5.1.2 - Excretion as an example of homeostatic control Flashcards
What is excretion ?
Excretion is the removal of the waste products of metabolism from the body
What are the main metabolic waste products in mammals ?
- Carbon dioxide
- Bile pigments
- Nitrogenous waste products (urea)
What is CO2 a waste product of ?
It is one of the waste products of cellular respiration which is excreted from the lungs
Where are bile pigments formed from ?
Formed from the breakdown of haemoglobin from old red blood cells in the liver
Where are bile pigments excreted from ?
liver into the small intestine via the gall bladder and the bile duct
What do the bile pigments do ?
They colour the urea
How is urea formed ?
- Formed from the breakdown of excess amino acids by the liver
Where is urea excreted from ?
Kidneys -> bladder -> urine
What nitrogenous waste products do fish produce ?
Ammonia
What nitrogenous waste products do birds and insects produce ?
Uric acid
What process is the liver involved in ?
Homeostasis
How much of the body mass does the liver make up ?
- 5% of the bodies mass
- It is the largest internal organ of the body
Where does the liver lie in the body ?
It lies just below the diaphragm and is made up of several lobes
What is special about the liver as an organ ?
The liver is very fast growing and damaged areas generally regenerate very quickly
How rich is the blood supply of the liver ?
- Very rich blood supply
- About 1dm3 of blood flows through it every minute
Which artery supplies oxygenated blood to the liver ?
Hepatic artery
Which vein removes blood from the liver to the heart ?
Hepatic vein
What is the name of the second blood vessel that supplies the liver with blood ?
Hepatic portal vein
What does the hepatic portal vein carry ?
It carries blood from the intestines to the liver
How much of the blood flowing to the liver does the hepatic portal vein carry ?
Up to 75% of the blood flowing through the liver comes via the hepatic portal vein
What are liver cells called ?
Hepatocytes
What is the structure of a hepatocyte like ?
- Large nuclei
- Prominent golgi apparatus
- Lots of mitochondria
- Indicates that they are metabolically active cells
What property do hepatocytes have that is very useful ?
They divide and replicate which allows the liver to regenerate
Where does the blood from the hepatic artery and the hepatic portal vein get mixed ?
They are mixed in spaces called sinusoids
What surrounds the sinusoids ?
They are surrounded by hepatocytes
What does the mixing of the blood from the hepatic artery and portal vein lead to ?
- It increases the oxygen content of the blood from the hepatic portal vein
- Supplying the hepatocytes with enough oxygen for their needs
What cells do the sinusoids contain ?
Kupffer cells
What do the kupffer cells act as ?
They act as resident macrophages of the liver, ingesting foreign particles and helping to protect against disease
What do the hepatocytes secrete ?
Bile from the breakdown of the blood
Where do the hepatocytes secrete the bile into ?
Into spaces called canaliculi
from these the bile drains into the bile ductules
which take it to the gall bladder
How many metabolic pathways are linked to the liver ?
Around 500 different pathways
What are the main functions of the liver ?
- Carbohydrate metabolism
- Determination of excess amino acids
- Detoxification
What form of homeostatic control are hepatocytes closely involved with ?
Homeostatic control of glucose levels in the blood by their interaction with insulin and glucagon
What do hepatocytes do when blood glucose levels rise ?
- Insulin levels rise and stimulate hepatocytes to convert glucose to glycogen
- About 100g of glycogen is stored in the liver
What do hepatocytes do when blood glucose levels fall ?
The hepatocytes convert the glycogen back to glucose under the influence of the hormone glucagon
How are hepatocytes and plasma proteins related ?
Hepatocytes synthesise most of the plasma proteins
What process do hepatocytes carry out, related to amines ?
Transamination
What is transamination ?
The conversion of one amino acid to another
Why is transamination important ?
Transamination allows for there to be a balance of amino acids in the body
What is the most important role of the liver in protein metabolism ?
Deamination
What is deamination ?
The removal of an amine group from a molecule
What would happen to excess ingested proteins if it was not for the role of hepatocytes ?
They would be excreted and therefore wasted if it were not for the action of the hepatocytes
What do the hepatocytes do to the excess ingested proteins ?
They deaminate the amino acids
then converting it first into ammonia which is very toxic
then convert it to urea
When is urea toxic ?
In high concentrations
How is urea secreted ?
Via the kidneys
What happens to the remainder of the amino acids ?
Fed into cellular respiration
Converted into lipids for storage
How is the ammonia produced in the deamination of proteins converted into urea ?
- In a set of enzyme controlled reactions
- Known as the ornithine cycle
What happens to the level of toxins in the body over time ?
They increase over time
What does the liver do to potentially poisonous substances ?
Liver is the site where most of these substances are detoxified and made harmless
What is an example of the liver breaking down toxic substances ?
The breakdown of hydrogen peroxide
What enzyme does a hepatocyte contain ?
Catalase
What does catalase do to hydrogen peroxide ?
Catalase breaks down hydrogen peroxide into oxygen and water
What is another example of the liver breaking down a poisonous substance ?
Liver detoxifying ethanol
What other enzyme does a hepatocyte contain ?
Alcohol dehydrogenase
What does alcohol dehydrogenase do ?
- It breaks down ethanol into ethanal
- Ethanal is then converted to ethanoate
Ethanoate can be used to build up fatty acids or used in cellular respiration
Where are the kidneys located ?
Attached to the back of the abdominal cavity
What are the kidneys surrounded by ?
Surrounded by a thick protective layer of fat and a layer of fibrous connective tissue
What roles do the kidneys have ?
- Excretion
- Osmoregulation
How are the kidneys involved in excretion ?
They filter nitrogenous waste products out of the blood, especially urea
How are the kidneys involved in osmoregulation ?
They help to maintain the water balance and pH of the blood, and hence the tissue fluid that surrounds the cell
What vessel supplies the kidneys with blood ?
Renal arteries that branch off from the abdominal aorta
What vessel removes blood that has circulated through the kidneys ?
Renal vein
What are the kidneys made up of ?
- Nephrons
- Millions of them
What do the nephrons act as ?
Filtering units
What liquid is produced by the kidney tubules ?
Urine
How does urine pass out of the kidney ?
It passes out of the kidney down tubes called ureters
Where is the urine collected once out of the kidney ?
The bladder
What happens when the bladder is full ?
The sphincter at the exit of the bladder opens and the urine passes out of the body down the urethra
What are the three main areas of the kidney ?
- Cortex
- Medulla
- Pelvis
What is the cortex ?
- The dark outer layer
- This is where the filtering of the blood takes place and it has a very dense capillary network carrying the blood from the renal artery to the nephrons
What is the medulla ?
- It is lighter in colour
- It contains the tubules of the nephrons that form the pyramids of the kidney and the collecting ducts
What is the pelvis ?
The central chamber where the urine collects before passing out down the ureter
What takes place in the nephrons ?
Ultrafiltration and selective reabsorption
What are the main structures of the nephrons ?
- Bowmans capsule
- Proximal convoluted tube
- Loop of Henle
- Distal convoluted tube
- Collecting duct
What is the function of the Bowmans capsule ?
Cup shaped structure that contains the glomerulus, a tangle of capillaries
What takes place at the glomerulus ?
More blood goes into the glomerulus than leaves it due to the ultrafiltration processes that take place
wider arteriole in and narrower arteriole out
What is the function of the proximal convoluted tube ?
- The first coiled region of the tubule after the Bowmans capsule, found in the cortex
- This is where many of the substances needed by the body are reabsorbed into the blood
What is the function of the loop of henle ?
It is a long loop of tubule that creates a region with a very high solute concentration in the tissue fluid deep in the kidney medulla.
What is the structure of the loop of henle like ?
- The descending loop runs down from the cortex through the medulla to a hairpin bend at the bottom of the loop
- The ascending limb travels back up through the medulla to the cortex
What is the function of the distal convoluted tube ?
- A second twisted tubule where the fine tuning of the water balance of the body takes place
- ADH affects the permeability of the walls to water
- Further regulation of the ion balance and pH of the blood also takes place in this tubule
What is the function of the collecting duct ?
- The urine passes down the collecting duct through the medulla to the pelvis.
- More fine tuning of the water balance takes place - the walls of this part of the tubule are also sensitive to ADH
What is the blood composed of when it leaves the kidney ?
- Greatly reduced levels of urea
- Levels of glucose and other substances such as amino acids needed by the body are the same
- Mineral ion concentration is at ideal levels
What are the two main functions of the nephrons ?
- Ultrafiltration
- Reabsorption
Where does ultrafiltration take place ?
In the Bowmans capsule
Why does ultrafiltration take place ?
As a result of the high blood pressure in the glomerulus
What is ultrafiltration in the kidney tubules ?
- It is the first step in the removal of nitrogenous waste and osmoregulation of the blood
- It is a specialised form of the process that results in the formation of tissue fluid in the capillary beds of the body
How is the glomerulus supplied with blood ?
It is supplied with blood by a relatively wide afferent (incoming) arteriole from the renal artery
How does the blood leave the glomerulus ?
- It leaves through a narrower efferent (outward) arteriole and causes larger pressure in the capillaries of the glomerulus
- This increased pressure forces the blood out of the capillary walls through fenestrations
What does the fluid pass through once it has left the glomerulus ?
It passes through the basement membrane
What is the basement membrane made out of?
It is made up of a network of collagen fibres and other proteins that make up a second ‘sieve’
What can and what cant pass through the basement membrane ?
- They can not pass through the fenestrations
Blood cells and plasma proteins can not pass through because of their size
Everything else can
What cells does the wall of the Bowmans capsule involve ?
Podocytes
What do the podocytes act as ?
They act as an additional filter
What special feature do the podocytes have on them ?
- They have extensions called pedicels that wrap around the capillaries
- Proteins that have got through the epithelial cells and the basement membrane do not get through into the tubule itself
What does the filtrate that enter the capsule contain ?
It contains glucose, salt, urea and many other substances
What is the glomerular filtration rate ?
The volume of blood that is filtered through the kidneys at any given time
What is the downside of ultrafiltration in the kidneys ?
- It removes a lot of water along with the glucose, salt and other substances which are present in the plasma.
- Many of these substances are needed by the body
What is the main function of the nephron after the Bowmans capsule ?
- To return most of the filtered substances back to the blood
- This is the process of selective reabsorption
What is moved in the proximal convoluted tube ?
Glucose, amino acids, vitamins and hormones
What ions are reabsorbed in the proximal convoluted tube ?
Chloride and sodium ions as well as water
How are chloride ions reabsorbed ?
Passively down a concentration gradient
How are sodium ions reabsorbed ?
Via active transport
What are the adaptations of the cells lining the proximal convoluted tube ?
- They are covered with microvilli, greatly increasing the surface area over which substances can be reabsorbed
- They have many mitochondria to provide the ATP needed in active transport systems
What is the filtrate like when it reaches the loop of henle ?
It is isotonic with the tissue fluid surrounding the tubule and isotonic with the blood
What is the loop of henle ?
It is the section of the kidney tubule that enables mammals to produce urine more concentrated than their own blood
What does the loop of henle act as ?
It acts as a counter current multiplier
How does the loop of henle act as a countercurrent multiplier ?
It uses energy to produce concentration gradients that result in the movement of substances such as water from one area to another
How do cells transport ions in the loop of henle ?
They use ATP using active transport and this produces a diffusion gradient in the medulla
What happens in the descending limb of the loop of henle ?
This is the region where water moves out of the filtrate down a concentration gradient
What is the permeability of water like in the descending limb ?
The upper part is impermeable to water but the lower part is permeable to water and runs down into the medulla
What is the concentration of Na and Cl ions like in the descending limb ?
It gets higher and higher moving through the cortex to the medulla
What is the filtrate entering the descending limb like ?
It is isotonic with the blood
Describe the movement of the filtrate down the descending limb
- As it travels down the limb, water passes out of the loop into the tissue fluid by osmosis
- It then moves down a concentration gradient into the blood of the surrounding capillaries
What is the blood surrounding the capillaries called ?
The vasa recta
What is the permeability of Na and Cl ions like in the descending limb ?
It is not permeable to them and no active transport takes place in the descending limb
What is the fluid like in the hairpin ?
It is very concentrated and hypertonic to blood in the capillaries
How permeable is the first section of the ascending limb to sodium and chlorine ?
- It is very permeable to sodium and chloride ions
- They move out of the concentrated solution by diffusion down a gradient
What happens to sodium and chlorine ions in the second section of the ascending limb ?
- They are pumped out into the medulla tissue fluid against a concentration gradient
- This produces very high sodium and chloride ion concentrations in the medulla tissue
What is the permeability of water like in the ascending limb ?
- It is impermeable to water
- Water cannot follow the chloride and sodium ions down a concentration gradient
What is the fluid like when it reaches the top of the ascending limb ?
It is hypotonic to the blood again
What takes place in the distal convoluted tube ?
- Balancing the water needs of the body
- Balancing the pH of blood
What is the ADH like in the distal convoluted tube ?
The level of ADH varies therefore so does the level of permeability of the walls
What adaptations do the cells surrounding the distal convoluted tube have ?
They have many mitochondria so they are adapted to carry out active transport
What happens if the body lacks salt ?
- Na ions will be actively pumped out of the distal convoluted tube with Cl ions following down an electrochemical gradient
- Water can also leave the distal tube, concentrating the urine, only if the walls are permeable in response to ADH
What happens at the collecting duct ?
This is the main site where the concentration and volume of the urine produced is determined
What is the movement of water like at the collecting duct ?
Water moves out of the collecting duct by diffusion down a concentration gradient as it passes through the renal medulla
What does water moving out of the collecting duct cause ?
The urine becomes more concentrated
What allows water to be moved out of the collecting duct ?
The level of sodium ions in the surrounding fluid increases through the medulla from the cortex to the pelvis
What is the permeability of the collecting duct to water dependent on ?
It is dependent on the level of ADH produced
Give some reasons why the kidney may fail
- Kidney infections
- Raised blood pressure
- Genetic conditions
What can be caused by the kidneys being infected or affected by high blood pressure ?
- Protein in the urine
- Blood in the urine
How can protein end up in the urine ?
If the basement membrane or podocytes of the bowmans capsule are damaged, they no longer act as filters and large plasma proteins can pass into the filtrate and are passed into the urine
How can blood end up in the urine ?
The filtering process stops working
What happens if the kidneys fail completely ?
The concentrations of urea and mineral ions build up in the body
What are the effects of kidney failure ?
- Loss of electrolyte balance
- Build up of toxic urea in the blood
- High blood pressure
- Weak bones
- Pain and stiffness
- Anaemia
How can kidney failure cause loss of electrolyte balance ?
If the kidneys fail, the body cannot excrete excess sodium, potassium and chloride ions. This causes osmotic imbalances in the tissues and eventual death
How can kidney failure cause build up of toxic urea in the blood ?
If the kidneys fail, the body cannot get rid of urea and it can poison the cells
How can kidney failure cause high blood pressure ?
If the kidneys fail, the blood pressure increases and this can cause a range of health problems including heart problems and strokes
How can kidney failure cause weak bones ?
The calcium/phosphorous balance in the blood is lost
How can kidney failure cause pain and stiffness ?
Abnormal proteins build up in the blood
How can kidney failure cause anaemia ?
The kidneys are involved in the production of erythropoietin that stimulates the formation of red blood cells and when they fail it can reduce the production of red cells causing lethargy and tiredness
What is the glomerular filtration rate used for ?
- The GFR is used as a measure to indicate kidney disease
- A simple blood test measures the level of creatinine in the blood
What is creatinine ?
It is a breakdown product of muscles and it is used to give an estimated GFR (eGFR)
What does an increase in creatinine mean ?
It means that the kidneys are not working properly
How does GFR levels change with age ?
The GFR levels change with age even if you are healthy
How do creatinine levels differ with gender ?
Men usually have more muscle mass and therefore more creatinine than women
What GFR level indicates chronic kidney disease ?
Below 60 for more than three months
What GFR level indicates kidney failure ?
Below 15
What are the two main ways in which kidney failure is treated ?
- Renal dialysis
- Kidney transplants
What happens in renal dialysis ?
The function of the kidneys is carried out artificially
What happens in a kidney transplant ?
A new healthy kidney is put into the body to replace the functions of the failed kidneys
What are the two main types of dialysis ?
- Haemodialysis
- Peritoneal dialysis
What does haemodialysis involve ?
Involves the use of a dialysis machine
Where is haemodialysis carried out ?
It is usually carried out in hospital although sometimes patients will have a machine in their own home
What occurs in haemodialysis ?
Blood leaves the patients body from an artery and flows into the dialysis machine, where it flows between partially permeable dialysis fluid
What must happens during haemodialysis that is vital ?
- It is vital that patients lose the excess urea and mineral ions that have built up in the blood
- It is important that they do not lose useful substances such as glucose and some mineral ions
What prevents the loss of important substances such as glucose ?
Careful control of the dialysis fluid
What does the dialysis fluid have in it ?
- Normal plasma level of glucose
- Normal plasma levels of mineral ions
- No urea
What does having normal plasma levels of glucose allow ?
There is no net movement of glucose out of the blood
What does having normal plasma levels of mineral ions allow ?
- Any excess mineral ions in the blood move out by diffusion down a concentration gradient into the dialysis fluid
- Thus restoring the correct electrolyte balance of the blood
What does no urea in the dialysis fluid allow ?
- There is a very steep concentration from the blood to the fluid
- Therefore a lot of urea leaves the blood
In what directions do the blood and the dialysis fluid flow ?
In opposite directions to maintain a countercurrent exchange system and maximise the exchange that takes place
What does the whole process of dialysis depend upon ?
- Diffusion down concentration gradients
- No Active transport takes place
What do patients that require haemodialysis have to manage ?
- Their diets
- They have to eat relatively little protein and salt and monitor their fluid intake to keep the blood chemistry as stable as possible
Where does peritoneal dialysis take place ?
- Inside the body
- It makes use of the natural dialysis membranes formed by the lining of the abdomen, that is, the peritoneum
Where is peritoneal dialysis usually done ?
Usually done at home and the patient can carry on with their normal life
How is the dialysis fluid introduced into the individual ?
Using a catheter into the abdomen
What occurs in peritoneal dialysis ?
- The fluid is left for hours for the dialysis to take place across the peritoneal membranes
- This is so that urea and excess mineral ions pass out of the blood capillaries into the tissue fluid and out across the peritoneal membrane into the dialysis fluid
- The fluid is then drained off and discarded, leaving the blood balanced again and the urea and excess minerals removed
What happens in a kidney transplant ?
The blood vessels are joined and the ureter of the new kidney is inserted into the bladder
What is the main problem with transplanted organs ?
There is always a risk of rejection
Why do organs sometimes get rejected ?
The antigens on the donor organ differ from the antigens on the cells of the recipient and the immune system is likely to recognise this
How can we reduce the risk of rejection ?
- Give immunosuppressant drugs to the patient
- Make sure that the match between the antigens of the donor and the recipient is made as close as possible
How do immunosuppressants reduce the risk of rejection ?
They suppress the immune response
What are the disadvantages associated with immunosuppressant drugs ?
They prevent the patients from responding effectively to infectious diseases
What homeostatic role does the kidney play ?
Osmoregulation
What is osmoregulation ?
This involves controlling the water potential of the blood within very narrow boundaries
Why is osmoregulation important ?
If water moves into or out of the cells by osmosis it can cause damage and even death
Which hormone controls the amount of water lost in the urine ?
ADH
Where is ADH produced ?
By the hypothalamus and secreted into the posterior pituitary gland where it is stored
What is the role of ADH ?
It increases the permeability of the DCT and the collecting duct to water
Where does ADH have its effect ?
The cells of the collecting duct
Does ADH cross the membrane of the tubule cells ?
No it can not cross the membrane of the tubule cells
What happens to ADH when it reaches the membranes of the tubule cells ?
It binds to a receptor on the cell membrane and triggers the production of cAMP
What is cAMP ?
It is a secondary messenger in the cell
What is a secondary messenger ?
A molecule which relays signals received at cell surface receptors to molecules inside the cell
What does cAMP cause to happen in the collecting duct ?
Vesicles in the cells lining the collecting duct fuse with the CSM’s on the side of the cell in contact with the tissue fluid of the medulla
What do the membranes of the vesicles contain ?
They contain protein based water channels called aquaporins
What do aquaporins do ?
They are inserted into the cell surface membrane and make it permeable to water
What do aquaporins provide a route for ?
For water to move out of the tubule cells into the tissue fluid of the medulla and the blood capillaries by osmosis
What receptors are involved in the negative feedback control of osmoregulation ?
Osmoreceptors
What are osmoreceptors sensitive to ?
The concentration of inorganic ions in the blood and are linked to the release of ADH
What happens to the blood when water is in short supply ?
- Concentration of inorganic ions rises
- Water potential of the blood becomes more negative
What happens to the blood when water is in short supply ?
- Concentration of inorganic ions rises
- Water potential of the blood becomes more negative
What detects the change in water potential in the blood ?
Osmoreceptors in the hypothalamus
What do the osmoreceptors do when they detect too low water in the blood ?
They send nerve impulses to the posterior pituitary which in turn releases stored ADH into the blood
What does ADH do when water is in short supply ?
- It is picked up by receptors on the collecting duct
- It increases the permeability of the tubules to water
What does increased ADH result in ?
A small volume of concentrated urine being produced
What happens to the blood when water is in excess ?
The blood becomes more dilute and its water potential becomes less negative
What detects the change in water potential in the blood ?
Osmoreceptors in the hypothalamus
What do the osmoreceptors do when an excess of water is detected in the blood ?
They send nerve impulses to the posterior pituitary which inhibit the release of ADH
What does ADH do when water is in excess ?
Very little reabsorption of water takes place because the walls of the collecting duct remain impermeable to water
What does decreased ADH result in ?
Large amounts of urine are produced
What does urine contain ?
- Water
- Urea
- Mineral salts
- Etc
How can you tell someone is affected by a disease from examining their urine ?
New substances will appear in their urine
What chemical does the site of the developing placenta produce ?
- Human chorionic gonadotrophin
- hCG
Where can hCG be found ?
In the blood and the urine of the mother
What used to be the most effective way of testing for pregnancy in women ?
- Inject urine from a pregnant woman into a toad
- If she was pregnant, the hCG triggered egg production in the toad within 10 hours
What is said to be a problem with the old pregnancy testing method ?
It could not be used until the woman was several weeks pregnant
What chemical do pregnancy tests test for ?
hCG
What do modern pregnancy tests rely on ?
Monoclonal antibodies
What are monoclonal antibodies ?
Antibodies from a single clone of cells that are produced to target particular cells or chemicals in the body
How are monoclonal antibodies produced ?
- A mouse is injected with hCG so it makes the appropriate antibody
- The B cells that make the antibody are then removed
What happens when the B cells that make the antibody are removed from the mouse ?
They are fused with a myeloma
What is a myeloma ?
A type of cancer cell that divides rapidly
What does the antibody and the myeloma produce ?
A hybridoma
What is the role of the hybridoma ?
It reproduces rapidly forming the desired antibody
What happens to the monoclonal antibodies once they are collected ?
They are collected and then purified
What is the first stage in the pregnancy test ?
The wick is soaked in the first urine passed in the morning
Why is the first urine in the morning used ?
This is when the hCG levels are at their highest
What does the test contain ?
Mobile monoclonal antibodies that have very small coloured beads attached to them
What does the hCG bind to in a pregnancy test ?
The mobile monoclonal antibodies
What is formed if the woman is pregnant ?
- A hCG/antibody complex
- Complete with a coloured bead
How many windows are in a pregnancy test ?
There are two windows in a pregnancy test
What happens at the first window of the pregnancy test ?
There are immobilised monoclonal antibodies arranged in a line or a pattern such as a positive sign that only bind to the hCG/antibody complex
What will show if the woman is pregnant ?
A coloured line or pattern will appear in the firs window
What happens at the second window of the pregnancy test ?
There is usually another line of immobilised monoclonal antibodies that bind only to the mobile antibodies
What is the purpose of the second window of the pregnancy test ?
- Simply indicates that the test is working
- There will always be one line even if the woman is not pregnant
What does 1 line on a pregnancy test mean ?
- Not pregnant
- Test is working
What does 2 lines on a pregnancy test mean ?
Woman is pregnant
What are anabolic steroids ?
Drugs that mimic the action of testosterone and they stimulate the growth of the muscles
How are anabolic steroids secreted ?
In the urine
How can scientists tell whether an athlete is using anabolic steroids ?
- The urine sample is vaporised with a known solvent and passed along a tube
- The lining of the tube absorbs the gases and is analysed to produce a chromatogram
- The chromatogram shows the presence of drugs
What are metabolites ?
The breakdown products of drugs
Where do drugs and metabolites pass through ?
- They are filtered through the kidneys and stored in the bladder
- Therefore drug traces can be found in the urine
What will happen if someone is suspected of taking an illegal drug ?
- They will be asked to provide a urine sample
- The urine sample is then split into two
What happens in the first sample that is taken ?
Tested by an immunoassay, using monoclonal antibodies to bind to the drug or its breakdown product
What happens if the first sample is positive for a drug ?
The second sample is tested
What happens in the second sample that is taken ?
It is passed through a gas chromatograph/mass spectrometer to confirm the presence of the drug
