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Module 104 - Nutrition, metabolism & excretion > T3 L3 Formation of urine > Flashcards

T3 L3 Formation of urine Flashcards

1
Q

What are the 5 processes of urine formation?

A

1) Glomerulus - filtration of blood
2) Proximal tubule - reabsorption of filtrate and secretion into tubule
3) Loop of Henle - concentration of urine
4) Distal tubule - modification of urine
5) Collecting duct - final modification of urine

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2
Q

What are the 3 major functions of the nephron?

A

Filtration of blood to produce a filtrate
Reabsorption of water, ions and organic nutrients from filtrate
Secretion of waste products into tubular fluid

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3
Q

What is the force for filtration?

A

Blood pressure

Differing diameter of afferent and efferent arterioles

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4
Q

What molecules are filtered in glomerular filtration?

A 
All small molecules
Electrolytes
Amino acids
Glucose
Metabolic waste
Some drugs, metabolites
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5
Q

What molecules remain in the blood after glomerular filtration?

A

Red blood cells
Lipids
Proteins
Most drugs, metabolites

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6
Q

What does the filtrate have to pass through in glomerular filtration?

A

1) Pores in glomerular capillary epithelium
2) Basement membrane of Bowman’s capsule - includes contractile mesangial cells
3) Epithelial cells of Bowman’s capsule via filtration slits into capsular space

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7
Q

What is glomerular filtration rate (GFR?)

A

Rate at which filtrate is produced in the kidneys

125ml/min

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8
Q

What are the 2 hypothesises for autoregulation of renal blood flow?

A

Myogenic - auto regulation due to a response of renal arteries to stretch
Metabolic - renal metabolites modulate vasodilation such as nitric oxide, endothelin

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9
Q

What happens when the afferent arteriole dilates?

A

GFR decreases due to decreased BP
Efferent arteriole constricts (due to Ang II)
Increases GFR back to normal

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10
Q

What causes the afferent arteriole to dilate?

A 
Prostaglandins
Dopamine
ANP
NO
Kinins
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11
Q

What happens when afferent arterioles constrict?

A

GFR increases due to increased BP
Efferent arteriole will dilate (due to adenosine)
GFR decreases back to normal

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12
Q

What causes the afferent arteriole to constrict?

A

Noradrenaline
Endothelin
Adenosine
ADH

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13
Q

What happens to GFR when there is a drop in filtration pressure?

A

1) Drop in filtration pressure causes a drop in glomerular filtration rate
2) Lower GFR means less Na+ enters proximal tubule
3) Macula densa senses a change in tubular Na+ levels
4) Stimulates juxtaglomerular cells to release renin into the blood
5) Increased blood pressure causes filtration pressure to increase & GFR returns to normal

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14
Q

What is reabsorbed from the glomerular filtrate in the proximal tubule?

A

60-70% of filtered water, Na+, HCO3-, Cl-, K+, urea, glucose, amino acids, small amounts of filtered proteins

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15
Q

What is the driving force for reabsorption from the glomerular filtrate in the proximal tubule?

A

Na+/K+ ATPase

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16
Q

Describe sodium reabsorption from the proximal tubule

A

Cells have a low intracellular sodium concentration due to Na+/K+ ATPase - overall negative charge due to presence of intracellular proteins
Goes against concentration gradient
Cl- follows Na+ by facilitated diffusion
Phosphate & sulphate are co-transported with sodium

17
Q

What is the driving force for water reabsorption in the proximal tubule?

A

Active transport of Na+ out of the cell

18
Q

What are the main aquaporins in the kidney?

A

AQP1
AQP2
AQP3
AQP4

19
Q

Describe aquaporin 1

A

Abundance distribution in proximal tubule

Wide distribution - also found in lungs and brain

20
Q

Describe aquaporin 2

A

Present in collecting duct on apical surface

AQP2 channel expression is controlled by ADH

21
Q

Describe aquaporin 3 & 4

A

Present on basolateral surface of collecting duct cells

22
Q

How does glucose move into the proximal tubule cell?

A

Cotransported with sodium

23
Q

What are SGLT2 inhibitors?

A

New drugs for controlling type 2 diabetes
Make diabetic patients excrete more glucose
Causes sugary urine which could increase risk of UTI

24
Q

How is potassium reabsorbed?

A

70% of filtered potassium is reabsorbed in the proximal tubule
Mostly by passive transport through tight junctions - paracellularly

25
Q

How is urea reabsorbed?

A

40-50% of filtered urea is absorbed passively in proximal tubule

26
Q

How are amino acids reabsorbed?

A

7 independent transport processes for reabsorption

High Tm for transport to maximise the amount reabsored

27
Q

How are proteins reabsorbed?

A

From the proximal tubule via receptor-mediated endocytosis
Small amounts of protein pass into filtrate via glomerulus
Reabsorbed by pinocytosis
Only a limited transport capacity - low Tm

28
Q

What does proteinuria suggest?

A

Sign of glomerular damage and impending renal failure

29
Q

Describe the process of pinocytosis for protein reabsorption?

A

Vesicles transported into cell
Degraded by lysosomes
Amino acids returned to blood

30
Q

Describe the secretion of PAD into the proximal tubule

A

PAD is secreted into the proximal tubule from the blood with alpha-ketoglutarate or other di/try carboxylates
Not an endogenous compound so can be used to measure tubular secretion
Transported out of proximal tubule cells in exchange for another anion present in proximal tubule lumen

31
Q

What are some endogenous organic acids secreted into the urine?

A 
cAMP
Bile salts
Hippurates
Oxalate
Prostaglandins
Urate (uric acid)
32
Q

What are some organic acid drugs secreted into the urine?

A 
Acetazolamide
Chlorothiaze
Furosemide
Hydrochlorothiazide
Bumentaide
Penicillin
Probencid
Salicylate
33
Q

What are some endogenous organic bases secreted into the urine?

A 
Creatinine
Dopamine
Adrenaline
Noradrenaline
Histamine
Choline
Thiamine, guanide
34
Q

What are some organic base drugs secreted into the urine?

A 
Atropine
Isoproterenol
Cimetidine
Morphine
Quinine
Amiloride
Procainamide

Module 104 - Nutrition, metabolism & excretion (31 decks)

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