Module 5 Section 2- Excretion

Question 1

What is metabolism?

Answer 1

All the chemical reactions that happen in the cells.

Question 2

What is excretion?

Answer 2

The removal of waste products of metabolism from the body.

Question 3

Why is excreting waste important?

Answer 3

Excreting waste products from the body maintains normal metabolism. It also maintains homeostasis by keeping levels of certain substances in the blood roughly constant.
An example is carbon dioxide (waste product of respiration). Too much in the blood is toxic, so is removed by the lungs or gills.

Question 4

What are the main vessels in the liver?

Answer 4

1) Hepatic artery
2) hepatic vein
3) hepatic portal vein
4) Bile duct

Question 5

What does the hepatic artery do?

Answer 5

It supplies the liver with oxygenated blood from the heart, so it has a good supply of oxygen for respiration, providing lots of energy. Blood enters kidney through narrow vessel.

Question 6

What does the hepatic vein do?

Answer 6

It takes deoxygenated blood away from the heart.

Question 7

What does the hepatic portal vein do?

Answer 7

It brings blood from the duodenum and ileum (parts of small intestine), so it’s rich in products of digestion. This means any ingested harmful substances are filtered out and broken down straight away. Blood enters kidney through branched vessel.

Question 8

What does the bile duct do?

Answer 8

It takes bile (a substance produced by the liver to emulsify fats) to the gallbladder to be stored.

Question 9

What is the main structure of the liver?

Answer 9

1) the liver is made up of liver lobules, which are cyclindrical structures made of hepatocytes that are arranged in rows radiating from the centre.

2) each lobule has a central vein. Many branches of the hepatic artery, hepatic portal vein and bile duct are also connected to each lobule.

Question 10

What is the structure of the lobule + movement of blood ?

Answer 10

1) the hepatic artery and the hepatic portal vein are connected to the central vein by capillaries called sinusoids.
2) Blood runs through the sinusoids, past the hepatocytes that remove harmful substances from the blood.
3) The harmful substances are broken down by the hepatocytes into less harmful substances and re-enter the blood.
4) the blood runs through the central vein, and the central veins from all the lobules connect to form hepatic vein.
5) Kupffer cells are attached to the wall of sinuosoids to remove bacteria and break down old red blood cells.
6) Hepatocytes produce bile and secrete it into tubes called bile canaliculi. These tubes drain into the bile ducts.

Question 11

What is deamination?

Answer 11

It is the breaking down of excess amino acids in the liver. This is because nitrogenous substances cannot usually be stored by the body.

Question 12

What is the process of deamination?

Answer 12

1) amine groups are removed from excess amino acids, forming ammonia and organic acids. This is known as deamination.

2) the organic acids can be respired to give ATP or converted to carbohydrate and stored as glycogen.

3) Ammonia is too toxic to be excreted directly so is combined with CO2, in the ornithine cycle to create urea and water.

4) urea is released from the liver into the blood. The kidneys then filter the blood and remove urea as urine, which is excreted from the body.

Question 13

What is the ornithine cycle?

Answer 13

1) ammonia + CO2 forms carbamoyl phosphate. This connects to big loop.
2) starts from citrulline, which has an arrow connected to argininosuccinate.
3) there is an atp to amp arrow and aspartate to water arrow in between.
4) then there is an arrow from argininosuccinate to arginine.
5) then there is an arrow from arginine to ornithine.
6) between this arrow there is an arrow from water to urea.
7) ornithine connects to citrulline to Form a loop.

Question 14

What is detoxification?

Answer 14

This is where the liver breaks down other harmful substances eg alcohol drugs and unwanted hormones into less harmful compounds that can then be excreted by the body.

Question 15

What are some harmful substances broken down by the liver?

Answer 15

1) alcohol - it’s broken down into ethanol , which is then broken down into acetic acid. Excess alcohol over a long period of time can lead to cirrhosis of the liver. (When cells of the liver die and scar tissue blocks blood flow.

2) paracetamol - it is broken down by the liver. Excess paracetamol in the blood can lead to liver and kidney failure.

3) Insulin - excess broken down by the liver as it can cause a problem with blood sugar levels.

Question 16

How does the liver store glucose?

Answer 16

The liver converts excess glucose in the blood to glycogen by glycogenesis and stores it as granules until the glucose is needed for energy.

Question 17

How does liver tissue look under a microscope?

Answer 17

1) the large white circular shape is the central vein
2) the cells that radiate from the central vein are hepatocytes.
3) the white gaps between hepatocytes are sinusoids.

Question 18

Overview of how the kidney excretes waste products

Answer 18

1) blood enters the kidney through the renal artery and then passes through the capillaries in the cortex of the kidneys.

2) as the blood passes through the capillaries, substances are filtered out of the blood and into long tubules that surround the capillaries. This process is ultrafiltration.

3) useful substances eg glucose are reabsorbed back into the blood from the tubules in the medulla and cortex. This is selective reabsorption.

4) the remaining unwanted substances pass along the tubules, then along the ureter to the bladder, where they’re expelled as urine.

5) filtered blood passes out of kidneys through the renal vein.

Question 19

What are the Structures in kidney

Answer 19

Cortex
Medulla
Renal calyx
Renal capsule
Renal artery
Renal vein
Ureter
Bladder
Urethra

Question 20

What is a nephron?

Answer 20

The long tubules along the bundle of capillaries where the blood is filtered

Question 21

What is the process of ultrafiltration?

Answer 21

1) blood from the renal artery enters the smaller arterioles in the cortex.

2) Each arterioles splits into a glomerulus. This structure is a bundle of capillaries looped inside the bowman’s capsule. This where ultrafiltration takes place

3) the arteriole that takes blood into each glomerulus is the afferent arteriole. The efferent arteriole takes blood away from the glomerulus and is under high pressure.

4) the high pressure forces liquid and small molecules in the blood out of the capillary into the bowman’s capsule. Large molecules eg proteins can’t pass through

5) the liquid and small molecules pass through three layers to get into the bowman’s capsule and enter the nephron. The layers are the endothelium of the capillary, the basement membrane and the podocytes.

6) the liquid and small molecules are now called filtrate and pass along the rest of the nephron.

Question 22

What is the difference in structure between the afferent and efferent arteriole?

Answer 22

The efferent arteriole is smaller in diameter than the afferent arteriole so the blood in the glomerulus is under high pressure.

Question 23

What is the process of selective reabsorption?

Answer 23

1) it takes place as the filtrate passes along the proximal convoluted tubule (PCT), through the loop of henle, and along the distal convoluted tubule (DCT).

2) useful substances leave tubules and enter capillary network that’s wrapped around them.

3) the epithelium of the wall of the PCT has microvilli to provide large surface area for reabsorption of useful substances from the filtrate into the blood.

4) useful solutes like glucose, amino acids, vitamins and some salts are reabsorbed along the PCT by active transport and facilitated diffusion. Some urea is also reabsorbed by diffusion.

5) water enters blood by osmosis because the water potential of the blood is lower than the filtrate. Water is reabsorbed from the loop of henle, DCT and collecting duct.

6) the filtrate that remains is urine, which passes along the ureter to the bladder.

Question 24

What is urine usually made up of?

Answer 24

1) water and dissolved salts
2) urea
3) other substances such as hormones and excess vitamins

Question 25

What does urine not usually contain?

Answer 25

1) proteins and blood cells, they’re too big to be filtered out of the blood.

2) glucose, amino acids and vitamins, they’re actively reabsorbed back into the blood.

Question 26

What does microscope slide of cortex look like?

Answer 26

It contains the glomerulus. The bundle of capillaries is the glomerulus. The white ring outside the capillaries is the bowman’s capsule. The circular areas surrounding the glomerulus are PCTs and DCTs.

Question 27

What does a microscope slide of the Medulla look like?

Answer 27

The white strips are the loops of henle. They are surrounded by capillaries. The red dots are the red blood cells in the capillaries.

Question 28

What is the external examination of the kidney?

Answer 28

1) it’s covered with a thin strong membrane called the renal capsule.
2) beneath this, is the outside of the cortex.
3) the part of the kidney that is indented is the renal helium and usually has tubes coming from here.
4) the tubes are the renal vein, renal artery and ureter. The artery will ave a thicker wall than the vein and the ureter is likely to have more adipose tissue around it.

Question 29

What is the internal examination of the kidney?

Answer 29

1) cut the kidney in half lengthways from one side.
2) the cortex should appear dense and grainy and is a lighter shade than the medulla.
3) in the medulla, there are many cone shaped structures called renal pyramids. They appear stripy because they contain straight sections of nephrons.
4) in between the the pyramids are renal columns
5) the hollow cavities from the base if the pyramids are renal calyces
6) these lead to a larger hollow structure called the renal pelvis which connects to the ureter.

Question 30

How does water potential affect the amount of water reabsorbed?

Answer 30

1) is water potential is too high, less water is reabsorbed into the blood so urine is more dilute and more water is lost by excretion.

2) if water potential is too low, more water is reabsorbed by osmosis into the blood so the urine is more concentrated and less water is lost during excretion.

Question 31

What is the mechanism to help reabsorb water called?

Answer 31

The countercurrent multiplier mechanism.

Question 32

How does the countercurrent multiplier mechanism work?

Answer 32

1) near the top of the ascending limb, Na+ and Cl- ions are actively pumped out into the medulla. The ascending limb is impermeable to water , so water stays inside the tubule. This lowers water potential in medulla, because there is a higher concentration of ions.

2) there is a lower water potential in the medulla than the descending limb, so water moves out the descending limb into medulla by osmosis. This makes filtrate more concentrated. Ions cannot diffuse out because descending limb is impermeable to them. Water in medulla is reabsorbed into blood by capillary network.

3) Near the bottom of the ascending limb, Na+ and Cl- ions diffuse out into medulla, further lowering water potential in the medulla.

4) the first three stages massively increase ion concentration in the medulla, which lowers water potential. This causes water to move out of the collecting ducts by osmosis and is reabsorbed into the blood.

Question 33

Why is the loop of henle different lengths in different animals?

Answer 33

A longer loop of henle means more water can be reabsorbed from the filtrate. This means animals that live in areas where there is little water, they have long loops to save as much water as possible eg the fennec fox, the desert kangaroo rat and camel.

Frigs and toads don’t have a loop of henle at all because they live in a wet environment so do not need to conserve water.

Question 34

How is water reabsorption controlled by hormones?

Answer 34

1) the water potential of the blood is monitored by cells called osmoreceptors in the hypothalamus.

2) when the osmoreceptors are stimulated by low water potential in the blood, the hypothalamus sends nerve impulses to the posterior pituitary gland to release a hormone called anti diuretic hormone (ADH) into the blood.

3) ADH molecules bind to receptors on the plasma membranes of the cells in the DCT and the collecting duct. This causes protein channels called aquaporins to be inserted into the plasma membrane.

4) these allow water to pass through via osmosis, making the walls of these vessels more permeable to water. This means more water is reabsorbed from these tubules into the medulla and into the blood by osmosis.

Question 35

How can kidney failure be detected?

Answer 35

By measuring the glomerular filtration rate (GFR). This is the rate at which blood is filtered from the glomerulus into the bowman’s capsule.

Question 36

What are two things that can cause kidney failure?

Answer 36

Kidney infections - they can cause inflammation of the kidneys, which damage the cells. This interferes with the filtering in the bowman’s capsule and reabsorption in other parts of the nephron.

High blood pressure- this can damage the glomeruli. Capillaries can become damaged so larger molecules like proteins can get through the capillary walls into the urine.

Question 37

What are some problems arising from kidney failure?

Answer 37

1) waste products eg urea begin to build up in the blood. Too much urea in the blood causes weight loss and vomiting.

2) Fluid starts to accumulate in the tissues because kidneys cannot remove excess water. This causes parts of the body to swell eg a person’s legs, face and abdomen.

3) electrolytes in the body become unbalanced. The blood may become too acidic and an imbalance of calcium and phosphate can lead to brittle bones. Salt build up causes more water retention.

4) long term kidney failure causes anaemia. A lack of Haemoglobin in the blood.

Question 38

What are two treatments for kidney failure?

Answer 38

1) renal dialysis
2) kidney transplant

Question 39

How does haemodialysis work?

Answer 39

A dialysis machine is used to filter a patient’s blood.

1) the blood flows on one side of a partially permeable membrane and dialysis fluid flows in the opposite direction. This maintains steep concentration gradient between fluids to increase rate of diffusion.

2) waste products and excess water and ions diffuse across the membrane into the dialysis fluid, removing them from the blood. Larger molecules eg proteins remain in the blood.

Question 40

What are the advantages and diadvantages of renal dialysis?

Answer 40

Advantages
- keeps a person alive until a transplant is available
- less risky than having a major surgery involved in a transplant

Disadvantages
- patients may feel ill between dialysis sessions due to waste products building up in the blood
- they usually take up to 3-5 hours, happens 2-3 times a week in hospital. So very inconvenient.

Question 41

How does a kidney transplant work?

Answer 41

A new kidney is implanted into a patient’s body to replace a damaged kidney. The new kidney has to be from a person with the same blood and tissue type (usually a relative) or an organ donor.

Question 42

Advantages and disadvantages of a kidney transplant?

Answer 42

Advantages
- it is more convenient than dialysis
- do not have the problem of feeling unwell between dialysis sessions.

Weaknesses
- it is a major operation which is risky
- immune system may reject the kidney so the patients have to take drugs to suppress it.

Question 43

What is the hormone found in the urine of pregnant women?

Answer 43

Human chorionic gonadotropin (hCG)

Question 44

How do pregnancy tests work?

Answer 44

1) a stick is used with an application area that contains monoclonal antibodies for hCG bound to a coloured bead (blue). Monoclonal antibodies are identical to each other.

2) when urine is applied to the application area, any hCG will bind to the antibody on the beads.

3) the urine moves up the test strip, carrying the beads with it.

4) the test strip has immobilised antibodies to hCG.

5) if hCG is present, the test strip turns blue because the immobilised antibody binds to any hCG attached to the blue beads, concentrating the blue beads in that area. If no hCG is present, the blue beads will pass straight through without binding to anything, so it won’t go blue.

Question 45

What are anabolic steroids?

Answer 45

Anabolic steroids are drugs that build up muscle tissue eg testosterone and nandrolone.

Some athletes are banned from taking anabolic steroids as it is considered unfair and can have dangerous side effects eg liver damage.

Question 46

How to test for anabolic steroids

Answer 46

Athletes regularly have their urine tested for steroids.

1) In gas chromatography, the urine sample is vaporised and passed through a column containing a polymer. Different substances move through the column at different speeds so substances in the urine sample seperate out.

2) one the substances are separated, a mass spectrometer converts them into ions, then separates the ions depending on mass and charge.

3) the results are analysed and compared to the results of known substances to tell which substances are present in the urine.

Question 47

How to test for recreational drugs?

Answer 47

Some recreational drugs are cannabis, ecstasy or cocaine.

1) a sample of urine is applied to a test strip and if a certain amount of the drug is present, a colour change will occur, indicating a positive result.

2) if the first test is positive, a sample is usually sent for further testing. The second test uses gas chromatography and mass spectrometry like the test for steroids.

Question 48

What is peritoneal dialysis?

Answer 48

Peritoneal dialysis makes use of the natural dialysis membranes formed by the lining of the abdomen called peritoneum. It is usually done at home. The fluid enters the abdomen via a catheter. Excess urea and ions are drained.