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Module 104: Theme 3 > Formation of urine 1 > Flashcards

Formation of urine 1 Flashcards

1
Q

Overall function of proximal convoluted tubule

A

Reabsorption:

  • water
  • Ions
  • all organic nutrients
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2
Q

Overall function of Loop of Henle

A

Descending limb- more absorption of water.

Ascending limb-
Absorption of NaCl

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3
Q

Overall function of distal convoluted tubule

A

Secretion:

  • Ions
  • Acids
  • Drugs
  • Toxins

Reabsorption:

  • Water
  • Na+
  • Ca2+
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4
Q

Overall function of the collecting duct

A

Variable absorption of water

Reabsorption of:

  • Na+
  • K+
  • H+
  • HCO3-
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5
Q

Papillary duct

A

Section of the nephron that delivers urine to the minor calyx.

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6
Q

Two forces that drive filtration in the nephrons

A

Blood pressure

Differing diameter of afferent and efferent arterioles/ renal blood flow

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7
Q

GFR

A

Glomerular filtration rate
- The rate at which glomerular filtrate is produced.

  • Normally 125mL/min
  • Used as an indicator of renal function.
  • Stays constant even when systemic BP changes due to autoregulation of renal blood flow
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8
Q

Ultrafiltration

  • Definition
  • Molecules filtered
  • Things that stay in the blood
A

The filtration of the blood at a molecular scale.

Small molecules filtered:

  • Electrolytes
  • Amino acids
  • Glucose
  • Metabolic waste
  • Some drugs and metabolites.

Cells and larger molecules stay in the blood.

  • RBCs
  • Lipids
  • Large proteins
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9
Q

Sequence the filtrate passes through during filtration.

A
  1. Pores in glomerular capillary
  2. Basement membrane of Bowman’s capsule.
  3. Filtration slits in podocytes into the capsular space
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10
Q

Two forces that filter fluid out of the blood.

A

This is the Glomerular capillary hydrostatic pressure
- Filtrate leaving glomerulus into capsular space.

It is also the oncotic pressure of the Bowman’s space but this is almost 0.

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11
Q

Two forces that oppose ultrafiltration

A

Glomerular capillary oncotic pressure

Bowman’s capsule hydrostatic pressure.

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12
Q

Overall equation of net filtration pressure

A

[Glomerular capillary hydrostatic pressure]- [Bowman’s capsule hydrostatic pressure + Glomerular capillary oncotic pressure]

This decreases significantly at the end of glomerular capillary.

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13
Q

Autoregulation of renal blood flow

- hypotheses

A

In the kidneys, renal blood flow and GFR stay the same when blood pressure is 90-200 mmHg.

Not due to neuronal or hormonal response.

Two hypotheses for this mechanism:
- Myogenic: arterioles respond to stretch..

  • Metabolic: renal metabolites modulate vasodilation
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14
Q

Change in GFR according to afferent and efferent arterioles

A

Afferent arteriole is usually wider than efferent.

To increase GFR:

  • Afferent dilates and efferent constricts
  • GFR returns to normal

To decrease GFR due to high BP:
- Afferent constrict and efferent dilates

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15
Q

Substances that dilate the afferent artery

A

Prostaglandins

ANP (atrial natriuretic peptide)

Dopamine

NO

Kinins

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16
Q

Factor that constricts the efferent arteriole

A

Angiotensin II

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17
Q

Decrease in GFR according to afferent and efferent arterioles
- Include what causes dilation and constriction

A

The afferent arterioles constricts and efferent arterioles dilates.

Constriction of afferent:

  • Adrenaline
  • Endothelin
  • Adenosine
  • ADH

Dilation of efferent:
- Adenosine

18
Q

Explain how changes in GFR can alter system blood pressure

A

When blood pressure drops, filtration pressure drops:

  • Decreases GFR
  • Less Na+ is filtered

Less Na+ in proximal tubule is sensed by macula densa:
- Stimulates juxtaglomerular cells to release renin into the blood.

Renin release leads to Ang II release:
- Increases BP via vasoconstriction until it returns back to normal

19
Q

Effects of angiotensin II in the RAAS

  • Ions
  • Water
  • Blood pressure
  • Hormone secretion
A

Increases sympathetic activity

Increases reabsorption of:
Na+
Cl-

Increase secretion of K+

Increases H2O retention.

Increases aldosterone secretion

Arteriolar vasoconstriction- increases BP

Stimulates ADH secretion

Increase H20 absorption in collecting duct.

20
Q

Reabsorption at proximal tubule

A

The following are almost completely reabsorbed:

  • Glucose
  • Amino acids
  • Filtered proteins
60-70% of the following:
Water
Na+ Cl-
HCO3-
K+
Urea
21
Q

What protein drives reabsorption at the proximal tubule?

A

Na+/K+- ATPase

  • 3 Na+ out of cells into blood
  • 2+ K+ into cells
22
Q

Na+ reabsorption at PT

A

Gradient for Na+ absorption is driven by Na+/K+ pump at basolateral membrane of tubular cells.

Na+ enter the cells via Na+/H+ pump.
- Also co-transported with Phosphate and sulfate ions.

Cl- follows reabsorption of Na+ through facilitated diffusion

23
Q

Water reabsorption at PT

A

Movement of solutes out of the tubular lumen (Na+, Cl- and HCO3-) increases osmolarity of interstitial fluid.

This drives water out of tubular fluid into interstitial spaces via paracellular and transcellular (aquaporins) routes
- Aquaporins are on the basolateral and apical membranes

24
Q

Aquaporin-1

A

Widely distributed aquaporin.

Abundantly found in the PCT.

25
Q

Aquaporin-2

A

Aquaporin found on the apical surface of the collecting duct.

Controlled by ADH

26
Q

Aquaporin-3 and Aquaporin-4

A

Aquaporin found on the basolateral surface of the collecting duct

27
Q

Glucose reabsorption at the PT

A

Co-transported with Na+ into the tubular cell- apical membrane

  • At PCT the co-transporter has high capacity and low affinity for glucose.
  • At PST the co-transporter has low capacity and high affinity.

Moves down a concentration gradient.

Exits cell via basolateral membrane:

  • GLUT-2 at PCT
  • GLUT-1 at PST

This mechanism ensures very little glucose is excreted.

28
Q

Transport maxima

A

Maximum transport capacity of glucose.

Maximum amount of glucose that can be reabsorbed at the PT. The rest is excreted.

Excess urinary excretion of glucose= diabetes

29
Q

SGLT2

A

Na+/ Glucose co-transporter in the PCT.

  • Low affinity
  • High capacity

SGLT2 inhibitors

30
Q

K+ reabsorption in the PT

A

70% absorbed- mainly down concentration gradient through tight gap junctions

31
Q

Urea reabsorption in the PT

A

40-50% reabsorbed down conc gradient

32
Q

Amino acid reabsorption in the PT

A

7 different transport processes, depending on amino acids.

High transport maxina

33
Q

Protein reabsorption in the PT

A

Small amount of proteins reabsorbed enter the cell via pinocytosis.

They are enclosed in vesicles and degraded by lysosomes to release amino acid into the blood.

This method has a very limited transport maxima.

34
Q

Secretion into the PT

A

Some drugs/ substances are to large or bound to proteins.

OAT and URAT pumps compounds from plasma to nephron.

35
Q

OAT

A

Organic anion transporter.

Pump that moves substances from the blood into the lumen.

Located on both apical and basolateral membranes.

36
Q

PAH

A

Para-amino hippourate.

Secreted into the PT with alpha-ketoglutarate or di/tricarboxylates- from the blood.

Transported out of PT cells in exchange with another anion into lumen.

Used to measure tubular secretion as it is not endogenous.

37
Q

Endogenous acids secreted into the urine by PT (6)

A

cAMP

Bile salts

Hippurates

Urate

Oxalate

Prostaglandins

38
Q

Endogenous bases secreted into the urine by PT (8)

A

Creatinine

Dopamine

Adrenaline + Noradrenaline

Histamine

Choline

Thiamine, Guadine

39
Q

Acidic drugs secreted into the urine by the PT (7)

A

Acetozolamide

Chlorothiazide

Furosemide

Pencillin

Salicylate

Hydrochlorothiazide

Bumetanide

40
Q

Organic basic drugs secreted into urine by the PT

A

Atropine

Isoproterenol

Cimetidine

Morphine

Quinine

41
Q

SGLT2 inhibitors

A

‘Flozins’- Used to treat diabetes by increasing excretion of glucose

Dapagliflozin
Canagliflozin
Empagliflozin

Module 104: Theme 3 (13 decks)

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