chapter 8 - homeostasis of blood sugar and gas concentration

Question 1

how is blood glucose regulated

Answer 1

• source: carbohydrates in the food that we eat (glucose), excess glucose is stored as glycogen
• organs: liver, pancreas, adrenal glands
• glycogen: long chains of glucose stored in liver and muscle cells, can be converted back to glucose (up to 100g in liver and 400g in skeletal muscles)

Question 2

how is the liver involved

Answer 2

• glucose is absorbed into blood from small intestine - carried to liver via hepatic portal vein
• in liver: used by liver cells as energy source and glucose -> glycogen to be stored in liver
• after liver: continues into hepatic vein where it is used by cells as an energy source, stored in muscles as glycogen, converted to fat for long term storage and continues in blood to maintain BG level (chemoreceptors aren’t stimulated)
• glycogenesis: glucose -> glycogen, stimulated by insulin
• glycogenolysis: glycogen -> glucose, stimulated by glucagon

Question 3

how is the pancreas involved

Answer 3

• islets of langerhans (IOL): beta cells (secrete insulin to due high BG), alpha cells (secrete glucagon due to low BG)
• high BG: chemo rec. in beta cells of IOL - secrete insulin - enables entry of glucose into cells of skeletal muscle / glycogenesis (promotes conversion of glucose to glycogen in liver and muscles) / promotes fat storage / promotes protein synthesis - decrease BG - -ve feedback, beta cells no longer stimulated
• low BG: chemo rec. in alpha cells of IOL - secrete glucagon - glycogenolysis (in liver glycogen to glucose) / promotes gluconeogenesis (breakdown of fats and protein (amino acids) -> sugar molecules) - increase BG - -ve feedback, alpha cells no longer stimulated

Question 4

how are the adrenal glands involved in low BG

Answer 4

• adrenal cortex: chemo rec. in hyp - RF - anterior pituitary - ACTH - adrenal cortex - glucocorticoids (cortisol) - glycogenolysis (glycogen to glucose in liver) / gluconeogenesis (protein breakdown in muscles / conversion of amino acids -> sugar molecules in liver) - increased BG - -ve feedback, chemo rec. in hyp. no longer stimulated
• adrenal medulla: chemo rec. in hyp - cerebral cortex - adrenal gland - adrenaline / noradrenaline - glycogenolysis (glycogen to glucose in liver / release of glucose into blood) / glycogen -> lactic acid -> glucose - increase BG - -ve feedback, chemo rec. in hyp no longer stimulated

Question 5

how is breathing / gas concentration controlled

Answer 5

• diaphragm and intercostal muscles need to be stimulated by nerve impulses to initiate muscle contraction
• receptors: central chemo rec. (medulla oblongata), peripheral chemo rec. (carotid and aortic bodies)
• nerves: phrenic nerve and intercostal nerve
• centre: respiratory centre in medulla oblongata, two regions (inspiration and expiration), nerve messages move between regions
• equation: CO2 + H2O H2CO3 H+ + HCO3- , therefore high CO2 = high H (low pH)

Question 6

how is concentration of oxygen involved

Answer 6

• movement: O2 enters cells -> decreased O2 in blood, [O2] needs to drop significantly to trigger response (little role in BR)
• feedback: significant drop in O2 - central chemo rec. - medulla oblongata (RC) - nerve impulses - diaphragm / intercostal muscles - increased BR - increased O2 - -ve feedback

Question 7

how is concentration of CO2 involved

Answer 7

• major factor: small increase in [CO2] = increased BR, high [CO2] = high [H+] - directly proportional relationship
• central chemo rec.: most sensitive to changes in CO2, CO2 is responsible for 70-80% increase in BR
• feedback: increased [CO2] - central chemo rec. - medulla oblongata (RC) - nerve impulses - diaphragm / intercostal muscles - increased BR - decreased CO2 - -ve feedback, chemo rec. no longer stimulated

Question 8

how is concentration of H involved

Answer 8

• peripheral chemo rec.: respond to changes in H+ (changes in pH)
• ‘feedback: increase H+ - low pH - peripheral chemo rec. - medulla oblongata (RC) - nerve impulses - diaphragm / intercostal muscles - increased BR - decreased H+ / increased pH - -ve feedback

Question 9

explain the voluntary control of breathing

Answer 9

• we can control rate and depth, comes via connections in cerebral cortex to descending tracks in spinal chord (bypasses RC in medulla oblongata)
• protection: allows us to prevent the breathing in of irritating gases
• hyperventilation: rapid, deep breathing, removes more CO2 than necessary, voluntary or caused by emotional / physical stress
• > effect: causes dizziness, sometimes fainting, usually corrects itself as breathing is not stimulated until [CO2] returns to normal
• > diving: high CO2 stimulates breathing, because of low CO2 causes O2 to become dangerously low before CO2 triggers breathing leading to unconsciousness (O2 levels enter blackout period)

Question 10

how does exercise influence our breathing

Answer 10

• contracting muscle cells require large amounts of O2 and produce large amounts of CO2
• increased demand for gas exchange to occur (10-20 x faster), increase in blood flow to and from cells

Question 11

what is cellular respiration

Answer 11

• C6H12O6 + H2O –> 6H2O + 6CO2 + energy + heat, energy released is used for movement, reproduction, active transport and synthesising molecules

Question 12

explain the processes of conversion and breakdown of glucose and glycogen

Answer 12

• genesis: to make
• lysis: to break down
• neo: new
• glycogenesis: glucose to glycogen
• lipogenesis: glucose to fat
• gluconeogenesis: proteins / aa to simple sugars
• glycogenolysis: glycogen to glucose
• lipolysis: fat to glucose