The Kidney

1
The Kidney

• The structure and function of the nephron

2
Structure of the nephron

• The nephron is the functional unit of the kidney
• There are about a million in each kidney.
• They consist of
• a cup-shaped Bowmans capsule
• immediately below the capsule a twisted region
  called the proximal convoluted tubule.

3
Structure of the nephron

• followed by the long hair-pin like loop of
  Henle, which runs deep into the medulla and then
  back into the cortex
• this is followed by another twisted region
  called the distil convoluted tubule
• This is joined to the collecting duct which
  carries urine through the medulla to the pelvis
  of the kidney

4
(No Transcript)
5
Glomerulus, a knot of capillaries
6
afferent arteriole
Glomerulus, a knot of capillaries
7
afferent arteriole
efferent arteriole
Glomerulus, a knot of capillaries
8
afferent arteriole
efferent arteriole
Glomerulus, a knot of capillaries
venuole
9
Bowmans capsule
afferent arteriole
efferent arteriole
Glomerulus, a knot of capillaries
venuole
10
Bowmans capsule
afferent arteriole
proximal tubule
efferent arteriole
Glomerulus, a knot of capillaries
distil tubule
venuole
11
Bowmans capsule
afferent arteriole
proximal tubule
efferent arteriole
Glomerulus, a knot of capillaries
distil tubule
venuole
loop of Henle
12
Bowmans capsule
afferent arteriole
proximal tubule
efferent arteriole
Glomerulus, a knot of capillaries
distil tubule
venuole
ascending loop descending loop
loop of Henle
13
Bowmans capsule
afferent arteriole
proximal tubule
efferent arteriole
Glomerulus, a knot of capillaries
distil tubule
venuole
ascending loop descending loop
Collecting duct
loop of Henle
14
Bowmans capsule
afferent arteriole
proximal tubule
efferent arteriole
Glomerulus, a knot of capillaries
distil tubule
venuole
ascending loop descending loop
Collecting duct
loop of Henle
to renal pelvis
15
Bowmans capsule
afferent arteriole
proximal tubule
efferent arteriole
Glomerulus, a knot of capillaries
distil tubule
venuole
ascending loop descending loop
Collecting duct
capillary net
loop of Henle
to renal pelvis
16
(No Transcript)
17
Structure of the nephron

• Each nephron has a rich blood supply
• Each Bowmans capsule is supplied with blood by
  an afferent arteriole
• This branches inside the Bowmans capsule to form
  the glomerulus
• Taking blood away from the capsule is the
  efferent arteriole.
• The afferent arteriole is much wider than the
  efferent arteriole..

18
Structure of the nephron

• .. So there is more blood carried to the
  glomerulus than is carried away, and pressure in
  the glomerulus is high.

19
Ultrafiltration

• ..the filtering of small molecules (under
  pressure) out of the blood and into the Bowmans
  capsule.

20
Bowmans Capsule
21
Bowmans Capsule
glomerulus
22
Bowmans Capsule
glomerulus
afferent arteriole
23
Bowmans Capsule
glomerulus
efferent arteriole
afferent arteriole
24
Bowmans Capsule
glomerulus
efferent arteriole
distil convoluted tubule
afferent arteriole
25
Bowmans Capsule
proximal convoluted tubule
glomerulus
efferent arteriole
distil convoluted tubule
afferent arteriole
26
Bowmans Capsule
proximal convoluted tubule
glomerulus
efferent arteriole
distil convoluted tubule
capsular space
afferent arteriole
27
(No Transcript)
28
(No Transcript)
29
(No Transcript)
30
Ultrafiltration

• The blood entering the glomerulus is separated
  from the space inside the Bowmans capsule, by
  two cell layers and a basement membrane.

31
podocyte cell
32
podocyte cell
nucleus
33
podocyte cell
nucleus
Basement membrane
34
podocyte cell
nucleus
Basement membrane
capillary endomethium
35
podocyte cell
nucleus
Filtrate in lumen of capsule
Basement membrane
capillary endomethium
36
Ultra filtration

• The first layer is the wall or endothelium of the
  capillary. In the glomerulus this single layer of
  cells has thousands of gaps.
• The basement membrane between the two cell layers
  is composed of glycoprotein and collagen fibres.
  Its mesh-like structure acts as a filter during
  ultrafiltration.

37
Ultra filtration

• The second cell layer is the wall of the Bowmans
  capsule
• The epithelial cells in this wall are called
  podocytes
• They have foot-like processes and do not fit
  tightly together so have gaps between them.

38
(No Transcript)
39
(No Transcript)
40
Ultra filtration

• Most molecules in the blood can pass through the
  gaps in he capillary and the podocyte.
• BUT the basement membrane acts as a filter
  preventing large molecules such as proteins and
  blood cells from passing through.
• Only the small soluble molecules can pass through
  due to the high pressure in the kidney

41
Reabsorbtion
42
Reabsorbtion

• Up to 70 of water and solutes are removed from
  the plasma as it passes through the glomerulus
• These include some useful substances such as aa
  and glucose, these must be reabsorbed back into
  the body.
• This process is called selective reabsorbtion.

43
Reabsorbtion

• All the glucose, aa, vitamins and many Na and Cl
  ions are actively transported out of the proximal
  tubule and back into the blood.

44
Adaptations of the proximal tubule

• The cells possess microvilli to provide a large
  surface area for absorption
• Numerous mitochondria are present to provide ATP
  for active transport.

45
Reabsorbtion

• The uptake of these substances means that the
  blood in the capillaries surrounding the nephron
  now has a a relatively high solute concentration.
• So large amounts of water passes from the
  filtrate back to the blood in the proximal tubule
  by osmosis

46
(No Transcript)
47
The Loop of Henle

• Its function is to create an area of high solute
  concentration deep in the medulla.
• The collecting ducts of each nephron pass through
  this area and so a lot of water can be reabsorbed
  from the ducts by osmosis
• A concentrated urine can be produced as a result

48
(No Transcript)
49
Descending limb
50
Descending limb
Ascending limb, impermeable to water but
permeable to NaCl
51
Descending limb
Ascending limb, impermeable to water but
permeable to NaCl
Descending very permeable to water
52
Ascending limb very thick
Descending limb
Ascending limb, impermeable to water but
permeable to NaCl
Descending very permeable to water
53
Ascending limb very thick
Descending limb
Water moves out tubule into back into capillary
Ascending limb, impermeable to water but
permeable to NaCl
Descending very permeable to water
54
Ascending limb very thick
Descending limb
Water moves out tubule into back into capillary
Ascending limb, impermeable to water but
permeable to NaCl
Descending very permeable to water
Na and Cl ions move out of tubule
55
Ascending limb very thick
Descending limb
Water moves out tubule into back into capillary
Ascending limb, impermeable to water but
permeable to NaCl
Descending very permeable to water
Na and Cl ions move out of tubule
Increasing salt conc. in interstitial fluid
56
Ascending limb very thick
Descending limb
Decreasing salt conc. in interstitial fluid
Water moves out tubule into back into capillary
Ascending limb, impermeable to water but
permeable to NaCl
Descending very permeable to water
Na and Cl ions move out of tubule
Increasing salt conc. in interstitial fluid
57
Ascending limb very thick
isotonic filtrate
Descending limb
Decreasing salt conc. in interstitial fluid
Water moves out tubule into back into capillary
Ascending limb, impermeable to water but
permeable to NaCl
Descending very permeable to water
Na and Cl ions move out of tubule
Increasing salt conc. in interstitial fluid
58
Ascending limb very thick
isotonic filtrate
Descending limb
Decreasing salt conc. in interstitial fluid
Water moves out tubule into back into capillary
Ascending limb, impermeable to water but
permeable to NaCl
Descending very permeable to water
Na and Cl ions move out of tubule
hypertonic filtrate
Increasing salt conc. in interstitial fluid
59
Ascending limb very thick
isotonic filtrate
hypotonic filtrate
Descending limb
Decreasing salt conc. in interstitial fluid
Water moves out tubule into back into capillary
Ascending limb, impermeable to water but
permeable to NaCl
Descending very permeable to water
Na and Cl ions move out of tubule
hypertonic filtrate
Increasing salt conc. in interstitial fluid
60
The loop of Henle

• The ascending limb is more permeable to salts and
  less permeable to water
• As filtrate moves up Na and Cl ions move out
  passively and then actively
• This cause water to move out of the descending
  limb by osmosis.
• Thus filtrate become more concentrated as it
  passes down the descending limb

61
The loop of Henle

• The solute conc. in any part of the loop is
  always lower in the ascending limb than the
  descending limb
• This mechanism is called the countercurrent
  mulitplier mechanism.

62
The loop of Henle

• As the collecting ducts pass through the medula
  to the pelvis they pass through this region of
  high solute concentration
• So water is also drawn out the collecting ducts
  due to osmosis resulting in a far more
  concentrated urine.