A2 OCR Biology - Excretion

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  • Created by: Jess
  • Created on: 19-04-14 14:11
Define excretion
The removal of waste products from the body
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Why is it important to remove waste productes from the body?
Because they will be toxic if they build up
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What is a function of the liver?
To break down metabolic waste products and other substances that can be harmful - like drugs and alcohol - into less harmful, smaller products that can then be excreted
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Name the 4 main arteries, veins or ducts connected to the liver
Hepatic artery, hepatic vein, hepatic portal vein and the bile duct
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What does the hepatic artery do?
Supply the liver with oxygenated blood from the heart so the liver has a good supply of oxygen for respiration
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What does the hepatic vein do?
Takes deoxygenated blood away from the liver
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What does the hepatic portal vein do?
Brings blood from the duodenum and ileum (small intestine) so it's rich in the products of digestion
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What is important about the role of the hepatic portal vein?
The blood is rich in the products of digestion, so harmful substances can be filtered out and broken down straight away
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What does the bile duct do?
Takes bile to the gall bladder to be stored
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Where is bile produced and what is its role?
In the liver - to emulsify fats
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What is the liver made up of?
Lobules - cylinders made of hepatocytes arranged in rows radiating out from the centre
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What do sinusoids connect?
The hepatic artery and hepatic portal vein to the central vein
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What are sinusoids?
Capillaries
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Describe the structure of a lobule
Has a central vein in the middle connected to the hepatic portal vein, but also has many other connections to the hepatic artery, hepatic portal vein and bile duct
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Describe the journey of blood through the sinusoids and beyond
Runs through sinusoids, past hepatocytes, hepatocytes remove harmful substances and oxygen --> broken down and then re-enter blood, runs to central vein, through hepatic vein
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What are Kupffer cells and where are they found?
Attached to walls of the sinusoids - they remove bacteria and break down old RBC's
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What are the names of the tubes that connect the bile duct to the central vein?
Canaliculi
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What are 4 substances that the liver removes from the blood?
Excess amino acids, alcohol, paracetamol and insulin
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Why do excess amino acids have to be broken down by the liver?
They contain nitrogen in their amino groups which can't be stored by the body
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Describe how amino acids are broken down in the liver
Amino groups removed, forms ammonia and organic acids (deamination), respiration of organic acids or conversion to carbohydrate (stored as glycogen), ammonia + CO2 --> urea, filtered out by kidneys, urine
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What is detoxification?
When harful substances like drugs and alcohol are broken down into less harmful compounds that can be excreted from the body
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What is alcohol broken down by the liver into?
Broken down into ethanal (by liver), then acetic acid
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Why is excess alcohol over a long period of time bad?
Leads to cirrhosis of the liver - when the liver cells die and scar tissue blocks blood flow
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Why is paracetamol broken down?
Excess amounts can lead to liver and kidney failure
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What is the problem with excess insulin?
Can cause problems with blood sugar levels
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What are 2 of the main functions of the kidney?
To excrete waste products (e.g. urea) produced by the liver and regulate the body's water content
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Describe the journey of the blood when it enters the kidney
Enters through renal artery, capillaries in kidney cortex, substances filtered out into long tubules (ultrafiltration), useful substances reabsorbed into blood, leave through renal vein (as unwanted substances go to the ureter to bladder as urine)
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Approximately how many nephrons are there in each kidney?
Thousands
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What is the Bowman's capsule also known as?
The renal capsule
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Describe the journey of the blood through a nephron
Enters arterioles in cortex, afferent arteriole, small molecules forced out by high pressure, efferent arteriole, selective reabsorption of wanted products occurs as blood goes around the proximal convoluted tubule
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What happens to the liquid and small molecules forced out of the blood and into the renal capsule in the Bowman's capsule?
Pass through capillary wall, basement membrane, renal capsule epithelium, pass along rest of nephron, useful substances reabsorbed along the way, collecting duct, ureter, urine
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What are the names of the 2 processes that occur around the nephron?
Ultrafiltration and selective reabsorption
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What are the substances normally found in urine?
Water, dissolved salts, urea, hormones, excess vitamins
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What are the substances not normally found in urine?
Proteins, blood cells (too large) / glucose, amino acids, vitamins (selectively reabsorbed)
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Where does selective reabsorption take place?
As the filtrate flows along the proximal convoluted tubule through the loop of Henle and the distal convoluted tubule
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What makes up the filtrate?
All substances filtered out of the blood - regardless if they're reabsorbed or not
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How is the PCT adapted for reabsorption?
The epithelium of its wall has microvilli which provide a large SA for the reabsorption of useful substances in the filtrate
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How are useful substances (like glucose, amino acids, vitamins, salts) reabsorbed into the blood?
By active transport and facilitated diffusion
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Why does water enter the blood?
Because the WP of the blood is lower than that of the filtrate (osmosis: down concentration gradient)
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Where is water reabsorbed from?
Loop of Henle, DCT and the collecting duct
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What does PCT and DCT stand for?
Proximal and distal convoluted tubule
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Name 2 places where water is lost from in the body
As sweat, during excretion by the kidneys as urea is passed out IN SOLUTION
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What happens to the urine if the water content of the blood is too low?
More water is reabsorbed by osmosis into the blood from the nephron tubules, less water lost during excretion, urine is more concentrated
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What happens to the urine if the water content of the blood is too high?
Less water is reabsorbed by osmosis into the blood from the nephron tubules, more water lost during excretion, urine is more dilute
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How is the volume of water reabsorbed controlled by?
Hormones
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What makes up the loop of Henle?
2 limbs - the ascending limb and the descending limb
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What is the name of the mechanism that is set up by the loop of Henle?
Countercurrent multiplier mechanism
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Where is the cortex on the kidney (inside or outside of medulla)?
Outer side
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Where is the medulla on the kidney (inside or outside of cortex)?
Inner side
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STEP 1. What happens near the top of the ascending limb?
Na+ and Cl- ions are actively pumped out and into the medulla, water stay sinside the tubule, low WP in medulla (because of the high ion concentration)
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STEP 2. What happens along the descending limb?
Lower WP in medulla than d. limb, water moves out by osmosis into medulla, concentrated filtrate, water in medulla reabsorbed into blood through capillary network
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What is the ascending limb not permeable to?
Water
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What is the descending limb not permeable to?
Ions
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STEP 3. What happens near the bottom of the ascending limb?
NA+ and Cl- diffuse out into the medulla, lowers WP in medulla, water stays in tubule (impermeable ascending limb)
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STAGE 4. What happens along the collecting duct?
Massive increase medulla's ion concentration, therefore has a lower WP, water moves out of collecting duct by osmosis, water reabsorbed into blood through capillary network
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What is the difference in the loop of Henle between different animals?
They have different length loops of Henle
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What happens if there is a longer loop of Henle?
More water can be reabsorbed from the filtrate, more ions pumped out of a. limb into medulla, low WP in medulla, more water moves out of nephron into capillaries, concentrated uring
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What sort of animal has a longer loop of Henle and why?
Animals that live in areas with little water - so as much water as possible is saved
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How is the water content/potenital of the blood monitored?
By osmoreceptors in the hypothalamus (in the brain)
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What happens once the osmoreceptors have been stimulated by a low water content in the blood?
Stimulated osmoreceptors, hypothalamus sends nerve impulses to the posterior pituitary gland to release a hormone (ADH) into the blood
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What does ADH stand for?
Andidiuretic hormone
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What does ADH do?
Makes the walls of the DCT and collecting duct more permeable to water - so more water is reabsorbed into the medulla, concentrated urine, less water lost from body
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What happens when you are dehydrated?
Water content and WP of blood drops, detected by osmoreceptors, posterior pituitary gland stimulated, ppg. releases more ADH into blood, DCT and collecting duct become more permeable, more water reabsorbed, small amout of highly concentrated urine
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What happens when you are well hydrated?
Water content and WP of blood rises, detected by osmoreceptors, ppg. releases less ADH into blood, DCT and collecting duct less permeable, less water reabsorbed, lots of dilute urine produced
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What does diuresis mean?
When lots of dilute urine is produced
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Which gland releases ADH?
The posterior pituitary gland (I've referred to it as ppg.)
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Define kidney failure
When the kidneys can't carry out their normal functions because they can't work properly
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Name 2 things that cause kidney failure
Kidney infections and high blood pressure
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How do kidney infections cause kidney failure?
Causes kidney inflammation, damages cells, interferring with filtering in the renal capsules/reabsorption in nephrons
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How does high blood pressure cause kidney failure?
Damages glomeruli as capillaries are damaged so larger molecules can get through the capillary walls and into the urine
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What problems are caused by kidney failure?
Waste products build up in blood, too much urea causes weight loss/vomiting, fluid accumulates in tissues, body parts swell, unbalanced ion conc. in body, brittle bones, anaemia (lack of haemoglobin in blood), death
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Describe renal dialysis
Patient's blood passed through dialysis machine, flowing on one side of partially permeable membrane, waste/excess ions and water diffuse across membrane into dialysis fluid (removed from blood), larger molecules don't leave blood
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What are the advantages of kidney dialysis?
Less risky than major surgery, keeps you alive until a transplant is available
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What are the disadvantages of kidney dialysis?
3-5 hour session, 2-3 sessions a week, expensive, inconvenient, can feel increasingly unwell between dialysis sessions as waste produces and fluid builds up in their blood
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What are the advantages of a kidney transplant?
Cheaper than dialysis, more convenient, don't fell unwell
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What are the disadvantages of a kidney transplant?
Major risky operation, immunosuppressants must be taken, risk of rejection
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What are the criteria for having a certain kidney for a transplant?
Must be from a person with the same blood and tissue type
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What do pregnancy tests detect?
hCG hormone - human chorionic gonadotropin, found only in the urine of pregnant women
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How does a pregnancy test work?
Urine applied to application area, hCG binds to antibodies on the beads, urine moves up to the test strip - carrying beads with it, test strip turns blue as immobilised antibodies bind to hCG with blue bead, blue beads in that area get concentrated
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What is on the application area of a pregnancy test stick?
Antibodies for hCG bound to a coloured bead (blue)
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What is on the test strip of a pregnancy test stick?
Antibodies to hCG - stuck in place (immobilised)
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What are anabolic steroids?
Drugs that build up muscle tissue
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Name 2 anabolic steroids
Testosterone and Nandrolone
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Why are athletes banned from using anabolic steroids?
They can have dangerous side-effects (e.g. liver damage), can be unfair during competitions as they build up muscle tissue
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What technique tests urine for steroids?
Gas chromatography
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Why do athletes have their urine tested?
Steroids are removed from the blood through the urine
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How does gas chromatography (urine test for steroids) work?
Urine sample vaporised (to gas), passed through column containing a liquid, length of time taken for substances in urine sample to move through column is compared to time taken for a steroid to pass through the column, time taken is the same= steroid
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Why is it important to remove waste productes from the body?

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Card 3

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Card 4

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Name the 4 main arteries, veins or ducts connected to the liver

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Card 5

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