Transcript 11.3 The Kidney

11.3 The Kidney
Cleaning the blood and water
regulation
Where are the kidneys?
http://www.nlm.nih.gov/medlineplus/ency/images/ency/fullsize/19615.jpg
The Urinary system
http://image.tutorvista.com/content/excretion/urinary-system-of-man.jpeg
The parts of a kidney as seen in dissection.
http://femmenoir.net/wp-content/uploads/2009/10/kidney.gif
A diagramatic Nephron….
This is the diagram to
learn to draw and
label! Try to place this
in relation to the
previous slide.
http://www.mrothery.co.uk/module4/webnotes/Image8.gif
….looks more like this though.
Look at the blood
supply and how it
is related to the
tubule and the
loop of henle.
http://www.ratical.org/radiation/vzajic/nephron.jpg
Now we know the anatomy….
The Kidney has 2 major functions we
need to know about (and a few others we
don’t!):
1. Cleaning the blood.
2. Regulating the water content of the blood.
Cleaning the blood.
• Occurs in two main stages:
1. Ultra-filtration
2. Selective reabsorbtion.
Ultra-filtration
• A big blood
tube coming
in and a little
blood tube
going out
creates
pressure that
pushes fluid
out of the
glomerulus.
http://click4biology.info/c4b/11/11.3/glomerulus.gif
The substances go through 2
membranes
1. The capillary membrane.
2. Bowman’s capsule
membrane.
• Cells and large plasma
protein macromolecules
cannot pass through this
structure
• Note the filtrate does not
pass through the cells of
either the glomerulus or the
Bowman's capsule .
http://www.colorado.edu/intphys/Class/IPHY3430-200/image/19-4d.jpg
Selective reabsorbtion
• The process of control and regulation in the
kidney begins with a non discriminating filtration
(ultrafiltration) that removes just as many
useful substances as harmful ones from the
blood to make filtrate.
• The kidney then takes back from the filtrate to
the blood those substances that it still requires in
the blood.(Selective Reabsorption)
• The beauty of the way the kidney works is that it
is able to control how much of a substance it
reabsorbs back into the blood (Regulation)
The proximal convoluted tubule (PCT)
• The PCT has a microvilli cell border to increase
the SA for absorption from filtrate. There are
also a large number of mitochondria which
produce the extra ATP required for active
transport.
• 1. All glucose, all amino acids and 85% of
mineral ions are reabsorbed by active transport
from the filtrate to the tissue fluid. They then
diffuse into the blood capillaries.
• 2. Small proteins are reabsorbed by pinocytosis,
digested, and the amino acids diffuse into the
blood.
• 3. 80% of the water is reabsorbed to the blood
by osmosis.
• 4. As urea molecules are so small and carry no
charge that they diffuse passively through the
cell membrane. In part this explains why not all
urea is excreted as blood passes through the
kidney.
http://click4biology.info/c4b/11/hum11.3.htm
The descending loop of Henle
Function:
1. The function of the loop of Henle is to create a salt
bath concentration in the surrounding medullary fluid.
2. Later this results in water reabsorption in the
collecting duct
3. There is also a reduction in the filtrate volume.
Mechanism:
1. There is a concentrated gradient down through
the medullary fluid (a).
2. The descending limb is permeable to water but not to
salt.
3. Filtrate enters the loop hypotonic to the medullary fluid
so water is lost(b).
4. The concentration difference between medullary fluid
and the filtrate is small.
5. The amount of water lost at each stage is small but
accumulates on descent.
6. The water is lost but immediately taken up by the
blood.
7.. Filtrate volume reduces and filtrate salt concentration
increases.
8. The base of the loop is impermeable (c)
http://click4biology.info/c4b/11/hum11.3.htm
The ascending loop of Henle.
1.The filtrate moves up the ascending limb.
2.The ascending limb is permeable to salt.
3.The ascending limb is impermeable to water.
4.The filtrate is slightly more concentrated than the
surrounding fluid.
5.There is a small but accumulating loss of salt (
Na+ and Cl-)at each level.
6.The concentration of the filtrate is gradually
reduced.
7.The medullary gradient is maintained through
exchange with the surrounding blood vessels
• Note that this has resulted in:
1.Filtrate entering and leaving the loop of henle are
approx isotonic
2.Reduced volume of the filtrate
3.Creation and Maintenance of the medullary salt
bath gradient
http://click4biology.info/c4b/11/hum11.3.htm
The Distal Convoluted Tubule (DCT)
and The collecting duct
• The concentration gradient of the
medullary fluid brings about the removal
of water from the collecting duct by
osmosis.
• The permeability of both Distal
Convoluted Tubule (DCT) and the
Collecting tube(CT) can be increased by
the hormone ADH (Vasopressin).
• The cell membranes of these tubules do
not allow the movement of water by
simple diffusion. Rather pores called
Aquaporin can be opened the action of
ADH.
• The DCT is involved in other homeostatic
functions such as the secretion of H+in
pH regulation or K+ in salt regulation
http://click4biology.info/c4b/11/hum11.3.htm
Osmoregulation
• Osmoregulation is the control of the water
balance of the blood, tissue or cytoplasm
of a living cell.
•The water content of body fluids has to be controlled such that the movement
of water to and from cells can changes be controlled.
•The body experiences external and internal changes such as drinking water
availability, sweating and the accumulation of salts that require adjustments in
the water content of blood, tissues and cytoplasm.
•Osmoregulation is under the control of receptors in the hypothalamus.
•In responses to changes the hypothalamus controls the sensation of thirst and
also the endocrine secretion of anti-diuretic hormone.(ADH).
•ADH is secreted from the pituitary and causes the opening of cell membrane
pores called aquaporins which allows water reabsorption into the blood.
Comparison of glomerular filtrate
and urine
•
•
•
•
•
The collecting duct is permeable to both water which as the filtrate descends this collecting duct
is removed concentrating the filtrate (urine). However the collecting duct also leaks some urea
which to the kidney interstitial fluid. Some of this lost urea is reabsorbed by the ascending limb
of the loop of henle but not all, hence the 50% reabsorption. This cycling of urea is an important
feature of the kidneys ability to produce a concentration gradient through the medulla.
Uric acid is a fairly toxic molecule (main nitrogenous excretion in birds) and is largely removed
from blood and tissue fluids.
Glucose is 100% reclaimed by selective reabsorption. The presence of glucose in the urine
would be an indication of diabetes.
Amino acids are all selectively reabsorbed in the nephron and then undergo deamination in the
liver (urea excretion).
Proteins and other macromolecules should not be filtered in the Bowman's capsule and any
presence in urine is usually regarded as an indicator of high blood pressure and damage to the
basement membrane (nephritis) of the bowman's capsule.
Some animations
• A very fast summary…..
http://www.youtube.com/watch?v=glu0dzK4
dbU
• A bit slower but too much detail….
http://www.youtube.com/watch?v=6Wc4f2Kn
bYo&feature=related