Module 5 Section 2: Excretion Flashcards
Different vessels connected to the liver
Hepatic artery
Hepatic vein
Hepatic portal vein
Bile duct
Function of hepatic artery
Hepatic artery supplies the liver with oxygenated blood from the heart
Liver has a good supply of oxygen for respiration to provide lots of energy
Function of hepatic vein
Hepatic vein takes deoxygenated blood away from the liver
Function of hepatic portal vein
Hepatic portal vein brings blood from the duodenum and ileum (part of small intestine)
Rich in products of digestion
This means any harmful substances are filtered out and broken down straight away
Always shown as branched vessels leading into cells
Function of bile duct
The bile duct takes bile to the gall bladder to be stored
Bile then released into duodenum via bile duct
Bile is produced by the liver to emulsify fats
Structure of liver
Liver made up of liver lobules
These are cylindrical structures made of cells called hepatocytes
These are arranged in rows radiating out from the centre
Structure of lobules
Each lobule has a central vein in the middle which connects to the hepatic vein
Many branches of the hepatic artery, hepatic portal vein and bile duct are also found surrounding and connecting to each lobule to supply them with blood
Lobules are separated by connective tissue made up of extracellular matrix
Structure of hepatocytes
Large nuclei
Prominent golgi apparatus
Lots of mitochondria
Function of sinusoids
Exchange materials directly with hepatocytes
Contain kupffer cells which act as the macrophages of the liver
Kupffer cells are attached to the walls of the sinusoids and remove bacteria and break down old red blood cells
The harmful substances are removed along with oxygen and broken down by hepatocytes into less harmful substances that then re-enter the blood and drain into a central vein
Lined with incomplete layer of endothelial cells to allow blood to reach hepatocytes for substance exchange
How are the hepatic artery and hepatic portal vein connect to the central vein
Hepatic artery and hepatic portal vein are connected to the central vein by capillaries called sinusoids
How is bile made in the liver
Heptacytes produce bile and secrete it into tubes called bile canaculi
These tubes drain into the bile ducts
The bile ducts from all the lobules eventually connect up and leave the liver
How is the hepatic vein formed in the liver from sinusoids
Blood runs to the central vein in each sinusoid
The central veins from all sinusoids in all lobules connect up to form the hepatic vein
What is excretion
This is the removal of the waste products of metabolism from the body
How does excretion help metabolism
Metabolism is all the chemical reaction that happen in the cells
Produces carbon dioxide and nitrogenous waste which aren’t needed by the body
If they were to build up in the body then they would cause damage
Excretion removes these
How is carbon dioxide a waste product and how is it removed
CO2 is a waste product of respiration
Too much in the blood is toxic so it’s removed through the lungs or gills
Lungs and gills act as excretory organs
What does excreting waste products in the blood do for the body
Excreting waste products from the body maintains normal metabolism
Also maintains homeostasis by helping to keep the levels of certain substances in the blood roughly constant
Why are amino acids broken down by the liver
Amino acids from the diet contain nitrogen in their amino groups
Nitrogenous substances can’t usually be stored by the body
Means that excess amino acids can be damaging to the body
This means they must be used by the body (e.g. to make proteins) or be broken down and excreted
How are excess amino acids broken down by the liver
The amino groups (NH2) are removed from excess amino acids forming ammonia and organic acids (this is deamination)
Organic acids can be respired to give ATP or converted to glycogen and stored
Ammonia is too toxic to be directly excreted
It’s combined with CO2 in the orthinine cycle to make urea
The urea is released from the liver into the blood
The kidneys then filter the blood and remove the urea as urine which is excreted from the body
What can the liver break down
Excess amino acids
Alcohol
Drugs
Unwanted hormones
What is detoxification
Where harmful substances (e.g. alcohol, drugs, hormones, amino acids) are broken down into less harmful compounds
These are then excreted from the body
How does the liver break down alcohol
Ethanol is a toxic substance that can damage cells
It’s broken down by the liver into ethanal and then into less harmful acetic acid (using ethanol hydrogenase and ethanal dehydrogenase)
Excess alcohol over a long period of can lead to cirrhosis of the liver which is where liver cells die and scar tissue blocks blood flow
Example of the liver breaking down drugs
Paracetamol is broken down by the liver
Excess of this can lead to liver and kidney failure
Why does the liver need to break down hormones
E.g. insulin
This is a hormone that controls blood glucose concentration
Insulin is broken down by liver as in excess is can cause problems with blood sugar levels
Excess hormones in the blood can cause too much of a response from cells which could be problematic for conditions inside body
How and why does the liver store glycogen
The body needs glucose for energy
Liver converts excess glucose in the blood to glycogen (glycogenesis) and stores it as granules in the cytoplasm of its cells until glucose is needed for energy
How is lactate detoxified
Lactate is the end product of anaerobic respiration
It is an energy rich compound which is absorbed by hepatocytes and metabolised into pyruvate
This pyruvate enters mitochondria and is respired to produce energy to convert the rest of the lactate into glucose
How to notice liver on microscope
Deamination
Excess amino acids cannot be stored by the body.
So they are broken down (deamination) and excreted.
Deamination is the removal of the amine group (oxidation)
Occurs in the mitochondria and cytoplasm of the hepatocytes
This forms ammonia and carbon dioxide
Steps of excretion of urea
Deamination
Ornithine cycle
Label diagram
Process of the ornithine cycle
The ammonia and carbon dioxide are combined with ornithine to make citrulline
Citrulline leaves mitochondria by facilitated diffusion into the cytoplasm of the liver cell
Citrulline gets converted to argino-succinic acid by adding ATP (forms AMP) - 2 phosphate bonds are broken.
More nitrogen is added as NH2 and water is released.
Argino-succinic acid is converted to the intermediate compound arginine.
Water is added, ornithine and urea is released - into the bloodstream where it is removed by the kidneys
Function of kidney
Excretes waste products e.g. urea from liver
Regulate water potential of the blood
Label diagram
Function of renal pelvis
Central chamber where urine collects before passing out down ureter
Function of renal medulla
Contains tubules of the nephrons that form pyramids of the kidney and collecting ducts
Function of renal cortex
Outer layer where filtering of blood takes place
Dense capillary network carrying blood from renal artery to nephrons
Function of ureter
Where waste travels out of kidney to form urine in bladder
Function of renal vein
Delivers deoxygenated blood out of kidney after filtration
Function of renal artery
Delivers oxygenated blood to kidney to be filtered
Process of how kidneys excrete waste products
Blood enters the kidney through renal artery and then passes through capillaries in the cortex of the kidneys.
As the blood passes through the capillaries, substances are filtered out of the blood and into long tubules that surround the capillaries (ultrafiltration)
Useful substances (e.g. glucose) are reabsorbed back into the blood from the tubules in the medulla and cortex (called selective reabsorption)
The remaining unwanted substances (e.g. urea) pass along the tubules, then along the ureter to the bladder, where they’re expelled as urine.
The filtered blood passes out of the kidneys through the renal vein
Label nephron
What are the structures that filter blood in the kidneys called
Nephrons
Overview of process of how blood is filtered in nephrons
Blood from renal artery enters smaller arterioles in the cortex
Each arteriole splits into a structure called glomerulus inside the Bowman’s capsule
Ultrafiltration takes place
Efferent arteriole is smaller in diameter than afferent arteriole so blood in glomerulus is under high pressure
High pressure forces liquid and small molecules in the blood out of capillary into Bowman’s capsule
Liquid and small molecules pass along rest of nephron and useful substances are reabsorbed
Filtrate then flows through collecting duct and passes out of kidneys along ureter
Different arterioles connected to bowman’s capsule
Afferent arteriole: arteriole that takes blood into each glomerulus
Efferent arteriole: arteriole that takes filtered blood away from the glomerulus
Bowman’s capsule
Cup shaped structure containing glomerulus
Ultrafiltration processes take place
Proximal convoluted tubule
Useful substances reabsorbed into blood
Loop of Henle
Loop of tubule that creates region of very high solute concentration in tissue fluid deep in kidney medulla
Descending limb runs from cortex to medulla
Ascending limb travel back up through medulla to cortex
Distal convoluted tubule
Fine tuning of water balance in body take place
Permeability of walls varies due to ADH
Regulation of ion balance and pH of blood also take place
Collecting duct
Where urine passes down from medulla to pelvis
More fine tuning of water balance takes place
Walls of tubule sensitive to ADH
Process of ultrafiltration
Liquid and small molecules pass through 3 layers to get to Bowman’s capsule and enter nephron tubule
Capillary wall, basement membrane and epithelium of Bowman’s capsule
Larger molecules like proteins and blood cells can’t pass through and stay in blood
Structure of capillary epithelium
Acts like a sieve so liquid and small molecules only can pass out of capillary into bowman’s capsule
Structure of basement membrane
Made up of a networks of collagen fibres and other proteins that make up a second sieve
Most plasma can pass through but blood cells and many proteins are retained in capillary due to size
Structure of Bowman’s capsule epithelium
Made of podocytes which provide an additional filter as they have extensions called pedicels
Pedicels wrap around capillaries to form slits that make sure any cells, platelets or large plasma proteins that have got through basement membrane do not get into tubule
Where does selective reabsorption take place
Takes place as the filtrate as the filtrate flows along the PCT, loop of Henle and DCT
What happens in selective reabsorption
Useful substances leave the tubules of the nephrons and enter capillary network wrapped around them (vasa recta)
What substances are selectively reabsorbed and how
Glucose, amino acids, vitamins, some salts
These are actively transported into blood or move by facilitated diffusion
Some urea also enters by diffusion
Water enters blood by osmosis because water potential of the blood is lower than that of filtrate
Features of cells lining walls of PCT
Lots of mitochondria to provide energy from ATP for active transport
Microvilli for large surface area for reabsorption
Process of selective reabsorption
Na+ actively transported out of cells (across basal membrane)
Therefore the Na+ concentration inside the cell drops below the Na+ concentration in the lumen of the PCT
Creates a concentration gradient from the filtrate in lumen of PCT down to cytoplasm of cells lining PCT
Therefore Na+ diffuses from the lumen into the cell via co-transporter protein
This allows amino acids and glucose to be transported in simultaneously which increases their concentration inside the cell
They can then diffuse down a concentration gradient through cell into blood
From the influx of solutes to the cells of the PCT, water potential in those cells decreases
Water moves down the water potential gradient from the nephron to the blood
Urea is absorbed by diffusion due to its small size
Process of producing urine in loop of Henle (long one)
Near the top of the ASCENDING limb, Na+ and Cl - ions are actively pumped out into medulla
The ASCENDING limb is impermeable to water, so the water stays inside the tubule.
This creates a low water potential in the medulla, because there’s a high concentration of ions.
Because there’s a lower water potential in the medulla than in the DESCENDING limb, water moves out of the DESCENDING limb into the medulla by osmosis (fluid was isotonic when entering loop of Henle)
This makes the filtrate more concentrated (hypertonic) as the ions can’t simply diffuse out because the DESCENDING limb isn’t permeable to them).
The water in the medulla is reabsorbed into the blood through the capillary network (vasa recta)
Near the bottom of the ASCENDING limb Na+ and CI-ions diffuse out into the medulla, further lowering the water potential in the medulla.
(The ASCENDING limb is impermeable to water, so it stays in the tubule.)
When fluid reaches top of ascending limb it is hypotonic (lower conc of solute) to the blood again and enters DCT and collecting duct
The first three stages massively increase the ion concentration in the medulla, which lowers the water potential.
This causes water to move out of the collecting duct by osmosis.
As before, the water in the medulla is reabsorbed into the blood through the capillary network.
Role of DCT
Permeability of walls of DCT are variable depending on ADH
Balances water in the body
Water can leave DCT if walls are permeable in response to ADH (this would concentrate urine)
If body lacks salt then Na+ and Cl- are actively pumped out of DCT down electrochemical gradient
Balances pH of blood
Role of collecting duct
Collecting duct passes down through the concentrated tissue fluid of renal medulla
This is where the concentration and volume of urine is determined
Water moves out of collecting duct by diffusion down concentration gradient
So urine becomes more concentrated
Level of Na+ and Cl- increases through medulla from cortex to pelvis
Means that water can be removed from collecting duct along the whole length
This can produce hypertonic urine when body needs to conserve water
How is the amount of water reabsorbed in collecting duct controlled
Controlled by ADH
What is kidney failure
When the kidneys can’t carry out their normal functions because they don’t work properly
Can also be called renal failure
How can kidney failure be detected
Detected by measuring the glomerular filtration rate (GFR)
The rate at which blood is filtered from the glomerulus into the Bowman’s capsule.
A rate lower than the normal range indicates the kidneys aren’t working properly
High levels of creatinine as if a kidney fails then it will not be excreted enough
How can kidney failure be caused
Kidney infections
High blood pressure
How can kidney failure be caused by kidney infections
Infections can cause inflammation (swelling) of the kidneys
These can damage the structure of podocytes and tubules
This interferes with filtering in the Bowman’s capsules, or with reabsorption in the other parts of the nephrons.
How can kidney failure be caused by high blood pressure
High blood pressure can damage the glomeruli, epithelial cells and basement membrane of Bowman’s capsule
The blood in the glomeruli is already under high pressure and the capillaries can be damaged if the blood pressure gets too high.
This means larger molecules like proteins can get through the capillary walls and into the urine.
Consequences of kidney failure
If problems caused by kidney failure can’t be controlled it can eventually lead to death
Problems caused by kidney failure
Waste products that kidneys normally remove (e.g. urea) begin to build up in the blood.
Too much urea in the blood causes weight loss and vomiting.
Fluid starts to accumulate in the tissues because the kidneys can’t remove excess water from the blood.
This causes parts of the body to swell,
e.g. legs, face and abdomen can swell up.
The balance of electrolytes (ions) in the body is unbalanced.
The blood may become too acidic, and an imbalance of calcium and phosphate can lead to brittle bones.
Salt build-up may cause more water retention.
Long-term kidney failure causes anaemia lack of haemoglobin in the blood.
High blood pressure where water isn’t removed from blood
Pain in joints where proteins have built up
Main treatments of renal failure
Renal dialysis
Kidney transplant
Two types of renal dialysis
Haemodialysis
Peritoneal dialysis
Process of haemodialysis
Patient’s blood passed through dialysis machine
Blood flows on one side of partially permeable membrane (mimicking basement membrane) and dialysis fluid flows on other side
Waste products and excess water and ions diffuse across the membrane into dialysis fluid and are removed from blood
Possible effects of haemodialysis plan of treating kidney failure
Each dialysis session takes 3-5 hours and patients need 2 or 3 sessions a week in hospital usually
Patients can feel increasingly unwell between dialysis sessions because waste products and fluid build up in blood
Process of peritoneal dialysis
Dialysis fluid is put through a tube that passes from the outside of a patient’s abdomen into their abdominal cavity.
Waste products diffuse out of patient’s blood into the dialysis fluid across the peritoneum (the membrane the lines the abdominal cavity).
After some time, the fluid is drained out via the tube.
Possible effects of peritoneal plan of treating kidney failure
This dialysis is usually carried out by the patient at home either several times a day or in one long session overnight.
Risk of infection around the site of the tube and the patient doesn’t have any dialysis-free days
Comparison of types of dialysis
Haemodialysis:
Sessions take 3-5 hrs,
2-3 sessions a week
In hospital
Less risk of infection
Can feel unwell between sessions
Peritoneal
Several times a day or overnight
Everyday
At home
Risk of infection
Advantages of having dialysis
Keeps a person alive until transplant available
Less risky than having major surgery involved in transplant
What is a kidney transplant
A kidney transplant is where a new kidney is implanted into a patient’s body to replace a damaged kidney.
Who can a kidney transplant come from
The new kidney has to be from a person with the same blood and tissue type.
Often donated from a living relative, as people can survive with only one kidney.
Can also come from other people who’ve recently died (organ donors)
Advantages of transplant over dialysis
Cheaper to give a person a transplant than keep them on dialysis for a long time and it’s more convenient for a person than regular dialysis sessions.
Disadvantages of transplant compared to dialysis
Patient will have to undergo a major operation, which is risky.
The immune system may also reject the transplant, so the patient has to take drugs to suppress it.
May still need dialysis
Why do different animals have different lengths of the loop of Henle
The longer an animal’s loop of Henle, the more water they can reabsorb from the filtrate.
Different animals live in different environments so need to retain more water than others (desert vs aquatic)
Why will animals that live in hotter climates need a longer loop of Henle
Animals that live in areas where there’s little water usually have long loops to save as much water as possible.
When there’s a longer ascending limb, more ions are actively pumped out into the medulla, which creates a really low water potential in the medulla.
This means more water moves out of the nephron and collecting duct into the capillaries, giving very concentrated urine
How is water potential of the blood monitored
Water potential of the blood is monitored by cells called osmoreceptors in the hypothalamus
How is ADH released
When osmoreceptors are stimulated by low water potential in the blood the hypothalamus sends nerve impulses to to the posterior pituitary gland to release AntiDiuretic Hormone (ADH) into the blood
What does ADH do
ADH makes the walls of the DCT and collecting duct more permeable to water as more aquaporins inserted into membrane
Means that more water is reabsorbed from these tubules into medulla and into the blood by osmosis
A small amount of concentrated urine is produced, which means less water is lost from the body
How is the volume of water reabsorbed from the collecting duct controlled
The permeability of the collecting duct changes due to ADH
How does ADH make the walls of the tubules more permeable to water
ADH released from pituitary gland and carried to cells of collecting duct
ADH binds to receptors on cell membrane of tubule cells (primary messenger)
Triggers formation of cAMP as a secondary messenger
cAMP causes:
Vesicles in the cells lining the collecting duct fuse with the cell surface membranes on side of the cell in contact with the tissue fluid of the medulla
Membranes of these vehicles contain aquaporins (protein based water channels)
When they are inserted into the cell surface membrane they make it permeable to water
This provides a route for water to move out of tubule cells into tissue fluid of medulla and the blood capillaries by osmosis
What happens when more ADH is produced
The more ADH that is released the more water channels (aquaporins) are inserted into the membranes of the tubule cells
This makes it easier for more water to leave the tubules by osmosis
This creates a small amount of concentrated urine
Water returned to capillaries to maintain water potential of blood
What happens when less ADH is produced
When ADH levels fall levels of cAMP fall
Water channels (aquaporins) removed from tubule cell membranes and enclosed in vesicles
Collecting duct becomes more impermeable to water so no water can leave
Result in production of large amounts of dilute urine
Maintains water potential of blood and tissue fluid
What happens in the negative feedback loop when water is in short supply
Concentration of inorganic ions in the blood rises and the water potential of the blood and tissue fluid becomes more negative.
Detected by the osmoreceptors in the hypothalamus.
They send nerve impulses to the posterior pituitary which releases stored ADH into the blood.
ADH is picked up by receptors in the cells of the collecting duct and increases the permeability of the tubules to water by increasing amount of aquaporins in membrane
Water leaves the filtrate in the tubules and passes into the blood in the surrounding capillary network.
A small volume of concentrated urine is produced
What happens in the negative feedback loop when water is in excess
Blood becomes more dilute and its water potential becomes less negative.
Change detected by the osmoreceptors of the hypothalamus
Nerve impulses to the posterior pituitary are reduced or stopped so the release of ADH by the pituitary is inhibited.
Very little reabsorption of water can take place because the walls of the collecting duct remain impermeable to water as less aquaporins inserted into membrane
In this way the concentration of the blood is maintained
Large amounts of dilute urine are produced
How do pregnancy tests work
Wick soaked in urine passed in morning as it has highest levels of hCG
Test contains mobile monoclonal antibodies that have very small coloured beads attached
These monoclonal antibodies will only bind to hCG
If woman if pregnant the hCG in the urine binds to the mobile monoclonal antibodies and forms a hCG/antibody complex
Urine carries on along the test until it reaches a window
In the window there are immobilised monoclonal antibodies arranged in a line that only bind to hCG/antibody complexes
If woman is pregnant, a coloured line or pattern appears in the first window as the hCG/antibody complexes are held in place and beads collect at this line to make a clear colour change
Urine continues up through the test to a second window
At the second window there are a line of immobilised monoclonal antibodies that bind only to the mobile antibodies regardless of whether they are bound to hCG or not
This coloured line forms as a control even if woman isn’t pregnant to show test is working
If woman is pregnant two coloured patterns form, if she is not only one appears
What are monoclonal antibodies
Monoclonal antibodies are antibodies from a single clone of cells that are produced to target particular cells or chemicals in the body
How are monoclonal antibodies made for pregnancy tests
A mouse is injected with hCG so makes the appropriate antibody
The B-cells that make the required antibody are then removed from the spleen of the mouse
B-cells then fused with myeloma: type of cancer cell which divides rapidly
New fused cell is known as a hybridoma
Each hybridoma reproduces rapidly which results in a clone of millions of cells making the desired antibody
These monoclonal antibodies are collected, purified and used in variety of different ways
How are steroids tested for in urine
Steroids and the products made when they’re broken down can be tested for by gas chromatography and mass spectrometry
How are steroids tested for by gas chromatography (GC)
Urine sample vaporised
Passed through column containing a polymer
Different substances move through the column at different speeds so substances in the urine sample separate out
Once substances have separated out a mass spectrometer converts them into ions
It then separates them out depending on mass and charge
Results are analysed by a computer and by comparing them with the results of known substances it’s possible to tell which substances were in urine sample
How to test for recreational drugs
Test strips contain antibodies which drug or products made when it’s broken down bind to (cannabis🍁, ecstasy💊 or cocaine❄️)
Sample of urine is applied to test strip
If a certain amount of drug (or it’s products) is present a colour change will occur indicating a positive result
If it’s first test shows a positive result a sample of urine is usually sent for further testing to confirm which drugs have been used
Second test uses gas chromatography and mass spectrometry
