12.3.5 The Fate of Absorbed Nutrients

Question 1

The Fate of Absorbed Nutrients

Answer 1

• The body has two metabolic states.
• During the absorptive state, food is present in the digestive tract and the body is using, and storing, the nutrients leaving the digestive tract.
• Glucose is stored in the liver and skeletal muscles, lipids are stored in fat tissue, and amino acids are used in protein synthesis.
• During the postabsorptive state, the digestive tract is empty and the body is using stored reserves of energy to maintain metabolism.
• Stored glucose is released from the liver and skeletal muscles to maintain brain function, lipids are metabolized to provide energy for the rest of the body, and protein may be metabolized to build glucose for respiration.

Question 2

absorptive state

Answer 2

• The bodys metabolic condition can be divided into two states: the absorptive and postabsorptive states.
• In the absorptive state, food is still present in the digestive tract, and nutrients are entering and being moved by the circulatory system. In the absorptive state, nutrients are being used, but they are also being stored for later use.
• Amino acids enter the liver with the blood in the veins leaving the digestive system. The liver absorbs some of these amino acids and uses them to synthesize protein. Most of the amino acids continue on to the body tissues to be used in protein synthesis.
• Glucose also enters the liver where some of it is absorbed and converted to glycogen for storage. The glucose that leaves the liver is used by body tissues in respiration to produce ATP or is stored as glycogen in skeletal muscle.
• Lipids enter the blood stream from the lymphatic system. They are used by skeletal muscles in the production of ATP or are stored in adipose tissue.

Question 3

postabsorptive state

Answer 3

• In the postabsorptive state the digestive system is empty and energy is supplied by the breakdown of stores.
• Adipose tissue releases stored lipids that are broken into glycerol and fatty acids. The fatty acids are metabolized to produce ATP in the bodys tissues.
• Skeletal muscles convert their stores of glycogen into glucose that is used to make ATP. The glycogen can also be broken down into pyruvate and lactic acid that can be converted into glucose by the liver. This process is called gluconeogenesis. The purpose of this glucose production is to supply the brain, which must use glucose as its energy source.
• The liver uses its stores of glycogen to supply the brain with glucose.

Question 4

deamination

Answer 4

• The liver is also able to deaminate amino acids to produce keto acids that can be used in gluconeogenesis. Deamination is the removal of an amine group, which results in the production of ammonia. The ammonia is converted to urea that is removed from the blood stream by the kidney