5.2: Homeostasis

Question 1

What is excretion?

Answer 1

The removal of metabollic waste from the body

Question 2

What are the main excretory products?

Answer 2

• CO2 from respiration
• Nitrogen-containing compounds such as ureaa
• Bile pigments

Question 3

What are the excretory organs?

Answer 3

1. Lungs
2. Liver
3. Kidneys
4. Skin

Question 4

What is excreted out of the lungs and how?

Answer 4

• Carbon dioxide from respiring tissues —> bloodstream as hydrogencarbonate ions —> llungs
• CO2 diffuses into the alveoli to be excreted as you breathe out

Question 5

What is excreted out of the liver and how?

Answer 5

• Some substances prroduced from metabolic roles will be passed into bile for excretion
• Involved in converting excess amino acids into urea (broken down by deammination)
• Nitrogen containing part of molecule is combined in CO2 to make urea

Question 6

What is excreted out of the kidneys and how?

Answer 6

• Urea passed into the bloodstream to the kidney
• Transported in solutions: dissolved in plasma
• Removed from blood to be part of urine

Question 7

What is excreted out of the skin and why?

Answer 7

• Sweat contains salts, urea, water, uric acid & ammonia
• Losing this maintains body temperature and water potential of the blood

Question 8

Why is excretion important?

Answer 8

Some products are toxic and may interfere with cell processes, altering the pH
This means normal metabolism is prevented
Other products may act as inhibitors

Question 9

What is deammination and why does it occur?

Answer 9

Amino acid + oxygen —> keto acid + ammonia

• The body cannot store excess amino acids

Question 10

What is the formation of urea and why does it occur?

Answer 10

Ammonia + carbon dioxide —> urea + water

• Urea is less toxic than ammonia

Question 11

What does the liver do?

Answer 11

Responsible for ensuring that everything in the blood is at the correct concentration (products of digestion, toxins and vitamins)

Question 12

What is the hepatic artery?

Answer 12

• Oxygenated blood from the heart travels towards the liver
• Supplies the oxygen that is essential for aerobic respiration

Question 13

What is the hepatic portal vein?

Answer 13

Deoxygenated blood enters the liver from the digestive system

Question 14

What is the deoxygenated blood like in the hepatic portal vein?

Answer 14

• Blood is rich in the products of digestion
• Concentration are uncontrolled
• Important that substances do not continue to circulate around the body before their concentrations are adjusted

Question 15

What is the structure of the liver?

Answer 15

• Liver is divided into lobes
• Lobes are further divided into lobules
• Cells, blood vessels and chambers are arranged to ensure the greatest possible contact between the blood and the liver cell

Question 16

What are interlobular vessels?

Answer 16

Smaller vessels that are split from hepatic artery and hepatic portal vein when they enter the liver

• They run parallel to the lobules

Question 17

What are sinusoids?

Answer 17

Special chamber lined with liver cells where the mixed blood from the two vessels are passed through

• Blood concentrations is modified and regulated when it reaches the end of the sinusoid

Question 18

What are liver cells?

Answer 18

• Relatively unspecialised
• Simple cubiodal shape with many microvilli on their surface

Question 19

What are the metabolic functions of liver cells?

Answer 19

• Protein synthesis
• Transformation
• Storage of carbohydrates
• Synthesis of cholesterol

Question 20

What is the role of the kidney?

Answer 20

Helps make urine and remove urea

Question 21

What makes up the nephron?

Answer 21

• Glomerulus
• Bowman’s capsule
• Proximal convulated tubule
• Loop of Henle
• Distal convulated tubule
• Collecting duct

Question 22

Where does ultrafiltration occur?

Answer 22

Glomerulus and bowman’s capsule

Question 23

What are the barriers in ultrafiltration?

Answer 23

1. Gaps between the cells of the endothelium of the capillary - also contain fenestrations
2. Basement membrane - consists of a mesh of collagen fibres and glycoproteins
3. Epithelial cells of the bowman’s capsule - have podocytes which have finger like projections

Question 24

What filtrate can pass through the bowman’s capsule?

Answer 24

Glucose
H2O
Urea
Salt
Amino acids
Vitamins
Hormones

Question 25

What is the mechanism of reabsorption in the proximated convulated tubule

5 steps

Answer 25

1. Sodium ions are actively pumped out of the cells lining the tubule
2. Concentration of sodium ions in cell cytoplasm decreases, creating a concentration gradient
3. Sodium ions diffuse into the cell through a cotransport protien - carrying glucose or an amino acid at the same time
4. Water moves into the cell by osmosis
5. Glucose/ amino acids diffuse into the blood

Question 26

What happens at the distal convulated tubule?

Answer 26

Reabsorption selective to body needs

• Balance the H2O, salt, needs and pH of the blood