions (Na+): 65%
• water: 65%
• chloride ions (Cl-): 50%
• potassium ions (K+): 50%
• bicarbonate ions (HCO3-): 90%
• calcium ions (Ca +2): most
• phosphate ions (PO4 -3): most
• magnesium ions (Mg +2): most

Question 4

materials reabsorbed in descending limb of Henle (1)

Answer 4

water: 15%

ion channels block anything else from leaving filtrate

Question 5

materials reabsorbed in ascending limb of Henle (2)

Answer 5

• Na+ : 25%
• K+ : 40%
  (ion channels block water from leaving filtrate)

Question 6

non-waste materials in filtrate when reaches DCT (3)

Answer 6

• Na+ : 10%
• Cl- : 10%
• water: 20%

Question 7

reabsorption in DCT

Answer 7

regulated by hormones that control ion channels

Question 8

tubular secretion

Answer 8

• movement of substances and water from circulation into nephron tubule from peritubular capillaries –> how certain undesirable substances (i.e. urea, excess K+, drugs) are removed from fluid & excreted in urine
• also includes increasing concentration of filtrate

Question 9

tubular secretion’s role in blood pH control

Answer 9

body secretes bicarbonate and H+ in different amounts to maintaining constant pH of blood

Question 10

regulation of urine concentration

Answer 10

• kidneys alter the concentration of urine to maintain homeostasis of the total solute concentration in all body fluids
• regulation made possible via counter current flow

Question 11

counter current flow

Answer 11

movement of fluids in oppositve directions through adjacent channels in nephron

(filtrate in renal tubules flows one way, blood in vasa recta/peritubular capillaries flows other way)

Question 12

osmotic gradient

Answer 12

• concentration of solute in solution, protected by capillaries
• established + maintained via counter current flow

Question 13

isosmotic

Answer 13

concentration of solute inside = concentration of solute outside

Question 14

measurement units of osmolarity

Answer 14

milliosmoles per liter (mOsm/L)

Question 15

osmolarity of renal cortex vs. osmolarity of renal medulla

Answer 15

• osm. of cortex < osm. of medulla
• also related to urea concentration: DCT + cortex regions of the collecting ducts have more urea bc it can’t leave the ducts. once urea reaches medulla, the ducts allow urea to leave and it flows into surrounding tissue, increasing osmolarity of medulla

Question 16

urea

Answer 16

converted ammonia that must be excreted

Question 17

filtrate’s osmolarity when enters PCT

Answer 17

~ 300 mOsm/L

same as surrounding plasma

Question 18

what happens to filtrate’s osmolarity when goes down descending loop of Henle?

Answer 18

solute concentration (aka osmolarity) increases

Question 19

what happens to filtrate’s osmolarity when goes up ascending loop of Henle?

Answer 19

solute concentration (aka osmolarity) decreases

Question 20

filtrate’s osmolarity at hairpin turn of loop of Henle

Answer 20

~1200 mOsm/L

Question 21

filtrate’s osmolarity when enters DCT

Answer 21

~100 mOsm/L

Question 22

what happens to filtrate’s osmolarity when goes down collecting duct?

Answer 22

solute concentration (aka osmolarity) increases