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NME > Formation of Urine > Flashcards

Formation of Urine Flashcards

1
Q

5 major stages of urine formation:

A

1) Glomerulus: filtration of blood
2) PCT: re-absorption of filtrate; secretion
into tubule
3) Loop of Henle: concentration of urine
4) DCT: Modification of urine
5) Collecting duct: final modification of urine

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2
Q

Glomerular filtration: hydrostatic pressure:

A

pushes fluid out of blood vessel into glomerulus = afferent (largest)

pushes fluid into blood = efferent (smallest)

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3
Q

Glomerular filtration: Osmotic Pressure:

A

pushes fluid into the afferent

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4
Q

Net filtration pressure =

A

hydrostatic - osmotic - hydrostatic
45-25-10 = 10

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5
Q

Net filtration of glomerulus must be

A

positive

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6
Q

Renal Blood Flow is subject to autoregulation over a wide systemic BP range.

Autoregulation due to:

A
  • Myogenic: due to response of renal
    arterioles to stretch (starlings
    law). If BP decreases, renal
    artery and effernt arterioles
    constrict to maintain constant
    RBF
  • Metabolic: renal metabolites modulate
    afferent and efferent arteriolar
    contraction
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7
Q

The afferent and efferent arterioles

A
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8
Q

Changes in GFR can also alter systemic BP

A
  • drop in filtration pressure (hypotension)
    can cause drop in GFR
  • reduced GFR - reduced Na= entering PCT
  • macula densa senses a change in tubular
    Na+ levels
  • stimulates juxtaglomerular cells to release
    renin
  • renin release; generation of angiotensin II
  • angiotensin II is a vasoconstrictor leads to
    an increase in BP
  • increased BP causes filtration pressure to
    increase and GFR returns to normal
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9
Q

Re-absorption and Secretion in the Nephron

A

insert diagram

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10
Q

Re-absorption from PCT:

A
  • 65% filtered water, NA+, HCO3-, CL-, K+ and
    urea are reabsorbed
  • Complete re-absorption (almost):
    • glucose
    • amino acids
    • small amount of filtered proteins
  • Transcellular routes involve aquaporin
    channels on apical and basolateral surfaces
  • no active water re-absorption; only
    osmosis

*Driving force for this re-absorption is
Na+/K+ATPase

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11
Q

Na+ Re-absorption from PCT:

A
  • Na+/K+ATPase pumps 3 Na+ from cells into
    peri-tubular capillaries against chemical
    and electrical gradients
  • requires ATP
  • Cl- follows Na+ by diffusion and
    **Phosphate and sulphate co-transported
    with Na+
  • glucose is co-transported into the PCT with
    Na+
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12
Q

Glucose Re-absorption from PCT:

A

**Glucose in PCT co-transported with sodium into the PCT walls via theSGLT2cotransporter

Smaller amino acids also transported in this way

Once in tubule wall, glucose and amino acids diffuse directly into the blood capillaries along concentration gradient
Na/K sodium ion active transport pumps, remove sodium from tubule wall and into the blood, maintaining a sodium concentration gradient in the proximal tubule lining

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13
Q

Very little K+ is re-absorbed in the PCT.

True or False?

A

False
70%
mostly passively via tight junctions

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14
Q

Urea re-absorption in the PCT is passive.

True or False?

A

True
40-50% of urea

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15
Q

Secretions into PCT:

A

2 types of specilaised pumps:

1) Organic Acid pumps: uric acid, diuretics,
penicillin
2) Organic Base pumps: Creatinine

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16
Q

The PCT Re-absorption and Secretion

A

insert slide

17
Q

Re-absorption in the Loop of Henle can be divided into two stages:

A

1) Re-absorption of water in the descending
limb
2) Re-absorption of Na+ and Cl- in the
ascending limb

18
Q

Re-absorption: Thin descending limb:

A
  • no active transport of salts
  • freely permeable to water via Aquaporin 1
    channels
  • water leaves filtrate and enters interstitial
    fluid
19
Q

Re-absorption: Thick ascending limb:

A
  • tubular wall is impermeable to water
  • ** specialised Na/K+/2Cl- co-transporters
  • Na+, K+, Cl- re-absorbed into interstitial
    fluid
20
Q

Loop of Henle:

where is the fluid in the loop isotonic, hypotonic, hypertonic?

A
  • isotonic: fluid entering LOH from PCT

water re-absorbed out of descending limb

By the tip of ascending, the filtrate is very concentrated

  • hypertonic: water finished re-absorbing

Solutes are then pumped out the ascending limb

  • hypotonic: filtrate entering DCT
21
Q

Loop of Henle: Countercurrent multiplication:

A
  • creates a large osmotic gradient within the
    medulla
  • facilitated by Na+/K+/2Cl- co-transporter in
    ascending limb of LOH
  • permits passive re-asborption of water
    from filtrate in descending loop of Henle
22
Q

Countercurrent Multiplication: Effect of urea on osmolality:

A
  • urea freely filtered at glomerulus
  • some re-absorption in PCT
  • LOH and DCT relatively impermeable to
    urea
  • urea absorbed from the inner medullary
    collecting duct
  • urea secreted into the thick ascending limb
  • urea can diffuse out collecting duct into
    medulla down conc grad
23
Q

Loop of Henle

A

insert slide

24
Q

The distal convoluted tubule re-absorption and secretion:

A
  • active re-absorption and secretion
  • Na+ and Cl- actively re-absorbed in
    exchange for K+ or H+ secreted into
    tubular fluid
25
Q

DCT: Re-absorption: NA+/K+

A
  • Na+ exchanged for K+ in late DCT/early
    collecting duct
  • involves PRINCIPAL CELLS
  • sensitive to ALDOSTERONE
26
Q

DCT: Re-absorption: Na+/H+:

A
  • Na+ exchanged for H+ in DCT and early
    collecting duct
  • involves specialised ALPHA INTERCALATED
    CELLS
27
Q

Renal Actions of Aldosterone:

A

insert diagram
so more water and sodium re-absorption hence increases BP, more K+ secreted/excreted

28
Q

Principal beta intercalated cells

A

alpha = taller columnar epithelium
beta = shorter, flatter

beta contain chloride bicarb exchanger

29
Q

The DCT and collecting duct are involved in acid-base regulation:

A
  • alpha intercalated cells: secretes acid via
    H+/Na+, reabsorbs
    bicarb which is
    main buffer
  • beta intercalated cells: secretes bicarb via
    pendrin, reabsorbs
    acid
30
Q

Carbonic anhydrase found in kidney tubules reaction

A

insert

31
Q

ADH in the collecting duct:

A

ADH in plasma binds to V2 receptors on principal cells in DCT and collecting duct, opening more aquaporin-2 on tubular slide; G-alpha-s

  • stops water excretion; increases water re-
    absorption
  • more ADH = more conc urine = less volume
32
Q

Where is ADH released from?

A
  • posterior pituitary gland
  • following hypothalamic input
33
Q

Maximal Circulating ADH when

A
  • severe dehydration
  • collecting duct becomes permeable to
    water due to maximal aquaporin 2
    insertion
  • re-absorbs 66% of water in CD, low urine
    volume
34
Q

No circulating ADH

A
  • re-absorption of water occurs at various
    sites in the nephron
  • however no ADH means no/less aquaporin
    2 so a large volume of urine
35
Q

Lack of ADH results in

A

diabetes insipidus
treated using synthetic ADH

36
Q

Renin-Angiotensin-Aldosterone-System

A

insert diagram

37
Q

RAAS effects

A

insert slide

NME (52 decks)

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