Lecture 21: Kidney function I Flashcards Preview

1060 Human form and function > Lecture 21: Kidney function I > Flashcards

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

A image thumb
6

What does the nephron consist of?

1. Renal copuscle

2. Tubule

A image thumb
7

how many nephrons are there in the kidney

>1 million nephrons/kidney

8

1??

Q image thumb

Afferent arteriole

9

2??

Q image thumb

Efferent arteriole

10

3??

Q image thumb

Glomerulus or Glomerular Capillaries 

11

4??

Q image thumb

Bowman’s capsule 

12

5??

Q image thumb

Tubule

13

Renal Corpuscle-

focus on filtration interface 

A image thumb
14

1??

Q image thumb

Ascending thin limb of Henle's loop

15

2??

Q image thumb

Thick ascending limb of Henle's loop

16

3??

Q image thumb

Descending thin limb of Henle's loop

17

4??

Q image thumb

Proximal straight tubule

18

5??

Q image thumb

Proximal convoluted tubule

19

6??

Q image thumb

Efferent arteriole

20

7??

Q image thumb

Distal convoluted tubule

21

8??

a?

b?

c?

Q image thumb

Renal corpuscle

Bowman's capsule

Bowman's space

Glomerulus

22

9??

Q image thumb

Cortical collecting duct from another tubule

23

10?

Q image thumb

Cortical collecting duct

24

11??

Q image thumb

Macula densa

25

12??

Q image thumb

Afferent arteriole

26

13??

Q image thumb

Medullary collecting duct

27

14??

Q image thumb

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 

A image thumb
29

What does the juxtaglomerular apparatus consist of?

juxtaglomerular cells and macula densa cells

A image thumb
30

where are juxtaglomerular cells found?

in the walls of the afferent arteriole

A image thumb
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. 

A image thumb
33

Basic Renal Processes ??

1) Glomerular Filtration

2) Tubular Reabsorption

3) Tubular Secretion 

4) Metabolism 

A image thumb
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. 

A image thumb
35

Tubular secretion ??

The secretion of solutes from the peritubular capillaries into the tubules 

A image thumb
36

Tubular reabsorption ??

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

A image thumb
37

amount secreted in the urine = ??

A image thumb
38

what happens to substance x??

Q image thumb

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

39

what happens to substance y??

Q image thumb

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

40

what happens to substance z??

Q image thumb

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) 

A image thumb
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. 

A image thumb
44

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

A image thumb
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 

A image thumb
46

CLEARANCE DEFINITION ??

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

47

Equation for clearance??

A image thumb
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

A image thumb
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

Q image thumb

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

51

 

 

Q image thumb

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. 

A image thumb
55

How are the walls of the proximal tubule??

Walls are a single layer of columnar cells 

A image thumb
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. 

A image thumb
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%. 

A image thumb
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). 

A image thumb
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+. 

A image thumb