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Renal Physiology - Also medical student

Also medical student
Course

Reference Systems and Coordinate Transformation (GSE0098)

37 Documents
Students shared 37 documents in this course
Academic year: 2022/2023
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Addis Ababa Institute of Technology

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Renal Physiology

I. Introduction

II. Functional Aspects of the Renal System

A. Renal Vasculature

--parallel vs. series arrangement --relationship between pressure, flow and resistance

B. Glomerular Filtration

  1. Determinants of filtration

EFP = Pc - Pt - IIc EFP = effective filtration pressure

  1. Normal values

Pt = 10 mmHg *Pc = 45 mmHg IIt = 0 mmHg *IIc = 27 mmHg

EFP = 45 - 10 - 27 = 8 mmHg

GFR = 120 ml/min

  1. Filtration and filtered load

The filtration rate (load) of a freely filtered substance is equal to:

GFR X Px Px = plasma concentration of substance

Question: Given the following information:

GFR = 120 ml/min plasma glucose = 100 mg/100ml plasma sodium = 140 mM plasma potassium = 5 mM plasma bicarbonate = 24 mM

What is the filtration rate (load) of the preceding substances?

Questions 1-2. Select all the correct answers.

  1. Which of the following would tend to increase glomerular filtration rate?

  2. an increase in glomerular-capillary oncotic pressure

  3. vasoconstriction of the afferent arteriole

  4. an increase in hydraulic pressure in Bowman’s capsule

  5. an increase in renal blood flow

  6. Which of the following would be expected to cause a large reduction in glomerular filtration rate?

  7. a reduction in mean arterial pressure from 100 to 95 mmHg

  8. a reduction in plasma oncotic pressure by one-half

  9. a decrease in sympathetic activity

  10. complete urethral obstruction

  11. The glomerulus:

A. is permeable to all molecules with a molecular weight (M) over 5000 B. contains no active transport systems (“pumps”) that produce an important effect on the composition of the glomerular filtrate C. produces a filtrate with a lower concentration of amino acids than found in plasma D. produces a filtrate with a higher concentration of urea than found in plasma E. all of the above statements are correct

  1. The glomerular filtration rate:

A. is greater than 50% of the plasma flow to the glomeruli B. falls to approximately 25% of normal when mean arterial pressure changes from 100 to 25 mmHg C. is decreased by a decrease in plasma colloid osmotic pressure D. increases ipsilateral to a ureteral obstruction E. none of the above statements are true

Question 5. Select all the correct answers.

  1. Sympathetic stimulation of the renal arterioles causing a marked reduction in renal blood flow results in:

  2. increased reabsorption of fluid by the nephron

  3. decreased glomerular filtration rate

  4. decreased peritubular hydrostatic pressure

  5. a decreased filtration fraction

  6. Sympathetic stimulation of the renal arterioles results in:

A. a greater percentage of filtrate being absorbed by the renal tubule B. a decreased renal filtration fraction C. increased peritubular hydrostatic pressure in the kidney D. an increased glomerular filtration rate

Question 7, true or false.

  1. The filtration fraction of the kidney is normally about 20%, and is increased due to the vasoconstrictor effects of angiotensin II.

  2. In a healthy individual, what percentage of the effective renal plasma flow would you expect to pass into the glomerular capsule?

A. less that 5% B. between 15% and 20% C. between 40% and 50% D. between 70% and 80% E. greater than 90%

C. Tubular Reabsorption and Secretion

  1. Tubular reabsorption
  • processes involved: diffusion, facilitated diffusion, primary active transport, secondary active transport (co-transport, counter transport)

a. transport maximum (Tm) systems e., proximal tubule glucose - carrier easily saturated

b. secretion not exhibiting Tm e., potassium

  1. Net effects of reabsorption and secretion

filtered load = CFR x Px

GFR = glomerular filtration rate (ml/min)

Px = plasma concentration of substance

excretion = Ux x V

Ux = urine concentration of substance

V = urine flow rate (ml/min)

net transport rate = filtration rate - excretion rate

= (0) no tubular modification

= (+) net reabsorption

= (-) net secretion

Question: Given the following information:

GFR = 120 ml/min plasma glucose = 300 mg/100 ml plasma sodium = 140 mM plasma potassium = 5 mM plasma bicarbonate = 24 mM

urine flow = 2 ml/min urine glucose = 10 mg/ml urine sodium = 180 mM urine potassium = 8 mM urine bicarbonate = 0

Calculate the reabsorption rate of the preceding.

  1. Which one of the following substances does not have a Tm value: albumin, arginine, beta hydroxybutyrate, glucose, hemoglobin, phosphate, sulfate, urea, uric acid?

D. Regional Transport along the Nephron

Proximal Tubule Cell

tubule blood

Summary of proximal tubule alterations

  • approximately 75% of the sodium that is filtered is reabsorbed here (requires ATP)

  • about 75% of the filtered H 2 O, K+, C1- follow sodium and the osmolarity of urine at the end of the proximal tubule is 300 mOsm

  • all CHO, protein, peptides, and aa reabsorbed here via secondary active transport (require luminal sodium)

  • all filtered bicarbonate reabsorbed here a loop of henle

Loop of Henle

  • the mechanisms of the counter current multiplier produce the high interstitial osmolarity in the medulla

  • fluid leaving it hypotonic

  • the vasa recta are counter current capillary loops, flow is slow

  1. Increased blood flow through the vasa recta of the kidney allows less time for equilibrium between the medullary interstitium and the blood. This would be expected to:

A. increase the solute concentration gradient between the medullary interstitial fluid and collecting duct B. concentrate the urine C. facilitate the action of anti-diuretic hormone D. reduce the osmolarity of the urine

  1. The following description is most characteristic of which renal tubular segment:

A. proximal tubule B. thick ascending limb of Henle’s loop C. distal convoluted tubule D. medullary collecting duct

Questions 3 - 7. Select all the correct answers

  1. Which of the following describe glucose reabsorption by the kidney?

  2. secondary active co-transport at the luminal membrane

  3. characterized by a transport maximum of approximately 200 mg per 1200 ml of plasma

  4. the filtered load and reabsorption rate are the same at plasma concentrations below threshold

  5. active extrusion of glucose across the contraluminal membrane by the Na+ - K+ ATPase

  6. A person in previously normal potassium balance maintains neurotic hyperventilation for several days. During this period, what happens to potassium balance?

  7. hyperkalemia is observed

  8. aldosterone stimulates potassium reabsorption

  9. renal excretion of potassium is unchanged

  10. renal tubular secretion of potassium is increased

  11. Potassium:

  12. reabsorption occurs primarily in the late distal and collecting tubule

  13. excretion would be expected to increase in response to a diuretic which inhibits reabsorption of sodium chloride in the proximal tubule

  14. secretion is under the control of aldosterone, by inhibiting sodium-potassium ATPase activity in the renal proximal tubule

  15. has a direct effect on cells of the zona glomerulosa of the adrenal cortex to secrete aldosterone

  16. Which of the following are co-transported with sodium in the renal proximal tubule?

  17. phosphate

  18. amino acids

  19. glucose

  20. potassium

  21. An osmotic diuretic would be expected to:

  22. increase urine flow

  23. reduce net reabsorption of sodium in the renal proximal tubule

  24. enhance sodium excretion

  25. increase back-diffusion of sodium in the renal proximal tubule

  26. Reabsorption of filtered bicarbonate:

A. contributes to excretion of titratable acid B. is reduced during respiratory acidosis, resulting in increased excretion of bicarbonate C. is accomplished by net secretion of sodium D. is enhanced by carbonic anhydrase

  1. Potassium:

A. reabsorption occurs primarily in the late distal and collecting tubule B. excretion would be expected to increase in response to a diuretic which inhibits reabsorption of sodium chloride in the proximal tubule C. reabsorption in under the direct control of vasopressin, which stimulates sodium- potassium ATPase activity in the renal proximal tubule D. has a direct effect on cells of the zona glomerulosa of the adrenal cortex to prevent secretion of aldosterone

Questions 10-13. Select all the correct answers

  1. If renal tubular carbonic anhydrase were completely inhibited, you would expect increased excretion of which of the following?

  2. sodium

  3. water

  4. bicarbonate

  5. potassium

E. Clearance concept and renal calculations

  1. clearance definition

C = U x V U = urine concentration P V = urine flow rate P = plasma concentration

= ml/min

Clearance = the minimum volume of plasma at the prevailing plasma concentrations that could have supplied the material appearing in the urine in the given time interval.

List the following from the least to the greatest clearance:

sodium glucose creatinine inulin PAH

  1. GFR measurements

GFR = Cin = Uin x V Pin

  • inulin

  • freely filtered, not metabolized, not secreted, not reabsorbed

  • substances used instead of inulin: mannitol, sucrose, creatinine* (some secreted in humans)

Cx > Cin - substance filtered and secreted (e., PAH)

Cx < Cin - substance filtered and reabsorbed or not freely filtered (e., glucose)

  • concentration of inulin in the tubule is an index of water reabsorption
  1. Renal blood flow measurement

PAH - filtered + completely secreted

Cpah = ERPF (effective renal plasma flow)

ERPF = Vpah x V Ppah

renal blood flow = ERPF (1 – Hct)

  1. Filtration fraction (FF)

FF = GFR = Cin RPF Cpah

  1. Free water clearance
  • denotes the volume of pure water that must be removed from or added to the flow of urine to make it isosmotic with plasma

Cosm - Vosm x V Posm

C H 2 O = V - Cosm

C H 2 0 (+) = plasma being concentrated, dilute urine is formed

CH 2 0 (-) = plasma diluted, concentrated urine is formed

  1. Fraction of filtered material excreted (Fractional excretion)

FE = Ux / Px = excretion = clearance of x

Uin / Pin filtered load clearance of inulin

> 1 = net secretion < 1 = net reabsorption

  1. Given the following data:

urine concentration of sodium 1400 mEq/ urine concentration of inulin 1 mg/ml plasma concentration of sodium 140 mEq/ plasma concentration of inulin .01 mg/ml

What is the fractional excretion of sodium?

A. 1. B. 0. C. 0. D. 0.

  1. Calculate the renal filtered load of sodium:

glomerular filtration rate: 100 ml/min urine flow rate 2 ml/min urine concentration of inulin 1 mg/ml plasma concentration of sodium 0 mEq/ml

A. 20 ml/min B. 100 mg/min C. 12 mEq/min D. 50 ml/min

  1. Renal clearance of inulin provides a measure of:

A. renal blood flow B. cardiac output C. glomerular filtration rate D. renal plasma flow

  1. Calculate the free-water clearance in a patient with the following laboratory date:

urine output 1 L/24 hours glomerular filtration rate 125 ml/min osmolarity of the urine 150 m0smol/L osmolarity of the plasma 300 m0smol/L

A. 2 L/24hours B. 1 L/24 hours C. 3 L/24 hours D. 0 L/24 hours

  1. calculate the bicarbonate reabsorption in a patient with the following data:

clearance in inulin: 175 L/day plasma bicarbonate 25 mmol/L urine bicarbonate 0 urine pH 5. titratable acid in urine 26 mmol/day urine ammonium ion 48 mmol/day

A. 4449 mmol/day B. 74 mmol/day C. 26 mmol/day D. 4375 mmol/day

  1. How much new bicarbonate has been added to the blood of the above patient?

A. 48 mmol/day B. 26 mmol/day C. 4449 mmol/day D. 74 mmol/day

  1. Calculate the renal plasma flow of a patient given the data below:

effective renal plasma flow 585 ml/min uncorrected measured hematocrit 45% renal extraction of PAH 0. (i., 90% of PAH is removed from the plasma by the kidney in a single passage)

A. 1064 ml/min B. 961 ml/min C. 1066 ml/min D. 650 ml/min

Question 12. Select all correct answers.

  1. Regarding the fractional excretion of a freely filtered susbstance:

  2. a value greater than one suggests that net secretion of the substance has occurred

  3. in hypernatremia (high sodium in plasma) the fractional excretion of sodium is greater than one

  4. the renal clearance of a substance X divided by the inulin clearance is a measure of the fractional excretion of substance X

  5. it is necessary to measure urine flow rate to determine the fractional excretion of a substance

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Renal Physiology - Also medical student

Course: Reference Systems and Coordinate Transformation (GSE0098)

37 Documents
Students shared 37 documents in this course

University: Addis Ababa Institute of Technology

Was this document helpful?
Renal Physiology
I. Introduction
II. Functional Aspects of the Renal System
A. Renal Vasculature
--parallel vs. series arrangement
--relationship between pressure, flow and resistance

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