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Flashcards in Urinary S3 (Done) Deck (40):
1

What are the two types of nephron?

Cortical

Juxtamedullary

2

Describe blood flow in the glomerulus

20% filtered

80% leaves via efferent arteriole

Same in both nephron types

3

In general, what can pass through the glomerular filter and what cant?

Filtered:

Water

Salts

Small molecules (Small molecular weight and radius of <1.48nm)

Retained:

Large proteins

Cells

4

Compare ultrafiltrate in the Bowman's capsule to plasma

Idnetical to plasma without the large proteins and cells

5

What are the 3 layers of the glomerular filtration barrier

Give a brief outline of each's form and function

Capillary endothelium

Permeable to water, salts and glucose

Filtrate moves between cells

Basement membrane

Acellular, gelatinous, collagen and glycoproteins

Permeable to small proteins

negative glycoproteins repel protein movement

Podocyte layer

Pseudopodia interdigitate to form filtration slits

6

What is the effect of charge on glomerular filtration?

What's the clinical relevance?

Negative charge of the basement membrane glycoproteins repels movement of proteins across barrier

If this negative charge is lost (ie. disease process occurs) then the proteins are more readily filtered

This is Proteinurea

7

Outline the forces behind flitration (include numbers)

Give the normal filtration pressure

Hydrostatic pressure in the capillary:

Favours filtration

50mmHg

Hydrostatic pressure in tubule/capsule:

Opposes filtration

15mmHg

Osmotic pressure in glomerulus:

Opposes filtration

25mmHg

Total:

10mmHG net filtration pressure

8

Describe the functions of myogenic autoregulation in the renal corpuscle

Keeps GFR within limits:

Increase in blood flow leads to afferent arteriole constriction to maintain filtration pressure and hence GFR

Decrease in blood pressure leads to afferent arteriole dilation or efferent arteriole constriction to maintain filtration pressure and hence GFR

9

Outline the control of myogenic autoregulation

Changes in tubular flow rate as a result of GFR changes leads to change in amount of NaCl which reaches the distal tubule

E.g. Inc. BP = Inc. Glomerular capillary pressure = Inc. GFR

Macula densa cells in the DCT respond to changes in luminal [Na+] and [Cl-] and trigger autoregulation to correct GFR

Only applies in acute changes, long-standing change not regulated this way

 

10

Where is the macula densa found?

DCT

Close to the Renal corpuscle

11

Describe the mechanism by which macula densa cells detect NaCl changes in lumen and respond

Concentration dependent salt intake via NaK2Cl cotransporter in apical membrane of macula densa cells

Stimulates juxtaglomerular apparatus to release chemicals which affect afferent arteriolar tone:

Adenosine - Vasoconstriction

Prostaglandins - Vasodilation

12

Give the response of the macula densa should NaCl conc rise or fall in DCT

NaCl increase:

GFR must fall

Therefore Adenosine released to vasoconstrict AA

NaCl decrease:

GFR must rise

Therefore prostaglandins released to vasodilate AA

13

What is tubular reabsorption?

Solutes and water are removed from the tubular fluid and transported back to blood

Called reabsorption because the substances have already been absorbed into the blood somewhere else

14

Outline reabsorption in the PCT

Isosmotic

Driven by Na+ uptake

Other ions accompany to maintain electro-neutrality (Cl- and HCO3-)

Solutes moved from lumen to interstitium to capillaries

Transcellular or paracellular

15

Give the proportions of solutes reabsorbed for common solutes in the PCT (oh, and include water)

100% of nutrient (Glucose)

80-90% HCO3-

67% Na+

65% Water

65% K+

50% Cl-

 

16

Outline the tubular reabsorption of Na+ and water in the PCT

Na+ pumped out of cells on basolateral membrane by Na+/K+ ATPase

Na+ moves across apical membrane down conc gradient

Na+ channel or membrane transporter utilised

Common transporters in PCT are Na+/H+ antiporter and Na+/Glucose symporter

Water moves down osmotic gradient created

17

What are the types of channels and transporters involved in Na+ reabsorption outside of the PCT (but within the nephron, as context might imply)

Loop of Henle:

Na-K-2Cl symporter

Early DT:

Na-Cl symporter

Late DT and CD:

ENaC

18

Describe the reabsorption of Glucose

How does the mechanism of this allow for dysfunction?

SGLUT co-transporters in PCT

Transport 2Na+ ions with 1 Glucose into cell

Glucose moves out of basolateral membrane of cell via facilitated diffusion into peritubular capillaries

100% normally reabsorbed

Dysfunction:

Transport maximum (finite number of transporters have maximum rate)

Tm = 200mg/100ml

If exceed the rest of glucose spills into urine

Water follows

Polyuria

19

Outline secretion in the nephron and the common substances secreted

Involves transepithelial transport

Second route for solutes into lumen (useful considering only 20 of blood filtered)

Substances:

H+

K+

Organic anions and cations

20

Outline organic cation secretion

Basolateral:

Na+/K+ ATPase creates favourable electrical and concentration gradient 

Passive carrier mediated transport of Organic cations (OC+) into cell (uniport)

Apical:

Na+/H+ antiporter creates H+ gradient on apical membrane (H+ efflux)

H+/OC+ exchanger allows secretion of OC+ into lumen

Restrictions:

OC+ subject to transport maximums like any transporter mediated secretion/absorption process

21

Give some examples of Endogenous organic products that are secreted and drugs that are secreted

Endogenous Anions:

Urate

Bile salts

Fatty acid

Anionic drugs:

Pinicillin

Salicylate

NSAIDs

Endogenous Cations:

Ach

Dopamine

Adrenaline

Histamine

Serotonin

Cationic drugs:

Sulfonamides

Morphine

Atropine

 

22

What are the normal GFRs for men and women?

Men:

115-125ml/min

Women:

90-100ml/min

23

Why is GFR clinically important?

Gives an indication as to how well the kidney works

24

What measurements should we be able to calculate for a renal patient?

Filtration fraction

GFR

Clearance

Filtered load (Applied to Tm)

25

Describe how Renal plasma flow is calculated

Input into renal artery per unit time (usually 1.1L/min)

All blood flows through glomeruli in the cortex

Haemocrit/Erythrocyte volume fraction is percentage of blood that is RBCs

Normally 45%

Therefore:

Renal plasma flow x (100 - Haemocrit) = RPF (605ml/min)

26

What is filtration fraction?

How is filtration fraction calculated?

Give normal values

Proportion of substance actually filtered

605ml of plasma enters glomeruli every minute

20% is filtered (filtration fraction)

Therefore

125ml/min is filtered

480ml/min passes to peritubular capillaries

GFR / RPF = filtration fraction

27

What is renal clearance?

Give an example

"The volume of plasma from which any substance is completely removed by the kidney in a given amount of time"

(usually 1min)

E.g. Clearance of urea = 65ml/min

i.e. Kidney removes all urea from 65ml of plasma per minute

 

28

How is renal clearance rate related to GFR?

 

In a substance that is completely filtered at the glomerulus and is not reabsorped at all, the renal clearance (amount of plasma cleared) is equal to the amount of plasma filtered (GFR)

29

What compounds can we use to calculate GFR?

Inulin

Para-aminohippurate

30

Give the equation for calculating renal clearance of a perfectly filtered non-reabsorbed substance and hence GFR

Clearance rate/GFR (ml/min)

=

( Urine conc of substance x Urine flow rate (ml/min) )

/

Plasma conc of substance

 

Yeah, it's ugly, once again sorry about the equations!

31

What is 'Filtered load'?

Calculate the Filtered load of glucose, show your working!

The amount of each substance filtered per unit volume of filtrate

GFR of a substance x Plasma conc of a substance

E.g. Glucose

GFR = 125ml/min

Plasma conc = 200mg/ml OR 2mg/ml

125ml/min x 2mg/ml = 250mg/min

32

Define renal threshold

The plasma concentration of a substance at ehich the transport maximum of a substance is reached and the substance starts spilling into urine

33

What is Transport maximum?

The maximum rate of removal of a substance from the urinary filtrate

Units are Mg/ml

Filtered load - Tm = Substance lost per minute

34

Give some examples of disease/physiological causes of glycosuria

Physiological:

Following a carbohydrate rich meal

During pregnancy

In new borns due to un developed reanl system

Pathological:

Diabetes mellitus

Chronic renal failure

Genetic defects leading to reduced symporters in kidney lumen

35

Describe how glycosuria affects the filtrate

PCT cannot filter all glucose

So at the end of the PCT an increased amount of filtrate is present in the urine

This is due to the increased number of solutes, therefore more water is retained to maintain isosmotic filtrate

Polyuria results

36

37

Where in the kidney tubule are amino acids reabsorbed?

100% PCT

38

What are the two types of aminoaciduria?

Overflow proteinuria

Renal proteinuria

39

Describe overflow aminoaciduria

Two types:

General and specific overflow

General:

Increased excretion of all amino acids

Specific:

Increased secretion of specific amino acid(s)

40

Describe renal aminoaciduria

What other clinical condition may arise?

Mainly confined to dibasic acids

Genetic cause (Lack of transport proteins)

Impaired reabsorption of cysteine (an abnormally insoluble amino acid) is associated with renal stone formation