Excretion is the process of removing metabolic waste, including carbon dioxide and nitrogenous compounds like urea, from the body to prevent toxicity. Carbon dioxide is transported to the lungs for exhalation, while urea is produced in the liver from deaminated amino acids and excreted by the kidneys. The liver plays a crucial role in metabolism, detoxification, and maintaining homeostasis, working closely with the kidneys to filter blood and produce urine.

1. A2 – Module 1 – Unit 2 -
Excretion
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2. 1.2.1 Excretion
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3. What is excretion?
 Excretion = the removal of metabolic waste from the body
 Metabolic waste = consists of waste substances that may be toxic or are
produced in excess by the reactions inside cells.
 There are 2 substances that are produced in very large amounts:
 Carbon dioxide
 Nitrogen containing compounds such as urea
 Note: EGESTION is when your body removes undigested food by the process of
defecation. EXCRETION is when your body removes metabolic waste which has
entered your cells.
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4. Where are these substances
excreted?
 Carbon dioxide is passed from the cells of respiring tissues into the
bloodstream. It is transported in the blood (mostly in the form of
hydrogencarbonate ions) to the lungs. In the lungs the carbon dioxide diffuses
into the alveoli to be excreted as we breathe.
 Urea is made from the break down of excess amino acids in the liver. This
process is called deamination. Urea is passed into the bloodstream to be
transported to the kidneys.
 it is transported in solution (dissolved in plasma)
 In the kidneys, urea is removed from the blood to become a part of urine.
 Urine is stored in the bladder before being excreted via the urethra.
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5. Why must these substances be remove?
Part I
Carbon dioxide:
 Excess carbon dioxide can lead to toxicity via three main effects:
1. Carbon dioxide is transported in the blood as hydrogencarbonate ions. This occurs
inside the red blood cells under the influence of carbonic anhydrase
H2CO3  H+ + HCO3
-
The hydrogen ions combine with haemoglobin. They compete with oxygen for space
on the haemoglobin. If there is too much carbon dioxide in the blood it will reduce
oxygen transport
2. Carbon dioxide when bound to haem forms carbaminohaemoglobin. (Carbon
dioxide has a higher affinity for haem, when the compound is formed
carbaminohaemoglobin will have a lower affinity for oxygen than normal haem)
Therefore it becomes difficult for oxygen to attach onto haem as carbon dioxide
is strongly associated with haem.
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6. Why must these substances be removed?
Part II
3. Excess carbon dioxide can cause respiratory acidosis. The carbon dioxide dissolves in
the blood plasma. Once dissolved it can combine with water to produce carbonic acid:
CO2 + H2O  H2CO3
The carbonic acid dissociates to release hydrogen ions
H2CO3  H+ + HCO3
-
 The hydrogen ions lower the pH  acidity within the blood circulation. Proteins in the
blood act as buffers to resist the change in pH.
 If the pH change is small the extra H+ ions are detected by the respiratory centre in the
medulla oblongata of the brain resulting in
 Increased breathing rate removing excess carbon dioxide
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7. Why must these substances be removed?
Part III
  If the pH drops below 7.3 it results
in
 slowed or difficult breathing, headache,
drowsiness, restlessness, tremor and confusion.
 May also be a rapid heart rate and changes in
blood pressure.
 THIS IS RESPIRATORY ACIDOSIS (A MEDICAL
EMERGENCY, NEEDS TREATMENT IMMEDIATELY)
Respiratory acidosis can also be caused by
diseases or conditions that affect the lungs
themselves due to blockage of airway
leading to increase in carbon dioxide.
These diseases include; emphysema,
chronic bronchitis, asthma or severe
pneumonia. Conditions such as swelling, a
foreign object or vomit in the airways are
also causative.
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8. Why must these substances be removed?
Part IV
 Nitrogenous Compounds:
 The body cannot store proteins or amino acids(aa). However, aa contain as much
energy as carbohydrates, therefore we do not want to waste this energy source.
AA are transported to the liver and the potentially toxic amino group is removed
(deamination).
 Step 1 -The amino group initially forms a very soluble and highly toxic compound =
ammonia
 Amino acid + oxygen  keto acid + ammonia
 Step 2 - Ammonia is converted to a less soluble and less toxic compound = urea
 Ammonia + carbon dioxide  urea + water
2NH3 + CO2  CO(NH2)2 + H2O
 Urea is then transported to the kidneys for excretion. The remaining keto acid can
be used directly in respiration to release its energy or it may be converted to a
carbohydrate or fat for storage.
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9. 1.2.2 The Liver
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10. The structure of the liver
 The liver cells namely the
hepatocytes carry hundreds of
metabolic processes and has an
important role in homeostasis.
Therefore it is essential for a
continuous supply of blood. The
internal structure of the liver is
arranged to ensure that as much
blood flows past as many liver cells
as possible
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11. Blood flow to the liver
 TO:
 The liver has two blood supplies
 Oxygenated blood from the heart. Blood
travels from the aorta via the HEPATIC
ARTERY INTO THE LIVER.
 This supplies the oxygen essential for
aerobic respiratory. Hepatocytes are very
active and require energy in the form of
ATP so it is essential there is a good
oxygen supply.
 Deoxygenated blood from the digestive
system. This enters the liver via the
HEPATIC PORTAL VEIN. This blood is
rich in the products of digestion. The
concentration of the various compounds
will be uncontrolled and the blood may
contain toxic compounds that have been
absorbed by the intestine.
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12. Blood flow from the liver
 FROM:
 Blood leaves the liver via the
HEPATIC VEIN. This re-joins the vena
cava and the blood returns to normal
circulation
 A Fourth vessel connected to the
liver is not a blood vessel. It is the
bile duct. Bile is a secretion from the
liver. It has both a digestive function
and an excretory function. The bile
duct carries bile from the LIVER TO
THE GALLBLADDER where it is stored
until required to aid the digestion of
fats in the small intestine.
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13. The arrangement of cells inside the liver
 The liver is divided into lobes and further divided into
cylindrical lobules.
 As the hepatic artery and hepatic portal vein enter the
liver, they split into smaller and smaller vessels which run
parallel or between the lobules and are known as inter-
lobular vessels.
 The blood from two blood vessels are mixed and passed
through a special chamber called sinusoid which
furthermore empty into the intra-lobular vessels a branch of
the hepatic vein.
 The branches of the hepatic vein from different lobules join
together to form the hepatic vein draining blood from the
liver.
 As blood moves along the sinusoid it is in very close contact
with the liver cells. They are able to remove molecules
from the blood and pass molecules into the blood.
 One of the many functions of the liver cells is to
manufacture bile. This is released into the bile canaliculi
(small canals). These join together to form the bile duct,
which transports the bile to the gall bladder.
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14. Liver Cells
 Hepatocytes are unspecialised simple cuboidal shaped cells which have many
microvilli on their surface
 They are however involved in many metabolic functions including;
 Protein synthesis
 Transformation
 Storage of carbohydrates
 Synthesis of cholesterol and bile salts
 Detoxification and other processes
 This means that their cytoplasm must be very dense and is specialised in the
amounts of certain organelles that it contains
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15. Kupffer cells
 Kupffer cells are specialised macrophages
moving about in the sinusoids involved in the
breakdown and recycling of red blood cells. A
product it produces during breakdown is
bilirubin which is excreted as part of the bile
and in faces. Bilirubin is the brown pigment is
faeces.
 Application Scenario:
 A common condition in newborns, jaundice
refers to the yellow color of the skin and
whites of the eyes caused by excess bilirubin
in the blood.
 It is also seen in adults where an excess
chronic consumption of alcohol can have
damaging effects on your liver meaning that
you are not removing bilirubin from your liver
and bile ducts quickly enough, as it builds up in
the blood it is deposited in the skin… The
resulting is jaundice.
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16. 1.2.3 – Functions of the
liver
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17. Wide Range of functions of the liver
 Control of:
 Blood glucose levels, amino acid levels, lipid levels
 Synthesis of:
 RBC in the fetus, bile, plasma proteins, cholesterol
 Storage of:
 Vitamins A, D and B12 , iron, glycogen
 Detoxification of:
 Alcohol and drugs
 Breakdown of hormones
 Destruction of RBCs
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18. Formation of Urea
 Daily requirement is 40-60g of protein, but daily consumption is far
more greater therefore, breakdown of amino acids are needed as
accumulation leads to toxicity.
 Two step process occurs in the liver before the amino acid component
is excreted
 DEAMINATION
 ORNITHINE CYCLE
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19. Formation of Urea
 DEAMINATION:
 Removal of NH3 group fro the amino acid with oxygen forming a keto acid (-RCOCOOH) and
Ammonia (NH3)
 Ammonia is highly toxic and very soluble therefore should not be allowed to accumulate in the
blood circulation.
 On removal of NH3 group energy is released.
 THE ORNITHINE CYCLE:
 Ammonia is converted into a less soluble and less toxic substance when combined with CO2
forming Urea.
 Urea is further passed into the blood circulation and into the kidneys where it is filtered out
of the blood circulation and is concentrated in the urine.

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20. Detoxification
 The liver detoxifies alcohol and drugs. Toxins can also be rendered harmless by oxidation,
reduction, methylation or a combination with another molecule.
 Liver cells contain many enzymes that enable rendering of toxic molecules  less toxic form.
 This includes catalase which converts H2O2 to oxygen and water
 DETOXIFICATION OF ALCOHOL:
 Alcohol is a CNS depressant; contains a lot of energy that can be used for respiration.
 STEP 1: Ethanol  Ethanol dehydrogenase  Ethanal (occurs in the hepatocytes)
 STEP 2: Ethanal  Ethanal dehydrogenase  Ethanoic acid
 STEP 3: Ethanoic acid  Ethanoate + CoA  Acetyl CoA
 The hydrogens release in the steps above are combined with NAD  NADH
 NAD is required to oxidise and breakdown fatty acids for use in respiration
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21. Future Possible Complications
 If the liver has to detoxify too
much alcohol it has insufficient
NAD to deal with the fatty acids.
 These fatty acids are converted
back to lipids and are stored in the
hepatocytes, causing the liver to
become enlarged
 Causes a condition known as fatty
liver  alcohol-related hepatitis
or cirrhosis.
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22. Stretching Your Knowledge
Scenario:
 Liver cells contain a large group of enzymes called the cytochrome P450 enzymes.
These are responsible for the breakdown of some toxic molecules, such as cocaine
and other drugs (recreational and medicinal). The P450s are most concentrated in
the endoplasmic reticulum of liver cells. As a result of variation these enzymes can
be more effective in some people than in others (Caucasian population compared
to Afro-Caribean population)
 Many drugs can be more effective in some people than in others and may also
cause variable side effects
Task:
1. Suggest why the P450s are most concentrated in the endoplasmic reticulum?
2. Suggest why many medicinal drugs have different side effects in different people
3. Explain why the P450s are not identical in every person.
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The P450s are proteins; these are manufactured by the ribosomes that are attached to the
endoplasmic reticulum – they can be packaged in vesicles and transported to where they are
needed
Each person may have slightly different enzymes (evolution). These may break the drugs down in a
slightly different way producing different by-products (SEs)
Genetic variation means that different people will have different alleles – these will produce
slightly different enzymes.

23. Questions:
1. Why must ammonia be converted to urea?
2. Explain why excess amino acids and alcohol should not be excreted?
3. Suggest why the liver cells have large number of mitochondria and ribosomes
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Ammonia is highly soluble and very toxic; urea is less soluble and less toxic
They contain valuable energy that can be converted to useable forms. Some
amino acids can be converted into other amino acids
The mitochondria provide ATP (metabolic energy) for the active or energy-
requiring processes, e.g. protein synthesis, mitosis, active transport, endo
and exocytosis. The ribosomes manufacture the many enzymes that are
needed in liver cells.

24. 1.2.4 The Kidney
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25. The structure of the kidney
 Positioned at each side of the spine
just below the lowest rib
 Supplied with blood from a renal
artery and is drained by a renal
vein
 JOB: - remove waste products from
the blood and to produce urine.
 Urine passes out of the kidney
down the ureter to the bladder
where it can be stored before
release
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26. The Nephron
- Part I
 The bulk of each kidney consists of
tiny tubules called nephrons.
 They are closely associated with
tiny blood capillaries
 Each nephron starts in the cortex
 In the cortex the capillaries form a
knot called the glomerulus
 This is surrounded by a cup-shaped
structure called the Bowman’s
Capsule
 Fluid from the blood is pushed into
the Bowman’s capsule by the
process of ultrafiltration
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27. The Nephron
- Part II
 The capsule leads into the nephron which
is divided into 4 parts:
 The proximal convoluted tubule
 Loop of Henle (Descending and
Ascending Limb)
 Distal convoluted tubule
 Collecting duct
 As fluid moves along the nephron its
composition is altered. This is achieved
by selective reabsorption. Substances are
reabsorbed back into the tissue fluid and
blood capillaries surrounding the nephron
tubule.
 The final product in the collecting duct is
urine, passed into the pelvis  ureter 
bladder.
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28. How does the composition of the fluid
change?
 In the PCT the fluid is altered by the reabsorption of all the sugars, most salts
and some water
 In total about 85% of the fluid is reabsorbed here
 In the DL of the Loop of Henle, the water potential of the fluid is decreased
by the addition of salts and removal of water
 In the AL of the Loop of Henle, the water potential of the fluid is increased as
salts are removed by active transport
 In the collecting duct the water potential is decreased again by the removal
of water.
 This ensures that the final product (urine) has a low water potential.
 Urine has a higher concentration of solutes than is found in the blood and tissue
fluid.
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29. Questions:
1. Suggest why the nephrons are convoluted
2. Why are there many capillaries around each nephron?
3. Explain why reabsorption from the nephron must be selective
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The fact that the nephrons are convoluted allows there to be an increase the
length for greater surface area for absorption or filtration. This ensures
accuracy and minimizes loss in terms of absorption of useful molecules
required for the body.
Materials reabsorbed from the fluid in the tubule can re-enter the blood
circulation
Some of the molecules in the nephron are waste and must be left in the fluid
to be excreted. Other molecules are useful to the body and must be
reabsorbed.

30. Practice Exam Questions:
1. What is meant by the term excretion? [2 marks]
2. Name the two excretory products produced in mammals [2 marks]
3. Name the two organs that remove these products from the body [2 marks]
4. Name the blood vessels that carry blood to the liver [2 marks]
5. What is a sinusoid and where is it found? [2 marks]
6. What is a hepatocyte? [1 marks]
7. What is meant by the term deamination? [2 marks]
8. What occurs during the ornithine cycle? [2 marks]
9. Name the three sections of the kidney as seen in longitudinal section [3 marks]
10. Name the tubules found in the kidney [2 marks]
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31. Practice Exam Question:
ANSWERS
1. The removal of waste products from cell metabolism
2. Carbon dioxide and urea
3. The lungs and the kidneys
4. The hepatic artery( oxygenated blood) and hepatic portal vein (deoxygenated
blood)
5. A sinusoid is a channel between the liver cells; they are found in the liver lobules
6. A liver cell
7. The removal of the amino group from an amino acid forming ammonia and leaving
a ketose residue
8. The conversion of ammonia to urea by the addition of carbon dioxide
9. Cortex, medulla and pelvis
10. Nephrons
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32. 1.2.5 – Formation of
Urine
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33. Overview Videos:
 https://www.youtube.com/watch?v=wWsdcfGta4k
 https://www.youtube.com/watch?v=Vqce2dtg45U
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34. Ultrafiltration
- PART I
 Blood flows through the afferent
arteriole into the glomerulus and blood
leaves through the efferent arteriole
 Afferent arteriole is wider in diameter
than the efferent arteriole
 Efferent arteriole is an arteriole – which
is muscular and can constrict to raise the
blood pressure in the glomerulus. In most
organs a venule carries away blood away
 This difference ensures the glomerulus
is higher in pressure in comparison to
the pressure in the Bowman’s capsule
 This pressure differences pushes the
fluid from the blood into the Bowman’s
capsule
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35. Ultrafiltration
- PART II
 The barrier between the blood in
the capillary and the lumen of the
Bowman’s capsule consists of three
layers:
 Endothelium of the capillary
 A basement membrane
 The epithelial cells of the
Bowman’s capsule (podocytes)
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36. Ultrafiltration
- PART III
 Each structure is adapted to allow ultrafiltration:
 Fenestrated Endothelium – narrow gaps between each endothelium cells – blood
plasma and substances dissolved in blood plasma can pass through these narrow
gaps
 Basement membrane – fine mesh of collagen fibres and glycoprotein
 This filter prevent the passage of molecules with a relatively high molecular mass. All
proteins (and all blood cells) are held in the capillaries of the glomerulus
 Epithelial cells of the Bowman’s capsule are called PODOCYTES which have a
specialized shape.
 Podocytes have finger-like projections called major processes. Ensuring that gaps are
present in between cells.
 The fluid from the blood in the glomerulus can pass between these cells into the lumen of
the Bowman’s capsule
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37. What is filtered out of the blood?
 Blood plasma containing dissolved substances is pushed under pressure from
the capillary into the lumen of the Bowmans capsule. This includes the
following substances:
 Water
 Amino acids
 Glucose
 Urea
 Inorganic ions (Na+, Cl-, K+)
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38. What is left in the capillary?
 The blood cells and proteins are left in the capillary
 Presence of the proteins means that the blood has a very low (very negative)
water potential
 Due to this low water potential it ensures that some of the fluid is retained in the
blood, and this contains some of the water and dissolved substances listed above
 The very low water potential of the blood in the capillaries is important to help
reabsorb water at a later stage.
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39. Stretching Your Knowledge
Scenario:
 High Blood pressure can damage the capillaries of the glomerulus and the
epithelium of Bowman’s capsule.
Task:
 Explain why the presence of protein in urine can be a sign of hypertension?
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Proteins are normally filtered by the basement membrane. If this has been damaged by high
blood pressure then proteins can enter bowmans capsule from the blood and pass into the urine
presenting as proteinuria

40. Selective Reabsorption
- PART I
 Reabsorption is achieved by a combination of processes described below. The cells
lining the proximal convoluted tubule are specialized to achieve this reabsorption:
 PCT cells are highly folded forming microvilli for increase surface area for reabsorption
 PCT cells also have special co-transporter proteins transporting glucose or amino acids,
in association with sodium ions from the tubule into the cell  facilitated diffusion
 Molecules are moving from a high water potential to a low water potential (no ATP is required)
 PCT cells lined towards the capillaries are also highly folded forming microvilli for
increased surface area. This membrane contains sodium-potassium pumps that pump
sodium ions out of the cell and potassium ions into the cell.
 These pumps require ATP, so have high amounts of mitochondria surrounding
 Large molecules, such as small proteins that may have entered the tubule, will be
reabsorbed by endocytosis.
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41. Selective Reabsorption
- PART I
5/17/2015 41PCT cells lining towards the capillaries
PCT cells lining

42. 5/17/2015 42

43. Questions:
1. Explain what is meant by ultrafiltration?
2. Suggest what might happen if water is not reabsorbed from the nephron
3. Explain why the concentrations of glucose and amino acids are the same in
the glomerular filtrate as in the blood plasma
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Filtering on a molecular scale. Small molecules pass through the basement
membrane, which acts as a filter, while larger molecules are held in the
blood
A large volume of very dilute urine would be produced and dehydration would
occur
Because the amino acids and glucose have been passed from the blood
plasma to the glomerular filtrate by ultrafiltration in the glomerulus

44. 1.2.6 – Water
reabsorption
OCR – A2 – Module 2
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45. Reabsorption of Water
 Each minute 125cm3 of fluid is filtered from the blood and enters the nephron
tubules
 After selective reabsorption in the proximal convoluted tubules about 45cm3
is left
 The role of the loop of henle is to create a low (very negative) water
potential in the tissue of the medulla  ensures that more water can be
reabsorbed from the fluid in the collecting duct
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46. The Loop of Henle
- Part I
 Consists of a descending limb which descends into the medulla and an
ascending limb that ascends back out to the cortex.
 The overall effect of the loop of henle:
 Filter the fluid entering the descending limb which is slightly concentrated.
 Osmotically removing water from the descending limb into the Vasa Recta
 Water potential decreases and is highly concentrated as you enter the ascending
limb
 Here Na+ and Cl- ions are actively removed from the ascending limb into the Vasa
Recta
 The ascending limb is impermeable to water, so cannot leave the tubule.
 The ascending limb increases in water potential as it enters the DCT
 = COUNTERCURRENT MULTIPLIER
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47. The Loop of Henle
- Part II
 Vasa Recta surrounds the loop of
henle in an opposing fashion;
 As you go down the descending limb
in the loop of henle you are
ascending in the Vasa Recta, as you
go up the ascending limb in the loop
of henle you are descending in the
Vasa Recta
 The top of the ascending limb urine
is highly dilute (watery) therefore as
you continue from the DCT and CT
water is reabsorbed leaving a
concentrated fluid which is excreted
 The amount of water reabsorbed
depends on the needs of the body
and so the kidney is also an organ of
osmoregulation.
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48. The Collecting Duct
 At the top of the ascending limb it
connects to the DCT which is very
short in comparison to your PCT,
active transport is used to reabsorb
water from your DCT into your
surrounding tissue fluid
 From the DCT  CD water has a
high water potential therefore the
CD carries on removing water
leaving as it descends from the
medulla into your pelvis.
 The remaining solute left becomes
highly concentrated and is
excreted.
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49. Stretching Your Knowledge
Scenario:
 Question: Why do camels have humps?
Answer: It was a myth that the hump was due to a long loop of henle.
However current research shows that the hump stores fat which can be
metabolized to release energy and water. But why do camels need an extra
long loop of Henle? All mammals adapted to living in arid regions share this
feature. It provides them with a longer countercurrent mechanism that can
increase the salt concentration in the medulla more than in other mammals.
Task:
 Explain why it is beneficial to mammals living in arid regions to have higher
salt concentrations in their medullas?
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A higher salt concentration in the medulla means that a greater water potential gradient can be
achieved between the urine in the CD and the medulla. This means that more water can be
reabsorbed from the CD and then pass into blood capillaries and the urine is made more
concentrated. There will be less urine produced and less water lost.

50. Stretching Your Knowledge
Scenario:
 The tissue fluid in the medulla has a low water potential, so how can water
pass from the tissue fluid into the blood plasma by osmosis?
Task:
 Explain an arrangement of the blood vessels that could create blood plasma
with an even lower water potential than the tissue fluid.
5/17/2015 50
A higher salt concentration in the medulla means that a greater water potential gradient can be
achieved between the urine in the CD and the medulla. This means that more water can be
reabsorbed from the CD and then pass into blood capillaries and the urine is made more
concentrated. There will be less urine produced and less water lost.

51. Questions:
1. Why must the collecting duct pass back through a region of low water
potential?
1. Why is it important for terrestrial mammals to reabsorb as much water as
possible?
2. Suggest why beavers have short loops of Henle
5/17/2015 51
This arrangement allow water to be reabsorbed from the collecting ducts
back into the tissue fluid of the medulla. This concentrates the urine.
Terrestrial mammals gain water by eating and drinking. They lose water
through sweat, exhaling, excretion and egestion. It is important not to lose
more water than necessary, as it may not be readily available.
Beavers live beside or in water. Water is readily available and they do not
need to conserve it as much.

52. 1.2.7 - Osmoregulation
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53. Osmoregulation
 Osmoregulation = control of water levels and salt levels in the body.
 Water is gained from: Food, drink, metabolism
 Water is lost in: urine, sweat, water vapor in exhaled air, faeces
 When drinking plentiful fluid you will produce a large volume of dilute urine
 When drinking a less amount of fluid you will produce smaller volumes of more
concentrated urine
 The walls of the collecting duct can be made more or less permeable according to
the needs of the body
 On a cool day your requirement of water is lower therefore the walls of the collecting
duct are less permeable and less water is reabsorbed therefore producing more urine
 On a warmer day you requirement of water is much more greater therefore the walls of
the collecting duct are more permeable and more water is reabsorbed therefore
producing a smaller volume of urine.
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54. Altering the permeability of the CD
- PART I
 The walls of the collecting duct respond to Antidiuretic hormone (ADH) in the
blood.
 ADH has an antidiuretic action that prevents the production of dilute urine
(and so is called an antidiuretic)
 Cells in the wall have membrane-bound receptors for ADH.
 The ADH binds to these receptors and causes a chain of enzyme-controlled
reactions inside the cell.
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55. Altering the permeability of the CD
- PART II
 If there is more ADH in the blood then
vesicles containing water-permeable
channels (aquaporins) will fuse into the
cell surface membrane
 Therefore, the walls more permeable to
water. More ADH = More permeable
channels inserted  more water
reabsorbed by osmosis  More
concentrated urine
 If there is less ADH in the blood then the
cell surface membrane folds inwards to
create new vesicles that remove water-
permeable channels from the membrane
 Therefore, the walls less permeable to
water  less water is reabsorbed via
osmosis into the blood  more water
passes out into the (dilute) urine.
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56. Normal Effect:
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57. Too Much Water:
57

58. Too Little Water:
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59. Adjusting the concn of ADH in the blood
- PART I
 The Water potential of the blood is monitored by osmoreceptors in the
hypothalamus of the brain
 When water potential of the blood is low the osmoreceptor cells lose water by
osmosis causing them to shrink  stimulates neurosecretory cells in the
hypothalamus
 The neurosecretory cells are specialized neurons (nerve cells) that produce
and release ADH.
 ADH releasing cell bodies are found to lie in the hypothalamus
 ADH flows down the axon to the terminal bulb in the posterior pituitary gland
and stored until needed
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60. Adjusting the concn of ADH in the blood
- PART II
 When the neurosecretory cells are stimulated they send an AP down their
axons and cause the release of ADH
 ADH enters blood capillaries running through the posterior pituitary gland 
around the body  acts on the cells of the collecting ducts
 Once water potential rises, less ADH is released
 ADH is slowly broken down and collecting ducts will receive less stimulation –
half-life of about 20minutes
 Half-life of a substance is the time taken for it’s concentration to drop to half it’s
original value.
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61. 5/17/2015 61

62. Control of water potential in the blood
by negative feedback
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Increase in water
potential of blood
Detected by
osmoreceptors in
hypothalamus
Less ADH released
from the posterior
hypothalamus
Collecting duct
walls less
permeable
Less water reabsorbed
into blood; more
urine produced
Decrease in water
potential of blood
Normal water
potential of blood
Decrease in water
potential of blood
Detected by
osmoreceptors in
hypothalamus
More ADH released
from the posterior
hypothalamus
Collecting duct
walls more
permeable
More water
reabsorbed into blood;
less urine produced
Decrease in water
potential of blood

63. Stretching Your Knowledge
Scenario:
A number of drugs have an effect on urine production. Some have effects that
are unwanted or may be a nuisance. Alcohol inhibits the production of ADH, and
certain antibiotics, such as tetracycline, can cause renal failure through a variety
of mechanisms including direct toxicity to the nephron tubules.
Other drugs have effects that may be useful. Diuretic drugs increase urine
production and antidiuretic drugs do the opposite by increasing the reabsorption
of water at the distal tubule and collecting ducts without significantly modifying
the rate of glomerular filtration.
Task:
 Explain why drinking too much alcohol can cause a hangover?
 Suggest what symptoms may be relieved by the use of (i) Diuretics and (ii)
antidiuretics
63
Alcohol inhibits the release of ADH therefore the collecting ducts are not very permeable and less
water is reabsorbed. This means that more water is lost in urine and dehydration occurs. The
ethanal produced form the metabolism of ethanol also contributes to the headache
(i) – Diuretic drugs can be used to relieve water retention, which can cause swelling and high
blood pressure.
(ii) Antidiuretic drugs can be used to relieve diabetes insipidus (a form of diabetes caused by a
lack of ADH, resulting in very large amounts of watery urine) and bed wetting.

64. Questions:
1. How do neurosecretory cells differ from normal nerve cells?
1. Explain what is meant by negative feedback?
2. Why is it important that ADH is broken down?
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Neurosecretory cells manufacture a hormone in their cell body; this is
transferred down the axon. When it is released it goes straight into the blood
rather than to another nerve cell
Negative feedback occurs when a change in the internal conditions stimulates
a reversal of that change – so the conditions are kept constant
ADH must be broken down so that it is not continually acting on the walls of
the collecting ducts

65. 1.2.8 – Kidney Failure
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66. Kidney Failure
 Most common causes are:
 Diabetes mellitus (both type I and type II sugar diabetes)
 Hypertension
 Infection
 Once the kidneys fail completely the body is unable to remove excess water
and certain waste products from the blood
 This includes urea and excess salts.
 It is also unable to regulate the levels of water and salts in the body  rapid
death
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67. Treatment of Kidney Failure
- PART I
 Two main treatments for CKD:
 Dialysis (2 subtypes):
 most common treatment removing waste, excess fluid from blood by passing the blood
over a dialysis membrane. The membrane is a partially permeable membrane that allows
the exchange of substances between the blood and dialysis fluid.
 This fluid contains the correct concentrations of salts, urea, water and other substances in
blood plasma
 Any substances in excess in the blood diffuse across the membrane into the dialysis fluid
 Any substances that are too low in concentration diffuse into the blood from the dialysis
fluid.
 Dialysis must be combined with a carefully monitored diet.
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68. Treatment of Kidney Failure
- PART II
 Hemodialysis
 Blood from a vein is passed into a
machine that contains an artificial
dialysis membrane. Heparin is
added to avoid blood clotting and
any bubbles are removed before
the blood returns to the body
 Hemodialysis is usually performed
at a clinic 3 times a week for
several hours at each sessions, but
some patients learn to carry it out
at home
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69. Treatment of Kidney Failure
- PART III
 Peritoneal Dialysis
 The filter is the body’s own abdominal
membrane (peritoneum).
 First a surgeon implants a permanent
tube in the abdomen.
 Dialysis solution is poured through the
tube and fills the space between the
abdominal walls and organs
 After several hours, the used solution
is drained from the abdomen.
 PD is usually performed in several
consecutive sessions daily at home or
work.
 As the patient can walk around having
dialysis, the method is sometimes
called ambulatory PD
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70. Treatment of Kidney Failure
- PART IV
 Kidney Transplant
 In a kidney transplant the old kidneys are left in place unless they are likely to
cause infection or are cancerous. The donor kidney can be from a living relative
who is willing to donate one of their healthy kidneys or from someone who has
died
 A kidney transplant is major surgery. While the patient is under anesthesia,
the surgeon implants the new organ into the lower abdomen and attaches it
to the blood supply and the bladder
 Many patients feel much better immediately after the transplant, which is the
best life-extending treatment for kidney failure.
 However, the patient’s immune system will recognize the new organ as a
foreign object and produce a reaction
 Patients are given immunosuppressant drugs to help prevent rejection
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71. Advantages and Disadvantages of Kidney
Transplant
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Advantages Disadvantages
Freedom from time-consuming dialysis Need immunosuppressant's for the life of the
kidney
Diet is less limited Need major surgery under a general anesthetic
Feeling better physically Risks of surgery include infection, bleeding and
damage to surrounding organs
A better quality of life i.e. able to travel Frequent checks for signs of organ rejection
No longer seeing oneself as chronically ill Side effects: anti-rejection medicines cause
fluid retention and high blood pressure;
immunosuppressant's increase susceptibility to
infections

72. Testing Urine Samples
- PART I
 Substances or molecules with a relative molecular mass of less than 69,000
can enter the nephron. This means that any metabolic product or other
substance that is in the blood can be passed into the urine – as long as it is
small enough.
 If these substances are not reabsorbed further down the nephron they can be
detected in urine
 Pregnancy Testing:
 Once implanted in the uterine lining, a human embryo starts secreting a pregnancy
hormone called human chorionic gonadotrophins (hCG) (Mr. = 36,700)
 It can be found in urine as early as 6 days after conception. The pregnancy tests on
the market today are manufactured with monoclonal antibodies.
 Antibody is specific, it will only bind to hCG, not to other hormones.
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73. Testing Urine Samples
- PART II
 When someone takes a home pregnancy test, she soaks a portion of the test strip
in her urine.
 Any hCG in the urine attaches to an antibody that is tagged with a blue bead
 This hCG-antibody complex moves up the strip until it sticks to a band of
immobilized antibodies
 As a result all the antibodies carrying a blue bead and attached to hCG are held in
one place forming a blue line
 There is always one control blue line to use for comparison; a second blue line
indicates pregnancy
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74. 74

75. Testing Urine Samples
- PART III
 Testing for anabolic steroids:
 Anabolic Steroids – increase protein
synthesis within cells  build-up of
cell tissues especially in the muscles
 Non-medical uses for anabolic
steroids are controversial because
they can give advantage in
competitive sports and they have
dangerous side effects (use in sports
is now banned)
 Half-life of about 16 hours and
remain in the blood for many days.
 Relatively small molecules and enter
the nephron easily
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76. Testing Urine Samples
- PART IV
 Testing for anabolic steroids involves
analyzing a urine sample in a laboratory
using gas chromatography or mass
spectrometry
 In a gas chromatography the sample is
vaporized in the presence of a gaseous
solvent and passed down a long tube
lined by the absorption agent
 Each substances dissolves differently in
the gas and stays there for a unique,
specific time, the retention time.
 Eventually the substances comes out of
the gas and is absorbed onto the lining
 detector  creates a chromatogram
 Standard samples of drugs, as well as
the urine samples are run so that the
drugs can be identified and quantified in
the chromatograms
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77. Questions:
1. What components of the diet must be carefully monitored in someone who
undergoes dialysis
2. Explain why hemodialysis fluid has to be sterile and at 37oC
3. Create a table of advantages and disadvantages of dialysis as a treatment for
kidney failure
4. Explain why standard samples of drugs must be run alongside a urine sample
in gas chromatography
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78. Module Summary:
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79. Module Summary:
 1.2.1 – Excretion
 Key Definitions:
 Excretion  removal of metabolic waste form the body
 Metabolic waste  consists of waste substances that may be toxic or are produced in
excess by the reactions inside cells
 Deamination  removal of an amine group from an amino acid to produce ammonia
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80. Module Summary:
 1.2.2 – The Liver
 Key Definitions:
 Hepatic Portal Vein  unusual blood vessel that has capillaries at both ends – it carries
blood from the digestive system to the liver
 Function of Kupffer cells  appears to be the breakdown and recycling of old red blood
cells. Bilirubin is ne of the waste products from the breakdown of hemoglobin
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81. Module Summary
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 1.2.3 – Functions of the Liver
 Key Definitions:
 Urea  excretory product formed from the breakdown of excess amino acids
 Ornithine cycle  the process in which ammonia is converted to urea. It occurs partly in
the cytosol and partly in the mitochondria, as ATP is used
 Detoxification – conversion of toxic molecules to less toxic or non-toxic molecules

82. Module Summary:
 1.2.4 – The Kidney
 Key Definitions:
 Nephron the functional unit of the kidney. Microscopic tubule that receives fluid from
the blood capillaries in the cortex and converts this to urine, which drains into the ureter
 Glomerulus  fine network of capillaries that increases the local blood pressure to
squeeze fluid out of the blood. It is surrounded by a cup-or funnel-shaped capsule which
collects the fluid and leads into the nephron
 In selective reabsorption useful substances are reabsorbed form the nephron into the
bloodstream while other excretory substances remain in the nephron
 The PCT is the closest to the Glomerulus / The DCT is the furthest from the
glomerulus
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83. Module Summary:
 1.2.5 – Formation of Urine
 All organs have afferent vessels – they bring blood into the organ. Similarly, efferent vessels carry blood away
from the organ. In a glomerulus the efferent vessels is an arteriole – which is muscular and can constrict to
raise the blood pressure in the glomerulus. In most organs a venule carries blood away
 Ultrafiltration is filtration at a molecular level – as in the glomerulus where large molecules and cells are left
in the blood and smaller molecules pass into the Bowman’s capsule
 Podocytes are specialized cells that make up the lining of the Bowman’s capsule
 TIP: the endothelium of the capillary and the epithelium of Bowman’s capsule contains gaps or pores. These two
layers of cells do little to filter out larger molecules. IT is the basement membrane that is actually involved in
ultrafiltration
 Key Definitions:
 Microvilli are microscopic folds of the cell surface membrane that increase the surface area of the cell
 Co-transporter proteins are proteins in the cell surface membrane that allow the facilitated diffusion of simple
ions to be accompanied by transport of a larger molecule such as glucose
 Facilitated diffusion is diffusion that is enhanced by the action of proteins in the cell membrane
 Sodium-Potassium pumps are special proteins in the cell surface membrane that actively transports sodium and
potassium ions against their concentration gradient
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84. Module Summary:
 1.5.6 – Water reabsorption
 Key definitions:
 A hairpin countercurrent multiplier is the arrangement of a tubule in a sharp hairpin so
that one part of the tubules passes close to another part of the tubule with the fluid
flowing in opposite directions. This allows exchange between the contents and can be
used to create a very high concentration of solutes
 Osmoregulation is the control and regulation of water potential of the blood and body
fluids. In humans the kidney controls the water potential of the blood
 The distal convoluted tubule is the coiled portion of the nephron between the loop of
henle and the collecting duct.
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85. Module Summary:
 1.5.7 – Osmoregulation
 Key definitions:
 Antidiuretic Hormone (ADH) is released from the pituitary gland and acts on the
collecting ducts in the kidneys to increase their reabsorption of water
 Osmoreceptor are receptor cells that monitor the water potential of the blood. IF the
blood has a low water potential then water is moved out of the osmoreceptor cells by
osmosis, causing them to shrink. This causes stimulation of the neurosecretory cells
 Hypothalamus is part of the brain that contains neurosecretory cells and various receptors
that monitor the blood
 Neurosecretory cells are specialized cells that act like nerve cells but release a hormone
into the blood. ADH is manufactured in the cell body and passes down the axon to be
stored in the terminal bulb. If an action potential passes down the axon then ADH is
released from the terminal bulb
 Posterior pituitary gland is the hind part of the pituitary gland, which releases ADH.
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86. Module Summary:
 1.5.8 – Kidney Failure
 Key Definitions:
 Human chorionic gonadotrophins (hCG) is a hormone released by human embryos; it’s
presence in the mothers urine confirms pregnancy
 Monoclonal antibodies are identical because they have been produced by cells that are
clones of the original cell
 Anabolic steroids are drugs that mimic the action of steroid hormones that increase
muscle growth
 Gas chromatography is a technique used to separate substances in a gaseous state. A
Chromatogram is a chart produced when substances are separated by movement of a
solvent along a permeable material such as paper or gel
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87. Thank you, feel free to ask for any
help.
By Piril Erel
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