Lecture 14

Question 1

How is nitrogenous waste produced?

Answer 1

Breakdown of proteins and nucleic acids:
In the digestive system,
For energy conversion to fats/carbohydrates,
Amino group NH2 is removed.

Question 2

What are the consequences of nitrogenous waste formation?

Answer 2

Nitrogenous waste forms toxic ammonia which raises the pH of body fluids and inhibits key enzymes.

Question 3

What are the three types of nitrogenous waste?

Answer 3

Ammonia
Urea
Uric acid

Question 4

What animals produce ammonia?

Answer 4

Teleosts, amphibians, acquatic invertebrates.

Question 5

What are the advantages of ammonia?

Answer 5

Doesn’t require energy to produce.

It’s a small molecule with rapid diffusion.

Question 6

What are the costs of ammonia?

Answer 6

It’s very toxic and highly soluble in water (body fluids).

Requires access to a lot of water.

Question 7

What animals produce urea?

Answer 7

Mammals, most amphibians, cartilagionus fish.

Question 8

How is urea produced?

Answer 8

In the liver from nitrogen and CO2.

Question 9

What are the advantages of Urea?

Answer 9

It’s 1000x less toxic than ammonia.

Requires less water.

Question 10

What are the costs of urea?

Answer 10

It requires energy to make.

Question 11

What animals produce uric acid?

Answer 11

Birds, insects, reptiles, some amphibians.

Question 12

How is uric acid produced?

Answer 12

Carbon, N, Hydrogen, Oxygen.

Question 13

What are the advantages of uric acid?

Answer 13

Insoluble so won’t change body pH.
Less toxic than urea.
Excreted as a semi-solid so is good for conserving water.
Insolubility means it doesn’t build up to toxic concentrations in the egg.

Question 14

What are the costs of uric acid?

Answer 14

Requires 3x as much energy to make as urea.

Question 15

How does habitat effect they type of nitrogenous waste an organism excretes?

Answer 15

Tadpoles excrete ammonia whereas adult frogs excrete urea due to the differences in water availability.
For the same reason, terrestrial turtles excrete uric acid but acquatic turtles excrete urea and ammonia.
Also W. African lungfish excrete ammonia when in water but urea on land to conserve water.

Question 16

What are some examples of generalised excretory organs?

Answer 16

Protozoa have contractile vacuoles for waste removal.
Annelids/molluscs/platyhelminths have nephridia pores.
Insects have malphigian tubules.
Vertebrates have kidneys.

Question 17

What are some examples of specialised excretory systems?

Answer 17

Chloride cells in fish gills used to secrete salt.

Nasal salt glands extract salt from the blood and secrete it out of the nostrils in seabirds.

Question 18

Describe the insect excretory system.

Answer 18

High S.A:V ratio means high rate of water loss so insects excrete uric acid to compensate. They have an open circulatory system so they have no high pressure filtering system so must use malphigian tubules.

Question 19

Describe malphigian tubules.

Answer 19

Blind ended tubes (closed at one end) with walls 1 cell thick. Placed between the mid and hindgut and float in the haemolymph.
Number differs between species from 2 tubules in coccids to 250 in desert locusts.

Question 20

Describe the function of malphigian tubules.

Answer 20

Tubules move salt and Nitrogenous waste by active transport into the gut lumen, with water following by osmosis.
Waste moves into the digestive tract and salts etc. that need to be kept are pumped back into the lumen and water follows.

Question 21

What allows the insect to conserve water?

Answer 21

Uric acid is insoluble and so nitrogenous waste is excreted as dry matter with faeces, thus conserving water. This has contributed to the success of insects.

Question 22

What is the human excretory system made up of?

Answer 22

2 kidneys which receive blood from the renal artery which contain waste. Kidneys filter waste and transport it to the bladder.

Question 23

How much energy do the kidneys use?

Answer 23

20-25% of the body’s cardio-power.

Question 24

What is the process of kidney filtration?

Answer 24

1. Blood fluids are collected in tubules.
2. Needed substances are selectively reabsorbed and transported back to tissue fluid/blood.
3. Unneeded toxic/in excess substances are excreted into filtrate.
4. Filtrate is excreted.

Question 25

What are the key features of the kidney system?

Answer 25

Selectively permeable membranes which change over time and location. Blood is in close contact with the excretory systems.

Question 26

What are the main features of the kidney?

Answer 26

Renal artery/vein, ureter pelvis, ureter, Renal medulla and renal cortex.

Question 27

What is the function of the renal medulla and renal cortex?

Answer 27

Renal medulla regulates water and salt in blood whereas the renal cortex is in charge of ultrafiltration. Both are filled with nephrons.

Question 28

What are nephrons?

Answer 28

Single long tubules with a network of capillaries.

Question 29

Describe ultrafiltration.

Answer 29

Blood pressure in glomerous (ball of capillaries) forces fluid into the Bowman’s capsule. The fluid contains small solutes and non-selective filtration occurs by diffusion. Osmolarity of blood and filtrate is equal at this stage.

Question 30

What happens in the proximal tubule?

Answer 30

Water and salt is reabsorbed, osmolarity therefore doesn’t change.

Question 31

Whats the difference between the ascending and descending loop of Henle?

Answer 31

Descending loop is where water leaves the filtrate which increases the osmolarity of the filrate.
Ascending loop is where salt leaves the filtrate which decreases the osmolarity of the filtrate.

Question 32

What is the function of the distal tubule?

Answer 32

Regulates salt concentration, pH and water balance.

Question 33

How is the human excretory system able to produce hypo or hyper osmotic urine?

Answer 33

The counter-current multiplier system creates a steep concentration gradient because the 2 loops of Henle flow in opposite directions to each other. The loops increase solute potential of surrounding tissue fluid setting up a concentration.

Question 34

How is amount of water reabsorbed homeostatically controlled?

Answer 34

An increased osmolarity of extracellular fluids -> detected by osmoreceptors -> hypothalamus releases vasopressin (anti-diuretic) -> increases water permeability of the distal tubule and collecting duct -> decrease in the osmolarity of the extracellular fluids.