Excretion

Question 1

What is excretion?

Answer 1

The removal of metabolic waste from the body.

CO2 when we breathe out

Nitrogenous waste in the urine

Question 2

Why is excretion important for homeostasis?

Answer 2

It prevents build up of substances that could cause tissue damage.

Question 3

What are the functions of the liver?

Answer 3

Breaking down amino acids into urea
Detoxifying the blood
Storing glycogen
Producing bile.

Question 4

what is the process where liver converts excess amino acids to urea?

Answer 4

Deamination

Ornithine cycle

Question 5

What is the ornithine cycle?

Answer 5

Metabolic pathway where amino acids are deaminated to form ammonia and organic acids

Ammonia is converted into urea by reacting with CO2

Urea is released into the blood stream

Question 6

How does urea get excreted?

Answer 6

Urea is released into the bloodstream

Filtered by the kidneys and excreted by the body in urine

Question 7

What vessels are involved in liver function?

Answer 7

Hepatic artery - oxygenated blood
Hepatic vein - deoxygenated blood
Hepatic portal vein - liver to intestines
Bile duct - liver to gall bladder

Question 8

What is the structure of the liver made up of?

Answer 8

Liver lobules which are cylindrical structures made of hepatocytes

Question 9

What are sinusoids in the liver?

Answer 9

Special capillaries that connect the central vein to hepatic artery and portal vein

Allows blood to flow through liver

Question 10

What is the role of Kupffer cells in the liver?

Answer 10

Break down old red blood cells and remove bacteria from blood stream

Question 11

What are the 2 main parts of the kidney?

Answer 11

The Medulla - inner part
The Cortex - outer part

Question 12

How does blood flow to and from the kidney?

Answer 12

Blood is carried to the kidney via the renal artery

Filtered blood is taken away by renal vein

Question 13

What are nephrons?

Answer 13

Individual structures in the kidneys that filter the blood and remove waste products.

Question 14

What substances do our kidneys remove from the blood?

Answer 14

Excess water
Excess ions
Urea

Question 15

What processes are involved in the removal of substances from the blood stream?

Answer 15

Ultrafiltration and selective reabsorbtion

Question 16

What happens during ultrafiltration?

Answer 16

Blood is placed under high pressure in the glomerelus

the efferent arteriole has a smaller diameter than the afferent arteriole

Small molecules are pushed out the blood into the Bowman’s capsule

Question 17

What are the 3 layers that small molecules pass through?

Answer 17

The capillary endothelium

The basement membrane

The epithelium of the Bowman’s capsule - podocytes

Question 18

What is glomerular filtrate?

Answer 18

Substance formed when small molecules are pushed out of the bloodstream

Question 19

What happens to larger molecules during ultrafiltration?

Answer 19

large molecules remain inside the capillaries during ultrafiltration

Question 20

What is the proximal convoluted tubule (PCT)?

Answer 20

In the PCT, useful substances are reabsorbed back into the blood

Question 21

How is glucose reabsorbed in the PCT?

Answer 21

Na+ is actively transported into the capillaries

Na+ concentration decreases in the PCT epithelial cells

Na + moves from PCT lumen to epithelial cells down a concentration gradient

Na+ is co-transported with glucose into the epithelial cells

Glucose diffuses into the blood

Question 22

What structures in the PCT aid in reabsorbtion?

Answer 22

The PCT has microvilli that provide large surface area

Question 23

How is water reabsorbed in the kidneys?

Answer 23

At the top of the ascending limb, sodium ions are pumped into the medulla

this lowers the water potential of the medulla so water moves out of the nephron by osmosis from the descending limb

More water moving out means filtrate becomes more concentrated so sodium ions diffuse out ascending limb

Water potential in medulla is lowered more and water moves out by osmosis

Question 24

What is ADH?

Answer 24

ADH controls the water content of urine by increasing the reabsorption of water from the collecting duct.

It is released by the pituitary gland when water levels are low

Question 25

Explain the negative feedback mechanism of ADH

Answer 25

Osmoreceptors in the hypothalamus detect a drop in blood water potential

Hypothalamus signals the posterior pituitary gland to secrete ADH

ADH causes the walls of the DCT to become more permeable to water

More water moves out of the DCT by osmosis and reabsorbed into the blood - DCT water potential increases.

Smaller volume of concentrated urine produced

Question 26

How does the DCT become more permeable to water?

Answer 26

Incorporation of more aquaporins into the membranes of the cells that line these parts of the nephron

Question 27

What is kidney faliure?

Answer 27

Kidney faliure occurs when the kidneys stop filtering toxic substances out of the blood

Question 28

What causes kidney failure?

Answer 28

Infection - inflammation in kidney which damages cells so the nephron cant reabsorb substances

High blood pressure - damages the glomeruli so large substances like proteins can pass into the nephron

Question 29

How is kidney failure diagnosed?

Answer 29

Measuring glomerular filtration rate (GFR) - the rate at which blood is filtered from the Bowman’s capsule

Low GFR = kidney failure

Question 30

Problems of kidney failure

Answer 30

Build up of waste products - urea

Ion imbalance - acidic blood, brittle bones and water retention

Accumulation of fluids in tissue - swelling

Anaemia - low blood haemoglobin

Mortality

Question 31

What is dialysis?

Answer 31

Connecting patients blood supply to a dialysis machine

Blood passes through partially permeable membrane surrounded by dialysis fluid

Urea is removed and glucose, water and salts are maintained

Question 32

Negatives of dialysis

Answer 32

Multiple hospital visits

Long sessions connected to machine

Expensive

Patients must maintain a controlled diet

Question 33

What are some alternative treatments to kidney failure?

Answer 33

A kidney transplant

Major surgery which comes with the risk of organ rejection

requires immunosupressant drugs

Question 34

How are drugs detected in urine?

Answer 34

Detected using test strips with antibodies that bind to the drug, causing a color change

confirmed by gas spectrometry/ mass spectrometry

Question 35

How do pregnancy tests work?

Answer 35

Pregnancy tests detect human chorionic gonadotropin (hCG) in the urine

Test stick contains monoclonal antibodies bound to coloured beads that attach to hCG

Urine moves up test strip and immobilized antibodies capture the hCG