Carbohydrate Metabolism Flashcards
What is Metabolic homeostasis?
The process of maintaining optimal metabolite concentrations and managing chemical energy reserves in tissues
What is Catabolism ?
The degradative phase of metabolism; releases energy
What is Anabolism (biosynthesis) ?
The building phase of metabolism: requires energy
What is the Blood glucose ideally kept at ?
~4.5mM (70−100 mg/100mL), with some fluctuation occurring after a meal
What is the brain most vulnerable ?
Hypoglycaemia as cerebral cells derive their energy predominantly from aerobic metabolism of glucose
When the brain is vulnerable to hypoglycaemia, it cannot ?
- store glucose in significant amounts or synthesise glucose
- metabolise substrates other than glucose or ketone bodies
- extract sufficient glucose for their needs from the extracellular fluids at low concentrations because glucose entry into the
brain is not facilitated by hormones
Blood glucose varies relatively little over 24hr despite changes in food intake. Controlled by ?
Changes in circulating levels of insulin and glucagon
Alterations in the ratio of
insulin:glucagon within the blood are essential for ?
The maintenance of blood glucose
When is Glucose absorbed from the intestine ?
2-3 hours following a meal
When is Glycogen degraded?
Between meals and and lasts for 12-24 hours
During sleep/extended food deprivation there is a gradual dependence on ?
De novo glucose
synthesis by gluconeogenesis as glycogen stores are depleted
Blood glucose is under strict homeostatic control, by two main hormones ?
Insulin and Glucagon
Insulin stimulates ?
Glucose uptake and storage when levels are high
Glucagon stimulates ?
Breakdown of stores/synthesis when levels are low
How does glucose enter the cells ?
by facilitated diffusion i.e. it is a carrier-mediated process with glucose entering the cells down its concentration gradient
How is the entry of glucose mediated ?
Entry mediated by a family of glucose transporter proteins (Gluts) which are structurally related but encoded by different genes that are expressed in tissue specific manner
Explain GLUT 1 in detail and where it is found ?
- Found everywhere - all mammalian tissues
- Constitutive glucose transporter: basal glucose uptake
- High affinity (1mM), low capacity: glucose continually taken up at steady rate irrespective of the blood glucose concentration
Explain GLUT 2 in detail and where it is found ?
- Found in the liver and pancreatic beta cells
- Low affinity (15-20mM), high capacity: rate of glucose entry is proportional to the glucose concentration
- High plasma glucose leads to accelerated glucose entry.
- Low affinity prevents glucose entering the liver when blood glucose is low, allowing glucose to preferentially enter brain and red blood cells
Explain GLUT 3 in detail and where it is found ?
- Found mostly in the brain
- Supplements GLUT 1 in tissues with high energy demands
Explain GLUT 4 in detail and where it is found ?
- Found in the skeletal muscle and adipose tissue
- Affinity ~5mM, therefore controlled by the blood glucose concentration.
- Insulin-dependent: increases the number of transporters on the plasma membrane (so high
uptake when high blood glucose)
Explain GLUT 5 in detail and where it is found ?
- Found in the small intestine
- This is a fructose transporter by facilitating fructose absorption by moving the sugar down a chemical gradient
What is Glycogen ?
Polysaccharide storage form of glucose; mainly in liver and muscle
What is difference between the way Liver glycogen and Muscle glycogen are used ?
Liver glycogen is used to maintain plasma glucose levels between meals, whereas muscle glycogen is used for contraction
How is glycogen synthesised and degraded ?
- Glycogen is synthesised via glycogenesis
- Degraded via glycogenolysis, producing glucose-1-phosphate (G1P)
