Excretion

Question 1

What is the lining of a capillary called?

Answer 1

Endothelium

Question 2

What three layers do substances have to pass through to get from the capillary to the Bowman’s capsule?

Answer 2

• Endothelium (fenestrations)
• Basement Membrane (contains fibrous collagen- sieve)
• Podocytes

Question 3

What goes into the Bowman’s capsule? (Glomerular filtrate)

Answer 3

• Water
• Ions
• Urea
• Glucose

Question 4

What does not go into the Bowman’s capsule?

Answer 4

• Cells
• Proteins

Question 5

Describe ultrafiltration.

Answer 5

Ultrafiltration occurs when blood enters the glomerulus, the efferent arteriole has a smaller diameter than the afferent arteriole which causes high hydrostatic pressure which causes water, glucose, urea and ions to be filtered out into the Bowman’s capsule. It is now called the glomerular filtrate. Cells and proteins remain in the blood.

Question 6

What are three functions of the liver:

Answer 6

• Detoxification
• Deamination
• Stores glycogen

Question 7

What is the definition of excretion?

Answer 7

Removal of waste products (byproducts from normal cell processes) from the body. Helps to maintain pH and osmotic pressure within the body

Question 8

What five things need to be excreted from the body?

Answer 8

• CO2
• H2O
• Bile pigments (bilirubin)
• Salts
• Urea

Question 9

What is the definition of secretion?

Answer 9

Movement of materials within the body

Question 10

What happens when blood glucose is too high in the liver?

Answer 10

• Beta cells in the Islets of Langerhans release insulin which bind to receptors on target cells on hepatocytes. This induces tyrosine kinase to phosphorylate inactive enzymes to become active enzymes. A cascade of enzyme controlled reactions causes vesicle containing glucose transporter proteins to implant within the cell surface membrane. Extra glucose enters the cell and is converted to glycogen, conversion to fats and used in respiration.

Question 11

What happens when blood glucose is too low in the liver?

Answer 11

• Alpha cells in Islets of Langerhans release glucagon which binds to receptors on target cells in hepatocytes. This stimulates activation of a G protein to activate adenylyl cyclase. Adenylyl cyclase stimulates conversion of ATP to cAMP (second messengar)

Question 12

How is alcohol broken down by the liver?

Answer 12

Ethanol diffuses through he membrane and is converted to ethanal in the cytosol by ethanol dehydrogenase. The 2H produced are used to reduce NAD. Ethanol enters the mitochondria and is converted to ethanoate and releases 2H which reduces NAD.

Question 13

How does fatty liver form?

Answer 13

Reduces too much NAD in alcohol breakdown so cannot use fatty acid in respiration. Deposited in liver as lipids and cause fatty liver. Acidity can cause damage leading to liver cirrhosis.

Question 14

In what ways are the cell lining in the PCT specialised?

Answer 14

• PCT is folded to have a high S for facilitated diffusion/ active transport/ osmosis/ diffusion
• Mitochondria
• Basolateral membrane has high numbers of Na+/K+ pumps
• Membrane has cotransporter proteins

Question 15

What happens to hepatocytes when blood glucose is too high.

Answer 15

Beta cells in the Islets of Langerhans release insulin which binds to complementary receptors on hepatocytes. This stimulates tyrosine kinase to phosphorylate inactive enzymes to form active enzymes. A cascade of enzyme controlled reactions occurs, causing vesicles containing glucose transporter proteins to undergo exocytosis, implanting glucose transporter proteins into the plasma membrane. Glucose enters the cell and is used up in respiration or converted to glycogen/fats.

Question 16

Outline deamination/ Ornithyne cycle

Answer 16

• Amino acid + Oxygen -> Keto Acid + Ammonia
• Ammonia + Carbon Dioxide -> Urea + Water

Question 17

What happens when water potential in the blood is too low?

Answer 17

Osmoreceptors in the osmoregulatory centre in the hypothalamus detect change in water potential in the blood. This stimulates the posterior pituitary gland to release ADH. ADH binds to receptors in the PCT where a cascade of enzyme controlled reactions occurs, causing vesicles containing newly produced aquaporins to undergo exocytosis and implant into the membrane. Water can now move out of the collecting duct and be reabsorbed into the bloodstream.

Question 18

Why can peritoneal dialysis membranes undergo active transport?

Answer 18

It is made out of living tissue and therefore contains mitochondria which can produce ATP for active transport.

Question 19

What can cause disparities in creatine in people?

Answer 19

• Creatine declines with age
• Males typically have more creatine than females due to increased muscle mass
• Exercise
• Diet

Question 20

How does selective reabsorption occur in the PCT?

Answer 20

• Na+ are actively pumped out of the epithelium cells lining the PCT into the blood plasma
• Na+ concentration in the cell decreases - creatine a concentration gradient
• Na+ flow down their concentration gradient into the cell by facilitated diffusion. They cotransport glucose or amino acids with them against their concentration gradient. This is called secondary active transport.
• As a result the water potential of the cell decreases and water moves into the cell by osmosis
• Glucose and amino acids diffuse from the cell into the blood

Question 21

What could be observed if ADH does not have the desired effect on the collecting duct?

Answer 21

Excess urine volume/feeling thirsty due to less water reabsorption as less aquaporins are implanted into the collecting duct plasma membrane

Question 22

What can urine analysis be used for?

Answer 22

• Pregnancy tests
• Drug testing
• Glucose (diabetes) : Benedict’s test
• Protein (Kidney Function)