Module 1 Section 5

Question 1

explain metabolism

Answer 1

• describes the sum of all chemical reactions that occur in all organisms, including the synthesis, degradation, transport of substances into and between different cells, and transformation of proteins, carbs, and fats
• these reactions within the cell are called intermediary metabolism or fuel metabolism

Question 2

explain anabolic reactions

Answer 2

leads to the synthesis of larger organic macromolecules from smaller organic molecular subunits and are used for repair, growth, and the storage of excess ingested nutrients

Question 3

explain catabolic reactions

Answer 3

the breakdown of larger organic macromolecules either through the process of hydrolysis into smaller molecules, or oxidation of smaller molecules, such as glucose, to yield ATP

Question 4

explain nutrient storage

Answer 4

because we do not constantly ingest food, excess nutrients need to be stored for when they are needed

Question 5

what happens to excess glucose

Answer 5

• excess glucose is stored in the liver and skeletal muscle as glycogen
• once these glycogen stores are full, any additional glucose is converted into free fatty acids and glycerol for the synthesis of triglycerides which occurs mainly in adipose tissue

Question 6

what happens to excess fatty acids

Answer 6

excess fatty acids are stored as triglycerides

Question 7

what happens to excess amino acids

Answer 7

excess aa not needed for protein synthesis are not stored but rather either used for structural proteins or converted to glucose and fatty acids for eventual storage as triglycerides

Question 8

what are the body’s 2 functional metabolic states

Answer 8

1. absorptive state
2. postabsorptive state

Question 9

explain absorptive state

Answer 9

• anabolism dominates as ingested food is digested and absorbed into the circulation
• ingested simple carbs are converted in the liver to glucose, which is then released to be available as fuel, or it is stored as glycogen
• ingested fats and proteins are also immediately used or stored

Question 10

explain postabsorptive state

Answer 10

• several hours after ingesting food, catabolism dominates
• glycogen stores in the liver and skeletal muscle becomes the primary energy source
• if the postabsorptive state persists, glycogen alone cannot meet the body’s energy needs, so lipolysis occurs to break down triglycerides

Question 11

what are the organic intermediates that can serve as energy sources

Answer 11

1. glycerol
2. lactic acid
3. ketone bodies

Question 12

explain glycerol

Answer 12

comes from the backbone of triglycerides when they are broken down and it can be converted to glucose by the liver

Question 13

explain lactic acid

Answer 13

• can be formed by glycolysis
• can also be converted to glucose by the liver

Question 14

explain ketone bodies

Answer 14

• a group of compounds produced in the liver in times of glucose shortages
• when the liver uses free fatty acids as an energy source, they are oxidized to acetyl CoA, which does not produce any additional energy through the citric acid cycle
• this actyl CoA is converted to ketone bodies and released into the blood
• in times of starvation, the brain can use ketone bodies, instead of glucose, as an energy source

Question 15

what is the pancreas

Answer 15

an organ that has both exocrine and endocrine functions, the latter of which play key roles in determining the bodys metabolic state

Question 16

explain the exocrine and endocrine functions of the pancreas

Answer 16

• exocrine functions are important for digestion
• endocrine functions are localized to the islets of Langerhans, which are clusters of cells found throughout the pancreas

Question 17

what are alpha cells of the pancreas

Answer 17

these cells produce and secrete glucagon

Question 18

what are beta cells of the pancreas

Answer 18

these cells produce and secrete insulin

Question 19

what are delta cells of the pancreas

Answer 19

these cells produce and secrete somatostatin

Question 20

what are PP cells of the pancreas

Answer 20

these cells secrete pancreatic polypeptide which may play a role is reducing appetite

Question 21

explain somatostatin

Answer 21

• in response to circulating glucose and amino acids following a meal, the delta (δ) cells release somatostatin
• the effect is to slow down the digestive system to inhibit digestion and absorption of nutrients
• in this negative feedback manner, somatostatin prevents too many nutrients being absorbed

Question 22

is the pancreas the only source of somatostatin

Answer 22

• NO
• it is produced in cells lining the digestive tract, where it acts as a paracrine hormone to inhibit digestion
• it is also released by the hypothalamus (same chemical as GHIH) where it inhibits the secretion of growth hormone and TSH

Question 23

what is insulin

Answer 23

• it is a small peptide hormone produced by beta cells of the pancreatic islets and is the most well known of the pancreatic hormones
• it is the dominant hormone in the absorptive state and plays a major role in anabolism
• it has primarily been associated with the regulation of blood sugar, but its effects go well beyond carbs and has effects on fats and proteins too

Question 24

what are factors that increase blood glucose

Answer 24

1. glucose absorption from the digestive tract
2. hepatic glucose production
   
   • through glycogenolysis of stored glycogen
   • through gluconeogenesis

Question 25

what are factors that decrease blood glucose

Answer 25

1. transport of glucose into cells - for utilization for energy production - for storage as glycogen through glycogenesis - for storage as triglycerides 2. urinary excretion of glucose (occurs only abnormally, when blood glucose level becomes so high it exceeds the reabsortive capacity of kidney tubules during urine formation)

Question 26

what are the 4 main effects of insulin on carb metabolism

Answer 26

1. increase the uptake of glucose into most cells 2. inhibit glycogenolysis in the liver 3. stimulate glycogenesis in skeletal muscle and the liver 4. inhibit gluconeogenesis in the liver

Question 27

explain how insulin can increase the uptake of glucose into most cells

Answer 27

insulin causes the movement of GLUT-4 glucose transporters from an intracellular pool to the plasma membrane where they begin to transport glucose into the cells

Question 28

what parts of the body can uptake glucose independent of insulin

Answer 28

- the brain because the brain always has GLUT-1 and GLUT-3 glucose transporters in the plasma membrane - exercising skeletal muscles are also able to take up glucose independent of insulin - liver uptake of glucose is by GLUT-2 and is also independent

Question 29

explain how insulin can inhibit glycogenolysis in the liver

Answer 29

this prevents the catabolism of glycogen and further promotes glucose storage

Question 30

explain how insulin can stimulate glycogenesis in skeletal muscle and the liver

Answer 30

this promotes the storage of glucose as glycogen

Question 31

explain how insulin can inhibit gluconeogenesis in the liver

Answer 31

this prevents the formation of glucose from aa

Question 32

what are the 4 effects that insulin has on fats

Answer 32

1. enhances the entry of fatty acids into adipose tissue cells 2. increases GLUT-4 recruitment in adipose cells to increase glucose uptake for the synthesis of triglycerides 3. enhances the activity of the enzymes involved in synthesizing triglycerides 4. inhibits lipolysis

Question 33

what are the 3 main actions of insulin on proteins

Answer 33

1. promotes the uptake of aa into all tissues 2. enhances the activity of the enzymes involved in protein synthesis 3. inhibits the degradation of proteins

Question 34

explain the first component of the regulation of insulin secretion

Answer 34

- an elevation of blood glucose stimulates the islet beta cells to secrete insulin - the actions of insulin will then lower blood glucose levels and the secretion of insulin will stop - insulin promotes anabolism during the absorptive state and the lack of insulin promotes catabolism during the postabsorptive state

Question 35

explain the second component of the regulation of insulin secretion

Answer 35

- insulin release can also be caused by a feedforward system - gastrointestinal hormones secreted by the digestive tract can stimulate insulin release to prepare for the rise in blood glucose about to occur

Question 36

explain the third component of the regulation of insulin secretion

Answer 36

- the cells of the islets of Langerhans are innervated by the autonomic nervous system - the presence of food in digestive system activates the parasympathetic nervous system in a feedforward manner - the sympathetic nervous system has the opposite effect to decrease insulin secretion - this allows blood glucose levels to rise during fight-or-flight or while exercising

Question 37

what is glucagon

Answer 37

- the major pancreatic hormone involved during the postabsorptive state - the secretion of glucagon is triggered directly by the decrease in blood glucose levels - its major site of action is the liver, where its effects are the direct opposite of insulin

Question 38

what is the effect of glucagon on carbs

Answer 38

increases hepatic glucose production by decreasing glycogen synthesis, enhancing both glycogenolysis and gluconeogenesis

Question 39

what is the effect of glucagon on fats

Answer 39

- glucagon promotes lipolysis while inhibiting fat storage - it also enhances the formation of ketone bodies in the liver

Question 40

what is the effect of glucagon on proteins

Answer 40

promotes protein catabolism but only in the liver

Question 41

explain insulin and glucagon working as a team

Answer 41

fluctuations in blood fatty acid concentration result in the same pattern of insulin and glucagon release as changes in blood sugar concentration

Question 42

what stimulates the release of insulin and glucagon

Answer 42

- a rise in blood aa concentration - because the hyperglycaemic effects of glucagon counteract the hypoglycaemic actions of insulin, the net result is maintenance of normal blood glucose level following a high protein, low carb meal