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Animal Physiology > Urine formation > Flashcards

Urine formation Flashcards

1
Q

What are the 3 steps of urine formation?

A
  1. Glomerular filtration
  2. Tubular reabsorption
  3. Tubular secretion
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2
Q

What is formed by glomerular filtration?

A

Primary urine

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3
Q

Is glomerular filtration selective?

A

No, everything gets filtered

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4
Q

When does the primary urine become urine?

A

After reabsorption and secretion

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5
Q

What are the 4 ways the kidneys maximize filtration?

A
  1. Large surface area
  2. Permeability
  3. Receive higher than normal blood flow
  4. Have higher than normal blood pressure that comes into the kidneys
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6
Q

How much of the plasma that enters the glomerulus is actually filtered?

A

20%

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7
Q

What are the 2 regions of the nephron?

A

Renal corpuscle and renal tubule

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8
Q

What does the renal corpuscle do?

A

Includes the glomerulus and Bowman’s capsule. Does the glomerular filtration

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9
Q

What does the renal tubule do?

A

Includes the proximal and distal tubules and the loop of Henle. Does reabsorption and secretion

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10
Q

What is the structure of the glomerulus?

A

A twisted ball of specialized capillaries that are covered by podocytes, with mesangial cells in between the capillaries

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11
Q

What are mesangial cells?

A

Loosely connected endothelial cells around the podocytes

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12
Q

What are podocytes?

A

Specialized epithelial cells that cover the outside of the capillaries, with foot processes that interact with the basement membrane and form filtration slits

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13
Q

Why are podocytes important for determining what gets filtered out of the blood during glomerular filtration?

A

The foot processes keep red blood cells and proteins inside the blood vessel, so they don’t escape

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14
Q

What are the 3 components of primary urine?

A
  1. Water
  2. Inorganic ions
  3. Small organic molecules (glucose, amino acids, urea)
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15
Q

Why is fluid driven from the glomerulus to the Bowman’s capsule?

A

Bulk flow. There is high pressure in the glomerulus and low pressure in the Bowman’s capsule

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16
Q

What are the 3 pressures that net glomerular filtration depends on?

A

Hydrostatic pressure exerted by the glomerular capillaries (60 mmHg)
Hydrostatic pressure exerted by the lumen of the Bowman’s capsule (15 mmHg)
Oncontic pressure

17
Q

Which pressure force favours the movement of fluid into the Bowman’s capsule lumen?

A

Glomerular capillary hydrostatic pressure

18
Q

Which pressure forces resist the movement of fluid into the Bowman’s capsule lumen?

A

Bowman’s capsule hydrostatic pressure and oncotic pressure

19
Q

What is oncotic pressure?

A

The colloid osmotic pressure created by the high concentration of proteins in the plasma

20
Q

What is the net filtration pressure?

A

Difference between the pressure forces that favour inwards movement (glomerular capillaries hydrostatic) and pressure forces that favour outward movement (Bowman’s capsule hydrostatic and oncotic). 60 - 30 - 15 = 15 mmHg

21
Q

Is the primary urine hypo, iso, or hyperosmotic to the blood?

A

Isosmotic

22
Q

What is GFR? What is normal?

A

The glomerular filtration rate. Measures the rate of primary urine formation and is a very important indicator of kidney function. Normal GFR is 120 ml/min

23
Q

What was the way we used to measure GFR?

A

Inject the patient with inulin and then measure the amount of inulin in the patient’s urine after 24 hours

24
Q

Why was inulin a good way to directly measure GFR?

A

It isn’t reabsorbed or secreted after the Bowman’s capsule. So the amount of inulin in the urine equals GFR

25
Q

What changes in the kidney would change the GFR?

A

Blood flow, blood pressure, permeability

26
Q

How is the GFR of the entire kidney change?

A

Vasoconstriction or dilation of afferent or efferent blood vessels

27
Q

How is the GFR of an individual nephron changed?

A

Altering the mesangial cells

28
Q

What do we use now to measure GFR in a person?

A

Creatinine. Produced endogenously by muscle metabolism, so no need to inject the person. It is also not secreted or reabsorbed

29
Q

What is plasma clearance?

A

The volume of plasma cleared of a specific substance over time

30
Q

How does plasma clearance compared to GFR if a substance isn’t secreted or reabsorbed?

A

C = GFR

31
Q

How does plasma clearance compared to GFR if a substance is being secreted?

A

C > GFR

32
Q

How does plasma clearance compared to GFR if a substance is reabsorbed?

A

C < GFR

33
Q

Do the proximal tubules have controlled or uncontrolled reabsorption?

A

Uncontrolled

34
Q

Do the distal tubules have controlled or uncontrolled reabsorption?

A

Controlled

35
Q

How much glucose should be in the urine of a healthy person?

A

None, it should all be reabsorbed

36
Q

What is the specific clearance rate?

A

The clearance rate of a particular substance from the plasma

37
Q

What is the relative clearance rate?

A

The clearance rate of a particular substance from the plasma relative to GFR

Animal Physiology (32 decks)

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