Lecture 21: Kidney function I Flashcards Preview

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Flashcards in Lecture 21: Kidney function I Deck (62):
1

Functions of Kidney ??

EXCRETION OF METABOLITES OR INGESTED SUBSTANCES 

– Urea from protein catabolism
– Uric acid from nucleic acid breakdown
– Creatinine from muscle creatine
– End products of haemoglobin breakdown

– Foreign chemicals eg. drugs, pesticides 

 

CONTROL OF BODY FLUID COMPOSITION - plasma fluid conc.

– Volume Regulation i.e. linked to sodium concentration

– Osmoregulation i.e. water balance
– pH regulation 

2

What are some hormones that act on the kidney??

e.g. anti-diuretic hormone(ADH) (causes water to be reabsorbed back in to the body from the urine), aldosterone (causes Na+ reabsorbtion), natriuretic peptides(cause excretion of Na+ in to the urine) and parathyroid hormone (allows the kidney to excrete phosphate). 

3

What are some hormones produced by the kidney ??

e.g. renin (important in controlling Na+ concentration in plasma), vitamin D, erythropoietin (it enters the blood and acts at the level of bone marrow to increase the production of red blood cells) and prostaglandins (important in maintaining vascular tone). 

4

what are the two regions of the kidney ?

Cortex (outer)

Medulla (inner)

5

what is the basic unit of the kidney ??

the nephron

6

What does the nephron consist of?

1. Renal copuscle

2. Tubule

7

how many nephrons are there in the kidney

>1 million nephrons/kidney

8

1??

Afferent arteriole

9

2??

Efferent arteriole

10

3??

Glomerulus or Glomerular Capillaries 

11

4??

Bowman’s capsule 

12

5??

Tubule

13

Renal Corpuscle-

focus on filtration interface 

14

1??

Ascending thin limb of Henle's loop

15

2??

Thick ascending limb of Henle's loop

16

3??

Descending thin limb of Henle's loop

17

4??

Proximal straight tubule

18

5??

Proximal convoluted tubule

19

6??

Efferent arteriole

20

7??

Distal convoluted tubule

21

8??

a?

b?

c?

Renal corpuscle

Bowman's capsule

Bowman's space

Glomerulus

22

9??

Cortical collecting duct from another tubule

23

10?

Cortical collecting duct

24

11??

Macula densa

25

12??

Afferent arteriole

26

13??

Medullary collecting duct

27

14??

Medullary collecting ducts from other nephrons

28

What are the types of nephrons?

A. CORTICAL (85%)

outer 2/3 of cortex.
- short Loop of Henle 

 

B. JUXTAMEDULLARY(15%)

inner 1/3 cortex
– long Loop of Henle
– producing concentrated urine 

29

What does the juxtaglomerular apparatus consist of?

juxtaglomerular cells and macula densa cells

30

where are juxtaglomerular cells found?

in the walls of the afferent arteriole

31

where are macula densa cells found?

in the walls of the distal tubule - just as it arises out of the loop of henle

32

blood supply in the nephron??

2 sets of arterioles (afferent and efferent)
2 sets of capillary beds (glomeruli and peritubular) in series. 

33

Basic Renal Processes ??

1) Glomerular Filtration

2) Tubular Reabsorption

3) Tubular Secretion 

4) Metabolism 

34

Glomerular filtration ??

The movement of fluid and solutes from the glomerular capillaries into Bowman’s space.

20 percent of the plasma that enters the glomerulus is filtered. 

35

Tubular secretion ??

The secretion of solutes from the peritubular capillaries into the tubules 

36

Tubular reabsorption ??

The movement of materials from the filtrate in the tubules into the peritubular capillaries. 

37

amount secreted in the urine = ??

38

what happens to substance x??

Substance X is filtered and secreted but not reabsorbed. e.g. para-aminohippuric acid (PAH). 

39

what happens to substance y??

Substance Y is filtered and some of it is reabsorbed. e.g. water and most electrolytes. 

40

what happens to substance z??

Substance Z is filtered and completely reabsorbed. e.g. glucose 

41

What gets through the glomerular filtration barrier? 

Normally all plasma constituents MINUS proteins. 

NB: Molecules that bind to proteins are also excluded. 

 

However infection, damage to glomerulus, very high blood-pressure can result in:

-protein in urine (proteinuria)

-haemoglobin in urine (haemoglobinuria)

-red cells in urine (haematuria) 

42

what is the Glomerular fltration rate (GFR) ?

what does it depend on?

what is it regulated by??

volume of fluid filtered from the glomeruli per minute (ml/min).

GFR depends on a combination of:

1)  Starling forces

2)  Hydraulic permeability

3)  Surface area

And is regulated by both neural and hormonal input. 

43

what are the forces involved in filtration ?

Starling forces (opposing)

i) Hydrostatic
ii) Osmotic/Oncotic

Net glomerular filtration pressure = (60-15)-(29-0) = 16 mmHg 

 

*Note: protein concentration in Bowman’s space filtrate is so low that the oncotic pressure is considered to be zero. 

44

how does blood flow and vasoconstriction/dilation affect glomerular fltration rate (GFR) ?

45

Glomerular Filtration Rate ?

125 ml/min of filtrate formed 180 litres / day (180 litres/day)
 Urine output typically 1.5 litres/day
 because reabsorption occurs 

46

CLEARANCE DEFINITION ??

The volume of plasma that is cleared of a substance in a given time 

47

Equation for clearance??

48

Plasma Inulin Concentation PIN = 0.25 mg/ml

Urine Inulin Concentration UIN = 35 mg/ml

Urine Volume (per min) = 0.9 ml/min 

 

What is the clearance??

 

 

Units for U and P cancel so answer is in units for V

Note: Rate of excretion is 35 x 0.9 = 31.5 mg/min 

 

 

 

Inulin = plant polysaccharide

49

Clearance of inulin estimates GFR. Why? 

It is freely filtered, but not reabsorbed or secreted.

Not metabolised and easily measured.

Inulin is used experimentally.

Creatinine is used in the clinic routinely.

(NB: creatinine is slightly secreted) 

50

e.g. 1: most solutes     2: inulin     3: PAH
(Some substances that show net reabsorption may also be secreted (e.g. K)) 

51

 

 

Substance X

(e.g. para-aminohippuric acid; PAH).

is filtered and completely secreted, but not reabsorbed.

All the plasma that enters the kidney per unit time is cleared of PAH.

So the rate of excretion of PAH must have been provided by a volume of plasma that contained that amount.

Therefore the clearance of X is a measure of renal plasma flow.

i.e. PAH Clearance = Renal Plasma Flow

Effective renal plasma flow ~600 ml/min. 

52

Renal Plasma Flow is ~600ml/min 

Whole blood is 45% cells (Packed cell volume)

Plasma occupies 55% of blood volume.
 Therefore Renal Blood Flow is ????

The formula in general is ??

~600/0.55 = 1100 ml/min.

 i.e. over 20% of the cardiac output 

 

Blood Flow = (Plasma Flow)/(1 - haematocrit)
If haematocrit is given as a percentage (e.g. 45%) Then
Blood Flow = (100 x Plasma Flow)/(100 – haematocrit) 

53

The Kidney

1) Excretes  

but also ??

2) Keeps or saves (reabsorbs). 

54

Luminal membrane of tubule cells faces filtrate. 

Basolateral membrane faces peritubular capillary. 

55

How are the walls of the proximal tubule??

Walls are a single layer of columnar cells 

56

what happens to glucose in the kidney??

Filtered glucose normally reabsorbed.

1.SGLT-Na+-dependent glucose co-transporter.

2.GLUT facilitated transporter.

3. Na+-K+-ATPase pump. 

57

Renal handling of plasma glucose ??

Filtered load is linearly proportional to plasma concentration
and matches reabsorption below 200 mg% = 11 mM.

“Reabsorbed” line shows variation with plasma [glucose].
Excreted = Filtered – reabsorbed, and shows renal threshold at 200 mg%. 

58

Amino acids in the kidney??

Reabsorbed proximal tubule.
At least 8 amino acid transporters.

Overlapping amino acid specificity 

6 Na+-dependent 

59

Summary of PCT reabsorption 

Na+ coupled transporters for

– glucose, amino acids, phosphate, calcium, sulphate, chloride

Passive reabsorption

– urea, chloride, potassium

Hydrogen Carbonate (bicarbonate)

...related to H+ secretion, important in acid- base balance. 

60

Secretion in proximal tubule ??

ORGANIC ACIDS (Anions)

Endogenous molecules.

e.g. bile salts, fatty acids, prostaglandins.

Drugs.

e.g. furosemide, penicillin and acetazolamide

Diagnostic agent.

e.g. para-aminohippuric acid (PAH). 

ORGANIC BASES (Cations)

Endogenous molecules.

e.g. choline, creatinine, dopamine, guanidine, histamine, serotonin.

Drugs.

e.g. atropine, cimetidine and morphine 

61

Organic Anion Secretion in Proximal Tubule ??

1. Organic anion (OA-) enters cell in exchange for dicarboxylate (DC-) (A: organic anion transporters (OAT1 or OAT3))..

2. DC- accumulate in cells by metabolism and Na+-coupled cotransport (B).

3. OA- enters tubule lumen via ATP- dependent transporters (D). 

62

Organic Cation Secretion in PCT ??

1. Enter cell via facilitated organic cation transporters (OCT2).

2. Enter tubule lumen via multidrug and toxin extrusion proteins (MATEs) antiporter in exchange for H+.