Glomerular Ultrafiltrate

The fluid that enters the glomerular capsule is called ultrafiltrate (fig. 17.10) because it is formed under pressure—the hydrostatic pressure of the blood. This process is similar to the formation of tissue fluid by other capillary beds in the body in response to Starling forces (chapter 14; see fig. 14.9). The force favoring filtration is opposed by a counterforce developed by the hydrostatic pressure of fluid in the glomerular capsule. Also, since the protein concentration of the tubular fluid is low (less than 2 to 5 mg per 100 ml) compared to that of plasma (6 to 8 g per 100 ml), the greater colloid osmotic pressure of plasma promotes the osmotic return of filtered water. When these opposing forces are subtracted from the hydrostatic pressure of the glomerular capillaries, a net filtration pressure of only about 10 mmHg is obtained.

Because glomerular capillaries are extremely permeable and have an extensive surface area, this modest net filtration pressure produces an extraordinarily large volume of filtrate. The glomerular filtration rate (GFR) is the volume of filtrate produced by both kidneys per minute. The GFR averages 115 ml per minute in women and 125 ml per minute in men. This is equivalent to 7.5 L per hour or 180 L per day (about 45 gallons)! Since the total blood volume averages about 5.5 L, this means that the total blood volume is filtered into the urinary tubules every 40 minutes. Most of the filtered water must obviously be returned immediately to the vascular system, or a person would literally urinate to death within minutes.

■ Figure 17.8 The structure of the glomerulus and capsule. An illustration of the relationship between the glomerular capillaries and the inner layer of the glomerular (Bowman's) capsule. Notice that filtered molecules pass out of the fenestrae of the capillaries and through the filtration slits to enter the cavity of the capsule.

Filtration Slits

Glomerulus

Afferent arteriole

Blood flow

Proximal convoluted tubule

Glomerular (Bowman's) capsule

Podocyte of visceral layer of glomerular capsule

Primary process

Efferent arteriole

Parietal layer of glomerular capsule

Podocytes Visceral Layer

■ Figure 17.9 An electron micrograph of the filtration barrier. This electron micrograph shows the barrier separating the capillary lumen from the cavity of the glomerular (Bowman's) capsule.

Picture Starling Forces Glomerulus

■ Figure 17.10 The formation of glomerular ultrafiltrate. Only a very small proportion of plasma proteins (green spheres) are filtered, but smaller plasma solutes (purple spheres) easily enter the glomerular ultrafiltrate. Arrows indicate the direction of filtration.

Physiology of the Kidneys jBlood pressure

Exercise

Baroreceptor reflex f Sympathetic nerve activity f Sympathetic nerve activity

Steps Production Action Potential
j Urine production

t Blood volume

■ Figure 17.11 Sympathetic nerve effects. The effect of increased sympathetic nerve activity on kidney function and other physiological processes is illustrated.

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Responses

  • clifford
    What opposing forces are in the glomerular capsule?
    8 years ago
  • Benjamin McLean
    What process is powered by hydrostatic pressure in the blood?
    7 years ago
  • Ghenet
    How blood pressure in glomerulus affect the volume of filtrate produced?
    7 years ago
  • douglas
    How much ultrafiltrate is produced by the glomerulus per day?
    7 years ago
  • Furuta
    What happened to the filtrate pressure in Bowman's capsule and the glomerular filtration rate?
    7 years ago
  • ANYA
    How much glomerular filtrate is produced in one day?
    6 years ago
  • primula
    What is the ultrafiltrate of the plasma?
    6 years ago
  • HUGO
    How does glomerular ultrafiltrate produce?
    6 years ago
  • ferdinando
    How much filtrate is produced by the glomeruli each day?
    6 years ago
  • Sarah
    How much ultrafiltrate in body?
    6 years ago
  • Marmadoc
    How much ultra filtrate is produced per day?
    5 years ago
  • AATIFA
    How is the glomerular ultrafiltrate produces?
    5 years ago
  • Heidi
    How much ultrafiltrate does a person produce in a single day?
    4 years ago
  • Fethawit Hamid
    How ultrafiltrate is formed?
    4 years ago
  • iiro
    How much volume of glomerular capsule?
    4 years ago
  • hamilcar
    What are the forces that affect formation of glomerular ultra filtrate?
    3 years ago
  • Emilia
    What is the volume of glomerular filtrate in a day?
    3 years ago
  • dexter sinclair
    How much fluid is filtered by glomerulus in a day?
    3 years ago
  • odetta
    What is the volume of ultrafiltrate by glomeruli in kidneys?
    3 years ago
  • Kevin
    How many ultrafiltrates is formed per day?
    2 years ago
  • Orsola
    How glomerular ultrafiltrate is produced and why it has a low protein concentration?
    2 years ago
  • sheshy
    How to obtain 180L /day as an ultrafiltrate?
    2 years ago
  • mollie
    How a large number of about 180L of fluid is filtrated by the human kidneys per day?
    2 years ago
  • howard
    What is the relationship between blood pressure in the glomerulus and the formation of filtrate?
    2 years ago
  • Asmait
    What is total quantity of low glomerulus filtrate produced by us per day and what does it contain?
    2 years ago
  • magnus ahonen
    What is a filtrate and how is it formed?
    1 year ago
  • MIKE HUEBER
    How much fluid is produced daily by the glomeruli?
    1 year ago
  • Christine
    How much does ultrafiltrate decrease blood volume?
    1 year ago
  • cottar roper
    How is glomerular ultrafiltrate produced and why is it low on proteins?
    8 months ago
  • leighton
    How is plasma ultrafiltrate produced?
    6 months ago
  • malva
    How is the fluid in the glomerular capsule produced?
    6 months ago
  • marroc
    How is the fluid in the glomerular capsule produced and what does it consist of?
    6 months ago
  • rosamunda
    How much ultrafiltrate passes through the renal tubules per day?
    5 months ago
  • yerusalem aman
    How much filtrate does the kidney produce per day?
    5 months ago
  • john greggs
    What is the total volume of glomerular filtrate a day?
    3 months ago
  • hiewan
    How much filtrate is formed per day in a healthy individual?
    1 month ago

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