Human Anatomy and Physiology Laboratory Manual, Cat Version: 4. Urinary System - Glomerular Filtration Flashcards


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1

Glomerular Filtration

Water and solutes in blood move across the wall of glomerular capillaries, where they are filtered and move into the capsule then tubule

2

Glomerular filtrate

The fluid that enters the capsular space

3

How much of the blood plasma delivered to the kidney via the renal artery is filtered

Only a portion

4

What happens to plasma, along with its protein and cellular elements during Glomerular filtration

  • Escapes filtration
  • Exits the renal corpuscle via the efferent arteriole
  • Perfuses the tubular capillary beds
  • Eventually collected in the renal venous system
5

How much of the glomerular filtrate returns to the bloodstream via tubular reabsorption

Nearly 99%

6

What happens to the glomerular filtrate that is not returned to the bloodstream via tubular reabsorption

It is excreted in urine

7

Water (passive) - composition of plasma filtrate and urine

Total Amount in Plasma 3 L

Amount in 180 L of filtrate (/day) 180 L

Amount returned to blood/d (Reabsorbed) 178-179 L

Amount in Urine (/day) 1-2 L

8

Protein (active) - composition of plasma filtrate and urine

Total Amount in Plasma 200 g

Amount in 180 L of filtrate (/day) 2 g

Amount returned to blood/d (Reabsorbed) 1.9 g

Amount in Urine (/day) .1 g

9

Glucose (active) - composition of plasma filtrate and urine

Total Amount in Plasma 3 g

Amount in 180 L of filtrate (/day) 162 g

Amount returned to blood/d (Reabsorbed) 162 g

Amount in Urine (/day) 10 g

10

Urea (active) - composition of plasma filtrate and urine

Total Amount in Plasma 1 g

Amount in 180 L of filtrate (/day) 54 g

Amount returned to blood/d (Reabsorbed) 24 g (about 1/2)

Amount in Urine (/day) 30 g (about half)

11

Creatinine - composition of plasma filtrate and urine

Total Amount in Plasma .03 g

Amount in 180 L of filtrate (/day) 1.6 g

Amount returned to blood/d (Reabsorbed) 0 - all filtered

Amount in Urine (/day) 1.6 g (none reabsorbed)

12

What is filtration controlled by

card image

Two opposing hydrostatic forces and 1 osmotic force at the glomerular membrane

  • Glomerular blood hydrostatic pressure
    • Promotes filtration
  • Capsular hydrostatic pressure
    • Opposes filtration
13

Glomerular blood hydrostatic pressure

The main force that pushes water and solutes through the filtration membrane

  • Promotes filtration
  • 55mmHg
14

Capsular hydrostatic pressure

Exerted against the filtration membrane by fluid in the capsular space

  • Opposes filtration
  • 15 mmHg
15

Blood colloid osmotic pressure

  • The pressure of plasma proteins pulling on water
  • Opposes filtration
  • 30 mmHg
  • Very little protein escapes through filtration membrane except in certain disease states
16

Net filtration (formula)

Blood Hydrostatic Pressure - Blood Osmotic Pressure - Capsular Hydrostatic Pressure = Net filtration

55-30-15 = 10mmHg

17

Glomerular filtration rate (GFR)

The amount of filtrate formed in all the renal corpuscles of both kidneys each minute

18

GFR regulation

  • Critical to maintaining homeostasis
  • Done by an assortment of local and systemic mechanisms
    • Renal autoregulation
    • Neural regulation
    • Hormonal regulation
19

How can GFR be regulated

Adjusting the following

  • Blood flow in and out of the glomerular capillaries
  • Surface area of glomerular capillaries
20

Renal autoregulation

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Occurs when the kidneys themselves regulate GFR

21

Myogenic contraction

  • Occurs in Renal autoregulation
  • Triggered by stretching in the glomerular cappilaries
  • Smooth muscle cells in afferent arterioles contract
  • Reduces GFR
22

Tubuloglomerular feedback

  • Occurs in Renal autoregulation
  • Feedback provided to the glomerulus provided by pressure and flow monitored in the macula densa
  • Can cause the afferent arterioles to constrict (decreasing GFR)
  • Or dilate (increasing GFR)
23

Neural regulation

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Occurs when the ANS regulates renal blood flow and GFR

24

How is Neural regulation possible

  • Renal blood vessels are supplied by sympathetic ANS fibers that release norepinephrine
  • Causes vasoconstriction
  • Most important with extreme drops of blood pressure (as occurs with hemorrhage)
25

Hormonal regulation

card image

Involves angiotensin II and atrial natriuretic peptide (ANP)

26

Angiotensin II

  • Potent vasoconstrictor of both afferent and efferent arteriole
  • Reduces GFR
27

Atrial Natriuretic Peptide (ANP)

  • Released by a sudden increase in BP, which stretches the cardiac atria
  • Causes the glomerulus to relax, increasing the surface area for filtration
  • Increases GFR