Chapter 18 - Excretory system

Question 1

Explain why living organisms need to excrete

Answer 1

• Some waste products can be poisonous and, if not excreted, can slow down metabolism in cells
• Some waste products like salts and water in are in excess, and if not excreted, can damage cells

Question 2

Name the main excretory organs, along with the waste products excreted by each organ

Answer 2

Lungs: Carbon dioxide and water vapour
Skin: Water, salts, small amounts of urea
Kidneys: Nitrogenous waste products, excess water and excess salts

Question 3

Name the waste products of metabolism, and explain how they are formed

Answer 3

• Carbon dioxide: Produced during the Krebs cycle in mitochondria
• Bile pigments: Formed in the liver and spleen during the breakdown of haemoglobin. Excreted in faeces
• Urea: Formed in the liver during deamination
• Water vapour: Formed during cellular respiration
• Excess water: Taken in with fluids during nutrition
• Excess salts: Taken in during nutrition

Question 4

Name the part in the brain responsible for osmoregulation

Answer 4

Hypothalamus

Question 5

Define excretion

Answer 5

The removal of metabolic waste from the body, along with the removal of excess substances like water and salts from the body

Question 6

Describe cellular secretion, and give a few examples

Answer 6

Cells produce usefull substances during metabolism and release it to perform important funcitons, like hormones, digestive juices and milk

Question 7

Where does the carbon dioxide which is used during deamination come from?

Answer 7

Respiration in the liver

Question 8

Describe the breaking down of alcohol, drugs and hormones in the liver

Answer 8

• Alcohol is broken down into water and carbon dioxide. This process is known as detoxification
• Drugs are broken down by the liver
• Hormones which are continuously produced by endocrine glands are broken down in the liver to prevent accumilation thereof in tissue

Question 9

Study the sketches of the kidneys and excretory system

Answer 9

Heh?

Question 10

Describe the functions of the kidneys

Answer 10

• Excretion of nitrogenous waste
• Osmoregulatory function by excreting excess water or reabsorbing water when necessary
• Regulate salt concentrations by excreting salts or reabsorbing water and salts
• Regulation of pH
• Reabsorbtion of usefull substances

Question 11

Name the cells, their adaptions and function, of which the inner wall of the bowman’s capsule consists

Answer 11

• Podocytes
• Filtration slits
• Ultra-filtration

Question 12

Why is the blood pressure in the glomerulus so high?

Answer 12

The diameter of the afferent arteriole is much larger than the efferent arteriole

Question 13

Study the sketch of the nephron

Answer 13

Ehe!

Question 14

Give another name for “vasa recta”

Answer 14

Peritubular capillaries

Question 15

Name the three main functions of the nephron

Answer 15

• Ultra-filtration
• Tubular reabsorbtion
• Tubular secretion

Question 16

Why are small molecules in blood able to filtrate into the bowman’s capsule?

Answer 16

• The walls of glomerulus is made of one epithelial cell layer
• The podocyte layer has filtration slits which form an ultrafine filter

Question 17

Name the adaptations of the Malpighian body for ultra-filtration

Answer 17

• Very high blood pressure in glomerulus
• Capillary network of glomerulus provides a large surface area
• Bowman’s capsule is cup-shaped to give it a large surface area
• Thin walls of bowman’s capsule and walls of glomerulus
• Podocytes have filtration slits
• Capillaries of glomerulus are in close contact with the bownman’s capsule

Question 18

Describe tubular reabsorbtion of usefull substances in the proximal convoluted tubule

Answer 18

• Usefull substances like glucose and amino acids which pass into filtrate must now be reabsorbed
• Selective reabsorbtion of substances like ALL glucose, amino acids etc. are absorbed by active transport
• Usefull minerals such as sodium ions are absorbed by active transport and facilitated diffusion

Question 19

Name the adaptations of the proximal convoluted tubule for tubular reabsorbtion

Answer 19

• Micro villi to maximise absorbtion area
• Endothelial cells contain many mitochondria to release energy for active transport
• Endothelial layer is a single layer for easy passage of substances

Question 20

Describe tubular reabsorbtion of water in the loop of Henle

Answer 20

• Filtrate enters the loop of Henle where water is conserved
• There is always a high Na and Cl concentration outside the loop
• The higher the NaCl concentration outside the loop, the more water will be reabsorbed by osmosis
• The descending limb is permeable to water and water is absorbed into vasa recta by osmosis
• Sodium ions are actively pumped out of the ascending limb, and chlorine follows passively
• Water will not follow because the ascending limb is inpermeable to water
• The longer the loop of Henle, the more water can be absorbed

Question 21

Describe tubular reabsorbtion of usefull substances in the distal convoluted tubule

Answer 21

• Further absorbtion of usefull substances occurs here
• Regulates pH of blood
• When blood is acidic, H+ ions is secreted into the blood
• When blood is alkaline, less H+ ions are secreted and bicarbonate ions are secreted from the blood into the tubules

Question 22

Describe osmoregulation in terms of hormones released

Answer 22

• Water content too low: Posterior pituitary gland secretes ADH, which causes the walls of the collecting duct to become more permeable so more water can be absorbed
• Vica versa for too high water content

Question 23

Describe tubular secretion

Answer 23

• Substances are secreted from blood in vasa recta into proximal and distal convoluted tubules

Question 24

Name the main constituents of urine

Answer 24

• Water
• Metabolic waste
• Inorganic salts
• Foreign substances
• Drugs

Question 25

Suggest reasons for kidney failure

Answer 25

- Infections of kidneys - Accidents - Hypertension - Diabetes mellitus - Heart failure - Cysts

Question 26

Explain dialysis

Answer 26

- Blood enters from patient's artery in arm - Blood pumped - Blood passes through dialysis tubing - Tubing is partially permeable and filters blood - Tubing surrounded by dialysis fluid - Fluid contains glucose and amino acids, and some salts, BUT NO urea or uric acid - Dialysis fluid has same osmotic potential as blood - Waste substances and excess substances diffuses into dialysis fluid - Bubble trap removes air bubbles and warms blood - "Clean" blood enters through a vein in patient's arm

Question 27

Name the advantages of kidney transplants

Answer 27

- Normal life - Independent of machines - Continuous filtration

Question 28

Name the disadvantages and risks of kidney transplants

Answer 28

- Rejection of transplanted kidneys could occur - Immunosuppressant drugs need to be taken (may even be lifelong) - Isolation - Operation is risky - Very expensive - The tissue type and blood group of donor must closely match

Question 29

Name the advantages of dialysis

Answer 29

- No donor - Rejection impossible - A life saver if transplant is not immediately possible

Question 30

Name the disadvantages of dialysis

Answer 30

- Time consuming - No normal life - Must live close to hospital - There may be a shortage of machines - Expensive - No continuous filtration - Loss of some minerals like calcium and iron - No sport :(