nephron function 1

Question 1

describe the concentration of K+ along the nephron

Answer 1

only 30% remaining within the proximal tubules, it continues to decrease when it reaches the LOH with only 5. However, as it gets to the distal tubule and collecting duct it increases again

Question 2

describe starlings forces in relation to the nephron

Answer 2

• the blood following the nephron has a hydrostatic pressure, which forces solutes and water out of the blood
• as proteins are too big to be filtered through they remain and exert an oncotic pressure inwards
• in contrast, the renal corpuscle capsule itself has fluid in it exerting a hydrostatic pressure causing solutes to move into the blood

Question 3

what is the average glomerular filtration rate

Answer 3

125ml/min (both kidneys)

Question 4

briefly, describe renal autoregulation

Answer 4

• mechanism to maintain a constant level of pressure in the glomerulus (regardless of systemic)
• works as a feedback mechanism to either dilate or constrict afference arterioles or constrict efferent arterioles

Question 5

describe the extrinsic (hormonal) mechanisms involved in renal autoregulation

Answer 5

renin-angiotensin 2 = constrict efferent arteriole

ANP = dilate afferent arteriole

SNS = constrict afferent arteriole

Question 6

describe the intrinsic mechanism involved in renal autoregulation

Answer 6

myogenic = increased arterial pressure stretches the afferent arteriole inducing it to constrict and maintain GFR

Question 7

describe the tubuloglomerular feedback mechanism

Answer 7

macula densa cells monitor NaCl levels in the distal tubule, if high levels are present they signal to the afferent arteriole to constrict

Question 8

describe the renin-angiotensin mechanism

Answer 8

1. too low GFR
2. less NaCl passing macula densa cells
3. paracrine signals released
4. JG cells release renin
5. angiotensin 2 produced
6. constriction of efferent arteriole & release of aldosterone
7. aldosterone increases Na+ uptake from distal nephron
8. increased BV and BP

Question 9

describe the major site of filtrate reabsorption

Answer 9

(proximal tubule)

• involves both transcellular and paracellular transport mechansims
• Na+ coupled transport predominates therefore Na/K/ATPase is critical for function

Question 10

describe the reabsoprtion of bicarbonate

Answer 10

bicarbonate cant diffuse across the cell membrane and therefore depends on carbonic anhydrase on the brush border

Question 11

describe how new bicarbonate is formed in the proximal tubule and what stimulates this process

Answer 11

Cells metabolize glutamine to ammonium ion and bicarbonate (NH4 & HCO3-)
- the NH4 is secreted into the lumen by a Na/NH4 exchanger
- HCO3- transported into the blood
(this pathway is stimulated by an increase in ECF H+)

Question 12

describe Cl- reabsorption in the late proximal tubule

Answer 12

• Most of the Na+ and H20 gets reabsorbed into the blood leaving behind a high concentration of Cl-
• Cl- moves paracellularly down its concentration gradient however in doing so creates an electropositive lumen
• this electropositive lumen repels more Na+

Question 13

what is the central role of the loop of Henle

Answer 13

producing a urine that is more concentrated than plasma or more dilute than plasma
works by a countercurrent multiplication & ‘passive hypothesis’