Module 5.2

Question 1

Define excretion.

Answer 1

The removal of metabolic waste from the body.

Question 2

Define metabolic waste.

Answer 2

Any substance made by metabolism that is toxic or made in excess.

Question 3

Define metabolism.

Answer 3

The sum total of all cell reactions.

Question 4

What are the two main types of metabolic waste from the human body?

Answer 4

1. Carbon Dioxide

2. Urea

Question 5

Why is Carbon dioxide produced in the body?

Answer 5

Every living cell in the body produces carbon dioxide as a result of RESPIRATION.

Question 6

Explain what happens if the Carbon Dioxide levels rise too much? (Hint: H+ ions)

Answer 6

1. Excess carbon dioxide dissolves in the plasma
2. Once dissolved it combines with water to produce carbonic acid.
3. The carbonic acid dissociates to release H+ ions
4. The H+ ions lower the pH of the blood plasma and makes it more acidic.
5. Proteins in the blood acts as buffers to resist pH changes.
6. If the change is small the increased H+ are detected by the respiratory centre in the medulla oblongata of the brain.
7. This causes an increase in breathing rate to remove the excess Carbon Dioxide.

Question 7

Where and why is urea produced?

Answer 7

• Produced in the LIVER

- Removes excess amino acids (excess of amino acids can be toxic to the body)

Question 8

Where does the hepatic artery come from when entering the liver and what type of blood does it carry?

Answer 8

• Comes from the HEART

- Carries OXYgenated blood

Question 9

Where does the hepatic portal vein come from when entering the liver and what type of blood does it carry?

Answer 9

• Comes from the INTESTINE

- Carries DEoxygenated blood

Question 10

Where is bile in the liver get transported to? And what vessel carries bile?

Answer 10

The gall bladder is where the bile is transported.

It is carried via the bile duct.

Question 11

Where does the hepatic vein go to when leaving the liver?

Answer 11

Goes towards the HEART

Question 12

What is the liver divided into?

Answer 12

Lobules

Question 13

What are the vessels in between lobules called?

Answer 13

Inter-lobular vessels

Question 14

What are the vessels within lobules called?

Answer 14

Intra-lobular vessels

Question 15

What is the common shape of a liver lobule?

Answer 15

Cylindrical, almost hexagonal-shaped.

Question 16

What (type of) vessel is the intra-lobular vessel?

Answer 16

(A branch of) Hepatic vein

Question 17

What types of vessels are located in the interlobular vessel? (3)

Answer 17

1. Branch of hepatic portal vein
2. Branch of hepatic artery
3. Branch of bile duct

Question 18

What is a sinusoid?

Answer 18

A chamber within the liver lobules where blood from both the hepatic artery and the hepatic portal vein are mixed and pass along.

Question 19

Give 4 specialised features of hepatocytes.

Answer 19

1. Cuboidal in shape
2. Many microvilli
3. Dense cytoplasm with many organelles (especially ATP)
4. Metabolic functions, such as protein synthesis, detoxification, synthesis of cholesterol, etc.

Question 20

Give 3 specialised features of Kupffer cells.

Answer 20

1. They’re specialised macrophages
2. Move within sinusoids
3. Involved in the breakdown and recycling of red blood cells

Question 21

Briefly describe how Kupffer cells break down Haemoglobin.

Answer 21

1. Haemoglobin is broken down to bilirubin

2. Bilirubin is excreted as part of the bile and faeces (gives faeces that brown pigment)

Question 22

State 5 functions of the liver.

Answer 22

1. Control of blood glucose, amino acids, and lipid levels
2. Synthesis of red blood cells in the fetus, bile, plasma proteins, cholesterol
3. Storage of vitamins A, D, B12, Iron, glycogen
4. Detoxification of alcohol, drugs
5. Destruction of red blood cells

Question 23

Briefly describe how alcohol is detoxified (4).

Answer 23

1. Ethanol gets oxidised to ethanal via ethanol dehydrogenase (NAD → NADH)
2. Ethanal gets oxidised further to ethanoic acid via ethanal dehydrogenase (NAD → NADH)
3. Ethanoic acid is converted to Ethanoate (Acetate)
4. The acetate is combined with Coenzyme A to form Acetyl CoA (used in respiration)

Question 24

How is urea formed? (2)

Answer 24

Deamination: Amino acid gets converted to ammonia and keto acid

Ornithine Cycle: Amino is converted to Urea

Question 25

State the symbol equation for deamination.

Answer 25

(2) NH2CH(R)COOH + O2 → (2) CO(R)COOH + 2NH3

Question 26

State the general symbol equation for the conversion of ammonia to urea.

Answer 26

2NH3 + CO2 → CO(NH2)2 + H2O

Question 27

Briefly describe the ornithine cycle.

Answer 27

1. Ammonia and CO2 combine to make citrulline, water is released. 2. Ammonia and Citrulline are combined to make Arginine, water is released. 3. Arginine is combined with water to make ornithine and release UREA.

Question 28

What are the 2 main roles of the kidney.

Answer 28

1. Filter Urea from the Blood | 2. Osmoregulation - Control the amount of water that leaves the body

Question 29

From top to bottom of the kidney, state the 7 structures of the kidney.

Answer 29

1. Capsule 2. Cortex 3. Nephron tubule 4. Medulla 5. (Branches of) renal vein, renal artery 6. Pelvis 7. Ureter

Question 30

State all the structures in a nephron (renal) tubule (5).

Answer 30

1. Glomerulus (with Bowman's capsule) 2. Proximal convoluted tubule 3. Loop of Henle 4. Distal convoluted tubule 5. Collecting duct

Question 31

Define ultrafiltration.

Answer 31

The filtering of molecules from the blood by at a molecular level (anything less than 69000 Daltons) under pressure

Question 32

Using keywords such as hydrostatic pressure, briefly explain the process of ultrafiltration (5)

Answer 32

1. Blood flows into the glomerulus via the afferent arteriole and leaves by the efferent arteriole 2. The afferent arteriole has a wider lumen than the efferent arteriole 3. This creates a bottleneck effect in the glomerulus (network of capillaries) 4. This generates a high hydrostatic pressure inside the glomerulus compared to the lumen of the Bowman's capsule. 5. As the hydrostatic pressure is high, small molecules are squeezed out of the blood and into the Bowman's capsule.

Question 33

State the three key components of the specialised exchange surface between the glomerulus and the Bowman's capsule that it enables ultrafiltration.

Answer 33

1. ENDOTHELIUM OF CAPILLARIES 2. BASEMENT MEMBRANE 3. EPITHELIAL CELLS OF BOWMAN'S CAPSULE (PODOCYTES)

Question 34

Explain how the endothelium of capillaries is adapted to enable ultrafiltration.

Answer 34

Contains gaps/pores between endothelial cells to allow blood plasma/dissolved substances to pass out of capillary.

Question 35

Explain how the basement membrane is adapted to enable ultrafiltration.

Answer 35

A mesh of collagen fibres, prevents molecules greater than 69000 Daltons to enter (most proteins remain in glomerulus capillaries)

Question 36

Explain how epithelial cells (podocytes) are adapted to enable ultrafiltration.

Answer 36

Contains finger-like projections called major processes; and gaps called foot/minor processes which allow fluid from glomerulus blood to enter Bowman's space (hydrostatic pressure)

Question 37

State 5 things that the glomerular filtrate contains.

Answer 37

1. Water 2. Glucose 3. Inorganic mineral ions (Na+/Cl-) 4. Amino Acids 5. Urea

Question 38

What are the 2 things left in the blood during glomerular filtration?

Answer 38

1. Red blood cells | 2. Large proteins

Question 39

Explain how fluid is able to be retained in the capillaries

Answer 39

Because the blood is left with a very low water potential

Question 40

What is selective reabsorption?

Answer 40

The reabsorption of useful molecules back into the blood.

Question 41

Where does selective reabsorption take place?

Answer 41

At the PCT (Proximal Convoluted Tubule)

Question 42

What does the PCT have that is an adaptation to maximise selective reabsorption?

Answer 42

- A BRUSH BORDER: cells that line it have a folded membrane which generate microvilli, so a higher S.A.

Question 43

Briefly explain the process of selective reabsorption (4).

Answer 43

1. Na+ actively pumped into the blood from the cells lining the PCT (REQUIRES ATP) 2. Concentration of Na+ in cells fall, creating a concentration gradient. 3. Na+ diffuse back through a cotransporter protein; carries glucose/amino acids at the same time. 4. Water follows into the cell by osmosis.

Question 44

What is the aim/function of the Loop of Henle.

Answer 44

To reduce the volume of urine without changing its concentration.

Question 45

What is the name of the system that the Loop of Henle uses?

Answer 45

HAIRPIN COUNTERCURRENT MULTIPLIER SYSTEM | a dynamic system, creates different levels of water potential down the Loop

Question 46

What is the overall effect of the Loop of Henle?

Answer 46

Reduces the water potential of the medulla

Question 47

Briefly describe how the Loop of Henle works (7)

Answer 47

1. Na+ / Cl- actively pumped OUT of the THICK ascending limb. 2. The water potential is reduced in the medulla 3. Water moves out of the THIN descending limb 4. This concentrates the fluid in the Loop of Henle 5. Na+ and Cl- start to DIFFUSE (passive) out of the THIN ascending limb 6. So as a result, there's an increasing concentration of solutes down the medulla (reduces W.P.), allows Water to move out of the collecting duct (important) 7. But ultimately, the body can regulate how much is H2O is reabsorbed by adjusting the permeability of collecting duct to water.

Question 48

Why do kangaroo rats (desert) have longer Loops of Henle than beavers (wet)?

Answer 48

The longer the Loop of Henle, the more concentrated the interstitial fluid. Therefore, the more water can be absorbed back into the blood. (so kangaroo rats can conserve as much water as possible)

Question 49

What adaptation/feature do the collecting duct walls have that enable osmoregulation to occur?

Answer 49

The walls of the collecting duct can be modified to change the PERMEABILITY to water. e.g. If water needs to be conserved, the walls can be made more permeable to allow water to be reabsorbed, producing CONCENTRATED urine.

Question 50

Explain all the steps in osmoregulation.

Answer 50

1. The water potential (wp) of the blood is monitored by osmoreceptors in the hypothalamus of the brain. 2. When the wp of the blood is very low, the osmoreceptors shrink and stimulate neurosecretory cells in the hypothalamus. 3. These produce and release anti-diuretic hormone (ADH) which flows down the axon to the posterior pituitary gland where it is stored until needed. 4. When the neurosecretory glands are stimulated they send action potentials down their axons and cause the release of ADH into the blood. 5. ADH enters the capillaries running through the posterior pituitary gland. It is transported around the body and acts on the cells of the collecting ducts. 6. When it binds to the receptors, it causes a chain of enzyme-controlled reactions. The end-result is the insertion of vesicles containing water-permeable channels (aquaporins) which are fused into the membranes of the collecting duct wall cells. (so more permeable to water). 7. More water is reabsorbed by osmosis into blood. 8. Less urine, with a lower water potential, is released. 9. Less ADH is released when the wp in the blood rises again. 10. ADH is slowly broken down and the collecting ducts receive less stimulus.