Metabolism

Question 1

WHY DO WE EAT AND DRINK?

Answer 1

• To make up for water we lose every day
• Supply building blocks for cells and tissues
• Supply atoms and molecules body can’t make and supply fuel to for energy (ATP)

Question 2

ATP (Adenosine triphosphate)

Answer 2

• Breakdown of nutrients (glucose, fatty acids, some amino acids) releases energy used to make ATP from ADP
• ATP is major way that energy is stored in cells
• Breakdown of ATP to ADP releases energy the cells need to do work

Question 3

DIGESTION AND ABSORPTION AND BLOOD NUTRIENT LEVELS

Answer 3

• Digestion/absorption of water and food occurs in GIT→ then water and individual nutrients go to circulatory system
• After a meal→ concentration of nutrients is elevated
• Don’t eat all the time but cells are using nutrients all the time; without continual supply→ levels drop
• Body needs to ensure blood nutrient levels don’t stay high but also don’t drop below cell requirements

Question 4

REGULATION OF BLOOD NUTRIENT LEVELS

Answer 4

• 2 metabolic states of body responses to changes in blood nutrient levels:
• Absorptive state→ first few hours after a meal
• Post- absorptive state→ hours before lunch, before dinner and overnight

Question 5

THE ABSORPTIVE STATE

Answer 5

• Rise in blood nutrient levels (particularly glucose) stimulates insulin secretion→ leads to;
• Increases glucose uptake and consumption by cells
• Storage of excess glucose as glycogen (liver and muscles)
• Conversion of excess glucose to fatty acids that can be used for triglyceride production (adipose tissue)
• Increased amino acid uptake by cells for use in protein synthesis
• Net result→ restores blood glucose and other nutrients back to homeostatic level

Question 6

BETWEEN MEALS→ WITHOUT MEALS

Answer 6

• Between meals→ body cells continue metabolising; body draws on fat reserves
• If time to next meal is extended; ration glucose available and make more glucose
• With prolonged fasting/starving→ ketones become major fuel

Question 7

POSTABSORPTIVE (1) RAISING BGL AND GLUCOSE SPARING

Answer 7

• Glucose breakdown and reduced glucose consumption in liver→ rapid increase in blood glucose level (BGL)
• Increased amino acid uptake by liver→ used to make glucose→ further increases BGL

Question 8

USING FATTY ACIDS TO MAKE ATP

Answer 8

• Glucose not immediately used by cells→ stored as glycogen
• Glucose used to form fatty acids→ can be stored as triglycerides
• When needed→ triglycerides can be broken down to fatty acids
• Some cells can consume fatty acids to make ATP
• Increased fatty acids supply as an alternative fuel for those organs which can use them

Question 9

FATTY ACIDS AND KETONES

Answer 9

• During long periods of fasting or starvation→ ability to maintain BGL is lost
• In these circumstances→ fatty acids are used to make ketones/ketone bodies
• Organs that cannot use fatty acids to make ATP (e.g. brain) rely on ketone instead during fasting

Question 10

USING GLUCOSE TO MAKE ATP

Answer 10

• Central to use of nutrients to make ATP is breakdown of glucose; 2 stage process
• Glycolysis produces some ATP and doesn’t require oxygen
• Cellular respiration produces much more ATO and requires oxygen and generates CO2

This means a big demand for ATP that can only be provided by cellular respiration; which means

• Need for regular refuelling
• Constant demand for oxygen
• Constant need to remove excess carbon dioxide