hormone regulation of metabolism Flashcards
what are the different energy reserves in humans & where are they located?
- fat (adipose tissue)
- protein (muscle)
- glycogen (muscle)
- glycogen (liver)
- glucose (ECF)
in what organs or tissues is glycogen stored?
the liver and muscle
can glycogen be rapidly metabolised?
yes - it can be ‘instant’ glucose
what kind of energy reserve are fatty acids?
they are medium to long term energy reserves
what occurs as a result of endogenous fatty acid synthesis exceeds the energy requirements?
the stores expand over time and lead to obesity
Describe glucose as a metabolic fuel?
- excellent fuel
- yields a significant amount of energy upon oxidation
- can be utilised by virtually all cells
How does the brain utilise glucose?
- the brain consumes 25% of all the glucose that is oxidised in the body
- glycogen is not stored in the neurons so it requires a constant supply of glucose
what are the main sources of glucose?
- through diet
- glycogen reserves (180-200g) - 1 day supply
what are the 4 major pathways of glucose metabolism?
- glycogenesis
- glycogenolysis
- gluconeogenesis
- glycolysis
what is glycogenesis?
making glycogen from glucose for storage
what is glycogenolysis?
breaking down glycogen to use for energy
what is gluconeogenesis?
making new glucose from non carbohydrate sources eg fatty acids
what is glycolysis?
breaking down glucose for energy
is glycogen a short term or long term energy reserve?
- short term energy reserve
- plays essential role in maintaining blood glucose between meals
what is the main enzyme that activates glycogenesis?
glycogen synthase
what is the main enzyme that controls glycogenolysis?
glycogen phosphatase
Describe the** opposing effects that phosphorlyation by protein kinases** has on glycogen synthase and glycogen phosphotase
- **phosphorylation of GS inactivates it **/ dephosphorylation activates it
- phosphorylation of GP activates it/ dephosphorylation inactivates it
What hormone stimulates glycogenesis?
insulin
what does insulin signal?
energy abundance - ie too much energy
how does insulin stimulate glycogenesis?
- activates protein phosphatase
- this phosphatase** activates glycogen synthase** and dosent activate glycogen phosphatase
- **decreases the activity of phosphorylase kinase **
- therefore the** net effect of insulin stimulation **causes an increase in glycogen synthesis and a decrease in glycogenolysis
what 2 hormones stimulate glycogenolysis?
- glucagon
- epinephrine
what does glucagon signal to the body?
glucagon signals that glucose is running low
what does epinephrine signal to the body about glucose?
it signals that glucose is** urgently needed**
how does glucagon and epinephrine stimulate glycogenolysis?
-
activates glycogen phosphatase - by activating phosphorylase kinase
* inhibits glycogen synthase - mediated by protein kinase A - therefore the net effect is an** increase in glycogenolysis **and a decrease in glycogenesis
- opposite effect to insulin
when is gluconeogenesis most active?
- it is most active in fasting state
- during prolonged exercise
- conditions of carbohydrate starvation
where does gluconeogenesis mainly occur?
- organs that rely least on glucose for energy - the liver
what are the raw ingredients that the liver uses to synthesise glucose and what is an example?
- supplied by the muscle and other tissues
- eg RBC’s
what is the starting molecule of gluconeogenesis?
pyruvate
what is a** critical enzyme that allows glucose to leave the cell and that is not found in muscle**?
- glucose 6 phosphatase
During fasting what 2 hormones are prevalent and what actions do they have?
- glucagon and cortisol
- they induce gluconeogenic enzymes and inhibit glycolytic enzymes - ie they favour gluconeogenesis
during the feeding stage, what hormone is prevalent and what actions does it have?
insulin
* insulin induces glycolytic enzymes
* inhibits gluconeogenic enzymes
* favours glycolysis
what are fatty acids?
they are a long hydrocarbon chains (C10-24) with a terminal COO- group
how are fatty acids mainly stored in the body?
triglycerides
where does Beta oxidation ( FA metabolism) occur?
occurs in mitochondria
what occurs in beta oxidation?
- FA chains broken down to a 2C compound - acetyl CoA
- when glucose and FA metabolism are balanced, acetyl Co A is oxidised in the TCA cycle
- if acetyl CoA is in excess, the surplus is converted to ketone bodies
what is an important enzyme involved in fatty acid synthesis?
acetyl CoA carboxylase
What 2 hormones regulate ACC by controlling the activity of protein kinases and phosphatases?
- glucagon
- insulin
how does glucagon influence ACC?
- glucagon activates protein kinases which phosphorlyate and therefore inhibit acetyl CoA carboxylase
- glucagon signals that energy is low and lipid metabolism should switch from FA synthesis to oxidation
How does insulin influence ACC?
- insulin activates** protein phosphatase** which dephosphorylates (ie activates) ACC
- insulin** signals energy abundance** and lipid metabolism **should switch from FA oxidation to synthesis **
what hormones stimulate lipolysis & why?
- epinephrine - energy needed immediately
- glucagon - no more glucose, switch to fatty acids as energy source
how do epinephrine and glucagon stimulate lipolysis?
they activate** hormone sensitive lipase **which hydrolyses TG’s to FA’s and glycerol
what hormone inhibits hormone sensitive lipase and what does it favour?
insulin
* favours triglyceride synthesis
what is the anorexigenic pathway in the brain?
a pathway which leads to a feeling of being full - and signals that you should stop eating
what is the orexigenic pathway in the brain?
a pathway in the brain that stimulates appetite
what hormone stimulates the anorexigenic pathway? (ie the pathway that leads to the feeling of fullness)
insulin
what** hormone produced in the stomach **stimulates the orexigenic pathway (ie favours appetite)?
GHRELIN
what is GLP-1 and what is it’s** function**?
glucagon like peptide 1
* function : causes the glucose induced secretion of insulin from the pancreatic beta cells
what pathway does GLP-1 favour?
the anorexigenic pathway
what is leptin?
hormone predominantly made by** adipose cells** and enterocytes in the small intestine that helps to** regulate energy balance** by inhibiting hunger, which in turn diminishes fat storage in adipocytes
what pathway does leptin favour?
the anorexigenic pathway
what is the 1st metabolic priority in prolonged starvation?
- to provide sufficient glucose to brain and other tissues that are dependent on it
what is the 2nd metabolic priority in prolonged starvation?
- a shift from the utilization of glucose to utilization of fatty acids/ ketone bodies & preserve protein
