5.5 - Excretion

Question 1

What is excretion ?

Answer 1

Excretion is the Removal of Waste Products from the Body

Question 2

What is metabolism ?

Answer 2

All the chemical reactions that happen in your cells make up your metabolism. Metabolism produces waste products substances that aren’t needed by the cells, such as carbon dioxide and nitrogenous (nitrogen-containing) waste. Many of these products are toxic, so if they were allowed to build up in the body they would cause damage, e.g. by affecting other metabolic reactions.

Question 3

What is an example of this ?

Answer 3

For example, carbon dioxide is a waste product of respiration. Too much in the blood is toxic, so it’s removed from the body by the lungs (e.g. in mammals) or gills (e.g. in fish). The lungs and gills act as excretory organs.

Question 4

Reasons for excretion

Answer 4

Excreting waste products from the body maintains normal metabolism. It also maintains homeostasis by helping to keep the levels of certain substances in the blood roughly constant.

Question 5

What is the functions of the liver ?

Answer 5

• Excess amino acids are broken down
• liver removes other harmful substances
• liver stores glycogen

Question 6

Explain how excess amino acids are broken down

Answer 6

Excess Amino Acids are Broken Down by the Liver
One of the liver’s most important roles is getting rid of excess amino acids produced by eating and digesting protein.
Amino acids contain nitrogen in their amino groups. Nitrogenous substances can’t usually be stored by the body.
This means excess amino acids can be damaging to the body, so they must be used by the body (e.g. to make proteins) or be broken down and excreted. Here’s how excess amino acids are broken down in the liver:
1) First, the nitrogen-containing amino groups (-NH,) are removed from any excess amino acids, forming ammonia (NH,) and organic acids — this process is called deamination.
2) The organic acids can be respired to give ATP or converted to carbohydrate and stored as glycogen.

3) Ammonia is too toxic for mammals to excrete directly, so it’s combined with CO2 in the ornithine cycle to create urea.

4) The urea is released from the liver into the blood. The kidneys then filter the blood and remove the urea as urine (see p. 151-152), which is excreted from the body.

Question 7

How does live remove harmful substances and what are they ?

Answer 7

• The Liver Removes Other Harmful Substances from the Blood
  The liver also breaks down other harmful substances, like alcohol, drugs and unwanted hormones.
  They’re broken down into less harmful compounds that can then be excreted from the body
  — this process is called detoxification. Some of the harmful products broken down by the liver include:

1) Alcohol (ethanol) — a toxic substance that can damage cells. It’s broken down by the liver into ethanal, which is then broken down into a less harmful substance called acetic acid.
Excess alcohol over a long period can lead to cirrhosis of the liver — this is when the cells of the liver die and scar tissue blocks blood flow.
Paracetamol — a common painkiller that’s broken down by the liver. Excess paracetamol in the blood can lead to liver and kidney failure.
Insulin - a hormone that controls blood glucose concentration. Insulin is also broken down by the liver as excess insulin can cause problems with blood sugar levels.

Question 8

Explain how liver stores glycogen

Answer 8

The Liver Stores Glycogen
The body needs glucose for energy. The liver converts excess glucose in the blood to glycogen and stores it as granules in its cells until the glucose is needed for energy.
The liver is involved in the control of blood glucose concentration

Question 9

What is the structure of the liver

Answer 9

• think about picture explain
• 1) The hepatic artery supplies the liver with oxygenated blood from the heart, so the liver has a good supply of oxygen for respiration, providing plenty of energy.
  2) The hepatic vein takes deoxygenated blood away from the liver.
  3) The hepatic portal vein brings blood from the duodenum and ileum (parts of the small intestine), so it’s rich in the products of digestion. This means any ingested harmful substances are filtered out and broken down straight away.
  4) The bile duct takes bile (a substance produced by the liver to emulsify fats) to the gall bladder to be stored.

Question 10

What is the liver made up of ?

Answer 10

-Liver Lobules: Cylindrical structures made of hepatocytes arranged in rows around a central vein.

Question 11

What is found in the middle of each liver lobule ?

Answer 11

• central vein that connects to the hepatic vein.

Question 12

Q: What vessels are connected to each liver lobule?

Answer 12

A: Branches of the hepatic artery, hepatic portal vein, and bile duct.

Question 13

What connects the hepatic artery and portal vein to the central vein?

Answer 13

Capillaries called sinusoids.

Question 14

What do hepatocytes do as blood flows through the sinusoids?

Answer 14

They remove harmful substances and oxygen from the blood.

Question 15

How are harmful substances in the blood dealt with?

Answer 15

Hepatocytes break them down into less harmful substances, which then re-enter the blood.

Question 16

What happens to blood after it passes through the sinusoids?

Answer 16

It flows into the central vein, and central veins from all lobules join to form the hepatic vein.

Question 17

What are Kupffer cells, and what is their function?

Answer 17

Cells attached to sinusoid walls that remove bacteria and break down old red blood cells.

Question 18

What do hepatocytes produce, and where is it secreted?

Answer 18

They produce bile, which is secreted into bile canaliculi.

Question 19

Where does bile go after leaving the bile canaliculi?

Answer 19

It drains into bile ducts, which connect and exit the liver

Question 20

Draw and label liver cross section

Answer 20

did you get it right ??

Question 21

How to identify liver tissue under a light microscope

Answer 21

• Large white circular shape is central vein
• These cells radiate out from the central vein are the hepatocytes.
  -The red dots are nuclei
  -The white spaces are the sinusoids

Question 22

What is the structure of the kidney ?

Answer 22

• remember the photo

Question 23

How does excretion happen in the kidney ?

Answer 23

• 1) Blood enters the kidney through the renal artery and then passes through 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 called ultrafiltration (see below).
  3)
  Useful substances (e.g. glucose) are reabsorbed back into the blood from the tubules in the medulla and cortex - this is called selective reabsorption (see next page).
  4) The remaining unwanted substances (e.g. urea) pass along the tubules, then along the ureter to the bladder, where they’re expelled as urine.
  5) The filtered blood passes out of the kidneys through the renal vein.

Question 24

Where does the blood go after entering through renal artery?

Answer 24

• Smaller arterioles in the cortex

Question 25

What happens to the arterieoles ?

Answer 25

2) Each arteriole splits into a structure called a glomerulus
— a bundle of capillaries looped inside a hollow ball called the Bowman’s capsule.
from renal artery
3) This is where ultrafiltration takes place.
4) The arteriole that takes blood into each glomerulus is called the afferent arteriole, and the arteriole that takes the filtered blood away from the glomerulus is called the efferent arteriole.
5) The efferent arteriole is smaller in diameter than the afferent arteriole, so the blood in the glomerulus is under high pressure.
6) The high pressure forces liquid and small molecules in the blood out of the capillary and into the Bowman’s capsule.
7) The liquid and small molecules pass through three layers to get into the Bowman’s capsule and enter the nephron tubule - the capillary wall, a membrane (called the basement membrane) and the epithelium of the Bowman’s capsule. Larger molecules like proteins and blood cells can’t pass through and stay in the blood.
8) The liquid and small molecules, now called filtrate, pass along the rest of the nephron and useful substances are reabsorbed along the way - see next page.
9) Finally, the filtrate flows through the collecting duct and passes out of the kidney along the ureter.

Question 26

What is glomerulus ?

Answer 26

— a bundle of capillaries looped inside a hollow ball called the Bowman’s capsule.

Question 27

Explain ultrafiltration

Answer 27

4) The arteriole that takes blood into each glomerulus is called the afferent arteriole, and the arteriole that takes the filtered blood away from the glomerulus is called the efferent arteriole.
5) The efferent arteriole is smaller in diameter than the afferent arteriole, so the blood in the glomerulus is under high pressure.
6) The high pressure forces liquid and small molecules in the blood out of the capillary and into the Bowman’s capsule.
7) The liquid and small molecules pass through three layers to get into the Bowman’s capsule and enter the nephron tubule - the capillary wall, a membrane (called the basement membrane) and the epithelium of the Bowman’s capsule. Larger molecules like proteins and blood cells can’t pass through and stay in the blood.
8) The liquid and small molecules, now called filtrate, pass along the rest of the nephron and useful substances are reabsorbed along the way - see next page.
9) Finally, the filtrate flows through the collecting duct and passes out of the kidney along the ureter.

Question 28

How does kidneys regulate water potential of the blood ?

Answer 28

If the water potential of the blood is too low (the body is dehydrated), more water is reabsorbed by osmosis into the blood from the tubules of the nephrons (see p. 151-152 for more).
This means the urine is more concentrated, so less water is lost during excretion.
If the water potential of the blood is too high (the body is too hydrated), less water is reabsorbed by osmosis into the blood from the tubules of the nephrons. This means the urine is more dilute, so more water is lost during excretion (see next page).

Question 29

Where is it regulated in the kidney

Answer 29

• Loop of Henle
• Distal consulted tubule
• Collecting duct

Question 30

Explain counter current mechanism

Answer 30

Pg 154

Question 31

How is water potential controlled ?

Answer 31

Water Reabsorption is Controlled by Hormones

1) The water potential of the blood is monitored by cells called osmoreceptors in a part of the brain called 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 antidiuretic hormone (ADH) into the blood.

3) ADH makes the walls of the DCT and collecting duct more permeable to water.

4) This means more water is reabsorbed from these tubules into the medulla and into the blood by osmosis. A small amount of concentrated urine is produced, which means less water is lost from the body.

Question 32

What happens when you’re dehydrated ?

Answer 32

Dehydration is what happens when you lose water, e.g. by sweating during exercise, so the water content of the blood needs to be increased:
1) The water content of the blood drops, so its water potential drops.
2) This is detected by osmoreceptors in the hypothalamus.
3) The posterior pituitary gland is stimulated to release more ADH into the blood.
4) More ADH means that the DCT and collecting duct are more permeable, so more water is reabsorbed into the blood by osmosis.
5) A small amount of highly concentrated urine is produced and less water is lost.

Question 33

What happens when you’re hydrated ?

Answer 33

2
Blood ADH Level Falls When You’re Hydrated

If you’re hydrated, you’ve taken in lots of water, so the water content of the blood needs to be reduced:

1) The water content of the blood rises, so its water potential rises.

2) This is detected by the osmoreceptors in the hypothalamus.
3)
The posterior pituitary gland releases less ADH into the blood.
4)
Less ADH means that the DCT and collecting duct are less permeable, so less water is reabsorbed into the blood by osmosis.

5) A large amount of dilute urine is produced and more water is lost.

Question 34

What is kidney failure ?

Answer 34

Kidney Failure is When the Kidneys Stop Working Properly
Kidney failure is also called renal failure.
Kidney failure is when the kidneys can’t carry out their normal functions because they lon’t work properly. Kidney failure can be detected by measuring the glomerular filtration rate (GFR) - his is 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.

Question 35

What causes kidney failure ?

Answer 35

1)
Kidney infections — these can cause inflammation (swelling) of the kidneys, which can damage the cells.
This interferes with filtering in the Bowman’s capsules, or with reabsorption in the other parts of the nephrons.
2) High blood pressure — this can damage the glomeruli. The blood in the glomeruli is already under high pressure but 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.

Question 36

What problems does kidney failure cause ?

Answer 36

Kidney failure causes lots of problems, for example:
If the problems caused by kidney failure can’t
Waste products that the kidneys would normally remove (e.g. urea
- be controlled, it can eventually lead to death.
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 the kidneys can’t remove excess water from the blood.
This causes parts of the body to swell, e.g. the person’s legs, face and abdomen can swell up.
3) The balance of electrolytes (ions) in the body becomes, well, 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.
4) Long-term kidney failure causes anaemia — a lack of haemoglobin in the blood.

Question 37

How is Kidney failure treated ?

Answer 37

-
1) HAEMODIALYSIS — this is where the patient’s blood is passed through a dialysis machine - the blood flows on one side of a partially permeable membrane and dialysis fluid flows on the other side.
Waste products and excess water and ions diffuse across the membrane into the dialysis fluid, removing them from the blood. Blood cells and larger molecules like proteins are prevented from leaving the blood. Each dialysis session takes three to five hours, and patients need two or three sessions a week, usually in hospital. Patients can feel increasingly unwell between dialysis sessions because waste products and fluid start to build up in their blood

There are disadvantages to both types of dialysis, but it can keep a person alive until a transplant is available (see below), and it’s a lot less risky than having the major surgery involved in a transplant.
Kidney transplant
1) A kidney transplant is where a new kidney is implanted into a patient’s body to replace a damaged kidney.
2) The new kidney has to be from a person with the same blood and tissue type. They’re often donated from a living relative, as people can survive with only one kidney. They can also come from other people who’ve recently died - organ donors.
3)
Transplants have a lot of advantages over dialysis — it’s 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.
4)
But there are also disadvantages to having a kidney transplant: the 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.

Question 38

Why can urine be used to test for pregnancy, drug use, and medical problems?

Answer 38

Urine is made by filtering the blood, so it reflects what’s in a person’s blood.

Question 39

What hormone is detected in pregnancy tests?

Answer 39

Human chorionic gonadotropin (hCG).

Question 40

How does a pregnancy test work?

Answer 40

The application area contains monoclonal antibodies for hCG bound to a coloured bead.
When urine is applied, hCG binds to the antibodies on the beads.
Urine moves up the test strip, carrying the beads with it.
The test strip has immobilised antibodies to hCG.
If hCG is present, it binds to the immobilised antibodies, concentrating the beads and turning the strip blue.

Question 41

Why doesn’t the test strip turn blue if hCG is absent?

Answer 41

The beads pass through the test area without binding to anything.

Question 42

What are anabolic steroids, and why are they banned for athletes?

Answer 42

Drugs like testosterone and nandrolone that build muscle tissue. They are banned due to dangerous side effects (e.g., liver damage) and to prevent unfair advantages.

Question 43

What technique is used to test for steroids in urine?

Answer 43

Gas chromatography/mass spectrometry (GC/MS).

Question 44

How does gas chromatography work?

Answer 44

The urine sample is vaporised and passed through a column containing a polymer.
Substances move through at different speeds and separate out.
A mass spectrometer converts the substances into ions and separates them by mass and charge.
A computer compares the results with known substances to identify them.

Question 45

What is the first step in testing for recreational drugs?

Answer 45

Using a test strip with antibodies that bind to the drug or its breakdown products.

Question 46

What indicates a positive result on a drug test strip?

Answer 46

: A colour change if a certain amount of the drug or its products is present.

Question 47

What happens after a positive result on the test strip?

Answer 47

The urine sample is sent for further testing using GC/MS to confirm which drugs were used.

Question 48

What happens after a positive result on the test strip?

Answer 48

The urine sample is sent for further testing using GC/MS to confirm which drugs were used.