Session 3 - Filtration Flashcards Preview

Semester 3 - Urinary > Session 3 - Filtration > Flashcards

Flashcards in Session 3 - Filtration Deck (95):
1

Outline the sequence of arteries leading into the kidney

• Renal Artery -> Segmental Arteries -> Interlobar Arteries -> Arcuate Arteries -> Interlobular Arteries -> Afferent Arterioles

2

Give one way in which the structure of the renal arteries increases pressure in the glomerulus

• The diameter of each afferent arteriole is slightly greater than the diameter of the associated efferent arteriole

3

What is the size limit and effective molecular radius for filtration?

• Size limit - 5,200
• Effective molecular radius - 1.48 nm

4

Why are proteins not usually filtered into the kidney?

• Size
• Basement membrane and podocyte glycocalyx have many negatively charged glycoproteins which repel protein movement

5

How much blood is filtered by the renal artery at any one time?

• 20%

6

What happens to blood not filtered by the glomerulus?

• Exits via efferent arteriole

7

What are the two types of kidney nephron?

• Cortical
• Juxtamedullary

8

Why is a juxtamedullary nephron named thus?

• Glomeruli located in cortex, but next to medullary bounds

9

Give two differences between cortical and juxtamedullary nephrons

• Juxtamedullary has longer loops of henle
• Arrangement of peritubular capillaries around cortical nephrons messy
• Structured and organised arrangement of capillaries in juxtamedullary nephron
• Countercurrent flow in organised juxtamedullary nephron

10

How is filtration a selective process?

• Cells and large proteins do not get filtered through
• Water, salts and small molecules pass through
• Thanks to filtration mesh provided by podocytes

11

Where do the glomerula tufts always lie?

• In the cortex

12

Where does blood to be filtered arrive in the kidney?

• Glomerula tuft

13

What are the three layers in the filtration barrier?

• Capillary endothelium
○ Water, salts, glucose
• Basement membrane
○ Acellular gelatinous layer of collagen/glycoprotein
○ Permeable to small proteins
○ -'ve charge to repel protein movement
• Podocyte layer
○ Pseudopods interdigitate and form filtration slits

14

It is more difficult for a positive protein to pass through membrane than a negative. Do you agree?

• No, negative repelled by -vely charged basement membrane

15

What happens if a clinical conditions results in negative proteins being stripped of their charge?

• They will be filtered and appear in the urine

16

Give conc of following in plasma and ultrafiltrate

• Glucose 100
• Na+ mmol/l 140
• Urea mg/dl 15
• Creatinine umol/l 60-120

17

Give three physical forces involved in plasma filtration

• Hydrostatic pressure in the capillary (regulated) (capillary -> tubule)
• Hydrostatic pressure in bowman's capsule (tubule -> capillary)
• Osmotic (oncotic) pressure differences between the capillary and tubular (tubular -> Capillary)

18

What is the net filtration pressure in the glomerulosa?

• 10mmHg

19

What is the average hydrostatic pressure between capillaries and tubule?

• 50mmHG (about half of normal pressure)

20

What is the effect of charge on filtration?

• Neutral molecule - The bigger it is, the less likely to get through
• Anions - Negative charge also repels, more difficult to get through
• Cations - Positive charge allows slightly bigger molecules through

21

How is blood in afferent arteriole (going out) different to efferent (going in)?

• Oncotic (protein) pressure higher
• Blood is more concentrated

22

Give one cause of proteinuria involving filtration forces

• In many disease processes the negative charge is lost on the filtration barrier, so proteins are more readily filtered

23

What is osmotic pressure?

• Force generated because of solute within solvent

24

What is oncotic pressure?

• Oncotic force in generated because of protein within solute

25

Why is absorption in kidney called reabsorption?

• Already been absorbed once by GI tract

26

Give three mechanisms by which reabsorption occurs

• Osmosis
• Diffusion
• Active transport

27

What is tubular secretion?

• Substances secreted into renal tubular lumen from peritubular capillaries

28

By what mechanism are substances secreted into the tubular lumen?

• Active transport

29

What two main types of substances are secreted into the tubular lumen?

• Those present in great excess
• Natural poisons

30

What does secretion help to maintain?

• Blood pH

31

Give three examples of things actively secreted

• Protons
• Potassium
• Creatinine

32

What are two methods of secretion into the PCT?

• Entry by passive carrier
• Secretion into the lumen

33

What is entry by passive carrier?

• Diffusion across basolateral membrane down conc grad created by Na+/K+ ATPase

34

How does entry by active secretion differ to passive?

• Directly uses ATM and H+ gradient creat by Na+-H+ antiporter

35

Give two forms of reabsorption?

• Transcellular
• Paracellular

36

How easy is it for a cation to get through the filter compared to an anion?

• Positive charge of cation allows slighty bigger molecules through than anions

37

What is reabsorption in PCT driven by?

• Sodium uptake

38

How is Na+ reabsorbed in tubular cells

• 3Na-2K-ATPase (Na into ECF, K+ into cell)
• Na+ moves across the apical membrane from tubule lumen down its concentration gradient
• Water follows into cell

39

In what way do solutes move in the PCT?

• Tubular lumen -> Intersticium -> Capillaries

40

What are the three mechanisms via which tubular reabsorption occurs?

• Osmosis
• Diffusion
• Active transport

41

What does iso-osmotic mean when applied to reabsorption?

• Osmosis does not take effect

42

Where does unregulated absorption occur?

• Proximal convoluted tubule

43

What is the method via which reabsorption occurs?

• Co-transport, following active transport

44

What is the transport maximum?

• If plasma conc exceeds Tm, the rest spills over into urine

45

What is the reabsorption path?

• Lumen -> Intersticium -> Peritubular capillaries

46

How is reabsorption different from glomerula filtration?

• Occurs primarily through cells

47

What 7 main substances are secreted into glomerula filtrate?

• Protons
• Potassium
• Ammonium ions
• Creatinine
• Urea
• Some hormones
• Some drugs

48

Why do we need kidney secretion?

• Only 20% of plasma filtered in renal corpuscle each time

49

From where does tubular secretion occur?

• From the epithelial cells that line the renal tubules and collecting duct into the glomerular filtrate

50

How are organic cations secreted?

1) Entry by passive carrier into tubular lumen cell
a. Positive cation from ECF moves into negative cell down electrical gradient. This is as a result of basolateral 3 Na+/2 K+ ATPase
2) Secretion into the lumen
a. H-OC exchanger driven by H+ gradient created by the Na+-H+ antiporter
b. Na+ into cell from lumen, H+ out cell into lumen
c. Drives H+ into cell from lumen by creating conc grad
d. Organic Cation out by active transporter

51

Name three endogenous cations

• Dopamine
• Adrenaline
• Histamine

52

Name three cationic drugs

• Morphine
• Atropine
• Sulfonamides

53

Name three endogenous anions

• Urate
• Bile salts
• Fatty acids

54

Name two anionic drugs

• Penicillin
• Salicylate

55

What is secondary active transport?

• Na+/K+ ATPase used to generate Na+ gradient

56

Where is glucose reabsorbed in the nephron?

• Proximal convoluted tubule

57

Through what transporter is glucose reabsorbed in the proximal convoluted tubule?

SGLUT

58

What is SGLUT?

• 2 Na+ ions and 1 glucose
• Glucose travels from lumen of tubule to the peritubular capillaries (moves into peritubular capillaries by facillitated diffussion

59

What is Tm?

• Transport maximum from tubule to capillaries

60

What is the renal threshold for glucose?

• 200mg/100ml

61

What occurs if transport maximum for glucose exceeded?

• Rest of glucose spills over into urine
• Causes polyuria

62

Where does reabsorption of amino acids occur?

• Proximal convoluted tubule via Na+ co-transporters

63

What is clearance?

• The volume of plasma from which any substance is completely removed by the kidney in a given amount of time (usually 1 minute)

64

What is the clearance calculation?

• Clearance rate = Urine concentration of substance x Urine flow rate / Plasma concentration of the substance

65

What is excretion rate?

• Amount in urine x Urine flow rate

66

When are the inputs and outputs of the kidney?

• One input - Renal artery
• Two outputs - Renal vein and Ureter

67

What can we measure from the rate at which a substance appears in the urine, provided that that substance is completely cleared

• The GFR

68

What is the Tm for glucose in males and females?

• Males - 375mg/min
• Female 300 mg/min females

69

What is glomerular filtration rate?

• The volume of plasma from which any substance (X) is completely removed by the kidney in a given amount of time

70

What is GFR a measure of?

• Kidneys ability to filter a substance (overall function)

71

What does a fall in GFR indicate?

• Kidney disease is progressing

72

In order to measure GFR, what properties must a substance have?

• Must be freely filtered across the glomerulus
• Must not be reabsorbed, secreted or metabolised
• Must pass directly into the urine

73

What is standard renal blood flow?

• 1.1l/min

74

How can we find out renal plasma flow?

• Heamatocrit is the volume (%) of RBC in blood
• Normally 45%
• 0.55 x 1.1 (RBF) = 605ml - Plasma flow

75

What is the filtration fraction of 605 ml plasma?

• 605ml x 0.2 = 125ml (20% blood processed per minute)

76

What is GFR for males?

• 115-125 ml/min

77

What is GFR in females?

• 90/100 mi/min

78

Outline the GFR of inulin, glucose and para-aminohippurate

Inulin - 125ml/min - Not reabsorbed, not secreted
Glucose - 0 - Completely reabsorbed
Para-aminohippurate - 625 ml/min (Secreted!)

79

Outline use of urea

• Used as an active osmol by the kidney

80

What is filtration fraction?

• Proportion of a substance actually filtered
• If renal plasma flow is 605ml/min, 20% of all plasma is filtered, 125ml filtered through into bowman's space and 480ml passes through into peritubular capillaries
• Filtration fraction = Glomerular filtration rate/Renal plasma flow
• Filtration fraction about 20%

81

What is autoregulation?

• Auto-regulatory mechanisms keep GFR within normal limits when arterial BP within physiological limits (80-120 average BP)

82

What is myogenic autoregulation?

• Smooth muscles of afferent capillaries of glomerulus (those going in) contract to increase or decrease pressure

83

What are the limits of myogenic autoregulation?

• Normal average blood pressure between 80-120 mmHG

84

What is GFR?

• Glomerular filtration rate
• A measure of the kidney's ability to filter a substance

85

Give two mechanisms of controlling blood flow to glomerulosa

a
• Smooth muscle control in afferent and efferent arterioles
• Tubular Glomerular feedback

86

What happens to smooth muscle in afferent arterioles to glomerulosa if blood pressure drops?

Vasodilation

87

What happens to smooth muscle in afferent arterioles to glomerulosa if blood pressure increases

• Vasoconstriction

88

Outline tubular glomeruola feedback

• If arterial pressure too high
• Increases glomerular capillary pressure
• Increased glomerula filtration rate
• More Na+ and Cl- in distal convoluted tubule
• Macula densa cell in the JGA respond

89

How do the macula densa cells in the JGA oppose high GFR

• Release adenosine (vasoconstrictor) or prostaglandin (Vasodilator)

90

How much blood is received by the kidney each minute?

• 1.1 litres of blood

91

What is general overflow aminoaciduria?

• All amino acids present in urine
• Due to inadequate deamination in the liver, or increased GFR

92

When is general overflow aminaciduria often seen?

• Early pregnancy

93

What is specific overflow aminoaciduria?

• Only a specific AA is present in the urine.
• This is usually do to a genetic inability to break down one AA
• PKU
• Homocysteinuria

94

How can kidney stones develop as a result of renal aminoaciduria?

• Caused by dibasic acids, due to failure of transport system
• Cystein abnormally insoluble, and is strongly associated with kidney stone formation
• Cysteinuria associated with stone formation

FUN FACT

95

What is the difference between clearance rate and GFR?

GFR does not take into account secreted ions, but clearance rate does.